Geochronological, geochemical, and Nd-Hf isotopic studies of the Qinling Complex, central China: Implications for the evolutionary history of the North Qinling Orogenic Belt
Geochronological, geochemical, and Nd-Hf isotopic studies of the Qinling Complex, central China: Implications for the evolutionary history of the North Qinling Orogenic Belt
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DOI：
10.1016/j.gsf.2014.04.001
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发表时间：
2014-07
影响因子：
8.9
通讯作者：
Chunrong Diwu;Yong-gang Sun;Yan Zhao;Bingxiang Liu;Shaocong Lai
中科院分区：
文献类型：
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作者：
Chunrong Diwu;Yong-gang Sun;Yan Zhao;Bingxiang Liu;Shaocong Lai
秦岭杂岩是北秦岭造山带最古老的岩石单元，也是北秦岭造山带的内核。因此，秦岭杂岩是了解华北造山带前古生代演化的关键。该杂岩体由变质杂岩和大理岩组成，经历了区域角闪岩相变质作用。本文将秦岭杂岩的形成时代限定在中元古代晚期和新元古代早期之间（约1062-962 Ma），而不是以前认为的古元古代。LA-ICP-MS数据显示了两个主要的变质年龄（约。499、我420-400 Ma）。前者与秦岭杂岩中高压-超高压岩石的峰期变质年龄一致，表明高压-超高压岩石及其围岩在奥陶纪均经历了强烈的区域变质作用。后者的年龄可能会限制在晚志留世和早泥盆世之间的NQOB部分熔融的时间。秦岭杂岩主要伴随着沿着活动大陆边缘的俯冲-增生过程，并应含有弧前盆地沉积的碎屑，现有资料表明，至少在新元古代之前，秦岭杂岩是一个独立的微大陆，在1.2-0.8 Ga期间包括格伦维尔造山带的一部分。华北造山带经历了一个独特的地质历史，与华北造山带和扬子造山带在前寒武纪的地质历史明显不同。侵入秦岭杂岩的新元古代花岗岩类可解释为Rodinia超大陆拼合的产物。NQOB是从Rodinia分离出来的。830-740 Ma。随后，NQOB向NCC的北方边缘移动，并在晚寒武世至早奥陶世与NCC发生了初始的增生或碰撞。
The Qinling Complex of central China is thought to be the oldest rock unit and the inner core of the North Qinling Orogenic Belt (NQOB). Therefore, the Qinling Complex is the key to understanding the pre-Paleozoic evolution of the NQOB. The complex, which consists of metagraywackes and marbles, underwent regional amphibolite-facies metamorphism. In this study, we constrained the formation age of the Qinling Complex to the period between the late Mesoproterozoic and the early Neoproterozoic (ca. 1062–962 Ma), rather than the Paleoproterozoic as previously thought. The LA-ICP-MS data show two major metamorphic ages (ca. 499 and ca. 420–400 Ma) for the Qinling Complex. The former age is consistent with the peak metamorphic age of the high- and ultra-high pressure (HP-UHP) rocks in the Qinling Complex, indicating that both the HP-UHP rocks and their country rocks experienced intensive regional metamorphism during the Ordovician. The latter age may constrain the time of partial melting in the NQOB between the late Silurian and early Devonian. The Qinling Complex is mostly affiliated with subduction–accretion processes along an active continental margin, and should contain detritus deposited in a forearc basin.The available data indicate that the NQOB was an independent micro-continent at least prior to the Neoproterozoic, and included a portion of the Grenville orogenic belt during the period of 1.2–0.8 Ga. The NQOB has experienced a unique geological history, which is obviously different from that of the North China Craton (NCC) and the Yangtze Craton during the Precambrian. The Neoproterozoic granitoids that intruded the Qinling Complex can be interpreted as the products of assembly of the supercontinent Rodinia. The NQOB was separated from Rodinia at ca. 830–740 Ma. Subsequently, the NQOB moved closer to the northern margin of the NCC, and the initial accretion or collision with the NCC occurred from the late Cambrian to the early Ordovician.