Scapolite phase equilibria and carbon isotope variations in high grade rocks: Tests of the carbon-dioxide-flooding hypothesis of granulite genesis.

Scapolite decarbonation reactions and carbon isotope analysis of CO\sb2 extracted from scapolite are used to determine the presence, composition, and source of fluid components in high grade rocks. Scapolite-plagioclase-garnet-quartz assemblages, common to many lithologies in high grade terranes, monitors CO\sb2 activity ($a$CO\sb2) by the reaction 2 Meionite + Quarts = 5 Anorthite + Grossular + 2 CO\sb2. The P-T-X location of this reaction was calculated using an internally consistent thermodynamic data set for meionite and phases in the CASCH system. Activity-composition relations for meionite in scapolite were calculated from the thermodynamic data set and compositional data on natural scapolite-plagioclase-calcite assemblages. Equilibration pressures of scapolite assemblages were calculated from clinopyroxene-garnet-plagioclass-quartz barometers calibrated for this study. The $a$CO\sb2 was calculated for a variety of high grade gneisses from the southwestern Grenville Province and other terranes. Granulites typically yield low to moderate values of $a$CO\sb2 (less than 0.5). Calc-silicates and meta-anorthosite yield moderate $a$CO\sb2. Deep crustal xenoliths yield a range of $a$CO\sb2. CO\sb2 for carbon isotope analysis was extracted from scapolite in mineral separates and whole rock gneisses with phosphoric acid at 75\sp\circC. Scapolite meta-anorthosite and calcite from adjacent marble have the same carbon isotope composition indicating marble was a local source of fluids leading to \sp{13}C enrichment of the anorthosite. \delta\sp{13}C of granulites and mafic gneisses from the southwestern Grenville range from $-3$ to $-10$ per mil, consistent with a variety of carbon sources and a lack of regional homogenization of carbon in the gneisses via a pervasive fluid. The fluid calculations and isotope data are not consistent with pervasive CO\sb2 flooding in the southwestern Grenville Province. Locally, the effects of interaction of rocks with a CO\sb2 rich vapor phase have been documented and serve as a model to evaluate CO\sb2-rock interaction in other terranes. The calculations are also consistent with the vapor absent granulite facies metamorphism in the Furua Complex of Tanzania, and either vapor absent metamorphism or a mixed CO\sb2-H\sb2O fluid in the Sargur Terrane (southern India), Bergen Arcs (Norway), and many lower crustal xenoliths.Ph.D.Earth SciencesGeologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/128275/2/8907106.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/128275/5/Moecher-DP_DeepBluepermissions_agreement-CCBY.pdfDescription of Moecher-DP_DeepBluepermissions_agreement-CCBY.pdf : Hidden Deep Blue OA and CC license agreemen

ANALYSIS AND ASSESSMENT OF LETHALITY AND SURVIVABILITY FOR THE MARINE LITTORAL REGIMENT

As the Marine Corps activates the Marine Littoral Regiment (MLR) to serve as the joint force’s reconnaissance and counter-reconnaissance effort, questions abound regarding the MLR’s ability to provide a persistent and lethal presence well inside the reach of our adversaries’ advanced long-range precision fires. In this study, the author uses agent-based combat simulations to inform future force design decisions, live-force experimentation, and tactics. The simulated scenario imagines a future MLR conducting sea control operations in the littorals of the Western Pacific against a peer naval threat. This research investigates the effect that a guard force of autonomous and/or semi-autonomous surface vessels, operating as the guard force of the MLR’s defense in depth, has on the survivability and lethality of the MLR’s land-based anti-ship missile platforms. Summary statistics generated by the simulation indicate that the future battlefield will see high losses on both sides. However, based on the results of 27,200 simulated engagements, this study finds that an MLR using a guard force of armed and unarmed “scouts” as described above can inflict a prohibitively high and unsustainable cost on an enemy naval force.Outstanding ThesisMajor, United States Marine CorpsApproved for public release. Distribution is unlimited

Zircon U-Pb Geochronology of Two Basement Cores (Kentucky, USA): Implications for Late Mesoproterozoic Sedimentation and Tectonics in the Eastern Midcontinent

Basement cores from two wells drilled west and east of the Grenville front consist of feldspathic litharenite and granitic orthogneiss, respectively. Detrital zircon U-Pb ages for the litharenite define a broad dominant U-Pb age mode at ca. 1115 Ma. The dominant mode matches that for the type locality of the Middle Run Formation in the Ohio subsurface and is interpreted to consist of detrital zircons sourced from East Continent Rift volcanic sources (ca. 1100 Ma) and Grenville Shawinigan granites/gneisses (1120–1180 Ma). The youngest detrital zircon ages (ca. 1020 Ma) require a maximum depositional age that is at least 70 My younger than the time of Midcontinent and East Continent rifting and magmatism. We propose that the litharenite is correlative with the Middle Run Formation in Ohio and was deposited in an evolving late Grenville rift/foreland basin adjacent to the exhuming Grenville orogen. Zircon U-Pb secondary-ion mass spectrometry ages from orthogneiss define a discordant array with intercepts of ca. 1500 and 1000 Ma. The oldest concordant dates (ca. 1450 Ma, from oscillatory-zoned cores) are interpreted as the crystallization age of the igneous protolith of the orthogneiss. Metamorphic zircon rims define a weighted mean U-Pb age of 1018 ± 19 Ma (2σ) Ma, interpreted to represent the time of high-grade metamorphism during the late Ottawan phase of the Grenville orogeny. This age pattern matches that of exposed basement in the Central Gneiss Belt of the Grenville Province (Ontario) and similar basement orthogneisses in Ohio and Kentucky that are interpreted to be of Eastern Granite-Rhyolite Province affinity. All age data are consistent with a provenance model of an actively exhuming Grenville orogen at ca. 1000 Ma producing sediment that is mixing with recycled East Continent Rift sediments

Extraction and carbon isotope analysis of CO2 from scapolite in deep crustal granulites and xenoliths

Carbon isotope compositions of scapolite from granulite facies gneisses and lower crustal xenoliths document the composition and constrain the source of carbon in scapolite from the lower crust. CO2 is extracted from scapolite without fractionating carbon isotopes by reaction with phosphoric acid at 25 or 75[deg]C. Thus, partial yields of CO2 from scapolite are sufficient for accurate carbon isotopic analysis. Isotopic compositions of coexisting scapolite and calcite in high-grade calc-silicate gneisses and marbles, and consideration of the crystal chemical environment of CO3 in the scapolite structure, indicate little fractionation of 13C/12C between scapolite and calcite (0.1 +/- 1.2%.) at equilibrium conditions of 650-800[deg]C.The carbon isotope composition of CO2 extracted from scapolite in twenty-nine samples of regional granulite facies gneisses, amphibolites, calc-silicate gneisses, and crustal xenoliths yield values of [delta]13C that range from -10 to -1%. (PDB). High-grade marbles and graphitic paragneisses are precluded as major sources of carbon for scapolite in the high grade rocks analyzed in this study, as the former are isotopically enriched, and the latter isotopically depleted in 13C/12C relative to the range of isotopic compositions determined here. The [delta]13C values for mafic granulites and amphibolites in granulite terranes composed of supracrustal sequences (-10.1 to -4.0%.) may reflect the isotopic composition of diagenetic carbonate present in their basaltic protoliths. The values of [delta]13C for scapolite in mafic xenoliths and some granulite facies orthogneisses (-8.2 to -1.2%.) are consistent with crystallization of the scapolite from a mafic melt or derivation of CO2 from mafic melts emplaced in the lower crust or upper mantle. The values of [delta]13C for scapolites from calc-silicate gneisses and calc-silicate xenoliths (-10.0 to -2.9%.) may result from depletion of 13C/12C as a result of decarbonation of calcite-bearing protoliths during prograde metamorphism.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31945/1/0000898.pd

Location of Cerium in Coal-Combustion Fly Ashes: Implications for Recovery of Lanthanides

Given the worldwide demand for rare earth elements (REEs) in modern electronics, all potential sources of the REEs should be investigated. Coal-combustion fly ash represents a potential source of REEs. Fly ashes, derived from the combustion of coals from Kentucky in the United States and Jungar in China, were examined by wavelength-dispersive spectrometry electron microprobe analysis of epoxy-bound polished pellets. From previous studies, it was known that the REEs did not show any enrichment relative to flue gas temperature at the point of collection or to the particle size, that is, external surface area, of the particles. Cerium, the most abundant of the REEs in these fly ashes, was used as a proxy for the entire suite of REEs. For fly ashes from both sources, Ce is disbursed throughout the glassy fly ash particles. For fly ash processing with respect to the recovery of REEs, this implies that the entire particle must be leached to maximize the element recovery

Source to sink zircon grain shape: Constraints on selective preservation and significance for Western Australian Proterozoic basin provenance

The effect of selective preservation during transportation of zircon grains on the detrital age spectrum is difficult to quantify and could potentially lead to systematic bias in provenance analysis. Here we investigate whether the shape of detrital zircon grains holds provenance information and if the grain shape can assist in understanding preservation. We applied multiple linear regression analysis to identify significant shape properties in detrital zircons from Proterozoic metasediments of the Capricorn and Amadeus basins and their Archean and Proterozoic sources in the Yilgarn Craton and the Musgrave Province in Western Australia. Digital images and isotopic data from 819 SIMS U-Pb dated zircons were examined for correlation between grain shape, age, U and Th content. Out of twelve shape descriptors measured, Minor Axis, the width of zircon grains perpendicular to the crystallographic c-axis, consistently shows the most significant correlation with isotopic age. In the studied population Archean grains are narrower than Proterozoic grains: the probability that grains wider than 75 µm are Archean is less than 30%.Calculations of the proportions of source material in sedimentary rocks relative to the proportions of source material in the overall catchment area (erosion parameter '. K' calculated based on age spectra) produced values typical for mature river systems, with K = 6 for the Yilgarn-Capricorn and K = 5.5 for the Musgrave-Amadeus source-sink system. For the Yilgarn-Capricorn system, we also calculated '. K' based on Minor Axis, to determine whether grain width can be linked to age populations. Results of the shape-based K of 5.3 suggest a similarity between age-based and shape-based '. K' values, demonstrating that zircon grain width may be a useful discriminator of provenance. Contrary to commonly applied qualitative shape classifications, we found no consistent correlations between shape descriptors of magmatic zircons and the composition of their host rock. While metamict zircons were preferentially removed during transport, the similarities in grain shape and age distribution of magmatic and detrital populations suggest that hydraulic sorting did not have a significant effect. We conclude that transport of zircon grains from magmatic source to sedimentary sink affects their width less than their length

Earthquake nucleation in the lower crust by local stress amplification

Deep intracontinental earthquakes are poorly understood, despite their potential to cause significant destruction. Although lower crustal strength is currently a topic of debate, dry lower continental crust may be strong under high-grade conditions. Such strength could enable earthquake slip at high differential stress within a predominantly viscous regime, but requires further documentation in nature. Here, we analyse geological observations of seismic structures in exhumed lower crustal rocks. A granulite facies shear zone network dissects an anorthosite intrusion in Lofoten, northern Norway, and separates relatively undeformed, microcracked blocks of anorthosite. In these blocks, pristine pseudotachylytes decorate fault sets that link adjacent or intersecting shear zones. These fossil seismogenic faults are rarely >15 m in length, yet record single-event displacements of tens of centimetres, a slip/length ratio that implies >1 GPa stress drops. These pseudotachylytes represent direct identification of earthquake nucleation as a transient consequence of ongoing, localised aseismic creep

Does pebble abrasion influence detrital age population statistics? A numerical investigation of natural datasets

Pebble abrasion is a key factor controlling the release of minerals into sand, but few attempts have been made to model how it could influence the liberation of minerals into the size fraction used in detrital geochronology. We perform a series of experiments with an abrasion model to test this influence using natural and synthetic data sets. Our results demonstrate that pebble abrasion can change the zircon mixing proportions of upstream source units as well as the age distribution of mixed fluvial sands. This change is particularly significant when there is strong contrast in rock resistance within the watershed. Pebble abrasion is one of many factors that can change the mixing proportion of sands, including hillslope gravel supply, erosion rates, and mineral fertility. In our study case (Marsyandi watershed, Himalaya), the abrasion model predicts age distributions that are statistically indistinguishable from those predicted by a no‐abrasion model. However, the relative erosion rates estimated by our model largely differ from the results of a no‐abrasion model and are closer to those from other studies that suggest a strong correlation between modern erosion rates, tectonics, and precipitation intensity in the Marsyandi watershed. These findings highlight that, even in cases where there is no statistical evidence of change between the modeled age distributions, abrasion can affect the erosion rates estimated from them. Therefore, quantifying the influence of abrasion on sand production is an essential step not only to predict mixing proportions but also to accurately retrieve erosion rates from the measured grain age distributions