海南岛二叠纪—三叠纪构造演化:源自岩浆岩和变质岩同位素年代学和地球化学的约束
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本文为国家自然科学基金项目(编号42072239,41822205,42102274)和中国地质科学院地质力学研究所基本科研业务费项目 (编号DZLXJK202005)联合资助的成果。


Permian- Triassic tectonic evolution of Hainan Island: Constraints from geochronology and geochemistry of magmatic and metamorphic rocks
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    摘要:

    本文对海南岛广泛出露的中- 酸性花岗质岩体和中—高级变质岩开展了系统的岩石学、年代学、地球化学及Lu- Hf同位素研究,识别出270~259 Ma和242 Ma两期岩浆事件和251~248 Ma变?湿采钊凼录?70~259 Ma岩浆岩包括花岗(石英)闪长岩和含石榴子石花岗岩。花岗(石英)闪长岩为准铝质I型花岗岩,锆石εHf(t)值变化较大,Mg#和CaO/Na2O比值较高,Rb/Sr比值较低,起源于玄武质下地壳,并存在少量幔源岩浆的混入;含石榴子石花岗岩为典型的强过铝质S型花岗岩,锆石εHf(t)值为负,CaO/Na2O比值较高,源岩主要为壳源贫黏土的碎屑岩。它们均富集LREEs(轻稀土元素)和LILEs(大离子亲石元素),明显亏损HFSEs(高场强元素),显示出与洋壳俯冲相关的岛弧岩浆岩的地球化学特征,形成于大陆弧背景下。251~248 Ma变质- 深熔事件与区域上广泛分布的壳源S型花岗岩和韧性剪切变形同期,推测为一期弧- 陆碰撞造山事件。242 Ma花岗岩为A2型花岗岩,具正的锆石εHf(t)值,其源岩为新生的玄武质下地壳物质,标志造山已进入伸展垮塌阶段。海南岛在二叠纪末期到三叠纪初期完成了由洋壳俯冲向弧- 陆碰撞造山的转换,该时期构造演化主要受古特提斯构造域控制。

    Abstract:

    This paper presents a combined petrologic, geochemical and geochronological study and Lu- Hf isotopic analysis of granitic plutons and metamorphic rocks in Hainan Island. Two- stage (270~259 Ma and 242 Ma) magmatic events and a 251~248 Ma tectonothermal event are identified. The 270~259 Ma magmatic rocks include quartz diorites, granodiorites and garnet- bearing granites. Quartz diorites and granodiorites are metaluminous I- type granitoids with variable zircon εHf(t) values, high Mg# and CaO/Na2O ratios, and low Rb/Sr ratios. They are interpreted to form by partial melting of basaltic lower crust with minor involvement of mantle- derived melts. The garnet- bearing granites are strongly peraluminous S- type granites. They display negative zircon εHf(t) values and high CaO/Na2O ratios, indicating a crustal clay- poor, plagioclase- rich, psammitic source. All 270~259 Ma magmatic rocks are enriched in LREEs and LILEs, and depleted in HFSEs, sharing the common features of arc- related magmatic rocks. They are interpreted to be formed in the continental arc setting associated with the subduction of oceanic plate. The 251~248 Ma tectonothermal event, combined with coeval crust- derived S- type granites and ductile shearing deformation, is interpreted to be caused by arc- continent collision. The ~242 Ma granites are A2- type granites with positive zircon εHf(t) values. They were generated by partial melting of juvenile basaltic crustal material at high- temperature conditions in the post- orogenic setting. During late Permian to early Triassic, the Hainan Island experienced a tectonic transition from oceanic subduction to arc- continent collision, which was closely associated with the evolution of the Paleo- Tethys Ocean.

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吕方,辛宇佳,李建华,王金铭.2023.海南岛二叠纪—三叠纪构造演化:源自岩浆岩和变质岩同位素年代学和地球化学的约束[J].地质学报,97(1):30-51.
Lü Fang, Xin Yujia, Li Jianhua, Wang Jinming.2023. Permian- Triassic tectonic evolution of Hainan Island: Constraints from geochronology and geochemistry of magmatic and metamorphic rocks[J]. Acta Geologica Sinica,97(1):30-51.

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  • 收稿日期:2022-03-14
  • 最后修改日期:2022-05-01
  • 录用日期:2022-05-03
  • 在线发布日期: 2022-06-04