Paleogeographic evolution of the South West Gondwana margin based on the Apparent Polar Wander Path during the Permian–Triassic boundary.

TOMEZZOLI R.N.,; KLEIMAN, L.E.; TICKYJ, H.; WOROSZYLO, M.E.; SALVARREDI, J.

Foz de Iguazu, Brazil

Congreso; The Meeting of the Americas; 2010

American Geophysical Union

&amp;lt;!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} p.MsoBodyTextIndent, li.MsoBodyTextIndent, div.MsoBodyTextIndent {margin:0cm; margin-bottom:.0001pt; text-align:justify; text-indent:36.0pt; line-height:150%; mso-pagination:widow-orphan; text-autospace:none; font-size:12.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; color:black; mso-ansi-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --&amp;gt; Current paleomagnetic results are summarized from the southwest Gondwana boundary, in the western part of an orogenic belt known as the “Samfrau Geosyncline” or Cordón de las “Gondwánides”, exposed along central Argentina. This area may represent the suture zone between Gondwana and the Patagonia terrane. This collision model is still uncertain and there are many controversies related to the evolution of this orogenic belt. Paleomagnetism and the exploration of the magnetic fabric signatures (AMS) are useful to evaluate the regional deformation and provide a better understanding of the assembly, deformation, and fragmentation of Gondwana / Pangea. Systematic paleomagnetic studies have been performed for many years on Late Paleozoic rocks along this belt. Those studies include: a) the Sierras Australes (38°S, 62°W; 55 sites on sedimentary rocks), b) the Carapacha basin (38°S, 65°5W; 24 sites on sedimentary and volcanic rocks), c) Sierra Chica (37ºS, 65ºW; 11 sites on volcanic rocks), d) the Bloque the San Rafael (34ºS, 68ºW; 27 sites on volcanic rocks and d) Cerro El Centinela (36ºS, 67ºW;  44 sites on volcanic rocks belonging to the Choiyoi Group). Standard high temperature demagnetization techniques were selected as the demagnetization procedure. A high un­blocking temperature component carried generally by hematite and seldom by magnetite was defined between 500°C and 680°C, showing very good within-site consistency (alfa 95<15° and k>20). All rocks are carriers of reversed characteristic remanent magnetization, suggesting that the magnetization was acquired during the Kiaman reverse superchron. High quality paleomagnetic poles were computed in each locality on the basis of the best grouping mean directions and allow a more precise tracking of the apparent polar wander path for South America during the late Paleozoic. All poles are consistent with the age of the rocks and with coeval paleomagnetic poles from others regions. With these poles it is possible to constrain the age of the deformation along this belt to the early Permian and related to the San Rafaelic orogenic phase. The presence of younger magnetizations that postdates any deformation implies a migration of the orogenic front, with a gradual attenuation of the deformation. The paleogeographic implication of these results are interpreted as a significant counter-clockwise movement of Gondwana between the Early and Late Permian. In accordance with these results, the deformation (probable collision between Patagonia and the South American craton) began during the Devonian in the west and propagated eastward until the Permian and this movement could be the consequence of a late adjustment between the continental blocks before the final assembly of Pangea.