Successive deformation episodes along the Lungmu Co zone, west-central Tibet

Field study, thermochronology and geochemistry of the east Lungmu Co (LMC) range highlight some of the geological events that shaped western Tibet. The LMC fault zone has long been interpreted as the boundary between the Tianshuihai terrane of Laurasian affinity and the Qiangtang block of Gondwanian affinity. In the LMC range, the Paleozoic series is intruded by the Mangtsa leucogranite whose zircon have a U/Pb age of 116.9 ± 1 Ma and by mafic rocks with U/Pb zircon ages ranging from 116.9 ± 1 to 95.1 ± 1.7 Ma. Geochemistry of the mafic rocks indicates that they have been emplaced in a supra-subduction zone setting, probably the north dipping Nujiang suture zone. 40Ar/39Ar micas ages of the granite indicate that cooling below ~ 350 °C occurred between 105 and 85 Ma. 40Ar/39Ar K-feldspar data suggest a fast cooling event at 60–55 Ma, which we relate to the reactivation of the LMC suture zone as a thrust at the onset of the India–Eurasia collision. The last, and still active, deformation event corresponds to left-lateral strike-slip faulting along the ENE–WSW LMC fault.

Figure optionsDownload as PowerPoint slideHighlights
► Lungmu Co (west Tibet) mafic rocks and granite resulting from Cretaceous Jinsha subduction.
► Cooling in the early Upper Cretaceous and final exhumation in Paleocene.
► Paleocene NW Tibet uplift as a far field effect of India/Eurasia collision.