Redefinition and Significance of Metamorphism Xilinhot Group in Xilinhot Area, Inner Mongolia, China
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摘要: 通过大比例尺填图和剖面研究, 将内蒙古锡林浩特地区的"锡林郭勒杂岩"解体分为3大部分: 一套表壳岩、晚元古代基性-超基性侵入岩和早古生代酸性侵入岩.在此基础上根据变质岩的岩性组合和变形变质特点, 可将其中的表壳岩化分为4个岩性段: 黑云(石榴石)斜长片麻岩, 间夹多层条纹状斜长角闪岩, 在其顶部多见薄层含磁铁石英岩; 中粗粒黑云斜长片麻岩和细粒长英质片麻岩; 混合岩化条带状黑云(角闪)斜长片麻岩, 含石榴石黑云二长片麻岩夹条纹状斜长角闪岩组合; 夕线石黑云斜长片麻岩, 条纹状黑云斜长片麻岩, 间夹含石榴石黑云母石英片岩.通过对比区域内宝音图群、艾勒格庙组、白乃庙群等古老地块的岩石组合, 发现在原岩建造、变质级别、沉积环境等特征上均有区别, 应将这套表壳岩单独厘定为锡林浩特岩群, 它们组成了锡林郭勒微陆块前寒武变质基底岩系, 其地质特征的研究对锡林郭勒微陆块基底的形成和演化及华北板块与西伯利亚板块的构造关系演化有重要意义.Abstract: Based on large scale geologic mapping and measuring section, the Xilin Gol complex is divided into three parts: supracrustal rock, Late Proterozoic basic-ultrabasic rock and Early Paleozoic acid intrusive rocks. According to lithologic association and characteristics of deformation and metamorphism, biotite (garnet) plagioclase gneiss intercalated with several layers barred amphibolite, with thin layer magnetite quartzite on its top; medium-coarse biotite plagioclase gneiss and fine-grained felsic gneiss; lithologic association of migmatization banding biotite (hornblende) plagioclase gneiss and garnet monzonitic gneiss intercalated with barred amphibolite; sillimanite biotite plagioclase gneiss, barred biotite plagioclase gneiss, intercalated with garnet bearing biotite quartz schist. Comparison study on the different lithologic association, metamorphic characteristics and depositional environment of Baoyintu Group, Ailegemiao Formatio, Bainaimiao Group and others. This paper proposes to redefine these supercrustal rocks named "Xilinhot Group", which compose the Precambrian metamorphic basement of Xilin Gol micro block. It's important to study the formation and development of Xilin Gol micro block and the evolution of structural relationship between Siberia plate and North China plate.
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Key words:
- Xilinhot Group /
- metamorphic basement /
- Xilin Gol complex /
- Xilin Gol micro block /
- petrology
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图 1 内蒙古自治区锡林浩特市锡林浩特岩群(Pt2XL1-4)分布
1.中新生代火山岩;2.奥陶系包尔汉图群;3.志留系徐尼乌苏组;4.锡林浩特岩群;5.锡林浩特岩群第一岩组;6.锡林浩特岩群第二岩组;7.锡林浩特岩群第三岩组;8.锡林浩特岩群第四岩组;9.早石炭世辉长岩;10.早石炭世花岗闪长岩;11.早石炭世二长花岗岩;12.奥陶世S型片麻状电气石二云母花岗岩;13.新元古代角闪辉石岩;14.新元古代变辉长岩;15.磁铁石英岩标志层;16.斜长角闪岩标志层;17.同位素采样位置及年龄值;18.剖面起始位置
Fig. 1. Geological map of Xilinhot Group (Pt2XL1-4) near Xilinhot City, Inner Mongolia
图 2 内蒙古自治区锡林浩特市1167-1227高地锡林浩特岩群(Pt2XL1-4)地层实测剖面
1.含砾砂土;2.黑云斜长片麻岩;3.黑云母片麻岩;4.黑云母二长片麻岩;5.二云母片麻岩;6.二长片麻岩;7.矽线石片麻岩;8.石榴子石黑云斜长片麻岩;9.混合岩化片麻岩;10.混合岩化黑云母斜长片麻岩;11.含矽线石混合岩化黑云母斜长片麻岩;12.斜长角闪岩;13.角闪岩;14.石榴石片岩;15.磁铁石英岩;16.碎裂岩化;17.绿泥石化;18.伟晶岩脉;19.二长花岗岩脉;20.斜长角闪岩脉;21.闪长岩脉;22.产状;图中数字为层号
Fig. 2. Stratagraphic section of Xilinhot Group (Pt2XL1-4) near 1167-1227 high place Xilinhot City, Inner Mongolia
表 1 内蒙古锡林浩特地区变质辉长岩的锆石SHRIMP分析结果
Table 1. Zircon SHRIMP age of the Metagabbro in Xilinhot area, Inner Mongolia
点号 U (10-6) Th (10-6) 232Th/ 238U 206Pb* (10-6) 206Pbc (%) 206Pb/238U年龄(Ma) 207Pb*/ 206Pb* ±% 207Pb*/ 235U ±% 206Pb*/ 238U ±% 1 721 303 0.43 84.10 0.10 820 ±20 0.08416 10 1.574 2.8 0.1356 2.6 2 569 40 0.07 59.10 0.39 733 ±24 0.0679 3.3 1.127 4.7 0.1204 3.4 3 34 14 0.44 6.50 5.83 1229 ±45 0.086 26 2.5 26 0.21 4 4 792 153 0.2 83.60 0.40 744 ±18 0.117 1.7 1.974 3.1 0.1223 2.6 5 186 241 1.33 7.74 2.97 295.3 ±8.9 0.047 24 0.301 24 0.0469 3.1 6 175 154 0.91 7.37 4.24 295.7 ±9.9 0.062 27 0.4 27 0.0469 3.4 7 239 164 0.71 8.33 2.00 251.5 ±7.6 0.054 21 0.298 22 0.0398 3.1 8 386 438 1.17 85.90 0.50 1478 ±34 0.1423 1.1 5.05 2.8 0.2576 2.6 9 225 221 1.01 8.41 6.29 257.9 ±8.2 0.037 41 0.208 41 0.0408 3.2 10 159 112 0.73 10.10 4.15 439 ±15 0.044 31 0.42 31 0.0704 3.6 11 290 61 0.22 29.60 1.08 718 ±18 0.0729 5.9 1.184 6.5 0.1178 2.7 12 353 147 0.43 38.40 0.73 763 ±19 0.0722 3.1 1.251 4 0.1256 2.6 13 199 152 0.79 6.48 2.19 234.5 ±7.2 0.053 22 0.269 23 0.037 3.1 注:206Pb*为放射性成因铅;206Pbc为普通铅;数据均经204Pb校正. 表 2 锡林浩特岩群及其邻区元古代地层划分对比
Table 2. The classification and division about Xilinhot Group and other Proterozoic formations in Xilinhot area
地层单元 艾勒格庙组 白乃庙群 白银都西群 宝音图群 锡林浩特岩群 岩石组合特征 白色大理岩、结晶灰岩、石英片岩、变质石英粉砂岩、板岩夹凝灰岩及流纹岩的一套中浅变质岩石组合 下部为斜长角闪片岩、阳起斜长片岩和绿泥斜长片岩段,中部为长英片岩和变质流纹英安岩段, 上部阳起斜长片岩, 变质安山质熔岩和绿泥斜长片岩段 以长英质变粒岩类、云母质片岩类和角闪质岩石为主的岩石组合原岩中大量石英碎屑的出现和基性火山岩岩石化学具有大陆拉斑玄武岩特征 一套片岩组合:下部为绿泥片岩、石英岩夹含铁石英岩;上部为石榴石石英片岩、石英蓝晶二云片岩、石英岩及大理岩等 黑云(石榴石)斜长片麻岩、条纹状斜长角闪岩、薄层磁铁石英岩、细粒长英质片麻岩、混合岩化条带状黑云角闪斜长片麻岩、含石榴石黑云二长片麻岩、夕线石黑云斜长片麻岩、石榴石黑云母石英片岩 沉积- 构造环境 浅海相沉积 海相火山喷发-沉积建造:代表陆缘进一步拉张解体并向洋盆转化的趋势,可能是古大陆边缘海构造环境中火山活动的产物 拉张条件下古大陆边缘裂陷槽环境,具火山型被动大陆边缘建造特征,代表中晚元古代陆缘拉张解体早期阶段形成的拉张型过渡壳 较为活动的稳定大陆边缘 活动大陆边缘环境(岛弧-弧后盆地) 变质级别 中浅变质(绿片岩相) 中浅变质(绿片岩相) 中高级变质 中级变质(角闪岩相) 中级变质(角闪岩相-高角闪岩相) 时代 新元古代 中元古代 中元古代 早元古代 中元古代 分布 艾勒格庙地区 仅分布于白乃庙一带 白乃庙-温都尔庙一带 宝音图-锡林浩特-乌兰浩特-扎兰屯 锡林浩特一带 备注 含微古植物化石,可与蒙古托托尚山托累努力斯群对比;与周围古生代地质体均为断层接触 锆石U-Pb:1130±16Ma(周和平等,1992);被晚志留纪一套类复理石建造(志留纪徐尼乌苏组?)不整合覆盖 Sm-Nd:1394±46Ma;与温都尔庙群及白乃庙群均为断层接触(聂风军等,1994) 斜长角闪片岩的Sm-Nd全岩等时线年龄:2485±128Ma(徐备等,2000)侵入其中的斜长花岗岩锆石U-Pb年龄2209.3±38Ma 碎屑岩中的锆石变质核年龄集中在1005~1026Ma;457.6Ma的“S”型片麻状电气石二云母花岗岩侵入(葛梦春等,2011);上部被奥陶纪包尔汗图群角度不整合覆盖 -
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