Geochronology and geochemistry of Middle-Late Ordovician granites and gabbros in the Erguna region, NE China: Implications for the tectonic evolution of the Erguna Massif
Geochronology and geochemistry of Middle-Late Ordovician granites and gabbros in the Erguna region, NE China: Implications for the tectonic evolution of the Erguna Massif
复制标题
DOI：
10.1007/s12583-014-0476-9
复制
发表时间：
2014-10
影响因子：
3.3
通讯作者：
Shuo Zhao;Wenliang Xu;Wei Wang;Jie Tang;Yihan Zhang
中科院分区：
文献类型：
--
作者：
Shuo Zhao;Wenliang Xu;Wei Wang;Jie Tang;Yihan Zhang
本文介绍了额尔古纳地块中晚奥陶世辉长岩和花岗岩的锆石U-Pb年龄、Hf同位素数据和全岩主微量元素数据。讨论了这些岩石的成因和地块早古生代的构造演化。花岗岩和辉长岩中的锆石阴极发光（CL）图像显示锆石为岩浆成因。花岗岩中20个锆石点的206pb /238U年龄在446±9 ~ 464±10 Ma之间，加权平均年龄为455±10 Ma；辉长岩锆石上有16个斑点，年龄范围为465±10 ~ 466±7 Ma，加权平均年龄为465±2 Ma。在化学性质上，额尔古纳地块晚奥陶世花岗岩为弱过铝质花岗岩，与a型花岗岩相似。花岗岩和辉长岩均富集轻稀土元素和大离子亲石元素（如Rb、K），贫重稀土元素和高场强元素（如Nb、Ta、Ti）；它们都表现出明显的负Eu异常。它们的锆石Hf(t)值主要在+1.86 ~ +6.21（花岗岩）和+1.39 ~ +3.89（辉长岩）之间，只有一个点的值为- 0.27（辉长岩）。辉长岩的tdm1年龄在928 ~ 1 091 Ma之间，花岗岩的tdm2年龄在1 287 ~ 1 675 Ma之间。花岗岩的原始岩浆可能是由中元古代新增加的地壳物质的部分熔融产生的，而辉长岩的原始岩浆可能是由俯冲板块产生的流体交代的枯竭的地幔楔的部分熔融产生的。中晚奥陶世花岗岩与辉长岩构成了典型的双峰火成岩组合，暗示了一个可能与早古生代早期额尔古纳和兴安地块碰撞后发育有关的伸展环境。
Zircon U-Pb ages, Hf isotope data and whole-rock major and trace element data for the Middle to Late Ordovician gabbros and granites in the Erguna Massif, NE China were presented in this paper. The petrogenesis of these rocks and the Early Paleozoic tectonic evolution of the massif were discussed. Zircons from the granites and gabbros are of magmatic origin based on their cathodoluminescence (CL) images. The206Pb/238U ages obtained from 20 spots on zircons from the granites range from 446±9 to 464±10 Ma, yielding a weighted mean age of 455±10 Ma; and 16 spots on zircons from the gabbros range from 465±10 to 466±7 Ma, yielding a weighted mean age of 465±2 Ma. Chemically, the Late Ordovician granites in the Erguna Massif are weakly peraluminous and similar to A-type granites. The granites and gabbros are all enriched in light rare earth elements and large ion lithophile elements (e.g., Rb, K), and depleted in heavy rare earth elements and high field strength elements (e.g., Nb, Ta, and Ti); they all exhibit marked negative Eu anomalies. Their zirconɛHf(t) values range mainly from +1.86 to +6.21 (for the granites) and +1.39 to +3.89 (for the gabbros), except for one spot with a value of −0.27 (for a gabbro). TheTDM1ages for the gabbros andTDM2ages for the granites vary from 928 to 1 091 Ma and from 1 287 to 1 675 Ma, respectively. It is concluded that the primary magma of the granites could have been derived by partial melting of Mesoproterozoic newly accreted crustal material, whereas the primary magma of the gabbros originated by partial melting of a depleted mantle wedge that had been metasomatized by fluids derived from a subducted slab. These Middle-Late Ordovician granites and gabbros constitute a typical bimodal igneous rock association, implying an extensional environment that was probably related to the post-collisional development of the Erguna and Xing’an massifs in the early Early Paleozoic.