山东新生代火山岩K-Ar年龄和Pb-Sr同位素特征

K-Ar AGES AND Pb, Sr ISOTOPIC CHARACTERISTICS OF CENOZOIC VOLCANIC ROCKS IN SHANDONG, CHINA

我国山东境内分布有一定数量的新生代火山岩，主要在临朐、沂水、蓬莱及栖霞一带(图1)。对这些火山岩曾在不同程度上做过地质、岩石及岩石化学工作。王慧芬等进行了临朐山旺组玄武岩K-Ar年龄测定工作。

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.