Tectonic controls on the late Miocene-Holocene volcanic eruptions of the Tengchong volcanic field along the southeastern margin of the Tibetan plateau

摘要

The Tengchong volcanic field, located along the southeastern margin of the Tibetan plateau, experienced multiple eruption stages since the late Miocene, including time intervals of ～5.5-4.0 Ma, 3.9-0.9 Ma, 0.8-0.01 Ma, and younger than 0.01 Ma. These eruption stages produced different volcanic rocks, principally basaltic and basaltic-andesite series. At the same time or prior to volcanic eruptions in the Tengchong volcanic field, NE-NNE-trending rift basins and NS-striking normal faults formed during the late Miocene-Pliocene. In addition, rapid exhumation of the neighboring mountains occurred at ～6-5 Ma constrained by apatite fission track dating and its ther-mochronological modeling. At present, the state of stress in the Tengchong volcanic field and its surroundings is NNE-NE-compression and WNW-NW-extension based on seismic foci mechanisms. Petrologic and geochemical data indicate that the source of the Tengchong volcanic rocks belongs to an intracontinental tectonic setting, but not a subduction or collision zone between Indian and Eurasian plates. Since the late Miocene, the dextral strike-slip motion of the Sagaing fault induced E-W-extension. The Sagaing dextral strike-slip motion might disturb the lower crust-upper mantle of the Tengchong block, resulting in the partial melting of the upper mantle which, in turn, induced volcanic eruptions characterized by mature island-arc features.