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This study presents the simulated response of regional climate and the oxygen isotopic composition of precipitation (δ18 O p) to different along-strike topographic evolution scenarios. These simulations are conducted to determine if the previously hypothesized diachronous surface uplift in the Western and Eastern Alps would produce δ18 O p signals in the geologic record that are sufficiently large and distinct to be detected using stable isotope paleoaltimetry. We present a series of topographic sensitivity experiments conducted with the water-isotope-tracking atmospheric general circulation model (GCM) ECHAM5-wiso. The topographic scenarios are created from the variation of two free parameters, (1) the elevation of the Western–Central Alps and (2) the elevation of the Eastern Alps. The results indicate Δδ18 O p values (i.e., the difference between δ18 O p values at the low- and high-elevation sites) of up to -8 ‰ along the strike of the Alps for the diachronous uplift scenarios, primarily due to changes in orographic precipitation and adiabatic lapse rate driven localized changes in near-surface variables. These simulated magnitudes of Δδ18 O p values suggest that the expected isotopic signal would be significant enough to be preserved and measured in geologic archives. Moreover, the simulated slight δ18 O p differences of 1 ‰–2 ‰ across the low-elevation sites support the use of the δ – δ paleoaltimetry approach and highlight the importance of sampling far-field low-elevation sites to differentiate between the different surface uplift scenarios. The elevation-dependent rate of change in δ18 O p ("isotopic lapse rate") varies depending on the topographic configuration and the extent of the surface uplift. Most of the changes are significant (e.g., -1.04 ‰ km -1 change with slope error of ±0.09 ‰ km -1), while others were within the range of the statistical uncertainties (e.g., -0.15 ‰ km -1 change with slope error of ±0.13 ‰ km -1). The results also highlight the plausible changes in atmospheric circulation patterns and associated changes in moisture transport pathways in response to changes in the topography of the Alps. These large-scale atmospheric dynamics changes can complicate the underlying assumption of stable isotope paleoaltimetry and therefore require integration with paleoclimate modeling to ensure accurate reconstruction of the paleoelevation of the Alps. [ABSTRACT FROM AUTHOR]

The European Alps are hypothesized to have experienced diachronous surface uplift in response to post-collisional processes such as, e.g., slab break-off. Therefore, understanding the geodynamic and geomorphic evolution of the Alps requires knowledge of its surface uplift history. This study presents the simulated response of regional climate and oxygen isotopic composition of precipitation (δ18Op) to different along-strike topographic evolution scenarios. These responses are modeled to determine if diachronous surface uplift in the Western and Eastern Alps would produce δ18Op signals in the geologic record that are sufficiently large and distinct for stable isotope paleoaltimetry. This is tested with a series of sensitivity experiments conducted with the water isotope tracking atmospheric General Circulation Model (GCM) ECHAM5-wiso. The topographic scenarios are created from the variation of two free parameters, (1) the elevation of the West-Central Alps and (2) the elevation of the Eastern Alps. Results suggest significant changes in the spatial patterns of δ18Op, the elevation-dependent rate of change in δ18Op ("isotopic lapse rate"), near-surface temperatures, precipitation amounts, and atmospheric circulation patterns in response to the different scenarios. The predictions for the diachronous surface uplift experiments are distinctly different from simulations forced with present-day topography and for simulations where the entire Alps experience synchronous surface uplift. Topographic scenarios with higher elevations in the West-Central Alps produce higher magnitude changes and an expansion of the affected geographical domain surrounding the Alps when compared to present-day topography. Furthermore, differences in δ18Op values of up to -2 to -8 ‰ are predicted along the strike of the Alps for the diachronous uplift scenarios, suggesting that the signal can be preserved and measured in geologic archives. Lastly, the results highlight the importance of sampling far-field and low-elevation sites using the δ-δ paleoaltimetry approach to discern between different surface uplift histories. [ABSTRACT FROM AUTHOR]

The Middle Miocene (15.99–11.65 Ma) of Europe witnessed major climatic, environmental, and vegetational change, yet we are lacking detailed reconstructions of Middle Miocene temperature and precipitation patterns over Europe. Here, we use a high‐resolution (∼0.75°) isotope‐enabled general circulation model (ECHAM5‐wiso) with time‐specific boundary conditions to investigate changes in temperature, precipitation, and δ18O in precipitation (δ18Op). Experiments were designed with variable elevation configurations of the European Alps and different atmospheric CO2 levels to examine the influence of Alpine elevation and global climate forcing on regional climate and δ18Op patterns. Modeling results are in agreement with available paleobotanical temperature data and with low‐resolution Middle Miocene experiments of the Miocene Model Intercomparison Project (MioMIP1). However, simulated precipitation rates are 300–500 mm/yr lower in the Middle Miocene than for pre‐industrial times for central Europe. This result is consistent with precipitation estimates from herpetological fossil assemblages, but contradicts precipitation estimates from paleobotanical data. We attribute the Middle Miocene precipitation change in Europe to shifts in large‐scale pressure patterns in the North Atlantic and over Europe and associated changes in wind direction and humidity. We suggest that global climate forcing contributed to a maximum δ18Op change of ∼2‰ over high elevation (Alps) and ∼1‰ over low elevation regions. In contrast, we observe a maximum modeled δ18Op decrease of 8‰ across the Alpine orogen due to Alpine topography. However, the elevation‐δ18Op lapse rate shallows in the Middle Miocene, leading to a possible underestimation of paleotopography when using present‐day δ18Op—elevation relationships data for stable isotope paleoaltimetry studies. Key Points: A high‐resolution isotope‐enabled general circulation model is used to explore Middle Miocene climate and precipitation δ18O across EuropeMiddle Miocene bi‐directional precipitation change consistent with herpetological fossils and account for precipitation δ18O variationsGlobal Miocene climate forcing contributed a max δ18O change of ∼2‰ over the high Alpine elevation and to ∼1‰ over low elevation [ABSTRACT FROM AUTHOR]

Reconstructing Oligocene–Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps remain scarce. Here we present stable and clumped isotope measurements to provide a new paleoelevation estimate for the mid-Miocene (∼14.5 Ma) European Central Alps. We apply stable isotope δ – δ paleoaltimetry to near-sea-level pedogenic carbonate oxygen isotope (δ 18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δ D) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ 18O , δ 13C) and clumped (Δ47) isotope data from three foreland basin sections in different alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ 18O values and Δ47 temperatures (30±5 ∘C) yield a near-sea-level precipitation δ 18O w value of -5.8±1.2 ‰ and, in conjunction with the high-Alpine phyllosilicate δ D value of -14.6±0.3 ‰, suggest that the region surrounding the Simplon Fault Zone attained surface elevations of >4000 m no later than the mid-Miocene. Our near-sea-level δ 18O w estimate is supported by paleoclimate (iGCM ECHAM5-wiso) modeled δ 18O values, which vary between -4.2 ‰ and -7.6 ‰ for the Northern Alpine Foreland Basin. [ABSTRACT FROM AUTHOR]

Reconstructing Oligocene-Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth's surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps, however, remain scarce. Here we present stable and clumped isotope geochemistry measurements to provide a new paleoelevation estimate for the mid-Miocene (~14.5 Ma) European Central Alps. We apply stable isotope d-d paleoaltimetry on near sea level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (ΔD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30 ± 5°C) yield a near sea level precipitation δ18Ow value of -5.8 ± 0.2‰ and in conjunction with the high-Alpine phyllosilicate dD record suggest that the region surrounding the SFZ attained surface elevations of >4000 m no later than the mid-Miocene. Our near sea level δ18Ow estimate is supported by paleoclimate (iGCM Echam5-wiso) modeled δ18O values, which vary between -4.2 and -7.6‰ for the Northern Alpine Foreland Basin. [ABSTRACT FROM AUTHOR]

Many stable isotope paleoaltimetry studies have focused on paleoelevation reconstructions of orogenic plateaus such as the Tibetan or Andean Plateaus. We address the opportunities and challenges of applying stable isotope paleoaltimetry to "smaller" orogens. We do this using a high‐resolution isotope tracking general circulation model (ECHAM5‐wiso) and explore the precipitation δ18O (δ18Op) signal of Cenozoic paleoclimate and topographic change in the European Alps. Results predict a maximum δ18Op change of 4–5‰ (relative to present day) during topographic development of the Alps. This signal of topographic change has the same magnitude as changes in δ18Op values resulting from Pliocene and Last Glacial Maximum global climatic change. Despite the similar magnitude of the isotopic signals resulting from topographic and paleoclimate changes, their spatial patterns across central Europe differ. Our results suggest that an integration of paleoclimate modeling, multiproxy approaches, and low‐elevation reference proxy records distal from an orogen improve topographic reconstructions. Plain Language Summary: Here we use a climate model with water isotopes implemented to explore the maximum precipitation isotopic signal of Cenozoic topographic and paleoclimate change in the European Alps. Our results show that the impact of topography change has the same magnitude as changes in the isotopic composition of local precipitation resulting from Pliocene and Last Glacial Maximum global climatic change. Key Points: High‐resolution isotope tracking general circulation model (ECHAM5‐wiso) is used to explore changes in past oxygen isotope ratios in precipitation in the AlpsModel‐simulated isotopic signals of topographic change and difference between glacials and interglacials show the same magnitudeLow‐elevation proxy records improve reconstructions of paleotopography by reducing long‐term climate change bias [ABSTRACT FROM AUTHOR]

Inverted passive continental margins permit to comprehensively characterize fluid circulation in the continental crust in orogens from rifting to tectonic inversion. Since granitic rocks have low primary water contents and dominate the continental crust, their hydration exerts important control on metamorphism and deformation of the continental crust during orogeny. It is therefore of great interest to determine whether the granitic continental crust is hydrated during rifting phases or after tectonic inversion. Because fluid circulation may occur at both stages, a comprehensive picture of hydration of the continental crust in inverted passive continental margins can be obtained by the combination of different geochronometers and geochemical methods. In this study, we combine U Pb geochronology and Pb–Sr–O–H isotope geochemistry of epidote in hydrothermal veins in the Albula Pass area (eastern Swiss Alps) as powerful tools to trace hydration events in the continental crust in orogens. The Albula Pass area is part of the inverted Adriatic passive continental margin, which was extensively affected by seawater infiltration during continental rifting in Jurassic times. Epidote geochronology elucidates the fluid circulation history in this rifted crustal section by revealing two hydration events that are not recorded by other datable minerals: (1) 85.2 ± 9.7 Ma and (2) 59.9 ± 2.7 Ma, showing that fluid circulation in the Adriatic passive continental margin continued after Late Cretaceous tectonic inversion. Epidote Pb–Sr–O–H isotope geochemistry characterizes pathways and fluid sources of the epidote forming fluids, which differ between the Late Cretaceous and the Paleocene fluid circulation events. The Late Cretaceous epidote-forming fluids were produced by compaction of sedimentary units beneath the Err nappe and release of modified seawater (i.e., formation/connate water) from marine sediments, while Paleocene veining was mainly mediated by syn -kinematically infiltrated meteoric water. The present geochronological and isotope data argue for multi-stage hydration of the continental crust in the inverted Adriatic passive continental margin. This work promotes the importance of the interplay of newly introduced and recycled fluid components in the hydrothermal alteration of the continental crust, and it highlights epidote as a powerful hygrochronometer and isotope tracer. • Epidote dating unravels fluid circulation events in the granitic crust in orogens. • Pb–Sr–O–H isotope geochemistry of epidote characterizes fluid sources and pathways. • Syn-orogenic hydration of passive continental margins continues after rifting. • Hydration of granitoids in orogens is mediated by newly introduced and recycled fluids. • Epidote is a powerful new geochemical tool to date and trace fluid circulation. [ABSTRACT FROM AUTHOR]

Paleoelevation reconstructions have gained attention over the past decades due to theimportance of quantifying surface uplift for understanding the subsurface density structure,isostatic compensation of orogens, and interactions between surface processes, tectonics andclimate. However, most studies to date have focused on paleoelevation reconstructions oforogenic plateaus. Here, we address the potential and challenges of applying stableoxygen isotopes-based paleoaltimetry to 'smaller’ orogens such as the EuropeanAlps. We do this by answering two questions: i) what is the maximum signal oftopographic change that could be preserved in oxygen isotope paleo-precipitation records,and ii) what is the contribution of climatic changes to such isotopic records. Inorder to address these questions, we use a high-resolution (∼0.75∘) isotope trackinggeneral circulation model (ECHAM5-wiso) and provide sensitivity experiments withreduced and increased topography over the Alps, and experiments with realisticpaleoenvironmental boundary conditions for the Last Glacial Maximum (LGM) and thePliocene. Results indicate that although a maximum signal of 5-6 ‰ in oxygen isotoperatios of local precipitation is predicted during topographic development, this signalis likely obscured by a signal associated with climatic change. Our paleoclimatesimulations with realistic paleoenvironmental boundary conditions show that globalclimate change imprint precipitation δ18O within 5 ‰ i.e. is comparable to thesignal from the topographic uplift. Thus, we argue that the magnitude of the isotopicsignal from the topographic change is similar to that from global climate changeevents, thereby making it difficult to decipher the two in the proxy record withoutadditional knowledge on paleoclimate. Our modeling results allow disentangleclimatic and topographic signals in the geologic stable isotope record and indicate thatstable-isotope based reconstructions of paleotopography largely benefit from an integrationof multi-proxy methods, lowland reference proxy records and climate modeling. [ABSTRACT FROM AUTHOR]