Geochemistry of metamorphosed volcanic rocks in the Neoarchean Qingyuan greenstone belt, North China Craton: Implications for geodynamic evolution and VMS mineralization
Geochemistry of metamorphosed volcanic rocks in the Neoarchean Qingyuan greenstone belt, North China Craton: Implications for geodynamic evolution and VMS mineralization
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华北克拉通新太古代庆元绿岩带变质火山岩地球化学：对地球动力学演化和VMS成矿的启示
DOI：
10.1016/j.precamres.2017.12.033
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发表时间：
2017-12
影响因子：
3.8
通讯作者：
Tong Xiaoxue
中科院分区：
文献类型：
--
作者：
Peng Zidong;Wang Changle;Zhang Lianchang;Zhu Mingtian;Tong Xiaoxue
清远绿岩带位于北中国克拉通东北段，是中国唯一既有条带状铁建造又有火山成因块状硫化物矿床的成矿省。青藏高原传统上被浑河断裂隔开的浑北地体和浑南地体划分为下石棚子组、红头山中段和南天门上组，经历了角闪岩-麻粒岩相变质作用。出露的表壳岩石由斜长角闪岩和黑云斜长片麻岩组成，并有少量的BIF、大理岩和片岩。本文对青藏高原变质的镁铁质火山岩和长英质火山岩(斜长角闪岩和黑云斜长片麻岩)进行了详细的野外和岩石学观察、岩石地球化学、U-Pb年代学和全岩Sm-Nd同位素分析，以探讨构造演化和伴生的VMS成矿作用。浑北和浑南地区的表壳岩石分别在2.57~2.53 Ga之间同步形成，并经历了2.52~2.48 Ga的区域变质作用。具体地说，石棚子组下部主要由具有负Nb异常的过渡拉斑玄武岩组成，这表明它们可能是由于地幔来源的部分熔融而产生的，而地幔来源之前被不同数量的板源流体或熔体所改变。相反，岩性组合向上为层间双峰火山岩(即N-MORB型拉斑玄武岩和过渡到钙碱性亲和力的FI-FII型英安岩)，代表了与俯冲有关的构造体制从挤压到伸展的变化。其中玄武岩具有一致的正初始ND组分(εND(T) = +2.7~+3.4)，进一步指示亏损地幔源区；英安岩具有负至正的初始ND值(εND(T) = −4.6~+3.0)，表明它们是由亏损镁铁质源区(可能是下镁铁质地壳)部分熔融形成的，并伴随着古老地壳物质的不同添加。值得注意的是，VMS矿床在成因上与这一伸展事件有关，并与FII型英安岩密切相关，这些英安岩是在高温条件下和地壳浅层(可能10-15 Km)熔融程度较高而产生的。总之，地球化学特征(如负Nb异常和εNd值)，再加上大陆地壳对拉斑玄武岩和这些火山岩继承的锆石的污染，暗示了QGb形成的陆弧环境。
The Qingyuan greenstone belt (QGB) situated in the northeastern section of the North China Craton (NCC) is considered to be the unique metallogenic province in China that hosts both banded iron formations (BIFs) and volcanogenic massive sulfide (VMS) deposits. Traditionally, the QGB is divided into the Hunbei and Hunnan terranes separated by the Hunhe fault and grouped into the lower Shipengzi, middle Hongtoushan, and upper Nantianmen formations, which have undergone amphibolite- to granulite-facies metamorphism. Exposed supracrustal rocks are composed of plagioclase amphibolite and biotite plagioclase gneiss with minor amounts of BIF, marble, and schist. In this study, detailed field and petrographic observations, lithogeochemical, U-Pb geochronological, as well as whole-rock Sm-Nd isotope analyses were conducted on the metamorphosed mafic and felsic volcanic rocks (i.e. plagioclase amphibolite and biotite plagioclase gneiss, respectively) in the QGB in order to discuss implications for tectonic evolution and comitant VMS mineralization.The supracrustal rocks of both Hunbei and Hunnan regions were formed synchronously from 2.57 to 2.53 Ga and then had undergone 2.52–2.48 Ga regional metamorphism. Specifically, the lower section of the Shipengzi Formation is composed dominantly of transitional-tholeiitic basalts with negative Nb anomalies, suggesting that they were likely generated by partial melting of a mantle source that was previously altered by variable amounts of slab-derived fluids or melts. In contrast, the lithologic assemblages grade upward into interlayered bimodal volcanic rocks (i.e. N-MORB-type tholeiitic basalts and FI- to FII-type dacites of transitional to calc-alkalic affinities), representing a change in tectonic regime related to subduction from compression to extension. Among them all the basalts are characterized by consistently positive initial Nd compositions (εNd(t) = +2.7 to +3.4) further indicate a depleted mantle source; whereas those dacites possess negative to positive initial Nd values (εNd(t) = −4.6 to +3.0), suggesting they were formed by partial melting of depleted mafic source (likely lower mafic crust) and accompanied with variable addition of old crustal material. Significantly, VMS deposits are genetically linked to this extensional event and closely associated with the FII-type dacites that were generated by higher melting degree at high-temperature conditions and shallow crustal level (likely 10–15 km). In all, geochemical features (e.g., negative Nb anomalies andεNdvalue), together with contamination from continental crusts for tholeiitic mafic rocks and inherited zircons from these volcanic rocks, imply a continental arc setting where the QGB was evolved.
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影响因子：
3.9
作者：
Cherniak, DJ;Hanchar, JM;Watson, EB
通讯作者：
Watson, EB
影响因子：
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作者：
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通讯作者：
GU Lian-xing
影响因子：
3.5
作者：
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通讯作者：
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影响因子：
3.8
作者：
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通讯作者：
Lianchang Zhang;M. Zhai;Xiaojing Zhang;Peng Xiang;Yanpei Dai;Changle Wang;F. Pirajno
影响因子：
6.1
作者：
Changle Wang;Hua Huang;Xiaoxue Tong;Mengtian Zheng;Zidong Peng;Jingbo Nan;Lianchang Zhang;M. Zhai
通讯作者：
Changle Wang;Hua Huang;Xiaoxue Tong;Mengtian Zheng;Zidong Peng;Jingbo Nan;Lianchang Zhang;M. Zhai