Shrimp zircon geochronology constrains on Permian pyroclastic levels, Claromecó Basin, South West margin of Gondwana, Argentina

ARZADÚN, GUADALUPE; TOMEZZOLI R.N.; TRINDADE, R.I.F.; GALLO, L.C.; CESARETTI, N.N.; CALVAGNO, J.M.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2018 vol. 85 p. 191 - 208

0895-9811

Pyroclastic levels are descripted in Sierras Australes outcrops and Claromeco Basin sub-surface records, interbeddedwith mudrocks and coal beds in the base of the Tunas Formation sequence that correspond to thePermian South West margin of Gondwana. The pyroclastic levels classify as fine tuff. SHRIMP zircon ages obtainedare 291.7 ± 2.9 Ma in the outcrop and 295.5 ± 8.0 Ma in the subsurface. These ages are consistent withother zircon SHRIMP ages of other outcrops tuff of the Tunas Formation, with Permian flora, and with tuff agesof correlated Gondwana areas, in the Paraná, Karoo and Paganzo basins. These data, in addition with othergeological evidences, support a tectonically active and changing environment during the Permian of Gondwana.The ages allowed calculating a northward latitudinal speed of 2.7 cm/year for Gondwana during the Permian.This latitudinal movement is explained as the consequence of the final coupling of several continental microplates,gradually amalgamated from the southern margins of Gondwana and from the northern of Laurentia toconfigure the final Pangea during the Triassic. Since the main accretions in the southwestern margin ofGondwana could have started during the Devonian - Carboniferous, this Permian orogeny (San Rafael OrogenicPhase in Argentina) would be representing the post - collisional deformation, with a peak of compression in theEarly Permian that was attenuating towards the foreland during the Late Permian - Early Triassic. With theseresults, it is also possible to constraint the age of the upper Paleozoic glaciation up to 295, previous to thedeposition of the Tunas Formation in the Sauce Grande Formation.