Zircon geochemistry of two contrasting types of eclogite: Implications for the tectonic evolution of the North Qaidam UHPM belt, northern Tibet
Zircon geochemistry of two contrasting types of eclogite: Implications for the tectonic evolution of the North Qaidam UHPM belt, northern Tibet
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两种对比类型榴辉岩的锆石地球化学：对藏北柴北缘超高压变质带构造演化的启示
DOI：
10.1016/j.gr.2016.04.002
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发表时间：
2016-07
影响因子：
6.1
通讯作者：
Song, Shuguang
中科院分区：
文献类型：
--
作者：
Irel;, Trevor;Zhang, Lifei;Gao, Zhan;Song, Shuguang
与柴达木北地区广泛记录的超高压变质作用相比，大陆地壳和洋壳的变质前历史很少受到限制。从大陆和海洋基性岩变质榴辉岩的不同锆石域中获得的微量元素组成、U-Pb年龄、O和Lu-Hf同位素与揭示藏北柴达木北超高压变质带(UHPM)的榴辉岩的起源和多阶段岩浆/变质演化有关。对于大陆壳衍生的榴辉岩，来自两个样品的岩浆锆石核心875-856Ma的U-Pb年龄具有非常高的δ18O（10.6±0.5‰）和类地幔δ18O（平均为5.2±0.7‰），高Th/U和176Lu/177Hf比值，以及陡峭的MREE-HREE分布模式（球粒陨石归一化）和负Eu异常。结合 3.9-14.3 的正 εHf(t) 和 TDM（分别为 1.2-0.8 Ga 和 1.3-1.0 Ga），它们被解释为是从与俯冲相关的地幔楔或地幔中的回收材料中结晶出来的。虽然榴辉岩的变质边缘的 U-Pb 年龄为 436-431 Ma，但与岩心相比，氧同位素有所不同（遗传的、较低的和升高的）、较低的 Th/U 和 176Lu/177Hf 比率以及平坦的 HREE 分布模式，没有 Eu 异常。这些反映了继承锆石的固态重结晶和变质温度为 595–622 °C 的外部流体的沉淀（TTi-in-zircon）。对于洋壳衍生的榴辉岩，岩浆核心 (510 ± 19 Ma) 和变质边缘 (442.0 ± 3.7 Ma) 也显示出 Th/U 的区别和 176Lu/177Hf 比率，以及 REE 模式和 Eu 异常。结合 5.1 ± 0.3 ‰ 的类地幔 δ18O 特征和两组模型年龄（较年轻的 TDM 接近表观年龄，较老的 > 700 Ma），两个可能的池（幼年池和继承池）参与了幔源岩浆与地壳成分的混合。变质锆石边缘相对较高的δ18O为6.6±0.3‰，表明原岩在约440Ma洋壳俯冲之前经历了热液蚀变，或者在约440Ma超高压变质作用期间发生了外部较高的δ18O流体活动。因此，柴北缘超高压变质带见证了晚中元古代-新元古代的多次构造演化罗迪尼亚超大陆的组装/分裂及其相关的岩浆侵位，然后是古生代大洋俯冲，最后是与超高压变质作用相关的大陆俯冲/碰撞转变。
Compared to the extensively documented ultrahigh-pressure metamorphism at North Qaidam, the pre-metamorphic history for both continental crust and oceanic crust is poorly constrained. Trace element compositions, U–Pb ages, O and Lu–Hf isotopes obtained for distinct zircon domains from eclogites metamorphosed from both continental and oceanic mafic rocks are linked to unravel the origin and multi-stage magmatic/metamorphic evolution of eclogites from the North Qaidam ultrahigh-pressure metamorphic (UHPM) belt, northern Tibet.For continental crust-derived eclogite, magmatic zircon cores from two samples with U–Pb ages of 875–856 Ma have both very high δ18O (10.6 ± 0.5‰) and mantle-like δ18O (averaging at 5.2 ± 0.7‰), high Th/U and176Lu/177Hf ratios, and steep MREE-HREE distribution patterns (chondrite-normalized) with negative Eu anomalies. Combined with positive εHf(t) of 3.9–14.3 and TDM(1.2–0.8 Ga and 1.3–1.0 Ga, respectively), they are interpreted as being crystallized from either subduction-related mantle wedge or recycled material in the mantle. While the metamorphic rims from the eclogites have U–Pb ages of 436–431 Ma, varying (inherited, lower, and elevated) oxygen isotopes compared with cores, low Th/U and176Lu/177Hf ratios, and flat HREE distribution patterns with no Eu anomalies. These reflect both solid-state recrystallization from the inherited zircon and precipitation from external fluids at metamorphic temperatures of 595–622 °C (TTi-in-zircon).For oceanic crust-derived eclogite, the magmatic cores (510 ± 19 Ma) and metamorphic rims (442.0 ± 3.7 Ma) also show distinction for Th/U and176Lu/177Hf ratios, and the REE patterns and Eu anomalies. Combined with the mantle-like δ18O signature of 5.1 ± 0.3 ‰ and two groups of model age (younger TDMclose to the apparent ages and older > 700 Ma), two possible pools, juvenile and inherited, were involved in mixing of mantle-derived magma with crustal components. The relatively high δ18O of 6.6 ± 0.3‰ for metamorphic zircon rims suggests either the protolith underwent hydrothermal alteration prior to the ~ 440 Ma oceanic crust subduction, or external higher δ18O fluid activities during UHP metamorphism at ~ 440 Ma.Therefore, the North Qaidam UHPM belt witnesses multiple tectonic evolution from Late Mesoproterozoic–Neoproterozoic assembly/breakup of the Rodinia supercontinent with related magmatic emplacement, then Paleozoic oceanic subduction, and finally transition of continental subduction/collision related to UHP metamorphism.
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影响因子：
4.5
作者：
D. Rubatto;J. Hermann
通讯作者：
D. Rubatto;J. Hermann
影响因子：
6.1
作者：
T. Peters;John Cammerer Ayers;Shan Gao;Xiaoming Liu
通讯作者：
T. Peters;John Cammerer Ayers;Shan Gao;Xiaoming Liu
影响因子：
3.9
作者：
Shuguang Song;Lifei Zhang;Y. Niu;L. Su;B. Song;Dunyi Liu
通讯作者：
Shuguang Song;Lifei Zhang;Y. Niu;L. Su;B. Song;Dunyi Liu
影响因子：
5.3
作者：
STEIGER, RH;JAGER, E
通讯作者：
JAGER, E
北祁连山早古生代高压变质岩构造演化新视角
影响因子：
3
作者：
Liou, June G.;Su, Li;Zhang, Lifei;Niu, Yaoling;Wei, Chunjing;Song, Shuguang
通讯作者：
Song, Shuguang