HR: 13:55h
AN: GP13B-02    [Abstracts]
TI: Paleozoic and Mesozoic Orogenies Shaped Tertiary Tibet
AU: * Arnaud, N O
EM: Nicolas.Arnaud@dstu.univ-montp2.fr
AF: CNRS UMR5573 "Dynamique de la Lithosphere" ISTEEM - Univ. Montpellier 2, CC 066 Place Eugene Bataillon, Montpellier, 34000 France, Metropolitan
AU: ROGER, F
EM: Francoise.Roger@dstu.univ-montp2.fr
AF: CNRS UMR5573 "Dynamique de la Lithosphere" ISTEEM - Univ. Montpellier 2, CC 066 Place Eugene Bataillon, Montpellier, 34000 France, Metropolitan
AU: Gilder, S
EM: gilder@ipgp.jussieu.fr
AF: CNRS UMR 7577 "Laboratoire de Pal‚omagnetisme" IPGP, 5 Place Jussieu, Paris, 75252 France, Metropolitan
AU: JOLIVET, M
EM: marc.jolivet@dstu.univ-montp2.fr
AF: CNRS UMR5573 "Dynamique de la Lithosphere" ISTEEM - Univ. Montpellier 2, CC 066 Place Eugene Bataillon, Montpellier, 34000 France, Metropolitan
AB: The India-Asia collision zone is a key area on Earth to better understand deformation acting over continent length-scales. However, despite notable examples, it has been largely overlooked that the northeastern tip of the Plateau has undergone a long geologic history, at least from the beginning of the Phanerozoic times, where no less than 2 or 3 orogenic cycles have left their imprint on the present geological make-up of the region. Because of severe reworking by the present-day orogeny, the past geological framework is somewhat difficult to decipher solely by field data. Precise dating of magmatism and metamorphism is therefore an invaluable piece of information to reconstruct the geodynamic evolution of the Asian continental puzzle. We will present a collection of new U/Pb, Rb/Sr, 40Ar/39Ar and fission track dates along with a summary of available geochronological data from north and central Tibet. "Paleozoic" Tibet is widely distributed over the present day plateau, probably because it was largely dismembered by Tertiary deformation. Closure of a large oceanic basin separating Kunlun from northernmost terranes (including what is now Tian Shan, Alta‹ and mongolian terranes) led to probably south vergent oceanic subduction between 500 Ma and 450 Ma, followed by the construction of an Andean type active margin on the southern side of the ocean. A continental collision likely occurred in the North Tibet region around 400-380 Ma. "Mesozoic" northern Tibet is marked by the presence of two coeval suture zones that were active during the Early Triassic to Early Jurassic: the first strikes along the Kunlun suture, which separates the Bayan Har-Songpan Ganze (Songpan) terrane from the Tarim and Qaidam blocks and was active at ca 210-205 Ma (217ñ10 and 207ñ3 Ma). When magma production ceased, most of the northern Tibetan crust underwent rapid exhumation. The second follows the Jinsha suture, which separates the Songpan terranes from the Qiangtang blocks and was active at ca 205 Ma (206ñ7 Ma and 204ñ1 Ma). These data collected along the boundaries of the Kunlun-Songpan and Songpan-Qiangtang blocks improve the picture of the Early-Middle Mesozoic paleogeographic evolution of Tibet. The Kunlun and Qinling block boundaries, which were separated in the Permian, subsequently formed a continuous, Late Triassic, northward subducting plate margin. Similarly, our data confirm that the Jinsha suture correlates with the Benzilan and Nan-Uttaradit sutures, which together formed a single, south and west dipping, Late Triassic subduction zone. It is noteworthy that north of the Kunlun, in the Qilian and Altun Shan, no late Paleozoic nor Triassic thermal overprint is observed. In the Kunlun and further to the south in Tibet the younger so-called "Indosinian" (ca 230 Ma) event is widespread, but the imprint of a lower Paleozoic event still exists as exhibited in the Maqin area and also in the Kunlun range. Earlier reports underlined the possible existence of a Cretaceous local metamorphic and deformation event along some of the strike slip faults of northern Tibet. It is clear that this event should be very restricted to narrow zones and had no thermal effect at the crustal scale.
DE: 3652 Pressure-temperature-time paths
DE: 8038 Regional crustal structure
DE: 8102 Continental contractional orogenic belts and inversion tectonics
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005