Multi‐phase late‐Neogene exhumation history of the Aar massif, Swiss central Alps

Abstract

The late-Neogene evolution of the European Alps was influenced by both tectonic and climatically driven erosion processes, which are difficult to disentangle. We use lowtemperature thermochronometry data from surface and borehole samples in the Aar massif-Rhône valley (Swiss central Alps) to constrain the exhumation history of the region. Multiple exhumation events are distinguished and linked to regional-scale tectonic deformation (before 5 Ma), short-lived climatically driven orogen contraction (between 4 and 3 Ma), and glacial valley carving since c. 1 Ma. Compared with previous studies, we clearly show the existence of two separate exhumation phases in the Late Miocene-Pliocene and better constrain the onset of glacial valley carving. The hydrothermal activity and geothermal anomalies currently observed in the borehole have been local and short-lived, with only a minor influence on thermochronometric observations. We thus suggest that late-stage glacial valley carving may have triggered topography-driven fluid flow and transient hydrothermal circulation.Apatite grains were extracted from crushed bedrock samples using standard magnetic and heavy-liquid separation techniques. 384

Innovations in (U–Th)/He, Fission Track, and Trapped Charge Thermochronometry with Applications to Earthquakes, Weathering, Surface‐Mantle Connections, and the Growth and Decay of Mountains

“…FT, (U-Th)/He, and 4 He/ 3 He thermochronometry of basement rocks, sedimentary rocks, and sediments quantify the timing and tempo of erosional and tectonic exhumation in orogens ( Figure 6). In mountain ranges that develop in convergent orogens, these tools lay the foundation to investigate relationships between rapid erosion and surface uplift (e.g., Avdeev & Niemi, 2011;McDermott et al, 2019;Spencer et al, 2019; and many others), propagation of deformation into the foreland (e.g., Gautheron, Espurt, et al, 2013;Lease, Ehlers, & Enkelmann, 2016;Thomson et al, 2017), rapid Quaternary exhumation (Blythe et al, 2007;Shuster et al, 2011;Valla, Rahn, et al, 2016;Yang et al, 2018), and Quaternary climate influences on sediment storage and erosion (e.g., Lang et al, 2018).…”

“…Some fault systems host paleo and juvenile geothermal systems. Bedrock and borehole apatite He thermochronometry can document transient and long-lived thermal anomalies in faults and, together with other low-temperature thermochronometers, are useful tools for geothermal research and exploration (Gorynski et al, 2014;MacNamee & Stockli, 2015;Valla, Rahn, et al, 2016;Whipp & Ehlers, 2007).…”

Mapping a geothermal anomaly using apatite (U‐Th)/He thermochronology in the Têt fault damage zone, eastern Pyrenees, France

“…Few studies have so far been dedicated to the impact of hydrothermal activity on thermochronology (e.g. Deming, ; Forster & Smith, ) and more particularly on the behaviour of apatite in geothermal systems (Duddy, Green, Hegarty, Bray, & O'Brien, ; Gorynski, Walker, Stockli, & Sabin, ; Hickey, Barker, Dipple, Arehart, & Donelick, ; Luijendijk, ; Valla, Rahn, Shuster, & Beek, ; Whipp & Ehlers, ; Wölfler, Kurz, Danišík, & Rabitsch, ). Meteoric fluids infiltrated from reliefs adjacent to faults generate subsurface thermal anomalies along the fault during their upflow (McKenna & Blackwell, ).…”

Tracking geothermal anomalies along a crustal fault using (U-Th)/He apatite thermochronology and REE analyses, the example of the Têt fault (Pyrenees, France)

“…Actually, alongside these thoughts, the past decades revealed an increasing amount of studies about the influence of hydrothermal circulations on LT thermochronometers, rendering difficult their interpretation in terms of exhumation history along faults (e.g. Whipp and Ehlers, 2007;Wölfler et al, 2010;Gorynski et al, 2014;Danišík et al, 2015;Valla et al, 2016;Louis et al, 2019). In this study, we propose an extended analysis of (U-Th)/He on apatite (AHe) thermochronometer (a LT thermochronometer sensitive for a range of temperature between 30 and 90 °C, Gautheron et al, 2009;Shuster and Farley, 2009), in association to Rare Earth Elements (REE) analysis of dated apatites, to track the effects of surface and hidden thermal systems along the Têt normal fault (Pyrenees).…”