Episodic Jurassic intraplete compression during supercontinent breakup in southwestern Gondwana, central Patagonia

ANDRES ECHAURREN; GUIDO GIANNI; CESAR NAVARRETE; ANDRES FOLGUERA

Simposio; Primer Simposio de Tectónica Sudamericana; 2016

From Lower to Mid Jurassic, in a general context of crustal extension associated with Gondwana breakup, several intraplate compression events affected some sectors of Central Patagonia, as evidenced by 2D and 3D seismic and borehole data. These materials show partial inversion of Lower to Mid Jurassic extensional structures controlling marine and continental depocenters of the Chubut Basin, linked to the earliest stages of breakup. A comparison with surrounding areas in Patagonia, where similar Jurassic intraplate compression was described, allowed the discrimination of three discrete pulses of subtle compression (C1:~187-185 Ma; C2: ~170-163; C3:~157-136? Ma). Interestingly, these episodic intraplate compressional events followed closely the beginning of high flux magmatic events linked to the westward expansion of the Karoo thermal anomaly, which impacted on the lithosphere of Southwestern Gondwana. At the same time, according to new models of continental drift during the breakup of Gondwana, the South American plate would have suffered a change of direction and acceleration to the south from Lower to Mid Jurassic. On the other side and completing the geodynamic context, the opening of the Weddell Sea in the south of South America begins in the Upper Jurassic. These observations led us to propose that the thermo mechanic weakening of the continental interior due to LIP activity added to changes in plate motions and later ridge-push forces linked to Weddell Sea opening, produced an intraplate shortening through discrete pulses interrupted at the time by the magmatic invigoration of the Karoo LIP. In addition, we determined a N-S direction for the main compressive strain axis, which is compatible with other Jurassic intraplate belts developed throughout the South American plate interior.