Magnetic fabrics and microstructures of Paleoproterozoic intrusive bodies of Piedra Alta Terrane, Río de la Plata Craton, Uruguay: a reconnaissance study

SÁNCHEZ BETTUCHI, LEDA; RAPALINI, AUGUSTO E.; MILANESE, FLORENCIA N.; FRANCESCHINIS, PABLO R; MARTÍNEZ DOPICO, CARMEN I.

Brazilian Journal of Geology

Brazilian Geological Society

Año: 2020

2317-4889

Small to medium-sized intrusive bodies with ages between 2.1 and 2.0 Ga characterize Piedra Alta terrane and represent the final stabilizationof Río de la Plata Craton. A reconnaissance study of petro- and magnetic fabrics based on microscopic observations, anisotropy of magneticsusceptibility and anhysteretic remanent magnetization, was carried out on 41 sites from 14 intrusive bodies, in order to obtain preliminaryinformation on kinematics of their emplacement, degree of deformation, and regional stress regime during this magmatic event. The magneticfabrics coupled with the microstructural analysis are interpreted as generally reflecting magma kinematics near solidus temperature,although few cases of tectonically modified fabrics at local levels have been interpreted. Field evidence and magnetic fabrics in most plutonsshow subvertical to high angle E-W to NE-SW trending foliations and subvertical lineations. These data suggest that plutons were probablyintruded under a regional extensional to transtensional regime, which controlled the magma ascent and distribution of the intrusions. Lack ofmetamorphism and low to null deformation shown by the study plutons suggest a late-orogenic character for this magmatism, which has beenassociated with crustal stabilization after accretionary processes that led to the formation of Río de la Plata Craton in the Orosirian.