DOI: 10.12688/openreseurope.24310.1 ISSN: 2732-5121

Onshore surface–subsurface correlation of orogenic structures and the continuation of the late Paleozoic Gondwanides in the Tierra del Fuego fold-and-thrust belt, southern Patagonia

Jean-Baptiste P. Koehl, Rocio E. Gallardo Jara, Juan Ortiz, John Ballesteros Prada, Benjamín Sandoval-Leal, Sebastián Parra Irribarra
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Background The Cretaceous–Cenozoic Tierra del Fuego fold-and-thrust belt in southern Patagonia exposes Paleozoic–Cenozoic rocks recording the protracted, subduction-dominated tectonic evolution of South America, from Cambrian–Ordovician magmatism to Permian metamorphism, Jurassic backarc basin formation, Cretaceous–Cenozoic contraction, and ongoing transtension. Methods High-resolution seismic reflection data were used to interpret tectonic structures in the subsurface and correlate them with surface outcrops and nearby exploration wellbores. The study leverages recent findings in the subsurface architecture and seismic facies of orogenic structures. Results Hundred-meter-scale asymmetric, thrust-related and parasitic folds and related structures in surface outcrops are tied to equivalent structures in subsurface seismic data. Seismic structural mapping suggests that Paleozoic basement rocks in southern Patagonia were involved in more than one episode of contraction, including a pre-Jurassic episode and that Jurassic–Lower Cretaceous basins correspond to broad open synclines instead of fault-bounded (half-) grabens and recorded two phases of Cretaceous–Cenozoic contractional deformation. Conclusions The present study validates the seismic facies of hundred-meter- to km-scale orogenic structures in the subsurface, thus opening new avenues for detailed structural studies in intensely deformed crustal domains. The Permian Gondwanide Orogen extends to southern Patagonia, which should be considered as a single tectonic block with northern Patagonia, the Falkland Islands and Maurice Ewing Bank at least since the Permian and probably since the early Cambrian, thus providing valuable anchors for future plate reconstructions. Jurassic–Lower Cretaceous volcanosedimentary rocks were deposited during a period of tectonic quiescence, possibly in a passive backarc setting, and were later deformed (1) in the mid-Early to mid-Cretaceous and (2) mildly reworked in the Late Cretaceous–Paleogene during the formation of the Tierra del Fuego fold-and-thrust belt. Only tenuous traces of Cenozoic extension were found in the subsurface, thus suggesting a limited and/or localized impact of the ongoing transtensional tectonic regime.

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