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在内蒙狼山西南段原定为中元古代沉积建造(渣尔泰山群)中,新发现呈层产出、具有变余聚斑状和斑状结构、斑晶主要由石英和钠长石组成、岩石化学成分富钠低钾的酸性火山岩,其顶、底板均为细晶方解石大理岩(或结晶灰岩).两件代表性样品的锆石呈短柱状-长柱状,内部环状结构发育,具有较高的Th/U比值,表明是岩浆成因.A8-0样品20粒锆石的206Pb/238U加权平均年龄为(816.9±4.5)Ma.A14-5样品也测定20粒锆石,15粒锆石的206Pb/238U加权平均年龄为(805±5.0)Ma,其余5粒锆石(3.1,6.1,7.1,20.1,21.1)依次为(867.0±10),(829.1±8.0),(849.7±9.8),(839.2±9.7),(830.7±9.3)Ma.这证实酸性火山岩属于新元古代产物,其年龄区间正好在Rodinia(罗迪尼亚)超大陆裂解的时限范围内.且酸性火山岩轻稀土富集,重稀土亏损,铕负异常明显,高场强元素(HFSE)富集,大离子亲石元素等相对亏损,稀土和微量元素组成与华南扬子块体西缘和浙江次坞地区裂谷环境的新元古代酸性火山岩总体相似(但华南酸性火山岩的高场强元素Th,Nb,Ta,Hf,Zr均明显相对亏损),具有形成于张性裂谷盆地的特征.这表明内蒙狼山西南段存在与新元古代Rodinia超大陆裂解作用相呼应的海相火山-沉积变质建造,内蒙狼山地区可能有与Rodinia超大陆裂解作用相呼应的构造-岩浆-热事件发生.这一发现,结合在西部阿拉善邻区发现的晋宁期花岗岩年龄(814~872Ma)和金川超基性岩体的年龄(827Ma)及华北地台邻区新元古代岩浆(火山)活动的最新研究成果,对进一步研究Rodinia超大陆的构造演化历史有重要意义.
In the southwestern part of Langshan, Inner Mongolia, originally designated as Mesoproterozoic sedimentary structures (Zar Taishan Group), the newly discovered layers were stratified out with polygrind and spotted structures. The phenocrysts were mainly composed of quartz and albite, The chemical composition of sodium and potassium low-acid acidic volcanic rocks, the top and bottom plates are fine-grained calcite marble (or crystalline limestone) .Two representative samples of zircon was short columnar - long columnar, the internal ring structure, with The higher Th / U ratio indicates a magmatic origin.The 206Pb / 238U weighted average age of 20 zircons in the A8-0 sample was (816.9 ± 4.5) Ma.A14-5 samples also measured 20 zircons and 15 zirconiums The 206Pb / 238U weighted average age of the stone is (805 ± 5.0) Ma, and the remaining five zircons (3.1,6.1,7.1,20.1,21.1) are (867.0 ± 10), (829.1 ± 8.0), (849.7 ± 9.8) ), (839.2 ± 9.7) and (830.7 ± 9.3) Ma, respectively, confirming that the acidic volcanic rocks belonged to the Neoproterozoic, with an age interval just within the time limit of the supercontinent resolution of Rodinia (Rodinia) Enrichment, depletion of heavy rare earths, significant negative anomalies of europium, enrichment of high-field-strength elements (HFSEs), large ion-lithophile elements and other relative losses. The compositions of rare earths and trace elements are similar to those of the Yangtze The Neoproterozoic acidic volcanic rocks in the western margin of the block and the rifting area in the second dock area of Zhejiang are generally similar (but the relatively high depletion of high field strength elements Th, Nb, Ta, Hf, and Zr in southern China acidic volcanic rocks) This implies that the volcanic-sedimentary metamorphic formation in the southwestern segment of Langshan, Nei Monggol, which corresponds to the Neoproterozoic Rodinia supercontinent cleavage, may have the structure- This discovery combined with the age of the Jinning Period granite (814-872 Ma) and the age of the Jinchuan ultramafic rock (827 Ma) discovered in the Alzheian neighboring area in the west and Neoproterozoic The latest research results on magmatic (volcanic) activity are of great significance for the further study of the tectonic evolution history of the Rodinia supercontinent.