Isotope dilution thorium and uranium analyses of the Harleton chondrite show a\r\nlarger scatter than previously observed in equilibrated ordinary chondrites (EOC). The\r\nlinear correlation of Th/U with 1/U in Harleton (and all EOC data) is produced by\r\nvariation in the chlorapatite to merrillite mixing ratio. Apatite variations control the U\r\nconcentrations. Phosphorus variations are compensated by inverse variations in U to\r\npreserve the Th/U vs. 1/U correlation. Because the Th/U variations reflect phosphate\r\nampling, a weighted Th/U average should converge to an improved solar system Th/U.\r\nWe obtain Th/U=3.53 (1-mean=0.10), significantly lower and more precise than previous\r\nestimates.
\r\n\r\nTo test whether apatite also produces Th/U variation in CI and CM chondrites, we\r\nperformed P analyses on the solutions from leaching experiments of Orgueil and\r\nMurchison meteorites.
\r\n\r\nA linear Th/U vs. 1/U correlation in CI can be explained by redistribution of\r\nhexavalent U by aqueous fluids into carbonates and sulfates.
\r\n\r\nUnlike CI and EOC, whole rock Th/U variations in CMs are mostly due to Th\r\nvariations. A Th/U vs. 1/U linear correlation suggested by previous data for CMs is not\r\nreal. We distinguish 4 components responsible for the whole rock Th/U variations: (1) P\r\nand actinide-depleted matrix containing small amounts of U-rich carbonate/sulfate phases\r\n(similar to CIs); (2) CAIs and (3) chondrules are major reservoirs for actinides, (4) an\r\neasily leachable phase of high Th/U. likely carbonate produced by CAI alteration.\r\nPhosphates play a minor role as actinide and P carrier phases in CM chondrites.
\r\n\r\nUsing our Th/U and minimum galactic ages from halo globular clusters, we\r\ncalculate relative supernovae production rates for 232Th/238U and 235U/238U for different\r\nmodels of r-process nucleosynthesis. For uniform galactic production, the beginning of the\r\nr-process nucleosynthesis must be less than 13 Gyr. Exponentially decreasing production is also\r\nconsistent with a 13 Gyr age, but very slow decay times are required (less than 35 Gyr),\r\napproaching the uniform production. The 15 Gyr Galaxy requires either a fast initial\r\nproduction growth (infall time constant less than 0.5 Gyr) followed by very low decrease (decay\r\ntime constant greater than 100 Gyr), or the fastest possible decrease (\u22488 Gyr) preceded by slow in fall\r\n(\u22487.5 Gyr).
\r\n", "doi": "10.7907/hfsz-ym11", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:7374", "collection": "thesis", "collection_id": "7374", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01072013-160430261", "primary_object_url": { "basename": "LaTourrett_t_1993.pdf", "content": "final", "filesize": 44041987, "license": "other", "mime_type": "application/pdf", "url": "/7374/1/LaTourrett_t_1993.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Experimental Determination of U and Th Partitioning Between Clinopyroxene, Garnet, Olivine, and Natural and Synthetic Silicate Melt", "author": [ { "family_name": "LaTourrette", "given_name": "Thomas", "clpid": "LaTourrette-Thomas" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The distribution of U and Th between crystals and quenched silicate melt has been measured in experimentally crystallized natural and synthetic starting compositions. Clinopyroxene was crystallized from two natural basalts and a synthetic composition on the diopside-anorthite join, olivine from one of the natural basalts, and garnet from a synthetic andesite. Clinopyroxene and olivine were crystallized at atmospheric pressure under controlled oxygen fugacity and U and Th distributions were determined by particle track radiography. Garnet crystals were grown at 27 Kbars and actinide distributions were determined by secondary ion mass spectrometry. Crystals were grown by slow cooling in an effort to maintain chemical equilibrium at the crystal-melt interface.
\r\n\r\nClinopyroxene- and olivine-melt partition coefficients (Dixtl/liq = Cixtl/Ciliq) were calculated from track distributions by correcting for chemical zoning in the crystals (a result of fractional crystallization) and particle range differences between the crystals and glass. Over the range of \u0192O2s and compositions studied, DUcpx/liq = 0.0021 - 0.0093, = DThcpx/liq = 0.0047- 0.021, and DU;Thol/liq < 0.00005. Garnet-melt partition coefficients are DUgt/liq = 0.0013 and DThgt/liq = 0.0122. In order to study the effect of the U valence state distribution on U-Th fractionation, clinopyroxene crystallization experiments were run at oxygen fugacities corresponding to the Ni-NiO (NNO), Fa-Mt-Qz (FMQ) and 1 log unit more oxidizing than Fe-FeO (IW+ 1) oxygen buffers. All compositions show an increase in DUcpx/liq with decreasing \u0192O2, presumably from the increasing proportion of U4+ in the melt. DThcpx/liq displays little variation with \u0192O2, consistent with the fact that Th is solely tetravalent DThcpx/liq does show an apparent small decrease with decreasing \u0192O2 in one composition, and this is interpreted to be due to compositional changes stemming from variable amounts Na-loss with \u0192O2. A limited compositional analysis indicates that actinides may be incorporated into clinopyroxene by means of a (U,Th)4+ + 2Na+,\u21d4 3Ca2+ coupled substitution in the M2 site. This mechanism predicts a positive dependence of the actinide partition coefficients on (DCacpx/liq)3 / (DNacpx/liq)2.
\r\n\r\nWhile there is evidence for deviations from interfacial equilibrium during crystal growth, DThxtl/liq and DUxtl/liq are affected similarly. This results in DThxtl/liq/DUxtl/liq, which gives a measure of the degree of U-Th fractionation possible by crystal-melt partitioning, being insensitive to these deviations. DThcpx/liq/DUcpx/liq is well behaved, approximately independent of composition, and decreases by a factor of 2 - 3 as the \u0192O2 decreases from NNO to IW+1. This indicates that U-Th fractionation by crystal-melt partitioning is \u0192O2 dependent.
\r\n\r\nThese results indicate that U-Th fractionation by clinopyroxene-melt partitioning during partial melting will result in a melt with Th/U less than the clinopyroxene, U-Th fractionation by olivine will be insignificant for physically realistic melt fractions, and U-Th\r\nfractionation by garnet will result in a melt with ThiU greater than the garnet. The observed pattern of 238U-230Th disequilibrium in oceanic basalts (MORB and OIB) requires a net UTh fractionation that is large, ubiquitous, and results in (238U-230Th) < 1. With these constraints, fractionation by partial melting of spinel lherzolite is ruled out. The sense of U-Th fractionation by garnet is consistent with oceanic basalts, but the magnitude of fractionation is much smaller than the entire range in observed fractionations. Since partial melts of neither spinel nor garnet lherzolite can match the sense and magnitude of 238U-230Th disequilibrium in MORB and OIB, partial melting is considered unimportant in generating 238U-230Th disequilibrium in oceanic basalts. 238U-230Th disequilibrium in MORB and OIB must therefore result from some process other than partial melting, and possible alternative mechanisms are presented.
\r\n", "doi": "10.7907/4ww8-x445", "publication_date": "1993", "thesis_type": "phd", "thesis_year": "1993" }, { "id": "thesis:7994", "collection": "thesis", "collection_id": "7994", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10172013-085025235", "primary_object_url": { "basename": "Polanskey_ca_1989.pdf", "content": "final", "filesize": 19873642, "license": "other", "mime_type": "application/pdf", "url": "/7994/1/Polanskey_ca_1989.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Impact Spallation Experiments: Fracture Patterns and Spall Velocities. II. Craters in Carbonate Rocks: An Electron Paramagnetic Resonance Analysis of Shock Damage", "author": [ { "family_name": "Polanskey", "given_name": "Carol Ann", "clpid": "Polanskey-Carol-Ann" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This work is divided into two independent papers.
\r\n\r\nPAPER 1.
\r\n\r\nSpall velocities were measured for nine experimental impacts into San Marcos gabbro targets. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles were iron, aluminum, lead, and basalt of varying sizes. The projectile masses ranged from a 4 g lead bullet to a 0.04 g aluminum sphere. The velocities of fragments were measured from high-speed films taken of the events. The maximum spall velocity observed was 30 m/sec, or 0.56 percent of the 5.4 km/sec impact velocity. The measured velocities were compared to the spall velocities predicted by the spallation model of Melosh (1984). The compatibility between the spallation model for large planetary impacts and the results of these small scale experiments are considered in detail.
\r\n\r\nThe targets were also bisected to observe the pattern of internal fractures. A series of fractures were observed, whose location coincided with the boundary between rock subjected to the peak shock compression and a theoretical \"near surface zone\" predicted by the spallation model. Thus, between this boundary and the free surface, the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.
\r\n\r\nPAPER 2.
\r\n\r\nCarbonate samples from the nuclear explosion crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance, EPR. The first series of samples for OAK Crater were obtained from six boreholes within the crater, and the second series were ejecta samples recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen limestone, which had been shocked to known pressures.
\r\n\r\nThe results of the OAK borehole analysis have identified a thin zone of highly shocked carbonate material underneath the crater floor. This zone has a maximum depth of approximately 200 ft below sea floor at the ground zero borehole and decreases in depth towards the crater rim. A layer of highly shocked material is also found on the surface in the vicinity of the reference bolehole, located outside the crater. This material could represent a fallout layer. The ejecta samples have experienced a range of shock pressures.
\r\n\r\nIt was also demonstrated that the EPR technique is feasible for the study of terrestrial impact craters formed in carbonate bedrock. The results for the Meteor Crater analysis suggest a slight degree of shock damage present in the \u03b2 member of the Kaibab Formation exposed in the crater walls.
", "doi": "10.7907/3rgr-f070", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:7994", "collection": "thesis", "collection_id": "7994", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10172013-085025235", "primary_object_url": { "basename": "Polanskey_ca_1989.pdf", "content": "final", "filesize": 19873642, "license": "other", "mime_type": "application/pdf", "url": "/7994/1/Polanskey_ca_1989.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Impact Spallation Experiments: Fracture Patterns and Spall Velocities. II. Craters in Carbonate Rocks: An Electron Paramagnetic Resonance Analysis of Shock Damage", "author": [ { "family_name": "Polanskey", "given_name": "Carol Ann", "clpid": "Polanskey-Carol-Ann" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This work is divided into two independent papers.
\r\n\r\nPAPER 1.
\r\n\r\nSpall velocities were measured for nine experimental impacts into San Marcos gabbro targets. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles were iron, aluminum, lead, and basalt of varying sizes. The projectile masses ranged from a 4 g lead bullet to a 0.04 g aluminum sphere. The velocities of fragments were measured from high-speed films taken of the events. The maximum spall velocity observed was 30 m/sec, or 0.56 percent of the 5.4 km/sec impact velocity. The measured velocities were compared to the spall velocities predicted by the spallation model of Melosh (1984). The compatibility between the spallation model for large planetary impacts and the results of these small scale experiments are considered in detail.
\r\n\r\nThe targets were also bisected to observe the pattern of internal fractures. A series of fractures were observed, whose location coincided with the boundary between rock subjected to the peak shock compression and a theoretical \"near surface zone\" predicted by the spallation model. Thus, between this boundary and the free surface, the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.
\r\n\r\nPAPER 2.
\r\n\r\nCarbonate samples from the nuclear explosion crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance, EPR. The first series of samples for OAK Crater were obtained from six boreholes within the crater, and the second series were ejecta samples recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen limestone, which had been shocked to known pressures.
\r\n\r\nThe results of the OAK borehole analysis have identified a thin zone of highly shocked carbonate material underneath the crater floor. This zone has a maximum depth of approximately 200 ft below sea floor at the ground zero borehole and decreases in depth towards the crater rim. A layer of highly shocked material is also found on the surface in the vicinity of the reference bolehole, located outside the crater. This material could represent a fallout layer. The ejecta samples have experienced a range of shock pressures.
\r\n\r\nIt was also demonstrated that the EPR technique is feasible for the study of terrestrial impact craters formed in carbonate bedrock. The results for the Meteor Crater analysis suggest a slight degree of shock damage present in the \u03b2 member of the Kaibab Formation exposed in the crater walls.
", "doi": "10.7907/3rgr-f070", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:16216", "collection": "thesis", "collection_id": "16216", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10272023-170924439", "primary_object_url": { "basename": "Rigden_SM_1986.pdf", "content": "final", "filesize": 48886487, "license": "other", "mime_type": "application/pdf", "url": "/16216/1/Rigden_SM_1986.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Determination of the Equation of State of Molten Silicates at High Pressures Using Shock-Wave Techniques", "author": [ { "family_name": "Rigden", "given_name": "Sally Miranda", "clpid": "Rigden-Sally-Miranda" } ], "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": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Shock wave (Hugoniot) equation-of state experiments have been carried out on molten silicates in the petrologically important system CaMgSi\u2082O\u2086-CaAl\u2082Si\u2082O\u2088 via the projectile impact method. An RF heating technique was developed to heat silicate samples contained in pure Mo containers to the necessary high initial temperatures (up to 1773 K). Thermocouple techniques, a refractory sample holding system and optical shutter systems, were developed to allow utilization of a propellant gun apparatus at impact velocities ranging from 1.0 to 2.5 km sec\u207b\u00b9 corresponding to shock pressures of 4 to 40 GPa. The methodology for taking into account the effect of the Mo container in measuring the equation of state of the molten silicate is explicitly derived.
\r\n\r\nResults on molten diopside (CaMgSi\u2082O\u2086), anorthite (CaAl\u2082Si\u2082O\u2088) and an inter\u00ad mediate composition (36 mole % CaAl\u2082Si\u2082O\u2088, 64 mole % CaMgSi\u2082O\u2086: An_(0.36)Di_(0.64)) are presented. Reduction of the Hugoniot data for these materials to third-order Birch-\u00adMurnaghan isentropes yields 1 atm bulk moduli (K_s) in the range 18-24 GPa which are in good agreement with bulk moduli recently measured by ultrasonic methods at 1 atm and similar temperatures. The pressure derivatives of bulk modulus (K') vary\r\nfrom 5-7. Shock temperature calculations for An_(0.36)Di_(0.64) indicate temperatures of 2400-2600 K at ~25 GPa. The Hugoniot states are believed to lie metastably in the liquid field on the basis of measured bulk modulus, calculated Hugoniot density of a solid of the same composition and estimated crystallization times.
\r\n\r\nThe measured equation of state data for molten diopside is used in conjunction with other thermochemical data to constrain the diopside solidus via the Clausius\u00ad Clapeyron equation at pressures up to 20 GPa. The present data are consistent with\r\n measured fusion curve data of others to 5 GPa. Above ~10 GPa, a marked shallowing of the solidus is predicted as the difference in volume between crystalline and mol\u00adten diopside in equilibrium approaches zero.
\r\n\r\nComparison of the results for molten diopside with those from the intermediate composition indicates that the liquids exhibit ideal mixing behavior with respect to volume to within \u00b12% up to ~40 Gpa. Gradual changes in coordination of Al\u00b3\u207a and Si\u2074\u207a from tetrahedral at low pressures to octahedral at high pressures are believed to occur during compression of these materials. The integrated compressibility as reflected in the values of K_s and K' is related to the proportion of tetrahedrally coordinated cations at low pressure, and the volume at ~40 GPa is from 100-110% of that of a mixture of the dense, high-pressure phases MgSiO\u2083 (perovskite), CaSiO\u2083 (perovskite), Al\u2082P\u2083 (corundum) and SiO\u2082 (stishovite).
\r\n\r\nImportant petrological implications of our results include: (1) basic to ultrabasic melts become denser than olivine- and pyroxene-rich mantle at pressures of 6-10 GPa, and (2) there is a maximum depth from which basaltic melt can rise buoyantly within terrestrial planetary interiors.
", "doi": "10.7907/5v04-ws14", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "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-W-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:3133", "collection": "thesis", "collection_id": "3133", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08152006-132531", "primary_object_url": { "basename": "Piepgras_dj_1984.pdf", "content": "final", "filesize": 13047842, "license": "other", "mime_type": "application/pdf", "url": "/3133/1/Piepgras_dj_1984.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Isotopic Composition of Neodymium in the Marine Environment: Investigations of the Sources and Transport of Rare Earth Elements in the Oceans", "author": [ { "family_name": "Piepgras", "given_name": "Donald John", "clpid": "Piepgras-Donald-John" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "Patterson", "given_name": "Clair C.", "clpid": "Patterson-C-C" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In this study, the isotopic composition of neodymium in the marine environment has been determined from analysis of marine ferromanganese precipitates and seawater. An initial survey of the isotopic composition of Nd in the marine environment was made utilizing the analyses of authigenic ferromanganese sediments. These included ferromanganese nodules, metalliferous sediments, and hydrothermal ferromanganese crust deposits. Large variations in \u03b5Nd(0) values are observed which exhibit a clear separation of the ocean basin. Nd isotopic variations within an ocean basin fall within a relatively small, well defined range which is characteristic of the ocean basin sampled. Based on these results, the following average 143Nd/144Nd ratios for the ocean basins have been determined: Atlantic Ocean, \u03b5Nd(0) \u2248 -12; Indian Ocean, \u03b5Nd(0) \u2248 -8; Pacific Ocean, \u03b5Nd(0) \u2248 -3. These values are considerably lower than \u03b5Nd(0) values associated sources having oceanic mantle affinities, indicating that the REE in the oceans are dominated by continental sources. Therefore, the variations must reflect primarily the age and 147Sm/144Nd ratio of the continental masses being sampled.
\r\n\r\nDirect measurements of the isotopic composition of Nd in seawater samples from the Atlantic and Pacific are in excellent agreement with the values determined from the ferromanganese sediments indicating that these sediments accurately reflect the isotopic composition of Nd dissolved in seawater. The results clearly demonstrate the existence of distinctive Nd isotopic differences in waters of the major ocean basins. These values correspond to a difference in the absolute abundance of 143Nd between the Atlantic and the Pacific Oceans of ~ 10(6) atoms 143Nd per gram of seawater. In addition to the isotopic differences observed between the ocean basins, smaller but distinctive variations are observed in the water column of both the Pacific and the Atlantic, indicating different sources of REE at different levels in the water column. This suggests that it may be possible to distinguish the sources of water masses within an ocean basin on the basis of Nd isotopic composition.
\r\n\r\nThe isotopic composition of Nd was determined in seawater samples from the Drake Passage in order to monitor the exchange of REE between the Pacific and Atlantic Oceans. The Antarctic Circumpolar Current, which flows eastward through this passage, represents the primary conduit through which the major ocean basins communicate with each other. The isotopic composition of Nd is found to be uniform with depth at all stations and corresponds to \u03b5Nd(0) \u2243 -9.0. This value is intermediate between the values for the Atlantic and the Pacific and indicates that the Antarctic Circumpolar Current consists of about 70 percent Atlantic water. By using a box model to describe the exchange of water between the Southern Ocean and the ocean basins to the north together with the isotopic results, an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the Pacific and the Southern Ocean.
\r\n\r\nThe concentration of Nd exhibits a regular increase with depth at all locations studied. In contrast, Nd isotopic compositions can exhibit substantial variations in the water column which vary depending on the location. Where isotopic differences in the water column occur, substantial lateral transport of REE from different sources and at different levels in the water column is required to maintain these differences. It is shown that the concentration gradients are established without significantly affecting the isotopic distribution, and that the enrichment of Nd in the deep water cannot be a result of resolution of REE scavenged from surface waters.
\r\n\r\nThe isotopic distributions are compared to water mass analyses based on temperature and salinity characteristics in the water column at the various sampling locations. It is shown that differences in isotopic compositions in the water column are well correlated with changes in the temperature and salinity characteristics. Thus, the isotopic distributions are fully consistent with the circulation of major water masses. This indicates that while Nd is nonconservative in concentration, the isotopic composition is conserved and can be used as a tracer for studying the origin and circulation of water masses.
\r\n\r\nThe results of these studies have provided some important contributions to the understanding of trace element transport in the oceans. First, the Nd isotopic differences in the water column clearly indicate that transport of Nd from the surface to the deep ocean cannot account for the observed increase in concentration of Nd with depth. These isotopic differences must be maintained by lateral transport of the REE and indicates that the concentration gradients of the REE and possibly other trace elements must also be related in part to lateral transport processes. Second, the close correlation observed between changes in Nd isotopic compositions and temperature-salinity relationships in the water column indicates that the lateral transport of REE in the oceans is directly related to the origin and flow of water masses. Thus, the isotopic composition of Nd in seawater is shown to be a useful tracer for studying the sources of injection and transport of trace elements in the oceans.
\r\n\r\nIn addition to the seawater studies, the concentrations and isotopic compositions of Nd and Sr were determined in hydrothermal solutions emanating from hot springs on the crest of the East Pacific Rise at 21\u00b0N and at Guaymas Basin, Gulf of California. This study represents the first effort to measure the Nd isotopic compositions in hydrothermal solutions. Endmember samples (T = 350\u00b0C) from 21\u00b0N exhibit a small range in \u03b5Sr values from -13.4 to -15.7. Correcting to CMg = 0, the pure hydrothermal solutions are estimated to have \u03b5Sr \u2243 -18. These results indicate that the fluids have undergone extensive but not complete exchange with Sr in the depleted oceanic crust (\u03b5Sr \u2243 -30). CSr ranges from 5.8 to 8.7 ppm and is similar to seawater (7.6 ppm) indicating that there must be buffering. Hydrothermal solutions from Guaymas Basin (T = 315\u00b0C) rise through several hundred meters of sediment before reaching the sea floor. One sample from here has \u03b5Sr = +5.8, indicating that the solutions have reacted first with oceanic crust and then sediments. The high Sr concentration in this sample (19.3 ppm) is consistent with late stage interaction between the ascending fluid and carbonate rich sediments.
\r\n\r\nNd shows a wide range in concentration and isotopic compositions in solutions from 21\u00b0N. CNd ranges from 20 to 659 pg/g, indicating substantial enrichments of Nd over typical seawater concentrations of ~3 to 4pg/g. \u03b5Nd ranges from -10.8 to +7.9. The data clearly show substantial contributions of Nd from depleted oceanic crust to many of the samples analyzed. In spite of enrichments in Nd of up to about 100 times seawater, none of the samples have \u03b5Nd values equal to MORB (\u03b5Nd \u2243 +10). One sample from Guaymas Basin has \u03b5Nd = -11.4 consistent with leaching of Nd from sediments derived from old, continental sources. There is some inconsistency in the Nd isotopic data indicating that there is a possibility of contamination during sampling and/or handling of the solutions.
", "doi": "10.7907/GATW-C580", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:10832", "collection": "thesis", "collection_id": "10832", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04252018-105910410", "type": "thesis", "title": "Dynamic Properties of Carbonates and Applications to Cratering Processes", "author": [ { "family_name": "Vizgirda", "given_name": "Joana Marija", "clpid": "Vizgirda-Joana-Marija" } ], "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": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The response of carbonate minerals and rocks under shock compression is investigated using equation of state, shock metamorphism, and crater morphology studies. Coralline limestone samples from Cactus Crater, a nuclear explosion crater on Runit Island in Eniwetok Atoll, are used in the investigations of shock deformation as well as the crater structural study. Carbonate minerals and rocks shocked in the laboratory to known dynamic stress levels are used to calibrate shock pressures in the Cactus samples.
\r\n\r\nVery low shock pressure deformation effects are detected in the explosively and laboratory shocked samples by two bulk sample techniques: electron spin resonance (ESR) and powder X-ray diffraction. According to ESR studies on calcite from Cactus Crater samples, peak shock pressures of 4.5\u00b10.5 GPa were experienced by the material beneath the crater. Aragonite peak broadening analyses of powder X-ray diffraction spectra allows differentiation between two modes of material deformation, mosaicism (or reduction of crystallite size) and strain; both of these effects are detected in Cactus and in laboratory shocked samples. According to the X-ray analysis, peak pressures of 3\u00b11.5 GPa were experienced by the Cactus samples. A phase transition model, based on the variation of mosaicism and strain effects with shock pressure, is proposed. According to this model, residual strain in aragonite increases (crystallite size remaining approximately the same) until a threshold pressure of 8 to 10 GPa, corresponding to a phase transition, is reached; release from shock states above this pressure results in a discontinuous decrease in crystallite size and strain.
\r\n\r\nThe diagenetic high to low magnesium calcite transition boundary occurring in the immediate subsurface of Runit Island is used as a stratigraphic tracer to determine structural features beneath Cactus Crater, including the amount of permanent downward displacement, the presence of a 10 m thick breccia lens which is disturbed and extensively mixed in-situ, and a possible central uplift feature. Applying the Bingham plastic model to Cactus Crater gives a yield strength of approximately 1 bar for the shock-wave engulfed limestone rock; this value is similar to the yield strength of many clays, and suggests a partially liquefied state for the water-saturated limestone immediately after passage of the shock wave.
\r\n\r\nThe first aragonite Hugoniot equation of state data are presented. A Hugoniot elastic limit at 2.5\u00b10.8 GPa and a phase transition at 6.5\u00b11.5 GPa are observed. Above 10 GPa, the aragonite and calcite Hugoniots are approximately coincident, suggesting the transformation of both CaCO3 polymorphs to the same high pressure phase. Release adiabats centered at shock pressures above 18 GPa yield pressure-density isentropes which suggest possible dissociation, i.e. CO2 release, during the decompression process. These experimental data disagree with theoretical calculations, which predict incipient vaporization upon release from shock pressures of 55 and 33 GPa on the aragonite and calcite Hugoniots, respectively. Results from release adiabat experiments on calcite agree with the aragonite data and suggest vaporization upon unloading from shock pressures of approximately 37 GPa; a mass balance calculation using the experimental calcite release paths indicates that 45% of the CaCO3 has dissociated upon release to 0.2 GPa pressures.
\r\n\r\n", "doi": "10.7907/dat3-9s72", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:4284", "collection": "thesis", "collection_id": "4284", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10282005-135027", "primary_object_url": { "basename": "Stapanian_mi_1981.pdf", "content": "final", "filesize": 7536877, "license": "other", "mime_type": "application/pdf", "url": "/4284/1/Stapanian_mi_1981.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Induced Fission Track Measurements of Carbonaceous Chondrite Th/U Ratios and Th/U Microdistributions in Allende Inclusions", "author": [ { "family_name": "Stapanian", "given_name": "Maritza Irene", "clpid": "Stapanian-Maritza-Irene" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A double irradiation fission track radiography technique has been developed to measure Th/U ratios in carbonaceous chondrites and map Th/U microdistributions in Ca-Al-rich inclusions. (Th + \u00b2\u00b3\u2078U) fission is induced by high dose 35-40 MeV proton irradiations. These irradiations are coupled with reactor \u00b2\u00b3\u2075U thermal neutron fission measurements to obtain the corresponding Th/U ratios.
\r\n\r\nThe average solar system Th/U ratio is important in the theoretical modelling of the time scales for heavy element r-process nucleosynthesis. Earlier measurements (Morgan and Lovering, 1967, 1968) indicated CC Th/U ratios ranging from 2-6. This is in sharp contrast to ordinary chondrite, terrestrial, and lunar sample measurements which are tightly constrained to present day values of 3.8\u00b10.5. An objective of this study was to check the 2-6 spread in CC ratios. The fission track technique, while not a high precision technique, can give individual meteorite measurements to within 12-20%. This is adequate to verify the existence of highly fractionated (relative to terrestrial) CC Th/U ratios. The results of our analyses of six bulk samples mainly type C2, but also including the Ivuna type C1 chondrite, show within the errors of the measurements that bulk CC Th/U ratios lie within the normal 3.8\u00b10.5 range.
\r\n\r\nThe real strength of the fission track technique lies in the ability to map Th/U microdistributions in-situ. Our technique has the sensitivity to make U measurements within 10% counting statistics errors on 100\u00b5 grains with 20 ppb. Th+U measurements of similar precision can be made on 100\u00b5 grains with 1 ppm Th+U. We have focussed our Th/U mapping experiments on the Allende meteorite- in particular, the calcium-aluminum-rich inclusions (CAI). The chemical and mineralogical composition of these CAI conform to model predictions for the earliest forming nebular condensates. Because of the refractory nature of Th and U, location and identification of Th,U-rich carrier phases can test solar nebula condensation models. Our major results are: (1) The high concentrations of Th and U in the rims of two Type A coarse-grained CAI attests to the importance of rims in understanding Th,U condensation and perhaps other refractory trace elements as well. (2) Analysis of a compact Type A inclusion shows that incorporation of rim material into total inclusion values is necessary to obtain Th and particularly U enrichments over Cl levels on par with the uniform enrichment of other refractory elements (Grossman et al., 1977). (3) The highly fractionated Th/U ratios observed in Type A perovskite (~20), and the general tendency for our CAI bulk measurements which show fractionated Th/U ratios to give high ratios suggests support of the Boynton (1978) proposal of higher U volatility compared to Th under the conditions of the early condensing nebula. Alternatively, our Type A inclusions may be atypical, having formed from a reservoir (gas?) of high Th/U. One mechanism for preferential depletion in the early stages of condensation could be alloying of U with Pt metals as discussed by Jones and Burnett (1980), although there is no strong evidence to support this specific mechanism. (4) The Th/U fractionations observed in Type A CAI suggest the strong likelihood for \u00b2\u2074\u2074Pu/\u00b2\u00b3\u2078U fractionations as well. Such inclusions would probably not be appropriate for determining the solar system Pu/U or Pu/Th ratios.
", "doi": "10.7907/64g4-2a56", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:16381", "collection": "thesis", "collection_id": "16381", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05132024-183001142", "primary_object_url": { "basename": "Furst_MA_1979.pdf", "content": "final", "filesize": 51197610, "license": "other", "mime_type": "application/pdf", "url": "/16381/1/Furst_MA_1979.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Use of Boron Concentrations in Fossil Materials as a Paleosalinity Indicator", "author": [ { "family_name": "Furst", "given_name": "Marian Judith", "clpid": "Furst-Marian-Judith" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Lowenstam", "given_name": "Heinz A.", "clpid": "Lowenstam-H-A" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The \u00b9\u2070B(n,\u03b1) \u2077Li nuclear reaction has been used in conjunction with alpha-sensitive plastic track detectors to determine boron concentrations in various biologically precipitated minerals. A correlation between the boron concentration in the water in which the precipitating organisms grew and the boron concentration in the materials analyzed was found in specimens of Mytilus edulis, related bivalves, diatoms, and siliceous sponge spicules. M. edulis shell boron concentrations in aragonite ranged from about 5 ppm in specimens from 5 \u2070/\u2080\u2080 salinity water to about 15 ppm in specimens from 35 \u2070/\u2080\u2080 salinity water. Salinities can not be distinguished quantitatively using carbonate shells beyond the general distinction of marine, brackish, or nearly-fresh water. Fossil shells showed evidence for some loss of boron from aragonite. Freshwater diatomites contained less than 10 ppm B, while marine diatomites and unconsolidated marine core samples contained about 100 ppm. Detailed studies of live\u00ad collected sponge spicules established that individual spicules larger than 20-25 microns in diameter can be analyzed, and that there is a correlation with water salinity for sponges from regions of low water temperature and high productivity. Measured concentrations ranged between nearly 0 for fresh-water sponges to 600-700 for marine sponges. However, spicules from sponges from tropical, low-productivity marine locations contained markedly less boron. The exact relationships\r\nbetween B concentration in the spicules and concentration in the water, temperature, nutrient supply, and food sources for the sponges are not known. Pleistocene spicules from deep-sea cores tended to contain somewhat less boron than might be anticipated by comparison with live-collected spicules based on present water temperatures and nutrient supplies. It is uncertain whether the lower concentrations are the result of diagenetic processes or the unknown effects of differences in the food supply and/or environmental conditions. Until the significance of the boron concentration in spicules is understood more fully, paleosalinity determinations will not be possible. If a relationship between boron content and water temperature or nutrient supply can be defined, it may be possible to use boron concentrations in spicules to trace oceanic circulation patterns in the past.", "doi": "10.7907/053m-sr84", "publication_date": "1979", "thesis_type": "phd", "thesis_year": "1979" }, { "id": "thesis:2258", "collection": "thesis", "collection_id": "2258", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-130623", "primary_object_url": { "basename": "Russ_gp_1974.pdf", "content": "final", "filesize": 20855042, "license": "other", "mime_type": "application/pdf", "url": "/2258/1/Russ_gp_1974.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Neutron Stratigraphy In the Lunar Regolith", "author": [ { "family_name": "Russ", "given_name": "Guston Price, III", "clpid": "Russ-Guston-Price-III" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nDifferences in the isotopic composition of Gd and Sm among lunar samples collected during the Apollo 11, 12, 14, 15, and 16 and Luna 16 missions have been measured by high precision mass spectrometry. These differences (up to 1.9% in [...]Gd/[...]Gd and 2.0% in [...]Sm/[...]Sm) can be attributed unambiguously to low energy neutron capture reactions and correspond to neutron fluences as high as 10[...] n/cm[...] (E < 0.18 eV). For the Apollo 16 samples, enrichments are reported for the [...]Gd/[...]Gd ratio which appear to be due to neutron capture by [...]Eu. The measured ratio of the number of neutrons captured per atom by [...]Sm to the number captured per atom by [...]Gd indicates that the low energy lunar neutron spectrum is in reasonable agreement with that calculated by Lingenfelter, Canfield, and Hampel but that the lunar spectrum is somewhat harder. A synthesis of all the available lunar neutron capture data for [...]Gd, [...]Gd,\t[...]Sm, [...]Eu, [...]Co, [...]Br, [...]Br, [...]Ba, [...]W, [...]U, [...]U, and [...]Ca indicates that only the [...]W and [...]U data are incompatible with the LCH neutron spectrum and flux.\r\n\r\nBased on the LCH neutron flux, the neutron fluences, [...], determined for the lunar soils are all lower than would be expected for materials mixed in the upper few meters of the regolith for > 3 x 10[...] yr. In terms of a uniform mixing model the measured neutron fluences imply that the depth of the regolith is between 10 and 14 m at all of the Apollo sites studied. These are greater than the depths implied from cratering theory. The [...]Xe/[...] ratios for the soils indicate that they have been well mixed to a depth of > 200 g/cm[...]. Detailed fluence studies in the Apollo 12 double core show that these materials could not have been undisturbed for > 10[...] yr. The upper layers of the Apollo 15 and 16 drill stems also imply mixing on this time scale. However, the Apollo 15 drill stem has a smooth peak in the fluence at a depth of ~ 190 g/cm[...]. From the magnitude of this peak, it can be concluded that below a depth of ~ 75 g/cm[...] these materials have been undisturbed for at least 400 my. The fluence profile in the Apollo 16 drill stem is more complicated but indicates an area where material has been accumulating for several hundred million years.\r\n\r\nA model is presented for the depth dependence of the ratio of [...]Xe produced by neutron capture on [...]Ba to [...]Xe produced by spallation reactions on Ba. Effective exposure depths are calculated for 24 rocks from Apollo 11 and 12. Detailed irradiation histories are presented for rocks 10017, 14310, and 15595. An erosion rate for Hadley Rille of ~1 cm/my is calculated from the neutron fluence of rock 15595.\r\n\r\nFrom Gd and Sm isotopic measurements it is shown that the Norton County meteorite has been exposed to a neutron flux with a spectrum compatible with that predicted by the LCH calculations. The neutron fluence to which our sample of Norton County has been exposed is 1.2 x 10[...] n/cm[...]. No neutron produced effects were observed in the isotopic composition of Gd from a bulk sample of the Allende meteorite.", "doi": "10.7907/DEP4-KJ41", "publication_date": "1974", "thesis_type": "phd", "thesis_year": "1974" } ]