青海南山“金水口岩群”的时代与构造属性研究
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国家自然科学基金项目(面上项目,重点项目,重大项目)


Formation Age and Tectonic Attribute of Jinshuikou Group Complex in the Nanshan Area, Qinghai
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    摘要:

    在青海南山出露一套变质程度达角闪岩相的变沉积岩组合,被认为可与东昆仑造山带中的金水口岩群相对应,其形成时代和构造属性仍存争议。本文对该套组合中的矽线石云母石英片岩和花岗伟晶岩侵入体进行了LA-ICP-MS锆石U-Pb测年和Lu-Hf同位素分析,结果表明矽线石云母石英片岩碎屑锆石U-Pb年龄峰值为779Ma,明显年轻于东昆仑造山带金水口岩群物源区最小年龄峰值(>1.9Ga);对应的εHf(t)值主要为负值(-23.7~-11.8),TDM2年龄为2436-3172Ma,来自于再循环的古元古代-太古代地壳物质,少量碎屑锆石年龄为1744-2819Ma。这些特征与南祁连构造带党河南山和化隆地区元古宙变沉积岩相一致,完全不同于东昆仑造山带中的金水口群。~779Ma碎屑锆石与中祁连和南祁连构造带中新元古代岩浆岩时代相一致。花岗伟晶岩形成于439±2Ma,相对应的ɛHf(t)和TDM2分别为-14.2~-7.7和1909-2316Ma,可能为形成于俯冲相关环境下古元古代地壳物质再循环形成的S型花岗岩;775Ma继承性锆石与矽线石云母石英片岩碎屑锆石年龄峰值一致,表明矽线石云母石英片岩可能为花岗伟晶岩的形成提供了部分物质来源。这些事实表明,青海南山所谓“金水口岩群”的形成时应为779-439Ma之间,其沉积物源区应为~779Ma岩浆岩,在空间上与南祁连构造带党河南山地区以及拉脊山南侧化隆地区的同时期变沉积岩具有相似的沉积物源区和构造属性。

    Abstract:

    A suit of amphibolites facies meta-sedimentary rocks outcrops at Qinghai Nanshan area. It has been previously considered to be comparable with Jinshuikou Group in the East Kunlun orogenic belt, but its formation age and tectonic attributes are still quarreled. We present new results from zircon U-Pb and Lu-Hf isotopic data on sillimanite-mica-quartz schist and granitic pegmatite pluton. Detrital zircon grains from sillimanite-mica-quartz schist yield a U-Pb main peak at~779Ma with εHf(t) values of -23.7~-11.8 and TDM2 ages of 2436-3172Ma, which is extraordinarily younger than Jinshuikou Group with detrital zircon ages older than 1.9Ga. Several Paleoproterozoic-Archean (1744-2819Ma) detrital zircon grains are also gotten. These detrital zircon ages are concordant with Proterozoic meta-sedimentary rocks in Danghe Nanshan and Hualong areas of the South Qilian belt. The ~779Ma detrital zircons ages are identical with the Neoproterozoic magmatism in Central Qilian and South Qilian belts. The S-type Granitic pegmatite was formed at 439±2Ma in the subduction-related setting. Magmatic zircons have ɛHf(t) values of -14.2~-7.7, evolved from recycled Paleoproterozoic crustal. Inherited zircon with 775Ma is identical with the peak age of detrital zircons from sillimanite-mica-quartz schist, indicating that the latter contributes to the granitic pegmatite magma. Thus, the zircon U-Pb analysis results constrain meta-sedimentary rocks from Qinghai Nanshan area is formed between 779Ma to 439Ma, dominated by sediments from ~779Ma magmatic source. They possess similar sediment sources and tectonic attributes with contemporary meta-sedimentary rocks in Danghe Nanshan and Hualong areas of the South Qilian belt.

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郭现轻,闫臻,付长垒,王宗起.2016.青海南山“金水口岩群”的时代与构造属性研究[J].地质学报,90(3):589-606.
Guo Xianqing, Yan Zhen, Fu Changlei, Wang Zongqi.2016. Formation Age and Tectonic Attribute of Jinshuikou Group Complex in the Nanshan Area, Qinghai[J]. Acta Geologica Sinica,90(3):589-606.

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  • 收稿日期:2015-08-17
  • 最后修改日期:2015-09-29
  • 录用日期:2016-03-14
  • 在线发布日期: 2016-03-14