LA-ICP-MS U-Pb dating and Hf isotopes of detrital zircon grains from siltstone of Danzhou Group in northern Guangxi and their geological significance
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摘要:
桂北丹洲群顶部拱洞组粉砂岩的碎屑锆石的阴极发光图像和Th/U(0.2~2.4)值显示,它们均为岩浆成因的锆石。锆石206Pb/238Pb年龄分布在730~769Ma和771~850Ma之间,这些锆石的Hf同位素成分范围较大,εHf(t)值和二阶段Hf模式年龄(TDM2)分别为-18.4~11.4和1020~2812Ma。此外,样品中还有一些年龄较老的锆石颗粒,207Pb/206Pb年龄为1910~3140Ma,εHf(t)值和二阶段Hf模式年龄(TDM2)分别为-13.6~3.4和2740~3635Ma。结合前人的研究推测,桂北丹洲群拱洞组沉积年龄小于等于706±10Ma,物源主要由扬子板块新元古代岩浆岩组成,也有少量太古宙岩浆岩的加入。推测中国华南地区存在对应于Rodinia超大陆聚合相关的格林威尔运动的响应。根据已测锆石的εHf(t)值和Hf二阶段模式年龄推断,研究区地壳生长主要经历3个阶段:① 3.64~3.25Ga,初生地壳出现在3.64Ga;② 2.98~2.37Ga;③ 2.19~1.28Ga,地壳生长的主要时期。
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关键词:
- 桂北丹洲群 /
- 碎屑锆石LA-ICP-MS U-Pb定年 /
- Hf同位素 /
- Rodinia超大陆 /
- 地壳生长
Abstract:This paper reports LA-ICP-MS U-Pb dating and Hf isotopes for detrital zircon grains of siltstone from Gongdong For-mation at the top of the Danzhou Group. The majority of zircon grains are transparent, euhedral and prismatic crystals with oscillato-ry zoning in CL images and have high Th/U ratios of 0.2~2.4, indicating an igneous origin for the zircon. The 206Pb/238Pb age distri-butions for the detrital zircon grains mainly range from 730Ma to 769Ma and 771Ma to 850Ma, and εHf(t)and two-stage Hf model ages (TDM2) range from -18.4 to 11.4 and from 1020Ma to 2812Ma, respectively. Moreover, there are some detrital zircon grains with relatively older ages with 206Pb/238Pb ages from 1910Ma to 3140Ma, and εHf(t)and TDM2 from -13.6~3.4 and 2740~3635Ma, respec-tively. Combined with previous researches, the authors infer that the maximum depositional age of the Gongdong Formation from Danzhou Group is 706±10Ma. The source region was predominated by Neoproterozoic magmatic rocks from Yangtze Block (ca. 750~830Ma) with the mixture of minor Archean magmatic rocks. There was developed the Greenville movement in South China re-sulting from the assembly of Rodinia supercontinent. In addition, on the basis of the εHf(t)and TDM2 data of the detrital zircon grains, the authors hold the existence of three stages for the crust growth in the study area:① 3.64Ga to 3.25Ga, with the juvenile crust at 3.64Ga; ② 2.98Ga to 2.37Ga; ③ 2.19Ga to 1.28Ga.
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江南造山带是Rodinia超大陆聚合背景下扬子板块与华夏板块之间历经洋壳俯冲、弧-陆碰撞、陆-陆碰撞等多期构造运动的产物[1-17]。江南造山带的研究对于认识Rodinia超大陆演化具有重要意义,一直以来是地学界研究的热点及重点地区。江南造山带西段桂北地区保存了相对完整的新元古代地层,如四堡群、角度不整合覆盖在四堡群之上的丹洲群,以及平行不整合覆盖在丹洲群之上的南华系。近年来,研究者对这些沉积地层开展了较深入的研究,并通过沉积岩中的碎屑锆石和凝灰岩锆石定年等手段厘定四堡群为新元古代地层,其沉积时代为840Ma左右[18-19]。但是关于丹洲群的沉积时代等科学问题仍存在争议,有些学者认为丹洲群的沉积时代为780~900Ma[5,20-22],也有一些学者认为其沉积时代为730~720Ma[23-27],限制了对新元古代时期Rodinia超大陆演化及华南陆壳生长的认识。
碎屑锆石具有较强的抗风化能力,单颗粒碎屑锆石U-Pb定年和Hf同位素分析可以指示沉积岩物质来源、沉积时代,以及区域构造-岩浆事件,还可以为物源区的地壳生长和演化提供约束[28-32]。本文报道了江南造山带西段桂北地区丹洲群粉砂岩碎屑锆石U-Pb定年结果和Hf同位素组成,旨在探讨沉积源区特征及沉积时代,为进一步揭示华南地壳生长和演化规律提供一定的约束。
1. 地质背景和样品特征
华南地区被划分为扬子板块和华夏板块2个构造单元,伴随着古华南洋的闭合,扬子板块与华夏板块在新元古代(1.0~0.8Ga)历经洋壳俯冲、弧-陆碰撞、陆-陆碰撞等构造运动(即四堡运动),形成了江南造山带[1-2,17,33-38](图 1-a)。江南造山带呈NEE向展布,西起黔东、桂北,经湘西北、赣西北、赣东北,东至皖南、浙西,长约1500km, 宽约200km, 面积约30×104km2[2,39]。造山带东段主要位于赣东北、皖南、浙西、浙东北等地,西段位于广西、湖南、贵州等地(图 1-a)。江南造山带西段出露的最古老地层为中元古界梵净山群、四堡群、冷家溪群,其次为角度不整合于其上的新元古界板溪群、下江群和丹洲群,还有平行不整合覆盖于板溪群、下江群和丹洲群之上的南华系(图 1-b),本区还出露震旦系、寒武系和泥盆系(图 1-b、c)。其中,丹洲群为一套浅海低绿片岩相变质沉积岩及火山岩组合,总厚度为1000~5000m。基于岩石组合特征,前人将丹洲群自下而上划分为白竹组、合桐组和拱洞组(图 1-b、c)。白竹组下部为灰绿色钙质页岩夹条带状大理岩和泥质灰岩,中部为浅灰绿色粉砂岩及泥岩,上部主要为变质砂岩、泥质岩、硅质岩和石英脉;合桐组下部主要为富含炭质和黄铁矿的泥页岩和灰色页岩夹灰绿色粉砂岩,中间夹一层凝灰岩,上部为一套灰白色凝灰岩和灰黑色页岩;拱洞组下部为一套凝灰岩,以及浅灰绿色凝灰质砂岩、粉砂岩,石英砂岩等,上部以灰绿色条带状粉砂质页岩为主,夹中厚层砂岩。
桂北地区出露的丹洲群为合桐组和拱洞组(图 1-c),研究对象为丹洲群顶部的拱洞组浅灰绿色粉砂岩,位于桂北龙胜县西南方的三门镇河口村附近(图 2)。该层粉砂岩较厚,厚度约为13m, 主要由石英和长石组成,还含有少量绢云母和绿泥石。
2. 分析方法
2.1 锆石U-Pb测年
对1件粉砂岩(HK-19)中的碎屑锆石进行了U-Th-Pb同位素测定,使用常规方法挑选出锆石颗粒,随后在双目镜下根据颜色、形态、透明度等特征进行初步分类,并挑选出具有代表性的锆石,将锆石样品分别用双面胶粘贴在载玻片上,放上PVC环,然后将环氧树脂和固化剂进行充分混合后注入PVC环中,待树脂充分固化后将样品从载玻片上剥离,并对其进行抛光,直到样品露出一个光洁的平面,然后进行锆石阴极发光(CL)照相。锆石U-Pb定年在国家地质测试中心的LA-ICP-MS上完成,实验分析用激光剥蚀系统为GeoLas Pro, 等离子质谱仪为Agilent 7700,激光能量为80mJ,频率为5Hz, 激光束斑直径为32μm, 具体分析条件及流程见参考文献[40-41]。年龄加权平均值计算和谐和图绘制采用3.0版本Isoplot程序完成[42]。
2.2 锆石Hf同位素
锆石Hf同位素测试在中国地质科学院地质研究所大陆构造与动力学实验室完成,所用仪器为Neptune Plus多接收等离子质谱和Compexpro.193nm紫外激光剥蚀系统(LA-MC-ICP-MS),实验过程中采用氦气作为剥蚀物质载气,剥蚀直径为32μm, 使用国际通用的锆石标样GJ-1作为参考物质,分析点与U-Pb定年分析点为同一位置,或在其附近。相关仪器运行条件及详细分析流程见参考文献[43]。分析过程中锆石标准GJ1的176Hf/177Hf测值的加权平均值为0.282015 ± 8(2σ,n=10),与文献报道值[43-44]在误差范围内完全一致。
3. 分析结果
3.1 锆石U-Pb年龄
锆石U-Pb测年样品为桂北地区丹洲群顶部拱洞组的浅灰绿色粉砂岩。锆石CL图像显示锆石较复杂(图 3),既有振荡环带发育的锆石颗粒(图 3,颗粒5、97、108、109和110),还有扇形结构的锆石颗粒(图 3,颗粒12、50、99和118),有一定的磨圆(图 3,颗粒38和106)。
本次对该样品中的94粒锆石颗粒进行了U-Pb年龄测定(表 1)。分析结果显示,数据投影点部分位于U-Pb谐和线及其附近,部分远离谐和线(图 4-a)。如锆石年龄直方图所示,这些锆石颗粒的年龄主要有4个年龄峰值(图 4-b)。第一组共3颗锆石(图 3,颗粒5、93、112),206Pb/238Pb年龄介于699±8~715±10Ma之间,年龄加权平均值为706±10Ma(MSWD=0.79),锆石的Th/U值为0.73~1.57,指示其为岩浆锆石。第二组共22颗锆石(图 3,颗粒7、104、105等),206Pb/238Pb年龄介于730±9~769±11Ma之间,年龄加权平均值为752±5Ma(MSWD=1.7)(图 4-b),锆石的Th/U值为0.81~2.24,指示这些锆石也是岩浆锆石。第三组共有29颗锆石(图 3,颗粒99、55、116等),206Pb/238Pb年龄介于771 ± 9~803 ±9Ma之间,年龄加权平均值为783±3Ma(MSWD=1.07),锆石的Th/U值为0.21~2.38,指示这些锆石为岩浆锆石。第四组共11颗锆石(图 3,颗粒39、50、61等),206Pb/238Pb年龄介于810±9~850±15Ma之间,年龄加权平均值为828±10Ma(MSWD=2.3),锆石的Th/U值为0.70~1.87,指示这些锆石为岩浆锆石。
表 1 丹洲群拱洞组碎屑锆石U-Th-Pb同位素数据(样品号:HK-19)Table 1. U-Th-Pb isotope data for detrital zircon grains fromGongdong Formation in Danzhou Group (Sample: HK-19)点号 Th/U 铅同位素比值及误差 年龄及误差/Ma 206Pb/238U ±1σ 207Pb/235U ±1σ 207Pb/206Pb ±1σ 208Pb/232Th ±1σ 206Pb/238U ±1σ 207Pb/235U ±1σ 207Pb/206Pb ±1σ 208Pb/232Th ±1σ 1 1.5 0.1279 0.0014 1.3656 0.0171 0.0805 0.0009 0.0447 0.0004 776 8 874 7 1208 21 885 7 2 1.4 0.1215 0.0019 1.0770 0.0597 0.0642 0.0026 0.0441 0.0008 739 11 742 29 749 82 872 15 3 1 0.1226 0.0019 1.2502 0.0600 0.0785 0.0023 0.0464 0.0009 745 11 824 27 1159 58 917 17 5 0.8 0.1160 0.0017 1.0137 0.0474 0.0688 0.0021 0.0458 0.0009 707 10 711 24 894 63 905 17 6 0.9 0.1214 0.0014 1.2101 0.0227 0.0757 0.0010 0.0486 0.0005 739 8 805 10 1086 27 959 9 7 1.1 0.1199 0.0016 1.0707 0.0369 0.0724 0.0017 0.0452 0.0006 730 9 739 18 996 46 893 12 8 0.8 0.3517 0.0042 5.7701 0.1901 0.1300 0.0019 0.1087 0.0014 1943 20 1942 29 2098 25 2085 26 10 0.3 0.1303 0.0015 1.3014 0.0227 0.0730 0.0009 0.0477 0.0006 790 8 846 10 1013 26 941 11 11 0.5 0.3653 0.0041 8.2370 0.1776 0.1622 0.0018 0.1070 0.0012 2007 19 2257 20 2478 19 2055 21 12 0.9 0.1286 0.0018 1.2802 0.0581 0.0721 0.0021 0.0420 0.0008 780 11 837 26 990 57 831 15 13 1.5 0.1284 0.0015 1.3790 0.0298 0.0804 0.0012 0.0425 0.0004 779 8 880 13 1207 29 841 8 14 1.2 0.1261 0.0014 1.5223 0.0273 0.0848 0.0011 0.0401 0.0004 765 8 939 11 1310 25 795 7 17 0.9 0.1314 0.0016 1.1880 0.0361 0.0671 0.0014 0.0421 0.0006 796 9 795 17 840 42 833 11 18 0.2 0.4065 0.0045 8.0073 0.1490 0.1416 0.0015 0.1349 0.0015 2199 21 2232 17 2247 19 2557 27 19 0.6 0.3909 0.0044 7.0752 0.1552 0.1320 0.0015 0.1055 0.0011 2127 20 2121 20 2125 20 2028 20 22 1.7 0.1248 0.0014 1.3757 0.0218 0.0808 0.0010 0.0374 0.0003 758 8 879 9 1217 23 743 6 24 0.9 0.4518 0.0053 10.3996 0.3385 0.1600 0.0020 0.1301 0.0015 2403 24 2471 30 2456 21 2472 27 25 0.9 0.1483 0.0019 1.4037 0.0532 0.0675 0.0015 0.0369 0.0006 892 11 891 22 854 46 732 12 27 1 0.1286 0.0016 1.3455 0.0452 0.0716 0.0015 0.0404 0.0006 780 9 866 20 974 42 800 11 28 1 0.1400 0.0016 1.4749 0.0230 0.0770 0.0009 0.0461 0.0004 845 9 920 9 1120 23 911 8 30 1 0.1294 0.0015 1.3466 0.0236 0.0763 0.0010 0.0416 0.0004 785 8 866 10 1104 25 825 8 31 0.5 0.2278 0.0026 3.8563 0.0745 0.1230 0.0014 0.0828 0.0009 1323 13 1605 16 2000 21 1609 16 34 1.6 0.1804 0.0030 1.9028 0.1375 0.0741 0.0025 0.0465 0.0010 1069 16 1082 48 1044 67 919 20 35 2.2 0.1327 0.0022 2.1332 0.1268 0.1069 0.0033 0.0427 0.0008 803 13 1160 41 1748 55 846 15 36 1.1 0.1375 0.0016 1.4122 0.0271 0.0755 0.0010 0.0402 0.0004 831 9 894 11 1082 27 798 8 37 1.5 0.1355 0.0015 1.4474 0.0257 0.0791 0.0010 0.0392 0.0004 819 9 909 11 1174 25 777 7 38 0.8 0.4790 0.0053 10.8197 0.1935 0.1657 0.0018 0.1191 0.0011 2523 23 2508 17 2515 18 2275 20 39 1.3 0.1339 0.0015 1.4799 0.0325 0.0773 0.0011 0.0414 0.0004 810 9 922 13 1128 29 819 8 40 1.9 0.1403 0.0016 1.5250 0.0283 0.0771 0.0010 0.0384 0.0004 846 9 941 11 1125 26 762 7 41 1.1 0.1242 0.0015 1.3032 0.0335 0.0761 0.0013 0.0381 0.0005 755 9 847 15 1097 33 755 9 42 2 0.1247 0.0017 1.4777 0.0609 0.0840 0.0021 0.0467 0.0006 757 10 921 25 1291 48 922 12 43 0.5 0.3277 0.0036 5.3420 0.0685 0.1236 0.0013 0.0841 0.0007 1827 17 1876 11 2008 18 1632 13 45 1.9 0.1278 0.0014 1.3844 0.0211 0.0807 0.0009 0.0402 0.0004 775 8 882 9 1214 23 797 7 46 1.7 0.1239 0.0014 1.4050 0.0228 0.0818 0.0010 0.0416 0.0004 753 8 891 10 1240 24 823 7 47 0.4 0.3664 0.0040 7.9664 0.1168 0.1566 0.0016 0.1193 0.0011 2012 19 2227 13 2419 17 2278 20 48 0.9 0.1278 0.0014 1.3298 0.0216 0.0736 0.0009 0.0441 0.0004 776 8 859 9 1031 24 873 8 50 1 0.1410 0.0026 1.5663 0.1190 0.0720 0.0031 0.0399 0.0012 850 15 957 47 986 86 791 22 52 0.8 0.1238 0.0024 1.0980 0.0891 0.0605 0.0032 0.0425 0.0013 753 14 752 43 621 32 842 26 53 0.6 0.5089 0.0057 12.6676 0.2778 0.1802 0.0020 0.1365 0.0014 2652 24 2655 21 2655 18 2587 24 55 0.2 0.1326 0.0015 1.2181 0.0234 0.0685 0.0009 0.0466 0.0007 803 9 809 11 884 28 920 13 56 0.6 0.3177 0.0035 6.6179 0.1242 0.1485 0.0016 0.0970 0.0009 1779 17 2062 17 2329 19 1871 17 57 0.8 0.1281 0.0014 1.2817 0.0236 0.0740 0.0010 0.0434 0.0004 777 8 838 10 1040 26 859 8 58 0.7 0.1290 0.0017 1.1541 0.0422 0.0669 0.0016 0.0426 0.0007 782 10 779 20 835 49 842 14 60 1.4 0.1278 0.0021 1.2811 0.0729 0.0737 0.0025 0.0484 0.0009 775 12 837 32 1034 68 955 16 61 1.2 0.1355 0.0020 1.2282 0.0567 0.0697 0.0020 0.0402 0.0007 819 11 814 26 918 59 797 14 62 1 0.1282 0.0015 1.2805 0.0254 0.0725 0.0010 0.0399 0.0004 778 8 837 11 1000 28 791 8 63 1.4 0.3886 0.0049 6.9856 0.3021 0.1323 0.0021 0.1000 0.0013 2117 23 2110 38 2129 28 1926 23 65 1.4 0.1278 0.0014 1.3714 0.0206 0.0797 0.0009 0.0423 0.0004 776 8 877 9 1191 23 837 7 66 0.9 0.1281 0.0015 1.3583 0.0273 0.0769 0.0011 0.0436 0.0004 777 8 871 12 1117 28 862 9 67 1.3 0.3407 0.0042 6.3821 0.2477 0.1361 0.0021 0.1135 0.0013 1890 20 2030 34 2179 27 2172 24 68 2 0.1265 0.0014 1.4306 0.0274 0.0814 0.0011 0.0399 0.0004 768 8 902 11 1231 26 791 7 69 1.6 0.1271 0.0015 1.4205 0.0366 0.0802 0.0013 0.0389 0.0004 771 9 898 15 1201 33 772 8 70 1.3 0.1277 0.0015 1.3916 0.0270 0.0788 0.0011 0.0443 0.0004 775 8 885 11 1168 27 877 8 72 1.5 0.1279 0.0020 1.3012 0.0687 0.0726 0.0024 0.0411 0.0008 776 11 846 30 1004 65 814 15 75 1.8 0.1247 0.0016 1.3630 0.0421 0.0809 0.0016 0.0423 0.0005 758 9 873 18 1218 38 838 9 76 0.6 0.5460 0.0060 18.7385 0.3436 0.2430 0.0025 0.1551 0.0014 2809 25 3029 18 3140 16 2914 25 77 1.1 0.1250 0.0015 1.3401 0.0323 0.0756 0.0012 0.0398 0.0004 759 8 863 14 1084 32 789 9 79 0.7 0.2967 0.0033 6.2970 0.1025 0.1512 0.0016 0.0851 0.0008 1675 16 2018 14 2359 18 1651 14 80 1 0.2948 0.0038 4.2902 0.1695 0.1207 0.0021 0.1044 0.0014 1666 19 1692 33 1966 31 2007 26 81 0.5 0.4567 0.0051 10.1246 0.2459 0.1589 0.0018 0.1121 0.0013 2425 23 2446 22 2444 19 2147 24 82 1.1 0.3620 0.0041 6.4596 0.1485 0.1343 0.0016 0.1019 0.0010 1992 19 2040 20 2155 20 1962 18 83 0.8 0.3374 0.0042 5.4538 0.1983 0.1255 0.0019 0.0854 0.0013 1874 20 1893 31 2036 27 1656 24 85 0.8 0.4594 0.0051 10.6858 0.2360 0.1717 0.0019 0.1289 0.0013 2437 23 2496 21 2574 18 2451 22 86 1.2 0.1323 0.0017 1.2307 0.0426 0.0713 0.0016 0.0422 0.0006 801 10 815 19 965 44 836 12 87 1.1 0.3678 0.0041 8.3767 0.1806 0.1640 0.0019 0.0807 0.0008 2019 19 2273 20 2498 19 1569 15 88 1.7 0.1341 0.0015 1.4328 0.0233 0.0778 0.0009 0.0411 0.0004 811 8 903 10 1141 24 814 7 89 0.2 0.4116 0.0045 7.9881 0.1218 0.1412 0.0015 0.1074 0.0011 2222 20 2230 14 2242 18 2061 20 90 1.4 0.1263 0.0015 1.2999 0.0297 0.0750 0.0012 0.0339 0.0004 767 8 846 13 1067 31 674 7 92 1 0.1235 0.0015 1.1300 0.0370 0.0665 0.0022 0.0351 0.0007 751 8 768 18 833 73 697 13 93 1.6 0.1173 0.0017 1.0583 0.0381 0.0652 0.0023 0.0330 0.0006 715 10 733 19 789 73 657 12 94 1.4 0.1210 0.0012 1.1084 0.0257 0.0663 0.0015 0.0295 0.0005 736 7 757 12 815 48 587 10 95 1.6 0.1354 0.0017 1.2053 0.0383 0.0648 0.0022 0.0373 0.0007 818 10 803 18 769 69 740 15 96 0.6 0.3508 0.0043 5.9422 0.1281 0.1225 0.0025 0.0942 0.0020 1938 20 1967 19 1992 37 1820 37 97 1.4 0.1316 0.0018 1.1608 0.0345 0.0639 0.0019 0.0372 0.0008 797 10 782 16 739 24 739 16 98 0.7 0.1392 0.0019 1.2991 0.0447 0.0677 0.0023 0.0398 0.0011 840 11 845 20 859 70 789 21 99 2.3 0.1276 0.0016 1.1130 0.0238 0.0632 0.0013 0.0339 0.0007 774 9 760 12 722 42 674 13 100 2 0.1290 0.0019 1.1084 0.0328 0.0630 0.0020 0.0312 0.0007 782 11 757 16 706 69 622 13 101 2.4 0.1294 0.0016 1.1673 0.0295 0.0657 0.0017 0.0328 0.0008 785 9 785 14 798 54 652 16 102 1.4 0.1391 0.0020 1.2490 0.0371 0.0659 0.0021 0.0341 0.0011 839 12 823 17 1200 67 678 21 104 1.4 0.1224 0.0019 1.0384 0.0436 0.0624 0.0028 0.0285 0.0011 744 11 723 22 700 99 568 21 105 1.6 0.1268 0.0018 1.0735 0.0356 0.0623 0.0021 0.0310 0.0010 769 11 740 17 683 73 618 19 106 0.3 0.5570 0.0065 16.1080 0.3605 0.2098 0.0041 0.1234 0.0034 2854 27 2883 22 2906 32 2353 62 107 1.5 0.1321 0.0022 1.1502 0.0506 0.0633 0.0027 0.0343 0.0009 800 13 777 24 717 86 681 17 108 1.3 0.1301 0.0015 1.0967 0.0300 0.0610 0.0015 0.0335 0.0007 788 8 752 15 639 58 665 15 109 1.2 0.1211 0.0015 1.0231 0.0287 0.0614 0.0017 0.0317 0.0007 737 9 715 14 654 64 632 14 110 1 0.1237 0.0021 1.0895 0.0394 0.0639 0.0022 0.0334 0.0008 752 12 748 19 739 73 663 15 111 1 0.3236 0.0048 5.2312 0.1328 0.1169 0.0027 0.0874 0.0020 1807 24 1858 22 1910 9 1694 38 112 0.7 0.1145 0.0014 0.9719 0.0193 0.0612 0.0010 0.0313 0.0006 699 8 689 10 656 37 622 11 113 1.2 0.3597 0.0057 6.0394 0.1412 0.1221 0.0029 0.0965 0.0022 1981 27 1982 20 1987 43 1863 40 114 1.1 0.3414 0.0036 5.6829 0.1087 0.1202 0.0024 0.1051 0.0021 1894 18 1929 17 1959 35 2019 39 115 2.2 0.1244 0.0013 1.1103 0.0220 0.0645 0.0012 0.0363 0.0006 756 8 758 11 767 41 720 12 116 1.7 0.1306 0.0013 1.1795 0.0234 0.0654 0.0013 0.0380 0.0007 791 7 791 11 789 43 753 14 117 2.2 0.1224 0.0012 1.0672 0.0214 0.0632 0.0012 0.0322 0.0006 744 7 737 11 722 41 641 11 118 1.3 0.1274 0.0016 1.1309 0.0269 0.0644 0.0014 0.0345 0.0007 773 9 768 13 754 46 686 15 注:锆石U-Pb年龄值使用说明(包括正文、图及锆石Hf同位素计算):小于12亿年的数据均用锆石的206Pb/238Pb年龄,大于12亿年的数据均用锆石的207Pb/206Pb年龄 除以上锆石颗粒外,该样品还有其他年龄的锆石颗粒。如有2颗锆石206Pb/238Pb年龄为892Ma(图 3,颗粒25)和1069Ma(图 3,颗粒34),这2颗锆石的形态学特征和高Th/U(0.94和1.61)值指示其为岩浆锆石。另外,还有一些年龄较老的锆石(图 4),207Pb/206Pb年龄为1910±9~3140±16Ma(图 3,颗粒31、53、116等),这些较老的锆石Th/U值为0.2~1.38,CL图像显示有一定的磨圆(图 3,颗粒38和106),指示这些锆石为岩浆成因锆石,经历了沉积搬运等地质过程。
3.2 锆石Hf同位素组成
本次对丹洲群顶部拱洞组样品中的63颗锆石进行了Lu-Hf同位素分析,结果见表 2。每颗锆石的εHf(t)值用各自的206Pb/238Pb(介于707~892Ma之间的锆石)或207Pb/206Pb(介于1910~2655Ma之间的锆石)年龄计算。2颗206Pb/238Pb年龄为707Ma和715Ma的锆石,176Hf/177Hf值分别为0.281938和0.282297,这2颗锆石的εHf(t)值均为负值(-14.8和-2.6),二阶段Hf模式年龄(TDM2)分别为1276Ma和1905Ma(图 5)。12颗206Pb/238Pb年龄介于730~768Ma之间的锆石,176Hf/177Hf值分布范围为0.282035~0.282480,相应的εHf(t)值为-11.7~5.3,二阶段Hf模式年龄(TDM2)为1284~2572Ma(图 5)。19颗206Pb/238Pb年龄介于773~803Ma之间的锆石,176Hf/177Hf值分布范围为0.281978~0.282469,相应的εHf(t)值为-13.8~5.5,二阶段Hf模式年龄(TDM2)为1020~2812Ma(图 5)。9颗206Pb/238Pb年龄介于810~850Ma之间的锆石,176Hf/177Hf值分布范围为0.281752~0.282587,相应的εHf(t)值为-18.4~11.4,二阶段Hf模式年龄(TDM2)为1455~2232Ma(图 5)。1颗206Pb/238Pb年龄为892Ma(图 5)的锆石,176Hf/177Hf值为0.282423,相应的εHf(t)值为6.4,二阶段Hf模式年龄(TDM2)为1404Ma(图 5)。20颗207Pb/206Pb年龄介于1910~2655Ma之间的锆石,176Hf/177Hf值分布范围为0.280947~0.281448,相应的εHf(t)值范围为-13.6~3.4,其中εHf(t)多为负值,仅有少量为正值,二阶段Hf模式年龄(TDM2)为2740~3635Ma(图 5-a)。
表 2 丹洲群拱洞组碎屑锆石Hf同位素数据(样品号:HK-19)Table 2. Hf isotope data for detrital zircon grains for from Gongdong Formation in Danzhou Group (Sample: HK-19)点号 年龄/Ma 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf 2σ εHf(0) εHf(t) 2σ TDM TDM2 fLu/Hf 1 776 0.219353 0.006281 0.282138 0.000030 -22.4 -8.6 1.1 1825 1020 -0.81 5 707 0.072002 0.001906 0.281938 0.000022 -29.5 -14.8 0.8 1894 1276 -0.94 6 739 0.058196 0.002005 0.282453 0.000029 -11.3 4.0 1.0 1162 1284 -0.94 7 730 0.114721 0.002999 0.282442 0.000023 -11.7 3.0 0.8 1210 1318 -0.91 9 737 0.052978 0.001515 0.282479 0.000022 -10.4 5.2 0.8 1109 1331 -0.95 11 2478 0.026945 0.000711 0.281292 0.000020 -52.3 2.0 0.7 2716 2878 -0.98 12 780 0.084112 0.002497 0.282416 0.000026 -12.6 3.3 0.9 1231 1357 -0.92 14 765 0.071027 0.002187 0.282358 0.000028 -14.6 1.1 1.0 1305 1376 -0.93 18 2247 0.010113 0.000281 0.281005 0.000021 -62.5 -12.7 0.8 3068 3635 -0.99 24 2456 0.012930 0.000350 0.280947 0.000027 -64.5 -10.1 1.0 3150 3633 -0.99 25 892 0.059806 0.001608 0.282423 0.000020 -12.4 6.4 0.7 1192 1404 -0.95 27 780 0.066628 0.002078 0.282221 0.000029 -19.5 -3.3 1.0 1497 1419 -0.94 28 845 0.111336 0.003463 0.282502 0.000029 -9.5 7.2 1.0 1135 1455 -0.90 31 2000 0.095880 0.002104 0.281371 0.000029 -49.6 -7.8 1.0 2707 3133 -0.94 36 831 0.070647 0.001974 0.282486 0.000029 -10.1 7.1 1.0 1113 1464 -0.94 37 819 0.079851 0.002488 0.282402 0.000030 -13.1 3.6 1.1 1251 1480 -0.93 38 2515 0.024262 0.000678 0.281306 0.000027 -51.8 3.4 0.9 2694 2818 -0.98 39 810 0.054110 0.001748 0.281968 0.000030 -28.4 -11.5 1.1 1844 1485 -0.95 41 755 0.047925 0.001671 0.282422 0.000029 -12.4 3.4 1.0 1196 1491 -0.95 43 2008 0.034244 0.000899 0.281269 0.000022 -53.2 -9.6 0.8 2760 3254 -0.97 45 775 0.087182 0.002445 0.282459 0.000027 -11.1 4.8 1.0 1166 1496 -0.93 48 776 0.060838 0.001670 0.282451 0.000024 -11.3 4.9 0.8 1154 1505 -0.95 50 850 0.055959 0.001554 0.282587 0.000027 -6.6 11.4 0.9 957 1542 -0.95 52 753 0.044033 0.001189 0.282224 0.000025 -19.4 -3.4 0.9 1458 1556 -0.96 53 2655 0.032016 0.000840 0.281053 0.000027 -60.8 -2.7 0.9 3048 3316 -0.97 55 803 0.096307 0.002506 0.282404 0.000029 -13.0 3.4 1.0 1249 1621 -0.92 56 2329 0.060331 0.001826 0.281380 0.000029 -49.2 0.0 1.0 2674 2892 -0.95 57 777 0.052260 0.001568 0.282393 0.000028 -13.4 2.9 1.0 1234 1643 -0.95 60 775 0.082866 0.002401 0.282354 0.000025 -14.8 1.1 0.9 1319 1674 -0.93 61 819 0.065627 0.001713 0.281999 0.000024 -27.4 -10.2 0.8 1798 1678 -0.95 62 778 0.060447 0.001703 0.282432 0.000025 -12.0 4.3 0.9 1181 1745 -0.95 63 2129 0.019084 0.000527 0.281344 0.000028 -50.5 -3.7 1.0 2633 2975 -0.98 65 776 0.181892 0.005012 0.282140 0.000030 -22.4 -7.8 1.1 1754 1800 -0.85 66 777 0.055295 0.001738 0.282379 0.000027 -13.9 2.3 1.0 1260 1800 -0.95 67 2179 0.026747 0.000692 0.281207 0.000030 -55.3 -7.7 1.1 2829 3265 -0.98 68 768 0.193127 0.004771 0.282366 0.000027 -14.4 0.1 0.9 1391 1808 -0.86 70 775 0.055633 0.001524 0.281995 0.000023 -27.5 -11.2 0.8 1794 1809 -0.95 79 2359 0.095668 0.002043 0.281448 0.000030 -46.8 2.7 1.0 2594 2740 -0.94 80 1966 0.018405 0.000473 0.281409 0.000022 -48.2 -5.0 0.8 2541 2929 -0.99 81 2444 0.027353 0.000719 0.281183 0.000023 -56.2 -2.6 0.8 2863 3148 -0.98 82 2155 0.014151 0.000423 0.281287 0.000024 -52.5 -5.0 0.8 2702 3076 -0.99 83 2036 0.038675 0.000924 0.281141 0.000022 -57.7 -13.6 0.8 2936 3525 -0.97 85 2574 0.051989 0.001255 0.281031 0.000030 -61.6 -6.1 1.1 3111 3466 -0.96 87 2498 0.026692 0.000816 0.281296 0.000022 -52.2 2.4 0.8 2718 2867 -0.98 88 811 0.161497 0.004032 0.281970 0.000030 -28.4 -12.7 1.1 1961 1886 -0.88 89 2242 0.015048 0.000415 0.281320 0.000022 -51.4 -1.9 0.8 2658 2944 -0.99 93 715 0.067517 0.001980 0.282279 0.000024 -17.4 -2.6 0.8 1410 1905 -0.94 94 736 0.057541 0.001597 0.282381 0.000025 -13.8 1.6 0.9 1252 2021 -0.95 95 818 0.030886 0.001072 0.282313 0.000029 -16.2 1.2 1.0 1329 2107 -0.97 96 1992 0.018463 0.000468 0.281237 0.000021 -54.3 -10.5 0.7 2773 3300 -0.99 97 779 0.081626 0.002245 0.282296 0.000029 -16.8 -0.8 1.0 1397 1371 -0.93 97 797 0.081366 0.002633 0.282469 0.000029 -10.7 5.5 1.0 1158 2186 -0.92 98 840 0.052788 0.001501 0.281752 0.000027 -36.1 -18.4 1.0 2134 2232 -0.95 99 774 0.218394 0.005379 0.281978 0.000029 -28.1 -13.8 1.0 2027 2306 -0.84 100 782 0.100439 0.002769 0.282180 0.000029 -21.0 -5.2 1.0 1587 2370 -0.92 104 744 0.055933 0.001592 0.282270 0.000030 -17.7 -2.1 1.1 1409 2395 -0.95 108 788 0.064820 0.001832 0.282317 0.000026 -16.1 0.3 0.9 1351 2404 -0.94 109 737 0.038962 0.001193 0.282480 0.000024 -10.3 5.3 0.9 1098 2444 -0.96 110 752 0.086209 0.002935 0.282427 0.000029 -12.2 2.9 1.1 1230 2517 -0.91 111 1910 0.060079 0.001492 0.281307 0.000030 -51.8 -11.2 1.0 2750 3277 -0.96 116 791 0.208042 0.006198 0.282101 0.000023 -23.7 -9.6 1.1 1880 2559 -0.81 117 744 0.161311 0.004125 0.282035 0.000029 -26.1 -11.7 1.0 1868 2572 -0.88 118 773 0.106784 0.002604 0.282274 0.000027 -17.6 -1.9 1.1 1443 2812 -0.92 注:锆石的εHf(t)值用各自的206Pb/238Pb(介于707~892Ma之间的锆石)或207Pb/206Pb(介于1910~2655Ma之间的锆石)年龄计算 4. 讨论
4.1 丹洲群沉积时代
丹洲群属于成层有序浅变质岩系,其下与四堡群呈角度不整合接触,其上与南华系长安组呈平行不整合或整合接触,自下而上分为白竹组、合桐组和拱洞组。近年来,虽然对丹洲群的形成时代做过详细深入的研究,但是仍然存在很大争议。董宝林[20]认为,丹洲群的沉积时代应限定在900~800Ma之间;丹洲群不整合沉积于桂北本洞花岗岩(820±7Ma)之上,因此有些学者认为,丹洲群底部沉积最大年龄约为820Ma[5,21,33],也有学者通过对丹洲群底部火山岩中的岩浆锆石及沉积岩中的碎屑锆石U-Pb年龄研究,将丹洲群的底部沉积年龄限制在820Ma左右[47-50]。高林志等[22]根据丹洲群合桐组和拱洞组凝灰岩锆石U-Pb年龄(分别为801±3Ma和786±6Ma),提出丹洲群的沉积时代为820~780Ma;也有些学者根据丹洲群顶部拱洞组的最大沉积时代约为730Ma, 确定丹洲群最小沉积时代约为720Ma[23-27];还有学者通过对丹洲群顶部沉积岩碎屑锆石的U-Pb年代学研究,获得丹洲群顶部的年龄应为720Ma左右[51-53]。
一般认为,地层的沉积年龄应小于等于碎屑锆石中最年轻的那组锆石年龄[54]。前已述及,丹洲群顶部拱洞组碎屑锆石有4个年龄峰值,其中最年轻的一组锆石共3颗(5、93、112号),206Pb/238Pb年龄介于699±8~715±10Ma之间,年龄加权平均值为706±10Ma(MSWD=0.79)。故可以认为,丹洲群拱洞组沉积年龄小于等于706±10Ma。
4.2 物源分析
由丹洲群拱洞组碎屑锆石年龄直方图可知,锆石年龄共有4个峰值,第一组共3颗锆石,206Pb/238Pb年龄介于699±8~715±10Ma之间,年龄加权平均值为706±10Ma;第二组22颗锆石,206Pb/238Pb年龄介于730±9~769±11Ma之间,年龄加权平均值为752±5Ma;第三组29颗锆石,206Pb/238Pb年龄介于771±9~803±9Ma之间,年龄加权平均值为783±3Ma;第四组11颗锆石,206Pb/238Pb年龄介于810±9~850±15Ma之间,年龄加权平均值为828±10Ma, 且这些锆石均为岩浆成因锆石,指示丹洲群拱洞组主要源区物质为约750Ma和约780Ma的岩浆岩,其次是约830Ma的岩浆岩。前人研究表明,新元古代时期,扬子板块发生了大规模的岩浆活动,岩浆活动主要集中在750~854Ma, 且这一时期的岩浆作用与Rodinia超大陆的聚合和裂解密切相关[3, 5, 7, 9, 33, 55-62, ],如桂北828Ma的辉长岩,桂北侵入到四堡群形成于约820Ma的三防、元宝山、本洞S型花岗岩[3,5-9],以及桂北和湘西760Ma的基性-超基性岩[62-64]。由此可见,丹洲群拱洞组的物源主要为扬子板块750~830Ma的岩浆岩,这与前人研究基本一致[23-24]。
Mcmenamin等[65]将1.0Ga以前由大陆碰撞形成的全球性联合大陆称为Rodinia超大陆,以1.3~1.0Ga期间的格林威尔造山带为缝合标志,将导致Rodinia超大陆形成的造山运动称为格林威尔运动。自20世纪90年代,诸多学者相继建立了Ro⁃dinia超大陆的复原图,并将华南中—新元古代的造山运动与格林威尔造山运动进行对比研究。在Hoffman[66]建立的新元古代Rodinia超大陆复原图中,Rodinia超大陆的聚合以劳伦大陆为中心,东冈瓦纳(澳大利亚、印度和东南极)与其相邻,西伯利亚位于劳伦大陆一侧,与另一侧的波罗的海、非洲和南美地块群遥相对应。该复原图为国内外地学界广泛认可,但该图中没有考虑中国华南在其中的位置。Li等[37]和Condie[67]在前人研究的基础上,重建了Rodinia超大陆复原图,并将华南置于Rodinia超大陆的中心位置。有部分学者认为,华南板块应该位于Rodinia超大陆西北缘而非中心位置[11,15,68]。华南在Rodinia超大陆中的位置,争议的关键在于华南中—新元古代是否存在与形成Rodinia超大陆的格林威尔造山运动相对应的造山运动,如桂北地区的四堡运动。本次研究结果表明,该样品有2颗锆石206Pb/238Pb年龄,分别为892Ma和1069Ma。另外,Wang等[18]研究表明,扬子地块早古生代地层的碎屑锆石有1088Ma的年龄峰值;Wu等[69]研究认为,华夏地块地层碎屑锆石存在1097Ma的年龄峰值。结合部分学者对扬子板块和华夏板块变质作用[70]、沉积特征[18,71]、基性-酸性岩石[6,33,72-73]及地质年代学[8,74-75]的系统研究,笔者认为,中国华南地区存在Rodinia超大陆聚合的格林威尔运动,华南板块并非位于Rodinia超大陆中心位置,而可能位于Ro⁃dinia超大陆西北缘。
Rogers等[76-77]和Zhao等[78]认为,2.1~1.5Ga是全球性的Columbia超大陆聚合和裂解的重要时期。本次研究的样品中有207Pb/206Pb年龄介于1910~2179Ma之间的锆石颗粒,这些锆石年龄可能代表了全球范围内Columbia超大陆聚合和裂解在扬子板块的响应。
前人研究表明,扬子板块存在太古宙基底,主要为扬子板块西北缘崆岭群的崆岭杂岩,主要时代为2650~3200Ma[79]。本次研究也发现,桂北丹洲群中有207Pb/206Pb年龄为2419~3140Ma的锆石颗粒,这些锆石均为岩浆成因锆石,指示扬子板块西南缘可能也存在太古宙基底。
4.3 地壳生长
碎屑锆石的U-Pb年龄不能判断源区寄主岩石的形成代表新生地壳的形成还是古老地壳的改造,只有锆石Hf模式年龄可以近似代表新生地壳从亏损地幔提取的时间,也就是地壳的生长时间[80]。一般而言,锆石主要在酸性岩石中结晶,而碎屑锆石也主要源自中酸性岩浆岩。因此笔者认为,在壳幔分离过程中,锆石的形成至少经历了2个阶段:岩浆从亏损地幔中抽取形成玄武质的原始地壳,此时可能会有斜锆石结晶出来;原始地壳在熔融形成长英质岩浆的过程中结晶形成锆石[81],通常用碎屑锆石的Hf同位素二阶段模式(TDM2)年龄来代表新生地壳的形成时代[31,82]。一般认为,如果锆石的εHf(t)为负值,表明其来自于古老地壳,或源区以古老地壳物质为主体;如果锆石的εHf(t)为正值,表明其来源于年轻地壳物质,或源区以年轻地壳物质占主导[45-46,83-84]。
结合前人[23]对扬子陆块地壳增生历史的研究,再根据本次对研究区已测锆石的εHf(t)值和Hf二阶段模式年龄的频率分布直方图(图 6),笔者推测,研究区地壳生长主要经历了3个阶段:① 3.64~3.25Ga, 研究区地壳第一次生长,初生地壳出现在3.64Ga;② 2.98~2.37Ga, 是研究区对全球陆核生长事件的响应[85];③ 2.19~1.28Ga, 对应Columbia超大陆的聚合和裂解[74-76],也是研究区地壳生长的主要时期。
5. 结论
(1)桂北丹洲群拱洞组沉积年龄小于等于706±10Ma。丹洲群拱洞组的物源主要来源于扬子板块新元古代约750Ma和780Ma的岩浆岩,其次是约830Ma的岩浆岩,还有源于较老时期的岩浆岩。
(2)中国华南地区存在Rodinia超大陆聚合的格林威尔运动,华南板块并非位于Rodinia超大陆中心位置,可能位于Rodinia超大陆西北缘。扬子板块西南缘可能也存在太古宙基底。
(3)根据研究区已测锆石的εHf(t)值和Hf二阶段模式年龄推测,研究区地壳生长主要经历了3个阶段:① 3.64~3.25Ga, 是研究区地壳的第一次生长,且初生地壳出现在3.64Ga;② 2.98~2.37Ga;③ 2.19~1.28Ga, 是研究区地壳生长的主要时期。
致谢: 感谢武汉上谱科技有限责任公司相关老师在U-Pb测年过程中给予的悉心指导和帮助,感谢中国地质科学院地质研究所大陆构造与动力学实验室王铮助理工程师在Hf同位素测试过程中给予的帮助,感谢审稿专家对论文提出的宝贵修改意见。 -
表 1 丹洲群拱洞组碎屑锆石U-Th-Pb同位素数据(样品号:HK-19)
Table 1 U-Th-Pb isotope data for detrital zircon grains fromGongdong Formation in Danzhou Group (Sample: HK-19)
点号 Th/U 铅同位素比值及误差 年龄及误差/Ma 206Pb/238U ±1σ 207Pb/235U ±1σ 207Pb/206Pb ±1σ 208Pb/232Th ±1σ 206Pb/238U ±1σ 207Pb/235U ±1σ 207Pb/206Pb ±1σ 208Pb/232Th ±1σ 1 1.5 0.1279 0.0014 1.3656 0.0171 0.0805 0.0009 0.0447 0.0004 776 8 874 7 1208 21 885 7 2 1.4 0.1215 0.0019 1.0770 0.0597 0.0642 0.0026 0.0441 0.0008 739 11 742 29 749 82 872 15 3 1 0.1226 0.0019 1.2502 0.0600 0.0785 0.0023 0.0464 0.0009 745 11 824 27 1159 58 917 17 5 0.8 0.1160 0.0017 1.0137 0.0474 0.0688 0.0021 0.0458 0.0009 707 10 711 24 894 63 905 17 6 0.9 0.1214 0.0014 1.2101 0.0227 0.0757 0.0010 0.0486 0.0005 739 8 805 10 1086 27 959 9 7 1.1 0.1199 0.0016 1.0707 0.0369 0.0724 0.0017 0.0452 0.0006 730 9 739 18 996 46 893 12 8 0.8 0.3517 0.0042 5.7701 0.1901 0.1300 0.0019 0.1087 0.0014 1943 20 1942 29 2098 25 2085 26 10 0.3 0.1303 0.0015 1.3014 0.0227 0.0730 0.0009 0.0477 0.0006 790 8 846 10 1013 26 941 11 11 0.5 0.3653 0.0041 8.2370 0.1776 0.1622 0.0018 0.1070 0.0012 2007 19 2257 20 2478 19 2055 21 12 0.9 0.1286 0.0018 1.2802 0.0581 0.0721 0.0021 0.0420 0.0008 780 11 837 26 990 57 831 15 13 1.5 0.1284 0.0015 1.3790 0.0298 0.0804 0.0012 0.0425 0.0004 779 8 880 13 1207 29 841 8 14 1.2 0.1261 0.0014 1.5223 0.0273 0.0848 0.0011 0.0401 0.0004 765 8 939 11 1310 25 795 7 17 0.9 0.1314 0.0016 1.1880 0.0361 0.0671 0.0014 0.0421 0.0006 796 9 795 17 840 42 833 11 18 0.2 0.4065 0.0045 8.0073 0.1490 0.1416 0.0015 0.1349 0.0015 2199 21 2232 17 2247 19 2557 27 19 0.6 0.3909 0.0044 7.0752 0.1552 0.1320 0.0015 0.1055 0.0011 2127 20 2121 20 2125 20 2028 20 22 1.7 0.1248 0.0014 1.3757 0.0218 0.0808 0.0010 0.0374 0.0003 758 8 879 9 1217 23 743 6 24 0.9 0.4518 0.0053 10.3996 0.3385 0.1600 0.0020 0.1301 0.0015 2403 24 2471 30 2456 21 2472 27 25 0.9 0.1483 0.0019 1.4037 0.0532 0.0675 0.0015 0.0369 0.0006 892 11 891 22 854 46 732 12 27 1 0.1286 0.0016 1.3455 0.0452 0.0716 0.0015 0.0404 0.0006 780 9 866 20 974 42 800 11 28 1 0.1400 0.0016 1.4749 0.0230 0.0770 0.0009 0.0461 0.0004 845 9 920 9 1120 23 911 8 30 1 0.1294 0.0015 1.3466 0.0236 0.0763 0.0010 0.0416 0.0004 785 8 866 10 1104 25 825 8 31 0.5 0.2278 0.0026 3.8563 0.0745 0.1230 0.0014 0.0828 0.0009 1323 13 1605 16 2000 21 1609 16 34 1.6 0.1804 0.0030 1.9028 0.1375 0.0741 0.0025 0.0465 0.0010 1069 16 1082 48 1044 67 919 20 35 2.2 0.1327 0.0022 2.1332 0.1268 0.1069 0.0033 0.0427 0.0008 803 13 1160 41 1748 55 846 15 36 1.1 0.1375 0.0016 1.4122 0.0271 0.0755 0.0010 0.0402 0.0004 831 9 894 11 1082 27 798 8 37 1.5 0.1355 0.0015 1.4474 0.0257 0.0791 0.0010 0.0392 0.0004 819 9 909 11 1174 25 777 7 38 0.8 0.4790 0.0053 10.8197 0.1935 0.1657 0.0018 0.1191 0.0011 2523 23 2508 17 2515 18 2275 20 39 1.3 0.1339 0.0015 1.4799 0.0325 0.0773 0.0011 0.0414 0.0004 810 9 922 13 1128 29 819 8 40 1.9 0.1403 0.0016 1.5250 0.0283 0.0771 0.0010 0.0384 0.0004 846 9 941 11 1125 26 762 7 41 1.1 0.1242 0.0015 1.3032 0.0335 0.0761 0.0013 0.0381 0.0005 755 9 847 15 1097 33 755 9 42 2 0.1247 0.0017 1.4777 0.0609 0.0840 0.0021 0.0467 0.0006 757 10 921 25 1291 48 922 12 43 0.5 0.3277 0.0036 5.3420 0.0685 0.1236 0.0013 0.0841 0.0007 1827 17 1876 11 2008 18 1632 13 45 1.9 0.1278 0.0014 1.3844 0.0211 0.0807 0.0009 0.0402 0.0004 775 8 882 9 1214 23 797 7 46 1.7 0.1239 0.0014 1.4050 0.0228 0.0818 0.0010 0.0416 0.0004 753 8 891 10 1240 24 823 7 47 0.4 0.3664 0.0040 7.9664 0.1168 0.1566 0.0016 0.1193 0.0011 2012 19 2227 13 2419 17 2278 20 48 0.9 0.1278 0.0014 1.3298 0.0216 0.0736 0.0009 0.0441 0.0004 776 8 859 9 1031 24 873 8 50 1 0.1410 0.0026 1.5663 0.1190 0.0720 0.0031 0.0399 0.0012 850 15 957 47 986 86 791 22 52 0.8 0.1238 0.0024 1.0980 0.0891 0.0605 0.0032 0.0425 0.0013 753 14 752 43 621 32 842 26 53 0.6 0.5089 0.0057 12.6676 0.2778 0.1802 0.0020 0.1365 0.0014 2652 24 2655 21 2655 18 2587 24 55 0.2 0.1326 0.0015 1.2181 0.0234 0.0685 0.0009 0.0466 0.0007 803 9 809 11 884 28 920 13 56 0.6 0.3177 0.0035 6.6179 0.1242 0.1485 0.0016 0.0970 0.0009 1779 17 2062 17 2329 19 1871 17 57 0.8 0.1281 0.0014 1.2817 0.0236 0.0740 0.0010 0.0434 0.0004 777 8 838 10 1040 26 859 8 58 0.7 0.1290 0.0017 1.1541 0.0422 0.0669 0.0016 0.0426 0.0007 782 10 779 20 835 49 842 14 60 1.4 0.1278 0.0021 1.2811 0.0729 0.0737 0.0025 0.0484 0.0009 775 12 837 32 1034 68 955 16 61 1.2 0.1355 0.0020 1.2282 0.0567 0.0697 0.0020 0.0402 0.0007 819 11 814 26 918 59 797 14 62 1 0.1282 0.0015 1.2805 0.0254 0.0725 0.0010 0.0399 0.0004 778 8 837 11 1000 28 791 8 63 1.4 0.3886 0.0049 6.9856 0.3021 0.1323 0.0021 0.1000 0.0013 2117 23 2110 38 2129 28 1926 23 65 1.4 0.1278 0.0014 1.3714 0.0206 0.0797 0.0009 0.0423 0.0004 776 8 877 9 1191 23 837 7 66 0.9 0.1281 0.0015 1.3583 0.0273 0.0769 0.0011 0.0436 0.0004 777 8 871 12 1117 28 862 9 67 1.3 0.3407 0.0042 6.3821 0.2477 0.1361 0.0021 0.1135 0.0013 1890 20 2030 34 2179 27 2172 24 68 2 0.1265 0.0014 1.4306 0.0274 0.0814 0.0011 0.0399 0.0004 768 8 902 11 1231 26 791 7 69 1.6 0.1271 0.0015 1.4205 0.0366 0.0802 0.0013 0.0389 0.0004 771 9 898 15 1201 33 772 8 70 1.3 0.1277 0.0015 1.3916 0.0270 0.0788 0.0011 0.0443 0.0004 775 8 885 11 1168 27 877 8 72 1.5 0.1279 0.0020 1.3012 0.0687 0.0726 0.0024 0.0411 0.0008 776 11 846 30 1004 65 814 15 75 1.8 0.1247 0.0016 1.3630 0.0421 0.0809 0.0016 0.0423 0.0005 758 9 873 18 1218 38 838 9 76 0.6 0.5460 0.0060 18.7385 0.3436 0.2430 0.0025 0.1551 0.0014 2809 25 3029 18 3140 16 2914 25 77 1.1 0.1250 0.0015 1.3401 0.0323 0.0756 0.0012 0.0398 0.0004 759 8 863 14 1084 32 789 9 79 0.7 0.2967 0.0033 6.2970 0.1025 0.1512 0.0016 0.0851 0.0008 1675 16 2018 14 2359 18 1651 14 80 1 0.2948 0.0038 4.2902 0.1695 0.1207 0.0021 0.1044 0.0014 1666 19 1692 33 1966 31 2007 26 81 0.5 0.4567 0.0051 10.1246 0.2459 0.1589 0.0018 0.1121 0.0013 2425 23 2446 22 2444 19 2147 24 82 1.1 0.3620 0.0041 6.4596 0.1485 0.1343 0.0016 0.1019 0.0010 1992 19 2040 20 2155 20 1962 18 83 0.8 0.3374 0.0042 5.4538 0.1983 0.1255 0.0019 0.0854 0.0013 1874 20 1893 31 2036 27 1656 24 85 0.8 0.4594 0.0051 10.6858 0.2360 0.1717 0.0019 0.1289 0.0013 2437 23 2496 21 2574 18 2451 22 86 1.2 0.1323 0.0017 1.2307 0.0426 0.0713 0.0016 0.0422 0.0006 801 10 815 19 965 44 836 12 87 1.1 0.3678 0.0041 8.3767 0.1806 0.1640 0.0019 0.0807 0.0008 2019 19 2273 20 2498 19 1569 15 88 1.7 0.1341 0.0015 1.4328 0.0233 0.0778 0.0009 0.0411 0.0004 811 8 903 10 1141 24 814 7 89 0.2 0.4116 0.0045 7.9881 0.1218 0.1412 0.0015 0.1074 0.0011 2222 20 2230 14 2242 18 2061 20 90 1.4 0.1263 0.0015 1.2999 0.0297 0.0750 0.0012 0.0339 0.0004 767 8 846 13 1067 31 674 7 92 1 0.1235 0.0015 1.1300 0.0370 0.0665 0.0022 0.0351 0.0007 751 8 768 18 833 73 697 13 93 1.6 0.1173 0.0017 1.0583 0.0381 0.0652 0.0023 0.0330 0.0006 715 10 733 19 789 73 657 12 94 1.4 0.1210 0.0012 1.1084 0.0257 0.0663 0.0015 0.0295 0.0005 736 7 757 12 815 48 587 10 95 1.6 0.1354 0.0017 1.2053 0.0383 0.0648 0.0022 0.0373 0.0007 818 10 803 18 769 69 740 15 96 0.6 0.3508 0.0043 5.9422 0.1281 0.1225 0.0025 0.0942 0.0020 1938 20 1967 19 1992 37 1820 37 97 1.4 0.1316 0.0018 1.1608 0.0345 0.0639 0.0019 0.0372 0.0008 797 10 782 16 739 24 739 16 98 0.7 0.1392 0.0019 1.2991 0.0447 0.0677 0.0023 0.0398 0.0011 840 11 845 20 859 70 789 21 99 2.3 0.1276 0.0016 1.1130 0.0238 0.0632 0.0013 0.0339 0.0007 774 9 760 12 722 42 674 13 100 2 0.1290 0.0019 1.1084 0.0328 0.0630 0.0020 0.0312 0.0007 782 11 757 16 706 69 622 13 101 2.4 0.1294 0.0016 1.1673 0.0295 0.0657 0.0017 0.0328 0.0008 785 9 785 14 798 54 652 16 102 1.4 0.1391 0.0020 1.2490 0.0371 0.0659 0.0021 0.0341 0.0011 839 12 823 17 1200 67 678 21 104 1.4 0.1224 0.0019 1.0384 0.0436 0.0624 0.0028 0.0285 0.0011 744 11 723 22 700 99 568 21 105 1.6 0.1268 0.0018 1.0735 0.0356 0.0623 0.0021 0.0310 0.0010 769 11 740 17 683 73 618 19 106 0.3 0.5570 0.0065 16.1080 0.3605 0.2098 0.0041 0.1234 0.0034 2854 27 2883 22 2906 32 2353 62 107 1.5 0.1321 0.0022 1.1502 0.0506 0.0633 0.0027 0.0343 0.0009 800 13 777 24 717 86 681 17 108 1.3 0.1301 0.0015 1.0967 0.0300 0.0610 0.0015 0.0335 0.0007 788 8 752 15 639 58 665 15 109 1.2 0.1211 0.0015 1.0231 0.0287 0.0614 0.0017 0.0317 0.0007 737 9 715 14 654 64 632 14 110 1 0.1237 0.0021 1.0895 0.0394 0.0639 0.0022 0.0334 0.0008 752 12 748 19 739 73 663 15 111 1 0.3236 0.0048 5.2312 0.1328 0.1169 0.0027 0.0874 0.0020 1807 24 1858 22 1910 9 1694 38 112 0.7 0.1145 0.0014 0.9719 0.0193 0.0612 0.0010 0.0313 0.0006 699 8 689 10 656 37 622 11 113 1.2 0.3597 0.0057 6.0394 0.1412 0.1221 0.0029 0.0965 0.0022 1981 27 1982 20 1987 43 1863 40 114 1.1 0.3414 0.0036 5.6829 0.1087 0.1202 0.0024 0.1051 0.0021 1894 18 1929 17 1959 35 2019 39 115 2.2 0.1244 0.0013 1.1103 0.0220 0.0645 0.0012 0.0363 0.0006 756 8 758 11 767 41 720 12 116 1.7 0.1306 0.0013 1.1795 0.0234 0.0654 0.0013 0.0380 0.0007 791 7 791 11 789 43 753 14 117 2.2 0.1224 0.0012 1.0672 0.0214 0.0632 0.0012 0.0322 0.0006 744 7 737 11 722 41 641 11 118 1.3 0.1274 0.0016 1.1309 0.0269 0.0644 0.0014 0.0345 0.0007 773 9 768 13 754 46 686 15 注:锆石U-Pb年龄值使用说明(包括正文、图及锆石Hf同位素计算):小于12亿年的数据均用锆石的206Pb/238Pb年龄,大于12亿年的数据均用锆石的207Pb/206Pb年龄 表 2 丹洲群拱洞组碎屑锆石Hf同位素数据(样品号:HK-19)
Table 2 Hf isotope data for detrital zircon grains for from Gongdong Formation in Danzhou Group (Sample: HK-19)
点号 年龄/Ma 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf 2σ εHf(0) εHf(t) 2σ TDM TDM2 fLu/Hf 1 776 0.219353 0.006281 0.282138 0.000030 -22.4 -8.6 1.1 1825 1020 -0.81 5 707 0.072002 0.001906 0.281938 0.000022 -29.5 -14.8 0.8 1894 1276 -0.94 6 739 0.058196 0.002005 0.282453 0.000029 -11.3 4.0 1.0 1162 1284 -0.94 7 730 0.114721 0.002999 0.282442 0.000023 -11.7 3.0 0.8 1210 1318 -0.91 9 737 0.052978 0.001515 0.282479 0.000022 -10.4 5.2 0.8 1109 1331 -0.95 11 2478 0.026945 0.000711 0.281292 0.000020 -52.3 2.0 0.7 2716 2878 -0.98 12 780 0.084112 0.002497 0.282416 0.000026 -12.6 3.3 0.9 1231 1357 -0.92 14 765 0.071027 0.002187 0.282358 0.000028 -14.6 1.1 1.0 1305 1376 -0.93 18 2247 0.010113 0.000281 0.281005 0.000021 -62.5 -12.7 0.8 3068 3635 -0.99 24 2456 0.012930 0.000350 0.280947 0.000027 -64.5 -10.1 1.0 3150 3633 -0.99 25 892 0.059806 0.001608 0.282423 0.000020 -12.4 6.4 0.7 1192 1404 -0.95 27 780 0.066628 0.002078 0.282221 0.000029 -19.5 -3.3 1.0 1497 1419 -0.94 28 845 0.111336 0.003463 0.282502 0.000029 -9.5 7.2 1.0 1135 1455 -0.90 31 2000 0.095880 0.002104 0.281371 0.000029 -49.6 -7.8 1.0 2707 3133 -0.94 36 831 0.070647 0.001974 0.282486 0.000029 -10.1 7.1 1.0 1113 1464 -0.94 37 819 0.079851 0.002488 0.282402 0.000030 -13.1 3.6 1.1 1251 1480 -0.93 38 2515 0.024262 0.000678 0.281306 0.000027 -51.8 3.4 0.9 2694 2818 -0.98 39 810 0.054110 0.001748 0.281968 0.000030 -28.4 -11.5 1.1 1844 1485 -0.95 41 755 0.047925 0.001671 0.282422 0.000029 -12.4 3.4 1.0 1196 1491 -0.95 43 2008 0.034244 0.000899 0.281269 0.000022 -53.2 -9.6 0.8 2760 3254 -0.97 45 775 0.087182 0.002445 0.282459 0.000027 -11.1 4.8 1.0 1166 1496 -0.93 48 776 0.060838 0.001670 0.282451 0.000024 -11.3 4.9 0.8 1154 1505 -0.95 50 850 0.055959 0.001554 0.282587 0.000027 -6.6 11.4 0.9 957 1542 -0.95 52 753 0.044033 0.001189 0.282224 0.000025 -19.4 -3.4 0.9 1458 1556 -0.96 53 2655 0.032016 0.000840 0.281053 0.000027 -60.8 -2.7 0.9 3048 3316 -0.97 55 803 0.096307 0.002506 0.282404 0.000029 -13.0 3.4 1.0 1249 1621 -0.92 56 2329 0.060331 0.001826 0.281380 0.000029 -49.2 0.0 1.0 2674 2892 -0.95 57 777 0.052260 0.001568 0.282393 0.000028 -13.4 2.9 1.0 1234 1643 -0.95 60 775 0.082866 0.002401 0.282354 0.000025 -14.8 1.1 0.9 1319 1674 -0.93 61 819 0.065627 0.001713 0.281999 0.000024 -27.4 -10.2 0.8 1798 1678 -0.95 62 778 0.060447 0.001703 0.282432 0.000025 -12.0 4.3 0.9 1181 1745 -0.95 63 2129 0.019084 0.000527 0.281344 0.000028 -50.5 -3.7 1.0 2633 2975 -0.98 65 776 0.181892 0.005012 0.282140 0.000030 -22.4 -7.8 1.1 1754 1800 -0.85 66 777 0.055295 0.001738 0.282379 0.000027 -13.9 2.3 1.0 1260 1800 -0.95 67 2179 0.026747 0.000692 0.281207 0.000030 -55.3 -7.7 1.1 2829 3265 -0.98 68 768 0.193127 0.004771 0.282366 0.000027 -14.4 0.1 0.9 1391 1808 -0.86 70 775 0.055633 0.001524 0.281995 0.000023 -27.5 -11.2 0.8 1794 1809 -0.95 79 2359 0.095668 0.002043 0.281448 0.000030 -46.8 2.7 1.0 2594 2740 -0.94 80 1966 0.018405 0.000473 0.281409 0.000022 -48.2 -5.0 0.8 2541 2929 -0.99 81 2444 0.027353 0.000719 0.281183 0.000023 -56.2 -2.6 0.8 2863 3148 -0.98 82 2155 0.014151 0.000423 0.281287 0.000024 -52.5 -5.0 0.8 2702 3076 -0.99 83 2036 0.038675 0.000924 0.281141 0.000022 -57.7 -13.6 0.8 2936 3525 -0.97 85 2574 0.051989 0.001255 0.281031 0.000030 -61.6 -6.1 1.1 3111 3466 -0.96 87 2498 0.026692 0.000816 0.281296 0.000022 -52.2 2.4 0.8 2718 2867 -0.98 88 811 0.161497 0.004032 0.281970 0.000030 -28.4 -12.7 1.1 1961 1886 -0.88 89 2242 0.015048 0.000415 0.281320 0.000022 -51.4 -1.9 0.8 2658 2944 -0.99 93 715 0.067517 0.001980 0.282279 0.000024 -17.4 -2.6 0.8 1410 1905 -0.94 94 736 0.057541 0.001597 0.282381 0.000025 -13.8 1.6 0.9 1252 2021 -0.95 95 818 0.030886 0.001072 0.282313 0.000029 -16.2 1.2 1.0 1329 2107 -0.97 96 1992 0.018463 0.000468 0.281237 0.000021 -54.3 -10.5 0.7 2773 3300 -0.99 97 779 0.081626 0.002245 0.282296 0.000029 -16.8 -0.8 1.0 1397 1371 -0.93 97 797 0.081366 0.002633 0.282469 0.000029 -10.7 5.5 1.0 1158 2186 -0.92 98 840 0.052788 0.001501 0.281752 0.000027 -36.1 -18.4 1.0 2134 2232 -0.95 99 774 0.218394 0.005379 0.281978 0.000029 -28.1 -13.8 1.0 2027 2306 -0.84 100 782 0.100439 0.002769 0.282180 0.000029 -21.0 -5.2 1.0 1587 2370 -0.92 104 744 0.055933 0.001592 0.282270 0.000030 -17.7 -2.1 1.1 1409 2395 -0.95 108 788 0.064820 0.001832 0.282317 0.000026 -16.1 0.3 0.9 1351 2404 -0.94 109 737 0.038962 0.001193 0.282480 0.000024 -10.3 5.3 0.9 1098 2444 -0.96 110 752 0.086209 0.002935 0.282427 0.000029 -12.2 2.9 1.1 1230 2517 -0.91 111 1910 0.060079 0.001492 0.281307 0.000030 -51.8 -11.2 1.0 2750 3277 -0.96 116 791 0.208042 0.006198 0.282101 0.000023 -23.7 -9.6 1.1 1880 2559 -0.81 117 744 0.161311 0.004125 0.282035 0.000029 -26.1 -11.7 1.0 1868 2572 -0.88 118 773 0.106784 0.002604 0.282274 0.000027 -17.6 -1.9 1.1 1443 2812 -0.92 注:锆石的εHf(t)值用各自的206Pb/238Pb(介于707~892Ma之间的锆石)或207Pb/206Pb(介于1910~2655Ma之间的锆石)年龄计算 -
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