U-Pb Zircon Age, Geochemistry and Geological Significance of the Late Silurian Diabase in the Southwest Margin of Tarim
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摘要:
塔西南缘铁克里克构造带叶城一带古元古代花岗岩体及赛图拉岩群中大量发育辉绿岩脉(墙)群,通过对其进行详细的地质、年代学、地球化学和构造环境研究,结果表明, 该辉绿岩属于亚碱性拉斑玄武岩系列,具有高Fe、Ti,富Na,贫K的特征,球粒陨石标准化稀土元素配分图表现为LREE略富集的右倾分配模式,富集大离子亲石元素,相对亏损高场强元素,具有板内玄武岩特征。岩石成因研究表明,其具亏损岩石圈地幔源区特征,并受俯冲流体或熔体交代混染,原始岩浆源区主要为尖晶石二辉橄榄岩。辉绿岩形成于板内拉张环境。辉绿岩获得LA-ICP-MS锆石U-Pb年龄为(424±2.7)Ma,形成于晚志留世,结合西昆仑区域构造演化,认为该时期处于造山期后阶段,代表了原特提斯洋构造旋回的结束。辉绿岩中含有大量捕获锆石,第一组捕获锆石年龄为(2 242±19)Ma,表明铁克里克陆块确实存在古元古代结晶基底,第二组捕获锆石年龄为(1 842±42)Ma,代表了塔里木克拉通古元古代晚期的岩浆和构造记录。
Abstract:There are a large number of diabase dikes (walls) developed in the paleoproterozoic granite body and Setula Group in the Yecheng area of Tiekerike structural belt, southwestern margin of Tarim Basin. Through detailed geological, chronological, geochemical and tectonic environment studies, the results show that the diabases belong to the subbasic lapidous basalt series, with the characteristics of high Fe, Ti, Na and low K.The chondrite normalized REE patterns show the slightly enriched of LREE, which are right-sloping distribution. The diabases enrich LILEs and relatively loses HFSEs, resembling the feature of intraplate basalts. The study of lithogenesis showed that the diabases had the characteristics of a depleted lithospheric mantle source, and were mixed by subduction fluid or melt, and the original magma source area were mainly spinel dipyroxene peridotite. Diabases were formed in an intraplate tensioning environment. The LA-ICP-MS zircon U-Pb age of (424±2.7) Ma was obtained from diabase, formed in the Late Silurian, combined with the tectonic evolution of the West Kunlun region, it is believed that this period is in the post-orogenic stage, representing the end of the tectonic cycle of the original Proto-Tethyan Ocean. Diabases contain a large amount of inherited zircon, the first group inherits the zircon age of (
2242 ±19) Ma, which indicates that there is a Paleoproterozoic crystalline basement in the Tiekerek block, and the second group inherits the zircon age of (1 842±42) Ma, representing the magmatic and tectonic records of late Paleoproterozoic Tarim Craton. -
大陆造山带是研究大陆岩石圈结构、构造和动力学的天然场所( Jahn et al.,2000;袁四化等,2009)。研究区地处西昆仑造山带和塔里木地块结合部位的铁克里克构造带,其位于塔里木板块西南缘。姜春发等(2000)将铁克里克构造带划为中央造山带重要组成之一的西昆仑北带,其构造演化与昆仑造山带的演化有着密切联系,经历了多期次、多机制和多旋回的洋陆转换,至石炭纪后开始进入了陆内演化阶段(Yin et al.,2000;肖文交等,2000;Yuan et al.,2002;王向利等,2010;Jiang et al.,2013;Gibbons et al., 2015;Zhang et al.,2018a,2018b;张传林等,2019)。研究区自元古代以来经历多期次板块构造的拼合和造山运动,发育多期次岩浆变质作用及成矿过程,是研究塔里木古陆和原-古特提斯洋构造演化的重要位置(姜春发,2000,魏博等,2018)。昆仑山岩浆岩分布广泛,出露元古宇、早古生代、晚古生代、中生代和新生代花岗岩带, 它们沿构造线呈带状分布(李荣社等,2008)。
近年来,随着地质研究工作的深入,特别是同位素年代学研究的不断完善与深入,在叶城地区越来越多前寒武纪、古生代岩浆活动被甄别并记录(廖世勇,2010;陶再礼等,2022),岩浆记录表明自奥陶纪以来塔里木克拉通南部可能存在与原特提斯洋俯冲相关的活动大陆边缘(Wang et al.,2020,2021),然而受自然环境及研究程度所限,前人对于叶城地区早古生代原特提斯洋的构造演化及其相关的岩浆作用认识尚未达成一致。主要对于蛇绿岩存在位置及闭合时限存在争议,特别是对原特提斯洋的闭合时限等仍存在较大争议,①认为昆仑造山带早古时代沿着库地–其曼于特发育原特提斯洋,早古时代末期闭合,之后晚古生代沿着麻扎–康西瓦–苏巴什蛇绿岩带发育古特提斯洋。②认为沿着麻扎–康西瓦–苏巴什蛇绿岩带发育原–古特提斯持续演化的大洋,而沿着库地–其曼于特蛇绿岩带发育的弧后盆地于早古生代末期闭合(Yuan et al.,2002;Xiao et al.,2003;张传林等,2019;Yin et al.,2020)。廖世勇(2010)认为原特提斯洋盆封闭时间为志留纪(大同岩体及其中暗色微粒包体,U-Pb锆石年龄473.4~447.7 Ma,奥依塔克斜长花岗岩U-Pb锆石年龄338~328 Ma)。计文化等(2007)以基性岩脉中单矿物角闪石的40Ar/39Ar年龄(382~284 Ma)为依据,认为其为从早古生代晚期的挤压环境转化为引张环境所持续的时间,代表古特提斯洋打开时间。此外也有学者对洋盆俯冲极性有争议,有学者认为早古生代原特提斯洋向北俯冲消亡(Yuan et al.,2002;袁超等,2003;韩芳林,2006;陶再礼,2022),闭合时限为晚奥陶世—早泥盆世(邓万明,1995;Wang,2004);也有大量学者认为原特提斯洋向南俯冲(Liao et al.,2010;张传林等,2019),于晚奥陶世—早志留世期间发生闭合(Jia et al.,2013;柳坤峰,2014;刘成军,2015)。
总之,前人研究基本认为本区原特提斯洋盆闭合时限应在晚奥陶世—志留纪。基性岩墙(脉)群和A1型花岗岩形成于板内环境,作为造山期后伸展和非造山岩浆活动(大陆裂解)的标志,在超大陆及岩浆闭合研究中受到高度重视,因此,研究西昆仑晚古生代岩浆活动,尤其是基性岩墙的研究,对于理解西昆仑造山带的形成与演化,尤其古特提斯洋洋壳闭合实现具有重要的意义(陆松年,2001)。
基于此,笔者对塔里木西南缘叶城地区早古生代基性岩脉群开展了详细的岩石学、全岩地球化学、锆石U-Pb定年,揭示其岩石成因和源区组成,并结合前人研究资料,探讨其形成时的构造环境,为进一步约束特提斯洋的及其动力学过程提供依据,将对西昆仑地区古特提斯洋裂解事件群,探索大陆裂解的地球动力学背景及西昆仑构造演化提供依据。
1. 区域地质背景
工作区大地构造位置位于西昆仑构造带与塔南缘铁克里克断隆带结合部位,以柯岗断裂为界,东北部为塔里木地块之铁克里克断隆带,西南部为西昆仑构造带(图1)。铁克里克断隆带主要由太古界赫罗斯坦岩群构成结晶基底(葛荣峰等,2024),主要为一套混合岩化片麻岩组成,其次为一套古元古代二长花岗岩与正长花岗岩体。元古代及以上地层构成盖层岩系,上古生界为稳定盖层沉积,主要为泥盆系海陆交互相碎屑岩、石炭系浅海相碳酸盐岩夹碎屑岩及二叠系海陆交互相杂色碎屑岩,下古生界沉积基本缺失。中新生代为一套陆相建造,主要为一套河湖相碎屑岩沉积夹少量碳酸盐岩沉积。西昆仑构造带在区内大部分地段为岩浆岩,地层只发育少量中元古界赛图拉岩群变质岩、火山岩建造。岩浆岩以早古生代中酸性侵入岩为主,基本沿哈拉斯坦河断裂两侧发育,主要分布于棋盘-西河休一带,其中以奥陶纪的要龙花岗岩体为代表。
本次研究区内岩脉主要为辉绿岩(玢)脉,以岩脉群形式分布于叶城棋盘乡萨木其村一带,以单条、多条或脉群形式产出,多呈岩脉、岩墙状主要侵入于古元古界赫罗斯坦岩群黑云二长片麻岩及古元古代花岗岩体中(图1、图2a、图2b),产状较为稳定,脉体近直立,局部共轭状产出,脉壁较平直,脉体宽为0.5~10 m,产状为60°~120°∠55°~80°;长度数百米~1千米及以上,侵入接触关系明显,与围岩界面清楚平直,变形变质程度较弱,具高绿片岩相变质,围岩多发育混合岩化作用。从宏观上看辉绿岩脉呈群体状产出,表现为辉绿岩呈密集的辉绿岩脉(墙)产出,密集区平均每隔10 m出露1条宽约0.5~15 m辉绿岩脉。
2. 岩石学特征
棋盘辉绿岩新鲜面深灰绿色,风化面呈灰绿色,块状构造,具典型辉绿结构,斜长石和辉石自形程度相近,颗粒大小较均匀,彼此均匀分布构成块状构造;次生蚀变较强(图2c)。斜长石:自形-半自形板状,表面较浑浊脏,呈土褐色,大部分表面分布次生黏土矿物和少量绢云母矿,颗粒大小较均匀,分布均匀,粒径约为0.60~2.80 mm;辉石:呈柱状或近八边形,几乎全部已被粉尘状绿泥石及少量纤维状绿泥石完全覆盖,干涉色已发生变化;少量完全被绿泥石交代,呈现异常蓝干涉色,部分沿解理析出细小黑色不透明金属矿物;个别粗粒辉石内部包含斜长石,构成嵌晶含长结构;辉石颗粒大小较均匀,分布均匀,粒径约为0.60~2.40 mm;金属矿物:他形粒状或者近板状,较均匀分布,主要与普通辉石分布一起,粒径约为0.12~0.20 mm。
3. 测试方法
用于岩石地球化学及U-Pb锆石年龄研究的辉绿岩样品采自叶城棋盘乡萨木其沟(图1b)。岩石地球化学样品分别进行主量元素和微量元素分析测试,测试在长安大学西部矿产资源与地质工程教育部重点实验室完成。主量元素使用X射线荧光光谱仪(XRF-1500)法测试,精度优于2%~3%,测定流程包括烧失量的计算和玻璃熔融制样,全岩稀土和微量元素分析,采用Thermo-X7电感耦合等离子体质谱仪(ICP-MS),分析精度和准确度优于10%。化学分析测试流程参考文献介绍的方法(Chen et al.,2000,2002)。锆石挑选及照相在北京锆年领航科技有限公司完成,用浮选和电磁选方法进行分选,然后在双目镜下挑选出晶形和透明度较好的锆石颗粒,将它们粘贴在环氧树脂表面,再对锆石表面进行抛光,直至锆石内部暴露。然后利用扫描电镜对其进行反射光、透射光和阴极发光(CL)显微照相。锆石U-Pb同位素分析在西北大学大陆动力学国家重点实验室的LA-ICP-MS仪器上用标准测定程序进行,采用国际标准锆石91500作为外标校正,以保证标准和样品的仪器条件完全一致。激光束的束斑为32 μm。将实验获得的数据进行同位素比值的校正,以扣除普通Pb的影响。所给定的同位 素比值和年龄误差(标准偏差)在1σ水平。详细的实验原理和流程见文献详解(Yuan,2004)。
4. 分析结果
4.1 LA-ICP-MS锆石U-Pb年龄结果
本次对辉绿岩样品HL-6TW进行了LA-ICP-MS锆石U-Pb同位素分析,共计28个测点分析(表1),分析数据应用分段校正,成岩年龄是对206Pb/238U数据进行统计分析。测试分析样品的锆石阴极图像CL显示了辉绿岩锆石有两类:一类长柱状锆石,具有较宽的黑色增生边和短柱状锆石,可见亮边或黑边,具有清晰的核幔结构特征,其中核部为较宽的韵律环带,边部为薄的黑色边,表明这些锆石为捕获锆石。二类锆石组成均匀,呈近等粒状、短柱状,但少量发生了碎裂,大小略有变化,粒径介于80~120 μm,个别粒度较大,发育清晰的韵律环带结构(图3),Th/U含量为0.42~0.92,比值较高(>0.40),与典型的岩浆锆石特征一致。数据点均落在谐和线上及附近,说明没有发生明显的Pb丢失。若不考虑孤立7个年龄数据,本次测试年龄主要划分为3组:第一组样品的206Pb/238U年龄为(424±2.7) Ma,(MSWD=0.49,n=11),代表辉绿岩的结晶年龄(即形成年龄),时代为晚志留世(图4b);第二组样品的锆石206Pb/238U年龄为(1 842±42 )Ma(MSWD=4.3,n=5)(图4c);第三组样品的锆石206Pb/238U年龄为(
2242 ±19) Ma(MSWD=0.75,n=5)(图4d)。表 1 辉绿岩的LA-ICP-MS锆石U-Pb分析结果Table 1. Table of dating analysis of diabase zircon LA–ICP–MS样品编号 含量(10−6) Th/U 同位素比值 同位素年龄(Ma) Pb Th U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ HL-6TW-1 315.95385 469.45 764.58 0.61 0.11275 0.00126 5.2058 0.05872 0.3349 0.00349 1844 9 1854 10 1862 17 HL-6TW-2 571.96792 949.62 1395.57 0.68 0.1115 0.00116 5.01132 0.05296 0.32601 0.00332 1824 9 1821 9 1819 16 HL-6TW-3 209.55952 215.47 345.33 0.62 0.16331 0.00214 10.57378 0.13946 0.46963 0.00541 2490 10 2486 12 2482 24 HL-6TW-4 31.56621 229.84 388.43 0.59 0.05612 0.00107 0.52255 0.00969 0.06754 0.00077 457 22 427 6 421 5 HL-6TW-5 23.91901 182.49 291.96 0.63 0.05695 0.00108 0.53845 0.00991 0.06858 0.00078 490 22 437 7 428 5 HL-6TW-6 136.2894 167.45 223.16 0.75 0.15963 0.00189 10.16874 0.12075 0.46203 0.00499 2452 9 2450 11 2449 22 HL-6TW-7 114.47227 375.83 1528.36 0.25 0.05587 0.00062 0.52261 0.00579 0.06785 0.00069 447 11 427 4 423 4 HL-6TW-8 46.12337 247.93 586.97 0.42 0.05539 0.00152 0.52327 0.01388 0.06851 0.0009 428 36 427 9 427 5 HL-6TW-9 37.08585 403.15 414.63 0.97 0.05517 0.00121 0.51669 0.01098 0.06793 0.00081 419 27 423 7 424 5 HL-6TW-10 23.93572 217.65 284.42 0.77 0.05564 0.00147 0.51453 0.01309 0.06707 0.00086 438 34 421 9 418 5 HL-6TW-11 182.96866 174.88 278.25 0.63 0.1638 0.00173 11.37392 0.12032 0.50359 0.00509 2495 8 2554 10 2629 22 HL-6TW-12 62.72011 631.34 705.88 0.89 0.05786 0.00079 0.54457 0.00726 0.06826 0.00071 524 14 441 5 426 4 HL-6TW-13 55.57702 288.19 696.72 0.41 0.05587 0.00079 0.52193 0.00724 0.06774 0.00071 447 14 426 5 423 4 HL-6TW-14 165.63799 161.21 275.45 0.59 0.16075 0.0017 10.18184 0.10693 0.45935 0.0046 2464 8 2451 10 2437 20 HL-6TW-15 310.96888 384.68 728.38 0.53 0.11283 0.00119 5.30526 0.05522 0.34099 0.00339 1845 8 1870 9 1891 16 HL-6TW-16 39.85422 376.9 453.41 0.83 0.05416 0.00099 0.51043 0.00902 0.06835 0.00075 378 21 419 6 426 5 HL-6TW-17 211.66882 226.43 337.64 0.67 0.16119 0.00171 10.43269 0.10897 0.46937 0.00468 2468 8 2474 10 2481 21 HL-6TW-18 16.15166 103.65 303.07 0.34 0.05164 0.0008 0.32983 0.00499 0.04632 0.00049 270 17 289 4 292 3 HL-6TW-19 187.78596 159.58 304.43 0.52 0.16261 0.00173 10.62133 0.11093 0.47367 0.00471 2483 8 2491 10 2500 21 HL-6TW-20 108.37869 203.95 246.97 0.83 0.11053 0.00119 4.93986 0.05231 0.3241 0.00322 1808 9 1809 9 1810 16 HL-6TW-21 44.88306 409.05 692.03 0.59 0.05358 0.00067 0.40163 0.00491 0.05436 0.00055 353 12 343 4 341 3 HL-6TW-22 310.28845 337.12 755.5 0.45 0.11184 0.00118 5.06654 0.05228 0.32852 0.00323 1830 8 1831 9 1831 16 HL-6TW-23 146.74297 143.78 235.26 0.61 0.16204 0.00178 10.43984 0.11226 0.46722 0.0047 2477 8 2475 10 2471 21 HL-6TW-24 37.47048 55.45 52.13 1.06 0.16889 0.00267 11.3314 0.17715 0.48654 0.00624 2547 12 2551 15 2556 27 HL-6TW-25 21.74959 93.65 206.22 0.45 0.05832 0.00219 0.6729 0.02423 0.08367 0.00131 542 51 522 15 518 8 HL-6TW-26 74.78277 136.35 946.08 0.14 0.05948 0.00126 0.56493 0.01149 0.06887 0.0008 585 25 455 7 429 5 HL-6TW-27 391.93267 818.2 964.51 0.85 0.10909 0.00314 4.28408 0.11341 0.28483 0.0032 1784 54 1690 22 1616 16 HL-6TW-28 106.79042 553.84 1308.16 0.42 0.05518 0.00072 0.5136 0.00647 0.06749 0.00068 420 13 421 4 421 4 4.2 岩石地球化学特征
4.2.1 主量元素特征
辉绿岩9件样品(PM101-8DH1、HL-1DH~HL-8DH)主量元素分析结果显示(表2):烧失量LOI含量为1.04%~5.24%,SiO2含量为47.23%~50.18%,平均为48.07%;Al2O3含量为12.55%~14.58%,平均含量为13.20%;MgO含量为4.26%~7.14%,平均含量为5.88%;Na2O含量为2.13%~3.36%,平均含量为2.77%;K2O含量为0.74%~1.88%,平均含量为1.09%,K2O/Na2O值为0.17~0.62,平均为0.40,显著富Na,类似板内玄武岩,K2O+Na2O含量介于3.16%~5.20%,反映岩石后期发生了不同程度的蚀变作用。TiO2含量介于1.74%~3.24%, 平均值为2.62%,明显高于大洋拉斑玄武岩平均值(1.44%)、岛弧拉斑玄武岩TiO2值(0.84%),与板内玄武岩一致。在TAS岩浆岩岩石类型判别图中(图5a),全部落入辉长/辉绿岩区,与薄片鉴定命名一致。在SiO2-FeOT/MgO图解(图5b)中,辉绿岩落在亚碱性拉斑系列区。主量元素整体具有高Fe、Ti,富Na,贫K的特征。
表 2 辉绿岩主量(%)、微量、稀土元素(10−6)分析结果Table 2. Analysis results of major (%), trace and rare earth elements (10−6) in diabase样品编号 PM101-8DH1 HL-1DH HL-2DH HL-3DH HL-4DH HL-5DH HL-6DH HL-7DH HL-8DH SiO2 47.23 50.18 47.43 47.77 47.83 49.8 46.73 47.61 48.03 TiO2 1.74 2.35 2.92 1.75 2.61 3.14 3.08 2.78 3.24 Al2O3 14.05 12.55 13 14.58 12.74 12.71 13.62 12.91 12.67 TFe2O3 12.39 11.94 16 12.54 16.42 14.96 14.58 14.31 15.44 MnO 0.19 0.17 0.23 0.19 0.25 0.22 0.23 0.19 0.18 MgO 6.82 6.43 5.27 7.14 6.42 4.26 6.24 5.41 4.96 CaO 10.74 6.28 9.65 10.95 6.38 7.41 8.89 10.29 8.12 Na2O 2.85 2.92 2.48 2.13 2.16 3.32 3.36 2.34 3.36 K2O 0.84 1.68 0.74 1.03 1.34 1.88 0.57 0.91 0.78 P2O5 0.19 0.26 0.37 0.21 0.48 0.41 0.51 0.39 0.39 LOI 2.62 5.24 1.04 1.90 3.40 2.37 1.34 1.55 2.02 TOTAL 99.66 100.00 99.13 100.19 100.03 100.48 99.15 98.69 99.19 Li 152.08 32.90 13.96 15.52 16.50 16.87 11.19 15.47 19.67 La 12.17 41.35 24.14 29.61 25.13 25.82 58.22 31.32 38.15 Ce 30.71 86.05 55.85 59.05 56.72 57.85 118.80 69.17 82.33 Pr 4.23 10.34 7.37 6.58 7.32 7.46 13.83 8.85 10.36 Nd 18.86 41.38 32.48 25.23 33.36 32.56 54.64 38.27 43.26 Sm 4.66 7.63 7.62 4.92 7.48 7.21 11.12 8.52 10.08 Eu 1.61 2.42 2.71 1.74 2.74 2.65 2.72 2.69 2.83 Gd 5.05 6.89 8.64 5.63 8.72 6.98 11.31 9.32 10.77 Tb 0.81 0.92 1.37 0.82 1.44 1.02 1.80 1.35 1.61 Dy 5.06 5.18 8.39 4.85 9.15 5.89 11.09 8.18 9.63 Ho 1.01 0.93 1.69 0.99 1.91 1.09 2.19 1.60 1.96 Er 2.98 2.34 4.71 2.68 5.59 2.97 6.30 4.50 5.58 Tm 0.41 0.34 0.63 0.41 0.78 0.38 0.91 0.65 0.80 Yb 2.51 2.07 4.47 2.38 5.40 2.56 5.78 4.16 5.09 Lu 0.42 0.31 0.66 0.37 0.80 0.37 0.90 0.57 0.72 Y 24.13 21.81 39.84 22.71 44.86 25.52 52.55 37.72 46.94 ΣREE 90.50 208.14 160.73 145.26 166.55 154.79 299.62 189.12 223.17 LREE 72.24 189.17 130.17 127.13 132.76 133.53 259.33 158.81 187.01 HREE 18.26 18.98 30.56 18.12 33.79 21.26 40.29 30.32 36.17 LREE/HREE 3.96 9.97 4.26 7.01 3.93 6.28 6.44 5.24 5.17 (La/Yb)N 3.47 14.32 3.87 8.92 3.34 7.24 7.23 5.40 5.37 δEu 1.01 1.00 1.02 1.01 1.03 1.13 0.73 0.92 0.82 δCe 1.05 0.99 1.02 0.99 1.01 1.01 0.99 1.00 1.00 Li 22.00 32.90 13.96 15.52 16.50 16.87 11.19 15.47 19.67 Be 0.41 1.49 1.23 0.72 0.81 0.65 2.63 1.36 1.82 Sc 38.43 27.63 32.97 29.00 43.05 26.13 31.54 35.58 28.96 V 295.10 273.13 406.23 271.99 340.19 295.18 341.59 366.63 400.37 Cr 200.39 271.56 43.62 136.57 91.70 97.13 54.23 76.02 43.80 Co 46.54 38.07 47.23 46.41 45.36 45.63 39.10 49.82 42.65 Ni 83.00 99.09 37.80 78.60 32.96 73.97 37.72 55.17 46.57 Cu 74.79 76.51 54.46 71.39 53.75 76.30 178.45 117.35 109.22 Zn 80.94 141.15 128.48 87.47 126.17 106.60 390.70 90.71 99.14 Ga 16.54 16.91 21.43 17.71 19.21 18.37 21.03 19.81 21.09 Rb 37.93 76.88 40.82 65.69 57.56 26.73 89.17 31.13 36.87 Sr 227.50 319.73 272.86 489.31 251.63 306.97 339.90 247.93 231.69 Zr 84.48 188.69 175.76 101.50 165.19 141.18 350.64 206.27 258.49 Nb 9.20 20.10 18.70 8.40 17.92 16.74 52.64 26.96 31.24 Mo 0.29 0.46 0.91 0.45 0.54 0.98 2.32 1.33 1.56 Cd 0.08 0.24 0.13 0.14 0.12 0.12 0.35 0.09 0.11 In 0.06 0.10 0.11 0.07 0.12 0.10 0.13 0.11 0.12 Cs 0.49 1.11 0.98 0.40 0.62 0.72 0.46 0.78 0.39 Ba 364.57 931.24 400.22 657.53 512.96 329.56 604.25 326.51 300.15 Hf 2.37 5.37 5.03 2.92 4.99 4.01 9.49 5.82 7.36 Ta 0.69 1.26 1.20 0.55 1.21 1.10 3.56 1.79 2.09 Pb 1.84 39.57 5.02 6.43 4.88 3.19 6.21 4.36 5.84 Bi 0.01 0.06 0.01 0.01 0.02 0.01 0.02 0.01 0.02 Th 1.82 6.15 5.96 7.04 2.82 5.23 9.47 3.60 4.53 U 0.57 1.35 0.93 0.52 0.91 0.74 2.10 1.22 1.34 4.2.2 稀土与微量元素特征
在稀土元素球粒陨石标准化配分图解上(图6a),辉绿岩表现出LREE略富集的右倾分配模式,稀土元素总量ΣREE为90.50×10−6~299.62×10−6,平均值为181.99,(La/Yb)N为3.47~14.32,平均值为6.57,(La/Sm)N为1.64~3.78,平均值为2.58,重稀土内基本不分馏,部分样品具有较弱的Eu负异常或正异常(δEu=0.73~1.13),这与岩石含有较多的斜长石有关。在微量元素蛛网图上(图6b),辉绿岩的微量元素分布形式表现为富集大离子亲石元素(如Rb、Ba),明显亏损Nb-Ta以及无明显Ti元素亏损。辉绿岩的不相容元素比值Zr/Nb=6.66~12.08,Nb/Ta=13.32~16.0,Zr/Hf=31.14~37.00。总体上辉绿岩表现出板内拉斑玄武岩相似稀土和微量分布形式。
图 6 辉绿岩稀土元素球粒陨石标准化配分模式图(a)和微量元素原始地幔标准化蛛网图(b)球粒陨石数值据 Boynton(1984);原始地幔数值据Sun等(1989)Figure 6. (a) Chondrite-normalized REE pattern for the diabases, (b) primitivemantle-normalized trace elements spidergram for the diabases5. 讨论
5.1 源区性质及构造背景
镁铁质岩石通常起源于岩石圈地幔或软流圈地幔,起源于岩石圈地幔的岩石通常相对原始地幔富集LILE和LREE,亏损HFSE(如 Nb、Ta 和 Ti),而起源于软流圈地幔的物质通常富集 LILE 和 HFSE(Sklyarov et al.,2003),本区辉绿岩样品相对于原始地幔富集LILE(Rb、Ba、K),亏损HFSE(如Nb、Ta和P),表明本区辉绿岩应起源于岩石圈地幔。并且辉绿岩的Sm/Nd值为0.20~0.25,略低于MORB的范围(平均值0.32) (Anderson,1994),也表明岩浆源区主体属于岩石圈地幔。其较低的Nb/Zr值(0.002~0.006),暗示岩浆源区可能为亏损地幔(Saunders et al.,1992;Kieffer et al.,2004)。但样品的Sr含量(227.50×10−6~489.31×10−6,平均值为299×10−6)显著高于地幔值(17.8×10−6,据Taylor et al.,1985),指示其岩浆源区并非单一来自地幔,可能受到围岩混染或俯冲板片流体交代作用的影响( McCulloch et al.,1991;Hawkesworth et al.,1993)。高场强元素Nb、Ta、Zr、Hf在蚀变和变质作用过程中具有良好的稳定性,是源区性质和岩石成因的良好示踪剂。辉绿岩的Nb/Ta值变化于13.33~15.95,平均值为15.00,且Zr/Hf值变化于33.10~36.95,平均值为35.14,其Nb/Ta与Zr/Hf值分别与大陆地壳值相近(Nb/Ta=11,Zr/Hf=33,据Taylor et al.,1985),而低于洋中脊玄武岩值(Nb/Ta=17.7,Zr/Hf=36.1,据Sun et al.,1989),指示辉绿岩受到明显的地壳混染的影响。辉长岩中Ce /Pb值为2.17~19.13,平均为13.11,而地壳中Ce/Pb值<15,典型地幔Ce/Pb=25±5(Hofmann et al.,1986),显示岩体受到同化混染作用;Nb/U、Nb/La值可作为判别地壳混染的标志,Nb/La值为0.28~0.90(小于1),Nb/U值为14.89~25.07,低于洋中脊玄武岩和洋岛玄武岩Nb/U值(47±10)及原始地幔Nb/U值(平均值33.59),而略高于大陆地壳8.93(Taylor et al.,1985),反映岩浆在上升过程中有陆壳物质的加入。综上所述,棋盘辉绿岩起源于岩石圈地幔,岩浆在演化过程中遭受了地壳物质的同化混染作用。
辉绿岩具有相对稳定的矿物组成和化学组成,且具有相对较高的MgO含量,并富含Cr和Co等相容元素,暗示岩浆没有经历明显的结晶分异(张海军,2018),它基本上代表了原始岩浆的组成,而相对不高的Ni含量则反映了地幔源区的不均一。尽管部分熔融程度、岩浆上升或滞留过程中结晶分异和陆壳混染等因素均对玄武质岩石最终的化学组成有影响,但源区性质是制约化学组成的最关键因素,厘定玄武质岩石的源区对理解不均一性具有重要的意义。辉绿岩具有相对较低的总碱含量(Na2O+K2O=3.16%~4.60%),属于典型的板内基性岩浆岩,因此它不是碳酸盐化橄榄岩、角闪岩部分熔融的产物,但是相对较低的CaO含量(6.28%~10.74%),排除它是纯地幔橄榄岩部分熔融产物的可能。同时,岩石具有较高FeO/(CaO-3MgO)/SiO2值(0.6~1.48),暗示其源区以辉石部分熔融为主,在图7中,辉绿岩投影点落在辉石区,但也均靠近橄榄石区域,表明橄榄石也对该类岩石的形成具有重要的贡献。Dy/Yb是诊断源区特征的重要地球化学指标,如果部分熔融发生在石榴石稳定区,其熔体的Dy/Yb值大于2.5,如果熔融作用发生在尖晶石稳定区,其熔体的Dy/Yb值小于1.5(Jiang ,2013)。本区辉绿岩的Dy/Yb值介于1.89~2.50,暗示原始岩浆源区以尖晶石二辉橄榄岩为主,并有少量石榴子石,这与La/Yb-Dy/Yb谐变图主要靠近尖晶石二辉橄榄岩(图8)一致。因此,其原始岩浆源区可能主要为尖晶石二辉橄榄岩源区,并有少量石榴子石混合。
图 7 辉绿岩Fe/Mn-CaO(a)、Fe/Mn-MgO(b)、Fe/Mn-Fe2O3T(c)和Fe/Mn-MnO(d)源区判别图解(底图据Li, 2016)Figure 7. (a) Fe/Mn-CaO, (b) Fe/Mn-MgO, (c) Fe/Mn-Fe2O3T and (d) Fe/Mn-MnO identification diagrams of source regions of diabase图 8 辉绿岩的La/Yb-Dy/Yb图解(据Bogaard et al., 2003)Figure 8. Illustration of La/Yb-Dy/Yb of diabase调查区辉绿岩脉呈直立、平行排列或者“共轭”状产出的岩墙群,它是伸展构造的重要样式,代表一次规模巨大的幔源岩浆事件,前人将其划为早古生代塔里木板块与西昆仑构造带俯冲碰撞后伸展的产物。辉绿岩样品全部组成低缓右倾型,轻重稀土分异较小,铕负异常不明显,具大陆拉斑玄武岩特征。不相容元素K,Rb,U,Ba富集,高场强元素Nb,Ta,Zr,Hf无富集,Ti亏损不明显,Nb,Ta,Th表现为有明显负异常,U富集可能指示有地壳物质加入,其较高的Nb/Y值(0.37~0.71),相对稳定的Zr/Hf(33.10~36. 95)和Nb/Ta(13.33~15.95)等比值,都表明辉绿岩的大陆板内特征显著。辉绿岩整体显示板内玄武岩特征,分布型式为裂谷属性(Condie,1989;Wilson,1989),且Yb-Th/Ta图解中(图9),投影点主要落在板内火山岩区域,且靠近活动大陆边缘,说明调查区内辉绿岩脉形成于板内环境。
图 9 辉绿岩Yb-Th/Ta图解(底图据Schandl et al.,2002)Figure 9. Illustration of diabase Yb-Th/Ta5.2 锆石年代学意义及岩浆事件
西昆仑古洋盆(原特提斯洋)于南华纪—寒武纪在西昆仑地块北缘开始拉张裂解,形成以柯岗、其曼于特、库地蛇绿岩为代表的寒武纪蛇绿岩带(年龄503~526 Ma)(肖序常等,2003;韩芳林,2006;李天福等,2014)。晚寒武世洋盆发展达到顶峰,开始俯冲消减,形成了一系列加里东早期岛弧岩浆岩(128 km岩体、阿卡孜岩体、要龙岩体、大同西岩体帕合堡岩体 I型俯冲(同碰撞)花岗岩(袁超等,2003;计文化等,2007;廖世勇等,2010;刘成军,2015),其中,以阿喀孜花岗岩体(456±2)Ma和赛图拉石英闪长岩体(452±2 Ma)为代表(陶再礼等,2022),年龄集中在499 ~449 Ma,洋壳俯冲作用至少持续到450~470 Ma(Yuan et al.,2002)。昆仑洋盆的闭合是以洋盆沿柯岗结合带一线俯冲消减形式完成的,并形成同期复合岩浆弧,俯冲消减过程中区内岩浆活动各个序列各自构成了由中性–酸性的同源岩浆演化序列。晚志留世,塔里木微板块和西昆仑构造带发生陆–陆碰撞,晚志留世“S”型同碰撞、后碰撞的过铝质碱性花岗侵入岩,其中以半德尔岩体、布隆岩体S型花岗岩(441±2 Ma)(王超等,2013),反映了大陆隆起作用,标志着古柯岗洋消亡,塔里木微板块和西微板块碰撞拼合在一起。棋盘一带晚志留世—早泥盆世,进一步俯冲碰撞,发生垂向增生,发生造山期后伸展作用,大量辉绿岩脉群产出,暗示了整个造山作用的结束,本次获得的辉绿岩结晶年龄为(424±2.7) Ma,比刘鑫等(2016)获得的古元古代花岗岩体中辉绿岩脉年龄较老(408.5±7.3) Ma,代表了原特提斯洋构造旋回的结束。
此外,本次获得锆石U-Pb年龄,具有明显集中的两组捕获锆石年龄,第一组捕获锆石年龄为(
2242 ±19) Ma(MSWD=0.75,n=5),与塔里木西南缘古元古代赫罗斯坦杂岩(主要为一套2.4~2.3 Ga的花岗质片麻岩)(Zhang,2013),及侵入东部喀拉喀什群斜长角闪岩(锆石U-Pb年龄2480 Ma)中的变辉绿岩中(锆石U-Pb年龄2200 Ma)(王向利等,2010)同位素年龄一致,表明铁克里克陆块确实存在古元古代基底。第二组捕获锆石年龄为(1 842±42) Ma(MSWD=4.3,n=5)(图2b),指示古元古代晚期Columbia超大陆裂解的岩浆和构造记录。Zhao等(2003)认为2.1~1.8 Ga全球范围内发生了大规模的俯冲碰撞事件,各个古老克拉通拼合形成了Columbia超大陆。而塔里木克拉通南缘的欧龙布鲁克微陆块中获得变质表壳岩达肯大坂岩群(变质年龄1.95~1.91 Ga),深熔成因的长英质浅色体(形成年龄1.94 Ga)(刘东晓等,2017),以及形成于活动大陆边缘或弧后伸展等构造环境的A2型花岗岩(锆石年龄为1.95 Ga),代表了Columbia超大陆裂解有关的构造热事件。欧龙布鲁克微陆块中环斑花岗岩(1.78 Ga)和基性岩墙(1.85 Ga)及塔里木周缘1.85 Ga的陆内伸展环境形成的A2-A1型花岗样的发现(张永旺等,2021),则指示了Columbia超大陆裂解,与华北克拉通周缘代表Columbia超大陆裂解的1.70 ~1.85 Ga的A型花岗岩(张健等,2014)的年龄基本一致,本次获得的捕获年龄(1 842±42) Ma代表了塔里木克拉通古元古代晚期的岩浆和构造记录。6. 结论
(1)叶城一带辉绿岩呈直立、平行排列或者“共轭”状产出的岩脉群状产出,主量元素具有高Fe、Ti,富Na,贫K的特征,属于亚碱性拉斑玄武岩系列。辉绿岩表现为LREE略富集的右倾分配模式,具较弱Eu异常,明显亏损Nb-Ta以及不明显Ti元素亏损,富集大离子亲石元素,相对亏损高场强元素,具有板内玄武岩特征。
(2)辉绿岩形成于板内拉张环境,地球化学属性表明其源区具亏损地幔特征,并受俯冲流体或熔体交代混染,原始岩浆源区主要为尖晶石二辉橄榄岩源区。
(3)笔者获得辉绿岩LA-ICP-MS锆石U-Pb年龄为(424±2.7)Ma,形成于晚志留世,结合西昆仑区域构造演化,认为该时期处于造山期后阶段,代表了原特提斯洋构造旋回的结束。辉绿岩中含有大量继承锆石,第一组继承锆石年龄为(
2242 ±19) Ma,代表铁克里克原始古陆的结晶基底,第二组继承锆石年龄为(1842±42) Ma,代表了塔里木克拉通古元古代晚期的岩浆和构造记录。致谢:对参加野外调查工作的中国冶金地质总局西北地质勘查院吴锋工程师及魏加斌、郑天天等技术员,在此表示衷心的感谢。同时感谢评审专家提出的宝贵意见。
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图 5 TAS岩石分类命名图解(a)(底图据Cox et al.,1979)及FeOT/MgO-TiO2图解(b)(底图据Miyasiro,1974)
Figure 5. (a) Illustration of TAS rock classification and nomenclature and (b) FeOT/MgO-TiO2 illustration
图 6 辉绿岩稀土元素球粒陨石标准化配分模式图(a)和微量元素原始地幔标准化蛛网图(b)
球粒陨石数值据 Boynton(1984);原始地幔数值据Sun等(1989)
Figure 6. (a) Chondrite-normalized REE pattern for the diabases, (b) primitivemantle-normalized trace elements spidergram for the diabases
图 7 辉绿岩Fe/Mn-CaO(a)、Fe/Mn-MgO(b)、Fe/Mn-Fe2O3T(c)和Fe/Mn-MnO(d)源区判别图解(底图据Li, 2016)
Figure 7. (a) Fe/Mn-CaO, (b) Fe/Mn-MgO, (c) Fe/Mn-Fe2O3T and (d) Fe/Mn-MnO identification diagrams of source regions of diabase
图 8 辉绿岩的La/Yb-Dy/Yb图解(据Bogaard et al., 2003)
Figure 8. Illustration of La/Yb-Dy/Yb of diabase
图 9 辉绿岩Yb-Th/Ta图解(底图据Schandl et al.,2002)
Figure 9. Illustration of diabase Yb-Th/Ta
表 1 辉绿岩的LA-ICP-MS锆石U-Pb分析结果
Table 1 Table of dating analysis of diabase zircon LA–ICP–MS
样品编号 含量(10−6) Th/U 同位素比值 同位素年龄(Ma) Pb Th U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ HL-6TW-1 315.95385 469.45 764.58 0.61 0.11275 0.00126 5.2058 0.05872 0.3349 0.00349 1844 9 1854 10 1862 17 HL-6TW-2 571.96792 949.62 1395.57 0.68 0.1115 0.00116 5.01132 0.05296 0.32601 0.00332 1824 9 1821 9 1819 16 HL-6TW-3 209.55952 215.47 345.33 0.62 0.16331 0.00214 10.57378 0.13946 0.46963 0.00541 2490 10 2486 12 2482 24 HL-6TW-4 31.56621 229.84 388.43 0.59 0.05612 0.00107 0.52255 0.00969 0.06754 0.00077 457 22 427 6 421 5 HL-6TW-5 23.91901 182.49 291.96 0.63 0.05695 0.00108 0.53845 0.00991 0.06858 0.00078 490 22 437 7 428 5 HL-6TW-6 136.2894 167.45 223.16 0.75 0.15963 0.00189 10.16874 0.12075 0.46203 0.00499 2452 9 2450 11 2449 22 HL-6TW-7 114.47227 375.83 1528.36 0.25 0.05587 0.00062 0.52261 0.00579 0.06785 0.00069 447 11 427 4 423 4 HL-6TW-8 46.12337 247.93 586.97 0.42 0.05539 0.00152 0.52327 0.01388 0.06851 0.0009 428 36 427 9 427 5 HL-6TW-9 37.08585 403.15 414.63 0.97 0.05517 0.00121 0.51669 0.01098 0.06793 0.00081 419 27 423 7 424 5 HL-6TW-10 23.93572 217.65 284.42 0.77 0.05564 0.00147 0.51453 0.01309 0.06707 0.00086 438 34 421 9 418 5 HL-6TW-11 182.96866 174.88 278.25 0.63 0.1638 0.00173 11.37392 0.12032 0.50359 0.00509 2495 8 2554 10 2629 22 HL-6TW-12 62.72011 631.34 705.88 0.89 0.05786 0.00079 0.54457 0.00726 0.06826 0.00071 524 14 441 5 426 4 HL-6TW-13 55.57702 288.19 696.72 0.41 0.05587 0.00079 0.52193 0.00724 0.06774 0.00071 447 14 426 5 423 4 HL-6TW-14 165.63799 161.21 275.45 0.59 0.16075 0.0017 10.18184 0.10693 0.45935 0.0046 2464 8 2451 10 2437 20 HL-6TW-15 310.96888 384.68 728.38 0.53 0.11283 0.00119 5.30526 0.05522 0.34099 0.00339 1845 8 1870 9 1891 16 HL-6TW-16 39.85422 376.9 453.41 0.83 0.05416 0.00099 0.51043 0.00902 0.06835 0.00075 378 21 419 6 426 5 HL-6TW-17 211.66882 226.43 337.64 0.67 0.16119 0.00171 10.43269 0.10897 0.46937 0.00468 2468 8 2474 10 2481 21 HL-6TW-18 16.15166 103.65 303.07 0.34 0.05164 0.0008 0.32983 0.00499 0.04632 0.00049 270 17 289 4 292 3 HL-6TW-19 187.78596 159.58 304.43 0.52 0.16261 0.00173 10.62133 0.11093 0.47367 0.00471 2483 8 2491 10 2500 21 HL-6TW-20 108.37869 203.95 246.97 0.83 0.11053 0.00119 4.93986 0.05231 0.3241 0.00322 1808 9 1809 9 1810 16 HL-6TW-21 44.88306 409.05 692.03 0.59 0.05358 0.00067 0.40163 0.00491 0.05436 0.00055 353 12 343 4 341 3 HL-6TW-22 310.28845 337.12 755.5 0.45 0.11184 0.00118 5.06654 0.05228 0.32852 0.00323 1830 8 1831 9 1831 16 HL-6TW-23 146.74297 143.78 235.26 0.61 0.16204 0.00178 10.43984 0.11226 0.46722 0.0047 2477 8 2475 10 2471 21 HL-6TW-24 37.47048 55.45 52.13 1.06 0.16889 0.00267 11.3314 0.17715 0.48654 0.00624 2547 12 2551 15 2556 27 HL-6TW-25 21.74959 93.65 206.22 0.45 0.05832 0.00219 0.6729 0.02423 0.08367 0.00131 542 51 522 15 518 8 HL-6TW-26 74.78277 136.35 946.08 0.14 0.05948 0.00126 0.56493 0.01149 0.06887 0.0008 585 25 455 7 429 5 HL-6TW-27 391.93267 818.2 964.51 0.85 0.10909 0.00314 4.28408 0.11341 0.28483 0.0032 1784 54 1690 22 1616 16 HL-6TW-28 106.79042 553.84 1308.16 0.42 0.05518 0.00072 0.5136 0.00647 0.06749 0.00068 420 13 421 4 421 4 表 2 辉绿岩主量(%)、微量、稀土元素(10−6)分析结果
Table 2 Analysis results of major (%), trace and rare earth elements (10−6) in diabase
样品编号 PM101-8DH1 HL-1DH HL-2DH HL-3DH HL-4DH HL-5DH HL-6DH HL-7DH HL-8DH SiO2 47.23 50.18 47.43 47.77 47.83 49.8 46.73 47.61 48.03 TiO2 1.74 2.35 2.92 1.75 2.61 3.14 3.08 2.78 3.24 Al2O3 14.05 12.55 13 14.58 12.74 12.71 13.62 12.91 12.67 TFe2O3 12.39 11.94 16 12.54 16.42 14.96 14.58 14.31 15.44 MnO 0.19 0.17 0.23 0.19 0.25 0.22 0.23 0.19 0.18 MgO 6.82 6.43 5.27 7.14 6.42 4.26 6.24 5.41 4.96 CaO 10.74 6.28 9.65 10.95 6.38 7.41 8.89 10.29 8.12 Na2O 2.85 2.92 2.48 2.13 2.16 3.32 3.36 2.34 3.36 K2O 0.84 1.68 0.74 1.03 1.34 1.88 0.57 0.91 0.78 P2O5 0.19 0.26 0.37 0.21 0.48 0.41 0.51 0.39 0.39 LOI 2.62 5.24 1.04 1.90 3.40 2.37 1.34 1.55 2.02 TOTAL 99.66 100.00 99.13 100.19 100.03 100.48 99.15 98.69 99.19 Li 152.08 32.90 13.96 15.52 16.50 16.87 11.19 15.47 19.67 La 12.17 41.35 24.14 29.61 25.13 25.82 58.22 31.32 38.15 Ce 30.71 86.05 55.85 59.05 56.72 57.85 118.80 69.17 82.33 Pr 4.23 10.34 7.37 6.58 7.32 7.46 13.83 8.85 10.36 Nd 18.86 41.38 32.48 25.23 33.36 32.56 54.64 38.27 43.26 Sm 4.66 7.63 7.62 4.92 7.48 7.21 11.12 8.52 10.08 Eu 1.61 2.42 2.71 1.74 2.74 2.65 2.72 2.69 2.83 Gd 5.05 6.89 8.64 5.63 8.72 6.98 11.31 9.32 10.77 Tb 0.81 0.92 1.37 0.82 1.44 1.02 1.80 1.35 1.61 Dy 5.06 5.18 8.39 4.85 9.15 5.89 11.09 8.18 9.63 Ho 1.01 0.93 1.69 0.99 1.91 1.09 2.19 1.60 1.96 Er 2.98 2.34 4.71 2.68 5.59 2.97 6.30 4.50 5.58 Tm 0.41 0.34 0.63 0.41 0.78 0.38 0.91 0.65 0.80 Yb 2.51 2.07 4.47 2.38 5.40 2.56 5.78 4.16 5.09 Lu 0.42 0.31 0.66 0.37 0.80 0.37 0.90 0.57 0.72 Y 24.13 21.81 39.84 22.71 44.86 25.52 52.55 37.72 46.94 ΣREE 90.50 208.14 160.73 145.26 166.55 154.79 299.62 189.12 223.17 LREE 72.24 189.17 130.17 127.13 132.76 133.53 259.33 158.81 187.01 HREE 18.26 18.98 30.56 18.12 33.79 21.26 40.29 30.32 36.17 LREE/HREE 3.96 9.97 4.26 7.01 3.93 6.28 6.44 5.24 5.17 (La/Yb)N 3.47 14.32 3.87 8.92 3.34 7.24 7.23 5.40 5.37 δEu 1.01 1.00 1.02 1.01 1.03 1.13 0.73 0.92 0.82 δCe 1.05 0.99 1.02 0.99 1.01 1.01 0.99 1.00 1.00 Li 22.00 32.90 13.96 15.52 16.50 16.87 11.19 15.47 19.67 Be 0.41 1.49 1.23 0.72 0.81 0.65 2.63 1.36 1.82 Sc 38.43 27.63 32.97 29.00 43.05 26.13 31.54 35.58 28.96 V 295.10 273.13 406.23 271.99 340.19 295.18 341.59 366.63 400.37 Cr 200.39 271.56 43.62 136.57 91.70 97.13 54.23 76.02 43.80 Co 46.54 38.07 47.23 46.41 45.36 45.63 39.10 49.82 42.65 Ni 83.00 99.09 37.80 78.60 32.96 73.97 37.72 55.17 46.57 Cu 74.79 76.51 54.46 71.39 53.75 76.30 178.45 117.35 109.22 Zn 80.94 141.15 128.48 87.47 126.17 106.60 390.70 90.71 99.14 Ga 16.54 16.91 21.43 17.71 19.21 18.37 21.03 19.81 21.09 Rb 37.93 76.88 40.82 65.69 57.56 26.73 89.17 31.13 36.87 Sr 227.50 319.73 272.86 489.31 251.63 306.97 339.90 247.93 231.69 Zr 84.48 188.69 175.76 101.50 165.19 141.18 350.64 206.27 258.49 Nb 9.20 20.10 18.70 8.40 17.92 16.74 52.64 26.96 31.24 Mo 0.29 0.46 0.91 0.45 0.54 0.98 2.32 1.33 1.56 Cd 0.08 0.24 0.13 0.14 0.12 0.12 0.35 0.09 0.11 In 0.06 0.10 0.11 0.07 0.12 0.10 0.13 0.11 0.12 Cs 0.49 1.11 0.98 0.40 0.62 0.72 0.46 0.78 0.39 Ba 364.57 931.24 400.22 657.53 512.96 329.56 604.25 326.51 300.15 Hf 2.37 5.37 5.03 2.92 4.99 4.01 9.49 5.82 7.36 Ta 0.69 1.26 1.20 0.55 1.21 1.10 3.56 1.79 2.09 Pb 1.84 39.57 5.02 6.43 4.88 3.19 6.21 4.36 5.84 Bi 0.01 0.06 0.01 0.01 0.02 0.01 0.02 0.01 0.02 Th 1.82 6.15 5.96 7.04 2.82 5.23 9.47 3.60 4.53 U 0.57 1.35 0.93 0.52 0.91 0.74 2.10 1.22 1.34 -
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