Timing of granite emplacement and cooling in the Songpan-Garzê Fold Belt (eastern Tibetan Plateau) with tectonic implications.
F. Roger a-b, J. Malavieille a, Ph. H. Leloup b, S. Calassou c and Z. Xu d
a Laboratoire de Géophysique, Tectonique et Sédimentologie,
Université Montpellier II, 34095 Montpellier cedex 5, France.
b Laboratoire de Tectonique, UMR 7578, IPG-Paris, 4 place Jussieu,
75252 Paris cedex 5, France
now at laboratoire de dynamique de la lithosphère, UMR
5570, 2 rue R. Dubois, 69622 Villeurbanne, France.
c Total-Fina-Elf, Pau, France.
d Institute of Geology, Baiwangzhuang road, 100 037 Beijing, China.
Corresponding author: Françoise Roger (e-mail:francoise.roger@dstu.univ-montp2.fr;
Phone: (33) 4 67 14 33 96 ; Fax: (33) 4 67 52 39 08)
Abstract: New U-Pb and Rb-Sr geochronology on syn- and post-orogenic granites provide constraints on the timing of major tectonic events in the Songpan-Garzê fold belt, west Sichuan, China. The Ma Nai granite probably synkinematic with the main deformation yields an age of 197±6 Ma which is interpreted as an upper age limit of the Indosinian event. Zircons and apatites from the post-kinematic Rilonguan granite also yield Jurassic ages (195±6 Ma and 181±4 Ma). The post-orogenic Markam massif gives two ages of 187±1 Ma and 153±3 Ma. Both granites are undeformed and cut the structures in Triassic sedimentary rocks. These results demonstrate that the major deformation and décollement tectonics in the Songpan-Garzê fold belt occurred prior to the Early Jurassic. The wide range of ages obtained for post-kinematic granites (from the Early Jurassic to Late Jurassic) suggests that, locally, magmatic activity persisted for a long time (at least 50 Ma) after the Indosinian compressional tectonism. No Tertiary ages have been obtained, suggesting that these granites were not affected strongly by the India-Asia collision.
Keywords: Indosinian orogeny, geochronology, isotopic geochemistry,
granites, décollement, Songpan-Garzê.
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