UH Faculty, Staff, and Student Works
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The collection gathers research products generated by University of Houston faculty, staff, and students
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Browsing UH Faculty, Staff, and Student Works by Department "Earth and Atmospheric Sciences, Department of"
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Item Osmium Isotope Constraints on Tectonic Evolution of the Mantle Lithosphere: evidence from Lunar Crater xenoliths, Nevada, USA(2019) Nguyen, GenevaThe relatively rapid removal of an original Proterozoic mantle lithosphere and subsequent replacement by the asthenospheric mantle via Rayleigh-Taylor instabilities is proposed to explain the formation of highly elevated plateaus and mountain ranges in the Basin and Range Province in the western United States. The Re-Os isotope system is useful in dating lithosphere formation due to Os resistance to being overprinted by later melting events. Hence, 187Os/188Os values provide direct information on the lithosphere’s evolution. In this study, we provide new 187Os/188Os compositions of 8 granular peridotite samples with mantle lithospheric origin from Lunar Crater volcanic field in central Nevada. The average 187Os/188Os value is 0.1222 ± 0.000163, overlapping with the range of abyssal peridotites that represent present-day convecting mantle. Lack of correlation between 187Os/188Os and melt depletion indicators such as bulk rock Al2O3 can indicate an influence of a subducted oceanic lithospheric origin for this suite of xenoliths. The bulk rocks display light rare earth element (REE) enriched primordial mantle-normalized patterns resulting from metasomatism. The temperatures recorded for these xenoliths using REE-in-two-pyroxene thermometer display a range of 1,278–1,338°C (~ 300°C higher than other localities in the Basin and Range) along with mylonitic deformation characteristics of recrystallized olivines grains suggests an asthenospheric influence and strain localization which facilitate lithospheric delamination (Dygert et al., 2019). These results contrasts with peridotite xenoliths Dish Hill in southern California (another Basin and Range locale ~ 260 miles south of Lunar Crater), where the 187Os/188Os ratios correlate with bulk rock AL2O3 from melt depletion (Armytage et al., 2014). While Lunar Crater xenoliths host basalt suggests decompression melting of asthenospheric mantle resulted from lithospheric removal, the Os isotope system beneath Dish Hill points to pulses of mantle melting as a SCLM stabilization mechanism for continental growth. Comparing results from these two locations allow us to gain insights into the influence that the subduction of the Farallon plate and how this can change temporally and spatially.Item Proto-South China Sea plate tectonics using subducted slab constraints from tomography(2017) Wu, Jonny; Suppe, JohnThe past size and location of the hypothesized proto-South China Sea vanished ocean basin has important plate-tectonic implications for southeast Asia since the Mesozoic. Here we present new details on proto-South China Sea paleogeography using mapped and unfolded slabs from tomography. Mapped slabs included: the Eurasia-South China Sea slab subducting at the Manila trench; the northern Philippine Sea plate slab subducting at the Ryukyu trench; and, a swath of detached, sub-horizontal, slab-like tomographic anomalies directly under the South China Sea at 450 to 700 km depths that we show is subducted ‘northern proto-South China Sea’ lithosphere. Slab unfolding revealed that the South China Sea lay directly above the ‘northern Proto-South China Sea’ with both extending 400 to 500 km to the east of the present Manila trench prior to subduction. Our slab-based plate reconstruction indicated the proto-South China Sea was consumed by double-sided subduction, as follows: [1] The ‘northern proto-South China Sea’ subducted in the Oligo-Miocene under the Dangerous Grounds and southward expanding South China Sea by in-place 'self subduction' similar to the western Mediterranean basins; [2] Limited southward subduction of the proto-South China Sea under Borneo occurred pre-Oligocene, represented by the 800-900 km deep 'southern Proto-South China Sea' slab.Item Reconstructed Paleoelevation in the Bolivian Andes Using Hydrated Volcanic Glass(2019) Nguyen, GenevaConstraints on temporal and spatial variations in surface elevations are crucial in understanding the geodynamic processes responsible for large-magnitude uplift of orogenic plateaux. At ~4–6 km elevations, the Central Andean Plateau is the Earth’s largest orogenic plateau produced by ocean-continent convergence and inevitably serves as a natural laboratory to study surface uplift mechanisms. Recent paleoaltimetry studies using paleotemperature from sedimentary carbonates point to a Neogene non-uniform pulse of rapid surface uplift across and along the Peruvian Western Cordillera and Bolivian Altiplano, consistent with foundering of mantle lithosphere via Rayleigh-Taylor instability. In this study, we present the first quantitative paleoelevation reconstruction of the timing and magnitude of surface uplift of the Bolivian Western Cordillera. We reconstruct the isotopic compositions of surface water using hydrogen isotopic composition of hydrated volcanic glass. Glass was isolated fourteen ignimbrites and air-fall tuffs and chronology is based on U-Pb zircon of the same samples. Ten samples exhibit acceptable water content (>1 wt%) and were included in our paleoelevation reconstruction. Paleoelevation is reconstructed based on differences between modern low-elevation δ18O and high-elevation δ18O of meteoric water (Δδ18O) using a one-dimensional thermodynamic Raleigh distillation model. Our data indicates that surface elevation of the Bolivian Western Cordillera was at modern elevation since at least 22.9 Ma, much earlier than previous reconstruction suggested by foliar physiognomy (~ 10 Ma). Two samples show anomalously positive δD values, implying highly evaporative depositional environments. Thus further investigations incorporating measured sections and stratigraphy evaluations are necessary. However, our reconstruction strongly suggests modern elevation of the Bolivian Western Cordillera was established since 22.9 Ma, consistent with Miocene stratigraphic record and provenance data of the Altiplano.