Paleogeography of Southwest Gondwana boundary during the Upper Paleozoic.

TOMEZZOLI R.N.,

Estados Unidos

Congreso; Eos Trans. AGU; 2005

Current results are summarized from the southwest Gondwana boundary, from rocks from La Pampa  province, Argentina. This area is the westward part of an orogenic belt, known as “Sam Frau geosincline” or Cordón de las “Gondwánides” and may represent the suture zone between the Gondwana and Patagonia terranes. This collision model is still uncertain and there are many controversies related to the age of the deformation of this belt. Paleomagnetism and the exploration of the magnetic fabric signatures (AMS) can be useful to evaluate the regional deformation and a better understanding of the assembly, deformation, and fragmentation of Gondwana / Pangea.               A systematic paleomagnetic study was done in the Cerro Centinela: 36ºS, 67ºW, belong to the Choiyoi Group and consist of Lower Paleozoic volcanic rocks. In this paleomagnetic study is present results from 19 sites (84 specimens), sampled from the base to the top in different layers. Samples were demagnetized with thermal procedures. A high un­blocking temperature component carried by hematite was defined between 580° and 680° C, showing very good within site consistency (a95<15° and k>20). Remanent magnetization ranges around 1500 mA m-1. In all samples it was possible to isolate one component with the same behavior and positive inclination. These stable remanent magnetization were group into two different Population: 1 and 2, clearly separated. Population 1 (from sites 1 to 12) in situ mean direction is: D=146°, I=63.5°, a95=4°, k=104, N=12. Population 2 (from sites 13 to 19) in situ mean direction is: D=164°, I=42°, a95=4°, k=197, N=7. Reversed characteristic remanence magnetization suggesting that the magnetization was acquired during the Kiaman interval, in accordance with their age. Two high quality paleomagnetic poles were computed for each population on the basis of the in situ remanence directions. The corresponding PP are for Population 1: 63°S,  353°E,  a95=7 and K=44 and for Population 2: 71º S, 60°E, a95=5, K=169. These two poles are consistent with the age of the rocks and with others PP from the Gondwánides, and are reflecting a huge displacement of the continents during the Permian, before the final assembly of the Pangea.