| 柴北缘从大洋俯冲到陆陆碰撞:来自开屏沟造山带M型橄榄岩的证据 |
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| 引用本文： | 蔡鹏捷,许荣科,郑有业,陈鑫,刘嘉,俞军真.柴北缘从大洋俯冲到陆陆碰撞:来自开屏沟造山带M型橄榄岩的证据[J].地球科学,2018,43(8):2875-2892. |
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| 作者姓名： | 蔡鹏捷 许荣科 郑有业 陈鑫 刘嘉 俞军真 |
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| 作者单位： | 1.中国地质大学地质调查研究院, 湖北武汉 430074 |
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| 基金项目： | 教育部长江学者和创新团队发展计划IRT14R54中国地质调查局项目12120113032800 |
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| 摘 要： | 造山带幔源（M型）橄榄岩虽然在高压/超高压变质带分布不多，但由于其来自俯冲板块上覆的岩石圈地幔，因此是研究俯冲隧道内俯冲板片与地幔楔之间相互作用的重要对象，对于还原超高压变质带的演化有重要意义.柴北缘鱼卡榴辉岩-片麻岩区边部附近的开屏沟存在一套橄榄岩，其岩石类型、成因、时代等都缺乏研究.对开屏沟橄榄岩全岩的主量和微量元素及铂族元素、橄榄石主量元素、锆石U-Pb年龄和Hf同位素进行了研究.结果显示，其全岩具有高的Mg#、Mg/Si和Ni值，同时表现出亏损难溶的HFSE和HREE，轻微富集LILE和LREE中与流体活动性相关的元素；橄榄石具有较高的Fo值（90.11~92.77）与NiO含量（0.32%~0.45%）、低的CaO含量（< 0.02%）；PGEs的球粒陨石标准化配分模式与交代橄榄岩和残留橄榄岩近似；两组变质锆石年龄为459.5±3.6 Ma和417.5±2.7 Ma，对应的εHf（t）值为-0.71~9.45和-11.96~-1.20，分别反映了洋壳流体（或早期大陆俯冲板片流体）和陆壳流体交代的性质和时限.开屏沟橄榄岩来源于俯冲带上覆地幔楔，遭受了不同来源流体不同程度的交代作用而获得地壳特征，同时为柴北缘大洋俯冲到陆陆碰撞的构造演化提供了新证据.
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| 关 键 词： | 柴北缘 开屏沟 造山带 M型橄榄岩 锆石U-Pb-Hf同位素 地球化学 地质年代学 |
| 收稿时间： | 2018-04-27 |
From Oceanic Subduction to Continental Collision in North Qaidam: Evidence from Kaipinggou Orogenic M-Type Peridotite |
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| Abstract: | Orogenic peridotites(M-type) are uncommon in high-pressure(HP) and ultrahigh-pressure(UHP) metamorphic belts. However, they are not only a key to study the metamorphic and metasomatic information from subducting slabs and mantle wedges in subduction channel, but also of great significance to the evolution of orogenic belt. There is a set of peridotite in Kaipinggou near the edge of the Iqe eclogite-gneiss region, of which rock types, genesis, and age are short of research. Whole-rock major and trace and platinum-group elements, olive mineral elements, and zircon U-Pb dating and Hf isotopes for peridotite at Kaipinggou are studied in this paper. Kaipinggou peridotites are characterized by high contents of Mg#, Mg/Si and Ni, showing similar distribution patterns of REE and trace elements, depletion in HFSE and HREE, and slightly enrichment in LILE and LREE. Olivines have high Fo(90.11-92.77)and NiO(0.32%-0.45%) contents, but low contents of CaO(0.02%). Whole-rock platinum group elements(PGEs) are similar to those of metamorphic and residual peridotites. There are two groups of metamorphic zircons in the Kaipinggou peridotites, with ages of 459.5±3.6 Ma and 417.5±2.7 Ma, corresponding to εHf(t) of -0.71 to 9.45 and -11.96 to -1.20, respectively, indicating the nature and timing of the fluid derived from oceanic crust(or early continental crust subduction) and continental crust. In conclusion, the Kaipinggou peridotites are derived from the mantle wedge of the lithosphere and record the crustal features due to the metasomatism of the oceanic and continental crust fluids. The novel findings provide new evidence for the evolution of oceanic lithosphere subduction to continental collision/subduction in the North Qaidam. |
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