标题：A Neoarchean arc-backarc pair in the Linshan Massif, southern North China Craton
作者：Deng H.; Kusky T.; Polat A.; Fu H.; Wang L.; Wang J.; Wang S.; Zhai W.
作者机构：[Deng, H] State Key Laboratory of Geological Processes and Mineral Resources, Center for Global Tectonics, School of Earth Sciences, China University 更多
通讯作者地址：[Deng, H] State Key Laboratory of Geological Processes and Mineral Resources, Center for Global Tectonics, School of Earth Sciences, China University 更多
关键词：Arc-backarc; Archean tectonics; Central Orogenic Belt; Linshan Massif; North China Craton
摘要：The Linshan Massif is located in the southern North China Craton (NCC) and consists mainly of tonalitic (TTG) and dioritic gneisses, and a volcano-sedimentary-dominated assemblage, all of which were intruded by post-collisional potassic granites. The volcano-sedimentary-dominated assemblage is composed mostly of deformed and foliated basaltic amphibolite and meta-sedimentary rocks, with minor interlaying meta-gabbros, forming a stack of tectonically imbricated sedimentary and volcanic rocks. The TTG gneisses formed at 2.6–2.52 Ga, and the meta-gabbros, basaltic amphibolites and diorites formed at 2.51–2.50 Ga. They underwent subsequent metamorphism at 2.49–2.48 Ga. Furthermore, all their igneous zircons possess large positive εHf (t) values (+2.9 to +7.4). The basaltic amphibolites can be divided into two groups: depleted basalts and enriched basalts. Depleted basalts are characterized by flat LREE patterns and low Th/Nb ratios with positive Nb anomalies, similar to N-MORB-type patterns. Enriched basalts display LREE-enriched patterns with high Th/Nb ratios and pronounced negative Nb anomalies, showing an arc-related affinity. The meta-gabbros have LREE-enriched patterns with negative Nb and Zr anomalies, consistent with subduction-related signatures. Considering mixed arc- and MORB- signatures with positive zircon εHf(t) values, we propose that the meta-gabbros and basaltic amphibolites may have formed in a back-arc setting. The tonalites and the diorites showing LREE-enriched patterns and depleted in HFSEs are interpreted to represent arc-related magmatism. Combined with the documented 2.55 Ga Dengfeng fore-arc accretionary complex, we propose the following geodynamic evolution model for the Southern NCC: (1) at 2.6–2.54 Ga, a TTG-dominated oceanic arc developed above a west-dipping subduction zone, forming the 2.55 Ga Dengfeng accretionary complex and related tectonic units; (2) at 2.52–2.50 Ga, slab rollback subsequently drove back-arc rifting of the mature TTG-dominated intra-oceanic arc, resulting in the formation of two arc segments with the intervening Linshan back-arc basin; and (3) at 2.50–2.48 Ga, the TTG-dominated arc collided with the Eastern Block resulting in the closure of the back-arc basin and formation of the accreted arc-back-arc package in the Linshan Massif. We suggest that the Neoarchean Central Orogenic Belt in the southern NCC contains at least two amalgamated oceanic arc terranes, separated by a belt of back-arc basin magmatic rocks caught within an intra-oceanic mélange/suture zone. © 2020 Elsevier B.V.