--> --> Linking Thermal Erosion of Mantle Lithosphere with Episodic Heating-Cooling Cycles and Surface Uplift in Hyper-Extended Rift Systems: the Example of the Alpine Tethys

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Linking Thermal Erosion of Mantle Lithosphere with Episodic Heating-Cooling Cycles and Surface Uplift in Hyper-Extended Rift Systems: the Example of the Alpine Tethys

Abstract

The thermal evolution of mantle lithosphere and continental crust in the Alpine Tethys, combined with the Middle Jurassic subsidence history, questions the validity of both pure and simple shear models alone in explaining the evolution of rift systems during hyper-extension. Uplift and emersion of parts of the future distal European margin during an advanced stage of rifting in late Early to Middle Jurassic is documented by erosion and karstification of the Middle Triassic to Lower Jurassic carbonate platform in the Briançonnais domain of the Western Alps and in Hercynian Corsica. Vertical uplift was coeval with a heating-cooling cycle inferred from Zircon Fission Track ages at 185–145 Ma from continental basement rocks from the underlying basement. A regional syn-rift heating-cooling cycle is also inferred for several Tethyan mantle peridotites, which underwent multiple episodes of melt stagnation, rising ambient temperatures by 100–300°C, while being exhumed from the spinel to the plagioclase stability field. Melt stagnation in the sub-continental mantle pre-dated the intrusion of gabbroic dykes at ca. 162 Ma and the deposition of the first post-rift sediments. These observations from different lithospheric depths suggest that syn-rift thinning of the mantle lithosphere is achieved by combined horizontal stretching and thermal erosion through melt stagnation. The resulting vertical advection of isotherms can drive a regional heating-cooling cycle in the overlying crust and sediments, potentially coupled with emersion of the carbonate platform, followed by complete crustal excision and conductive cooling. Thermal erosion of the sub-continental mantle may be an important factor in the syn-rift thermal evolution of the future distal part of rifted margins. Although the final relative thinning factors of the mantle lithosphere and crust along the Corsica and Briançonnais sections may have been very different during the final rift stage, both locations record the same evolution during the thinning stage of rifting. Therefore, significant heating-cooling cycles of the kind described here should not be restricted to the hyper-extended crust alone, but should also be expected in the most distal parts of the proximal margins.