Polarity and Timing of the Deformation along the Jinsha Suture Zone
(Yushu area, Northeastern Tibet)
Abstract
The Tibetan Plateau was formed by intense Cenozoic shortening (up to
1100 km) of a composite “proto-Tibet”, itself the product of a long
Paleozoic and Mesozoic history of accretion of Gondwana-derived
continental fragments and volcanic arcs against the Asian continental
margin. The difficult access and the scarcity of outcrops have long
limited the possibilities of studying these Mesozoic suture zones in the
heart of the Plateau. In this work, we present new U-Pb and 40Ar/39Ar
ages from the highly deformed units of the Yushu mélange, along the
Jinsha Suture in the northeastern Qiangtang terrane. Early Triassic (c.
253 Ma) to Middle Jurassic ages (c. 165 Ma) complement the existing
dataset and help to refine the chronology of the Paleo-Tethyan oceanic
subductions which have structured the northeastern part of the Qiangtang
terrane. The Yushu mélange records at least three successive
tectono-magmatic events. The opening of a back-arc basin during the
northward Paleo-Tethyan subduction along the Longmu Co-Shuanghu Suture
during Early to Middle Triassic; then its closure during the southward
subduction of the Songpan-Ganze Ocean along the Jinsha Suture in Late
Triassic. Finally, a shortening phase related to the continental
collision of the Songpan-Ganze and Qiangtang blocks from Late Triassic
to Early-Middle Jurassic. No evidence for any high- or mid-temperature
Cenozoic reactivation of the Jinsha suture in our study area is
recorded.