Early Permian plutons from the northern North China Block: constraints on continental arc evolution and convergent margin magmatism related to the Central Asian Orogenic Belt
Early Permian plutons from the northern North China Block: constraints on continental arc evolution and convergent margin magmatism related to the Central Asian Orogenic Belt
复制标题
DOI：
10.1007/s00531-008-0368-2
复制
发表时间：
2009-09
影响因子：
2.3
通讯作者：
Shuan‐Hong Zhang;Yue Zhao;A. Kröner;Xiao-Ming Liu;Liewen Xie;Fu Chen
中科院分区：
文献类型：
--
作者：
Shuan‐Hong Zhang;Yue Zhao;A. Kröner;Xiao-Ming Liu;Liewen Xie;Fu Chen
最近的锆石测年在北中国地块北缘的岩性组合中发现了几个晚石炭世至早二叠世的角闪辉长岩-石英闪长岩-花岗闪长岩-英云闪长岩-花岗岩组合，这些岩石组合以前被认为是太古代至古元古代。我们的年代学结果表明，晚石炭世至早二叠世，这些岩体的侵位是一个连续的过程，从324 Ma±16.6 Ma到274 Ma±9.6 Ma，至少持续了50 Ma。本文研究了该侵入杂岩中早二叠世辉长岩至花岗岩的成分。早二叠世深成岩具钙碱性或高钾钙碱性、偏铝质地球化学特征，二氧化硅含量变化较大。它们的REE配分模式无明显的Eu异常，在原始地幔归一化蜘蛛图中，Th、U、Nb、Ta、P、Ti亏损，而Ba、K、Pb、Sr富集，花岗岩体内的花岗岩体具I型和埃达克质地球化学特征。早二叠世岩石具有较低的全岩初始~(87)Sr/~(86)Sr比值(0.70520~0.70615)和负的全岩ε(T)值(−17.4~−9.3)和锆石εHf(T)值(−23.2~−10.5)。辉长岩具有较高的εND(T)值(−11.1~−9.3)和εHf(T)值(−16.5~−10.5)，花岗闪长岩的εND(T)值更低(−17.4)，锆石εHf(T)值更低(−23.2~−15.1)。地球化学、锶-钕和锆石Hf同位素组成表明，角闪辉长岩来自交代岩石圈地幔，闪长岩和石英闪长岩来自辉长岩岩浆，经分离结晶和古下地壳物质的差异同化作用而形成。花岗闪长岩可能是古下地壳部分熔融的产物，并与某些地幔成分有关。岩石圈地幔和古下地壳共同参与了早二叠世深成岩体的形成，表明北陆块北部壳幔相互作用强烈。岩石学组合、地球化学和锶-钕-氢同位素结果表明，早二叠世深成岩体是在古亚洲大洋板块向南俯冲到核壳之下时沿安第斯型活动大陆边缘侵位的。结合已发表的晚石炭世和晚二叠世至中三叠世侵入岩的资料，认为北缘大陆弧在晚古生代至少存在50 Ma，蒙古弧区与北缘大陆弧的最终融合可能发生在~270~~250 Ma之间，即晚二叠世至早三叠世。
Recent zircon dating identified several late Carboniferous to early Permian hornblende gabbro–diorite–quartz diorite–granodiorite–tonalite–granite plutons in lithological assemblages at the northern margin of the North China Block (NCB) that were previously regarded as Archaean to Palaeoproterozoic. Our geochronological results indicate that emplacement of these plutons was a continuous process during the late Carboniferous to early Permian, from 324 ± 6 to 274 ± 6 Ma, and lasted for at least 50 Ma. In this paper, the early Permian components with compositions from gabbro to granite within the intrusive complex were studied. The early Permian plutons exhibit calc-alkaline or high-K calc-alkaline, metaluminous geochemical features and highly variable SiO2contents. They have no significant Eu anomaly in their REE patterns, and in primitive-mantle-normalized spidergrams they display depletion in Th, U, Nb, Ta, P and Ti, and enrichment in Ba, K, Pb and Sr. The granitoid bodies within these plutons display I-type and adakitic geochemical signatures. The early Permian rocks exhibit low whole-rock initial87Sr/86Sr ratios from 0.70520 to 0.70615 and have negative whole-rockεNd(t) values ranging from −17.4 to −9.3 and zirconεHf(t)values of −23.2 to −10.5. The gabbros exhibit higherεNd(t) values from −11.1 to −9.3 andεHf(t) values from −16.5 to −10.5, and one granodiorite exhibits an even lowerεNd(t) value of −17.4 and zirconεHf(t) values of −23.2 to −15.1. Geochemical, Sr–Nd and in situ zircon Hf isotopic compositions suggest that the hornblende gabbros were derived from a metasomatized lithospheric mantle, and the diorite and quartz diorite were generated from a gabbroic magma by fractional crystallization, coupled with differential assimilation of ancient lower crustal material. The granodiorite was likely derived from partial melting of ancient lower crust with involvement of some mantle components. Involvement of both lithospheric mantle and ancient lower crust in the generation of the early Permian plutons indicates strong crust–mantle interaction in the northern NCB. Petrological associations as well as geochemical and Sr–Nd–Hf isotopic results show that the early Permian plutons were emplaced along an Andean-type active continental margin during southward subduction of the Palaeo-Asian oceanic plate beneath the NCB. Integration of our results with previously published data for late Carboniferous and late Permian to middle Triassic intrusions suggests that the continental arc on the northern margin of the NCB existed for at least 50 Ma during the late Palaeozoic, and final amalgamation of the Mongolian arc terranes with the northern NCB likely occurred during a period from ~270 to ~250 Ma, i.e, in the late Permian to earliest Triassic.