南祁连东段化隆岩群形成时代的进一步限定
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国土资源大调查项目(1212010610102)


The further age constraint of Hualong Rock Group in the eastern segment of South Qilian Mountains
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    摘要:

    作为南祁连造山带基底残块的化隆岩群,由于产出有与Cu-Ni(-PGE)矿紧密相关的基性-超基性岩而倍受关注。随着一些新元古代精细锆石同位素年代学数据的获得,化隆岩群形成于太古-古元古代的传统认识发生了动摇。通过高精度的LA-ICP-MS(激光剥蚀等离子体质谱)锆石微区原位U-Pb同位素测年,获得青海省湟源县南日月乡一带化隆岩群条带状二云斜长片麻岩(副变质岩)最新的蚀源区年龄为891±7 Ma,代表化隆岩群形成时代的下限;条带状黑云斜长角闪岩(原岩为中性火山岩)的形成年龄为884±9 Ma,将化隆岩群的形成时代进一步限定为新元古代。认为化隆岩群火山-沉积作用应为Rodinia超大陆裂解的地质记录,Rodinia超大陆裂解事件及其相关的成矿作用在祁连造山带及其邻区前寒武纪占据不可低估的重要地位。

    Abstract:

    The Hualong Rock Group of South Qilian orogenic basement remnants hasaroused much interest among geologists for the occurrence of basic-ultrabasic rocks closely related to Cu-Ni (-PGE) ore deposits. With the acquisition of some precise Neoproterozoic zircon isotopic age data, the traditional understanding that Hualong Rock Group was formed in Archean-Paleoproterozoic has been challenged. High resolution LA-ICP-MS zircon U-Pb in situ dating of banded two mica-plagiogneiss (para-metamorphic rocks) from Hualong Rock Group in Riyue village of southern Huangyuan County yielded an age of 891±7 Ma, which represents the lower age boundary of Hualong Rock Group. The age recently obtained from banded biotite-plagioclase amphibolite (whose protolith was intermediate volcanic rocks) is 884±9 Ma. Based on isotopic dating combined with the results obtained by previous researchers, the authors further restricted the age of Hualong rock Group to Early Neoproterozoic, i.e., Qingbaikou period. It is believed that the volcano-sedimentary rocks of Hualong Rock Group serve as geological records of the breakup of the Rodinia supercontinent. Recently, zircon U-Pb dating yielded an age of 724.4±3.7 Ma from gneissic plagioclase amphibolite (whose protolith was gabbro)near the Dadaoerji Cu-Ni ore deposit in the western part of the Qilian orogenic belt, whereas a U-Pb age of 724.4±3.7 Ma was yielded from zircon and baddeleyite in Jinchuan ultrabasic rock of Longshou Mountain area in northern Qilian orogenic belt; these data can also be regarded as geological records of the breakup of the Rodinia supercontinent. These results indicate that the importance of Rodinia supercontinent breakup event and its related mineralization in Precambrian period of the Qilian orogenic belt and its adjacent areas should not be underestimated.

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何世平,李荣社,王 超,等, 2011. 南祁连东段化隆岩群形成时代的进一步限定[J]. 岩石矿物学杂志, 30(1):34~44.
HE Shi_ping, LI Rong_she, WANG Chao, et al, 2011. The further age constraint of Hualong Rock Group in the eastern segment of South Qilian Mountains[J]. Acta Petrologica et Mineralogica, 30(1): 34~44.

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