Upper Triassic to Middle Jurassic magmatic evolution of northern Patagonia: Learned insights from the tectonic and crustal evolution of the Los Menucos area, North Patagonian massif, Argentina

JUAN IGNACIO, FALCO; NATALIA, HAUSER; NICOLÁS, SCIVETTI; WOLF UWE, REIMOLD; RALF THOMAS, SCHMITT; ANDRES, FOLGUERA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2021

0895-9811

The Upper Triassic magmatic and tectonic evolution of the central North Patagonian Massif is evaluated on the basis of the zircon U?Pb-Hf record and whole-rock geochemistry for volcanic rocks of the Los Menucos area. The sample analyzed on this study yields a 210 ± 3 Ma U?Pb zircon age, and the geochemical data for the Upper Triassic rocks are indicative of a high-K calk-alkaline arc-type magmatism, which also has adakitic signature related to melting of the subducted oceanic slab. In addition, the Hf isotope data for zircon from this sample, with ƐHf(T) values between −6.1 and −8.7, support a mixed source that may have involved melted slab and crustal reworking. The emplacement of the Upper Triassic magmatism far into the central North Patagonian Massif precedes a ca. 24 Ma stage of magmatic quiescence, which likely represents a crustal-shortening period related to a horizontalized subduction. Our interpretation of the Upper Triassic ? Lower Jurassic magmatic and tectonic evolution of northern Patagonia is in agreement with the hypothesis of Upper Triassic South Gondwanian flat-slab, which shifted the magmatic arc towards the continental interior at a time of crustal shortening and with arc-type adakitic magmatism. The Lower Jurassic magmatic record is consistent with slab detachment and later roll-back, which would have promoted crustal extension and intraplate magmatism, and also shifted the arc magmatism to the paleo-trench. As a consequence of this stage, the Subcordilleran and North Patagonian batholiths were emplaced. The progressively less negative Hf isotope signature for magmatic zircons is consistent with addition of more basic magmas generated throughout the Jurassic. The Upper Triassic-Middle Jurassic magmatism in northern Patagonia was part of a complex tectonic evolution, which involved crustal shortening and extension during plate reorganization on the critical period og the break-up of Gondwana supercontinent.