华北克拉通怀安杂岩新太古代和古元古代富铝变质表壳岩的地球化学特征及构造意义
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本文为中国地质调查局项目(编号DD20160042、DD20190035)和地质调查标准化与标准制修订项目(编号DD20190472)资助成果。


Geochemistry of the Neoarchean and Paleoproterozoic Alrich metamorphic supracrustal rocks in the Huai’an complex, North China craton and its tectonic significances
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    摘要:

    晋冀蒙三省交界地区富铝变质表壳岩的时代归属及形成的构造背景长期存在争议。通过天镇地区1∶5万区域地质调查,在怀安杂岩中识别出两期富铝变质表壳岩组合,分别为新太古代榴云片麻岩岩组和古元古代黄土窑岩组,两者在岩石组合、特征矿物组合、含矿性、同位素年龄以及岩石地球化学特征等方面存在明显区别,为不同沉积环境的产物。新太古代榴云片麻岩岩组野外呈带状、似层状或透镜状产出,以石榴黑云斜长片麻岩为主体,含少量斜长变粒岩,局部与BIF共生,矿物组合为石榴子石+黑云母+斜长石+石英±条纹长石±夕线石。岩石地球化学研究表明石榴黑云斜长片麻岩样品富Na2O、Al2O3和CaO,低K2O,属于过铝质岩石,铕异常不明显,轻重稀土元素分异相对较强((La/Yb)N=3. 69~27. 76)。古元古代黄土窑岩组以构造岩片形式产出,为一套孔兹岩系组合,产出石墨矿。其中变泥砂质岩石的矿物组合为石墨+夕线石+石榴子石+条纹长石+斜长石+石英,为过铝质,富Al2O3和K2O,低Na2O和CaO,负铕异常明显(δEu=0. 47~0. 80),轻重稀土元素分异弱((La/Yb)N=3. 37~10. 58)。两套富铝变质表壳岩具有相似的微量元素蛛网图特征,富集大离子亲石元素如Rb和Ba,高场强元素如Zr、Hf含量相对较低,明显亏损Nb、Ta、P和Ti等元素。石榴黑云斜长片麻岩中碎屑锆石年龄峰值为~2. 45Ga,黄土窑岩组中岩石碎屑锆石年龄主要介于1. 99~2. 30Ga,两套岩石均遭受古元古代末期(1. 81~1. 85Ga)麻粒岩相变质深熔作用叠加改造。新太古代榴云片麻岩岩组的原岩为一套含黏土质杂砂岩建造,成熟度较低,来源于英云闪长岩花岗闪长岩风化源区,形成于大陆岛弧环境。黄土窑岩组孔兹岩系原岩为一套富铝黏土岩和杂砂岩建造,夹少量碳酸盐岩和石英砂岩,沉积物源以古元古代中期(2. 3~2. 0Ga)上地壳长英质成分为主,可能形成于相对稳定的大陆边缘环境。怀安杂岩中两期富铝变质表壳岩组合均卷入了古元古代末期的造山作用,两者的厘定为研究华北克拉通北部新太古代—古元古代大陆地壳演化及构造格局恢复具有重要地质意义。

    Abstract:

    The age and tectonic setting of the Al- rich metamorphic supracrustal rocks at the border of Shanxi, Hebei provinces and Inner Mongolia autonomous region has long been controversial. Based on the 1∶50000 regional geological survey in the Tianzhen area, two- stage Al- rich metamorphic supracrustal rocks have been identified in the Huai’an complex: Neoarchean garnet- biotite- plagiogneiss Formation- complex (GBPF) and Paleoproterozoic Huangtuyao Formation- complex (HTYF), respectively. These two Al- rich metamorphic supracrustal rocks are different in rock association, mineral assemblage, ore potentiality, isotopic age and geochemistry, indicating that they formed in the different depositional environments. The Neoarchean GBPF occurs in banded sheets, interlayers and lenticular in the field, and are mainly composed of garnet biotite plagiogneiss with a small amount of plagioclase leptynite,locally associated with banded iron formation (BIF). The mineral assemblage of GBPF is garnet+biotite+plagioclase+quartz±perthite±sillimanite. Geochemical analyses reveal that the garnet biotite plagiogneiss samples are peraluminous with the enrichment of Na2O, Al2O3 and CaO, low K2O, displaying weak Eu anomalies and relatively strong fractionation ((La/Yb)N=3. 69~27. 76). The Paleoproterozoic HTYF presents ribbon- like tectonic slices, which is a suite of khondalite series and occurs in graphite ore. The mineral assemblage of meta- pelite/sandstone in the HTYF is graphite+sillimanite+garnet+perthite+plagioclase+quartz. They are peraluminous with enrichment in Al2O3 and K2O, lower Na2O and CaO contents, and obvious negative Eu anomalies (δEu=0. 47~0. 80) and weak fractionation ((La/Yb)N=3. 37~10. 58). Two sets of Al- rich metamorphic supracrustal rocks have the similar characteristics of trace element in the spider diagrams, which show the enrichment of large ion lithophile elements such as Rb and Ba, low contents of high field strength elements such as Zr and Hf, and obvious depletion of Nb, Ta, P and Ti. The peak age of detrital zircons in the GBPF is at ~2. 45 Ga and the ages of detrital zircons in the HTYF are mainly around 1. 99~2. 3 Ga, suggesting that both sets of rocks have experienced granulite facies metamorphism- anatexis at late Paleoproterozoic (1. 81~1. 85 Ga). The protoliths of the Neoarchean GBPF were clay- bearing graywacke with low maturity, which probably derived from the weathered tonalite- granodiorite that formed in a continental island arc environment. The protoliths of HTYF were Al- rich claystone and graywacke with a small amount of carbonatite and quartz sandstone. The main sedimentary sources are mid- Paleoproterozoic (2. 3~2. 0 Ga) uppercrust felsic materials and the khondalite series may form in the relatively stable continental marginal environment. Two periods of Al- rich metamorphic supracrustal rocks in the Huai’an complex were involved in the Paleoproterozoic orogeny, and determination of the both is of important geological significance for studying the continental crustal evolution and tectonic framework reconstruction of the Neoarchean- Paleoproterozoic in the northern part of the North China Craton.

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张家辉,王惠初,田辉,任云伟,施建荣,常青松,相振群,初航,王家松.2019.华北克拉通怀安杂岩新太古代和古元古代富铝变质表壳岩的地球化学特征及构造意义[J].地质学报,93(7):1618-1638.
ZHANG Jiahui, WANG Huichu, TIAN Hui, REN Yunwei, SHI Jianrong, CHANG Qingsong, XIANG Zhenqun, CHU Hang, WANG Jiasong.2019. Geochemistry of the Neoarchean and Paleoproterozoic Alrich metamorphic supracrustal rocks in the Huai’an complex, North China craton and its tectonic significances[J]. Acta Geologica Sinica,93(7):1618-1638.

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  • 收稿日期:2019-01-30
  • 最后修改日期:2019-04-21
  • 录用日期:2019-04-25
  • 在线发布日期: 2019-05-07