Petrogenesis and Geodynamic Setting of Late Triassic Quartz Diorites in Zhiduo Area, Qinghai Province
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摘要: 对羌塘地块东北缘甘孜-理塘缝合带南侧日啊日曲石英闪长岩进行了系统的锆石U-Pb年龄、主量-微量元素及Sr-Nd同位素分析, 以探讨其岩石成因及地球动力学意义.LA-ICP-MS锆石U-Pb定年结果表明, 石英闪长岩侵位年龄为218±1 Ma, 为晚三叠世岩浆活动的产物.岩石SiO2含量介于53.02%~62.06%之间, 富Al2O3(15.84%~17.00%)和CaO(6.71%~8.94%), 贫TiO2(0.49%~1.01%)和P2O5(0.04%~0.12%), 具有较高的MgO(3.31%~5.66%)和Mg#(50~62), 属准铝质钙碱性系列; 岩体稀土元素总量较低(38.05×10-6~61.58×10-6), 轻重稀土分馏不明显, LILE富集, HFSE亏损, 具有含量较高的Cr(33.45×10-6~176.64×10-6)和Ni(13.34×10-6~43.62×10-6).全岩(87Sr/86Sr)i比值较为一致(0.706 8~0.707 9), εNd(t)变化于-5.5~-1.6.主微量元素及同位素结果表明日啊日曲石英闪长岩具有高镁闪长岩的特征, 与赞岐岩地球化学特征类似, 为俯冲沉积物来源的熔体交代岩石圈地幔形成的尖晶石相金云母二辉橄榄岩低度(10%~15%)部分熔融的产物, 岩浆演化过程中经历了辉石、角闪石等矿物的分离结晶.微量元素构造判别图解表明岩石为俯冲环境下的弧岩浆岩, 结合区内蛇绿岩、研究区南部陆缘弧火山岩和义敦岛弧埃达克岩的发现, 认为古特提斯洋在晚三叠世时期可能仍处于消减状态, 日啊日曲高镁石英闪长岩形成于甘孜-理塘洋南西向俯冲过程中.Abstract: Zircon U-Pb age, major and trace elements and Sr, Nd isotope compositions of the Riariqu quartz diorites from the south of the Ganzi-Litang suture zone, northeastern Qiangtang terrane are studied to decipher its petrogenesis and geodynamic significance. LA-ICP-MS zircon U-Pb dating yields an emplacement age of 218±1 Ma for the intrusion. Bulk-rock analyses show that these rocks belong to the calc-alkaline series, with SiO2 contents ranging from 53.02% to 62.06%. They are enriched in Al2O3 (15.84%-17.00%) and CaO (6.71%-8.94%), depleted in TiO2 (0.49%-1.01%) and P2O5 (0.04%-0.12%), defining their metaluminous characteristics. All samples have high concentrations of MgO (3.31%-5.66%), Cr (33.45×10-6-176.64×10-6) and Ni (13.34×10-6-43.62×10-6), and resultant high Mg# (50-62). These rocks are enriched in LREE and LILE, and depleted in HFSE with low REE contents (38.05×10-6-61.58×10-6). The (87Sr/86Sr)i ratios range from 0.706 8 to 0.707 9, and εNd(t) values vary from -5.5 to -1.6. The geochemical and Sr-Nd isotopic compositions of the Riariqu quartz diorites are similar to those of high-Mg dioritoids/sanukitoids. We contend that the Riariqu quartz diorites were derived from low-degree partial melting (10%-15%) of a phlogopite-bearing spinel lherzolite mantle, which was metasomatized by sediment-derived melts. Fractional crystallization of pyroxene and amphibole might also occur during the magma evolution. The geochemical characteristics indicate that the Riariqu quartz diorites are arc-related magmatic rocks, and were generated in a subduction-related tectonic setting. Combined with the ophiolites and continental marginal arc lavas in the study area, and the regional adakites in the Yidun terrane, it is suggested that the Riariqu quartz diorites might be generated during the southwestward subduction of Ganzi-Litang Paleo-Tethys Ocean in the Late Triassic.
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图 1 青藏高原构造轮廓及三叠纪岩浆岩时空分布(a)和羌塘地块东北缘治多地区地质简图(b)
1.新近纪-第四纪沉积物;2.晚三叠世巴塘群碳酸盐岩组;3.晚三叠世巴塘群火山岩组;4.晚三叠世巴塘群碎屑岩组;5.中三叠-晚三叠世巴颜喀拉山群砂岩组;6.三叠纪查涌蛇绿混杂岩带;7.石炭-早中二叠世多彩蛇绿混杂岩带;8.晚三叠世中酸性侵入岩体;9.断层;10.采样位置;a图据Yin and Harrison, 2000; Chung et al., 2005修改
Fig. 1. Simplified tectonic map of the Tibetan plateau showing the temporal-spatial distribution of Triassic arc magmatic rocks (a) and regional geological map of the Zhiduo area (b)
图 3 治多地区日啊日曲石英闪长岩(GS2)中锆石阴极发光(CL)图像(a)、U-Pb年龄谐和图(b)和球粒陨石标准化稀土配分图(c)
图a中圆圈代表U-Pb年龄测试激光剥蚀点位;圈中数字为分析点号,编号同表 1,圈外年龄为206Pb/238U表面年龄
Fig. 3. Cathodoluminescence (CL) images (a), U-Pb concordia diagram (b) and Chondrite-normalized REE patterns (c) for zircons of Riariqu quartz diorite sample (GS2) from Zhiduo area
图 4 治多地区日啊日曲石英闪长岩(a)TAS分类图、(b)K2O-SiO2关系图、(c)A/NK-A/CNK关系图和(d)MgO-SiO2关系图
数据来源:日本岛弧Steouchi火山岩带新生代赞岐岩(Tatsumi and Ishizaka, 1982; Shimoda et al., 1998; Tatsumi et al., 2003);可可西里晚三叠世高镁安山岩(Wang et al., 2011b);义敦岛弧晚三叠世埃达克岩(Wang et al., 2011a);a图据Wilson, 1989;b图据Rollinson, 1993;c图据Maniar and Piccoli, 1989;d图据McCarron and Smellie, 1998
Fig. 4. Major-element plots for the Riariqu quartz diorite from Zhiduo area (a) Total alkalis vs.silica (TAS) diagram, (b) K2O vs.SiO2 diagram, (c) A/NK vs.A/CNK diagram, (d) MgO vs.SiO2 diagram
图 5 治多地区日啊日曲石英闪长岩球粒陨石标准化稀土配分曲线(a)和原始地幔标准化微量元素蛛网图(b)
图中岩浆岩数据来源同图 4;球粒陨石和原始地幔标准化数据引自Sun and McDonough, 1989
Fig. 5. Chondrite-normalized REE patterns (a) and primitive mantle-normalized trace element patterns (b) for the Riariqu quartz diorite from Zhiduo area
图 6 治多地区日啊日曲石英闪长岩εNd(t)-(87Sr/86Sr)i
数据来源:MORB和海相沉积物(Plank and Langmuir, 1998);义敦岛弧晚三叠世昌台玄武岩(Wang et al., 2013);其他岩浆岩数据同图 4
Fig. 6. Initial 87Sr/86Sr vs. εNd(t) values for the Riariqu quartz diorite from Zhiduo area
图 7 治多地区日啊日曲石英闪长岩(a)Ba/La-La/Yb和(b)Th/Yb-Th/Sm
数据来源:MORB(N-MORB据Sun and McDonough, 1989);沱沱河地区晚三叠世富Nb玄武岩(Wang et al., 2008);其他岩浆岩数据同图 4和6;a图据Yogodzinski et al., 1995;b图据Zheng et al., 2014
Fig. 7. Trace-element plots for the Riariqu quartz diorite from Zhiduo area (a) Ba/La vs.La/Yb diagram and (b) Th/Yb vs.Th/Sm diagrams
图 8 治多地区日啊日曲石英闪长岩Rb/Sr-Ba/Rb(a)和Yb-La/Yb(b)
图a据Furman and Graham(1999);图b中带短横线曲线为地幔岩浆熔融程度趋势线,两端元分别为含金云母尖晶石相二辉橄榄岩地幔源区和含金云母石榴石相二辉橄榄岩地幔源区.图中所有地幔成分参考数据Miller et al.(1999)及其文献;富集地幔源区组分La=0.648×10-6,Yb=0.347×10-6,Dy=0.578×10-6
Fig. 8. Rb/Sr vs.Ba/Rb (a) and Yb vs.La/Yb (b) diagrams for the Riariqu quartz diorite from Zhiduo area
图 9 治多地区日啊日曲石英闪长岩Nb-Y(a)和Rb-Y+Nb构造判别(b)
图中岩浆岩数据来源同图 4;syn-COLG.同碰撞花岗岩;WPG.板内花岗岩;VAG.火山弧花岗岩;ORG.洋中脊花岗岩;底图据Pearce et al., 1984
Fig. 9. Nb vs.Y and Rb vs.Y +Nb discrimination diagrams for the quartz diorite from Zhiduo area
表 1 治多地区日啊日曲石英闪长岩(GS2)锆石LA-ICP-MS U-Pb定年分析结果
Table 1. LA-ICP-MS zircon U-Pb dating results of the Riariqu quartz diorite sample (GS2) from Zhiduo area
测试点号 Pb(10-6) Th(10-6) U(10-6) Th/U U-Th-Pb同位素比值 年龄(Ma) 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 208Pb/232Th 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ GS2-1 281 906 850 1.07 0.050 1 0.001 3 0.235 1 0.006 3 0.034 0 0.000 4 0.010 8 0.000 3 198 29 214 5 216 2 GS2-2 267 821 843 0.97 0.051 4 0.001 3 0.242 5 0.006 1 0.034 1 0.000 3 0.010 7 0.000 2 257 59 220 5 216 2 GS2-3 199 622 894 0.70 0.052 4 0.001 3 0.246 5 0.006 1 0.033 9 0.000 3 0.010 3 0.000 2 302 49 224 5 215 2 GS2-4 289 873 868 1.01 0.050 9 0.001 3 0.242 0 0.006 1 0.034 4 0.000 3 0.010 9 0.000 2 235 64 220 5 218 2 GS2-5 202 631 711 0.89 0.050 6 0.001 5 0.240 6 0.007 3 0.034 5 0.000 4 0.010 7 0.000 3 233 70 219 6 219 2 GS2-6 203 630 764 0.82 0.050 3 0.001 3 0.239 6 0.006 2 0.034 4 0.000 4 0.010 5 0.000 3 209 92 218 5 218 2 GS2-7 253 780 1 096 0.71 0.050 8 0.001 3 0.242 7 0.006 4 0.034 6 0.000 4 0.010 8 0.000 4 232 64 221 5 219 2 GS2-8 442 1 378 1 315 1.05 0.051 0 0.001 1 0.244 3 0.004 7 0.034 7 0.000 3 0.010 0 0.000 4 243 48 222 4 220 2 GS2-9 147 419 638 0.66 0.050 6 0.001 3 0.241 8 0.006 4 0.034 6 0.000 4 0.010 9 0.000 7 233 61 220 5 219 2 GS2-10 99 295 442 0.67 0.050 2 0.001 6 0.240 1 0.007 8 0.034 8 0.000 4 0.010 0 0.000 7 211 76 218 6 220 3 GS2-11 255 721 1 036 0.70 0.049 0 0.001 2 0.255 9 0.006 6 0.037 7 0.000 4 0.011 2 0.000 8 146 62 231 5 238 2 GS2-12 117 357 435 0.82 0.050 8 0.002 6 0.234 8 0.010 6 0.033 9 0.000 4 0.009 8 0.000 6 232 112 214 9 215 3 GS2-13 285 890 872 1.02 0.051 3 0.001 3 0.247 2 0.006 5 0.034 8 0.000 3 0.010 0 0.000 5 257 64 224 5 220 2 GS2-14 178 509 614 0.83 0.050 4 0.001 5 0.259 3 0.008 1 0.037 2 0.000 4 0.012 4 0.000 7 213 72 234 7 235 3 GS2-15 514 1 673 1 287 1.30 0.049 5 0.001 6 0.233 7 0.005 9 0.034 3 0.000 4 0.010 2 0.000 3 172 81 213 5 217 2 GS2-16 196 621 709 0.88 0.049 7 0.001 6 0.237 1 0.007 7 0.034 4 0.000 4 0.010 4 0.000 3 189 76 216 6 218 2 GS2-17 126 384 512 0.75 0.050 3 0.001 4 0.239 9 0.006 5 0.034 6 0.000 3 0.010 6 0.000 3 209 65 218 5 219 2 GS2-18 179 572 601 0.95 0.050 9 0.001 5 0.243 7 0.006 9 0.034 6 0.000 3 0.010 4 0.000 3 235 65 221 6 219 2 GS2-19 87 271 389 0.70 0.050 6 0.001 5 0.244 2 0.007 5 0.034 8 0.000 4 0.010 5 0.000 3 233 73 222 6 220 2 表 2 治多地区日啊日曲石英闪长岩(GS2)锆石微量元素分析结果(10-6)
Table 2. Zircon trace element data of the Riariqu quartz diorite sample (GS2) from Zhiduo area
测试点号 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Eu/Eu* Hf Ta Y Ti Nb GS2-1 0.03 20.90 0.50 7.87 13.40 4.57 70.40 22.60 298 116.00 583 140.00 1 497 298 0.37 12 365 0.80 3 746 5.48 2.50 GS2-2 0.10 22.60 0.64 10.30 14.80 5.01 68.90 21.10 283 111.00 569 143.00 1 602 334 0.40 11 841 0.84 3 666 6.67 2.50 GS2-3 0.00 15.60 0.07 1.50 4.11 1.35 28.10 10.80 165 73.40 396 95.90 1 032 215 0.28 11 888 0.76 2 376 5.28 1.70 GS2-4 0.04 21.70 0.57 8.37 14.80 4.94 70.10 22.40 290 111.00 545 130.00 1 369 270 0.39 12 369 0.73 3 568 7.67 2.08 GS2-5 0.03 17.00 0.54 6.46 11.70 3.90 52.80 17.50 228 89.60 449 111.00 1 204 247 0.40 11 732 0.69 2 910 6.74 1.85 GS2-6 0.05 18.10 0.42 5.69 10.40 3.52 49.80 17.20 240 97.20 520 130.00 1 460 305 0.39 10 940 0.77 3 234 6.94 2.32 GS2-7 0.07 20.10 0.31 5.41 9.58 2.72 53.30 18.10 253 107.00 565 138.00 1 511 320 0.29 10 586 1.02 3 470 6.50 2.18 GS2-8 0.09 31.40 0.84 12.80 21.40 6.90 100.00 32.20 423 165.00 822 200.00 2 218 447 0.38 12 901 1.15 4 790 5.68 3.20 GS2-9 2.21 15.80 0.58 4.58 5.90 2.03 31.40 11.20 158 67.80 368 95.10 1 113 234 0.37 12 987 0.69 1 989 6.22 1.38 GS2-10 0.04 9.71 0.16 2.80 3.89 1.49 25.00 8.60 126 55.10 303 79.90 917 196 0.35 11 190 0.47 1 813 5.75 1.32 GS2-11 0.02 21.20 0.09 1.30 3.13 1.25 29.80 12.30 192 83.40 439 105.00 1 111 222 0.26 13 350 1.31 2 660 8.02 3.27 GS2-12 0.03 10.30 0.23 3.79 6.66 2.06 34.60 11.60 159 64.50 338 85.30 965 199 0.34 11 889 0.49 2 096 4.47 1.27 GS2-13 0.01 21.90 0.47 7.93 11.80 4.25 65.20 21.10 287 112.00 566 137.00 1 484 298 0.37 12 008 0.75 3 580 6.53 2.11 GS2-14 0.01 13.60 0.34 4.88 9.21 3.27 46.60 15.60 205 81.20 418 102.00 1 143 231 0.39 12 122 0.74 2 648 4.13 1.57 GS2-15 0.18 44.20 1.44 20.50 32.10 9.52 145.00 45.50 578 216.00 1 015 235.00 2 411 460 0.36 11 626 1.04 6 705 9.44 4.26 GS2-16 0.06 17.20 0.38 5.64 11.30 3.59 57.70 18.80 255 102.00 526 129.00 1 421 288 0.35 11 806 0.72 3 316 8.72 1.95 GS2-17 0.04 10.70 0.29 3.69 5.86 2.37 31.80 10.60 146 59.80 313 77.10 859 178 0.42 12 288 0.56 1 948 5.35 1.16 GS2-18 0.04 15.20 0.35 6.18 10.50 3.44 53.20 17.30 231 90.00 450 110.00 1 203 241 0.36 11 473 0.61 2 874 6.12 1.61 GS2-19 0.02 8.59 0.21 4.13 6.64 2.11 31.30 10.10 135 53.90 279 69.50 776 161 0.37 11 981 0.38 1 763 4.68 0.80 表 3 治多地区日啊日曲石英闪长岩主量元素(%)、微量及稀土元素(10-6)分析结果
Table 3. Major (%) and trace element (10-6) compositions of the Riariqu quartz diorites from Zhiduo area
样号 SC-2 SC-3 SC-4 SC-6 SC-8 SiO2 62.06 57.96 53.02 57.43 57.50 TiO2 0.59 0.51 1.01 0.49 0.69 Al2O3 15.93 15.84 16.94 17.00 16.75 Fe2O3T 6.56 6.81 9.36 6.30 7.13 MnO 0.13 0.14 0.18 0.14 0.14 MgO 3.31 5.66 5.06 5.06 4.55 CaO 6.71 8.54 8.94 7.91 8.07 Na2O 2.94 2.34 2.56 2.69 2.84 K2O 0.92 0.94 1.27 1.13 0.92 P2O5 0.07 0.06 0.04 0.05 0.12 LOI 0.60 1.36 1.58 1.18 1.43 Total 99.82 100.16 99.96 99.38 100.14 A/CNK 0.88 0.78 0.78 0.85 0.82 K2O/Na2O 0.31 0.40 0.50 0.42 0.32 Na2O+K2O 3.86 3.28 3.83 3.82 3.76 Mg# 50.00 62.00 52.00 61.00 55.00 La 8.70 8.40 8.80 7.30 11.20 Ce 20.40 16.70 14.10 13.60 21.90 Pr 2.78 2.07 1.70 1.56 2.70 Nd 11.70 8.60 6.70 6.10 10.40 Sm 3.12 2.16 1.56 1.50 2.31 Eu 0.75 0.62 0.55 0.59 0.74 Gd 3.34 2.32 1.64 1.66 2.35 Tb 0.60 0.41 0.30 0.31 0.42 Dy 3.80 2.66 1.95 2.01 2.8 Ho 0.85 0.56 0.41 0.42 0.58 Er 2.44 1.65 1.21 1.29 1.70 Tm 0.36 0.24 0.19 0.18 0.25 Yb 2.38 1.63 1.33 1.28 1.79 Lu 0.35 0.26 0.22 0.20 0.27 REE 61.58 48.33 40.72 38.05 59.31 Eu/Eu* 0.71 0.85 1.04 1.15 0.96 Cr 33.45 176.64 36.96 33.91 72.97 Co 17.40 23.78 30.66 20.84 21.92 Ni 13.34 43.62 15.87 18.69 23.76 Rb 33.90 38.00 48.00 44.80 35.40 Sr 168.90 157.00 186.50 190.00 197.00 Y 24.60 16.60 12.30 12.60 17.20 Zr 81.00 56.00 31.00 32.00 59.00 Nb 4.36 3.40 3.18 2.19 3.70 Ba 249.00 191.00 202.00 202.00 182.00 Hf 2.26 1.63 1.05 1.28 1.76 Ta 0.28 0.25 0.22 0.43 0.26 Pb 5.86 4.67 5.48 8.16 8.17 Th 1.07 2.83 2.09 5.26 1.98 U 0.40 0.75 0.55 1.53 0.66 注:LOI.烧失量;Mg#=100×Mg2+/(Mg2++0.9×Fe2O3T);A/CNK=Al2O3/(CaO+Na2O+K2O)摩尔百分比. 表 4 治多地区日啊日曲石英闪长岩全岩Sr-Nd同位素分析结果
Table 4. Sr-Nd isotopic compositions of the Riariqu quartz diorites from Zhiduo area
样号 87Rb/86Sr 87Sr/86Sr ±2σ (87Sr/86Sr)i 147Sm/144Nd 143Nd/144Nd ±2σ εNd(t) TDM2(Ma) SC-2 0.580 7 0.709 209 4 0.707 408 0.160 9 0.512 332 2 -5.0 1 398 SC-3 0.702 4 0.710 082 6 0.707 904 0.151 6 0.512 290 2 -5.5 1 444 SC-4 0.740 9 0.709 431 5 0.707 134 0.140 1 0.512 343 3 -4.2 1 334 SC-6 0.680 2 0.708 998 4 0.706 889 0.149 5 0.512 437 14 -2.6 1 206 SC-8 0.519 6 0.708 445 6 0.706 834 0.134 9 0.512 469 3 -1.6 1 122 注:εNd(t)值计算采用(147Sm/144Nd)CHUR=0.196 7;(143Nd/144Nd)CHUR=0.512 638;t代表成岩年龄(218 Ma);同位素亏损地幔模式年龄(TDM2)计算采用(147Sm/144Nd)DM=0.213 7;(143Nd/144Nd)DM=0.513 15. -
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