Field Relationships, Geochemistry, Zircon Ages and Evolution of a Late Archaean to Palaeoproterozoic Lower Crustal Section in the Hengshan Terrain of Northern China
Field Relationships, Geochemistry, Zircon Ages and Evolution of a Late Archaean to Palaeoproterozoic Lower Crustal Section in the Hengshan Terrain of Northern China
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发表时间：
2005
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通讯作者：
Kroner;Wilde;O'brien;Li;Jianghai;Passchier;Walte;Liu;Dunyi
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作者：
Kroner;Wilde;O'brien;Li;Jianghai;Passchier;Walte;Liu;Dunyi
横山杂岩体是华北克拉通中心带的一部分，主要由晚太古代至古元古代的韧性变形高级别花岗岩类正长岩组成，部分为混染岩，并被辉长岩基性岩脉侵入。许多高度应变的岩石以前被误解为上地壳序列，代表糜棱岩化的花岗岩类和剪切岩脉。单锆石定年记录岩浆花岗岩就位年龄在2.52 Ga ~ 2.48 Ga之间，2.7 Ga片麻岩罕见，可能反映了更古老的基底。少数花岗质片麻岩的侵位年龄在2.35 ~2.1 Ga之间，构造特征与较老岩石相同，表明主要变形发生在~2.1 Ga之后。辉长岩岩脉的侵入发生在~1920 Ma，所有横山岩石在1.88 ~ 1.85 Ga发生麻粒岩相变质作用，并经历了回退、剪切和隆升。横山及邻近的富坪花岗质片麻岩为晚太古代至早古元古代日本型岩浆弧的下部深成岩浆部分，上部火山部分为附近的五台杂岩。根据2.7 Ga锆石，该弧的组成部分可能在大陆边缘演化。吕梁造山期晚古元古代，华北克拉通东、西两块板块碰撞形成跨华北造山带，发生了大变形和HP变质作用。横山剪切带被解释为HP变质高峰后主要的下地壳不连续性，形成于晚古元古代（1.85 Ga）横山杂岩造山崩塌和隆升期间。
The Hengshan complex forms part of the central zone of the North China Craton and consists predominantly of ductilely-deformed late Archaean to Palaeoproterozoic high-grade, partly migmatitic, granitoid orthogneisses, intruded by mafic dykes of gabbroic composition. Many highly strained rocks were previously misinterpreted as supracrustal sequences and represent mylonitized granitoids and sheared dykes. Our single zircon dating documents magmatic granitoid emplacement ages between 2.52 Ga and 2.48 Ga, with rare occurrences of 2.7 Ga gneisses, possibly reflecting an older basement. A few granitic gneisses have emplacement ages between 2.35 and 2.1 Ga and show the same structural features as the older rocks, indicating that the main deformation occurred after ~2.1 Ga. Intrusion of gabbroic dykes occurred at ~1920 Ma, and all Hengshan rocks underwent granulite-facies metamorphism at 1.88–1.85 Ga, followed by retrogression, shearing and uplift. We interpret the Hengshan and adjacent Fuping granitoid gneisses as the lower, plutonic, part of a late Archaean to early Palaeoproterozoic Japan-type magmatic arc, with the upper, volcanic part represented by the nearby Wutai complex. Components of this arc may have evolved at a continental margin as indicated by the 2.7 Ga zircons. Major deformation and HP metamorphism occurred in the late Palaeoproterozoic during the Luliang orogeny when the Eastern and Western blocks of the North China Craton collided to form the Trans-North China orogen. Shear zones in the Hengshan are interpreted as major lower crustal discontinuities post-dating the peak of HP metamorphism, and we suggest that they formed during orogenic collapse and uplift of the Hengshan complex in the late Palaeoproterozoic (1.85 Ga).