Stable Isotope Paleoaltimetry of the Tibetan-Himalayan System

Abstract HKT-ISTP 2013 Opening Sessio

Porous polyethylene and proplast

A comparative animal study showed that, after implantation in skull defects in guinea pigs, porous high-density polyethylene (PHDPE) was substantially better anchored in the bone than Proplast, and had greater stability of form and structure. In Proplast, ingrowth of fibrous tissue caused partial structural dilatation and fragmentation, which could limit its suitability for use in reconstructive surgery

Miocene orographic uplift forces rapid hydrological change in the southern central Andes

Rainfall in the central Andes associated with the South American Monsoon and the South American Low-Level Jet results from orographic effects on atmospheric circulation exerted by the Andean Plateau and the Eastern Cordillera. However, despite its importance for South American climate, no reliable records exist that allow decoding the evolution of thresholds and interactions between Andean topography and atmospheric circulation, especially regarding the onset of humid conditions in the inherently dry southern central Andes. Here, we employ multi-proxy isotope data of lipid biomarkers, pedogenic carbonates and volcanic glass from the Eastern Cordillera of NW Argentina and present the first long-term evapotranspiration record. We find that regional eco-hydrology and vegetation changes are associated with initiation of moisture transport via the South American Low-Level Jet at 7.6 Ma, and subsequent lateral growth of the orogen at 6.5 Ma. Our results highlight that topographically induced changes in atmospheric circulation patterns, not global climate change, were responsible for late Miocene environmental change in this part of the southern hemisphere. This suggests that mountain building over time fundamentally controlled habitat evolution along the central Andes.Fil: Rohrmann, Alexander. Universitat Potsdam; AlemaniaFil: Sachse, Dirk. Universitat Potsdam; Alemania. German Research Centre for Geosciences; AlemaniaFil: Mulch, Andreas. Goethe Universitat Frankfurt; AlemaniaFil: Pingel, Heiko. Universitat Potsdam; AlemaniaFil: Tofelde, Stefanie. Universitat Potsdam; AlemaniaFil: Alonso, Ricardo Narciso. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Salta. Facultad de Ciencias Naturales; ArgentinaFil: Strecker, Manfred R.. Universitat Potsdam; Alemani

Eocene and Miocene extension, meteoric fluid infiltration, and core complex formation in the Great Basin (Raft River Mountains, Utah)

Metamorphic core complexes (MCCs) in the North American Cordillera reflect the effects of lithospheric extension and contribute to crustal adjustments both during and after a protracted subduction history along the Pacific plate margin. While the Miocene-to-recent history of most MCCs in the Great Basin, including the Raft River-Albion-Grouse Creek MCC, is well documented, early Cenozoic tectonic fabrics are commonly severely overprinted. We present stable isotope, geochronological (40Ar/39Ar), and microstructural data from the Raft River detachment shear zone. Hydrogen isotope ratios of syntectonic white mica (δ2Hms) from mylonitic quartzite within the shear zone are very low (-90‰ to -154‰, Vienna SMOW) and result from multiphase synkinematic interaction with surface-derived fluids. 40Ar/39Ar geochronology reveals Eocene (re)crystallization of white mica with δ2Hms ≥ -154‰ in quartzite mylonite of the western segment of the detachment system. These δ2Hms values are distinctively lower than in localities farther east (δ2Hms ≥ -125‰), where 40Ar/39Ar geochronological data indicate Miocene (18-15 Ma) extensional shearing and mylonitic fabric formation. These data indicate that very low δ2H surface-derived fluids penetrated the brittle-ductile transition as early as the mid-Eocene during a first phase of exhumation along a detachment rooted to the east. In the eastern part of the core complex, prominent top-to-the-east ductile shearing, mid-Miocene 40Ar/39Ar ages, and higher δ2H values of recrystallized white mica, indicate Miocene structural and isotopic overprinting of Eocene fabrics

Oligo-Miocene extensional tectonics and fluid flow across the Northern Snake Range detachment system, Nevada

The Northern Snake Range (Nevada) represents a spectacular example of a metamorphic core complex and exposes a complete section from the mylonitic footwall into the hanging wall of a fossil detachment system. Paired geochronological and stable isotopic data of mylonitic quartzite within the detachment footwall reveal that ductile deformation and infiltration of meteoric fluids occurred between 27 and 23 Ma. 40Ar/39Ar ages display complex recrystallization-cooling relationships but decrease systematically from 26.9 ± 0.2 Ma at the top to 21.3 ± 0.2 Ma at the bottom of footwall mylonite. Hydrogen isotope (δD) values in white mica are very low (-150 to-145 ‰) within the top 80-90 m of detachment footwall, in contrast to values obtained from the deeper part of the section where values range from-77 to-64 ‰, suggesting that time-integrated interaction between rock and meteoric fluid was restricted to the uppermost part of the mylonitic footwall. Pervasive mica-water hydrogen isotope exchange is difficult to reconcile with models of 40Ar loss during mylonitization solely by volume diffusion. Rather, we interpret the 40Ar/ 39Ar ages of white mica with low-δD values to date syn-mylonitic hydrogen and argon isotope exchange, and we conclude that the hydrothermal system of the Northern Snake Range was active during late Oligocene (27-23 Ma) and has been exhumed by the combined effects of ductile strain, extensional detachment faulting, and erosion. Copyright 2011 by the American Geophysical Union

Meteoric water circulation in a rolling-hinge detachment system (northern snake range core complex, Nevada)

Combined petrofabric, microstructural, stable isotopic, and 40Ar/39Ar geochronologic data provide a new perspective on the Cenozoic evolution of the northern Snake Range metamorphic core complex in east-central Nevada. This core complex is bounded by the northern Snake Range detachment, interpreted as a rolling-hinge detachment, and by an underlying shear zone that is dominated by muscovite-bearing quartzite mylonite and interlayered micaschist. In addition to petrofabric, microstructural analysis, and 40Ar/39Ar geochronology, we use hydrogen isotope ratios (δD) in synkinematic white mica to characterize fluid-rock interaction across the rolling-hinge detachment. Results indicate that the western flank of the range preserves mostly Eocene deformation (49-45 Ma), characterized by coaxial quartz fabrics and the dominant presence of metamorphic fluids, although the imprint of meteoric fluids increases structurally downward and culminates in a shear zone with a white mica 40Ar/39Ar plateau age of ca. 27 Ma. In contrast, the eastern flank of the range displays pervasive noncoaxial (top-tothe-east) fabrics defined by white mica that formed in the presence of meteoric fluids and yield Oligo cene-Miocene 40Ar/39Ar ages (27-21 Ma). Evolution of the Oligocene-Miocene rolling-hinge detachment controlled where and when faulting was active or became inactive owing to rotation, and therefore where fluids were able to circulate from the surface to the brittle-ductile transition. On the western flank (rotated detachment), faulting became inactive early, while continued active faulting on the eastern flank of the detachment allowed surface fluids to reach the mylonitic quartzite. The combined effects of synkinematic recrystallization and fluid inter action reset argon and hydrogen isotope ratios in white mica until the early Miocene (ca. 21 Ma), when the brittle-ductile transition was exhumed beneath the detachment

Coupled basin-detachment systems as paleoaltimetry archives of the western North American Cordillera

Stable isotope paleoaltimetry data from the Snake Range metamorphic core complex (MCC) and Sacramento Pass Basin (NV, USA) document that extensional mylonite zones and kinematically linked syntectonic basins reliably record paleotopography in the continental interior of western North America when compared to a sea-level reference. Here we show that this basin-MCC pair tracks meteoric fluid flow at different levels of actively extending crust in a high-topography region during Oligo-Miocene extension of the Basin and Range Province. For paleoaltimetry purposes we compare multi-proxy oxygen (δ 18O) and hydrogen (δD) isotope data as well as geochronological information from the Snake Range MCC to a time-equivalent (ca. 20Ma) stable isotopic proxy record from the Buckskin Mountains MCC (AZ, USA), which developed next to the Pacific Coast near Miocene sea level. We complement this paleoaltimetry study by comparing the Buckskin Mountains MCC data with older (~35Ma) lacustrine stable isotope and paleofloral records from the nearby House Range (UT, USA), whose paleoelevation has been determined independently through paleobotanical analysis. Each of the investigated compartments of the paleohydrologic system within the Snake Range MCC depicts a coherent scenario of low Oligo-Miocene δ 18O and δD values of meteoric water that reflect precipitation sourced at high elevation. A 77‰ difference in δD water between the Snake Range (δD water~-113‰) and the Buckskin Mountains (δD water~-36‰) is consistent with minimum mean paleoelevation of the Snake Range of about 3850±650m above Miocene sea level. Additional support for such elevations comes from a comparison between the Buckskin Mountains MCC and the Eocene House Range basin (UT, USA) where differences in δ 18O water values are consistent with 2300±500m minimum paleoelevation of the House Range. Based on the presence of brecciated rock-avalanche deposits within the Sacramento Pass Basin, we conclude that the Snake Range was a topographic high and locus of significant relief during regional scale extension within the Cordilleran hinterland. © 2012 Elsevier B.V

Contrasting magma types and timing of intrusion in the Permian layered mafic complex of Mont Collon (Western Alps, Valais, Switzerland): evidence from U/Pb zircon and 40Ar/39Ar amphibole dating

Abstract.: We have selected and dated three contrasting rock-types representative of the magmatic activity within the Permian layered mafic complex of Mont Collon, Austroalpine Dent Blanche nappe, Western Alps. A pegmatitic gabbro associated to the main cumulus sequence yields a concordant U/Pb zircon age of 284.2 ±0.6Ma, whereas a pegmatitic granite dike crosscutting the latter yields a concordant age of 282.9 ±0.6Ma. A Fe-Ti-rich ultrabasic lamprophyre, crosscutting all other lithologies of the complex, yields an 40Ar/39Ar plateau age of 260.2 ±0.7Ma on a kaersutite concentrate. All ages are interpreted as magmatic. Sub-contemporaneous felsic dikes within the Mont Collon complex are ascribed to anatectic back-veining from the country-rock, related to the emplacement of the main gabbroic body in the continental crust, which is in accordance with new isotopic data. The lamprophyres have isotopic compositions typical of a depleted mantle, in contrast to those of the cumulate gabbros, close to values of the Bulk Silicate Earth. This indicates either contrasting sources for the two magma pulses - the subcontinental lithospheric mantle for the gabbros and the underlying asthenosphere for the lamprophyres - or a single depleted lithospheric source with variable degrees of crustal contamination of the gabbroic melts during their emplacement in the continental crust. The Mont Collon complex belongs to a series of Early Permian mafic massifs, which emplaced in a short time span about 285-280Ma ago, in a limited sector of the post-Variscan continental crust now corresponding to the Austroalpine/Southern Alpine domains and Corsica. This magmatic activity was controlled in space and time by crustal-scale transtensional shear zone