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引用本文:孟元库 许志琴 陈希节 马绪宣 马士委. 冈底斯中段碱长花岗岩锆石U-Pb-Hf同位素特征及地质意义[J]. 中国地质, 2015, (5): 1202-1213.
MENG Yuan-ku, XU Zhi-qin, CHEN Xi-jie, MA Xu-xuan, MA Shi-wei. Isotope study of alkali-feldspar granite zircon in the middle Gangdise batholith and its geological significance[J]. Geology in China, 2015, (5): 1202-1213(in Chinese with English abstract).
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冈底斯中段碱长花岗岩锆石U-Pb-Hf同位素特征及地质意义
孟元库 许志琴 陈希节 马绪宣 马士委
中国地质科学院地质研究所 大陆构造与动力学国家重点实验室,北京 100037
摘要:
提要:本文对冈底斯岩浆带中段谢通门塔玛地区碱长花岗岩进行了原位LA-ICP-MS锆石U-Pb定年和LA-MC-ICP-MS 锆石Lu-Hf同位素分析。研究结果表明,采自该岩体不同部位的两件锆石U-Pb同位素加权平均年龄分别为(40.02±0.39)Ma和(40.65±0.32)Ma,具有几乎一致的地质年龄,即碱长花岗岩侵位结晶年龄为40 Ma左右。LA-MC-ICP-MS锆石Lu-Hf同位素研究显示,176Hf/177Hf比值在0.282633~0.282878,平均值为0.282765,计算所得的εHf(t)值介于-4.08~4.15,平均值为0.28,峰值在-1~+1之间;TDMC模式年龄在822~1373 Ma,平均值为1075 Ma,峰值年龄为1000~1200 Ma。其次,样品的εHf(t)值具有正负相间的特点,εHf(t)也相对较小,为典型的壳幔混染型,岩浆源区主要以古老地壳的熔融为主。综合研究表明,谢通门塔玛地区碱长花岗岩主要是由新特斯洋板片的断离,致使软流圈地幔上涌,引起拉萨地体地壳物质的熔融、再循环而形成的,在这个过程中有部分幔源物质的加入。
关键词:  锆石U-Pb测年  Lu-Hf同位素  碱长花岗岩  冈底斯岩浆带
DOI:
分类号:
基金项目:国家自然科学基金创新群体(40921001)、国土资源公益性基金项目(201211093)、中国地质调查局项目(12120115026801)以及大陆构造与动力学国家重点实验室资助基金(Z1301-a12)联合资助。
Isotope study of alkali-feldspar granite zircon in the middle Gangdise batholith and its geological significance
MENG Yuan-ku, XU Zhi-qin, CHEN Xi-jie, MA Xu-xuan, MA Shi-wei
State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
Abstract:
Abstract: In this paper, the authors conducted zircon LA-ICP-MS U-Pb dating and Lu-Hf analysis of the alkali-feldspar granite in Tama of Xietongmen region along the middle Gangdise magmatic belt. The results suggest that the weighted mean ages of two samples are (40.02±0.39)Ma and (40.65±0.32)Ma for the pluton, respectively. In essence, the two ages are of the same geological significance in that they both represent the crystallization age or emplacement age of the alkali-feldspar granite. Zircon Lu-Hf analytical data reveal that values of 176Hf/177Hf vary from 0.282633 to 0.282878 (averaging 0.282765), and the values of εHf(t) range from -4.08 to 4.15 (0.28 on average) , with the peak values of εHf(t)varying from -1 to 1. TDMC model ages are from 822 Ma to 1373 Ma (averaging 1075 Ma) with peak model ages being ca.1000-1200 Ma. The obvious feature is that the values of the εHf(t)show alternating positive and negative values, corresponding to a small value and indicating the crustal-mantle contamination process, which resulted from partial melting of the ancient crust. Combined with geological setting and study results, the authors consider that the alkali-feldspar granite might have generated from the slab break off of the Neo-Tethys oceanic crust, which led to upwelling of the asthenosphere and further induced the partial melting and recycling of the ancient crust. During the process, the mantle materials played a vital role in forming the alkali-feldspar granite in the study area.
Key words:  zircon U-Pb dating  Lu-Hf isotopes  alkali-feldspar granite  Gangdise magmatic belt