An island arc origin of Jurassic plagiogranite in the Shiquanhe ophiolite, western Bangong Suture, Tibet: Zircon U–Pb chronology, geochemistry, and tectonic implications of Bangong Meso‐Tethys
An island arc origin of Jurassic plagiogranite in the Shiquanhe ophiolite, western Bangong Suture, Tibet: Zircon U–Pb chronology, geochemistry, and tectonic implications of Bangong Meso‐Tethys
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DOI：
10.1002/gj.4137
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发表时间：
2021-02
影响因子：
1.8
通讯作者：
Wei Li;Nina Liu;R. Nayak;Yaoliang Ma;Jinjun Wang;Xi-chong Hu;Jinhui Pang;Wei-liang Huang
中科院分区：
文献类型：
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作者：
Wei Li;Nina Liu;R. Nayak;Yaoliang Ma;Jinjun Wang;Xi-chong Hu;Jinhui Pang;Wei-liang Huang
蛇绿岩中的斜长花岗岩体积很小，但可以为古代大洋岩石圈的起源和构造演化提供重要信息。本文对西藏中部班贡缝合带狮泉河-嘉利蛇绿岩带西端的狮泉河蛇绿岩中新发现的斜长花岗岩进行了年代学和地球化学研究。两个样品的锆石U-Pb年龄分别为(167.4±1.2)Ma和(167.5±1.5)Ma。斜长花岗岩具有正的全岩εNd(T)(4.2~4.9)和锆石εHf(T)(9.6~14.3)值，高Th/Nb比值(0.6~2.8)，而相对较低的La/Nb比值(0.9~9.9)，表明它可能来自少量俯冲沉积贡献的亏损地幔。轻稀土富集型、重稀土扁平型、Eu负异常、Nb-Ti负异常与剪切型斜长花岗岩相似，表明该岩石可能是变质基性岩部分熔融形成的。斜长花岗岩与狮泉河蛇绿变基岩无冷接触，表明斜长花岗岩可能来源于伴生的蛇绿变基岩。地球化学计算和模拟表明，斜长花岗岩可能是在低温(<；800℃)、低压(<；0.1 Gpa)条件下，由变基性岩低程度(<；10%)部分熔融和少量沉积物熔体补充形成的。狮泉河斜长花岗岩和同时代的拉格科尔科斜长花岗岩位于同一蛇绿岩亚带，表明中侏罗世班公中特提斯发育了大洋内岛弧体系。
The plagiogranites in ophiolites are minor in volume but can provide crucial information for the origin and tectonic evolution of ancient oceanic lithosphere. This paper presents the geochronology and geochemistry of a newly discovered plagiogranite in the Shiquanhe ophiolite, from the west end of the Shiquanhe‐Jiali ophiolite sub‐belt, Bangong Suture, central Tibet. Zircon U–Pb dating of two samples yields Middle Jurassic ages (167.4 ± 1.2 Ma and 167.5 ± 1.5 Ma). The plagiogranite has positive whole‐rock εNd(t) (4.2–4.9) and zircon εHf(t) (9.6–14.3) values, high Th/Nb ratios (0.6–2.8) but relatively low La/Nb ratios (0.9–9.9), indicating that it was possibly derived from a depleted mantle with the contribution of minor subducted sediments. The LREE‐enrichment but HREE‐flat patterns with negative Eu anomalies and negative Nb‐Ti anomalies resemble those of shear‐type plagiogranites, which mean that this rock was likely formed by partial melting of metabasite. Combined with the plagiogranite which does not exhibit chilled contacts against the Shiquanhe ophiolitic metabasite, suggests that the plagiogranite may have been derived from the associated ophiolitic metabasite. Geochemical calculating and modelling indicate that the plagiogranite was possibly produced by a low degree (<10%) partial melting of metabasite and replenished by minor sediments melts at low temperature (<800 °C) and low pressure (<0.1 GPa) conditions. The Shiquanhe plagiogranite, together with the contemporaneous Lagkorco plagiogranite in the same ophiolite sub‐belt, indicates that an intra‐oceanic island arc system was developed in the Bangong Meso‐Tethys during the Middle Jurassic.