Paleomagnetism of Middle-Late Jurassic Bahía Laura Group (Patagonia, southern Argentina)

RUIZ GONZÁLEZ, VÍCTOR; BOLTSHAUSER, BÁRBARA; RENDA, EMILIANO M.; VIZÁN, HAROLDO; PUIGDOMENECH, CARLA G.; ZAFFARANA, CLAUDIA B.

Hamburgo

Congreso; Latin-American Colloquium of Geosciences; 2019

Universidad de Hamburgo

Inthe present work, the results of the paleomagnetic analysis of theChon Aike and La Matilde formations, which make up the Bahía LauraGroup, are shown. These units are assigned a Middle-Late Jurassic age(Pankhurst et al., 2000, Feraud et al., 1999). Because both units aremainly composed of tuffs, ignimbrites, and rhyolitic lavas, it isvery difficult to establish a stratigraphy of both, and in someplaces, they seem to be interdigitated and in others, it seems thatone underlies the other. Unlike the ignimbrites of the Chon Aikeformation, the tuffs and ignimbrites of the La Matilde Formation showa certain degree of inclination in the studied outcrops. This isconfirmed by its magnetic fabric by studying the Anisotropy ofMagnetic Susceptibility (AMS). However, the paleomagnetic directionscoincide with each other without applying any tilt correction,despite the different magnetic fabric or inclinations of the rock .For this reason, it is interpreted that the ignimbrites of the LaMatilde Formation were adapted to the terrain and to the morphologyprior to depositing, because, if a tilt correction is applied, thepaleomagnetic directions are dispersed instead of grouped. Theresults of the paleomagnetic study show that the paleomagnetic poleof the La Matilde Formation and the paleomagnetic pole of the ChonAike Formation are equivalents. Both paleomagnetic poles pass areversal test, in to validate their statistical parameters.Therefore, both formations were formed in a similar time interval(150-160 Ma) and did not undergo vertical rotations of tectonicblocks. This shows that the Deseado Massif already made Patagonia asit is today, since at least the Middle Jurassic that it wasconstituted as a whole by then.p { margin-bottom: 0.25cm; line-height: 115%; }