Late Neoarchean crustal growth under paired continental arc-back arc system in the North China Craton

• 作者: Xin He Wei Wang M.Santosh Jiachen Yao Kangting Gao Yuhan Zhang Denggang Lu Lishuang Guo
• 来源期刊: 地学前缘（英文版）
• 年，卷（期）: 2021,（3）
• 所属期刊栏目: Research Paper
• 页码范围: 437-457
• 页数: 21页
• 语种: 英文

摘要

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 conten-tious. 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 amphibo-lites, 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 frac-tionated REE patterns, and mildly negative Th, Nb, and Ta anomalies, resembling those of Fe-tholeiites. In addi-tion, they display positive zircon?Hf(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 zircon?Hf(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 juve-nile 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.