Permian ridge subduction in the easternmost Central Asian Orogenic Belt: Magmatic record using Sr-Nd-Pb-Hf-Mg isotopes
Permian ridge subduction in the easternmost Central Asian Orogenic Belt: Magmatic record using Sr-Nd-Pb-Hf-Mg isotopes
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中亚造山带最东部的二叠纪山脊俯冲：使用Sr-Nd-Pb-Hf-Mg同位素的岩浆记录
DOI：
10.1016/j.lithos.2021.105966
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发表时间：
2021-03
期刊：
影响因子：
3.5
通讯作者：
Yang De-Bin
中科院分区：
文献类型：
--
作者：
Wang Feng;Xing Kai-Chen;Xu Wen-Liang;Teng Fang-Zhen;Xu Yi-Gang;Yang De-Bin
古收敛边缘保存的与异常高热流有关的火成岩为识别古脊俯冲化石提供了直接线索。康卡地块作为古亚洲洋晚古生代末期消亡的见证，为追踪古脊俯冲化石提供了一个理想的机会。二叠纪火成岩类型不同(282-255 Ma)，成分从镁铁质到长英质。地幔成因的镁铁质岩石进一步细分为两类。I组为弧形岩石，镁同位素具有正常的地幔特征。因此，二叠纪俯冲环境被认为是在坎卡地块西缘，由同时代弧形花岗岩和碎屑锆石累积比例曲线支持。相比之下，II组为拉斑玄武岩，具有与古亚洲大洋MORB相似的亏损的Sr-ND-Pb-Hf同位素组成。此外，锶-钕-铅-氟化氢和镁同位素之间的解偶合也指示了镁和钼之间的同位素交换。由于菱镁矿的分解反应，因此需要较高的加热条件。壳源长英质岩石具有明显的锶-钕-铅-氢氟镁同位素组成差异，表明陆壳和洋壳在高的锆石饱和温度(855-935℃)的支持下同步熔融。因此，由山脊俯冲和由此形成的板片窗口引起的“异常高温条件”是最有可能调和二叠纪康卡地块西缘多样化岩浆活动和构造演化的模式。因此，锶-钕-铅-氢氟化氢-镁同位素被证实是解释古俯冲带山脊-俯冲带岩浆响应的综合示踪剂。
Igneous rocks related to abnormal high heat flow preserved in ancient convergent margins provide direct clues to identify fossil ridge-subduction. The Khanka Massif, as a witness of the final termination of the Paleo-Asian Ocean in Late Paleozoic, provides an ideal opportunity to trace the fossil ridge-subduction. Different types of Permian igneous rocks (282–255 Ma) were identified in composition from mafic to felsic. The mantle-derived mafic rocks are further subdivided into two groups. Group I are arc-featured rocks with normal mantle-like features in Mg isotopes. Permian subduction setting was therefore proposed within western margin of Khanka Massif, supported by the coeval arc-featured granitoids and the detrital zircon cumulative proportion curves. By contrast, Group II are tholeiitic and have more depleted Sr-Nd-Pb-Hf isotopic compositions similar to MORB of Paleo-Asian Ocean. In addition, the decoupling between Sr-Nd-Pb-Hf and Mg isotopes indicate isotope exchange between MORB and magnesite. High heat condition is therefore required because of the decomposition reactions of magnesite. The crust-derived felsic rocks exhibit the prominent difference in Sr-Nd-Pb-Hf-Mg isotopic compositions, implying synchronous melting of the continental and oceanic crusts, which are supported by the high zircon saturation temperatures (855–935 °C). Consequently, an ‘abnormal high-heat condition’ caused by ridge subduction and resultant slab window is the most likely model to reconcile the diversiform magmatism and tectonic evolution along the west margin of the Khanka Massif in the Permian. Sr-Nd-Pb-Hf-Mg isotopes are therefore verified as an integrated tracer to decipher the magmatic response to the ridge-subduction in ancient subduction zone.
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