Lithotectonic elements of Precambrian basement in the North China Craton: Review and tectonic implications
Lithotectonic elements of Precambrian basement in the North China Craton: Review and tectonic implications
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DOI：
10.1016/j.gr.2012.08.016
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发表时间：
2013-05
影响因子：
6.1
通讯作者：
Guochun Zhao;M. Zhai
中科院分区：
文献类型：
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作者：
Guochun Zhao;M. Zhai
华北陆壳由太古宙-古元古代基底和中、新生代盖层组成。NCC东部局部存在少量的始新世至中太古代基底岩石，但由于后期事件的广泛改造，对其范围，性质和构造演化知之甚少。NCC的新太古代基底形成于两个不同的时期：2.8 - 2.7 Ga和2.6 - 2.5 Ga，其中前者被认为是NCC幼年地壳生长的主要时期，Nd和锆石Hf同位素数据证明了这一点，尽管2.8 - 2.7 Ga岩石没有广泛暴露。2.6-2.5Ga的岩石占NCC前寒武纪基底的80%左右，可分为高级片麻岩杂岩和中低级花岗岩-绿岩带，它们广泛分布于整个NCC，似乎支持NCC的花岗岩化作用发生在2.5Ga左右的观点。然而，华北克拉通东部和西部的2.6 - 2.5Ga岩石（东、西地块）与中部的同时代岩石不同（横贯华北造山带），前者以片麻岩穹隆为主，2.5Ga变质，具有等压冷却的逆冲P-T轨迹，反映了与幔源岩浆底侵作用有关的成因;后者以走滑韧性剪切带、大规模逆冲推覆和褶皱作用以及局部存在鞘状褶皱的穿流构造为特征，在1.85 Ga左右变质，具有等温减压的顺时针P-T轨迹，与俯冲和陆-陆碰撞背景相一致。此外，科马提岩/科马提质岩石存在于NCC东部和西部的花岗岩-绿岩带中，但在中部一般不存在。这些差异意味着华北克拉通东西部2.6-2.5Ga的基底岩石形成于与中部不同的构造环境。虽然岩浆弧和地幔柱模型都可以用来解释NCC东部2.6 - 2.5 Ga基底岩石的构造背景，但地幔柱模型更受青睐，因为它可以合理地解释：（1）在短时间内形成的花岗岩类侵入体异常大的暴露（2）科马提质岩浆的形成，喷发温度高达1650 ° C;（3）穹隆构造占优势;（4）绿岩序列中的双峰式火山岩组合;（5）基性岩与大陆拉斑玄武岩的亲合性;（6）变质作用与等压冷却的逆冲P-T轨迹。与此相反，华北克拉通中部2.6-2.5Ga的高级片麻岩和低级花岗岩-绿岩带则表现出与古元古代活动大陆边缘弧和陆-陆碰撞带的代表性岩石成分相同的构造和变质特征。华北克拉通古元古代岩石组合主要局限于西部、中部和东部的3个线性构造带，分别命名为"孔兹岩带（丰镇带/内蒙古缝合带）"、"横贯华北造山带（中央造山带）"和"胶辽吉（辽吉）带"。这三个带具有以下岩石构造单元，它们是板块构造体制中俯冲和碰撞构造的经典标志：（1）与弧有关的幼年地壳;（2）由走滑韧性剪切带限定的线性构造带;（3）与弧有关的碰撞构造带。
The North China Craton (NCC) consists of Archean to Paleoproterozoic basement overlain by Mesoproterozoic to Cenozoic cover. Minor Eoarchean to Mesoarchean basement rocks are locally present in the eastern part of the NCC, but little is known about their extent, nature and tectonic evolution due to widespread reworking by later events. The Neoarchean basement in the NCC was formed during two distinct periods: 2.8–2.7 Ga and 2.6–2.5 Ga, of which the former is considered as a major period of juvenile crustal growth in the NCC as evidenced by Nd and zircon Hf isotopic data, though the 2.8–2.7 Ga rocks are not widely exposed. The 2.6–2.5 Ga rocks make up ~80% of the Precambrian basement of the NCC and can be divided into high-grade gneiss complexes and low- to medium-grade granite-greenstone belts that are widespread over the whole NCC, seeming to support a notion that the cratonization of the NCC occurred at ~2.5 Ga. However, the 2.6–2.5 Ga rocks in the eastern and western parts of the NCC (Eastern and Western Blocks) are different from those similar-aged rocks in the central part (Trans-North China Orogen), with the former dominated by gneiss domes and metamorphosed at ~2.5 Ga, characterized by anticlockwise P–T paths involving isobaric cooling, reflecting an origin related to the underplating of mantle-derived magmas, whereas the latter, which are defined by strike-slip ductile shear zones, large-scale thrusting and folding, and transcurrent tectonics locally with sheath folds, were metamorphosed at ~1.85 Ga, characterized by clockwise P–T paths involving isothermal decompression, consistent with subduction and continent-continent collision settings. In addition, komatiites/komatiitic rocks are present in the granite-greenstone belts in the eastern and western parts of the NCC, but generally are absent in the central part. These differences imply that the 2.6–2.5 Ga basement rocks in the eastern and western parts of the NCC formed under different tectonic settings from those in the central part. Although both magmatic arc and mantle plume models can be used to explain the tectonic setting of the 2.6–2.5 Ga basement rocks in the eastern part of the NCC, a mantle plume model is favored as it can reasonably interpret: (1) the exceptionally large exposure of granitoid intrusions that formed over a short time period (2.55–2.50 Ga), without systematic age progression across a ~800 km wide block; (2) generation of komatiitic magmas with eruption temperatures as high as ~1650 °C; (3) dominant domal structures; (4) bimodal volcanic assemblages in the greenstone sequences; (5) affinities of mafic rocks to continental tholeiitic basalts; and (6) metamorphism with anticlockwise P–T paths involving isobaric cooling. In contrast, the 2.6–2.5 Ga high-grade gneiss terranes and low-grade granite-greenstone belts in the central part of the NCC exhibit the same structural and metamorphic characteristics as those of Paleoproterozoic lithological elements that typify active continental margin arcs and continent–continent collisional belts. Paleoproterozoic lithological assemblages in the NCC are mainly restricted to three Paleoproterozoic linear tectonic belts in the western, central and eastern parts of the NCC, which were, respectively, named the “Khondalite Belt (Fengzhen Belt/Inner Mongolia Suture Zone)”, “Trans-North China Orogen (Central Orogen Belt)” and “Jiao-Liao-Ji (Liaoji) Belt”. The three belts display some of the following lithotectonic elements that are classical indicators of subduction and collision tectonics in plate tectonic regimes: (1) arc-related juvenile crust; (2) linear structural belts defined by strike-slip ductile shear …