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机构地区:[1]吉林大学地球科学学院,长春130061 [2]四川省冶金地质勘查局成都地质调查所,成都610203
出 处:《岩石学报》2016年第9期2780-2792,共13页Acta Petrologica Sinica
基 金:国家自然科学基金项目(41272223);中国地质调查局项目(1212011120709;1212011220459;1212011085252)联合资助
摘 要:内蒙古苏尼特右旗温都尔庙地区发现一套以片理化安山岩和蚀变流纹岩为主的火山岩,其中测得安山岩的锆石SHRIMP年龄为333±4Ma。岩石可分为玄武岩-安山岩类和英安岩-流纹岩类,其中玄武岩-安山岩类火山岩Si O2含量47.40%-62.75%,Mg#值介于17.2-25.6,属于拉斑系列;稀土总量较低,总体趋势近水平,轻重稀土分馏不明显,Eu异常不明显(δEu=1.22-1.46);岩石经历了强片理化和蚀变作用,大离子亲石元素(LILEs)容易发生活动运移,变化较大,但总体呈富集状态,Ta、Nb和Ti明显亏损,类似岛弧火山岩,其原始岩浆应起源于受俯冲板片脱水熔融交代的地幔楔。英安岩-流纹岩类火山岩Si O2含量63.50%-79.80%,相对富集大离子亲石元素,亏损高场强元素(如Nb、Ta、Ti)及Sr、P元素,类似活动大陆边缘火山岩,其原始岩浆应源于地壳物质的部分熔融。综上所述,笔者认为早石炭世期间,华北板块北缘处于古亚洲洋的俯冲作用下,古亚洲洋的闭合时间应晚于早石炭世。A set of foliated andesite and altered rhyolite were found in Ondor Sum area of Sonid Right Banner, Inner Mongolia, zircons from andesite yielded 206pb/238U age of 333 + 4Ma. The volcanic rocks can be divided into basalt-andesite and dacite-rhyolite. The basalt-andesite volcanic rocks have SiO2 =47.40% - 62.75% , Mg# = 17. 2 -25.6, belonging chemically to the tholeiitic series; ∑REE is low, general trend display flat REE pattern, REE fractionation is not clear, and not obvious in Eu anomalies (δEu = 1.22 - 1.46). The rocks have experienced strong schistosity and alteration, LILEs prone to active migration, change is larger, but the overall state of enrichment, and depletion in Ta, Nb and Ti, similar chemically to a island arc volcanic rock. We consider that its primary magma could be derived from partial melting of a depleted lithospheric mantle. The dacite-rhyolite volcanic rocks have SiO2 = 63.50% - 79. 80% , relative enrichment in LILEs and depletion in HFSEs( such as Nb, Ta and Ti) and Sr, P, similar chemically to those from an active continental margin setting, the original magma should be partial melting of the crust material. Above all, we believe that during the Early Carboniferous, the subduction of the Paleo-Asian oceanic plate happened in the northern margin of the North China Plate, and the closing time of the Paleo-Asian Ocean should be later than the Early Carboniferous.
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