GEOCHRONOLOGY OF CENOZOIC VOLCANISM IN EAST CHINA AND GLOBAL CHANGES OF TECTONIC ENVIRONMENT
Zhu Bingquan Wang Huifen Yang Xucchang(Institute of Geochemistry, Academia Sinica)
K-Ar dating of the Cenozoic volcanics from East China and their petrochemistry indi-cate that early Tertiary volcanism is represented mainly by the eruptions of tholeiitic and calc-alkaline magmas. A relatively dormant stage occurred during Oligocene. Since Mio-cene (-26 Ma) alternative eruptions of tholeiites and alkali basalts took place. Strong erup-tions of alkali basalts in different tectonic directions occurred in the time-space age ranges of 19-21, 14-15, 5-8 and 1 Ma. The above time-space correlations and petrographical features of the volcanics are closely associated with great changes in global tectonic environ-ment.