Preservation of Archean mafic lower continental crust worldwide
Preservation of Archean mafic lower continental crust worldwide
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全球太古宙镁铁质下陆壳的保存情况
DOI：
10.1016/j.epsl.2023.118556
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发表时间：
2024-01
影响因子：
5.3
通讯作者：
Lang Zhao;Neng Jiang;Jinghui Guo;Danqing Liu;Jun-Cheng Hu;Xiaohui Zhang;Guangyu Huang
中科院分区：
文献类型：
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作者：
Lang Zhao;Neng Jiang;Jinghui Guo;Danqing Liu;Jun-Cheng Hu;Xiaohui Zhang;Guangyu Huang
在太古代克拉通中发现的镁铁质麻粒岩捕虏体通常被推断是由太古代后玄武岩底侵形成的，这意味着太古代镁铁质下地壳可能是通过分层作用被移除的。本文通过对麻粒岩地形、麻粒岩捕虏体和下地壳衍生花岗岩的综合研究，提出华北克拉通北部第三纪夹带碱性玄武岩的镁铁质麻粒岩捕虏体大部分是晚太古代镁铁质下地壳部分熔融产生中生代花岗岩后留下的残余岩。这与普遍认为的典型中生代玄武岩底侵背道而驰。我们进一步表明，太古代镁铁质下地壳目前在华北克拉通范围内以克拉通规模存在。对许多其他克拉通中被认为是元古界底侵产物的镁铁质麻粒岩包体进行重新考察表明，它们中的大多数与目前的情况具有相似的成因机制，表明它们可能形成于太古宙。这证明了太古代镁铁质下地壳在全球范围内得到了保存，这与人们普遍认为的太古代镁铁质下地壳大部分已经分层的概念相反。我们预测所有太古代克拉通下方都会保存这种镁铁质下地壳。这表明下地壳中太古宙岩石的数量可能远大于暴露的数量。
Mafic granulite xenoliths found in Archean cratons have generally been inferred to form from post-Archean basaltic underplating, implying that the Archean mafic lower crust was removed perhaps via delamination. Here based on an integrated study of granulite terrain, granulite xenoliths and lower crustal-derived granitoids, we make a compelling case that most of the Tertiary alkali basalt-entrained mafic granulite xenoliths from the northern North China craton are restites left after partial melting of the late Archean mafic lower crust to produce the Mesozoic granitoids. This runs counter to archetypical Mesozoic basaltic underplating as commonly believed. We further show that the Archean mafic lower crust persists on a cratonic scale in the North China craton presently.Re-examination of mafic granulite xenoliths from many other cratons that were considered to be products of Proterozoic underplating shows that most of them have similar genetic mechanism to the present case, suggesting that they may form in the Archean. This attests to preservation of the Archean mafic lower crust globally, contrary to the widely held concept that much of the Archean mafic lower crust has delaminated. We predict preservation of such mafic lower crust beneath all Archean cratons. It suggests that the quantity of Archean rocks in the lower crust may be much greater than that exposed.