Late Neoarchean crustal growth under paired continental arc-back arc system in the North China Craton
Late Neoarchean crustal growth under paired continental arc-back arc system in the North China Craton
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华北克拉通成对大陆弧背弧系统下新太古代晚期地壳生长
DOI：
10.1016/j.gsf.2020.12.003
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发表时间：
2021-05
影响因子：
8.9
通讯作者：
Lishuang Guo
中科院分区：
文献类型：
--
作者：
Xin He;Wei Wang;M. Santosh;Jiachen Yao;Kangting Gao;Yuhan Zhang;Denggang Lu;Lishuang Guo
晚太古代(~3.02.5 Ga)是全球大陆生长的关键时期，被广泛认为反映了强烈的板块构造活动的开始，尽管相关的大陆生长模式仍然存在争议。本文研究了中国克拉通北部胶北地体西南栖霞地区的一套晚太古代变质火山岩。该套岩石包括角闪岩、单斜辉石斜长角闪岩和角闪斜长片麻岩。我们给出的锆石U-Pb同位素数据表明，这些岩石的原岩形成于~2549-2511 Ma。(单斜辉石)角闪岩对应于变质玄武岩，其中一些含有高模式的钛铁矿。这些岩石具有中等到高的FeOT值(8.9613.62wt.%)和TiO2值(0.59wt.%)，稀土配分模式平缓到较少分馏，Th、Nb和Ta呈轻度负异常，类似于铁拉斑玄武岩。此外，它们还显示出正的锆石ƐHf(T)值(+2.6到+8.7)，没有地壳污染或分离结晶。结合低Nb/Yb(主要为~lt；1.60)和(Hf/Sm)N(主要为<；0.95)，低至中Th/Yb(0.08-0.54)和低V/Sc(5.53-9.19)比值，这些玄武岩被解释为来自相对减少和亏损的地幔源区，并被水化流体温和交代。角闪斜长片麻岩为变质安山岩，与玄武岩呈夹层状产出。它们是拉斑玄武岩系列和钙碱性岩系之间的过渡，稀土元素分馏模式，Th、Nb、Ta明显负异常。亏损锆石ƐHf(T)值(+2.4~+8.4Hf(T))和定量化学模拟表明，安山质岩石很可能是年轻的长英质岩浆与拉斑玄武岩岩浆的注入和混合形成的。总的来说，本区晚太古代变质玄武岩的化学特征和成因与马里亚纳弧后盆地玄武岩相似。结合区域地质资料，提出胶北地体在成对的大陆弧-弧后背景下经历了新太古代晚期地壳生长。在区域背景下，我们提出了新太古代晚期横跨北中国克拉通(特别是东部地块)的两种不同的地球动力学模式，即(1)沿东部地块西北部的弧陆增生；(2)东南部围绕~3.8~2.7 Ga陆核的成对大陆弧-弧后系统。
The late Archean (~3.0–2.5 Ga) was a key period of continental growth globally, which is widely considered to reflect the onset of vigorous plate tectonic activity, although related continental growth modes remain contentious. Here we investigate a suite of late Neoarchean metavolcanic rocks from the southwest Qixia area of the Jiaobei terrane in the North China Craton. The rocks in this suite include amphibolites, clinopyroxene amphibolites, and hornblende plagioclase gneisses. We present zircon U-Pb isotopic data which indicate that the protoliths of these rocks formed during ~2549–2511 Ma.The (clinopyroxene) amphibolites correspond to meta-basaltic rocks, with some containing high modal content of titanite. These rocks show moderate to high FeOT(8.96–13.62 wt.%) and TiO2(0.59–1.59 wt.%), flat to less fractionated REE patterns, and mildly negative Th, Nb, and Ta anomalies, resembling those of Fe-tholeiites. In addition, they display positive zirconƐHf(t) values (+2.6 to +8.7), and are devoid of crustal contamination or fractional crystallization. Combined with the low Nb/Yb (mostly < 1.60) and (Hf/Sm)N(mostly < 0.95), low to moderate Th/Yb (0.08–0.54), and low V/Sc (5.53–9.19) ratios, these basaltic rocks are interpreted to have been derived from a relatively reduced and depleted mantle source that was mildly metasomatized by hydrous fluids. The hornblende plagioclase gneisses are meta-andesitic rocks, and occur interlayered with the basaltic rocks. They are transitional between tholeiitic and calc-alkaline rock series, and show fractionated REE patterns with evidently negative Th, Nb, and Ta anomalies. The depleted zirconƐHf(t) values (+2.4 to +8.4) and quantitative chemical modeling suggest that the andesitic rocks were most likely generated by injection and mixing of juvenile felsic magmas with the tholeiitic basaltic magmas.In general, the chemical features and genesis of late Neoarchean meta-basaltic rocks in our study area resemble those of Mariana back-arc basin basalts. Combined with regional geological data, it is proposed that the Jiaobei terrane witnessed late Neoarchean crustal growth under a paired continental arc-back arc setting. On a regional context, we propose two distinct geodynamic mode of late Neoarchean continental growth across North China Craton (particularly the Eastern Block), i.e., (1) arc-continent accretion along northwestern part of the Eastern Block; and (2) paired continental arc-back arc system surrounding the ~3.8–2.7 Ga continental nuclei to the southeast.
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