Geochronological and stratigraphical characterization of lower Jurassic tectonically-controlled felsic tuff ring volcanism in Northwestern Patagonia, Argentina

STREMEL, AGUSTÍN J.; BENEDINI, LEONARDO; STRAZZERE, LEONARDO; GREGORI, DANIEL A.; BAHÍA, MARCOS E.; GERALDES, MAURO C.; PAVÓN PIVETTA, CECILIA; BARROS, MERCEDES; DOS SANTOS, ANDERSON COSTA

INTERNATIONAL GEOLOGY REVIEW

TAYLOR & FRANCIS INC

Año: 2024 p. 1 - 25

0020-6814

The early Jurassic syn-rift phase generated a significant set of half-grabens, calderas, and pull-apartbasins along the southwestern margin of South America. In particular, the Loncon Complex,located in the western Extra-Andean region of North Patagonia (∼40°S), forms part of suchstructures. In the present contribution, we characterize and define the Early Jurassic extensionalarchitecture of the Loncon Complex, constituted of a small-scale pull-apart basin associated withpolygenetic volcanism, based on outcrop-scale kinematic data from strike-slip faults, and strati-graphic analysis. Lithofacies analysis, texture, componentry, and structural data allow us to distin-guish four stages during the evolution of the Complex; the three early stages are followed by adeformational phase, and crowned by a limited felsic monogenetic volcano; stages consist of a) Acontinental alluvial to fluvial sedimentation related with an early pull-apart basin phase; b) localphreatomagmatic explosions with syn-eruptive sedimentation periods of a medium life cycle(~104-105 years), b) effusive andesitic stage generated by strike-slip transtension, resulting inpartial deformation and development of a local unconformity, and c) a final short-term silicic tuffring volcano construction (days to months’ time span). The measured faulting pattern is synchro-nous with the Loncon Complex’s sedimentation and volcanism. Kinematic data allow us tocharacterize the Loncon Complex evolution under NNE-NNW minimum horizontal stress(SHmin). This local NNE-oriented extension is interpreted as a consequence of a regional process,in a similar way to the report for the Neuquén Basin and the surrounding region in Patagonia. NewU-Pb data indicate the onset of volcanism began in the Sinemurian (193.08 ± 1.13 Ma) alsosupporting an equivalent timing with the vicinity half-grabens areas of the North Patagonia regionand the Neuquén Basin (Figure S1a). The process that occurred during the Sinemurian, andprobably during the Pliensbachian, affected the entire back-arc basin developed along the south-western border of Gondwana.