Composition and geochronology of the deep-seated xenoliths from the southeastern margin of the North China Craton
Composition and geochronology of the deep-seated xenoliths from the southeastern margin of the North China Craton
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DOI：
10.1016/j.gr.2012.06.009
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发表时间：
2013-04
影响因子：
6.1
通讯作者：
Yican Liu;An Wang;Shuguang Li;F. Rolfo;Y. Li;C. Groppo;Xiao Gu;Z. Hou
中科院分区：
文献类型：
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作者：
Yican Liu;An Wang;Shuguang Li;F. Rolfo;Y. Li;C. Groppo;Xiao Gu;Z. Hou
华北克拉通东南缘中生代家沟闪长斑岩中发育多种深层包体。在这项研究中，我们对不同类型的捕虏体进行了岩石学、年代学、Hf同位素和地球化学的综合研究，并利用这些数据更好地约束了该地区深部地壳的组成和年龄。捕虏体多为基性变质火成岩，其中含石榴石岩性较多。捕虏体可分为3大类岩石组：含尖晶石的石榴石斜辉石岩/辉云石斜辉石岩/尖晶石辉石岩（第1组），缺乏辉石岩的石榴石角闪岩或角闪石/石榴石麻粒岩/基性片麻岩（第2组），含石榴石的长英质（中酸）片麻岩（第3组）。其中，基性-超基性岩占主导地位。所研究的捕虏体的原岩范围从玄武岩到安山岩再到英安岩。地球化学和hf同位素数据表明，第2组和第3组的大部分捕虏体类似于汇聚大陆边缘弧背景下形成的岩浆岩。其中少数（主要属于第一类）代表地幔衍生产品。从多阶段矿物组合和年代中可以识别出俯冲相关或幔源流体或熔体的多交代印记。SHRIMP锆石U-Pb定年、Hf同位素和地球化学资料提供了NCC东南缘约2.5Ga和2.1Ga与俯冲有关的adak岩和弧相关岩石的证据，并证实了约1.8Ga存在高压麻粒岩相变质作用。这些资料表明，该地区前寒武纪下地壳经历了两次俯冲-增生和一次地幔源玄武岩岩浆在下地壳底部的垂直增生。此外，还发现了393±7Ma的晚幔源玄武岩岩浆活动。本文资料表明，北陆块东南缘深部地壳由古生代、古元古代和新太古代晚期的混合原岩组成。
A variety of deep-seated xenoliths occur within the Mesozoic Jiagou dioritic porphyry in the southeastern margin of the North China Craton (NCC). In this study we present a combined petrologic, geochronological, Hf isotope and geochemical study on the different types of xenoliths and use these data to better constrain the composition and age of the deep crust beneath the area. Most of the xenoliths are mafic meta-igneous rocks, among which garnet-bearing lithologies are common. The xenoliths can be classified into three broad petrographic groups: spinel-bearing garnet clinopyroxenite/phlogopite clinopyroxenite/spinel pyroxenite (Group 1), garnet amphibolite or hornblendite/garnet granulite/mafic gneiss lacking pyroxene (Group 2), and garnet-bearing felsic (intermediate-acid) gneiss (Group 3). Among these, the mafic–ultramafic rocks constitute the dominant category. The protoliths of the studied xenoliths range from basalt through andesite to dacite. Geochemical and Hf-isotope data indicate that most xenoliths belonging to Groups 2 and 3 resemble magmatic rocks formed at convergent continental margin arc setting. A few of them (mostly belonging to Group 1) represent mantle-derived products. Multiple metasomatic imprints, with contribution from subduction-related or mantle-derived fluids or melts have been recognized from the multistage mineral assemblages and ages. SHRIMP zircon U–Pb dating, Hf isotope and geochemical data offer evidence for subduction-related adakite-like and arc-related rocks in the southeastern margin of the NCC at ca. 2.5Ga and 2.1Ga, and confirm the occurrence of high-pressure granulite-facies metamorphism at ca. 1.8Ga. These data suggest an episodic growth of Precambrian lower crust beneath this region in response to two stages of subduction–accretion and one vertical accretion of mantle-derived basaltic magma at the base of the lower crust. Additionally, a previously unknown late mantle-derived basaltic magmatism at 393±7Ma has also been recognized. The data presented in this paper demonstrate that the deep crust beneath the southeastern margin of the NCC is composed of hybrid protoliths derived from Paleozoic, Paleoproterozoic and late Neoarchean sources.