ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    班公湖-怒江成矿带西段白板地北部晚侏罗世花岗闪长岩锆石U-Pb年龄、微量元素组成及地质意义

    Geochronology and Trace Element Compositions of Zircon in Granodiorite in the north of the Baibandi area, Western Bangong-Nujiang Metallogenic Belt and Their Geological Significance

    • 摘要: 白板地北部花岗闪长岩体位于班公湖-怒江缝合带北侧改则县境内。野外地质调查表明花岗闪长岩呈岩脉状侵入二叠系龙格组碳酸盐中,并在接触带上发育矽卡岩化蚀变和铜矿化,成矿潜力良好。但目前研究程度较低,尚未开展高精度年代学研究工作。笔者通过对白板地北部花岗闪长岩开展LA-ICP-MS锆石U-Pb年代学和微量元素研究,以精细厘定成岩年龄,揭示成矿温度并分析成矿潜力。结果表明,白板地北部花岗闪长岩锆石均为岩浆成因锆石,17个测点获得的锆石206Pb/208U谐和年龄为(154.8±1.2)Ma(MSWD=1.7),岩体侵位于晚侏罗世。锆石ƩREE值为6.1×10−6~24.04×10−6,平均值11.68×10−6,ƩLREEs和ƩHREE分别为0.41×10−6~9.44×10−6和4.93×10−6~23.55×10−6,具有亏损轻稀土,富集重稀土的特征;δEu值为0.26~0.64,δCe值为0.91~5.03,呈现显著的负Eu异常和正Ce异常特征。锆石Ti元素含量为0.89×10−6~1.43 ×10−6,估算的结晶温度为600.3~799.3℃,平均值为697.6℃,一定程度上反映了花岗闪长岩的成岩温度范围。综合成岩年龄和区域构造演化特征,推测白板地北部花岗闪长岩形成于班公湖-怒江洋壳北向俯冲的构造背景,为深入认识区域构造演化提供了新证据。

       

      Abstract: The granodiorite in the north of Baibandi is located in Gaize County, north of the Bangong Nujiang suture zone. The field geological survey shows that granodiorite intruded into the Permian Longge Formation carbonate. Skarn alteration and copper mineralization developed along the contact zone, showing good metallogenic potential. However, due to the absence of high-precision chronology research, the genesis of the granodiorite remains poorly understanding. In this paper, the LA-ICP-MS zircon U-Pb geochronology and trace element studies were carried out on for zircon from the granodiorite in the north of Baibandi area in order to determining the age and analyzing the metallogenic potential. The results show that zircons from the granodiorite in the north of Baibandi area are all magmatic zircons. 17 zircons show weighted average 206Pb/208U ages of(154.8 ± 1.2)Ma (MSWD=1.7), showing that the granodiorite was formed in the Late Jurassic. The ƩREE values zircon of are 6.1×10−6-24.04 ×10−6 (averaging 11.68 ×10−6). The ƩLREEs and ƩHREEs values are 0.41×10−6~9.44×10−6 and 4.93×10−6~23.55×10−6, respectively, showing the enrichment of heavy rare earths. The δEu and δCe values of zircons range from 0.26 to 0.64 and 0.91 to 5.03 respectively, showing significant negative Eu anomalies and positive Ce anomalies. The Ti contents of zircon range from 0.89~1.43 ppm, with estimated crystallization temperature of 600.3 to 799.3 ℃ (averaging 697.6 ℃). Based on these results and the characteristics of regional tectonic evolution, it is inferred that the granodiorite in the north of Baibandi was formed during northward subduction of Bangong-Nujiang oceanic crust. Our results provide new evidence for understanding the formation of the Bangong-Nujiang metallogenic belt.

       

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