Orogenic Root Delamination Induced by Eclogitization of Thickened Lower Crust in the Chinese Western Tianshan: Constraints From Adakites
Orogenic Root Delamination Induced by Eclogitization of Thickened Lower Crust in the Chinese Western Tianshan: Constraints From Adakites
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中国西天山加厚下地壳榴辉岩化引起的造山根拆沉：来自埃达克岩的制约
DOI：
10.1029/2019jb018354
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发表时间：
2019-11
期刊：
影响因子：
--
通讯作者：
Zhen-Hua Zhao
中科院分区：
文献类型：
--
作者：
Ning-Bo Li;He-Cai Niu;Wu-Bin Yang;Chun-Kit Lai;Zhen-Hua Zhao
除了板块俯冲作用外，造山带根部榴辉岩化作用引起的地壳拆沉作用也是地壳物质向地幔转移的重要过程。许多以前的研究已经证明了地壳拆沉和榴辉岩化之间的因果关系，但实际的岩浆记录的过程中很少有记录。本文详细研究了阿吾拉勒山晚古生代两个不同的埃达克岩套，即高（HN）和低（LN）Nb/Ta比值埃达克岩套，以制约区域地壳拆沉作用。这两套岩浆岩都具有埃达克质的亲合性，是由新生加厚的下地壳部分熔融形成的，其源区残留矿物组合不同。晚石炭世HN埃达克岩具有超球粒陨石Nb/Ta（21.4-23.3）和高Dy/Yb（2.66-2.88）比，可能是通过含金红石、榴辉岩控制的下地壳熔融形成的，意味着地壳增厚和榴辉岩化。相比之下，二叠纪LN埃达克岩的Nb/Ta（12.9-20.0）和Dy/Yb（1.35-2.53）比值变化较大且较低，这可能是由含石榴子石的角闪岩与少量含金红石的榴辉岩控制的熔体混合而成，意味着地壳变薄和榴辉岩化的结束。这两套埃达克岩的连续性表明，在晚石炭世至早二叠世期间，该地区发生了造山根的榴辉岩化，伴随着连续的地壳分层。因此，我们的研究结果意味着，具有不同地球化学特征的埃达克岩是潜在的造山根的矿物学示踪剂，重要的是，提供了令人信服的证据榴辉岩诱导的地壳拆沉造山带。
Crustal delamination induced by eclogitization of orogenic roots, in addition to plate subduction, is an important process that transfers crustal materials back into the mantle. Many previous studies have demonstrated a causal link between crustal delamination and eclogitization, but actual magmatic records of the process are rarely documented. Here we present detailed studies on two distinct late Paleozoic adakite suites in the Awulale Mountains (Chinese Western Tianshan), that is, the suites with high (HN) and low (LN) Nb/Ta ratios, to constrain the regional crustal delamination. Both igneous suites have adakitic affinity and formed by partial melting of the juvenile thickened lower crust with different residual mineral assemblages in their source regions. The late Carboniferous HN adakite has superchondritic Nb/Ta (21.4–23.3) and high Dy/Yb (2.66–2.88) ratios and may have formed via rutile‐bearing, eclogite‐controlled melting of the lower crust, implying crustal thickening and eclogitization. In contrast, the Permian LN adakites have varying and lower ranges of Nb/Ta (12.9–20.0) and Dy/Yb ratios (1.35–2.53), which were probably derived from mixing of garnet‐bearing amphibolite with minor rutile‐bearing, eclogite‐controlled melts, implying crustal thinning and the end of eclogitization. The succession of these two adakite suites suggests that during the late Carboniferous to early Permian, eclogitization of the orogenic root, accompanying successive crustal delaminations, occurred in this region. Accordingly, our results imply that adakites with different geochemical features are potential tracers for the mineralogy of orogenic roots and, importantly, provide convincing evidence for eclogitization‐induced crustal delamination in orogenic belts.
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期刊：
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影响因子：
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DOI：
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发表时间：
2017-02
期刊：
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