Geochronological Study On The Vocanic Rocks In The Great Xing'an Range, NE China

In this thesis, detailed geochronological data are reported for theLate Mesozoic volcanic rocks in the Great Xing'an Range, NE China.And a primary geochronological frame is founded based on these data.Results of high precise zircon U-Pb dating and whole rock 40Ar/39Ardating indicate that the volcanism in the Great Xing'an Range started inMiddle-Late Jurassic (~160Ma), whereas, the volcanic rocks weremainly erupted in the Early Cretaceous, with an age range between148±2Ma and 111±1Ma. And two episodes can be recognized based onthese age data. In the relative probability density diagram, peak of theseages appears at about 130Ma-120Ma, consistent with the Mesozoicintrusive rocks in the same area. The volcanic rocks both in the northand south Great Xing'an Range have the same geochronological frames.During the peak period of the volcanism, voluminous mafic and felsicvolcanic rocks were erupted contemporaneously. Mesozoic volcanicrocks in the Great Xing'an Range have the same geochronological frameand rock assemblages with the rocks in the large igneous belt in theeastern China, and they formed in a uniform extensional environment.The geochronological frame, feature of the rock assemblage and thespatial distribution of Mesozoic igneous rocks in the eastern Chinaindicate that the large scale lithospheric thinning also happened in thenortheastern China. Delamination and the subsequent upwelling of theasthenosphere, which were caused by the subduction of the Pacific plate,were the main causing of the lithospheric thinning in the eastern Chinaduring the period. As the result of the thinning, the voluminous igneousrocks formed in the eastern China.