Constraining the near-surface response to lithospheric reorientation: Structural thermochronology along AlpArray geophysical transects

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This proposal outlines a project to quantify the near-surface response of Central and Eastern Alps exhumation to hypothesized changes in lithosphere processes, such as a slab breakoff or a switch in subduction polarity, with an innovative combined analytical-modelling approach. This project follows the aims of the SPP 4D-MB by reconstructing the 4D evolution of the Alps with a combination of thermochronological dating, measurement of balanced cross sections and thermal-kinematic modelling. This multidisciplinary approach will resolve a ~30 Ma kinematic history of the Alps since at kilometre/million year scales to predict orogen-wide shortening rates and average slip velocities of primary tectonic structures (RT1-Reorg. of Lithosphere of the SPP 4D-MB); important context for complimentary studies focusing on the present-day surface motion and seismicity (RT-4-Motion patterns and Seismicity of the SPP 4D-MB). Most importantly, the full consideration of the kinematic history and large spatial scale of our project facilitates the discrimination of near-surface exhumation rates from the influence of deep crustal processes (RT2-Surface Response of the SPP 4D-MB). We propose to date 60 new samples collected along geologic-geophysical transects through the Central and Eastern Alps (NFP-20E, TRANSALP, EASI) with apatite and zircon (U-Th)/He and apatite fission track methods. This sampling strategy (i) covers the area in which a switch in subduction polarity is hypothesized to have occurred and (ii) overlaps with activity fields AF-A (DSEBRA), AF-C (SWAATH C) and AF-D (SWAATH D) of the SPP 4D-MB, ensuring that our project compliments the refined geophysical and geodynamic measurements from AlpArray. We will invert cooling ages with a coupled PECUBE-2DMove thermal-kinematic modelling approach maintaining the predicted structural context of available and newly constructed balanced cross sections along transects lines. Velocity fields extracted from 2Dmove will be subsequently incorporated into a thermal-kinematic model (PECUBE) and inverted to constrain the most likely combination of structural displacements and deep lithosphere induced long-wavelength rock uplift discernable from the composite thermochronological dataset. Our proposed project will therefore significantly contribute to get a better understanding of the 4D evolution of the Alps.