Tracing the thermal evolution of the Corsican lower crust during Tethyan rifting. Issue 10 (22nd October 2016)

• Record Type: Journal Article
• Authors: Seymour, Nikki M.; Stockli, Daniel F.; Beltrando, Marco; Smye, Andrew J.
• Is Part Of: Tectonics. Volume 35:Issue 10(2016)
• Page Start: 2439
• Page End: 2466
• Publication Date: 2016-10-22
• Subjects: Corsica -- thermochronology -- magma‐poor continental rifting -- Alpine Tethys -- U‐Pb depth profiling; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1002/2016TC004178
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: Continental rifting requires thinning the continental lithosphere from ~120 km to <20 km by a series of processes which each impart a characteristic thermal signature to the extending lithosphere. Here high‐resolution thermochronology is used to trace the synrift thermal evolution within a lower crustal section of an upper plate hyperextended margin sampled in Corsica. Novel zircon, rutile, and apatite 206 Pb/ 238 U depth profiling coupled with garnet trace element diffusion modeling provide compelling evidence for rift‐related crustal reheating. A Jurassic thermal pulse is recorded in the footwall of the Belli Piani Shear Zone (BPSZ), where 200–180 Ma zircon 206 Pb/ 238 U overgrowth ages on Permian core populations and the preservation of stranded diffusion profiles in resorbed garnets implies the dominant footwall fabric formed as a result of high‐temperature ( T ~ 800°C) ductile thinning of the lower crust. Conductive reheating of middle crustal rocks in the immediate BPSZ hanging wall, demonstrated by Jurassic apatite 206 Pb/ 238 U ages, was likely achieved by synkinematic juxtaposition against the hot footwall and wholesale conductive steepening of geothermal gradients. Subsequent rapid cooling from 180 to 160 Ma, coeval with extensional unroofing of the footwall, underscores the importance of extreme ductile thinning during crustal hyperextension. The results of this study suggest that early lithospheric‐scale depth‐dependent thinning follows an early phase of diffuse rifting and tectonic subsidence and triggers crustal reheating during early hyperextension. Continued extension results in rapid exhumation and cooling of the lower crust, extreme crustal attenuation, and mantle exhumation followed by relaxation to a steady state thermal field coeval with the start of seafloor spreading. Key Points: Reheating‐cooling cycle observed at fossil magma‐poor rift margin Thermal evolution of magma‐poor continental rifting mimics the structural evolution Rutile and apatite provide a continuous 600–400°C thermal history