Paleoproterozoic granulites from the Xinghe graphite mine, North China Craton: Geology, zircon U–Pb geochronology and implications for the timing of deformation, mineralization and metamorphism
Paleoproterozoic granulites from the Xinghe graphite mine, North China Craton: Geology, zircon U–Pb geochronology and implications for the timing of deformation, mineralization and metamorphism
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DOI：
10.1016/j.oregeorev.2014.03.014
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发表时间：
2014-12
影响因子：
3.3
通讯作者：
Huatian Zhang;M. Zhai;M. Santosh;Haozheng Wang;Lei Zhao;Zhiyao Ni
中科院分区：
文献类型：
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作者：
Huatian Zhang;M. Zhai;M. Santosh;Haozheng Wang;Lei Zhao;Zhiyao Ni
兴河石墨存款矿床位于华北地区中北部，主要岩石类型为太古宙灰色片麻岩、变沉积岩（孔兹岩）和镁铁质（高压）麻粒岩。在这项研究中，我们报告了兴和石墨矿周围详细的地质和构造测绘结果。我们识别出三个变形阶段（D1-D3），石墨矿化与D1或D1和D2之间的相关性。变形的第一阶段由无根的叶内褶皱代表，其轴向表面穿过D2的区域性穿透片麻质（S2），在约200 ℃时被限制。1.95- 1.90Ga的镁铁质高压麻粒岩锆石U-Pb年龄。第二阶段变形表现为致密褶皱，形成区域性穿透面理和强烈的韧性剪切作用，石榴子石破碎为斜长石+辉石。该阶段的年龄为约1.85 Ga，从U-Pb分析的混合片麻岩的浅色体中的锆石。第三阶段的变形以大规模褶皱为代表，其形成时间可能在1.85 ~ 1.80Ga之间。1.80切过寄主变质沉积物的未变形伟晶岩的Ga侵位年龄。在高压麻粒岩变质作用之前，大量的钙。2.15- 2.0Ga花岗岩侵位于孔兹岩中。石墨化滞后于这些花岗岩的侵位推断从变质花岗岩中的石墨的存在。在约400年侵入孔兹岩的基性高压麻粒岩脉的原岩。2.0 Ga在1.95-1.90 Ga时也发生了变质作用，是已开采石墨矿体的一部分。因此，我们将石墨矿化的时间限制在ca. 1.95和1.85 Ga.地质和年代学资料表明，兴和石墨矿各岩石单元均经历了高压麻粒岩相变质作用。1.95-1.90 Ga。
The Xinghe graphite deposit is located in the north-central part of the North China Craton (NCC) where Archean gray gneiss, metasedimentary rocks (khondalites) and mafic (high-pressure) granulites constitute the dominant rock types. In this study, we report results of detailed geological and structural mapping around the Xinghe graphite mine. We identify three stages of deformation (D1–D3) and the graphite mineralization is correlated with D1or between D1and D2. The first stage of deformation represented by rootless intrafolial folds whose axial surface cuts across the regional penetrative gneissosity (S2) of D2, was constrained at ca. 1.95–1.90 Ga by U–Pb age of zircon grains from a mafic high-pressure granulite. The second stage of deformation is represented by tight folds with formation of regional penetrative foliation and strong ductile shearing, when garnet broke down to plagioclase + pyroxene. This stage is dated as ca 1.85 Ga, from U–Pb analysis of zircons in leucosome from a migmatitic gneiss. The third stage of deformation is represented by large scale folding, which probably formed between 1.85 and 1.80 Ga, as constrained from the ca. 1.80 Ga emplacement age of an undeformed pegmatite that cuts across the host metasediments. Prior to the high-pressure granulite metamorphism, voluminous ca. 2.15–2.0 Ga granites were emplaced within the khondalites. The graphitization postdates the emplacement of these granites as deduced from the presence of flaky graphites in the metagranites. The protolith of the mafic high-pressure granulite dike that intruded the khondalite at ca. 2.0 Ga was also metamorphosed at 1.95–1.90 Ga, and is part of the exploited graphite ore body. We therefore constrain the timing of graphite mineralization to be between ca. 1.95 and 1.85 Ga. Our geological and geochronological data indicate that all the rock units in the Xinghe graphite mine were subjected to high-pressure granulite facies metamorphism at ca. 1.95–1.90 Ga.