Neodymium and strontium isotopic characterization of the Wrangellia, Alexander, Stikine, Taku and Yukon crystalline terranes of the Canadian Cordillera.Samson, Scott Douglas. January 1990 (has links)
Nd and Sr isotopic data are reported from samples of the Alexander, Wrangellia, and Stikine terranes of the Canadian Cordillera. Initial ε(Nd) values range from 0 to +9.5, for Alexander, -0.5 to +6.7 for Stikine, and +1 to +7.3 for Wrangellia. Initial ⁸⁷Sr/⁸⁶Sr ratios for igneous samples of the terranes range from 0.70276-0.70663 (Alexander), 0.70369-0.70531 (Stikine), and 0.70323-0.70481 (Wrangellia). These data indicate that the terranes are isotopically very juvenile and probably resided in intra-oceanic environments until their accretion to North America. The origin of the terranes is envisioned to have occurred via island-arc volcanic processes, with accompanying erosion, sedimentary recycling, metamorphism and plutonism, with the critical characteristic that none of these processes involved more than trivial amounts of old, pre-existing continental crustal material. The terranes are thus exceptional when compared to many other Phanerozoic crustal regions that are composed predominantly of remobilized, pre-existing crust. Isotopic data are also presented for the Gravina belt, the Taku terrane, the Yukon Crystalline terrane (YCT), and the Coast Mountains batholith. The Gravina belt is isotopically similar to the Alexander terrane and most of the material in the belt was probably derived from Alexander. The Taku terrane is composed of juvenile and evolved crust and its relation to surrounding terranes is poorly understood. Nd data from the YCT indicate that it is partly composed of material derived from an early Proterozoic source. The proximity of the YCT to Stikine therefore raises important questions about the styles of accretion of the terranes. It is possible that the YCT was positioned next to Stikine by strike-slip faults, that there is a stratigraphic link between the terranes, or Stikine and other inboard terranes are thrust fragments that were emplaced on top of YCT. The YCT is isotopically and lithologically similar to the Yukon-Tanana terrane and may be the southern continuation of that terrane. Nd and U-Pb data for the CMB requires that it is composed of a Proterozoic crustal component and an isotopically juvenile component. It is likely that the Proterozoic component is YCT crust and the juvenile component is a combination of mantel-derived material and juvenile terrane crust. The style of crustal growth in the Cordillera, the sweeping up of juvenile terranes, may be an important analog to Precambrian crustal genesis.
Schaper, Maxwell C.
01 December 2016
<p> Metamorphic core complexes of southeastern Arizona extend in a southeastern trending belt that includes the Picacho, Tortolita, Santa Catalina, and Rincon Mountains. The Picacho Mountains form a solitary north-south trending belt located between Tucson and Phoenix. The Picacho Mountains are composed of a variety of Tertiary, Cretaceous, or Proterozoic granitoids, gneisses, and schists that have been subjected to low-angle normal faulting, mylonitization, and exhumation associated with Tertiary formation of a metamorphic core complex. The Picacho Mountains form the footwall of the metamorphic core complex, which is separated from the hanging wall by a gently south- to southwest-dipping detachment shear zone. The hanging wall, composed of basaltic and andesite volcanic rocks, is best exposed in the scenic Picacho Peak in Picacho Peak State Park. The detachment shear zone is divided into three plates that record a progressive gradient of deformation, from undeformed granite to (ultra)mylonites and breccia.</p><p> I present stable isotope results from mylonite samples collected across the lower plate of the detachment shear zone. Oxygen stable isotope (δ<sup> 18</sup>O) analyses of biotite, hornblende, and quartz have values that range from 4.4‰ to 5.7‰, 4.6‰ to 7.0‰, and 10.2‰ to 11.9‰, respectively. Geothermometry based on quartz-biotite and quartz-hornblende pairs yield temperatures for equilibrium ranging from 415 to 632°C, similar to previously published data. Hydrogen stable isotope values (δ<sup>2</sup>H) of biotite and hornblende range from -99‰ to -76‰ and -93‰ to -72‰, respectively. These results suggest that, at equilibrium temperatures, the rock interacted with a fluid with δ<sup>2</sup>H values ranging from -37‰ to -56‰, consistent with a fluid of metamorphic/volcanic origin. These results are significantly different than other δ<sup>2</sup>H values reported for other North American metamorphic core complexes, suggesting that the Picacho shear zone had a lesser meteoric water component or that the detachment shear zone was deeper than others.</p>
Rasmussen, Stephen Eric
The technique of instrumental neutron activation analysis as applied to the analysis cf geological material has beer siudiel with particular emphasis on methods of reducing or eliminating analytical errors. The neutron flux gradients in the reactor irradiation facilities used were found to introduce errors of up to 20%. The use of iron foils to monitor both the thermal and fast neutron flux received by individual samples has been shown to reduce iiradiation errors to approximately 1%. The contribution of epithermal neutron resonances to (n, >’ ) reaction cross sections has been recognised. Estimated epithermal neutron flux factors have been shown to reduce the associated errors by as much as 7%.
A STUDY OF URANIUM AND THORIUM ISOTOPES IN GROUND WATERS AND SOLIDS OF TWO URANIUM MINES, SOUTH TEXASUnknown Date (has links)
Isotopic analysis was carried out on water and solid samples taken from both the ore zones and the general vicinity of two uranium mines in south Texas. The uranium deposits were of the roll-front type. The ore-bearing formations were the Catahoula Formation of Miocene age in Duval County and the Upper Jackson Formation of Eocene age in Karnes County. Solid samples were analyzed for ('234)U, ('238)U and ('230)Th, water for ('234)U and ('238)U. In order to test several models which have been proposed to explain the fractionation of various nuclides in the vicinity of a reduction-oxidation front, plots incorporating uranium concentration and ('234)U/('238)U activity ratio (AR) of the water and ('234)U/('238)U and ('230)Th/('238)U - ('234)U/('238)U of the solid were used. / The integration of data from each of these models, including contour maps of various isotopic parameters and statistical plots helped in predicting the presence, the stage of deposition (dispersing, stable or accumulating) and the degree of radioactive disequilibrium of the deposits under study. The uranium deposited at one mine has undergone a series of complex changes, including a possible change in the direction of the ground water flow system from southwest to north - northeast. The presence of a fault which acted as a conduit for the reductants and a separate ore deposit were successfully predicted. The occurrence of an upflow reduction and a downflow oxidation environments in one deposit was explained as due to episodic release of reductants from the fault. / The isotopic data were also useful in determining the position of the redox boundary and the environment of a sample. These methods may be useful in prospecting studies of other possible uranium deposits, both in the oxidized and/or the reduced environment. / Source: Dissertation Abstracts International, Volume: 43-07, Section: B, page: 2139. / Thesis (Ph.D.)--The Florida State University, 1982.
A geochronological investigation of the Precambrian rocks of Rajasthan, India, was undertaken to decipher the Precambrian geology of Rajasthan in general and the ages of the three episodes of granitization and metamorphism observed in Precambrian rocks in particular. / Discordant zircon ages from granites of the Precambrian rocks of Rajasthan suggest three periods of granitization. The ages of these three periods of granitization in ascending order are, 2600 m. y., 1700 m. y. and 800 m. y. Only 2600 m. y. old granites suggest an episodic lead loss at 710 m.y., probably due to a regional thermal event. The 1700 m. y. and 800 m. y. old granites give a lower intercept age of approximately 70 m. y. / The 2600 m. y. old tectonic event which seems to be confined to the central Aravalli range in Rajasthan, probably the core of the Aravalli mountain, and dates the Aravalli regional tectonic event. / The 1700 m. y. old regional tectonic event is recognized on a much wider area and dates the Delhi regional tectonic event. The granites of this period are either co-folded with the Delhi system of rocks or are post-Aravalli. / The latest regional tectonic event in the Precambrian of Rajasthan is the 800 m. y. old "Erinpura" type event and it is post-Delhi and are represented by massive granitization especially in the southwestern part of Rajasthan (Mt. Abu). / It appears that Malani rhyolites might have inherited some zircons from older rocks and a discordant zircon age of 863 m. y. obtained for these rhyolites is a maximum age for the Malani rhyolites. / Zircons from three different granitic plutons plot on a discordia chord with a crystallization age of approximately 1680 m. y. and a lower intercept age of approximately 70 m. y. It also appears that the 800 m. y. old granitic plutons of "Erinpura" type also give a lower intercept age of approximately 70 m. y. Zircons from these plutons do not fit a 1680 m. y. or any other diffusion curve, suggesting that these zircons represent a mixture of a concordant phase and a discordant phase. In the absence of independent geological evidence, the 70 m. y. old lower intercept age probably represents the age of uplift for the granitic plutons in the Precambrian rocks of Rajasthan. / Source: Dissertation Abstracts International, Volume: 44-07, Section: B, page: 2091. / Thesis (Ph.D.)--The Florida State University, 1983.
URANIUM-SERIES NUCLIDES IN SEDIMENTS AND PHOSPHATE NODULES FROM THE PERUVIAN CONTINENTAL MARGIN (RADIUM, BIOTURBATION, PHOSPHORITE)Unknown Date (has links)
Uranium-series disequilibrium techniques have been applied to sediments and phosphate nodules sampled from the Peru-Chile continental margin in order to decipher growth histories of the nodules and time scales of diagenetic processes occurring within the sediment. / Uranium-series analysis of 11 series of contiguous slices from individual phosphate nodules consistently show unidirectional growth at rates of 0.1 to 10 mm/Kyr with a trend of slow but persistent radium leakage with time. Estimated radium fluxes from these phosphate nodules are 1-3 orders of magnitude less than those calculated for deep-sea sediments and manganese nodules. / Growth curves based upon ('226)Ra and ('230)Th radiometric ages of sequential layers in a buried phosphate crust show that this crust grew upward toward the sediment-water interface at a rate of 12-13 mm/Kyr. Crystallographical analyses of this crust display a trend of enhanced crystallinity as a function of sample age. / An intercomparison of uranium-series and ('14)C ages of 9 phosphorite samples show that both methods agree reasonably well with each other for samples younger than 30 Kyr. A pelletal phosphorite displayed the greatest discrepancy between the two ages, probably due to post-depositional adsorption of thorium and/or carbon onto pellet surfaces. / A radiochemical study of sediments associated with these phosphorites produced ('210)Pb-derived sedimentation rates on the order of a few mm/yr in the vicinity of the most intense upwelling (12(DEGREES)S and 15(DEGREES)S) decreasing by a factor of approximately 100 on the shelf further north (7(DEGREES)S and 10(DEGREES)S). Particle mixing coefficients estimated from excess ('234)Th and excess ('210)Pb profiles were on the order of 10('1) cm('2)/yr near the center of intense upwelling and decreasing to about 10('-1) cm('2)/yr at the 7(DEGREES)S and 10(DEGREES)S sites. Several cores display evidence of mass movement of sediment on a time scale of decades. / Source: Dissertation Abstracts International, Volume: 46-01, Section: B, page: 0090. / Thesis (Ph.D.)--The Florida State University, 1984.
THE POTENTIAL ORIGIN OF THE POTASSIUM DEPTH RELATIONSHIP IN THE BATAAN OROGENE, THE PHILIPPINES (ISLAND ARC, ANDESITE, PETROLOGY, ISOTOPES, BASALT)Unknown Date (has links)
Three classic volcanic arcs have developed in western Luzon, the Philippines as a result of subduction associated with an eastward-dipping Benioff zone. A data set for about 200 samples was determined for this and earlier studies. This set includes: (1) major and various trace elements, (2) 30 initial ('87)Sr/('86)SR (0.7038 to 0.7054) and a few ('143)Nd/('144)Nd ratios (0.512921 to 0.512999), (3) 76 conventional K/Ar radiometric dates, and (4) in addition to standard model mineral analyses, over 600 microprobe analyses of 33 thin-sections. / Based on these data, several conclusions can be made: (1) Excellent linear correlations exist between SiO(,2) and the incompatible elements. The slopes of these trends increase progressively from western arc through the central to the eastern arc. Moreover, normalized potassium concentrations (K(,55)) increase with assumed depth to the subducting slab and away from the Manila Trench. (2) Incompatible elements do not appear to have been affected by alteration or weathering. (3) Based on geophysical and geochemical evidence, assimilation and contamination have played an insignificant role in affecting original magma compositions. (4) It can be argued that the sources for these volcanics are enriched (metasomatized) mantle above the Benioff zone. Derivation of the Bataan volcanic rocks by different degrees of partial melting of the mantle can be ruled out. The mantle sources become increasingly more enriched in incompatible elements and radiogenic strontium away from the Manila Trench. (5) All three arcs have apparently undergone early non-selective crystal fractionation of plagioclase, clinopyroxene, magnetitite, and/or olivine based on mass-balance calculations. It appears that very similar early fractionating assemblages and assemblage percents have been removed from original magmas in each of the three arcs. (6) Parallel trends noted in both whole-rock and groundmass Harker diagrams (except the potassium Harker diagrams) among the arcs are probably the result of crystal fractionation. The variations in slopes observed in potassium Harker diagrams between the arcs can be explained by a combination of original primary magma potassium variations between the arcs and the fractionation of similar phases within each arc. / Source: Dissertation Abstracts International, Volume: 47-02, Section: B, page: 0537. / Thesis (Ph.D.)--The Florida State University, 1985.
Mantle Source Compositions by LA-ICP-MS Analyses of Volcanic Glasses from Hawaii and the Mid-Oceanic RidgesUnknown Date (has links)
The chemical compositions of basaltic melts from diverse tectonic settings on Earth are interpreted in terms of mantle sources that are either a single lithology (peridotite) or composed of two mixed lithologies (peridotite + pyroxenite). The observation of an elevated Fe/Mn ratio in Hawaiian lavas relative to Mid-Oceanic Ridge basalts (MORBs) has been attributed to either Fe-addition from core-mantle interaction or to Mn-retention in pyroxenitic mantle sources. The discrimination of pyroxenitic melts from peridotitic melts is a first-order issue in mantle geochemistry. The first-row transition elements (FRTEs), Ga and Ge are mildly incompatible to compatible during mantle partial melting so the abundances of these elements are sensitive to lithological heterogeneities in the mantle source. Recent experimental determinations of partition coefficients (Ds) of FRTEs, Ga and Ge have made it possible to quantitatively model partial melting of mantle sources of various lithologies, which are now limited by the dearth of high-quality measurements of these elements. To effectively test the hypotheses, in this study, we analyzed 60 elements, including FRTEs, Ga and Ge, in 319 mid-oceanic ridge basalt (MORB) glasses and 199 Hawaiian oceanic island basalt (OIBs) glasses by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). A particular emphasis was placed on obtaining precise Ge abundances. The MORB dataset was used to revise the composition of MORB mantle. The available experimental data were carefully examined to assess the dependence of the partitioning behavior of FRTEs, Ga and Ge on the variation of temperature, pressure and mineral compositions. The Ge/Si ratio was developed as a useful discriminator of pyroxenite melts since such melts are high in silica but low in Ge/Si. It was found that enriched (E)- MORBs have lower Ge/Si than depleted (D)- MORBs due to the presence of a few percent recycled pyroxenite in E-MORB mantle. For Hawaiian glasses, we found that Ge is volatile during volcanic degassing from subaerially erupted lavas, but the effect is suppressed in submarine glasses. Submarine Hawaiian glasses exhibit correlated variations in Ge vs. SiO2 that overlap MORB glasses, and even the Mauna Kea high-SiO2 glasses show no evidence of the presence of pyroxenite melts. This discovery should prove transformative in petrological models of lithologic heterogeneity in the mantle. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Summer Semester 2015. / May 2, 2015. / Earth mantle, First-row transition elements, Ga, Ge, Hawaiian lavas, LA-ICP-MS, mantle lithological heterogeneity, Mid-Oceanic Ridge basalts / Includes bibliographical references. / Munir Humayun, Professor Directing Dissertation; Theo Siegrist, University Representative; Vincent Salters, Committee Member; William Landing, Committee Member.
MINERAL, CHEMICAL AND TEXTURAL VARIATIONS ALONG S-SURFACES IN SELECTED OUTCROPS OF AMPHIBOLITE, GEORGIA AND ALABAMA PIEDMONTUnknown Date (has links)
Amphibolites were systematically sampled along s-surfaces from two outcrops in the Alabama and Georgia Piedmont. S-surfaces are planar features that pervade rocks. In this study the s-surfaces have a metamorphic origin. Compositional and textural effects of two phases of metamorphism (one of increasing temperature and one of decreasing temperature) were examined within distances of centimeters along s-surfaces. Mineral, chemical and textural parameters were measured and were found to vary along the s-surfaces. / Chemical variations between s-surfaces show chemical differentiation that could have been present in an original basaltic body. The s-surfaces are oriented at oblique angles to the direction of inferred differentiation in both outcrops. Although the amphibolites have been affected by two metamorphic events, the original chemical variations in the basalt have not been obliterated. Hornblende 2V variations and the presence of both epidote and clinozoisite within thin sections indicates that major elements are immobile within distances of millimeters along these s-surfaces. These findings do not support the development in amphibolites of metamorphically differentiated features, such as layering, by the diffusion of elements through longer ranged distances. The process of recrystallization, occurring crystal by crystal, in a sequence is implied by the absence of hornblende intercrystal equilibria. / The major mineral transformation recorded in these rocks is plagioclase changing to clinozoisite. The degree of this mineral reaction varies along s-surfaces. The dependence of this reaction on the presence of water indicates that fluid pressure varies along the same s-surfaces over distances less than centimeters. / Hornblende crystals that were originally more randomly distributed have rotated and translated to a less random arrangement due to the volume decrease that accompanied the retrograde plagioclase-clinozoisite reaction. / This study includes the most detailed quantitative description of metamorphic rock textures thus far described in the literature. Quantitative textural parameters include the distribution of hornblende and clinozoisite in the rock, hornblende sizes and shapes, dispersion of hornblende optic Z-axes and dispersion of the traces of hornblende crystallographic bc planes in the dominant and secondary lineations. These textural parameters vary in an unsystematic fashion along the s-surfaces. / The textural values obtained from amphibolites in Alabama and Georgia are comparable to those of amphibolites from New Mexico, Scotland and Wyoming. Therefore, regardless of variations of metamorphic grade and degrees of strain, amphibolite hornblendes have narrowly defined spatial distributions and optical and crystallographic orientations. / Source: Dissertation Abstracts International, Volume: 41-03, Section: B, page: 0859. / Thesis (Ph.D.)--The Florida State University, 1980.
A geochemical cycle for tin through the marine system is proposed. The input fluxes from rivers and the atmosphere have been considered and the behavior of tin in the oceans has been investigated. / An analytical technique has been developed that is sensitive enough to directly measure tin at the concentrations found in most areas of the environment without contamination or preconcentration. Detection limits are 50, 50 and 20 picograms tin, with detection by graphite-furnace atomic absorption, quartz-cuvette atomic absorption and flame emission spectrometry, respectively. / On the basis of measurements from a large number of rivers from pristine and polluted regions, we estimate the riverine fluxes of tin to the oceans to be 0.42 x 10('6) moles/year for the dissolved fraction and 320-960 x 10('6) moles/year for the particulate fraction. The particulate flux agrees with the flux calculated from denudation rates. Estuaries were found not to have a large effect upon the transport of tin to the oceans. / Atmospheric tin concentrations in the northern hemisphere are up to three orders of magnitude greater than those in the southern hemisphere, indicating the importance of anthropogenic inputs to the atmospheric tin cycle. Most of the atmospheric burden of tin is removed either by dry deposition or without dissolution in wet deposition. The dissolved fraction of tin in rain represents only a minor component of the deposition flux of tin. Rates of deposition of atmospheric tin are consistent with estimated fluxes of tin to the atmosphere. / A large scale study of tin concentrations in seawater has revealed concentrations much lower than previously reported. Surface water concentrations are in the range of non-detectable (< 1.5 picomolar) to 16 picomolar. Almost all depth profiles have maxima in tin concentrations from 50 to 200 meters depth. / Source: Dissertation Abstracts International, Volume: 46-01, Section: B, page: 0089. / Thesis (Ph.D.)--The Florida State University, 1984.
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