藏北双湖地区海西期和印支期火山岩地球化学特征及其构造意义  

Geochemical characteristics and tectonic implications of Hercynian and Indosinian volcanics in Shuanghu area,northern Tibet

作　　者：李延平[1] 林振宏[1] 张宗雁[1] 伊三泉[2] 王岫岩[2] 姜耀俭[2] 

机构地区：[1]中国海洋大学海洋地球科学学院,山东青岛266003 [2]大庆石油学院秦皇岛分院,河北秦皇岛066004

出　　处：《世界地质》2005年第3期230-235,281,共7页World Geology

摘　　要：藏北双湖地区海西期和印支期火山岩均以夹层形式产于海相沉积岩层中。海西期火山岩高度富集轻稀土元素和明显富集Rb、Ba、K等大离子亲石元素与Nb、Ta、Ti、P等高场强元素,无Nb、Ta、Ti亏损等特点,表明其具有大陆裂谷碱性玄武岩和洋岛碱性玄武岩的特征;以其不相容元素比值,相当于Gough岛EMⅠOIB型洋岛玄武岩,其构造环境判别图进一步印证了海西期火山岩形成于洋岛碱性玄武岩环境。印支期火山岩贫轻稀土元素和Rb、Ba、K等大离子亲石元素,相对贫Nb、Ta、Ti、P等高场强元素;但Nb、Ta并不亏损以及稀土配分曲线较平缓等特点,表明其具有大陆裂谷拉斑玄武岩特征;其微量元素、稀土元素的丰度及曲线特征可以与确定环境的红海88GTV岩样、东非大裂谷B10C岩样的丰度及曲线特征相类比,且构造环境判别图也共同印证了印支期火山岩形成于类似红海—东非裂谷型的大陆裂谷,初始洋盆的环境。Hercynian and lndosinian volcanics occurred, as in intercalations, in marine sedimentary beds in Shuanghu district of northern Tibet. The Hercynian volcanics are highly enriched in LREE and LILE （e. g. Rb, Ba, K） as well as HFSE （e. g. Nb, Ta, Ti, P） and have no Nb, Ta, Ti negative abnormality. Its contents are similar to those of EM I OIB from the Gough islands, and show ocean island alkaline basalt characteristics including the discriminant diagrams of tectonic settings for volcanics, which implies that the Hercynian volcanics were formed in tectonic environment of ocean island. The lndosinian volcanics are poor in LREE and LILE （e. g. Rb, Ba, K） as well as HFSE （e. g. Nb, Ta, Ti, P）, and have low slight inclined REE patterns, with no Nb, Ta negative abnormality, which shows intraplate tholeitic basalt characteristics compare with 88GTV from Shaban Deep, northern Red Sea and B10C from Kivu,East African Rift,and shows similar characteristics in LREE and LILE and HFSE. All of these including the discriminant diagrams of tectonic settings for, volcanics imply that Indosinian volcanics were formed in tectonic environment of continental or protoceanic rift which is analogous to Red Sea as well as East African Rift.

关 键 词：火山岩 地球化学 洋岛碱性玄武岩 大陆裂谷 藏北 

分 类 号：P594[天文地球—地球化学]