扬子北缘七里峡地区晓峰基性岩墙岩石成因及其大地构造背景分析
首发时间:2017-05-12
摘要:扬子地块北缘七里峡地区的晓峰基性岩墙主要岩性为辉绿岩、辉绿玢岩,根据走向玫瑰花图统计,其走向多为NNE向,围岩为晓峰岩体。对研究区内基性岩墙代表性样品进行元素地球化学分析,具有如下特征:主量元素中SiO2%的含量在47.47%~52.68%之间,K2O含量较低,含量在0.95%~2.21%之间,(Na2O+K2O)含量在3.57%~6.58%之间。在w(Na2O+K2O)-w(SiO2) TAS 图解中基性岩墙绝大多数位于碱性系列岩区,少数在亚碱性系列区,大多数集中玄武岩、粗面玄武岩及玄武质安山岩区域。多数岩石的镁值(Mg#)低(31~52),指示它们为岩浆高度演化后产物。稀土元素判别图上,除4个基性岩墙样品外大部分具有较弱的Eu负异常。微量元素蛛网图上,绝大多数样品高场强元素Zr、Hf、Nb、Ta和Ti的亏损。然而样品KL11-15稀土元素和微量元素特征均与EMORB类似。在微量元素构造环境判别图上,大多数样品落入板内玄武岩区,可能为大陆裂谷岩浆上升过程中受到陆壳的混染,样品KL11-15落入MORB区域。结合以上特征,表明其可能与地幔柱活动有关。根据前人所测晓峰基性岩脉形成时代为806±4Ma左右,推测晓峰岩墙可能与Rodinia超大陆的裂解有关。
关键词: 地球化学 基性岩墙 晓峰岩套 扬子地块 Rodinia超大陆
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The Petrogenesis and Tectonic Implications of Xiaofeng Mafic Dykes in Qilixia Area, North Yangtze Block
Abstract:The Xiaofeng mafic dykes in Qilixia area are mainly diabase and diabase-prophyrite, with mainly NNE-trending and wall rock is Xiaofeng pluton. Geochemical characteristics of the dykes show that SiO2 contents range from 47.47% to 52.68%, K2O contents are low, varying from 0.95% to 2.21%, w(Na2O+ K2O) value ranges from 3.57%~6.58%. In the TAS figure, most samples are alkaline series, and belong to basalt, S1 and S2 areas. Most samples show low Mg# value (31~52), indicating they are products of highly evolved magma. In REE gram, the anomaly of Eu is not obvious, with four samples slightly positive anomaly and others slightly negative anomaly. In the spider gram of trace elements, Nb, Ta, Zr, Hf and Ti are relatively depleted, although sample KL11-15 are similar to the features of EMORB. In the trace element environment figures, most samples belong to WPB area, probably being CAB magma contaminated by crust materials, and sample KL11-5 belongs to MORB area. These features indicate that they are alkaline basalt formed in WPB, which would have been derived from lower crust of old continent or the mantle plume beneath. Based on the previous geochronological researches, it is concluded that the mafic dykes intruded at Neoproterozoic (806 Ma) and possibly be related to the breakup of the Rodinia supercontinent.
Keywords: geochemistry mafic dyke Xiaofeng Pluton Suite Yangtze Block Rodinia supercontinent
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扬子北缘七里峡地区晓峰基性岩墙岩石成因及其大地构造背景分析
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