K-Ar AGES AND Pb, Sr ISOTOPIC CHARACTERISTICS OF CENOZOIC VOLCANIC ROCKS IN SHANDONG, CHINA
Chen Daogong Pen Zicheng (Department of Earth and Space Science, University of Science and Technology of China)
28 samples of Cenozoic volcanic rocks collected from Shandong have been dated by K-Ar method. They are mainly Neogene with an age range of 4-19 m.y. The basalts from Linqu and Yishui in west Shandong are Miocene and those from Penglai and Qixia in east Shandong are Miocene and Pliocene in age. The basalts from "Wudi in north Shandong are Middle-Early Pleistocene in age. In each area the duration of volcanic eruption was estimated at about 2-3 m.y.Pb and Sr isotopic compositions and U, Th, Pb, Kb. Sr, and major elements in most of the sample's were determined. The isotopic compositions are: 206Pb/204Pb-16.92-18.48,207Pb/204Pb-15.30-15.59, 208Pb/204Pb-37.83-38.54, and (87Sr/8SSr)i-0.70327 -0.70632. There are some positive or negative linear correlations between 206Pb/204Pb and 207Pb/204Pb, Pb isotopes and Pb contents, Pb isotopes and Sr isotopes and Sr isoto-pes and other elements. The basaltic rocks from east and west Shandong have some what differences in isotopic composition and element content. The basalts probably are products of multi-stage evolution of the mantle. They have preserved the primary features of the source although they were influenced to some extent by the contamina-tion of crustal materials.