Abstract

Basement rocks of the Magellan basin at the Atlantic margin, in extra-Andean Tierra del Fuego (Chile), are predominantly formed of orthogneisses. They have been recovered only by drilling and their ages are mostly unknown. In this study, using the U-Pb method on zircons, age data have been obtained for a granodiorite gneiss from the basement of the Magellan basin near San Sebastian Bay close to the Chile–Argentina border. Data confirm that zircons of the granodiorite gneiss from the Gaviota 6 drill hole grew primarily during magmatic processes. The Concordia intercept age of unabraded zircons, 529±7.5 Ma, denotes the most probable time of intrusion. Abraded zircons revealed initial zircon growth at 549±6 Ma, probably under primary melt conditions and subsequent closed U-Pb system behaviour. The discordance of data points related to zircon re- and/or neo-crystallization attributed to metamict(?) cloudy domains is contemporaneous with Sr and Pb isotope homogenization in apatite and K-feldspar at 161.6±4.5 Ma. The contemporaneousness of total (Sr) or partial (Pb) equilibration of radiogenic isotopes in minerals of the granodiorite gneiss and formation of the nearly 2000 m thick Jurassic volcanic series leads to discussion of a fundamental heating of the lower crust at that time, controlled by the spatially distributed influx of a fluid phase. The Early Cambrian intrusion age of the precursor rock of the dated granodiorite gneiss suggests that basement rocks of Tierra del Fuego were generated contemporaneously with the Pampean orogenic cycle. The age of 529±7.5 Ma supports the idea of considering Tierra del Fuego as the ‘missing link’ between the Early Palaeozoic orogenic cycles of central and northwestern Argentina and the Late Cambrian/Early Ordovician Ross orogeny in central Antarctica.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.