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

• Published in: International geology review Vol. 66; no. 15; pp. 2768 - 2792
• Main Authors: 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
• Format: Journal Article
• Language: English
• Published: Philadelphia Taylor & Francis 21-08-2024; Taylor & Francis Ltd
• Subjects: Alluvial basins; Calderas; Data analysis; Deformation; Early Jurassic; Evolution; Explosions; felsic tuff-ring; Fluvial sedimentation; Geochronology; Geological faults; Gondwana; Graben; Horizontal orientation; Jurassic; Kinematics; Life cycle; Lithofacies; Loncon Complex; Northwestern Patagonia; Outcrops; pull-apart sedimentation and volcanism; Sedimentation; Sedimentation & deposition; Stratigraphy; Strike-slip faults; Tuff; Unconformity; Volcanic activity; Volcanism; Volcanoes
• ISSN: 0020-6814; 1938-2839
• DOI: 10.1080/00206814.2023.2301365

The early Jurassic syn-rift phase generated a significant set of half-grabens, calderas, and pull-apart basins 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 such structures. In the present contribution, we characterize and define the Early Jurassic extensional architecture of the Loncon Complex, constituted of a small-scale pull-apart basin associated with polygenetic volcanism, based on outcrop-scale kinematic data from strike-slip faults, and stratigraphic analysis. Lithofacies analysis, texture, componentry, and structural data allow us to distinguish four stages during the evolution of the Complex; the three early stages are followed by a deformational phase, and crowned by a limited felsic monogenetic volcano; stages consist of a) A continental alluvial to fluvial sedimentation related with an early pull-apart basin phase; b) local phreatomagmatic explosions with syn-eruptive sedimentation periods of a medium life cycle (~10
4
-10
5
years), b) effusive andesitic stage generated by strike-slip transtension, resulting in partial deformation and development of a local unconformity, and c) a final short-term silicic tuff ring volcano construction (days to months' time span). The measured faulting pattern is synchronous with the Loncon Complex's sedimentation and volcanism. Kinematic data allow us to characterize 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. New U-Pb data indicate the onset of volcanism began in the Sinemurian (193.08 ± 1.13 Ma) also supporting an equivalent timing with the vicinity half-grabens areas of the North Patagonia region and the Neuquén Basin (Figure S1a). The process that occurred during the Sinemurian, and probably during the Pliensbachian, affected the entire back-arc basin developed along the southwestern border of Gondwana.