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叶亚康, 周家云, 周雄. 川西塔公松林口岩体LA-ICP-MS锆石U-Pb年龄与地球化学特征[J]. 岩矿测试, 2020, 39(6): 921-933. DOI: 10.15898/j.cnki.11-2131/td.202005060008
引用本文: 叶亚康, 周家云, 周雄. 川西塔公松林口岩体LA-ICP-MS锆石U-Pb年龄与地球化学特征[J]. 岩矿测试, 2020, 39(6): 921-933. DOI: 10.15898/j.cnki.11-2131/td.202005060008
YE Ya-kang, ZHOU Jia-yun, ZHOU Xiong. Zircon LA-ICP-MS U-Pb Age and Geochemical Features of the Songlinkou Pluton, Western Sichuan[J]. Rock and Mineral Analysis, 2020, 39(6): 921-933. DOI: 10.15898/j.cnki.11-2131/td.202005060008
Citation: YE Ya-kang, ZHOU Jia-yun, ZHOU Xiong. Zircon LA-ICP-MS U-Pb Age and Geochemical Features of the Songlinkou Pluton, Western Sichuan[J]. Rock and Mineral Analysis, 2020, 39(6): 921-933. DOI: 10.15898/j.cnki.11-2131/td.202005060008

川西塔公松林口岩体LA-ICP-MS锆石U-Pb年龄与地球化学特征

Zircon LA-ICP-MS U-Pb Age and Geochemical Features of the Songlinkou Pluton, Western Sichuan

  • 摘要: 松林口岩体出露于松潘—甘孜造山带东缘,紧邻甲基卡超大型稀有金属伟晶岩型锂矿床,为确定松林口岩体侵位时代与物质来源,探讨该岩体与甲基卡成矿岩体的地球化学和含矿性差异,本文对采集的11件岩体样品,采用X射线荧光光谱法、电感耦合等离子体质谱法(ICP-MS)、激光剥蚀电感耦合等离子体质谱法(LA-ICP-MS)和多接收电感耦合等离子体质谱法(MC-ICP-MS),对岩石的主量和微量元素组成、锆石U-Pb年龄和锆石Lu-Hf同位素进行分析。结果表明:松林口岩体中富含闪长质暗色包体,SiO2含量介于56.56%~68.99%之间,全碱含量3.78%~6.82%,K2O/Na2O=1.02~1.93,里特曼指数σ=1.01~1.93,Mg#值总体为46.73~61.27,岩石属于高钾钙碱性Ⅰ型花岗岩系列,具有轻稀土富集的特点,LREE/HREE=2.67~8.31,LaN/YbN值为2.11~9.74,所有岩石样品均具有明显的负Eu异常;总体上松林口岩体及其包体富集LILE元素,Ta、Nb、P、Ti等HFSE元素相对亏损。松林口边部花岗闪长岩、中部二长花岗岩的锆石U-Pb年龄分别为212.6±1.0Ma(MSWD=0.55)、222.4±1.1Ma(MSWD=0.39),岩浆侵位时代为晚三叠世;二长花岗岩锆石Lu-Hf同位素结果εHft)介于-9.09~-6.86,二阶段模式年龄(TDMC)在1524.874~1666.002Ma之间,岩体物质来源是中元古代扬子克拉通基底物质部分熔融,并混有部分富集上地幔物质。甲基卡S型花岗岩为上地壳部分熔融形成的,与松林口岩体属不同的物质来源,且岩浆演化程度和成矿构造条件不同,这可能是松林口岩体不具有锂稀有金属成矿的主要原因。

     

    Abstract:
    BACKGROUNDThe Songlinkou pluton is located in the eastern margin of the Songpan-Ganzi orogenic belt, which is adjacent to the pegmatite-type lithium deposit of Jiajika.
    OBJECTIVESTo explore the similarities and differences between Songlinkou pluton and Jiajika mineralized intrusive rocks, and to study geological conditions of mineralization and magma sources of the pluton.
    METHODSMajor and trace elements were determined by X-ray fluorescence spectrometry (XRF) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. Zircon U-Pb age and Hf isotopes were analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and multiple collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), respectively.
    RESULTSThe Songlinkou pluton contained diorite enclaves, and has SiO2 contents of 56.56%-68.99%, total alkali of 3.78%-6.82%, K2O/Na2O of 1.02-1.93, and Rittmann indices of 1.01-1.93. The rock has relative high Mg# values (Mg#=46.73-61.27). The rock belongs to the high-potassium calcium-alkaline type I granite series showed light rare earth enrichment with LREE/HREE ratios of 2.67-8.31, LaN/YbN of 2.11-9.74. All samples have strongly negative Eu anomaly. It was rich in LILE, and depleted in Ta, Nb, P and Ti. The zircon U-Pb results of the granodiorite and monzogranite were 212.6±1.0Ma (MSWD=0.55) and 222.4±1.1Ma (MSWD=0.39), respectively. The εHf(t) of zircon in monzogranite ranged from -9.09 to -6.86, and TDMC ranged from 1524.874Ma to 1666.002Ma.
    CONCLUSIONSThe Songliankou pluton is produced by the partial melting of the middle Proterozoic Yangtze craton basement mixed with the enriched upper mantle. The Jiajika S-type granite is formed by partial melting of the upper crust, and is different from Songliankou pluton in terms of magma sources, evolution and mineralization tectonic conditions; this may be the main reason why the Songlinkou pluton does not have lithium rare metal mineralization.

     

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