Thermochronometry across the Austroalpine-Pennine boundary, Central Alps, Switzerland: Orogen-perpendicular normal fault slip on a major ‘overthrust’ and its implications for orogenesis

Tectonics
By: , and 

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Abstract

Fifty‐one new and 309 published thermochronometric ages (nine systems with closure temperatures ranging from ~450 to 70°C) from the Graubünden region of the Central Alps demonstrate that a pronounced thermal mismatch between the Austroalpine allochthon (Alpine “orogenic lid”) and the Pennine zone persisted until at least 29 Ma and, allowably, until circa 18 Ma. The observed mismatch supports previous suggestions that the famous “overthrust” between the Austroalpine allochthon and the Pennine zone, historically regarded as primarily an Eocene top‐north thrust fault, is in fact primarily an Oligocene‐Miocene normal fault that has a minimum of 60 km of displacement with top‐south or top‐southeast sense of shear. Two hallmarks of Alpine geology, deposition of the foredeep Molasse and emplacement of the Helvetic nappes, appear to be coeval, peripheral manifestations of crustal thickening via the interposition of the Pennine zone as a northward intruding wedge between the Austroalpine “lid” and the European cratonic margin, with the Helvetic system (European margin) acting as the “floor” of the wedge. We presume the Penninic wedge is driven by the buoyant rise of subducted crust no longer able to remain attached to the descending slab. If so, emplacement of the Pennine wedge could have occurred mainly after Adria was juxtaposed against cratonic Europe.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Thermochronometry across the Austroalpine-Pennine boundary, Central Alps, Switzerland: Orogen-perpendicular normal fault slip on a major ‘overthrust’ and its implications for orogenesis
Series title Tectonics
DOI 10.1002/2017TC004619
Volume 37
Issue 3
Year Published 2018
Language English
Publisher AGU
Contributing office(s) Central Mineral and Environmental Resources Science Center
Description 34 p.
First page 724
Last page 757