张士贞, 李奋其, 刘函, 李俊, 苟正彬, 秦雅东. 2021: 中拉萨地块亚热地区早白垩世辉长岩: 班公湖-怒江洋南向俯冲板片断离的岩浆作用响应. 地质通报, 40(11): 1852-1864.
    引用本文: 张士贞, 李奋其, 刘函, 李俊, 苟正彬, 秦雅东. 2021: 中拉萨地块亚热地区早白垩世辉长岩: 班公湖-怒江洋南向俯冲板片断离的岩浆作用响应. 地质通报, 40(11): 1852-1864.
    ZHANG Shizhen, LI Fenqi, LIU Han, LI Jun, GOU Zhengbin, QIN Yadong. 2021: The Early Cretaceous gabbro in Yare area, middle Lhasa Block: Magmatism response to the slab break-off of the southward subduction Bangong-Nujiang Ocean lithosphere. Geological Bulletin of China, 40(11): 1852-1864.
    Citation: ZHANG Shizhen, LI Fenqi, LIU Han, LI Jun, GOU Zhengbin, QIN Yadong. 2021: The Early Cretaceous gabbro in Yare area, middle Lhasa Block: Magmatism response to the slab break-off of the southward subduction Bangong-Nujiang Ocean lithosphere. Geological Bulletin of China, 40(11): 1852-1864.

    中拉萨地块亚热地区早白垩世辉长岩: 班公湖-怒江洋南向俯冲板片断离的岩浆作用响应

    The Early Cretaceous gabbro in Yare area, middle Lhasa Block: Magmatism response to the slab break-off of the southward subduction Bangong-Nujiang Ocean lithosphere

    • 摘要: 为深入认识拉萨地块中北部地区早白垩世构造-岩浆过程,对中拉萨地块西段亚热地区早白垩世辉长岩进行了研究。辉长岩的锆石U-Pb年龄为115.5±0.5 Ma。岩石属于拉斑玄武岩系列,具有与洋岛玄武岩(OIB)相似的稀土元素特征,Mg#值(46.07~48.05)、Cr(6.97×10-6~18.5×10-6)和Ni(6.87×10-6~11.2×10-6)元素含量较低,Rb、Ba、K、Sr等大离子亲石元素富集,Th、U和Pb元素呈现明显的正异常,Nb、Ta、Zr、Hf、P、Ti等高场强元素表现为负异常,显示具有部分弧火山岩性质;具有正的锆石εHft)值(+4.3~+7.9)和较年轻的Hf亏损地幔模式年龄(TDM1=489~614 Ma)。综合分析认为,亚热地区早白垩世辉长岩形成于南向俯冲的班公湖-怒江特提斯洋岩石圈板片断离的构造背景,可能是受近期俯冲板片熔体或超临界流体交代的软流圈地幔部分熔融的产物,并经历了不同程度的分离结晶作用。

       

      Abstract: In order to understand the Early Cretaceous tectonic-magmatic process in the central and north Lhasa Block, the Early Cretaceous gabbro in the Yare area of western part of middle Lhasa Block were studied.The zircon U-Pb age of gabbro is 115.5±0.5 Ma.The rocks belong to tholeiite series, and their characteristics of rare earth elements are similar to those of oceanic island basalt (OIB).Mg# value (46.07~48.05) and contents of Cr (6.97×10-6~18.5×10-6), Ni (6.87×10-6~11.2×10-6) are relatively low.The large ion lithophile elements such as Rb, Ba, K, Sr of gabbro samples are relatively enriched, Th、U and Pb show positive anomalies, and the high field strength elements such as Nb, Ta, Zr, Hf, P and Ti show negative anomalies, indicating that the gabbro samples have some "arc volcanic rock" properties.The gabbro show positive zircon εHf (t) values (+4.3~+7.9) and younger Hf-depleted mantle model ages (TDM1) of 489~614 Ma.By comprehensive analysis, it is proposed that the Early Cretaceous gabbro in the Yare area is most likely triggered by the slab break-off of the southward subducting Bangong-Nujiang Tethyan Ocean lithosphere, and can be considered as the product of partial melting of the asthenosphere mantle which was metasomatized by recent melts or supercritical fluids from the subduction slab, and subsequently experienced varying degrees of fractional crystallization.

       

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