大兴安岭南段林西地区中生代酸性岩类岩浆的混染作用  

Magma contamination of acidic rocks in Linxi area in southern Da Hinggan Mountains, northeast China.

作　　者：张永北[1] 孙世华[1] 本间弘次[1] 毛骞[1] 

机构地区：[1]中国科学院地质与地球物理研究所

出　　处：《岩石学报》2003年第3期369-384,共16页Acta Petrologica Sinica

基　　金：中国科学院资源与生态环境重大项目(项目号:KZ951-B1-404)资助

摘　　要：大兴安岭南段林西地区广泛出露以海相玄武安山岩、安山岩为主的晚古生代火山-沉积岩。中生代火山-侵入杂岩也广泛分布其中。花岗岩体的边部普遍二长花岗岩化和花岗闪长岩化(甚至出现闪长岩),并含有丰富的以玄武质-安山质为主的岩石包体。侵入体-围岩接触带附近为围岩被岩浆侵蚀的港湾状交代反应过渡带。英安岩-粗面英安岩也含有相同的岩石包体,并且与流纹岩密切共生。岩石包体周缘的寄主岩常见淬冷边,聚集针状磷灰石,表明它被捕获时已是冷却的岩石,而非热的玄武岩浆团;它们的Nb/Ta、Zr/Hf比值、弱交代者的化学成分与晚古生代火山-沉积岩一致,Rb-Sr同位素比值散布在 晚古生代火山-沉积岩等时线附近,其含量、未交代程度、尖棱状程度、刚性程度在侵入体中从内部到边部增多(强),且较新鲜者结构构造与围岩相同,表明它们来自晚古生代火山-沉积岩组成的围岩;其含量与岩体边部的位置及二长花岗岩、花岗闪长岩、(粗面)英安岩的成分变化有关,表明包体成分已加入到这些岩石当中。这些岩石的环带状斜长石有两种内核:一种较富钙;另一种较贫钙。两种内核的斜长石外环成分趋同,强交代岩石包体成分和富含岩石包体的酸性岩成分趋同。两者皆记录了两种来源的物质成分同化的过程。同一岩体边部(或火山岩中)The late Paleozoic (Rb-Sr, 275Ma, (Sr-87/Sr-86)(i) = 0. 70463) volcanic and pyroclastic sedimentary rocks that are dominated by submarine basalt and andesite are widely outcreped in Linxi area in the southern part of Dahinggan mountains. In the same area, the Mesozoic intrusive rocks and volcanic rocks also widely distributed there. In the margin of granite pluton, the rocks commonly transfer into adamellite and granodiotite gradually, and include plentiful enclaves dominated by mafic and intermediate rocks. The contact zone with wall rocks is a transitional metasomatic reaction zone, the boundary like a gulf shape is actually formed by magma eroding the wall rocks on the contact zone. Dacite, rachydacite with the acidity. lower than rhyolite also includes plentiful mafic-intermediate enclaves and closely co-exist with rhyolite. The chilled margins with plentiful acicular apatites are frequently observed in the contact zone surrounding those enclaves in the rocks. Most of the enclaves have various metasomatic reaction boundaries, and low grade metasomatic enclaves are similar to wall rocks in the features of texture and structure, minerals. The HFSE ratios (Nb/Ta, Zr/Hf) of the enclaves are close to the ones of late-Paleozoic volcanic rocks, and Sr isotope ratios data are scattered along the isochron of late-Paleozoic volcanic rocks. The content of the enclaves is related to position in the margin of a granite pluton and related to composition variation of adamellite, granodiorite and dacite, trachydacite. These evidences suggest that the enclaves, are the xenoliths actually from late-Paleozoic volcanic rocks, which were cool before they were captured by hot magma, and the acid rocks with low acidity had been added in the materials of late-Paleozoic volcanic rocks. There are two kinds of the kernel of zoning plagioclase in adamellite, granodiorite and dacite, trachydacite: one was rich in Ca and the other was low in Ca. But the compositions of outer zone of the zoning plagioclase only change into the same. The co

关 键 词：大兴安岭南段 岩浆成因 混染作用 同化作用 岩石包体 

分 类 号：P588.121[天文地球—岩石学] P594.1[天文地球—地质学]