Stable Isotope Paleoaltimetry of the Tibetan-Himalayan System

Abstract HKT-ISTP 2013 Opening Sessio

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

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

The Alps Paleoelevation and Paleoclimate Experiment (APE): Neogene Paleoelevation and Paleoclimate of the Central Alps

Stable isotope paleoaltimetry takes advantage of the relationship between orogen elevation and the stable isotope ratios in meteoric water, which are ultimately recorded in geological archives like foreland basins or orogen-internal shear zones. The δ-δ approach relies on contrasting time-equivalent δ18O and δD records from high- and low-elevation sites to constrain the height of the orogen at the time these geologic archives were formed. However, at the same time, different boundary conditions such as changing paleogeography, atmospheric CO2 concentrations or sea surface temperatures result in complex paleoclimate model outputs, which predict significant changes in the isotopic composition of meteoric water. These changes may be recorded in geological archives and thus complicate the reconstruction of past elevations. The 4DMB Phase 1 project APE aimed at generating a first quantitative estimate for the paleoclimatic signal in Alpine stable isotope records, so that these records may be corrected for and ultimately yield more accurate paleoelevation estimates. We addressed this challenge by integrating isotope-tracking climate model (ECHAM5-wiso) simulations with stable isotope and clumped isotope data from the foreland basin and high-elevation regions of the central Alps. ECHAM5-wiso simulations have been conducted with 1) boundary conditions based on paleogeographic reconstructions of the Last Glacial Maximum (LGM) and the mid-Pliocene (PLIO), and 2) different topographic scenarios for the Alps. The simulations show that modifying environmental conditions can produce similar magnitudes of δ18O change as changes in alpine topography. For example, the climatically induced δ18O changes in the PLIO and LGM experiments correspond to the magnitude of changes created by setting the entire orogen to 50% and 150% of its modern height, respectively (Botsyun et al., 2020). Our modelling results stress the need for the paleoaltimetry community to correct isotopic signals in geologic archives for climate-induced changes in isotope ratios. Pedogenic carbonate proxy data from alluvial megafans of the Swiss Molasse Basin revealed that 1) low-elevation, distal δ18O values are higher than previously assumed and thus, more adequately reflect low-elevation δ18O values required for paleoelevation estimates; 2) Mid-Miocene megafans had considerable topography and an internal elevation gradient; 3) clumped isotope-derived carbonate formation temperatures yield low-elevation paleoclimate estimates and help to embed δ18O data into global climate models. Under consideration of previous work and our modelling results, we conclude that the Central Alps, more specifically the region surrounding the Simplon Fault Zone, attained surface elevations of >4000 m no later than the mid-Miocene (Krsnik et al., 2021). In summary, our approach represents an important methodological advance that allows the disentangling of climatic and surface uplift signals in the geologic stable isotope record. Furthermore, new insights into the Alps elevation history can help to constrain the timing of slab inversion and/or break-off in the Western/Central Alps

Late Carboniferous paleoelevation of the Variscan Belt of Western Europe

Received 9 September 2020 Received in revised form 17 May 2021 Accepted 13 June 2021 Available online xxxx Editor: J.-P. Avouac Keywords: stable isotope paleoaltimetry meteoric fluids shear zone detachment Variscan Carboniferous 1. Introduction The Variscan belt, extending from South America to East Asia through North America and Central Europe, is a Himalayan-type collision belt that resulted from protracted convergence between the Laurentia-Baltica and Gondwana lithospheric plates between ∼ 410 and ∼ 310 Ma (e.g. Matte, 2001). This extensive mountain belt exposes vast amounts of granites, migmatitic complexes and granulite facies rocks and is considered a “hot orogen” character- ized by crustal thickening, syntectonic crustal melting, high-grade metamorphism, and syn- to post-convergence gravitational col- lapse (Fig. 1; e.g. Gébelin et al., 2009; Vanderhaeghe et al., 2020). * Corresponding author. E-mail address: [email protected] (C. Dusséaux). https://doi.org/10.1016/j.epsl.2021.117064 0012-821X/© 2021 Elsevier B.V. All rights reserved. abstract We present the first stable isotope paleoaltimetry estimates for the hinterland of the eroded Variscan Belt of Western Europe based on the hydrogen isotope ratios of muscovite from syntectonic leucogranites that have been emplaced at ∼ 315 Ma. We focus on the Limousin region (Western Massif Central, France) where peraluminous granites are spatially associated with strike-slip and detachment shear zones that developed as a consequence of Late Carboniferous syn- to post-orogenic extension. In this region, we show that the north-east corner of the Millevaches massif (located at the junction between brittle and ductile fault systems) represented a pathway for Earth surface-derived fluids that penetrated the crust and reached the ductile segment of the low-angle Felletin detachment zone. Using microstructural, thermometry, hydrogen isotope and 40Ar/39Ar geochronological data, we show that these Variscan meteoric fluids interacted with hydrous silicates during high temperature deformation between ∼ 318 and 310 Ma. For paleoaltimetry purposes, we reference our hydrogen isotope record (δD) of ancient meteoric fluids from mylonitic rocks to ∼ 295 Myr-old records retrieved from freshwater shark remains preserved in the Bourbon l’Archambault basin that developed in the external zones of the orogen. A ∼ 76 difference in δDmeteoric water values between the Millevaches massif (δDmeteoric water value = − 96 ± 8) and the Bourbon l’Archambault foreland basin (δDwater value = − 20 ± 6) is consistent with paleoaltimetry estimates of 3.4 ± 0.7 km based on a modern lapse rate of ∼ -22/km for δDwater values. The rather large difference in δD values between the foreland basin and the continental interior suggests that the hinterland of the Variscan belt of western Europe was high enough to act as a barrier to moisture transport from the south-south-east and induce an orographic rain shadow to the north

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

Provenance of Eocene river sediments from the central northern Sierra Nevada and implications for paleotopography

Geochronology of fluvial deposits can be used to characterize provenance, the paleotopography of sediment source regions, and the development of regional drainage systems. We present U-Pb and (U-Th)/He ages of detrital zircon grains from Eocene gravels preserved in several paleoriver systems along the western flank of the central and northern Sierra Nevada. These ages allow us to trace the sourcing of detritus in paleorivers and to constrain the evolution of the Sierra Nevada range front. U-Pb zircon age distributions are bimodal, with a dominant peak between 110 and 95 Ma and smaller but significant peaks in the Middle to Late Jurassic, matching the predominant ages of the Sierra Nevada batholith. A small fraction (<6%) of grains has pre-Mesozoic ages, which consistently match ages from prebatholithic assemblages within the northern part of the range. (U-Th)/He ages of a subset of double-dated zircons cluster between 114 and 74 Ma and are consistent with batholithic (U-Th)/He cooling ages in the northern Sierra. Our results indicate that the Eocene river systems in the central northern Sierra Nevada likely had proximal headwaters and had relatively steep axial gradients, draining smaller areas than was commonly thought. This also suggests that the northern Sierra Nevada would have had an established drainage divide and would have acted as a major topographic barrier during the early to mid-Cenozoic. The data presented here support a model of the Eocene northern Sierra Nevada characterized by a western slope with a gradient broadly similar to that of today

Eocene maar sediments record warming of up to 3.5 °C during a hyperthermal event 47.2 million years ago

Eocene hyperthermal events reflect profound perturbations of the global carbon cycle. Most of our knowledge about their onset, timing, and rates originates from marine records. Hence, the pacing and magnitude of hyperthermal continental warming remains largely unaccounted for due to a lack of high-resolution climate records. Here we use terrestrial biomarkers and carbon isotopes retrieved from varved lake deposits of the UNESCO World Heritage site ‘Messel Fossil Pit’ (Germany) to quantify sub-millennial to millennial-scale temperature and carbon isotope changes across hyperthermal event C21n-H1 (47.2 million years ago). Our results show maximum warming of ca. 3.5 °C during C21n-H1. We propose that two components are responsible for the warming pattern across the hyperthermal: (1) the massive release of greenhouse gases into the atmosphere-ocean system and (2) half-precession orbital forcing indicated by ~12.000-year temperature cycles. The carbon isotope record of bulk organic matter indicates a sharp, 7‰ decrease at the peak of the hyperthermal, corresponding to increased organic carbon content and a shift in the lake algal community. Collectively, our proxy data reveal the structure of continental temperature response during the hyperthermal event that is characterized by overall warming with a superimposed pattern of sub-orbital scale temperature fluctuations

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