文章摘要
内蒙古翁牛特旗地区早二叠世火山岩地球化学特征及其构造意义
Geochemical characteristics and tectonic implications of the early Permian volcanic rocks from Ongniud Banner, Inner Mongolia
  
DOI:
中文关键词: 翁牛特旗  火山岩  早二叠世  额里图组  地球化学  构造背景
英文关键词: Ongniud Banner  volcanic rocks  early Permian  Elitu formation  geochemistry  tectonic seting
基金项目:内蒙古自治区区域地质调查专项(NMKD2008-16)
作者单位
曹代勇1,赵发3,刘登1,2,刘新华2,杨荣丰2 1.中国矿业大学(北京)地球科学与测绘工程学院北京 1000832.湖南科技大学土木工程学院湖南 湘潭 4112013.云南永昌铅锌股份有限公司云南 保山 650217 
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中文摘要:
      研究区早二叠世火山-沉积岩系主要由火山角砾岩、凝灰质砂岩、凝灰岩、硅质岩、流纹岩、安山岩、珍珠岩等组成.其沉积建造和岩性组合表明:早二叠世,研究区位于岛弧和俯冲带之间的弧前盆地环境.二叠系下统额里图组火山岩的SiO2=50.23%~73.56%,Mg#=6.21~49.54,Na2O+K2O=5.27%~10.73%,Na2O/K2O=0.36~4.17,其中安山岩Mg#=49.54~62.61,归属为高钾钙碱性-钾玄岩系列.微量元素(La/Yb)N介于5.52~9.89之间,δEu=0.09~0.90,具有中等-强烈负铕异常,相对富集大离子亲石元素包括Rb,K,La,Th等,而等高场强元素P,Ta,Nb、Ti则表现亏损,指示岩浆形成于与俯冲带有关的岛弧或活动大陆边缘的构造环境.R1-R2因子投影判别图解亦表明其形成于同碰撞阶段,反映古亚洲洋板块向华北陆块俯持续冲过程持续的地球动力学环境.综上所述,可认为早二叠世期间,该地区仍处于古亚洲洋海域,而不是陆内裂陷槽.
英文摘要:
      The Early Permian volcano sedimentary sequences of Ongniud Banner consist mainly of andesite, rhyolite, perlite, volcanic breccia, tuff, tuffaceous sandstone, siliceous rock. Rock assemblage and sedimentary formations indicate that are of fore arc basin sedimentary feature between subduction zone and island arc in Early Permian. The volcanic rocks from Elitu Formation have SiO2=50.23%~73.56%, Mg#=6.21~49.54, Na2O+K2O=5.27%~10.73%, Na2O/K2O=0.36~4.17, belonging to high K cal alkaline (HK CA) ~ shoshonite (SHO) series. The volcanic rocks are characterized with(La/Yb)N=5.52~9.89, mid intensive negative Eu abnormality, LILE enrichment such as Rb, K, La, Th and HFSE depletion such as P, Ti, Ta, Nb, and indicating that magma was formed in the tectonic setting of the island arc and active continental margin related to the plate subduction. R1 R2 diagram also indicates that volcanic rocks are generated at syn collision or post orogenic period, perhaps representing the mid later subduction stage of the Palaeo Asian Ocean Plate and North China Plate. Taken together, it suggests that the region located still in the Palaeo Asian Ocean, rather than the intracontinental taphrogenic trough in Early Permian.
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