Paleogeography of Southwest Gondwana Boundary During the Upper Paleozoic

HR: 0830h
AN: GP41A-03 [Abstracts]
TI: Paleogeography of Southwest Gondwana Boundary During the Upper Paleozoic
AU: * Tomezzoli, R N
EM: renata@gl.fcen.uba.ar
AF: CONICET-Universidad de Buenos Aires, Departamento de Cs. Geol¢gicas. Facultad de Ciencias Exactas y Naturales. Pabell¢n 2, Ciudad Universitaria. , CABA, C1428EHA Argentina
AB: 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 Cord¢n 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: 36/deg S, 67/deg W, 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 unªblocking temperature component carried by hematite was defined between 580° C and 680° C, showing very good within site consistency (alpha 95<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°, alpha 95=4°, k=104, N=12. Population 2 (from sites 13 to 19) in situ mean direction is: D=164°, I=42°, alpha 95=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, Alpha 95=7 and K=44 and for Population 2: 71° S, 60° E, Alpha 95=5, K=169. These two poles are consistent with the age of the rocks and with others PP from the Gondw nides, and are reflecting a huge displacement of the continent during the Permian, before the final assembly of the Pangea.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
DE: 8110 Continental tectonics--general (0905)
DE: 8157 Plate motions--past (3040)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2005 Joint Assembly