Publication Date:
2023-07-11
Description:
Abstract
Description:
The new data set along the TRANSALP geophysical transect in the European Alps consists of three types: (i) new apatite and zircon fission data, (ii) a MOVE™ structural-kinematic model for the tectonic evolution along the transect since the Oligocene, and (iii) PECUBE input/output thermo-kinematic model data corresponding to the structural-kinematic MOVE™ model. The fission track data are provided as *.csv data tables formatted to be ideally opened and viewed in RadialPlotter (Vermeesch, 2009) or alternatively in any spreadsheet editor (e.g., Microsoft Excel). The MOVE™ files require the software MOVE™ licensed by Petroleum Experts. The PECUBE input/output files can be opened with any text editor (e.g., Microsoft Visual Code) or data analysis software (e.g., MATLAB™).
Description:
Methods
Description:
Apatite and zircon mineral extraction were conducted for four samples following standard techniques. Samples were crushed and sieved before undergoing magnetic and heavy liquid separation. Apatite and zircon separates were embedded in epoxy resin and Teflon™ sheets, respectively. The sample mounts were polished to expose internal surfaces at approximately half the grain size. Apatite mounts were etched in 5.5 mol HNO3 for 20 seconds at 21 ºC (Donelick et al., 2005), and zircon mounts in a KOH:NaOH eutectic melt at 228 ºC until fission tracks were visible (Garver, 2003). We employed the mica external detector method (Gleadow et al., 1981) for all samples to determine the Uranium content. After neutron irradiation at the nuclear reactor BR1 in Mol/Belgium, micas were etched in 40% HF for 30 minutes at 21 ºC. Spontaneous and induced fission tracks were counted at 1000x magnification on a Zeiss Axiolmager M2m microscope with AutoScan® soft- and hardware. Fission-track ages are calculated using the ζ age calibration method (Hurford & Greene, 1983) using ζ-values of 249.9±8.9 and 121.7±4.1 for the AFT and ZFT systems, respectively. Data visualization and age mixture distribution analyses were aided by RadialPlotter (Vermeesch, 2009).
Reconstruction of rock trajectories along TRANSALP were performed in MOVE™ through orogen-scale upper lithospheric cross-section balancing in 2D (e.g., Dahlstrom, 1969). Cross-section balancing provides a tool to reconstruct the displacement of rock material over geologic time scales while maintaining equal rock area before and after deformation under a brittle regime and honoring observed geology. Maintenance of line lengths before and after a deformation step is ensured above active décollements, whereas beneath, we assume crustal thickening occurs through unspecified ‘distributed deformation’ reflecting a hybrid ductile/brittle state. This enabled us to implement a simplified evolution of the Mohorovičić discontinuity (Moho) with time. Shortening above the décollement gives us a precise estimate of the area that needs to be accommodated between the décollement and the Moho. In this process, the Moho has been warped downward by the amount of space displaced between the décollement and the Moho with each deformation step (Fig. 4), assuming that crustal thickening is achieved through distributed deformation’ until the Moho reaches its present-day shape as determined by Kummerow et al. (2004). In this forward kinematic modeling process, we added flexural and isostatic crustal responses to rock displacement and different modes of erosion (i.e., changing the angle of taper topography). For details related to implementation of the geological structures and crustal parameters, please refer to the companion paper.
Viable structural-kinematic models are used to track rock displacement and simulate heat advection in a thermal model. The thermal model used is a University of Tübingen modified version of PECUBE (‘Pecube-D’; Whipp et al., 2009; Braun, 2003; McQuarrie & Ehlers, 2015; 2017). Pecube-D is modified from the original version of Pecube to include integration with the Move structural restoration software (McQuarrie and Ehlers, 2015), detrital thermochronometer age analysis (Whipp et al., 2009; Whipp and Ehlers, 2020), and inverse modelling of cooling ages for sample exhumation rates (Thiede and Ehlers, 2013). It solves the three-dimensional heat transport equation for user-defined topographies and surface boundary conditions. Age prediction algorithms for the (U-Th)/He and fission-track systems in apatite and zircon follow Farley (2000), Crowley et al. (1991), Reiners et al. (2004), and Brandon et al. (1998).
Keywords:
TRANSALP
;
thermochronology
;
continental collision
;
subduction polarity
;
thermo-kinematic modelling
;
EARTH SCIENCE 〉 SOLID EARTH 〉 GEOMORPHIC LANDFORMS/PROCESSES 〉 TECTONIC PROCESSES
;
EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS
;
EARTH SCIENCE SERVICES 〉 MODELS 〉 GEOLOGIC/TECTONIC/PALEOCLIMATE MODELS
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geology
;
surface processes
;
tectonics
;
thermochronology
Type:
Collection
,
Collection
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