1. The Shock Hugoniot of Solid Ice:
\r\n\r\nWe present a complete description of the solid ice Hugoniot based on new shock wave experiments conducted at an initial temperature of 100 K and previously published data obtained at 263 K. We identify five regions on the solid ice Hugoniot: (1) elastic shock waves, (2) ice Ih deformation shocks, transformation shocks to (3) ice VI, (4) ice VII, and (5) liquid water. In each region, data obtained at different initial temperatures are described by a single Us - Δup shock equation of state. The dynamic strength of ice Ih is strongly dependent on temperature. The Hugoniot Elastic Limit varies from 0.05 to 0.62 GPa, as a function of temperature and peak shock stress. We estimate the entropy and temperature along the 100 and 263 K Hugoniots and derive the critical pressures for shock-induced incipient (IM) and complete (CM) melting upon release. On the 100 K Hugoniot, the critical pressures are about 4.5 and between 5-6 GPa for IM and CM, respectively. On the 263 K Hugoniot, the critical pressures are 0.6 and 3.7 GPa for IM and CM, lower than previously suggested. Shock-induced melting of ice will be widespread in impact events.
\r\n\r\n2. Rampart Crater Formation on Mars:
\r\n\r\nWe present a model for the fluidization of Martian rampart crater ejecta blankets with liquid water based on the shock physics of cratering onto an ice-rich regolith. We conducted simulations of crater formation on Mars, explicitly accounting for the equations of state and shock-induced melting criteria for both the silicate and ice components and using strength models constrained by the observed transition diameter DTr from simple to complex craters on Mars, where DTr = 8 km corresponds to an effective yield strength of 107 Pa.
\r\n\r\nFor the observed size range of rampart craters (diameters D ≾ 30 km) and typical asteroidal impact conditions (silicate impactors, D ≾ 1 km, at 10 km s-1), we find that the hemispherical volume where subsurface ice is partially melted by the impact shock has a radius of about 15 projectile radii (rp), much larger than previous predictions of about 6 rp. The radius of the final crater is comparable to the radius of partial melting and more than half the ice within the excavated material is melted. Thus, the amount of shock-melted water incorporated into the continuous ejecta blanket is within a factor of two of the near-surface ground ice content.
\r\n\r\nWe find that fluidized ejecta blankets may form in the current climate with mean surface temperatures of 200 K. Decreasing the effective yield strength of the modeled materials, e.g., by increasing the ice content or porosity, modifies the impact-induced flow in the excavated cavity, resulting in deeper projectile penetration, steeper ejection angles, higher crater rim uplift, and reduced final crater diameter. The volume fraction of shock-melted water in the ejecta blanket increases with distance from the crater rim. The horizontal flow velocities during emplacement of fluidized ejecta (~ 10 - 1000 m s-1) is nearly constant in the continuous ejecta blanket and within the range of large terrestrial landslides. Therefore, ground-hugging debris flow conditions are achieved. The ejecta blanket properties from impacts into a Martian regolith containing 20-40%vol near-surface ice are consistent with the fraction of liquid water inferred from models of ejecta flow rheologies which produce rampart morphologies, about 10-30% liquid water by volume [Ivanov, B. A., Solar System Research, 30, 43-58, 1996].
\r\n\r\nWe present a model for the formation of different rampart ejecta morphologies which may be used in conjunction with an ejecta blanket debris flow model to map the distribution of ground ice. In addition, we find that formation of single or multiple-rampart ejecta blankets does not require pre-existing liquid water in the Martian crust. We estimate the minimum water content in observed rampart ejecta blankets to be equivalent to a global layer of water 0.6 m thick. Based on the crater sampling efficiency, the implied global Martian ice content, within the upper 2 km of the crust, is equivalent to a global layer of water 100 m deep. This result is comparable to other estimates of HM2O content in the Martian crust.
\r\n", "doi": "10.7907/0V4Q-VF61", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:903", "collection": "thesis", "collection_id": "903", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03092004-155058", "primary_object_url": { "basename": "Tulaczyk_s_1999.pdf", "content": "final", "filesize": 17782172, "license": "other", "mime_type": "application/pdf", "url": "/903/1/Tulaczyk_s_1999.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Basal mechanics and geologic record of ice streaming, West Antarctica", "author": [ { "family_name": "Tulaczyk", "given_name": "Slawek M.", "clpid": "Tulaczyk-Slawek-M" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" } ], "thesis_committee": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Engelhardt", "given_name": "Hermann", "clpid": "Engelhardt-H" }, { "family_name": "Scott", "given_name": "Ronald F.", "clpid": "Scott-R-F" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Piston coring in boreholes drilled at the UpB camp through Ice Stream B, West Antarctica, provided the first samples of sediments ever recovered from beneath an active ice stream. Sedimentological analyses indicate that the samples come from the layer of weak, subglacial till underlying this ice stream (the UpB till). Textural properties of the till and the Tertiary diatoms found in it suggest that the UpB till is recycled from the sediments of the inferred eastern subglacial extension of the Ross Sea sedimentary basin. Geotechnical tests show that the UpB till can be modeled as a compressible, Coulomb-plastic material whose strength is practically independent of deformation rate but is determined by effective stress which also determines the water content. Simulations of the subglacial behavior of such till have successfully reproduced fundamental features of the observed, subglacial till kinematics, e.g., viscous-like vertical distribution of strain and oscillations in tilt rates. The compressible-Coulomb-plastic till model offers a framework for understanding and modeling of ice stream motion and ice-till interactions. The high porosity of the UpB till ([approximately] 0.4) suggests that effective stress is consistently very low, ca. 0.1 to 30 kPa, in the subglacial zone of Ice Stream B. These conditions are explained by the 'undrained-bed' model of sub-ice-stream hydrology that includes only local exchange of water between the water stored in the till pore space and the water stored as basal ice. In this model, there is a negative feedback effect between the basal melting rate and till strength which forces a steady-state in which the basal melting rate is zero and the till is water-rich and weak. Coupling of the undrained-bed model with an equation for the velocity of ice stream sliding yields the undrained plastic-bed model of ice streaming (the UpB model). In accordance with the existing observations, the physics of the UpB model produces two stable modes: an active 'ice-stream' mode and an 'ice-sheet' mode. The model may experience thermally-triggered switches between the two modes and it can be used to test the hypothesis that the West Antarctic Ice Sheet will become unstable in the near-future.", "doi": "10.7907/N04E-S040", "publication_date": "1999", "thesis_type": "phd", "thesis_year": "1999" }, { "id": "thesis:5736", "collection": "thesis", "collection_id": "5736", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04222010-100328955", "primary_object_url": { "basename": "Haldemenn_afc_1997.pdf", "content": "final", "filesize": 37232907, "license": "other", "mime_type": "application/pdf", "url": "/5736/1/Haldemenn_afc_1997.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Interpreting Radar Scattering: Circular-Polarization Perspectives from Three Terrestrial Planets", "author": [ { "family_name": "Haldemann", "given_name": "Albert Frank Christian", "clpid": "Haldemann-Albert-Frank-Christian" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Planetary radar astronomy has used circular polarization radar signals to probe the surfaces of many solar system targets. However the trend for terrestrial observations has been toward greater use of linearly polarized imaging radars. Fortunately the latest generation of imaging radars has been developed with a multi-polarization capability. This should allow a synergy of the two research communities to occur.
\r\n\r\nOne of the unresolved debates on planetary radar astronomy is the nature of the scattering processes from cold planetary ices. This question recently received input from a terrestrial source: Greenland (Rignot et al. 1993). In this thesis a survey is made of high altitude sites to discover if the Greenland percolation zone scattering behavior is wide-spread on the Earth. The survey was carried out with the enormous, publicly available dataset from the 1994 missions of Shuttle Imaging Radar payload. This instrument (SIR-C) obtained full-polarization information with its linear-polarization system. These data allow reconstruction of circular polarizations for comparison to planetary results. The search proved fruitful. Hundreds of square kilometers in western Tibet's Kunlun Shan, and in the Central Andes at the latitude of Santiago display radar scattering behavior quite similar to that in Greenland where internal reflections of the radar waves within icy inclusions in the firn enhance scattering in the same sense of circular polarization.
\r\n\r\nA separate unresolved issue in the planetary radar astronomy is the question of the nature of the highlands of Venus that exhibit high radar reflectivity and low emissivity. These so-called anomalous radar behavior in these regions have alternately been ascribed to high-dielectric doping or low dielectric volume scatterinig. We present new dual circular-polarization radar maps of the western hemisphere of Venus. The results are from a 1993 experiment to image Venus with 3.5 cm radar. Maps of Venusian radar albedo were made for each of two days of observation in both OS (echo principally due to specular reflection) and SS (diffuse echo) channels. On both days, the sub-earth longitude was near 300E. The SS maps are dominated by a significant component of diffuse backscatter from the 285E longitude highlands: Beta, Phoebe, and Themis Regiones. Beta Regio includes previously observed radar-anomalous regions. The nature of these altitude-related electrical properties on Venus is one of the outstanding surface process questions that remain after the Magellan mission. Our experiment provides the first full-disk polarization ratio (\u00b5_c) maps. The data show that different geology determines different radar scattering properties within Beta. Diffuse scattering is very important in Beta, and may be due to either surface or volume scattering. We find a strong correlation of the SS albedo \u03c3_(SS) with altitude R_p (km) in Beta, \u03c3_(SS) \u221d0.3R_p. Also, \u03c3_(OS) \u221d0.7 R_p. The onset of this relationship is at the R_p~6054 km planetary radius contour. The nature and morphology of the highland radar anomalies in Beta is consistent with a diffuse scattering mechanism. In Beta Regio we find \u00b5_c > 0.5 in general, with \u00b5_c as high as 0.8 between Rhea and Theia Montes, to the west of Devana Chasma. These values are compatible with measurements of blocky terrestrial lava flows if surface scattering dominates. If volume scattering is important, the high RCP cross-sections may indicate an important decrease in embedded scatterer size with altitude, which could be related to enhanced weathering.
\r\n\r\nFinally, the techniques of planetary radar astronomy were used in an applied sense. Results are presented of 3.5-cm delay-Doppler and Doppler-only (continuous wave or CW) radar experiments to assess three potential Mars Pathfinder landing sites: Ares Vallis, Tritonis Lacus, and northwest (NW) Isidis. The regional relief at all of the landing sites is appropriate for a Pathfinder landing sequence: east-west slopes do not exceed 3\u00b0 at any of the sites. We find that Ares Vallis has a Hagfors rms slope of \u03b8_(rms)=4.8\u00b0\u00b11.1\u00b0 as measured by delay-Doppler radar, and \u03b8_(rms)=6.4\u00b0\u00b10.6\u00b0 measured by CW radar. These values are similar to, or less than the previous measurements of the Viking Lander 1 region (\u03b8_(rms)=6\u00b0, Tyler et al. 1976, Harmon 1997). The Tritonis Lacus landing site is rougher with delay- Doppler, \u03b8_(rms)=5.6\u00b0\u00b10.6\u00b0, while the NW Isidis landing site is very smooth, both in a regional sense (slopes < 0.7\u00b0) and in a Hagfors rms slope sense: \u03b8_(rms)=1.8\u00b0\u00b10.2\u00b0. Reflectivities at all of the sites should be sufficient to allow the radar altimeter on Pathfinder to function properly.
\r\n", "doi": "10.7907/YQ6F-ZS42", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:933", "collection": "thesis", "collection_id": "933", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03112009-141429", "primary_object_url": { "basename": "Svitek_t_1992.pdf", "content": "final", "filesize": 9657969, "license": "other", "mime_type": "application/pdf", "url": "/933/1/Svitek_t_1992.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Martian water frost : control of global distribution by small-scale processes", "author": [ { "family_name": "Svitek", "given_name": "Tomas", "clpid": "Svitek-T" } ], "thesis_advisor": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis analyzes the small\u2014scale physical processes occurring in the Martian water polar frosts. The small\u2014scale processes are considered from the point of view of how they control the global distribution and behavior of water on Mars. The analysis of the small\u2014scale properties of the surface frost is essential in efforts to find solutions for some outstanding, contradictory observations, to interpret correctly remote sensing observations, to model the surface\u2014frost thermal balance, and to implement the boundary conditions and parameterizations used in the global models of the volatiles' behavior on Mars. Two different problems are investigated in this thesis:\r\n\r\nThe effect of surface roughness on frost temperature and morphology is studied in Chapter 2 and 3. The investigation of the temperature/roughness feedback leads to the following suggestion: There is a natural tendency of volatile surfaces to develop spontaneously small-scale roughness in a sublimation\u2014dominated environment. The evidence for this claim consists of the model of a rough\u2014surface thermal balance, and of the terrestrial analogs of differential sublimation structures. Such a phenomenon can be tested by the Mars Observer and has important implications for the behavior of water frost on Mars.\r\n\r\nViking Lander 2 winter\u2014frost observations are described in Chapter 4. This study suggests that winter water frost occurred there in two forms: a) thin, almost continuous, early frost, and b) much thicker, patchy, later frost with local cold\u2014trapping of water vapor playing the crucial role. This conclusion is based on the correlation of multiple data sets (from both Viking Orbiter and Lander) and on the combined models of the physical processes occurring on a small scale \u2014 below the resolution of remote sensing. The evidence consists of the frost\u2014surface coverage and color transitions, and of the calculation of the vertical and horizontal water\u2014vapor transport near the surface. Again, this phenomenon can be confirmed or rejected by a set of observations from the Mars Observer.\r\n\r\nThe inherent rough\u2014surface morphology and the frost cold\u2014trapping must be a general property of at least some forms of the seasonal and residual frosts. Both effects must be considered in order to understand the global observations of the Martian frost and the surface environment of Mars in general.\r\n", "doi": "10.7907/EDK8-3457", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:6323", "collection": "thesis", "collection_id": "6323", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04132011-115331837", "primary_object_url": { "basename": "Rubin_cm_1991.pdf", "content": "final", "filesize": 329673042, "license": "other", "mime_type": "application/pdf", "url": "/6323/7/Rubin_cm_1991.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Structural, stratigraphic, and geochronologic analysis of the Alexander-Taku terrane boundary and the overlapping upper Jurassic to lower Cretaceous gravina sequence, southeast Alaska", "author": [ { "family_name": "Rubin", "given_name": "Charles Martin", "clpid": "Rubin-C-M" } ], "thesis_advisor": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "thesis_committee": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "An imbricate thrust belt that extends along strike for over 2000 km overprints the tectonic boundary between two of the largest allochthonous crustal fragments (Intermontane and Insular superterranes) in the North American Cordillera and affects rocks west of the Coast Plutonic Complex in southeast Alaska, western British Columbia and northern Washington. Deformation was broadly coeval with mid-Cretaceous magmatism and involved the emplacement of west-directed thrust nappes over a structurally intact and relatively unmetamorphosed basement. The Paleozoic and lower Mesozoic Alexander terrane forms structural basement for much of the thrust belt, along a moderately northeast-dipping ramp.
\r\n\r\nThe western metamorphic belt of the Coast Plutonic Complex consists of the Alexander and Taku terranes, and the Upper Jurassic and Lower Cretaceous Gravina sequence. The Alexander terrane consists of lower Paleozoic metavolcanic and metasedimentary rocks (Descon Formation) and dioritic plutons that are unconformably overlain by Lower Devonian clastic strata (Karheen Formation). These rocks are overlain locally by Upper Triassic basalt rhyolite and marine clastic strata (Hyd Group). The Taku terrane consists of polydeformed and metamorphosed strata that are divided into anupper Paleozoic and lower Mesozoic assemblage (Alava sequence) and a lower Paleozoic assembtage (Kah Shakes sequence). The lower Paleozoic Kah Shakes sequence consists of Devonian orthogneiss, quartz-rich metasedimentary rocks, metabasalt, meta-silicic tuff, marble, cate-silicate, and quartzite. The quartz-rich metasedimentary rocks may be correlative with the lower Paleozoic and mid-Paleozoic Yukon-Tanana terrane, which represents an east-Pacific fringing arc complex built on continental slope and rise deposits. The upper Paleozoic and lower Mesozoic Alava sequence consists of crinoidal and argillaceous marble, carbonaceous phyllite, argillite, mafic flows, pillow breccia, pyroclastic tuff, and minor quartz-rich metasedimentary rocks. The upper Paleozoic part of the Alava sequence is probably correlative with the mid- to late Paleozoic portion of the Yukon-Tanana terrane. The Middle and Upper Triassic portion of the Alava sequence may represent a metamorphiC vestige of the Stuhini Group, now exposed on the western flank of the Coast Batholitic belt.
\r\n\r\nUpper Jurassic and Lower Cretaceous metavolcanic and metasedimentary strata of the Gravina sequence unconformably overlie both the Alexander and Taku terranes. These rocks form two distinct lithotectonic units in southern southeast Alaska. The lower unit consists of coarse marine pyroclastic and volcaniclastic strata, mafic flows, breccia, and fine-grained tuff which are locally intruded by hypabyssal bodies of diorite and quartz diorite. Fine- to coarse-grained turbidites and related channel-fill deposits comprise the epiclastic part of the Gravina sequence. Conglomerate units contain mostly volcanic and plutonic lithic clasts that suggest they were derived from a composite igneous source. Clasts from the channel-fill deposits yield Pb-U zircon ages of 154 to 158 Ma. The pyroclastic and volcaniclastic rocks represent remnants of a Late Jurassic oceanic arc system that was constructed on a composite basement consisting of the Alexander and Taku terranes; the Taku terrane is inferred to represent the westernmost extent of the Stikine and Yukon-Tanana terranes. These data suggest that the Intermontane (Stikine and Yukon-Tanana terranes) and Insular (Alexander terrane) superterranes were juxtaposed prior deposition of the Upper Jurassic and Lower Cretaceous Gravina sequence.
\r\n\r\nThe lower Paleozoic to Early Cretaceous rocks were deformed in the mid-Cretaceous and tectonism was broadly coeval with arc magmatism. Deformation involved the emplacement of west-directed thrust nappes over a structurally intact and relatively unmetamorphosed basement. Mid-Cretaceous tonalite, granodiorite, and quartz diorite intrude rocks of the thrust belt and were locally affected by the deformation. Mid-Cretaceous deformation occurred during two episodes that were contemporaneous with the emplacement of sill-like plutonic bodies. Older structures record ductile southwest-vergent folding and faulting, regional metamorphism and contain a well developed axial-planar foliation. The second generation structures developed during the later stages of southwest-directed reverse faulting that juxtaposes rocks of contrasting metamorphic pressures and temperatures. The presence of syntectonic kyanite-staurolite-garnet-biotite assemblages in the more eastern high-strain zones indicates that at least some of the reverse faults were generated at depths in excess of 20 km during the later stages of thrust faulting and associated uplift.
\r\n\r\nPaleocene and younger (?) deformation has also affected rocks on the western margin of the Coast Plutonic Complex. Younger fabrics are dominated by low to moderate west-dipping foliation surfaces that are axial planar to asymmetric east-vergent folds. The east-verging fabrics have transposed earlier mid-Cretaceous fabrics . Late Paleocene pegmatite dikes are highly deformed and are affected by the west-dipping structures. Exposure of mid-crustal level rocks might be related to a reversal in vergence during Paleocene time, in which deep levels of the mid-Cretaceous thrust system were transported upward along east-vergent structures. A swarm of hornblende-bearing diabase dikes cross-cut all structures and fabrics. These dikes trend northeast and mark a regional change in the overall regional strain patterns during Miocene time.
\r\n\r\nStructural, stratigraphic and geochronologic data suggest that regional-scale deformation in southeast Alaska occurred between 113 Ma and 89 Ma. Rocks in the thrust belt were regionally uplifted by 70 Ma, at an average minimum rate of \u2248 0.9 mm/yr. Mid-Cretaceous deformation involved the collapse of marginal basin(s) and a magmatic arc, overprinting the older tectonic boundary between the Insular superterrane and the late Mesozoic western margin of North America (i.e., the Intermontane superterrane). Contractional deformation along the length of the thrust belt was broadly coeval with arc magmatism, and thus records intra-arc tectonism. Late Paleocene to Early Eocene deformation and uplift may mark the transition from contractional to extensional tectonism, and perhaps records the collapse of tectonically thickened crust.
", "doi": "10.7907/ZQ82-2077", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:1187", "collection": "thesis", "collection_id": "1187", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03282006-103736", "primary_object_url": { "basename": "bursik-mi-1989.pdf", "content": "final", "filesize": 10369362, "license": "other", "mime_type": "application/pdf", "url": "/1187/5/bursik-mi-1989.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Late Quaternary Volcano-Tectonic Evolution of the Mono Basin, Eastern California", "author": [ { "family_name": "Bursik", "given_name": "Marcus Ivan", "clpid": "Bursik-Marcus-Ivan" } ], "thesis_advisor": [ { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" } ], "thesis_committee": [ { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Sturtevant", "given_name": "Bradford", "clpid": "Sturtevant-B" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The Mono Basin of eastern California provides an ideal laboratory in which to study the interaction of volcanic and tectonic processes. The late Quaternary geological record of volcanic activity and range-front faulting is relatively complete in the basin. Range-front faults of the Sierra Nevada offset dateable late Pleistocene glacial moraines, thus affording the opportunity to estimate range-front slip rates. The first two chapters concern dating of moraines that are offset by range-front faults.
\r\n\r\nIn Chapter One, I discuss the ages of the glacial moraines of the Mono Basin and their correlation between canyons. I dated the moraines by studying their morphology and the relative weathering of granitic boulders atop their crests, and by use of the clast-sound velocity (CSV) dating technique. The CSV technique consists of measuring the p-wave speed (V\u209a) in morainal boulders. V\u209a decreases with age as boulders weather. Clast-sound velocities enabled statistical division of moraines in each canyon into differently weathered deposits. Relative weathering features of boulder surfaces further helped discern age differences between moraines in a single canyon. Finally, CSV, relative weathering and moraine morphology, considered together, allowed correlation of moraines to an established glacial sequence, and therefore, correlation between canyons. Regression of mean V\u209a against best estimates of glaciation ages within the glacial sequence provided a further check on the validity of the correlations.
\r\n\r\nMoraines in all major canyons from Lee Vining south were correlative with the standard late Pleistocene sequence of Tioga, Tenaya, Tahoe and Mono Basin deposits. At Lundy Canyon, however, Tahoe and Tenaya moraines are poorly, if at all, preserved. The prominent moraines extending into the basin are probably of Tioga age. Poor preservation of Tenaya and Tahoe deposits may be due to the narrow, steep-sided morphology of Lundy Canyon, and rapid down-dropping on the range-front fault.
\r\n\r\nIn Chapter Two, I discuss the application of a new quantitative dating technique to the moraines of Lee Vining Canyon. At Lee Vining Canyon, I measured cross-sectional profiles of lateral moraines of different ages to determine whether the degree to which they have been degraded could be used as a relative-dating method. Correlation of the degree of moraine degradation against an independent measure of age suggested that relative ages of late Pleistocene lateral moraines can be inferred from moraine profiles.
\r\n\r\nAnalysis of the degradation of moraine profiles with a diffusion model resulted in equations that relate profile width and maximum slope angle to age. In accordance with the diffusion model, the functional relationship between profile width and estimated age was found to be nearly linear for the moraines of Lee Vining Canyon. Fits of model to data were good, despite evidence of transport of material by non-linear diffusive processes along some of the profiles.
\r\n\r\nMaximum slope angle is inversely proportional to age according to the diffusion model. Regression of mean maximum slope angle against inverse age for the group of moraines from Lee Vining Canyon suggested that the relationship between the two variables is expressed by the diffusion model.
\r\n\r\nDeviations of model profile shapes from true shapes suggested that in addition to moraine age, initial profile shape and non-diffusive degradation processes are important in controlling the relationship between slope parameters and age over spans of 10\u2074 years.
\r\n\r\nIn Chapter Three, I use moraine ages determined in Chapter One to estimate slip rates of range-front faults. For Chapter Three, I measured fault-scarp profiles on the dated lateral moraines of the Mono Basin to determine fault slip rates. I compared these data with what can be deduced about the extension rate due to dike intrusion underneath the Mono Craters. I then considered extension rates in the context of regional strain patterns to infer the mode of deformation and strain relief in the Mono Basin during late Quaternary time.
\r\n\r\nThe extension-rate data indicate that dikes are being intruded underneath the Mono Craters in response to crustal stretching, and because of this, are now accommodating elastic strain that was once accommodated by range-front normal faulting. The section of the range front near the craters accommodated as much as 1 mm/yr of extension until 40,000 to 70,000 years ago. For the past 40,000 to 70,000 years, this section of range front has become inactive, even though extension along the range front to north and south has continued at up to 0.9 mm/yr. Dikes have been intruding underneath the Mono Craters for the past 40,000 years. Depending upon the assumptions used to calculate dike intrusion rates, the dikes accommodate 1 mm/yr of tectonic extension that was previously accommodated by range-front faulting.
\r\n\r\nConsideration of the extension rates in the context of regional tectonic strain patterns suggests that the Mono Craters are forming along one of the extensional boundary structures of a pull-apart basin, the other extensional boundary of which is the deactivated range-front segment.
\r\n\r\nIf the Mono Craters represent an early stage of caldera formation, then their formation within a pull-apart zone may indicate that this is an ideal tectonic environment in which to form certain types of calderas.
", "doi": "10.7907/mv55-ah24", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:2928", "collection": "thesis", "collection_id": "2928", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07192006-093757", "type": "thesis", "title": "Water Flow at the Base of a Surging Glacier", "author": [ { "family_name": "Brugman", "given_name": "Melinda Mary", "clpid": "Brugman-Melinda-Mary" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" } ], "thesis_committee": [ { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Meier", "given_name": "Mark", "clpid": "Meier-M" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Water tracing experiments were successfully conducted over a distance of ten kilometers along the base of Variegated Glacier for the purpose of characterizing the water drainage system of the glacier in the surging as compared to the non-surging state. Three tracing experiments were conducted, and fluorescent dyes, Rhodamine WT and Tinopal AMS, were injected into boreholes at separate locations. The two Rhodamine WT experiments were conducted over a 10 km distance, both during the most rapid surging motion of the glacier, and after its cessation.
\r\n\r\nIn each experiment, the terminus streams were monitored for stream discharge, sediment content and tracer concentration. Rhodamine WT tracer was significantly adsorbed on the suspended sediment, particularly during the surge. The adsorption behavior followed the Langmuir model, and calculated distribution coefficients of Kd = 100 to 1000 ml/g were measured for during the glacier surge. The Kd values measured after the surge were lower than during the surge by a factor of 10 to 1000. The much higher Kd values in the surging as compared to non-surging glacier states can be best explained by a factor of 10 to 1000 decrease in the modal and/or mean grain-size of the suspended sediment. The abundance of fine-grained sediment during the surge is probably due to increased grinding of rock material at the glacier bed.
\r\n\r\nTheoretical models of tracer dispersion in a single tunnel, were compared to models of dispersion in linked-cavity systems to infer the details of water flow at the glacier bed. The broad, roughly symmetrical, dye-return curve measured during the glacier surge conforms to diffusive dispersion theory, and differs sharply from the highly asymmetrical dispersion curve measured after the surge. Results indicate the dispersion behavior, and calculated Manning roughness, of the post-surge Variegated Glacier is similar to those of glaciers that do not surge. The drainage system of the Variegated Glacier in the surging state is consistent with a model of tracer dispersion in an interconnecting network of conduits and cavities, and is strikingly different from the tunnel system indicated for the non-surging state.
\r\n", "doi": "10.7907/VSHG-G674", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:1307", "collection": "thesis", "collection_id": "1307", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04082005-133814", "primary_object_url": { "basename": "Mattson_sm_1985.pdf", "content": "final", "filesize": 5745993, "license": "other", "mime_type": "application/pdf", "url": "/1307/1/Mattson_sm_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Optical Expressions of Ion-Pair Interactions in Minerals", "author": [ { "family_name": "Mattson", "given_name": "Stephanie Margaret", "clpid": "Mattson-Stephanie-Margaret" } ], "thesis_advisor": [ { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "thesis_committee": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Clusters of transition element cations in neighboring sites frequently govern the optical properties of minerals. This is particularly true of Fe-bearing minerals which may exhibit several types of ion-pair transitions. In this thesis four different types of interactions were distinguished: intensified spin-forbidden transitions of Fe3+ clusters, intensified Fe2+ spin-allowed transitions of Fe2+-Fe3+ clusters, heteronuclear charge transfer transitions of Fe2+-Ti4+ and Mn2+-Ti4+ clusters, and homonuclear charge transfer transitions of Fe2+-Fe3+ clusters.
\r\n\r\nThe optical characteristics of Fe3+ in red Fe3+ rich and black Fe3+,Fe2+-rich tourmalines were examined by absorption spectroscopy in the visible and near-infrared, M\u00f6ssbauer spectroscopy and magnetic susceptibility measurements. Intense optical absorption features at 485 and 540 nm were assigned to transitions of exchange-couple Fe3+ pairs in two different site combinations. Absorption spectra at variable temperatures and of samples which were oxidized and reduced were used to establish these assignments. Site assignments were based on intensity ratios in different polarizations according to the polarization of these transitions along the vector between the interacting cations. The 485 nm band occurs at an unusually low energy for Fe3+ in silicate minerals. Similar behavior was observed in the spectrum of coalingite, a Mg,Fe-hydroxy carbonate, and has been proposed to result from magnetic exchange in large, edge-shared octahedra. The antiferromagnetic exchange which is generally associated with intensity increases in Fe3+ clusters was confirmed by variable temperature magnetic susceptibility measurements. The M\u00f6ssbauer spectrum of a red tourmaline with 3.4% Fe exhibits an unusual decrease in width of peaks by ~30% from 298 K to 5 K which may be related to an unusual interaction between Fe3+ and trace amounts of Fe2+.
\r\n\r\nOptical absorption and M\u00f6ssbauer studies of Fe2+-bearing tourmalines with variable Fe3+ contents were used to examine Fe2+ transitions which are intensified through an interaction with Fe3+ neighbors. The variation of molar absorptivity of Fe2+ bands with the fraction of Fe2+ in Fe2+-Fe3+ pairs indicates that Fe3+ ions increase the absorptivity of Fe2+ bands to ~1200 M-1cm-1 as compared to ~5 M-1cm-1 for non-interacting Fe2+. Approximately equal degrees of intensification were observed for both components of the 5T2 \u2192 5E Fe2+ transition as well as for Fe2+ in two different sites. Although the detailed behavior of non-interacting Fe2+ ions differ in Mg-tourmalines and Li,Al-tourmalines, the characteristics of Fe2+-Fe3+ absorption are constant. Intensity increases were restricted to the polarization which coincided with the vector between the Fe2+ and Fe3+ ions. The intensified Fe2+ transitions are characterized by an unusual temperature response. The integrated intensity of these transitions increases by 10-50% at 83 K as compared to 296 K. The positions and widths of the intensified transitions maintain the values of the non-interacting Fe2+. Tourmalines with the lowest Fe3+ contents were the gemmy Li,Al-tourmalines which generally form in pockets within pegmatites. Fe,Mg-tourmalines exhibited consistently higher Fe3+ contents than any of the Li-bearing tourmalines examined. Oxidation of Fe2+ which resulted from gamma irradiation of blue Li-tourmalines which contained several percent each of MnO and FeO could be monitored by increases in Fe2+ intensity in one polarization.
\r\n\r\nFe2+-Ti4+ charge transfer transitions were examined in minerals which contain stoichiometric quantities of Fe and Ti -- taramellite, neptunite, and traskite -- and tourmaline. The wavelength of these transitions ranged between 400 and 500 nm, and the halfwidths ranged between 7000 and 9000 cm-1. These characteristics can generally be used to assign Fe2+-Ti4+ charge transfer transitions. The molar absorpitivities of these transitions, however, exhibit very large variations. The molar absorptivity of Fe2+-Ti4+ charge transfer in neptunite is ~225 M-1cm-1 in beta polarization, in taramellite it is ~1300 M-1cm-1 and in tourmaline it is ~4000 M-1cm-1. Tentative assignments of Fe2+-Ti4+ in more dilute minerals generally compare favorably with the energy and width stated above. However, sapphire and other Al-minerals such as kyanite have very different characteristics for bands assigned to Fe2+-Ti4+ charge transfer. The Fe2+-Ti4+ charge transfer transition in taramellite exhibits no change in integrated intensity with decreasing temperature but increases by 15% from 296 K to 83 K in tourmaline. Mn2+-Ti4+ charge transfer was also assigned to a transition at 320 nm in two unusual yellow tourmalines.
\r\n\r\nThe characteristics of Fe2+-Fe3+ charge transfer transitions were reviewed in light of recent data and with regard to their utility as diagnostic criteria. A correlation between charge transfer energy and the separation of the interacting cations proposed by Smith and Strens (1976) could not be supported by the expanded data base. Temperature variations of charge transfer transition areas were also examined. The magnetic behavior of two minerals which exhibited different temperature responses were investigated. General agreement with the theories of Cox (1980) and Girered (1983) that suggest that ferromagnetic exchange should produce intensity increases at low temperature and that antiferromagnetic exchange produces intensity decreases was confirmed by these examples of Fe2+-Fe3+ charge transfer but could not explain the temperature response of Fe2+-Ti4+ charge transfer transitions. In any case, an increase in intensity with decreasing temperature, which is generally expected on the basis of experimental observations, cannot be used in a negative sense to eliminate a charge transfer assignment. The large width of charge transfer transitions is generally the most useful diagnostic criterion.
\r\n\r\nCox, PA (1980) Electron transfer between exchange-coupled ions in a mixed-valency compound. Chem Phys Lett 69: 340-343
\r\n\r\nGirerd, J-J (1983) Electron transfer between magnetic ions in mixed valence binuclear systems. J Chem Phys 79: 1766-1775
\r\n\r\nSmith, G and Strens, RGJ (1976) Intervalence transfer absorption in some silicate, oxide and phosphate minerals. In: The Phyics and Chemistry of Minerals and Rocks, Strens, RGJ (ed.). New York: Wiley and Sons, pp. 583-612
", "doi": "10.7907/acn3-nr54", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1284", "collection": "thesis", "collection_id": "1284", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04072004-154813", "primary_object_url": { "basename": "Conca_jl_1985.pdf", "content": "final", "filesize": 22985051, "license": "other", "mime_type": "application/pdf", "url": "/1284/1/Conca_jl_1985.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Differential Weathering Effects and Mechanisms", "author": [ { "family_name": "Conca", "given_name": "James Louis", "clpid": "Conca-James-Louis" } ], "thesis_advisor": [ { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "thesis_committee": [ { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Sharp", "given_name": "Robert P.", "clpid": "Sharp-R-P" }, { "family_name": "Shoemaker", "given_name": "Eugene Merle", "clpid": "Shoemaker-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The physical and chemical characteristics of the two differential weathering effects, case hardening and core softening, are examined to determine their formation mechanisms by investigating several field areas exhibiting differential weathering effects. The terms differential weathering effects, factors, mechanisms, processes, morphologies and their cause and effect relationships are defined in the context of the overall problem.
\r\n\r\nBecause differential weathering effects are defined on the basis of spatial variations in relative and absolute hardness, a portable field instrument has been developed to measure rock hardness as manifested in the abrasion resistance of the material.
\r\n\r\nThe design and operation of the instrument as well as results from standard materials are discussed in light of abrasive wear theory. The way in which the instrument removes material appears dominated by abrasive wear mechanisms. However, the concept of hardness implied by such mechanisms is profoundly different for rock than for homogeneous materials, and the effective hardness calculated for rock material using this instrument is more insensitive to mineralogy than expected, and is sensitive to the character of the intergranular bond.
\r\n\r\nAt the first locality, Valley of Fire, Nevada, cavernous weathering of the Aztec Sandstone results from the differential weathering effect of case hardening. The case-hardened crust is an induration phenomenon consisting primarily of host rock, calcite cement, kaolinite and finegrained quartz. The calcite occurs in a wide range of concentrations (0.001 to 5.0 wt%). The hydrated calcium borate, colemanite, was also found as a non-cementing hardening agent on two outcrops and can be used as a tracer constituent. In all cases kaolinite and quartz were the major constituents of the indurating materials by weight and are necessary components of the crust. Eolian deposition and interaction with meteoric water were determined to be the primary differential weathering mechanism within the Valley of Fire.
\r\n\r\nAt Catavina, Baja California, tonalite exhibiting cavernous weathering is found to be core-softened. Soft cores are more chemically weathered than the exterior rock as indicated by higher kaolinite contents. Hematite formed from the leaching of biotite occurs in coatings on rock surfaces, but the hardening effect of the coating is insignificant compared to the core-softening of the interior. The hardness, measured by the abrasion resistance hardness tester, is inversely correlated with kaolinite content in the tonalite. A one-dimensional water flow model was developed for core-softened, cavernously weathered boulders, and indicates that during infiltration and dessication the moisture flux through a boulder's surface is greatest at the interior cavern wall because of changes in the hydraulic conductivities induced by core softening.
\r\n\r\nThe differential weathering effects developed in the Ferrar dolerite within the Labyrinth of the Dry Valleys, Antarctica are caused by two different mechanisms. The primary mechanism is precipitation of a brown, iron-stained silica coating in the exterior rock of outcrops and joint blocks. This is also true for the case-hardened Beacon Sandstone. Precipitation can occur in the rock's outer few millimeters to centimeters, thereby decreasing the exterior rock's permeability, and consequently its susceptibility to chemical weathering. The coating's effect on a dolerite block's internal moisture regime is modeled for the case of saturated flow, and shows that the contours of the pore water flow mimic subsequent morphology. Weathering of material underlying the coating results in core softening of the dolerite. In dolerite blocks of intermediate size, expansion of the interior owing to weathering can cause the less weathered outer zone to separate into an array of polyhedral cracks. Further weathering and removal of the underlying rock by the combined action of hydration, salt weathering and eolian processes leads to the development of cavernous weathering.
\r\n\r\nA less common differential mechanism occurs in the bottom of the Antarctic Labyrinth troughs in which an eolian polish develops on rock surfaces exposed to the austral winter winds. Development of the polish protects the underlying material with similar, but less dramatic effects, than accompanies the presence of the silica coating.
\r\n\r\nExposures of the Bishop Tuff in the Mono Basin exhibit the differential weathering effect of case hardening. Early devitrification along joint planes to an average depth of 1 cm greatly increased the resistance of the joint faces to weathering over that of the joint block interiors. The absolute and relative hardnesses between interior and exterior change systematically with exposure age, and cavernous weathering results only on outcrops with long enough exposure ages, on the order of ten to twenty thousand years.
\r\n\r\nThe Towel Creek Tuff in Cottonwood Basin, Arizona, weathers into peculiar forms: conical-shaped tepees which show cavernous weathering as a result of case-hardening by calcite precipitation in the exterior rock. Calcite contents of different materials are observed to vary directly with the abrasion hardness of the material. Basal surfaces are formed at the base of the tepees by heterogeneous fluvial erosion and the cavernous hollows are initiated in these zones. Although infiltration of meteoric water into the tepees occurs through all surfaces, moisture flow during dessication of the tepees occurs primarily through the basal surfaces and the lower cavernous hollows. Equilibrium aqueous chemistry limits the interior rock's carbonate content, but calcite can accumulate at the rock exterior.
\r\n\r\nBecause of the overall differences in the intergranular bonding character between crystalline materials such as granite and clastic materials such as sandstone, the results of this study indicate that crystalline rocks tend to core-soften whereas clastic materials case-harden. Clastic materials will be affected by redistribution of secondary cements and greater accumulation at an interface can result in case hardening. In clastic rocks therefore, the hardness of different areas can either increase or decrease with time. On the other hand, a crystalline rock in a weathering environment will have its intergranular and intragranular bonds disrupted by chemical alteration. Spatial variations in disruption can result in core softening or case softening, but the hardness of all areas will decrease with time. Accumulation of secondary cements can often enhance differential effects in crystalline rocks but without case hardening the rock.
\r\n ", "doi": "10.7907/VBEQ-RB90", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:7490", "collection": "thesis", "collection_id": "7490", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02212013-144447105", "primary_object_url": { "basename": "Lunine_ji_1985.pdf", "content": "final", "filesize": 46141459, "license": "other", "mime_type": "application/pdf", "url": "/7490/1/Lunine_ji_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Volatiles in the Outer Solar System: I. Thermodynamics of Clathrate Hydrates. II. Ethane Ocean on Titan. III. Evolution of Primordial Titan Atmosphere", "author": [ { "family_name": "Lunine", "given_name": "Jonathan Irving", "orcid": "0000-0003-2279-4131", "clpid": "Lunine-Jonathan-Irving" } ], "thesis_advisor": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Three investigations are conducted into the physical chemistry of volatiles in the outer solar system and the role of volatiles in icy satellite evolution.
\r\n\r\nPart I:
\r\n\r\nThe thermodynamic stability of clathrate hydrate is calculated under a wide range of temperature and pressure conditions applicable to solar system problems, using a statistical mechanical theory developed by Van der Waals and Platteeuw (1959) and existing experimental data on properties of clathrate hydrates and their components. At low pressure, dissociation pressures and partition functions (Langmuir constants) for CO clathrate (hydrate) have been predicted using the properties of clathrate containing, as guests, molecules similar to CO. The comparable or higher propensity of CO to incorporate in clathrate relative to N2 is used to argue for high CO to N2 ratios in primordial Titan if N2 were accreted as clathrate. The relative incorporation of noble gases in clathrate from a solar composition gas at low temperatures is calculated, and applied to the case of giant planet atmospheres and icy satellites. It is argued that non-solar but well-constrained noble gas abundances would be measured by Galileo in the Jovian atmosphere if the observed carbon enhancement were due to bombardment of the atmosphere by clathrate-bearing planetesimals sometime after planetary formation. The noble gas abundances of Titan's atmosphere are also predicted under the hypothesis that much of the satellite's methane accreted as clathrate. Double occupancy of clathrate cages by H2 and CH4 in contact with a solar composition gas is examined, and it is concluded that potentially important amounts of H2 may have incorporated in satellites as clathrate. The kinetics of clathrate formation is also examined, and it is suggested that, under thermodynamically appropriate conditions, essentially complete clathration of water ice could have occurred in high pressure nebulae around giant planets but probably not in the outer solar nebula; comets probably did not aggregate as clathrate. At moderate pressures, the phase diagram for methane clathrate hydrate in the presence of 15% ammonia (relative to water) is constructed, and application to the early Titan atmospheric composition is described. The high pressure stability of CH4, N2, and mixed CH4-N2 clathrate hydrate is calculated; conversion back to water and CH4 and/or N2 fluids or solids is predicted for pressures \u227312 kilobars and/or temperatures \u2273320 K. The effect of ammonia is to shrink the T-P stability field of clathrate with increasing ammonia concentration. A preliminary phase diagram for the high pressure ammonia-water system is constructed using new data of Johnson et al. (1984). These results imply that 1) clathrate is stable throughout the interior of Oberon- and Rhea-sized icy satellites, and 2) clathrate incorporated in the inner-most icy regions of Titan would have decomposed, perhaps allowing buoyant methane to rise. Brief speculation on the implications of this conclusion for the origin of surficial methane on Titan is given. A list of suggested experiments and observations to test the theory and its predictions is presented.
\r\n\r\nPart II:
\r\n\r\nWe propose a global Titanic ocean, one to several kilometers deep, the modern composition of which is predominantly ethane. If the ocean is in thermodynamic equilibrium with an atmosphere of 3' (mole fraction) methane then its composition is roughly 70% C2H6, 25% CH4, and 5% N2. Photochemical models predict that C2H6 is the dominant end-product of CH4 photolysis so that the evolving ocean is both the source and sink for ongoing photolysis. The coexisting atmosphere is compatible with Voyager data. Two consequences are pursued: the interaction of such an ocean with the underlying \"bedrock\" of Titan (assumed to be water-ice or ammonia hydrate) and with the primarily nitrogen atmosphere. It is concluded that although modest exchange of oceanic hydrocarbons with enclathrated methane in the bedrock can in principle occur, it is unlikely for reasonable regolith depths and probably physically inhibited by the presence of a layer of solid acetylene and complex polymeric hydrocarbons a couple of hundred meters thick at the base of the ocean. However, the surprisingly high solubility of water ice in liquid methane (Rebiai et al., 1983) implies that topographic features on Titan of order 100 meter in height can be eroded away on a time scale \u227e109 years; \"Karst\" topography could be formed. Finally, the large solubility difference of N2 in methane versus ethane implies that the ocean composition is a strong determinant of atmospheric pressure; a simple radiative model of the Titan atmosphere is employed to demonstrate that significant surface pressure and temperature changes can occur as the oceanic composition evolves with time. The model suggests that the early methane-rich ocean may have been frozen; scenarios for evolution to the present liquid state are discussed.
\r\n\r\nPart III:
\r\n\r\nA simple convective cooling model of a primordial, CH4-NH3-N2 Titan atmosphere is constructed, in an effort to understand the fate of volatiles accreted from a gaseous disk (\"nebula\") surrounding Saturn and released from accreting planetesimals during the satellite's formation. Near-surface temperatures are initially \u2273400 K consistent with the large amount of energy supplied to the atmosphere during accretion. As a consequence of accretional heating, the upper mantle of the satellite consists of an ammonia-water liquid, extending to the surface. This \"magma ocean\" is the primary buffer of atmospheric cooling because it is \u227310 times as massive as the atmosphere. The radiative properties of the atmosphere are assumed independent of frequency and the resulting temperature profile is found to be adiabatic; if the atmosphere contains dark particulates surface temperatures could be lower than calculated here. Three major processes drive the cooling: (1) hydrodynamic escape of gas from the top of the atmosphere, which determines the cooling time scales, (2) atmospheric ablation by high velocity impacts (not modeled in detail here), and (3) formation of clathrate hydrate at the ocean-atmosphere interface, at T \u2264 250 K. Cooling time scales driven by escape are sufficiently long (108-109 years) to allow ~10 bars of N2 to be produced photochemically from NH3 in the gas phase (Atreya et al., 1978); however, the abundance of NH3 at temperatures \u227e150 K (where the intermediate photochemical products condense out) is optically thick to the dissociative UV photons. Thus, N2 formation may proceed primarily by shock heating of the atmosphere during large body impacts, as well as by photochemistry (1) at T < 150 K if intermediate products supersaturate, or (2) in a warm stratosphere, with NH3 abundance fixed by its tropopause value. The clathrate formed during late stages of cooling sequesters primarily CH4, with some N2, and forces surface temperatures and pressures to drop rapidly. The clathrate is only marginally buoyant relative to the coexisting ammonia-water liquid. If it sinks, the atmosphere is driven to an N2-rich state with most of the methane sequestered in clathrate when the ocean surface freezes over at ~180 K. Implications of this scenario for the present surface state of Titan are contrasted with those obtained if the clathrate forms a buoyant crust at the surface.
", "doi": "10.7907/tw6n-qa60", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:11236", "collection": "thesis", "collection_id": "11236", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10172018-114703911", "primary_object_url": { "basename": "Hofmeister_AM_1984.pdf", "content": "final", "filesize": 138472836, "license": "other", "mime_type": "application/pdf", "url": "/11236/1/Hofmeister_AM_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A Spectroscopic and Chemical Study of the Coloration of Feldspars by Irradiation and Impurities, Including Water", "author": [ { "family_name": "Hofmeister", "given_name": "Anne Marie", "clpid": "Hofmeister-Anne-Marie" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Natural smoky color or smoky color induced by ionizing radiation develops only in potassium feldspars (KAlSi3O8) free of water bound in the feldspar structure. Neither fluid inclusion water nor \u2261SiOH have an effect. The optical absorption spectra of the smoky color consist of polarized bands at 11600, 16200, 19100, and 27200 cm-1, whose integrated intensities are linearly correlated with the integrated intensity of a broad, asymmetric first derivative at geff = 2.027 in electron paramagnetic resonance (EPR) spectra. This hole center forms only in KAlSi3O8 without structurally bound H2O, and in microcline is resolved into an asymmetric six-line pattern at geff = 2.024 and a single derivative at geff = 2.009 which are Si-O- -K and a hole shared between two nonbonding oxygens (NBO) on Si. In analogy to coloring in quartz and glass, the 11600 cm-1 band is caused by a hole trapped between two NBO's on silicon, the 16200 and 27200 cm-1 bands are due to the Si-O- -K center, and the 19100 cm-1 band results from a hole trapped on an oxygen attached to two aluminums. Smoky centers do not develop in feldspars with structural water because irradiation mobilizes protons which, while diffusing, destroy centers in their path, and finally then settle in sites similar to their original site. Smoky color also develops in sodic plagioclases, but high Al content inhibits its formation in labradorite.
\r\n\r\nAmazonite color is intrinsic and controlled by an absorption minimum between three overlapping bands in the ultraviolet and a broad band in \u03b2 at 630, or one UV band and a broad band in \u03b2 at 720 nm, or both superimposed. Comparison of EPR to optical integrated intensities shows that all three colors are connected with a first derivative at geff = 1.56 and two satellites of about 1/7 intensity at geff of 1.83 and 1.39. Analysis of the EPR pattern shows that this center is Pb3+ 31% of the time, with the hole located on coordinating oxygens for the remaining 69%. This center is only produced in samples which have in addition to Pb, H2O structurally bound in the lattice. The dependence of color intensity on the smaller molar concentration of structural water or lead implies that lead and structural water in a 1:1 ratio produce color centers in amazonite. The first order reaction kinetics of amazonite color formation by irradiation and the observation that water is not consumed in the process suggests that Pb2+ is oxidized to Pb3+ by the product OH of the irradiation-induced dissociation of water while H concurrently destroys a hole center on an oxygen, and is followed by the regeneration of the water molecule. The kinetics also show that the radiation necessary for the coloration is provided by internal decay of 40K. The two end-member color types (630 or 720 nm) occur for microcline or orthoclase local structure, respectively. Al/Si disorder increases first locally, and then overall as larger amounts Pb or H2O are incorporated, so that crystals with intermediate Pb contents have both color types. A spectrally similar blue radiation color also occurs for Pb-bearing sodic plagioclases.
\r\n\r\nGemmy labradorite phenocrysts from one Steens Mountain basalt flow in Rabbit Basin, Oregon, sometimes possess a pink schiller, or more rarely a transparent red or green coloration. Direct microprobe analysis of the schiller flakes show that these are metallic copper. XRF analysis of the different colored zones revealed that only the copper content varies with color: colorless samples, or sections of crystals, have 0-35 ppm Cu; greens average 80 ppm Cu; reds average 135 ppm Cu; while schiller bearing labradorites have 50 to 240 ppm Cu. Spectral similarity of the red color to copper-ruby color of glass shows that the red arises from the intrinsic absorption of colloidal Cuo particles that are too small to scatter light (ca. 4 to 22 nm). Spectra from the green regions strongly resemble that of amazonite. Because the temperature of exsolution is subsolidus and proportional to Cu content, diffusion proceeds more rapidly for crystals with higher Cu content and results in formation of larger particles. The Cuo reduction at low temperature (800\u00b0C) involves formation of hole center (O-) that is captured by Pb2+ to form the green amazonite color (Pb3+). At high temperatures (~ 900 to 1100\u00b0C) the reduction of Cu is controlled by whatever reactions occur in the basalt to keep fO2 along the QFM buffer. Migration of Cuo may cause the variation of Cu concentrations in a single sample; but the variation of Cu content among different crystals suggests that the composition of the megacrysts was not constant and changed in response to an increasing copper content in the melt as crystallization of the labradorite proceeded.
\r\n\r\nThe coloration process in feldspar strongly resembles that in glasses for both radiation colors (smoky) and exsolution phenomena (Cuo colloids, Cuo schiller) and also that of radiation colors in other crystalline solids (smoky quartz, Pb3+ or Tl2+ in KCl). Although quartz and glass are structurally and chemically similar to feldspar, KCl is not, suggesting that for the most part it is the behavior of the chemical impurity on an atomic level which controls the coloring mechanism.
\r\n", "doi": "10.7907/bj75-5674", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3214", "collection": "thesis", "collection_id": "3214", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08242006-080724", "primary_object_url": { "basename": "echelmeyer-ka_1983.pdf", "content": "final", "filesize": 11189946, "license": "other", "mime_type": "application/pdf", "url": "/3214/12/echelmeyer-ka_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Response of Blue Glacier to a Perturbation in Ice Thickness: Theory and Observation", "author": [ { "family_name": "Echelmeyer", "given_name": "Keith Alan", "clpid": "Echelmeyer-Keith-Alan" } ], "thesis_advisor": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" } ], "thesis_committee": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Meier", "given_name": "Mark", "clpid": "Meier-M" }, { "family_name": "Sharp", "given_name": "Robert P.", "clpid": "Sharp-R-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A unique natural experiment has occurred on Mt. Olympus, Washington, in which the lower part of Blue Glacier has undergone a marked increase in ice thickness and a general decrease in surface slope. In response to this, the glacier flow velocities have increased considerably. The detailed study of the surface configuration and flow of the glacier during the period 1957-59, before the thickening (Meier, et al., 1974) provides a complete baseline against which the recent changes in geometry and surface velocity field are measured.
\r\n\r\nA detailed evaluation of the flow response to the changes in thickness and slope is made, testing for the existence of a quantitative observational relation among u, H, and \u03b1. A linear relation between the percentage ice thickness change and the percentage velocity increase is found. The slope of this response line is related to the exponent n in the flow law of ice, and the negative intercept represents an overall decrease in surface slope.
\r\n\r\nDetailed quantitative interpretations of the field measurements on the flow of Blue Glacier and its response to the change in surface configuration are made, using analytical and finite-element techniques.
\r\n\r\nA theoretical discussion of the effects of longitudinal stress gradients on the flow of an ice mass is given. This discussion leads to the development of an exponential Green's function which determines the effect of surface slope and ice thickness variations on the flow. This Green's function provides a weighting factor for longitudinal averaging of slope and thickness. The characteristic length scale up- and downglacier is dependent on the longitudinal strain-rate, the amount of basal sliding, and the flow-law parameters, being approximately three times the mean ice thickness. Application of this longitudinal averaging to the observed slope and thickness changes results in a marked decrease in deviations of the response data from a linear regression on the velocity changes, showing that longitudinal stress gradients are important.
\r\n\r\nA finite-element computer code for the calculation of flow of ice in channel cross sections of arbitrary shape, including transverse flow components, is developed. The model is applied to flow in channels of idealized parabolic cross-sectional shape to reveal the basic effects of channel shape and flow-law parameters on stress and velocity distribution. The stresses are found to be dependent on the flow-law parameters. Components of transverse flow within the cross section that develop in response to transverse convexity of the glacier surface were calculated. Comparison with observations shows that much of the splaying of the velocity vectors within an ablation zone can be attributed to flow driven by this convex surface.
\r\n\r\nAnalytical models of the flow of a glacier in which the flow law parameters vary with position are developed. These models show that there is a nonuniqueness in flow-law parameters obtained from borehole deformation studies. Studies of the response of a glacier to a change in surface configuration can partially eliminate some of this ambiguity.
\r\n\r\nThe theory and finite element calculations are extended to channels that follow a curving course in map view, which is necessary for application to Blue Glacier, since in the reach studied the glacier flows around a gently curving bend of 90\u00b0. Longitudinal channel curvature causes asymmetry in the stress and velocity distribution within a symmetric channel. The stress centerline is shifted toward the inside of the bend, while the position of the maximum velocity is usually shifted outward of the center for n \u2265 3. The effects of curvature are readily observable in the flow and crevassing of Blue Glacier.
\r\n\r\nThe relation between perturbations in ice thickness and surface slope and the change in velocity is developed for arbitrary channels. Analytical and numerical results indicate that there is a linear relation between the changes in slope \u03b1, thickness H, and surface velocity u:
\r\n\r\n[Equation included in scanned thesis' abstract, pp. vii]
\r\n\r\nwhere \u03a8 is termed the response factor. For realistic channel geometries, \u03a8 is in the range 1/2 to 1. This factor represents the change in cross-sectional shape of an ice mass which accompanies a change in ice thickness within a given channel. The value of the stress exponent inferred from the observed flow response is significantly affected by this geometric factor, which is approximately equal to 0.82 for Blue Glacier. The slope of the response line implies that n = 4 for the flow of Blue Glacier when this response factor is taken into account.
\r\n\r\nFinite element models of flow and the flow response within the different cross sections of Blue Glacier (as determined by radio echo sounding) compare well with the observed velocity patterns and response to change in thickness if channel curvature is included. These results again imply a stress exponent of n = 4. The results also agree with the various field measurements which indicate that basal sliding contributes at most 10% to the overall motion of the glacier.
\r\n\r\nThe results presented in this thesis represent the most detailed evaluation of the response of a glacier to perturbations in ice thickness and surface slope. They show that non-linear flow theory with n = 4 is applicable to a good approximation. The relationship between the flow velocity, slope, and thickness found in this work has direct application to the study of effects of climatic change on an ice mass.
", "doi": "10.7907/ZQHK-NA29", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:11782", "collection": "thesis", "collection_id": "11782", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08302019-150635775", "type": "thesis", "title": "Holographic In-Situ Stress Measurement in Geophysics", "author": [ { "family_name": "Cohn", "given_name": "Stephen Norfleet", "clpid": "Cohn-Stephen-Norfleet" } ], "thesis_advisor": [ { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A new and still experimental method for measuring the absolute in-situ stress field in crustal rocks offers several advantages compared to existing in-situ stress measurement techniques. It employs optical holography to record strain-relief displacements in a borehole environment. We call the prototype instrument the holographic stressmeter. It operates in an uncased borehole where it drills strain-relieving side holes into the borehole wall. An interference holographic recording system records the resulting displacements onto film. The reconstructed interference holograms contain sufficient information in their fringe patterns to determine the three-dimensional vector displacements due to strain relief at every point surrounding the side hole. Assuming isotropic, homogeneous, linearly elastic rock, these displacements define the three stresses acting at the borehole wall at a single point. The three non-vanishing stresses acting at each of three points, distributed azimuthally, on the borehole wall provide sufficient constraint to determine all six components of the desired far-field or virgin-rock stress tensor.
\r\n\r\nThe holographic stressmeter employs an on-board side hole drilling system to produce strain relief. Thus it should be economical to operate and it is not restricted to shallow depths as are overcoring techniques. Furthermore, recording the whole displacement field resulting from drilling the side hole reduces the potential contamination of the measurement by residual stress mechanisms which often affect point strain measurements using foil resistance gauges.
\r\n\r\nTo date a complete stress determination in the field has not been attempted. However, a prototype stressmeter has demonstrated repeatedly that the stability necessary to conduct the measurement using this approach is attainable. Results from field deployment show that the stressmeter can make qualitatively correct measurements at one azimuth in a borehole. Modifications to make measurements at the three azimuths required for a complete determination of the stress tensor components should be easily achieved. We propose additional improvements to permit measuring rock elastic properties in situ to enable accurate, quantitative stress determinations. The theoretically predicted precision of the stress component magnitudes using this measurement approach is estimated at 20%.
", "doi": "10.7907/6vsd-wa54", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:2981", "collection": "thesis", "collection_id": "2981", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07252007-135803", "primary_object_url": { "basename": "Powell_re_1981.pdf", "content": "final", "filesize": 18615907, "license": "other", "mime_type": "application/pdf", "url": "/2981/16/Powell_re_1981.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Geology of the Crystalline Basement Complex, Eastern Transverse Ranges, Southern California: Constraints on Regional Tectonic Interpretation", "author": [ { "family_name": "Powell", "given_name": "Robert Edward", "clpid": "Powell-Robert-Edward" } ], "thesis_advisor": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "thesis_committee": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "About 3000 km2 within the crystalline basement complex of the Eastern Transverse Ranges in the Chuckwalla, Orocopia, Eagle, Cottonwood, Hexie, Little San Bernardino, and Pinto Mountains of Riverside County, California were mapped at scales of 1:36,000 and 1:62,500 and compiled at 1:125,000 (Plate I). Pre-Jurassic(?) (i.e., older than the Mesozoic batholiths) rocks of the crystalline complex comprise two lithologically distinct terranes. These terranes are called the Joshua Tree and San Gabriel terranes for regions of southern California in which their lithologies were initially characterized. The two terranes are superposed along a previously unrecognized low-angle fault system of regional extent, the Red Cloud thrust.
\r\n\r\nDuring the course of this study, the structurally lower Joshua Tree terrane has been defined as a stratigraphically coherent group of crystalline rocks that consists of Precambrian granite capped by a paleo-weathered zone and overlain nonconformably by orthoquartzite that interfingers westward with pelitic and feldspathic granofelses. The quartzite contains near-basal quartz/quartzite clast conglomerates, and has well-preserved cross-bedding that appears upright wherever it has been observed. Pelitic and feldspathic granofelses crop out to the west of the quartzite exposures in four lithologically different belts that trend northnorthwest throughout the area mapped. These lithologic belts are interpreted to have been derived from stratigraphically interfingering sedimentary protoliths deposited in a basin offshore from a quartzose beach-sand protolith. In proximity to the early Red Cloud thrust, this whole stratigraphic package was pervasively deformed to granite gneiss, stretched pebble conglomerate, lineated quartzite, and schist.
\r\n\r\nA northeast-trending pattern of metamorphic isograds was orthogonally superimposed on the northnorthwest-trending protoliths of the Pinto gneiss. A central andalusite zone, located in the southern Little San Bernardino and Hexie, and northern Eagle Mountains, is flanked to the northwest and southeast by sillimanite zones. Coincident with this symmetrical distribution of aluminosilicates is an asymmetrical distribution of other pelitic mineral zones, with prograde cordierite-aluminosilicate-biotite- and K-feldspar-aluminosilicate-bearing assemblages to the northwest in the northern Little San Bernardino and Pinto Mountains, staurolite-bearing assemblages in a narrow zone in the southern Little San Bernardino-Hexie and northern Eagle Mountains, and retrograde chlorite-muscovite-bearing assemblages in the southernmost Little San Bernardino, Cottonwood, southern Eagle, Orocopia, and Chuckwalla Mountains. One occurrence of chloritoid-sillimanite in the central Eagle Mountains is apparently also retrograde. The crossing isograds are interpreted to result from a temporal increase in PH2O relative to PT from south to north through the field area. Comparison of the pelitic assemblages with experimental studies suggests peak conditions of PT \u2248 3.5 to 4 kb, T \u2248 525 to 625\u00b0C. The early prograde metamorphism pre-dated the thrusting event; the retrograde stage may have overlapped in time with the emplacement of the San Gabriel terrane allochthon. Cordierite-orthoamphibole-bearing assemblages are present in one stratigraphic zone of the Pinto gneiss.
\r\n\r\nIn this study, the Precambrian lithologies of the San Gabriel terrane are viewed as a three-part deep crustal section, with uppermost amphibolite grade pelitic (Hexie) gneiss intruded by granodioritic (Soledad) augen gneiss at the highest level, retrograded granulite (Augustine) gneiss at an intermediate level, and syenite-mangerite-jotunite at the lowest level exposed in the Eastern Transverse Ranges. The Hexie gneiss, characterized by sillimanite-garnet-biotite-bearing assemblages, is thrust over andalusite-bearing granofels of the Pinto gneiss.
\r\n\r\nThe Red Cloud thrust system is inferred to have developed in three or four sequential structural events: 1) early thrusting that probably moved parallel to the ENE mineral lineations recorded in both plates; 2) regional folding of the initial thrust surface around NNE-trending axes; 3) later thrusting that broke with some component of westward movement across a fold in the older thrust surface to produce a stacking of crystalline thrust plates of the two terranes; 4) continued or renewed folding of both thrust faults with eventual overturning toward the SW. It is consistent with all observations to date to link these structural events into a single regional tectonic episode that resulted in westward-vergent allochthonous emplacement of the San Gabriel terrane over Joshua Tree terrane. The thrust timing can only be loosely bracketed in time between 1195 m.y. and 165 m.y. ago.
\r\n\r\nThe pre-batholithic terranes and the westward-vergent Red Cloud thrust are considered to be exotic with respect to the pre-batholithic rocks and structures exposed to the north and east of the field area. The bounding discontinuity has been obliterated by intrusion of both suites of Mesozoic batholithic rocks.
\r\n\r\nThe Mesozoic plutonic rocks comprise two batholithic suites, both of which intrude the Joshua Tree and San Gabriel terranes and the Red Cloud thrust system. NW-SE trending belts of plutonic lithologies have been mapped within each suite: the oldest lithology of the younger suite intrudes the youngest lithology of the older suite. The older suite, Jurassic(?), lying to the NE, appears to have an alkalic character; the younger suite, Cretaceous(?), appears calc-alkaline. The older suite consists of biotite- and K-feldspar-bearing gabbro-diorites intruded by low-quartz monzogranites. The younger suite includes hornblende-biotite-sphene granodiorite intruded by porphyritic monzogranites, intruded in turn by nonporphyritic monzogranite.
\r\n\r\nThe Eastern Transverse Ranges south of the Pinto Mountain fault are defined by several Cenozoic E-W left-lateral strike-slip faults that have a cumulative westward displacement from S to N of about 50 km. The left-lateral faults are interpreted to form part of a conjugate fault set with complementary right-lateral faults in the Mojave and Colorado Deserts. Along the western boundary of the Eastern Transverse Ranges in the Little San Bernardino Mountains, the crystalline rocks have been pervasively cataclasized by an event that post-dates intrusion of the Cretaceous(?) plutonic rocks. The cataclasis is attributed to the Vincent-Orocopia-Chocolate Mountain thrust that is thought to superpose the diverse pre-batholithic and batholithic rocks of the Eastern Transverse Ranges above Pelona-type schist. The cataclastic foliation is folded along the length of the Little San Bernardino Mountains in an antiform that is inferred to be cored with Pelona-type schist. This fold may have formed a single antiformal feature comprising all the crystalline-rock antiforms now recognized along the San Andreas fault that are cored by Pelona-type schist. Displacements of the piercing points formed by the antiformal axis apparently indicate 220 km of right-lateral offset on the present San Andreas strand and about 80 km of right-lateral offset along a fragmented older San Andreas strand that consisted of the San Francisquito, Fenner, and Clemens Well faults and a buried extension of this fault beneath the alluvial fill of the valley between the Chocolate and Chuckwalla Mountains.
\r\n", "doi": "10.7907/F22F-YX04", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:2788", "collection": "thesis", "collection_id": "2788", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06302006-083245", "primary_object_url": { "basename": "Raychaudhuri_b_1960.pdf", "content": "final", "filesize": 11453881, "license": "other", "mime_type": "application/pdf", "url": "/2788/1/Raychaudhuri_b_1960.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Studies of Amphibolites and Constituent Hornblendes From an Area of Progressive Metamorphism Near Lead, South Dakota", "author": [ { "family_name": "Raychaudhuri", "given_name": "Bimalendu", "clpid": "Raychaudhuri-Bimalendu" } ], "thesis_advisor": [ { "family_name": "Engel", "given_name": "Albert Edward John", "clpid": "Engel-A-E-J" } ], "thesis_committee": [ { "family_name": "Engel", "given_name": "Albert Edward John", "clpid": "Engel-A-E-J" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The progressive metamorphism and origin of the amphibolites of the Lead-Deadwood area, S. Dakota, are considered in detail. Eighty specimens of amphibolite were collected along a belt 3 miles long extending across the entire garnet zone and part of the staurolite zone of the enclosing meta-sediments. These amphibolites were studied petrographically and from them thirty-four were used for modal analysis and chemical analyses for total iron (as Fe2O3), CaO, TiO2, K2O, MnO and trace elements. Twelve of the constituent hornblendes were analysed for all major and minor elements and trace elements. The other 22 constituent hornblendes were analysed for total iron (as Fe2O3), CaO, TiO2, K2O, MnO and trace elements. Seven of the constituent horn-blendes and six constituent plagioclases were used for optical determinations and x-ray diffractometric studies.\r\n\r\nOn the basis of relict texture some of the amphibolites are concluded to be definitely ortho-amphibolites. Field relations of a few hornblende-bearing rocks suggest that they have meta-sedimentary origin. The origin of the remaining majority of the amphibolites is inconclusive.\r\n\r\nThe metamorphism of the amphibolites is essentially iso-chemical throughout the range of conditions represented by the appearance of successively the garnet and the staurolite isophases in the enclosing meta-sediments. What fluctuations in composition are observed appear to be random in character, attributable to minor variations in original composition or to retrograde alteration.\r\n\r\nThe compositions of the constituent hornblendes do not show any significant correlation with intensity of metamorphism and the average composition remains roughly constant throughout the sequence.\r\n\r\nThe concentrations of the various components in the horn-blendes seem to be closely related to the concentrations of the same components in the corresponding amphibolites. The ratios of the concentrations of the various components between horn-blende and amphibolite do not show any significant trend with metamorphic rank and are reasonably constant over the range of metamorphic conditions represented here.\r\n\r\nThe composition of the hornblendes is closely related to specific gravity and broadly related to dimensions of unit cells but there is no close correlation between composition and optics. Size of unit cells in hornblendes appear to be unrelated to metamorphic rank.", "doi": "10.7907/V56J-JE76", "publication_date": "1960", "thesis_type": "phd", "thesis_year": "1960" } ]