A refractory mantle protolith in younger continental crust, east-central China: Age and composition of zircon in the Sulu ultrahigh-pressure peridotite
A refractory mantle protolith in younger continental crust, east-central China: Age and composition of zircon in the Sulu ultrahigh-pressure peridotite
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DOI：
10.1130/g22569.1
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发表时间：
2006-09
期刊：
影响因子：
5.8
通讯作者：
Jianping Zheng;W. Griffin;S. O’Reilly;Jingsui Yang;R. Zhang
中科院分区：
文献类型：
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作者：
Jianping Zheng;W. Griffin;S. O’Reilly;Jingsui Yang;R. Zhang
锆石是从石榴橄榄岩及其围岩（片麻岩）中提取的，这些围岩与苏鲁超高压（UHP）变质带的中国大陆科学钻探项目（CCSD-PP1）的预先导孔相交。橄榄岩锆石记录了早期中生代超高压变质作用（ 206 Pb/ 238 U 年龄为 223.5 ± 7.5 Ma），但其 Hf 同位素组成表明橄榄岩原岩年龄至少为中元古代（最小贫乏地幔年龄 [ T DM ] 为 1.4 Ga）。片麻岩中的锆石也反映了中生代变质作用，206 Pb/ 238 U 簇的年龄为 224.5 ± 11.5 Ma；不一致的颗粒痕迹表明原岩年龄超过 800 Ma，与小于 1.2 Ga 的 T DM 模型年龄一致。橄榄岩锆石具有与金伯利岩和/或碳酸岩锆石相似的微量元素模式，而来自片麻岩的锆石与来自正长岩/二长岩的锆石有亲缘关系。这些差异表明，影响橄榄岩锆石的交代剂来自软流圈地幔而不是俯冲的大陆地壳。 CCSD-PP1橄榄岩中玄武岩成分的强烈贫化，以及橄榄岩锆石相对非放射性的Hf同位素组成（例如-16.3至∼-13.8 e Hf），表明橄榄岩体是经历了中元古代交代作用的难熔太古代地幔的碎片，代表了 构造侵入较年轻的地壳。
Zircons have been extracted from garnet peridotite and its wall rock (gneiss), which was intersected by the pre–pilot hole of the Chinese Continental Scientific Drilling project (CCSD-PP1) in the Sulu ultrahigh-pressure (UHP) metamorphic belt. The peridotitic zircons record early Mesozoic UHP metamorphism ( 206 Pb/ 238 U age of 223.5 ± 7.5 Ma), but their Hf isotope compositions indicate that the protolith of the peridotite is at least Mesoproterozoic in age (minimum depleted-mantle ages [ T DM ] of 1.4 Ga). Zircons from the gneiss also reflect the Mesozoic metamorphism, with a cluster of 206 Pb/ 238 U ages at 224.5 ± 11.5 Ma; a trail of discordant grains indicates a protolith age older than 800 Ma, consistent with T DM model ages of younger than 1.2 Ga. The peridotitic zircons have trace-element patterns similar to kimberlitic and/or carbonatitic zircons, while those from the gneiss have affinities with zircons from syenites/monzonites. The differences suggest that the metasomatic agents that affected the peridotitic zircons were derived from the asthenospheric mantle rather than from subducted continental crust. The strong depletion of the CCSD-PP1 peridotite in basaltic components, and the relatively unradiogenic Hf isotopic compositions (e.g., −16.3 to ∼−13.8 e Hf ) of the peridotitic zircons, indicate that the peridotitic body is a fragment of refractory Archean mantle that experienced Mesoproterozoic metasomatism and represents a tectonic intrusion into younger crust.