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Petrogenesis and tectonic regime of two types of Neoarchaean amphibolites in the northern margin of the North China Craton
International Geology Review ( IF 2.6 ) Pub Date : 2020-02-24 , DOI: 10.1080/00206814.2020.1731855
Xingan Wang 1 , Chad Deering 2 , Zhenghong Liu 3 , Xiaojie Dong 3 , Shichao Li 3 , Zhongyuan Xu 3
Affiliation  

ABSTRACT

The Neoarchaean crustal evolutionary processes of the North China Craton (NCC) provide a window to understanding the crust–mantle interaction in the Early Earth. The Jiefangyingzi amphibolites are located in the Bainaimiao arc belt, along the northern margin of the NCC. LA–ICP–MS U–Pb isotopic data reveal that the Type 1 amphibolites were formed at ~2562 Ma, and the Type 2 amphibolites were formed at ~2504 Ma, but were subsequently subjected to metamorphism at ~1889 Ma. Lu–Hf isotopic data of the Type 1 amphibolite show positive εHf(t) values (+1.2–+6.0) and TDM from 2612 Ma to 2791 Ma, suggesting a significant episode of 2.6–2.8 Ga crustal growth within the study area. Geochemically, the Type 1 amphibolites show high SiO2 contents (53.37%–55.19%), moderate LREE–enriched patterns (La/Sm)N = 2.42–3.15 and HREE–depleted patterns (Gd/Yb)N = 1.86–2.64, with negative Nb anomalies, which are similar to IAB–like rocks, suggesting that they were derived from partial melting of arc–related depleted mantle with intense subduction–related fluids metasomatism. The Type 2 amphibolites have lower SiO2 contents from 44.28% to 50.77%, and show LREE–depleted REE patterns ((La/Sm)N = 0.67–1.02), nearly unfractionated HREE patterns ((Gd/Yb)N = 0.89–1.77), with negative Nb, Th and positive Sr, Zr anomalies, which are close to N–MORB–like rocks, indicating that they were generated from partial melting of depleted mantle with slight fluid metasomatism. The geochronological, Lu–Hf isotopic and geochemical features show that the IAB–like rocks were formed in an intra–oceanic arc environment, coincide with the significant ~2.5–2.6 Ga episode of crustal growth in the NCC; The slightly younger MORB–like rocks reflect the spreading of the oceanic crust might last until ~2.5 Ga in the central zone.



中文翻译:

华北克拉通北缘两种新古生界角闪岩的成因与构造机制

摘要

华北克拉通(NCC)的新古生界地壳演化过程为了解早期地球的地幔相互作用提供了一个窗口。解放营子角闪石位于北新庙北缘的白乃庙弧带中。LA–ICP–MS U–Pb同位素数据表明,第1型闪石在〜2562 Ma形成,第2型闪石在〜2504 Ma形成,但随后在〜1889 Ma发生了变质作用。路-铪ε1型闪显示阳性的同位素数据的Hf(t)值(+ 1.2〜+ 6.0)和T DM从2612到马2791麻,提示2.6-2.8嘎地壳生长的研究区域内的显著插曲。从地球化学角度来看,类型1的闪石显示出较高的SiO 2含量(53.37%–55.19%),中等的LREE富集模式(La / Sm)N  = 2.42–3.15和HREE富集的模式(Gd / Yb)N  = 1.86–2.64,且Nb异常为负,与IAB相似像岩石一样,表明它们源自与弧相关的地幔的部分融化,以及与俯冲相关的强烈的流体交代作用。2型闪石具有较低的SiO 2含量,从44.28%降至50.77%,并且显示出LREE耗尽的REE模式((La / Sm)N  = 0.67–1.02),几乎没有碎裂的HREE模式((Gd / Yb)N = 0.89–1.77),Nb,Th负值和Sr,Zr负值异常,接近于N–MORB类岩石,表明它们是由贫化的地幔部分融化而形成的,具有轻微的流体交代作用。地质年代学,Lu-Hf同位素和地球化学特征表明,IAB样岩石形成于大洋内部弧形环境中,与NCC地壳生长的显着〜2.5-2.6 Ga相吻合。稍年轻的MORB状岩石反映了地壳的扩散可能会持续到中部地区〜2.5 Ga。

更新日期:2020-02-24
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