LATE MESOZOIC VOLCANISM IN THE GREAT XING'AN RANGE (NE CHINA): TIMING AND IMPLICATIONS FOR THE DYNAMIC SETTING OF NE ASIA

Abstract

Mesozoic volcanism is widespread throughout northeastern China, but precise geochronological constraints were previously lacking. Twenty samples, including basalt and basaltic andesites, from the Great Xing'an Range were collected and subjected to 40Ar/39Ar dating. The ages mainly concentrate in four periods: ∼ 163–∼ 160 Ma, ∼ 147–∼ 140 Ma, ∼ 125–∼ 120 Ma and ∼ 116–∼113 Ma, show that the volcanic succession pulsed from ∼ 160 Ma in the Late Jurassic until the Early Cretaceous. This result, combined with the previous compilation of data from the adjacent areas, suggest a volcanic migration from west to east in the northeastern Asia. These volcanic rocks were formed in an extensional setting, as indicated by the occurrence of A-type granites, mafic dyke swarms, metamorphosed core complexes and basins. The timing (∼ 160–140 Ma) of mantal underplating and transition from crustal contraction to extension in this region suggests that all these geological activities occurred immediately followed the closure of Mongol–Okhotsk ocean, which supposed to be closed by ∼ 160 Ma. Based on these observations, a shears-shaped lithospheric delamination mechanism is proposed to construe the geodynamic scenario of northeastern Asia during Late Mesozoic: the collision between north China and Siberia around ∼ 160 Ma obstructed the westwards movement of the lithosphere induced by the subduction of Pacific plate, this tremendous stress caused the thickened lithospheric delaminating from west edge of the northeast China–Mongolia block at ∼ 160 Ma and extended gradually eastwards. This led to mantle upwelling and underplating, resulting volcanism migration from west to east in northeastern Asia during Late Mesozoic.