樊炳良, 张鑫利, 于涛, 白涛, 冯德新. 藏东吉塘复式花岗岩成因——来自锆石U-Pb年龄和地球化学的证据[J]. 地质通报, 2019, 38(8): 1274-1286.
    引用本文: 樊炳良, 张鑫利, 于涛, 白涛, 冯德新. 藏东吉塘复式花岗岩成因——来自锆石U-Pb年龄和地球化学的证据[J]. 地质通报, 2019, 38(8): 1274-1286.
    FAN Bingliang, ZHANG Xinli, YU Tao, BAI Tao, FENG Dexin. The genesis of Jitang duplex granites in east Tibet: Evidence from the zircon UPb age and rock geochemistry[J]. Geological Bulletin of China, 2019, 38(8): 1274-1286.
    Citation: FAN Bingliang, ZHANG Xinli, YU Tao, BAI Tao, FENG Dexin. The genesis of Jitang duplex granites in east Tibet: Evidence from the zircon UPb age and rock geochemistry[J]. Geological Bulletin of China, 2019, 38(8): 1274-1286.

    藏东吉塘复式花岗岩成因——来自锆石U-Pb年龄和地球化学的证据

    The genesis of Jitang duplex granites in east Tibet: Evidence from the zircon UPb age and rock geochemistry

    • 摘要: 吉塘复式花岗岩位于澜沧江岩浆岩带北段,是研究澜沧江结合带演化过程的重要窗口。对澜沧江北段卡贡地区吉塘复式花岗岩中的黑云母二长花岗岩和花岗闪长岩开展了LA-ICP-MS锆石U-Pb年代学、岩石地球化学研究。研究结果表明,所选锆石样品均具有明显的生长环带,Th/U值普遍大于0.4,为典型的岩浆锆石,分别获得锆石206Pb/238U年龄加权平均值为222.8±1.5Ma(MSWD=1.60,n=16)、213.6±1.1Ma(MSWD=0.98,n=20)和221.1±1.5Ma(MSWD=1.30,n=15),时代均属于晚三叠世。岩石地球化学特征表明,吉塘黑云母二长花岗岩和花岗闪长岩具有较一致的主量、微量元素含量,其变化特征也具有一致性,反映这2类岩石可能为同一期岩浆演化而来;吉塘复式花岗岩属于过铝质S型花岗岩,与临沧花岗岩、纽多花岗岩具有一致的岩石地球化学性质,为澜沧江花岗岩带的重要组成部分,具有统一的构造岩浆活动模式;吉塘复式花岗岩的成因与碰撞造山导致地壳加厚增温及与岩石圈剪切、伸展期有关的深熔作用有关,澜沧江洋的闭合时间可能为273Ma左右。

       

      Abstract: Jitang duplex granites are located in the northern section of the Lancang River magma belt, and serve as an important window for studying the evolution process of Lancang River juncture zone. In this paper, the LA-ICP-MS zircon U-Pb chronology and rock geochemistry of biotite monzonitic granite and granitic diorite in Jitang duplex granites of Kakagong area along northern Lancang River were studied. The results show that the selected zircon samples exhibit obvious growth ring zone, the Th/U ratio is generally higher than 0.4, and the typical magma zircon has average weighted 206Pb/238U age of 222.8±1.5Ma (MSWD=1.60, n=16), 213.6±1.1Ma (MSWD=0.98, n=20) and 221.1±1.5Ma (MSWD=1.30, n=15), suggesting Late Triassic. The geochemical characteristics of rocks show that the Jitang biotite monzonitic granite and granitic diorite have relatively consistent content of main and trace elements, and their changing characteristics are also consistent. It is shown that these two kinds of rocks might have been derived from the same magma, and the Jitang duplex granites belong to the aluminum S-type granite, which has the same petrogeochemical properties as Lincang granite and Newcastle granite, and has a unified tectonic magmatic activity mode along the Lancang River granite belt. The formation of Jitang duplex granites was related to the thickening and warming of the crust and the deep melting effect related to the shearing and stretching period of lithosphere, with the closure time of Lancang Jiang Ocean was probably at about 273Ma.

       

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