Geochemistry of meta-sedimentary rocks associated with the Neoarchean Dagushan BIF in the Anshan-Benxi area, North China Craton: Implications for their provenance and tectonic setting
Geochemistry of meta-sedimentary rocks associated with the Neoarchean Dagushan BIF in the Anshan-Benxi area, North China Craton: Implications for their provenance and tectonic setting
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华北克拉通鞍山-本溪地区新太古代大孤山BIF相关变质沉积岩地球化学及其物源和构造环境的意义
DOI：
10.1016/j.precamres.2019.02.022
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发表时间：
2019
影响因子：
3.8
通讯作者：
Zhai Mingguo
中科院分区：
文献类型：
--
作者：
Tong Xiaoxue;Wang Changle;Peng Zidong;Huang Hua;Zhang Lianchang;Zhai Mingguo
安本地区位于华北陆块的东北部，以新太古代表壳岩和岩体为主，其次为早太古代至中太古代。这些表壳岩最初被认为是在活动大陆边缘的不同地点同时形成的（约2.5 Ga）。近年来，通过岩石学、地球化学和年代学等方面的研究，认为本溪地区的表壳岩（2.56- 2.53Ga）比鞍山地区的表壳岩（2.53- 2.51Ga）稍老，进一步表明它们分别形成于弧后盆地的开启和闭合时期。而鞍山地区的大孤山条带状含铁建造及其伴生的表壳岩则被解释为中太古代沉积在大孤山地区详细野外调查的基础上，对大孤山地区表壳岩的锆石U-Pb-Hf同位素组成进行了研究，并对大孤山地区表壳岩的锆石U-Pb-Hf同位素组成进行了分析，结果表明，大孤山地区表壳岩的锆石U-Pb-Hf同位素组成为：一套变质沉积岩（即，变质砂岩、变质页岩和高铁变质页岩），以提供对其沉积年龄、物源和构造背景的约束。大孤山地区变砂岩中最年轻的一组碎屑锆石U-Pb加权平均年龄，结合鞍本地区最大变质年龄为2.51 Ga，表明大孤山BIF的沉积时代为2.53 ~ 2.51 Ga。Al 2 O3/TiO 2、Th/Zr值和稀土元素模式等地球化学特征表明，变质砂屑岩和变质页岩主要来自长英质火成岩，而高铁变质页岩主要来自镁铁质岩。变砂岩中碎屑锆石U-Pb年龄谱图进一步表明，本溪地区的主要烃源岩可能是同时代的火山岩。锆石Hf同位素结合其他已发表的鞍山-本溪地区新太古代表壳岩锆石Hf同位素数据表明，主要的年轻地壳生长和改造事件分别发生在2.9- 2.7Ga和2.5Ga。大孤山变质沉积岩可能形成于古大陆边缘的弧后盆地。
The Anshan-Benxi area is situated in the northeastern part of the North China Craton (NCC) and consists predominantly of Neoarchean supracrustal rocks and plutons with minor Eoarchean to Mesoarchean rocks. These supracrustal rocks were originally considered to be formed synchronously (∼2.5 Ga) at different localities on an active continental margin. Recently, more detailed petrographic, geochemical, and geochronological analyses showed that the supracrustal strata in the Benxi area (2.56–2.53 Ga) were slightly older than those in the Anshan area (2.53–2.51 Ga), which further indicates that they were formed during opening and closure of the back-arc basin, respectively. However, the Dagushan banded iron formation (BIF) and associated supracrustal rocks in the Anshan area were interpreted to be deposited in Mesoarchean (∼3.10 Ga), which constructs a clear contrast with other supracrustal rocks in the Anshan-Benxi area and renders previous tectonic models controversial.On the basis of detailed field investigations in the Dagushan area, we presentin situzircon U-Pb-Hf isotopic, whole-rock geochemical and Sm-Nd isotopic data of a suite of meta-sedimentary rocks (i.e., meta-arenites, meta-shales, and high-Fe meta-shales), in order to provide constraints on their depositional age, provenance, and tectonic setting. The weighted mean U-Pb ages of the youngest group of detrital zircons for the meta-arenite in the Dagushan area, coupled with the maximum metamorphic age of ∼2.51 Ga in the Anshan-Benxi area, suggest that the Dagushan BIF was deposited between 2.53 and 2.51 Ga. Geochemical features such as the Al2O3/TiO2and Th/Zr values, and REE patterns suggest that the meta-arenites and meta-shales were mainly derived from felsic igneous sources, whereas the high-Fe meta-shales were predominantly sourced from mafic rocks. The U-Pb age spectrum diagram of detrital zircons within meta-arenites further indicates that the dominant source rocks may be the coeval volcanic rocks in the Benxi area. Our zircon Hf isotopes, coupled with other previously published zircon Hf isotopic data from Neoarchean supracrustal rocks in the Anshan-Benxi area, suggest that major juvenile crustal growth and reworking events occurred at 2.9–2.7 Ga and ∼2.5 Ga, respectively. In all, the Dagushan meta-sedimentary rocks were probably deposited in a back-arc basin on the ancient continental margin.