Paleomagnetic evidence of the brittle deformation of the Central Patagonian Batholith at Gastre area (Chubut Province, Argentina)

RUIZ GONZÁLEZ, VÍCTOR; PUIGDOMENECH, CARLA G.; ZAFFARANA, CLAUDIA B.; VIZÁN, HAROLDO; SOMOZA, RUBÉN

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2020 vol. 98

0895-9811

The Central Patagonian Batholith (CPB) in the Gastre area, central Patagonia, constitutes a set of two I-type LateTriassic plutonic suites, the Gastre superunit with a U-Pb zircon age of 221 ± 2 Ma, and the Lipetrén superunitwith a U-Pb SHRIMP age of 215 ± 1 Ma. The source of this calc-alkaline batholith is characterized by crustaland mantle contributions, and it registers NW-SE subvertical magmatic and solid-state fabrics. These features,together with its intraplate position away from the inferred proto-Gondwana margin, have made it the focus ofdifferent tectonic interpretations. Early studies have interpreted it as the record of major dextral motions alongthe transcontinental NW-SE-striking Gastre fault system in Jurassic times. Later interpretations have proposedthat the magmatic and tectonic foliations of the CPB were formed during a sinistral transpressive regime whichwas aided by Late Paleozoic widespread NW-SE subvertical structures in the North Patagonian Massif.Paleomagnetism, a unique tool to detect the presence of tectonic block rotations on vertical axes, was applied inthe CPB in order to constrain the timing and type of deformation in the area. A paleomagnetic pole was obtained,which statistical parameters are: N = 45, Lat. = 81.4°S, Long. = 207°E, K = 11.5, A95 = 6.6°. Although theposition of this pole does not coincide with equivalent Late Triassic poles, this position can be reconciled withthe presence of a NE tilting of about 11° of the sampled block of the batholith. The tilting would have been aidedby the NW-SE subvertical structures that affect the area. These paleomagnetic results rule out the possibility ofvertical axis rotations from Late Triassic to present times and suggest that the ductile syn- to post-emplacementdeformation of the CPB in Gastre area occurred during this period (Late Triassic), being the later brittle deformationtriggered by the Andean Orogeny a possible explanation for this tilting.