Generation of Nb-enriched mafic rocks and associated adakitic rocks from the southeastern Central Asian Orogenic Belt:Evidence of crust-mantle interaction
Generation of Nb-enriched mafic rocks and associated adakitic rocks from the southeastern Central Asian Orogenic Belt:Evidence of crust-mantle interaction
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中亚造山带东南部富铌基性岩及伴生埃达克岩的生成：壳幔相互作用的证据
DOI：
10.1016/j.gsf.2021.101341
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发表时间：
2022
影响因子：
8.9
通讯作者：
Xing Dehe
中科院分区：
文献类型：
--
作者：
Jing Yan;Ge Wenchun;Santosh M;Dong Yu;Yang Hao;Ji Zheng;Bi Junhui;Zhou Hongying;Xing Dehe
俯冲的大洋岩石圈的熔融以及汇聚板块边缘相关的熔体 - 地幔相互作用需要特定的地球动力学环境，使得大洋板块异常受热。在此我们聚焦于早中生代镁铁质岩石和花岗斑岩，它们为了解与古亚洲洋最终闭合相关的板块熔融过程提供了视角。花岗斑岩样品为钙碱性，其特征是具有高锶含量、重稀土元素强烈亏损，导致高的(La/Yb)_N和Sr/Y比值，以及可忽略不计的铕异常。基于它们高的Na₂O和MgO、低的K₂O含量、正的ε_(Hf)(t)和ε_(Nd)(t)以及低的(⁸⁷Sr/⁸⁶Sr)_i值，我们认为花岗斑岩可能源自俯冲的古亚洲洋壳的部分熔融。富铌镁铁质岩石富集Rb、Th、U、Pb和K，亏损Nb、Ta、Ba、P和Ti，证实了其与俯冲相关的成因。它们不均匀的Sr - Nd - Hf - O同位素组成以及其他地球化学特征表明，它们可能源自与大洋板块派生的埃达克质熔体相互作用的橄榄岩地幔楔的部分熔融。微量元素和同位素模拟结果以及升高的锆石δ¹⁸O值表明，有不同的俯冲沉积物输入到地幔楔中，且以陆源沉积物为主。综合索伦克 - 长春缝合带广泛发育的双峰式岩石组合、共轭岩脉、热变质作用、构造特征、古地磁约束以及古地理证据，我们确定了一个由板块断离引发的板块窗，它解释了中亚造山带东南部板块的熔融以及富铌镁铁质岩石和相关埃达克质花岗斑岩的形成。
Melting of subducting oceanic lithosphere and associated melt-mantle interactions in convergent plate margins require specific geodynamic environment that allows the oceanic slab to be abnormally heated.Here we focus on the Early Mesozoic mafic rocks and granite porphyry,which provide insights into slab melting processes associated with final closure of the Paleo-Asian Ocean.The granite porphyry samples are calc-alkaline and distinguished by high Sr contents,strong depletion of heavy rare earth elements,resulting in high (La/Yb)_N and Sr/Y ratios,and negligible Eu anomalies.Based on their high Na_2O and MgO,low K_2O contents,positive ε_(Hf)(t) and ε_(Nd)(t) and low (~(87)Sr/~(86)Sr)_i values,we propose that the granite porphyry was likely derived from partial melting of subducting Paleo-Asian oceanic crust.The Nb-enriched mafic rocks are enriched in Rb,Th,U,Pb and K,and depleted in Nb,Ta,Ba,P and Ti,corroborating a subduction-related origin.Their heterogeneous Sr-Nd-Hf-O isotopic compositions and other geochemical features suggest that they were likely derived from partial melting of peridotitic mantle wedge interacted with oceanic slab-derived adakitic melts.Trace element and isotope modeling results and elevated zircon δ~(18)O values suggest variable subducting sediments input into the mantle wedge,dominated by terrigenous sediments.Synthesizing the widely-developed bimodal rock associations,conjugated dikes,thermal metamorphism,tectonic characteristics,paleomagnetic constraints,and paleogeographical evidence along the Solonke-Changchun suture zone,we identify a slab window triggered by slab break-off,which accounts for slab melting and formation of the Nb-enriched mafic rocks and associated adakitic granite porphyry in southeastern Central Asian Orogenic Belt.