Metamorphic rock deformation characteristics, geochemical characteristics and geological significance of the Dakendaba Group in Buhete Mountain on the northern margin of Qaidam Mountain
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摘要:
古元古代达肯大坂岩群为柴北缘构造带的变质结晶基底，是柴北缘造山带的重要组成部分。前人在德令哈以西的鱼卡河-锡铁山-沙柳河一带和大柴旦等地对达肯大坂岩群做了较深入的研究，但对于柴北缘东段的研究还相对薄弱，缺乏东西段的对比研究。通过对布赫特山一带达肯大坂岩群中片麻岩和斜长角闪片岩的岩石学、岩石地球化学、年代学研究和区域对比，认为研究区的岩性、矿物组合、变质程度与德令哈以西鱼卡河-锡铁山-沙柳河一带达肯大坂岩群具有较高的相似性。布赫特山一带达肯大坂岩群主要为一套碎屑岩夹火山岩的岩石组合，变形强烈，其形成环境为岛弧与活动性陆缘的过渡环境，且岩浆来源为壳幔混染。由采集的2件Sm-Nd同位素样品得到了2组等时线年龄分别为2085±14Ma和2027±19Ma。由此可知达肯大坂岩群为古元古代柴北缘地区的变质结晶基底，是柴北缘古元古代造山带的重要组成部分。
Abstract:The Proterozoic Dakendaban Group is the metamorphic crystalline basement of the northern margin tectonic belt and is an important part of the orogenic belt on the northern margin of Qaidam Basin. Previous researchers have made in-depth studies of Dakendaban Group in the areas of Delingha to the west of the Yuka River-Xitieshan-Shaliu River and Da Qaidam, but the study of the east part of the northern Qaidam is relatively insufficient, with the lack of comparative study of the east part and the west part. The authors made meticulous researches on petrology, geochemistry and geochronology of gneiss and amphibolite hornblende schist in Dakendaban Group of Buhete Mountain. Regional correlation shows that the lithologies, mineral assemblage, and metamorphism in the study area are quite similar to things of Dakendaban Group in the west of Delingha Yuka River-Xitieshan-Shaliu River area. Dakendaban Group of Buhete Mountain is mainly a clastic rock intercalated with volcanic rock assemblage, with intense deformation. The environment was a transitional environment of island arc and active continental border, and the magma source experienced crust mantle contamination. Two Sm-Nd isotope samples yielded two groups of isochronal ages, i.e., 2085±14Ma and 2027±19Ma. It is thus concluded that the Dakendaban Group is Paleoproterozoic metamorphic crystalline basement on the northern margin of Qaidam Basin and is an important part of the Paleoproterozoic orogenic belt in northern Qaidam Basin.
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致谢: 参加本项研究工作的还有长安大学地球科学与资源学院许安东副教授、陕西区域地质矿产研究院王振东高级工程师，审稿人对本文的评阅和赐教使笔者受益匪浅，在此一并表示衷心的感谢。
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图 5 球粒陨石标准化稀土元素配分曲线和原始地幔标准化元素蛛网图[13]
Figure 5. Seawater-normalized REE patterns and MORB-normalized trace element patterns
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图 7 Sm-Nd样品等时线图
L1等时线年龄T=2085±14Ma，Ii=0.510305，εNd(T)=7.2，MSWD=0.13；L2等时线年龄T=2027±19Ma，Ii=0.510246，εNd(T)=4.6，MSWD=0.89
Figure 7. Sm-Nd sample isochron chart
表 1 达肯大坂岩群岩石化学分析结果
Table 1 Analytical results of petrochemistry of Dakendaban Group
样号 薄片定名 SiO2 Al2O3 Fe2O3 FeO CaO MgO K2O NazO TiO2 P2O5 MnO Total La Ce Ⅳ-31 角闪斜长变粒岩 59.9 13.08 1.08 4.28 13.23 2.97 3.72 0.79 0.54 0.1 0.32 100.01 43.93 89.73 Ⅳ-42/1 黑云斜长片麻岩 52.16 14.52 1.25 10.5 10.95 7.17 0.56 1.6 0.98 0.08 0.21 99.98 10.51 25.37 Ⅳ-58 黑云二长片麻岩 74.56 14.14 0.05 1.4 1.18 0.3 4.71 3.26 0.19 0.15 0.06 100 16.3 34.86 Ⅳ-59 黑云斜长片麻岩 74.1 14.27 0.1 2.03 1.6 1.21 3.2 2.98 0.36 0.1 0.05 100 43.27 95.81 Ⅳ-42 斜长角闪岩 48.07 14.18 2.5 12.95 9.99 7.17 0.55 2.17 1.97 0.18 0.25 99.98 10.12 23.07 样号 Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Rb Sr Y Ⅳ-31 10.64 42.26 7.678 1.278 8.451 1.099 6.656 1.275 3.891 0.54 3.825 0.553 143.6 467.8 33.68 Ⅳ-42/1 3.409 16.56 4.49 1.385 6.075 0.959 6.489 1.327 3.951 0.538 3.862 0.553 27.89 114.1 32.92 Ⅳ-58 3.897 14.41 2.853 0.393 3.295 0.535 4.182 0.963 3.319 0.527 4.027 0.589 239.5 87.54 25.34 Ⅳ-59 10.63 40.78 7.742 0.76 8.339 1.113 6.634 1.257 3.788 0.512 3.507 0.492 107.9 69.57 33.8 Ⅳ-42 3.069 14.51 3.824 1.248 4.986 0.742 4.988 1.018 3.047 0.404 2.849 0.414 33.41 155.3 24.92 样号 Zr Nb Cd In Cs Ba Hf Ta Pb Th U I REE δEu (La/Yb)N (La/Sm)N Ⅳ-31 202.4 13.82 0.37 0.09 10.81 391.6 5.56 0.98 22.25 15.28 3.05 221.81 0.48 7.76 3.6 Ⅳ-42/1 107.5 7.33 0.28 0.1 2.41 88.91 3 0.41 4.21 2.02 0.56 85.48 0.81 1.84 1.47 Ⅳ-58 67.21 8.05 0.09 0.06 1.57 244.1 2.02 0.53 26.25 4.2 3.87 90.15 0.39 2.74 3.6 Ⅳ-59 151.3 21.32 0.23 0.05 1.83 341.1 4.24 2 23.84 26.35 6.53 224.63 0.29 8.34 3.52 Ⅳ-42 94.52 7.47 0.33 0.09 2.37 107.9 2.57 0.4 6.76 1.82 0.59 74.29 0.87 2.4 1.67 注:所有样品均由西安地质矿产研究所实验测试中心测试，主量元素含量单位为%，稀土及微量元素为10-6 
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表 2 Sm-Nd样品测试结果
Table 2 Sm-Nd sample test results
编号 Sm/10-6 Nd/10-6 l47Sm/l44Nd 143Nd/144Nd 2σ 09SG.Sm-Nd2-Ⅳ-38 2.8736 9.5154 0.1826 0.512682 ±2 09SG.Sm-Nd2-Ⅳ-38/l 2.7092 8.3512 0.1961 0.512997 ±3 09SG.Sm-Nd2-Ⅳ-42 2.5765 10.0349 0.1552 0.512316 ±6 09SG.Sm-Nd2-Ⅳ-42/l 2.l4l7 8.0833 0.1602 0.512385 ±3 09SG.Sm-Nd2-V-42/2 2.06l2 7.3676 0.1691 0.512502 ±3 09SG.Sm-Nd2-V-42/3 4.7357 16.9831 0.1686 0.512620 ±3 09SG.Sm-Nd2-V-42/4 2.9693 11.2004 0.1603 0.512505 ±3 09SG.Sm-Nd2-V-60 12.6972 59.2546 0.1295 0.512083 ±5 注:天津地质矿产研究所测试
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