Geology of a Neoarchean suture: Evidence from the Zunhua ophiolitic mélange of the Eastern Hebei Province, North China Craton
Geology of a Neoarchean suture: Evidence from the Zunhua ophiolitic mélange of the Eastern Hebei Province, North China Craton
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新太古代缝合带地质：来自华北克拉通河北省东部遵化蛇绿混杂岩的证据
DOI：
10.1130/b35138.1
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Deng Hao
中科院分区：
文献类型：
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作者：
Wang Junpeng;Li Xiawen;Ning Wenbin;Kusky Timothy M;Wang Lu;Polat Ali;Deng Hao
混杂岩是显生宙会聚板块边界的特征，但在太古代造山带中很少有报道。在本文中，我们记录了华北克拉通河北省东部的新太古代蛇绿混杂岩。遵化蛇绿混杂岩由变泥岩、正片麻岩、副片麻岩和磁铁矿石英岩的结构混合物组成，与变玄武岩、变辉长岩和变辉绿岩的奇异构造镁铁质块体以及蛇纹石化橄榄岩和豆荚状铬铁矿的超镁铁质块体混合。遵化蛇绿混杂岩呈现出典型的“块状基质”结构。混杂岩的所有单元都被花岗岩岩脉和石英脉侵入，这些花岗岩脉和石英脉清楚地横切了混杂岩块和基质的叶理。激光烧蚀-电感耦合等离子体-质谱锆石U-Pb定年法对变沉积混杂岩基质和侵入花岗岩脉中的碎屑锆石进行定年，将遵化混杂岩的形成时间限制在2.52~2.46 Ga之间。变沉积混杂岩锆石上的变质边缘 基质的年龄为 2467±27 Ma，证实了混杂岩的变质作用发生在大约 2017 年。 2.47 Ga。高精度（比例1：20和1：50）岩石构造测绘，以及沿几条横断面的详细构造观察，记录了混杂岩的内部结构和运动学，揭示了从西北到东南的定向运输。遵化混杂岩中具有褶皱和断层事件的混杂岩中的不对称结构记录了运动学信息，并且类似于增生楔的构造样式。对各种基性块体的场关系和地球化学分析表明，这些块体形成于与弧相关的俯冲构造环境中。我们认为，遵化混杂岩标志着华北克拉通中央造山带新太古代弧陆碰撞事件的缝合带。结合我们之前的研究，我们证明了大约。中央造山带弧/增生棱柱地体与华北克拉通东地块之间存在2.5 Ga构造缝合带。我们将缝合线的这一段与沿走向的其他类似区域关联起来，超过 1000 公里，包括大约 1000 公里的部分。中央造山带南缘登封绿岩带约2.5 Ga， 2.5 嘎赞皇蛇绿混杂岩位于造山带中心。这些关系表明，太古代晚期的构造过程包括汇聚边缘的俯冲/增生，以及板块的水平运动，其方式类似于现代的增生汇聚边缘。
Mélanges characterize Phanerozoic convergent plate boundaries, but have rarely been reported from Archean orogens. In this paper, we document a Neoarchean ophiolitic mélange in the Eastern Hebei Province of the North China Craton. The Zunhua ophiolitic mélange is composed of a structural mixture of metapelites, ortho-and para-gneisses, and magnetite-quartzite mixed with exotic tectonic mafic blocks of metabasalts, metagabbroic rocks, and metadiabases, along with ultramafic blocks of serpentinized peridotites and podiform chromitites. The Zunhua ophiolitic mélange shows typical “block in matrix” structures. All units of the mélange have been intruded by granitic dikes and quartz veins that clearly cross-cut the foliation of blocks and matrix of the mélange. Laser-ablation–inductively coupled plasma–mass spectrometry zircon U-Pb dating of detrital zircons from the meta-sedimentary mélange matrix and intruding granitic dikes constrains the formation time of the Zunhua mélange to be between 2.52 and 2.46 Ga. Metamorphic rims on zircons from meta-sedimentary mélange matrix have ages of 2467±27 Ma, confirming metamorphism of the mélange occurred at ca. 2.47 Ga. High-precision (scale 1: 20 and 1: 50) litho-structural mapping, along with detailed structural observations along several transects documents the internal fabrics and kinematics of the mélange, revealing a northwest to southeast directed transportation. The asymmetric structures in the mélange with folding and faulting events in the Zunhua mélange record kinematic information and are similar to the tectonic style of an accretionary wedge. Field relationships and geochemical analysis of various mafic blocks show that these blocks formed in an arc-related subduction tectonic environment. We suggest that the Zunhua mélange marks the suture zone of a Neoarchean arc-continent collisional event in the Central Orogenic Belt of the North China Craton. Combined with our previous studies, we demonstrate that a ca. 2.5 Ga tectonic suture exists between an arc/accretionary prism terrane in the Central Orogenic Belt and the Eastern Block of the North China Craton. We correlate this segment of the suture with other similar zones along strike, for> 1000 km, including sections of the ca. 2.5 Ga in Dengfeng greenstone belt in the southern margin of the Central Orogenic Belt, and the ca. 2.5 Ga Zanhuang ophiolitic mélange in the center of the orogen. These relationships demonstrate that tectonic processes in the late Archean included subduction/accretion at convergent margins, and the horizontal movement of plates, in a style similar to modern-day accretionary convergent margins.