The role of continental fragments in the formation of intra-oceanic arcs: Constraints from Sr-Nd-Hf-O isotopes of gabbro from the Jiamusi Block, NE China
The role of continental fragments in the formation of intra-oceanic arcs: Constraints from Sr-Nd-Hf-O isotopes of gabbro from the Jiamusi Block, NE China
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大陆碎片在洋内弧形成中的作用：中国东北佳木斯地块辉长岩Sr-Nd-Hf-O同位素的约束
DOI：
10.1016/j.gr.2021.10.009
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发表时间：
2021-10
影响因子：
6.1
通讯作者：
吴浩然
中科院分区：
文献类型：
--
作者：
杨浩;葛文春;M. Santosh;纪政;董玉;景妍;吴浩然
洋内弧是产生地球大陆地壳的潜在候选者，是幼年弧和成熟大陆物质混合的活跃场所。然而，大陆碎片是否发生在洋内弧下，以及大陆物质如何参与岛弧岩浆仍然是模棱两可的。本文报道了中国东北部佳木斯地块东南部志留系岛弧辉长岩的锆石U-Pb-Hf-O同位素、全岩元素和Sr-Nd同位素数据。辉长岩位在约435 ~ 429 Ma，与古亚洲洋向北洋内俯冲有关，属于百乃庙弧系的东伸。锆石δ18O值（+5.5‰~ +7.9‰）升高，εHf(t)值（-2.1 ~ +4.0）变化，整体岩石εNd(t)值（-1.1 ~ - 1.6）为负值，表明地幔楔体中输入的远洋和陆源沉积物形成了丰富的地幔成分。陆源沉积物的贡献以及对古元古代地壳岩石的识别，首次证明了海内弧下存在大陆碎片。结合已发表的资料，我们认为塔里木克拉通型的分散大陆碎片发生在百乃庙弧系内，它们不仅通过浮力的增加促进了洋-洋俯冲的开始，而且还解释了古大陆锆石和年轻弧岩的丰富同位素变化。我们的研究突出了一个化石例子，可以帮助更好地量化大陆碎片在海洋内弧的起源和演化中的规模和作用。
Intra-oceanic arcs are potential candidates that generate Earth’s continental crust, and serve as active sites for the mixing of juvenile arc and mature continental material. However, whether continental fragments occur beneath intra-oceanic arcs, and how continental materials are involved in island arc magmas remain equivocal. Here we report zircon U-Pb-Hf-O isotopes and whole-rock elemental and Sr-Nd isotopic data on the Silurian island arc gabbro from the southeastern Jiamusi Block in NE China. The gabbro was emplaced at ca. 435–429 Ma associated with the northward intra-oceanic subduction of the Paleo-Asian Ocean, and belongs to the eastern extension of the Bainaimiao arc system. Elevated zircon δ18O (+5.5‰ to +7.9‰) and variable εHf(t) (-2.1 to +4.0) values, and negative whole rock εNd(t) (-1.1 to −1.6) values, suggest an enriched mantle component generated by pelagic and terrigenous sediments input into the mantle wedge. The contribution of terrigenous sediments, together with the recognition of Paleoproterozoic crustal rocks, proves for the first time that continental fragments existed beneath the intra-oceanic arc. In conjunction with published data, we propose that that Tarim Craton-type scattered continental fragments occurred within the Bainaimiao arc system, and that they not only facilitated the initiation of oceanic-oceanic subduction through increasing buoyancy, but also account for the old continental zircon and enriched isotopic variations of the young arc rocks. Our study highlights a fossil example that could help better quantify the scale and role of continental fragments in the origin and evolution of intra-oceanic arcs.
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