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松潘−甘孜地块中西部晚三叠纪花岗岩体成因及其构造意义

王鹏, 白建科, 王雁鹤, 韩昊, 宋伊圩, 周霖, 张吉廷, 肖紫珩, 陈威

王鹏, 白建科, 王雁鹤, 等. 松潘−甘孜地块中西部晚三叠纪花岗岩体成因及其构造意义[J]. 西北地质, 2023, 56(5): 223-244. DOI: 10.12401/j.nwg.2023052
引用本文: 王鹏, 白建科, 王雁鹤, 等. 松潘−甘孜地块中西部晚三叠纪花岗岩体成因及其构造意义[J]. 西北地质, 2023, 56(5): 223-244. DOI: 10.12401/j.nwg.2023052
WANG Peng, BAI Jianke, WANG Yanhe, et al. Petrogenesis and Tectonic Implication of Late−Triassic Granitoids in the West−Central Part of Songpan−Ganze Block[J]. Northwestern Geology, 2023, 56(5): 223-244. DOI: 10.12401/j.nwg.2023052
Citation: WANG Peng, BAI Jianke, WANG Yanhe, et al. Petrogenesis and Tectonic Implication of Late−Triassic Granitoids in the West−Central Part of Songpan−Ganze Block[J]. Northwestern Geology, 2023, 56(5): 223-244. DOI: 10.12401/j.nwg.2023052

松潘−甘孜地块中西部晚三叠纪花岗岩体成因及其构造意义

基金项目: 中国地质调查局项目“祁连成矿带金矿资源潜力动态评价”(DD20220979)和“东昆仑成矿带金矿资源潜力动态评价”(DD20220978)联合资助。
详细信息
    作者简介:

    王鹏(1992−),男,硕士,工程师,矿物学、岩石学、矿床学专业。E−mail:916459881@qq.com

    通讯作者:

    白建科(1983−),男,博士,正高级工程师,主要从事沉积学、盆地分析与造山带演化等领域的科研工作。E−mail:baijianke2003@163.com

  • 中图分类号: P581;P597.3

Petrogenesis and Tectonic Implication of Late−Triassic Granitoids in the West−Central Part of Songpan−Ganze Block

  • 摘要:

    通过岩相学、锆石U−Pb年代学、岩石地球化学和Lu−Hf同位素等多种手段,系统对比松潘−甘孜地块巴颜喀拉山南口地区和中部达日地区的花岗质岩体岩石学和地球化学特征,拟查明其岩石成因、岩浆源区和基底属性。巴颜喀拉山南口和达日地区花岗质岩石岩浆锆石U−Pb年龄为(212.0±2.2)Ma和(213.3±1.7)Ma、(217.0±1.9)Ma和(215.4±6.4)Ma。主量、微量元素研究表明,前者属于高钾钙碱性过铝质I型花岗闪长岩,而后者属于钾玄岩和高钾钙碱性、过铝质S型石英二长岩和花岗岩。巴颜喀拉山南口和达日地区花岗质岩石微量元素特征表现均为富集Rb、Th、U等大离子亲石元素,亏损Nb、Ta等高场强元素,且具有轻微的Zr、Hf负异常,但前者Nb、Ta等元素亏损程度明显高于后者,Eu异常也更为明显。巴颜喀拉山南口和达日地区花岗质岩石均为轻稀土富集型的稀土元素配分模式,但达日地区样品轻、重稀土含量均高于巴颜喀拉山样品。锆石Hf同位素数据显示,巴颜喀拉山地区花岗质岩石εHft)值为−3.62~2.92,平均值为−0.54,锆石Hf二阶段模式年龄为1.07~1.48 Ga。结合前人研究数据,推断巴颜喀拉山和达日地区花岗质岩石源区分别为下地壳镁铁质岩石和中地壳杂砂岩。松潘甘孜地块存在新元古代基底,且其基底与扬子地块基底存在亲缘性。研究区花岗质岩石为后碰撞背景下,岩石圈拆沉诱发的不同地壳岩石部分熔融的产物。

    Abstract:

    Through various methods such as petrography, zircon U−Pb geochronology, petrogeochemistry and Lu−Hf isotopes, the petrological and geochemical characteristics of the granitic rocks from the south entrace of Bayan Har Mountain and Dari area have been systematically compared, in order to find out its petrogenesis, magma source area and basement attributes. The magmatic zircon U−Pb ages of the granitic rocks from the south entrace of Bayan Har Mountain and Dari area are (212.0±2.2) Ma, (213.3±1.7) Ma, (217.0±1.9) Ma and (215.4±6.4) Ma. Studies on major and trace elements show that the former belongs to high−potassium calcium−alkaline peraluminous I−type granodiorite, while the latter belongs to potash basalt and high−potassium calc−alkaline, peraluminous S−type quartz monzonite and granite. The characteristics of the trace elements of the granitic rocks from the south entrace of Bayan Har Mountain and Dari area are: enrichment of large ion lithophile elements such as Rb, Th, U, depletion of high field strength elements such as Nb and Ta, and slight Zr. Hf negative anomaly, but the former Nb, Ta and other elements are significantly more depleted than the latter. Eu anomaly is also more obvious. The granitic rocks from the south entrace of Bayan Har Mountain area are both light rare earth−enriched rare earth element distribution models, but the content of light and heavy rare earths in the samples from the Dari area are higher than those of the Bayan Har Mountain samples. The zircon Hf isotopic data of granitic rocks from the Bayan Har Mountains area show that εHf(t)=−3.62~2.92, the average is −0.54, and the age of the zircon Hf two−stage model is between 1.07 and 1.48 Ga. Combining previous research data and the composition of major, trace and Hf isotopes in this paper, it is inferred that the source areas of the granitic rocks from the south entrace of Bayan Har Mountain and Dari area are lower crust mafic rocks and middle crust sandstones, respectively. The Songpan−Garze block has a Neoproterozoic basement, and its basement is related to the basement of the Yangtze block. It is speculated that the granitic rocks in the study area are the products of partial melting of different crustal rocks induced by lithospheric delamination under the background of post−collision. The granitic rocks in the study area are the products of partial melting of different crustal rocks induced by lithospheric delamination under the background of post−collision.

  • 松潘−甘孜地块位于华北地块、扬子地块和羌塘地块结合部位,是一个巨大的构造集合域(Sengör et al.,1985许志琴,1992Mattauer et al.,1992Bruguier et al.,1997)。松潘−甘孜地块上广泛分布花岗质岩体,前人对这些岩体已经开展了岩相学(Zhang et al.,2007Cai et al.,20092010Zhang et al.,2014)、年代学(Roger et al.,2004Zhang et al.,2006Xiao et al.,2007)和地球化学(Zhang et al.,2006Xiao et al.,2007)等方面工作。研究发现,这些岩体主要为晚三叠世至—侏罗纪的中酸性侵入岩(Roger et al.,20032004Zhang et al.,2007Weislogel,2008Cai et al.,2009Yuan et al.,2010Zhang et al.,2014),岩石成因类型多样,主要包括埃达克质花岗岩(Zhang et al.,2006Xiao et al.,2007)、A型花岗岩(Zhang et al.,2007)、I型花岗岩(Xiao et al.,2007)和强过铝质花岗岩(时章亮等,2009)。迄今为止,这些花岗质岩石的岩石成因和构造驱动仍然存在争议,部分学者认为这些岩石是后碰撞环境中岩石圈拆沉作用形成的(Zhang et al.,20062007Xiao et al.,2007);而其他学者认为这些花岗岩类与金沙江特提斯洋俯冲作用有关(Roger et al.,2003)。此外,松潘−甘孜地块的基底属性存在争议,争议焦点包括:①松潘−甘孜地块基底为残余洋盆(Sengör et al.,1985Yin et al.,19932000Hsü et al.,1995Bruguier et al.,1997Liu et al.,2019)。②松潘−甘孜地块三叠系具有陆相的地壳基底,基底与扬子地块具有密切的亲缘关系(Roger et al.,2004Zhang et al.,2006Xiao et al.,2007)。前人研究通常局限于一个区域,松潘−甘孜地块不同区域花岗质岩石是否存在差异,其成因类型、构造背景和基底属性是否相同,这些问题对于理解松潘−甘孜地块区域构造演化至关重要,然而区域之间此类对比研究较为薄弱。笔者选取松潘−甘孜地块西部巴颜喀拉山南口地区和中部达日地区花岗质岩石作为研究对象,通过岩相学、锆石U−Pb年代学、岩石地球化学和Lu−Hf同位素等多种手段研究,系统对比松潘−甘孜地块中西部花岗质岩石岩相学和地球化学组成差异,全面揭示松潘−甘孜地块中西部地区花岗质岩石成因与岩浆深部过程,力图探索该地区基底属性与岩浆−构造指示意义。

    松潘−甘孜地块位于青藏高原东北缘。该区北侧以阿尼玛卿缝合带为界与东昆仑−西秦岭造山带毗邻(许志琴,1992Sun et al.,2002Elena et al.,2003于浦生等,2007);东南缘以龙门山断裂带为界与扬子地块相邻(许志琴,1992Chen et al.,19951996);西南缘以金沙江缝合带为界,与羌塘−昌都地块相接(Sengör,1985Wang et al.,2000Hou et al.,2004Reid et al.,2005王辉等,2009)(图1a)。松潘−甘孜地块内震旦纪—古生界地层序列上覆盖着巨厚的三叠系沉积地层,厚度可达5~15 km(许志琴,1992王晖等,2012白国典等,2018)。松潘–甘孜地块南部丹巴地区分布的新元古代地层经历了绿片岩相到角闪岩相的变质作用(Huang et al., 2003),而该地块的三叠系复理石沉积地层仅经历了绿片岩相变质作用(许志琴,1992Bruguier et al.,1997Reid et al.,2005)。松潘–甘孜地块除在东部龙门山断裂带附近出露有前震旦纪结晶基底外,再无基底出露(许志琴,1992)。印支期,扬子板块、华北板块和羌塘板块之间相互挤压,导致松潘带内的沉积盆地缩小,古特提斯洋闭合,形成松潘造山带(Sengör,1985许志琴,1992Nie et al.,1994)。在造山期,震旦纪—古生界地层序列上覆的三叠系向南逐渐推覆至扬子板块之上。与此同时,震旦纪—古生界地层序列由于构造运动发生强烈变形,形成大规模的滑脱构造,从而使地壳明显增厚(Mattauer et al.,1992夏林圻等,2010),导致松潘带岩石圈发生重力不稳定性,岩石圈发生拆沉作用,这一过程不但促使岩石圈地幔的部分熔融,而且还促发中下地壳物质的部分熔融(Jung et al.,1998Wu et al.,20022005Chung et al.,20032005Ilbeyli et al.,2004)。

    图  1  松潘–甘孜地块地质构造简图(a)、巴颜喀拉山地质简图(b)与达日花岗岩类分布简图(c)(据蔡宏明,2010修改)
    Figure  1.  (a) Geological structure sketch of Songpan–Garze block, (b) geological sketch of granitoids in Bayankala and(c) geological sketch of granitoids in Dari area

    研究区位于松潘–甘孜地块中西部(图1b图1c),巴颜喀拉山位于达日地区西侧(图1a)。研究区花岗质岩体平面上多呈不规则椭圆形,以切割早期或主造山期逆冲及褶皱构造为特点,围岩均为三叠纪巴颜喀拉山群,普遍发育有宽度不等的接触变质晕带。其中,巴颜喀拉山南口地区花岗质岩体主要为花岗闪长岩,达日地区花岗质岩体为石英二长岩和花岗岩。笔者野外采集巴颜喀拉山花岗闪长岩样品3件,闪长岩样品1件,达日地区花岗岩样品6件,石英二长岩8件,二长岩1件,花岗闪长岩1件。这些样品与强烈变形的三叠系地层具有侵入接触关系,而岩体本身无变形。

    巴颜喀拉山南口地区花岗闪长岩(样品359):灰白色,半自形粒状结构,块状构造(图2a)。斜长石含量为58%,无规律分布,粒度大小为0.32~1.20 mm,为细粒结构,呈半自形板状,单偏光镜下,呈土灰色,正低突起,正交镜下一级灰干涉色,可见聚片双晶和环带结构,斜消光。石英含量为21%,呈他形粒状充填于斜长石矿物颗粒间,粒径为0.16~1.60 mm,主要为细粒结构,表面干净,平行消光。角闪石含量为12%,粒度大小为0.40~1.92 mm,细粒粒状结构,呈褐绿–浅黄绿,具多色性,长柱状、短柱状,正中–正高突起,可见横切面呈近菱形的六边形及角闪石式解理。钾长石含量为9%,呈他形粒状分布于斜长石矿物颗粒间,主要为条纹长石,粒度大小约为0.72~1.04 mm(图2b)。

    图  2  手标本照片与镜下矿物鉴定图
    a、b. 巴颜喀拉山南口地区花岗闪长岩(样品359);c、d. 达日地区查雀嘎玛石英二长岩(样品D2409);e、f. 达日地区波不弄公玛石英二长岩体(样品D2615);g、h. 达日地区日查花岗岩(样品D1710);Pl. 斜长石;Qtz. 石英;Bi. 黑云母;Ms. 白云母;Kfs. 钾长石;Ser. 绢云母;Per. 条纹长石;Chl. 绿泥石;Am. 角闪石
    Figure  2.  Hand specimen photograph and microphotographs of granitoids

    达日地区查雀嘎玛石英二长岩(样品D2409):灰白色,中细粒结构,块状构造,中细粒花岗结构(图2c)。斜长石含量为41%,无规律分布,粒度大小为0.4~2.72 mm,中细粒粒状结构,呈半自形板状。石英含量为17%,无规律分布,呈他形粒状充填于钾长石和斜长石矿物颗粒间,粒径为0.24~2.40 mm,中细粒结构。钾长石含量为35%,无规律分布,主要为正长石,半自形宽板状及不规则粒状,粒度大小为0.96~3.04 mm,中细粒结构。黑云母含量为4%,呈叶片状,鳞片状,无规律分布,粒径平均为0.60 mm,细粒结构。白云母含量为3%,呈叶片状,鳞片状,无规律分布,粒径平均为0.32 mm,细粒结构,由黑云母褪色形成(图2d)。

    达日地区波不弄公玛石英二长岩体(样品D2615):灰白色,似斑状结构,块状构造(图2e)。斜长石含量为38%,无规律分布,粒度大小为0.48~4.64 mm,中细粒粒状结构。钾长石为35%,无规律分布,主要为条纹长石、正长石,半自形宽板状及不规则粒状,粒度大小为0.88~17.60 mm,中细粒结构。石英含量为18%,无规律分布,呈他形粒状充填于钾长石和斜长石矿物颗粒间,粒径为0.16~3.60 mm,中细粒结构,表面干净,一级灰白干涉色,平行消光。黑云母含量为5%,呈叶片状,鳞片状,无规律分布,粒径平均为1.20 mm,细粒结构。白云母含量为4%,鳞片状,无规律分布,粒径平均为0.35 mm(图2f)。

    达日地区日查花岗岩(样品D1710):灰白色,中细粒粒状结构,块状构造(图2g)。斜长石含量为32%,无规律分布,粒度大小为0.24~2.56 mm,主要为细粒结构,呈半自形板状。石英含量为30%,呈他形粒状充填于斜长石矿物颗粒间,粒径为0.32~2.30 mm,细粒结构。钾长石含量为34%,呈他形粒状分布于斜长石矿物颗粒间,主要为条纹长石,其次为正长石,粒度大小约为2.16~3.06 mm。黑云母含量为5%,呈叶片状,鳞片状,无规律分布,粒径平均为0.80 mm,细粒结构。白云母含量为2%,呈叶片状,无规则分布,粒径为0.32~0.28 mm,细粒结构,由黑云母褪色形成(图2h)。

    所采20件样品全部进行主量元素、微量元素和稀土元素测试分析,测试工作在中国地质调查局西安地质调查中心实验测试室完成,挑选新鲜样品在无污染环境下粉碎至200目。主量元素采用荧光光谱方法(XRF)分析,测试仪器为荷兰帕纳科公司生产的Axios 4.0 KW顺序式X射线荧光光谱仪,分析误差小于5 %;微量、稀土元素采用ICP–MS分析方法测试,测试仪器型号为美国热电公司生产的X-SeriesII型电感耦合等离子质谱仪(ICP–MS),分析误差小于8 %。温度控制在22 ℃,检测依据为GB/T 14506.28-2010、GB/T 14506.14–2010和DZ/T 0223–2001。具体测试分析流程见 Qi等(2000),样品的溶解处理、精密度分析和准确度见 Liu等(2008)

    采集U–Pb样品锆石分选及锆石阴极发光显微照相、透射光及反射光照相工作均在河北省廊坊市宇能(宇恒)矿物分选综合实验室完成,锆石分选采用常规粉碎和电磁分选方法进行分选。锆石U–Pb年龄测试在中国地质调查局西安地质调查中心实验室利用激光剥蚀等离子体质谱(LA–ICP–MS)法测定。所用仪器为德国Coherent公司的GeoLasPro193nm准分子型激光剥蚀系统和与之联机的电感耦合等离子质谱仪为美国Agilent公司的Agilent7700x四级杆型等离子体质谱仪。测试过程中均采用单点剥蚀方式,每个测点总分析时间为60 s,其中背景信号为10 s,样品信号为40 s,吹扫信号为10 s。数据采集采用跳峰模式,同位素204Pb、206Pb、208Pb和232Th驻留时间为20 ms,238U为10 ms,207Pb为30 ms。测试中用国际标准锆石GJ-1进行仪器的最佳化,锆石年龄采用国际标准锆石91500作为外标标准物质,元素含量用NISTSRM610作为外标,29Si作为内标。每测定6个样品插入标样GJ-1,每12个样插入一组标样:NISTSRM610、91500与GJ-1,在样品测试开始与结束处分别测试一组标样,详细的实验原理和测试流程及仪器参见相关文献(Yuan et al.,2004)。测试所得数据应用Glitter计算程序计算锆石的表面年龄及标准偏差,并对测试过程中产生的元素分馏和质量歧视进行校正;应用Isoplot计算程序对锆石样品的206Pb/238U年龄和207Pb/235U年龄在谐和图上进行投图,并计算年龄谐和测点的加权平均值(Weighted Average,基于206Pb/238U年龄)(Ludwig,2003李艳广等,2023)。

    锆石原位Lu–Hf同位素测定在中国地质调查局西安地质调查中心实验室利用Agilent7700x四级杆型等离子体质谱仪完成。根据CL图像以及已有U–Pb年龄的点位确定 Hf同位素测试点,并采用其国家重点实验室LA–MC–ICP MS仪器进行锆石Hf同位素分析。运用ICP MS DataCal 10.0软件对Hf同位素数据进行离线处理,具体实验操作流程与数据处理方法见 Liu等( 20082010a2010b)

    本次对松潘–甘孜地块巴颜喀拉山花岗闪长岩体(359)、达日地区的查雀嘎玛石英二长岩体(D2409)、波不弄公玛石英二长岩体(D2615)、日查花岗岩体(D1710)样品分别进行U–Pb锆石定年。实验结果见表1表2

    表  1  巴颜喀拉山花岗闪长岩体(359)LA–ICP–MS锆石U–Pb年龄测试结果表
    Table  1.  LA–ICP–MS zircon U–Pb dating results of sample 359
    测点207Pb/235U206Pb/238U207Pb/235U206Pb/238U
    同位素比值同位素比值年龄(Ma)年龄(Ma)
    359N=25(有效点19个)
    GE010.2380.01280.032080.00049216.810.5216.810.4
    GE020.26430.01620.035270.00057238.112.9238.112.9
    GE030.22890.01240.032120.00049209.310.2209.310.2
    GE040.23270.0110.032160.00047212.49.0212.49.1
    GE050.22410.01920.034160.00061205.315.9205.315.9
    GE060.22480.01240.032510.0005205.910.2205.910.2
    GE070.22010.01340.031330.000520211.120211.2
    GE080.25530.0170.034190.00058230.913.7230.913.7
    GE090.23210.00950.033280.00046211.97.8211.97.8
    GE100.32450.01390.033540.0005285.310.6285.310.6
    GE110.22830.01560.032660.00055208.812.9208.812.9
    GE120.23210.01710.032570.0005821214.121214.1
    GE130.2280.01380.033080.00053208.611.4208.611.4
    GE140.22750.01210.033030.0005208.19.9208.19.9
    GE150.23590.01370.032850.0005221511.221511.3
    GE160.23570.01440.033530.00055214.911.8214.911.9
    GE170.23450.01770.033930.00059213.914.5213.914.5
    GE180.46620.03010.043980.00082388.620.8388.620.8
    GE190.23920.01460.033150.00054217.711.9217.711.9
    GE200.25520.02110.033090.00063230.817.0230.817.1
    GE210.22480.02110.032870.00063205.917.4205.917.5
    GE220.26020.01620.033850.00057234.913.0234.913.0
    GE230.23730.01280.033160.00051216.210.5216.210.5
    GE240.41560.01750.055830.0008352.912.5352.912.5
    GE250.2720.0170.035050.00059244.313.5244.313.5
    下载: 导出CSV 
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    表  2  查雀嘎玛石英二长岩体(D2409)、波不弄公玛石英二长岩体(D2615)和日查花岗岩体(D1710)LA–ICP–MS锆石U–Pb年龄测试结果表
    Table  2.  LA–ICP–MS zircon U–Pb dating results of sample D2409, D2615 and D1710
    测点207Pb/235U206Pb/238U207Pb/235U206Pb/238U
    同位素比值同位素比值年龄(Ma)年龄(Ma)
    D2409N=25(有效点16个)
    GB010.23120.01050.03270.0005211.28.7207.23.0
    GB020.22130.01260.03300.0005203.010.5209.13.1
    GB030.23660.01530.03360.0005215.612.6213.03.4
    GB040.24420.01170.03240.0005221.99.6205.33.0
    GB050.22870.01850.03300.0006209.115.3209.13.4
    GB060.22930.01370.03340.0005209.611.3212.03.3
    GB070.24050.01130.03390.0005218.89.2215.03.2
    GB080.21650.01410.03270.0005199.011.8207.13.2
    GB090.22950.01560.03410.0006209.812.9216.43.5
    GB100.24700.01810.03420.0006224.214.7216.73.6
    GB110.22810.02210.03510.0006208.618.3222.34.0
    GB120.26190.02010.03540.0006236.216.2224.23.9
    GB130.23130.03440.03550.0008211.328.3225.14.8
    GB140.28610.02520.03470.0007255.519.9219.94.3
    GB150.29210.03130.03220.0007260.224.6204.14.4
    GB160.21230.01640.03490.0006195.513.7221.03.5
    GB170.24760.02120.03530.0006224.617.2223.74.0
    GB180.26590.02830.03420.0007239.422.7217.04.5
    GB190.20330.02640.03380.0007187.922.3214.54.1
    GB200.27170.02320.03310.0007244.018.5210.14.2
    GB210.26730.02190.03340.0006240.517.6212.03.9
    GB220.10760.02820.03410.0006103.825.8216.14.0
    GB230.26600.01570.03450.0005239.512.6218.83.4
    GB240.23700.01760.03600.0006216.014.4227.83.6
    GB250.24130.01330.03350.0005219.410.9212.13.3
    D2615N=25(有效点17个)
    GC010.25920.01620.03380.0005234.113.0214.63.3
    GC020.20180.01210.03290.0005186.610.2208.93.0
    GC030.21010.01350.03250.0005193.611.3205.93.1
    GC040.28770.01640.03280.0005256.712.9207.83.3
    GC050.23000.01230.03390.0005210.210.2215.13.2
    GC060.29520.01730.03300.0005262.713.6209.13.4
    GC070.22250.02120.03370.0006204.017.6213.44.0
    GC080.26570.02680.03530.0007239.221.5223.64.3
    GC090.17770.02360.03420.0006166.120.4216.73.9
    GC100.22050.01790.03410.0006202.314.9216.03.7
    下载: 导出CSV 
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    续表2
    测点207Pb/235U206Pb/238U207Pb/235U206Pb/238U
    同位素比值同位素比值年龄(Ma)年龄(Ma)
    GC110.28800.02240.03310.0007257.017.7209.64.3
    GC120.06450.03410.03620.000763.532.5229.14.3
    GC130.37170.04120.03370.0009320.930.5213.35.5
    GC140.31550.02540.03540.0007278.519.6224.54.1
    GC150.32910.03280.03510.0008288.925.1222.34.9
    GC160.22510.01810.03440.0006206.215.0217.73.6
    GC170.21050.01730.03350.0006194.014.5212.53.6
    GC180.32040.02880.03560.0007282.222.1225.54.5
    GC190.24370.02080.03350.0006221.417.0212.33.6
    GC200.24910.02840.03280.0007225.923.1208.24.3
    GC210.30010.02250.03300.0006266.517.6209.23.9
    GC220.10110.02860.03370.000697.826.4213.93.9
    GC230.22720.01410.03400.0005207.911.7215.43.2
    GC240.22810.01870.03290.0005208.715.5208.43.4
    GC250.23780.01120.03330.0005216.69.2211.13.1
    D1710N=25(有效点19个)
    GD010.71070.022910.03500.00057545.113.6222.23.5
    GD020.28870.020590.03370.00058257.616.2213.83.6
    GD030.24820.015280.03390.00054225.112.4215.33.3
    GD040.23230.016680.03320.00055212.113.7210.63.4
    GD050.27600.015740.03430.00055247.412.5217.83.4
    GD060.23560.016220.03390.00056214.813.3215.53.5
    GD070.27850.023840.03290.00071249.518.9208.74.4
    GD080.27940.019280.03390.00060250.215.3215.13.7
    GD090.34400.024230.03400.00065300.218.3215.54.0
    GD100.94480.029600.03650.00060675.415.4231.53.8
    GD110.20610.028700.03510.00071190.324.1222.44.4
    GD120.27810.021800.03470.00068249.117.3220.44.2
    GD130.25650.019180.03490.00064231.815.5221.23.9
    GD140.23930.021950.03460.00066217.817.9219.54.1
    GD150.21750.017690.03330.00059199.814.7211.73.7
    GD160.26980.029210.03390.00067242.623.3215.34.2
    GD170.25090.015610.03370.00056227.312.6213.73.5
    GD180.31580.017610.03480.00059278.713.5220.83.7
    GD190.53700.027100.03730.00065436.417.9236.64.1
    GD200.21940.017170.03510.00057201.414.3222.53.6
    GD210.25540.009640.03430.00048230.97.8217.73.0
    GD220.28130.023270.03470.00070251.718.42204.3
    GD230.14340.023780.03480.00056136.121.1220.83.5
    GD240.27470.011800.03460.00050246.49.4219.43.2
    GD250.24520.012620.03510.00052222.710.3222.73.2
    下载: 导出CSV 
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    所有样品锆石多为短柱状自形晶,晶棱尖锐,表面光滑,颗粒长度多为100 ~150 μm,长宽比多数为2∶1~3∶1,振荡环带发育明显,且较细密,宽度多小于10 μm,指示岩浆锆石形态特征。此外,5个样品中所选锆石Th值为12.40×10−6~43.70×10−6,U值为1.94×10−6~5.82×10−6,Th/U值为3.20~15.36,均大于0.1,表明分析锆石均为岩浆锆石(Hoskin et al.,2010)。

    巴颜喀拉山地区样品(359)分析了25个测试点,经过矫正筛选删除因U、Pb明显丢失引起的锆石年龄较小的数据,最终获得19个有效数据点,其 206Pb/238U加权平均年龄为(215.4±6.4 )Ma(置信度95%,MSWD=1.8)(图3a)。

    图  3  锆石U–Pb谐和图及代表性锆石颗粒阴极发光图
    a. 巴颜喀拉山花岗质岩石;b、c、d. 达日地区花岗质岩石
    Figure  3.  Zircon U–Pb concordant diagrams and parts of Cathodoluminescence (CL) images of four samples

    达日地区3件样品(D2409、D2615、D1710)分别分析了25个测试点,经过矫正筛选,最终获得有效数据点分别为16个、17个和19个,206Pb/238U加权平均年龄分别为(213.3±1.7) Ma(置信度95%,MSWD=1.09)(图3b)、(212.0±2.2) Ma(置信度95%,MSWD=1.5)(图3c)和(217.0±1.9) Ma(置信度95%,MSWD=1.2)(图3d)。上述样品数据有效点均落在谐和线及其附近,显示出较好的谐和性,说明这些锆石形成后U–Pb体系保持封闭,样品206Pb/238U加权平均年龄可代表岩浆结晶年龄。

    样品的主量元素、微量元素和稀土元素数据见表3。巴颜喀拉山样品SiO2含量为59.05 %~65.59 %,全碱含量(Na2O+K2O)为5.54 %~6.05 %,达日地区样品SiO2含量为58.58 %~73.77 %,全碱含量(Na2O+K2O)为6.61 %~8.66 %,可见达日地区样品SiO2含量和全碱含量相对较高(表3)。在TAS图解中(图4a),巴颜喀拉山样品有3件落在花岗闪长岩范围,1件落在闪长岩范围内;达日地区样品6件落在花岗岩范围内,8件落在石英二长岩范围内,1件落在二长岩范围内,1件落在花岗闪长岩范围内,与前人岩性判别基本一致(沙淑清等,2007Cai et al.,2009)。在A/NK–A/CNK图解中(图4b),所有样品的铝饱和指数A/CNK值为1.09~1.41,说明样品均为过铝质花岗质岩石,巴颜喀拉山样品A/NK值相对较高。在K2O-SiO2图解中(图4c),巴颜喀拉山样品主要为高钾钙碱性系列,1件样品为钾玄岩系列;达日地区样品均为高钾钙碱性系列和钾玄岩系列。在K2O–Na2O图解中(图4d),巴颜喀拉山样品均为钾质岩石,达日地区样品为钾质和高钾质岩石。

    表  3  巴颜喀拉山和达日地区花岗质岩石主量元素(%)和微量元素数据(10 −6)结果表
    Table  3.  Major (%) and trace element contents (10−6) of granitoids in Bayankala and Dari area
    样品号巴颜喀拉山样品达日地区样品
    357358359363D2902D2610D2615D2409D2410D1710
    岩性花岗闪长岩闪长岩花岗闪长岩花岗闪长岩二长岩石英二长岩石英二长岩石英二长岩石英二长岩花岗岩
    SiO265.0959.0565.5963.3458.5865.4567.7066.3765.2873.77
    TiO20.600.820.690.731.040.730.540.540.650.17
    Al2O315.9514.6814.2614.1116.9015.0415.5614.7415.6413.69
    Fe2O30.921.580.852.611.490.910.720.490.801.93
    FeO3.374.833.794.124.243.082.182.883.100.28
    MnO0.110.140.100.0980.0990.0640.0480.0590.0730.065
    MgO1.694.402.862.873.141.791.241.191.450.11
    CaO3.365.354.114.544.923.012.602.333.030.28
    Na2O3.103.863.432.933.052.872.993.113.073.24
    K2O2.952.052.462.614.534.725.445.275.015.42
    P2O50.150.180.140.180.310.160.140.150.190.041
    LOI4.244.831.952.742.942.701.184.292.581.44
    Total101.53101.77100.23100.88101.24100.52100.34101.42100.87100.44
    K2O+Na2O6.055.915.895.547.587.598.438.388.088.66
    CaO/Na2O1.082.611.671.741.611.050.870.750.990.09
    K2O/Na2O0.951.881.391.121.491.641.821.691.631.67
    A/CNK1.411.01.181.201.171.201.181.141.181.20
    A/NK1.921.711.721.851.701.531.441.361.491.22
    Rb94.3225129120220262297306262263
    Ba880397696695901647538635747229
    Th12.821.118.429.818.728.743.732.231.928.8
    U2.955.823.071.942.92.633.374.475.324.91
    Nb15.715.618.750.530.230.526.023.927.742.3
    Ta1.531.431.761.42.312.082.182.162.054.14
    La29.9032.0034.9089.3047.8050.8084.7046.8059.6076.00
    Ce62.5075.8075.80272.00103.00114.00156.00100.00126.00142.00
    Pr7.388.678.0845.4011.9012.3016.3010.8013.6015.60
    Sr27425228031138925020216324354.5
    Nd26.4032.8029.80204.0043.2042.5054.3038.1047.0056.00
    Zr175172168170251283278226244236
    Hf4.916.754.996.688.346.794.745.015.425.08
    Sm4.916.335.4618.007.787.418.817.188.0510.20
    Eu1.361.371.322.831.821.331.291.121.350.69
    Gd4.155.374.8812.206.946.678.156.757.289.25
    Tb0.550.860.731.351.000.951.091.061.041.46
    Dy2.474.543.794.185.134.865.415.805.227.77
    Ho0.430.950.780.801.030.971.081.231.071.57
    Y13.7024.5020.8021.8026.0025.7027.8032.3027.5039.60
    Er1.172.712.222.902.852.753.083.553.024.47
    Tm0.170.440.350.340.460.430.480.610.500.73
    Yb1.092.942.342.192.932.723.094.123.154.97
    Lu0.160.460.360.330.450.400.460.630.480.76
    ∑REE56.5683.2772.83270.9299.5996.69115.04102.45105.66137.47
    (La/Sm) N6.095.066.394.966.146.869.616.527.407.45
    (La/Yb) N19.687.8110.7029.2511.7013.4019.668.1513.5710.97
    Eu/Eu0.300.230.260.190.250.190.150.160.180.07
    下载: 导出CSV 
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    续表3
    达日地区样品
    样品号D1604D1608D1610D1611D0114D0114360361362D2313
    岩性花岗岩花岗闪长岩花岗闪长岩二长岩花岗岩花岗岩花岗岩花岗岩石英二长岩石英二长岩
    SiO267.6865.5066.8460.8171.7971.0870.5969.0265.8965.81
    TiO20.510.760.710.940.240.280.280.330.660.66
    Al2O314.8415.8215.5716.7714.2514.5614.7415.5915.6215.34
    Fe2O30.800.991.181.410.640.510.500.560.850.71
    FeO2.093.422.934.071.641.801.831.922.983.17
    MnO0.0570.0860.0780.100.0420.0480.0490.0520.0610.070
    MgO1.121.681.592.640.540.910.921.151.391.58
    CaO2.493.162.233.431.812.302.152.572.762.81
    Na2O2.633.072.903.073.493.613.684.033.043.01
    K2O3.984.264.124.704.533.653.722.945.315.18
    P2O50.120.170.160.220.0830.0970.0950.110.190.19
    LOI5.171.542.862.741.351.742.082.651.791.91
    Total101.49100.46101.17100.90100.41100.59100.63100.92100.54100.44
    K2O+Na2O6.617.337.027.778.027.267.406.978.358.19
    CaO/Na2O0.951.030.771.120.520.640.580.640.910.93
    K2O/Na2O1.511.391.421.531.301.011.010.731.751.72
    A/CNK1.361.261.381.271.161.221.221.281.181.17
    A/NK1.721.641.691.651.341.471.461.591.451.45
    Rb187200210237187155161147301286
    Ba554663526653432572610792687634
    Th22.0019.9021.3024.4024.6013.7014.0012.435.338.7
    U3.873.343.633.052.764.282.663.205.155.57
    Nb21.227.523.732.227.821.423.221.827.930.5
    Ta2.132.432.082.922.962.022.762.272.212.79
    La36.2039.2041.5048.6037.1030.2029.2027.5071.3072.40
    Ce78.8089.6094.20106.0084.4057.7054.8047.50134.00137.00
    Pr8.569.8810.0011.909.567.196.945.8614.7015.20
    Sr131254200301171305301470219208
    Nd30.9034.8036.0042.9035.6026.0025.9020.9052.3051.90
    Zr185232225292190177173198290268
    Hf3.445.925.338.324.353.643.985.016.705.78
    Sm5.686.716.878.437.375.305.373.938.828.85
    Eu1.171.391.201.430.921.001.001.121.381.30
    Gd5.476.516.337.496.824.784.893.657.968.36
    Tb0.891.030.981.191.070.750.800.561.141.19
    Dy4.945.695.376.265.733.934.292.935.816.10
    Ho1.001.171.151.261.110.770.820.571.171.25
    Y27.6030.1029.1032.4029.2021.1022.3017.2032.2031.50
    Er2.963.243.313.623.022.082.281.523.313.50
    Tm0.490.530.540.590.470.320.350.250.530.56
    Yb3.353.433.523.773.042.062.281.693.453.65
    Lu0.510.520.550.560.460.310.340.260.530.57
    ∑REE84.9695.1294.92109.9094.8168.4070.6254.58125.30118.73
    ( La/Sm) N6.375.846.045.775.035.705.447.008.088.18
    ( La/Yb) N7.758.208.469.258.7510.529.1911.6714.8214.23
    Eu/Eu0.210.210.180.180.130.200.190.300.160.15
     注:Eu/Eu= 2×EuN/(SmN+ GdN);A/CNK= (2×Al2O3/101.96)/(CaO/56.08+2×Na2O/61.98+2×K2O/94.2)。
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    图  4  研究区花岗岩TAS图解(a)(据Middlemost,1994); A/CNK–A/NK分类图解(b)(据Richwood, 1989);SiO2–K2O判别图(c)(据Peccerillo et al.,1976); Na2O–K2O判别图(d)(据Turner et al.,1993
    Figure  4.  (a) TAS diagram, (b) A/CNK–A/NK diagram, (c) SiO2–K2O diagram and (d) Na2O–K2O diagram of granites

    在原始地幔标准化微量元素蛛网图解中(图5a),巴颜喀拉山样品的微量元素组成,均表现出相似的微量元素原始地幔标准化模式,微量元素特征表现均为:富集Rb、Th、U等大离子亲石元素,亏损Nb、Ta等高场强元素,且具有轻微的Zr、Hf负异常,具有较弱的Eu异常特征,高的Rb、Th、U、Pb和Sm含量,低的Sr、Nb、Ta、Zr和Hf含量,与典型的地壳源区岩浆特征相似(Chappell et al.,19741992Harris et al.,1992),指示了花岗质岩浆主要源于地壳部分熔融。与巴颜喀拉山花岗质岩石相比,达日地区花岗质岩石微量元素特征表现为富集Rb、Th、U等大离子亲石元素,亏损Nb、Ta等高场强元素,但达日地区样品Nb、Ta、La、Ce、Pr和Zr等元素含量高于巴颜喀拉山地区样品,而Sr含量则低于巴颜喀拉山地区样品,Eu异常更为明显。

    图  5  巴颜喀拉山和达日地区花岗质岩石微量元素原始地幔标准化蛛网图(a)和稀土元素球粒陨石标准化图解(b)
    前人巴颜喀拉山花岗质岩石数据引自Cai等(2009);前人达日地区花岗质岩石数据引沙淑清等(2007);标准化值据Sun等(1989)
    Figure  5.  (a) Primitive mantle–normalized trace element patterns and (b) chondrite–normalized REE patterns for the granitoids Bayankala and Dari area

    在稀土元素球粒陨石标准化图解中(图5b),巴颜喀拉山样品和达日地区样品稀土元素组成表现均出强烈的稀土分异模式,为轻稀土富集型的稀土元素配分模式。相比而言,达日地区样品轻、重稀土含量均高于巴颜喀拉山样品。巴颜喀拉山样品稀土元素总含量跨度很大,ΣREE值为54.56~270.92,平均为120.90;轻重稀土分异比值较高,(La/Yb)N值为7.81~29.25;具有弱的负Eu异常,Eu/Eu*值为0.19~0.30)。达日地区样品稀土元素总含量跨度较小,ΣREE值为54.58~137.47,平均为98.39;轻重稀土分异比值较低,(La/Yb)N值为7.75~19.66;具有中等的负Eu异常,Eu/Eu*值为0.07~0.30。

    巴颜喀拉山花岗闪长岩(359)锆石Hf同位素测试数据见表4。 在359样品中,25个锆石Lu–Hf同位素分析点与已分析岩浆锆石区域重叠。结果显示,176Hf/177Hf 值为 0.282539~0.282727,176Yb/177Hf 值为0.013301~0.051967,176Lu/177Hf值为0.000377~0.001435,所有分析点176Lu/177Hf的值均小于0.002,表明样品锆石形成后没有积累其他放射性成因Hf,可以用初始176Hf/177Hf值代表锆石形成时的176Hf/177Hf值(吴福元等,2007)。计算得到εHft)值为 −3.62~2.92,平均值为−0.54,锆石Hf二阶段模式年龄为1.07~1.48 Ga。

    表  4  巴颜喀拉山地区花岗质岩石锆石Hf同位素统计表
    Table  4.  Zircon Hf isotopic data of granitoids in Bayankala
    点号176Yb/177Hf176Lu/177Hf176Hf/177Hf±2σεHf(t)±1σtDM1(Ma)tDM2(Ma)
    样号359(N=25)t=215 Ma
    10.0350930.0009920.2826630.0000250.750.8686958321207
    20.0318250.0013070.2826840.0000251.500.8884088011159
    30.0353190.00060.2826710.0000271.020.9504268231190
    40.0447790.0007960.2826740.0000251.060.8733998271187
    50.0219610.000690.2826390.000029−0.081.0136658601260
    60.0267090.0006920.2825540.000028−3.100.9898649831451
    70.0248280.0012080.2826220.000026−0.680.9266118851298
    80.0235070.0014350.2826240.000037−0.611.3004288831293
    90.0393560.0006690.2826210.000031−0.781.096098991304
    100.0519670.0008210.2827270.0000282.920.9804837531069
    110.0232060.0005270.2826520.0000260.380.9121938431230
    120.0291540.0011150.2826020.000032−1.411.1307279171344
    130.0176740.0009730.2826460.0000260.190.9005528481243
    140.0372240.0005610.2827050.0000262.200.9116387781114
    150.0326880.0005730.2826250.000027−0.610.9589718871293
    160.0193920.0003770.2825410.000024−3.520.8350799951478
    170.0190880.000690.2825850.000025−1.980.8864569341380
    180.0133010.0007050.2825580.000027−2.900.9476279671438
    190.0236230.0005920.2825620.000027−2.800.9546759691432
    200.0246320.0006260.2826190.000025−0.800.8584468901305
    210.020760.0006250.282640.000027−0.030.9564518581257
    220.0216550.0006440.2825960.000026−1.600.9194859211356
    230.0211390.0006160.2826280.000025−0.450.878358751283
    240.0246040.0014350.2826830.0000231.470.8192538001161
    250.0222380.0003770.2825390.000025−3.620.87545610001484
     注:εHft)的计算采用球粒陨石现今的176Hf/177Hf =0.282772和176Lu/177Hf=0.0332(据Blichert et al.,1997);Hf同位素二阶段模式年龄(tDM2 )分别采用平均下地壳176Lu/177Hf =0.022(据Altherr et al.,2000)和平均大陆壳176Lu/177Hf =0.015(据Griffin et al.,2002)。
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    在哈克图解中(图6),巴颜喀拉山和达日地区花岗质岩石主量元素含量均有线性的变化趋势,说明在岩浆演化过程中广泛存在着结晶分异现象。随着SiO2含量的增加,Al2O3、MnO2、TiO2、FeOT、MgO和CaO的含量逐渐降低,并且巴颜喀拉山花岗质岩石的MnO2、TiO2、FeOT、MgO和CaO的含量均高于达日地区花岗质岩石。结合岩相学特征与哈克图解,笔者认为巴颜喀拉山花岗岩分离结晶作用的产物为镁铁质矿物(如角闪石)、铁钛氧化物、长石和磷灰石,而达日地区花岗岩则主要为高铝矿物(如白云母、黑云母)、富 Ca矿物(如磷灰石)和铁钛氧化物(如钛铁矿、榍石等)(Wu et al.,2003Zhong et al.,2009)。此外,巴颜喀拉山和达日地区花岗质岩石具有中等到弱的负Eu异常(Eu/Eu=0.07~0.30)和强的负Sr异常(图5a),表明有斜长石的分离结晶。强的负Ba异常(图5a)指示在岩浆在演化过程中有存在斜长石和钾长石的分离结晶作用。

    图  6  研究区花岗岩哈克图
    Figure  6.  Harker diagrams for the major elements of granitoids

    花岗岩一般可划分为A、I、S和M型4种成因类型(Chappell et al.,19741992Bonin,2007)。M型花岗岩是由俯冲大洋地壳或者上覆地幔衍化而来,其特征为K2O含量通常<1%(Chappell,1999Healy et al.,2004),巴颜喀拉山花岗岩和达日地区花岗岩K2O含量分别为2.98%~5.18%和2.93%~5.42%,均高于1%,故研究区花岗岩不属于M型花岗岩。研究区花岗岩具有较低的高场强元素含量,如巴颜喀拉山花岗岩Nb含量为15.60×10−6~30.50×10−6,Ta含量为1.43×10−6~2.79×10−6;达日地区花岗岩Nb含量为15.60×10−6~21.20×10−6,Ta含量为1.40×10−6~4.14×10−6。A型花岗岩高场强元素含量相对较高(Eby,1992),因此研究区花岗岩不属于A型花岗岩。

    I型花岗岩的特征为,K2O/Na2O值通常<1,CIPW刚玉分子指数<1%,特征矿物为角闪石(Clemens et al.,2011Chappell et al.,2012)。巴颜喀拉山花岗质岩石主要造岩矿物中均含有角闪石,且K2O/Na2O值<1(0.72~0.95),CIPW刚玉分子指数<1%,表现出I型花岗岩特征,主量元素化学组成与基性岩部分熔融形成的花岗岩体基本一致。基于以上特征,笔者认为巴颜喀拉山花岗岩为I型花岗岩。

    在花岗岩成因判别图中,达日地区样品全部落入A型和未分异区间(图7a),所有样品( Na2O+K2O)/CaO值(1.54~4.43,除过最大值30.93)和FeOT/MgO值(1.78~4.10,除过最大值18.33)较低,而A型花岗岩的( Na2O+K2O)/CaO和FeOT/MgO相对较高,故达日地区花岗质岩石样品不符合A型花岗岩的特征(Collins et al.,1982Whalen et al.,1987)。相比于I型花岗岩,达日地区花岗质岩石Si含量相对较高(SiO2含量为58.58 %~73.77 %),Na含量相对较低(Na2O含量为2.63 %~4.03 %,均值为3.18%),Ca含量也相对较低(CaO含量为0.28 %~4.92%,均值为 2.62 %),铝饱和指数较高(A/CNK值为1.14~1.38),这些特征都与I型花岗岩不相符(Chappell et al.,1992Li et al.,2007)。S型花岗岩岩浆源区为变沉积岩,其特征为K2O/N2O通常>1,铝饱和指数(A/CNK)>1. 1,CIPW刚玉分子指数>1 %,特征矿物为堇青石、石榴子石、白云母和夕线石。达日地区花岗质岩石铝饱和指数>1 (A/CNK=1.14~1.38),属于过铝质花岗岩;CIPW标准矿物计算结果含有刚玉(C),含量为0.11 %~2.71 %,只有一个值小于1 %;样品均含白云母和黑云母。此外,分异I型花岗岩和分异S型花岗岩的Th和Y含量也有差异,这是由于Th和Y在过铝质岩浆演化早期优先进入Th和Y富集的矿物(如独居石),所以分异S型花岗岩的Th和Y含量相对较低,并与Rb含量呈负相关;而分异I型花岗岩的Th和Y含量高,是因为Th和Y富集的矿物不在准铝质岩浆演化早期优先结晶,并且Th和Y含量与Rb含量呈正相关。样品的Th–Rb和Y–Rb演化趋势与S型花岗岩是一致的(图7b图7c)(Chappell,1999)。在ACF判别图中(图7d),样品点均落在S型花岗岩区域(Nakada et al.,1979)。综上所述,笔者认为达日地区花岗质岩石为过铝质S型花岗岩。

    图  7  达日地区花岗岩成因判别图
    前人达日地区花岗岩数据引沙淑清等(2007);底图a据Whalen等(1987);底图b、c 据Chappell( 1999);底图d据Nakada等(1979);A=Al2O3–( Na2O+K2O);F=FeO+MgO;C=CaO
    Figure  7.  Discrimination diagrams for the genetic types of granites in Dari area

    巴颜喀拉山样品表现出较强的稀土元素分异模式,而HREE元素配分曲线较为平缓(图5b),Y/Yb值为7.84~12.57,大多数样品的TiO2含量较低(<1 %),Rb/Sr值较小(<0.8),这些特征与角闪石残留物特征一致(Petford et al.,1996)。实验表明,玄武岩的角闪石脱水反应生成的熔体是闪长质的,与斜长石、辉石和铁钛矿物为主的残余物共存(Beard et al.,1991Rushmer,1991Wolf et al.,1992);而玄武岩在流体作用下部分熔融形成的熔体Si、Al含量高,与角闪石、斜辉石、铁钛矿物和少量斜长石的残余物共存(Beard et al.,1991)。上述2种情况下的熔体组成和残余矿物组合有很大的不同。前一种情况下产生的熔体具有一定的负的Eu异常(Tepper et al.,1993)。巴颜喀拉山地区花岗质岩石具有中等的负Eu异常,Eu/Eu*值为0.19~0.30),表明其由玄武岩来源的角闪石脱水、熔融再作用形成。在CaO/(MgO+FeOT)–Al2O3/(MgO+FeOT)图解(图8b)和Rb/Sr–Rb/Ba图解(图8c)中,巴颜喀拉山花岗岩数据点主要落在下地壳的铁镁质玄武岩范围,支持上述推论。此外,锆石Hf同位素组成为εHft)值为−3.62~2.92,平均值为−0.54,指示源区存在铁镁质成分。综上所述,笔者认为巴颜喀拉山地区花岗质岩石的岩浆来源于下地壳铁镁质。

    图  8  巴颜喀拉山和达日地区花岗质岩石岩浆源区判别图
    前人巴颜喀拉山花岗质岩石数据引自Cai等(2009);前人达日地区花岗质岩石数据引自沙淑清等(2007));底图a、c据Sylvester(1998);底图b据Altherr et al.,2000;底图d据Icenhower等(1996)Nash等(1985)Nabelek等(1998)
    Figure  8.  Discrimination diagrams for the potential magma source of granitoids in Dari area

    实验表明,基性岩石(玄武岩)的部分熔融可产生偏铝质花岗岩类(Beard et al.,1991Wolf et al.,1992Rapp et al.,1995Johannes et al.,1996Sisson,2005),而沉积碎屑岩的部分熔融则可以产生过铝质花岗岩体(Johannes et al.,1996Patino-Douce et al.,1998a1998b)。达日地区过铝质花岗岩,样品表现出很强的稀土元素分馏模式,轻稀土元素(LREE)富集,而重稀土元素(HREE)亏损(7B),富集大离子亲石元素(如Rb、Th、U),亏损高场强元素(如Nb、Ta),δEu值为0.07~0.30,显示中等负Eu异常。以上特征表明岩体的岩浆来源可能是地壳中富铝质沉积物。

    过铝质花岗岩CaO、Na2O含量相对较低,其原因是长石在形成黏土的过程中会丢失这些组分,该特征与其沉积源区有关(Chappell et al.,1992)。因此,一般用CaO/Na2O值来判断岩石源区。根据实验研究(Skjerlie et al.,1992),以泥质岩为源区的花岗岩CaO/Na2O值小于0.3,而以杂砂岩为源区的过铝质花岗岩,其CaO/Na2O值大于0.3。达日地区花岗岩CaO/Na2O值为0.09~2.61,绝大部分值大于0.3,据此推测达日地区花岗质岩石的岩浆源区主要为杂砂岩。达日地区花岗岩样品相比较于变泥质岩的岩浆源区普遍具有高CaO/Na2O值(0.09~1.61,其中只有一个比值小于0.3)和低的Al2O3/TiO2值(16.25~52.64,除去最大值80.53),表明其岩浆源区并不是泥质岩。在CaO/Na2O–Al2O3/TiO2图解中(图8a),花岗质岩石样品大部分落在以变杂砂岩为岩浆源区的范围内,说明达日地区花岗质岩石可能是由变杂砂岩部分熔融形成的。在CaO/(MgO+FeOT)–Al2O3/(MgO+FeOT)图解中(图8b),达日地区花岗质岩石样品主要落入变杂砂岩区域(Altherr et al.,2000)。过铝质花岗岩的Rb–Sr–Ba含量变化受控制于其源岩成分(Sylvester,1998),杂砂岩在熔融后会残余大量的长石,而泥质岩熔融后留下很少的斜长石(Skjerlie et al.,1992Patino-Douce et al.,1995)。Sr、Ba是斜长石的相容元素,Rb则为不相容元素,由泥质岩为源岩产生的强过铝质花岗岩Rb/Sr和Rb/Ba值较高,而以杂砂岩为源岩熔融产生的过铝质花岗岩Rb/Sr和Rb/Ba值较低。因此,可以通过Rb/Sr和Rb/Ba值变化来判断研究区花岗岩的岩浆源区。依据Rb/Ba和Rb/Sr值投图,达日地区的花岗质岩石样品落入贫黏土源区,指示其是由地壳中的杂砂岩类熔融形成的(图8c)。对于判别过铝质花岗岩的源岩性质,斜长石是一个很好的指示矿物,泥质岩和杂砂岩在熔融过程中形成的熔体会有差别,泥质源岩会相比富黏土贫斜长石(<5%),而杂砂岩则富斜长石(>5%)贫黏土。Rudnick等(2003)利用大陆地壳的平均组成作为初始组分,模拟了不同残余相(如钾长石、斜长石和黑云母)在部分熔融实验中的影响(图8d)。结果显示,达日地区花岗质岩石成分变化在源区残留7 %~60 %的斜长石,说明其岩浆来源为杂砂岩的部分熔融。综上所述,笔者认为达日地区花岗质岩石的岩浆源区可能是中地壳附近的杂砂岩。

    在松潘–甘孜地块中,除了已知的沿扬子地块西缘出露的部分元古界基底外,再无其他基底出露,是制约其基底属性认知的主要因素。目前,对松潘–甘孜地块基底属性的认识存在2种观点:①古特提斯洋的残余(Yin et al.,1993)和与扬子地块关系具有亲缘性的元古代基底(Zhang et al.,2006Xiao et al.,2007)。松潘–甘孜巴颜喀拉山地区花岗质岩石与松潘–甘孜地块东部花岗质岩体具有相似的Sr、Nd同位素组成和二阶段模式年龄,巴颜喀拉山花岗质岩石εNdt)值为 −4.3~−5.5,TDM2 值为1.38~1.46;松潘–甘孜东部花岗质岩石εNdt)值为 −6.0~−9.5,TDM2值为 1.3~1.65,表明其岩浆具有共同来源,进而说明地壳基底属性一致(Cai et al.,2009)。巴颜喀拉山地区花岗质岩石的锆石Hf二阶段模式年龄为1.07~1.48 Ga,位于1.0~1.5Ga地壳演化线之间,与扬子地块西缘存在的新元古代镁铁质岩石相同,表明松潘–甘孜地块存在新元古代基底,且基底与扬子地块基底存在亲缘性(图9)(Zheng et al.,2007)。

    图  9  巴颜喀拉山花岗质岩石锆石εHft)值与U–Pb年龄图解
    前人巴颜喀拉山花岗质岩石数据引自Cai等(2009);扬子西缘花岗质岩石数据引自Zheng等(2007)
    Figure  9.  Plots of zircon U–Pb ages vs. εHft) values for the Bayankala granitoids

    在金沙江缝合带(包括甘孜–理塘缝合带)中,金沙江蛇绿岩组合中的2个斜长花岗岩体,U–Pb锆石年龄分别为(340±3)Ma和(294±3)Ma,表明金沙江洋形成于晚泥盆世至早石炭世(Wang et al.,2000)。在该区及其邻近地区,已鉴定出2个花岗岩类的年龄群,即245~227 Ma(侵入古生代变质沉积物)和219~216 Ma(侵入三叠纪沉积物)。前人结合地质背景认为,245~227 Ma的花岗岩类为同碰撞花岗岩,219~216 Ma花岗岩类为后碰撞花岗岩,表明古特提斯洋的闭合时间不晚于中三叠世,而不是早侏罗世(Wang et al.,2000Reid et al.,2005Xiao et al.,2007)。松潘–甘孜地块巴颜喀拉山地区和达日地区的岩浆结晶年龄(212~218 Ma)明显晚于金沙江缝合带的同碰撞花岗岩的年龄,且与金沙江缝合带的后碰撞花岗岩年龄是一致的。据此,笔者认为巴颜喀拉山地区和达日地区花岗质岩石可能也形成于后碰撞构造坏境。

    松潘–甘孜地块巴颜喀拉山地区花岗质岩石是下地壳角闪石脱水熔融反应的产物,但是这种脱水反应一般需要>800 ℃的温度(Beard et al.,1991Rushmer,1991)。如果没有额外的热源供应,碰撞造山带的地壳温度达到>800 ℃是不可能的(Patino-Douce et al.,1998b)。在后碰撞构造背景下,热源的可能来源包括:①地壳增厚引起的放射性同位素衰变热。②地壳剪切产生的热量。③幔源岩浆的热量。④由岩石圈分层引起的软流圈上涌的热量。但是,前2种热源的热量不会轻易造成大范围的地壳熔融。地壳增厚引起的地壳熔融只会在120 Ma左右的时间尺度上发展(Turner et al.,1993)。地壳剪切热引起的岩浆作用通常呈线性分布,而松潘–甘孜地块的花岗岩并非线性分布,所以排除第二种热源可能。由于在松潘–甘孜地块内缺少印支期幔源岩浆活动的证据。因此,岩浆底侵作用并不是印支期花岗岩类的形成的原因。岩浆底侵作用通常会导致下地壳发生部分熔融,尽管第③种提供热源的方式有可能发生,但是松潘–甘孜地块的下地壳没有底贴的岩浆(Liu et al.,2008),并且松潘–甘孜地块中幔源岩浆作用也很罕见,因而排除第③种热源可能。在后碰撞环境,区域伸展,之前加厚的岩石圈由于重力原因拆沉,诱发软流圈上涌,已经成为解释后碰撞花岗岩浆形成的主要机制(Jung et al.,1998Wu et al.,20022005Chung et al.,20032005Ilbeyli et al.,2004)。松潘–甘孜地块东部的埃达克花岗岩(216~228 Ma)可能为地壳增厚的证据(Zhang et al.,2006Xiao et al.,2007),A型花岗岩(211 Ma)是软流圈上涌导致岩石圈伸展的标志(Zhang et al.,2007),松潘-甘孜地块东南部后碰撞I型花岗岩是由下地壳镁铁质物质的部分熔融形成的。Xiao等(2007)Zhang等(2007) 提出,松潘–甘孜地块东部岩石圈拆沉作用可以解释后碰撞的埃达克、A型和I型花岗质岩浆作用组合。Sylvester(1998)认为,过铝质花岗岩通常形成在后碰撞构造环境中,并可划分为高压型和高温型2种成因类型。高压型是由于地壳增厚,引起放射性同位素衰变产生热量,在后碰撞阶段地壳减压熔融形成,形成的花岗岩规模通常为小到中等;而高温型是由于地幔软流圈物质的上涌,带来的热量将地壳部分熔融,这种方式形成的花岗岩规模相对较大。后碰撞花岗岩在松潘–甘孜地块东部和中部分布都很广泛。这些花岗岩体的岩浆结晶年龄都为晚三叠世,因其具有相同的地球动力学背景。巴颜喀拉山地区和达日地区花岗质岩石的形成时间(212~218 Ma)与上述的花岗岩体的结晶时代相近。因此,笔者认为巴颜喀拉山地区和达日地区花岗质岩石可以解释为后碰撞环境下,由于岩石圈拆沉,软流圈上涌,分别导致下地壳和中地壳发生部分熔融所致。

    (1) 松潘–甘孜地块巴颜喀拉山地区花岗质岩石属于高钾钙碱性过铝质I型花岗闪长岩,而达日地区花岗质岩石属于钾玄岩和高钾钙碱性、过铝质S型石英二长岩和花岗岩,两地区花岗质岩石侵位时间均为~215 Ma。

    (2) 松潘–甘孜地块巴颜喀拉山地区花岗质岩石的源区可能为下地壳镁铁质岩石,而达日地区花岗质岩石的源区可能为中地壳变杂砂岩。

    (3) 松潘–甘孜地块存在新元古代基底,且其基底与扬子地块基底存在亲缘性。结合锆石U–Pb年代学和区域构造演化,推测研究花岗质岩石是后碰撞背景,岩石圈拆沉,诱发的不同地壳岩石部分熔融的产物。

  • 图  1   松潘–甘孜地块地质构造简图(a)、巴颜喀拉山地质简图(b)与达日花岗岩类分布简图(c)(据蔡宏明,2010修改)

    Figure  1.   (a) Geological structure sketch of Songpan–Garze block, (b) geological sketch of granitoids in Bayankala and(c) geological sketch of granitoids in Dari area

    图  2   手标本照片与镜下矿物鉴定图

    a、b. 巴颜喀拉山南口地区花岗闪长岩(样品359);c、d. 达日地区查雀嘎玛石英二长岩(样品D2409);e、f. 达日地区波不弄公玛石英二长岩体(样品D2615);g、h. 达日地区日查花岗岩(样品D1710);Pl. 斜长石;Qtz. 石英;Bi. 黑云母;Ms. 白云母;Kfs. 钾长石;Ser. 绢云母;Per. 条纹长石;Chl. 绿泥石;Am. 角闪石

    Figure  2.   Hand specimen photograph and microphotographs of granitoids

    图  3   锆石U–Pb谐和图及代表性锆石颗粒阴极发光图

    a. 巴颜喀拉山花岗质岩石;b、c、d. 达日地区花岗质岩石

    Figure  3.   Zircon U–Pb concordant diagrams and parts of Cathodoluminescence (CL) images of four samples

    图  4   研究区花岗岩TAS图解(a)(据Middlemost,1994); A/CNK–A/NK分类图解(b)(据Richwood, 1989);SiO2–K2O判别图(c)(据Peccerillo et al.,1976); Na2O–K2O判别图(d)(据Turner et al.,1993

    Figure  4.   (a) TAS diagram, (b) A/CNK–A/NK diagram, (c) SiO2–K2O diagram and (d) Na2O–K2O diagram of granites

    图  5   巴颜喀拉山和达日地区花岗质岩石微量元素原始地幔标准化蛛网图(a)和稀土元素球粒陨石标准化图解(b)

    前人巴颜喀拉山花岗质岩石数据引自Cai等(2009);前人达日地区花岗质岩石数据引沙淑清等(2007);标准化值据Sun等(1989)

    Figure  5.   (a) Primitive mantle–normalized trace element patterns and (b) chondrite–normalized REE patterns for the granitoids Bayankala and Dari area

    图  6   研究区花岗岩哈克图

    Figure  6.   Harker diagrams for the major elements of granitoids

    图  7   达日地区花岗岩成因判别图

    前人达日地区花岗岩数据引沙淑清等(2007);底图a据Whalen等(1987);底图b、c 据Chappell( 1999);底图d据Nakada等(1979);A=Al2O3–( Na2O+K2O);F=FeO+MgO;C=CaO

    Figure  7.   Discrimination diagrams for the genetic types of granites in Dari area

    图  8   巴颜喀拉山和达日地区花岗质岩石岩浆源区判别图

    前人巴颜喀拉山花岗质岩石数据引自Cai等(2009);前人达日地区花岗质岩石数据引自沙淑清等(2007));底图a、c据Sylvester(1998);底图b据Altherr et al.,2000;底图d据Icenhower等(1996)Nash等(1985)Nabelek等(1998)

    Figure  8.   Discrimination diagrams for the potential magma source of granitoids in Dari area

    图  9   巴颜喀拉山花岗质岩石锆石εHft)值与U–Pb年龄图解

    前人巴颜喀拉山花岗质岩石数据引自Cai等(2009);扬子西缘花岗质岩石数据引自Zheng等(2007)

    Figure  9.   Plots of zircon U–Pb ages vs. εHft) values for the Bayankala granitoids

    表  1   巴颜喀拉山花岗闪长岩体(359)LA–ICP–MS锆石U–Pb年龄测试结果表

    Table  1   LA–ICP–MS zircon U–Pb dating results of sample 359

    测点207Pb/235U206Pb/238U207Pb/235U206Pb/238U
    同位素比值同位素比值年龄(Ma)年龄(Ma)
    359N=25(有效点19个)
    GE010.2380.01280.032080.00049216.810.5216.810.4
    GE020.26430.01620.035270.00057238.112.9238.112.9
    GE030.22890.01240.032120.00049209.310.2209.310.2
    GE040.23270.0110.032160.00047212.49.0212.49.1
    GE050.22410.01920.034160.00061205.315.9205.315.9
    GE060.22480.01240.032510.0005205.910.2205.910.2
    GE070.22010.01340.031330.000520211.120211.2
    GE080.25530.0170.034190.00058230.913.7230.913.7
    GE090.23210.00950.033280.00046211.97.8211.97.8
    GE100.32450.01390.033540.0005285.310.6285.310.6
    GE110.22830.01560.032660.00055208.812.9208.812.9
    GE120.23210.01710.032570.0005821214.121214.1
    GE130.2280.01380.033080.00053208.611.4208.611.4
    GE140.22750.01210.033030.0005208.19.9208.19.9
    GE150.23590.01370.032850.0005221511.221511.3
    GE160.23570.01440.033530.00055214.911.8214.911.9
    GE170.23450.01770.033930.00059213.914.5213.914.5
    GE180.46620.03010.043980.00082388.620.8388.620.8
    GE190.23920.01460.033150.00054217.711.9217.711.9
    GE200.25520.02110.033090.00063230.817.0230.817.1
    GE210.22480.02110.032870.00063205.917.4205.917.5
    GE220.26020.01620.033850.00057234.913.0234.913.0
    GE230.23730.01280.033160.00051216.210.5216.210.5
    GE240.41560.01750.055830.0008352.912.5352.912.5
    GE250.2720.0170.035050.00059244.313.5244.313.5
    下载: 导出CSV

    表  2   查雀嘎玛石英二长岩体(D2409)、波不弄公玛石英二长岩体(D2615)和日查花岗岩体(D1710)LA–ICP–MS锆石U–Pb年龄测试结果表

    Table  2   LA–ICP–MS zircon U–Pb dating results of sample D2409, D2615 and D1710

    测点207Pb/235U206Pb/238U207Pb/235U206Pb/238U
    同位素比值同位素比值年龄(Ma)年龄(Ma)
    D2409N=25(有效点16个)
    GB010.23120.01050.03270.0005211.28.7207.23.0
    GB020.22130.01260.03300.0005203.010.5209.13.1
    GB030.23660.01530.03360.0005215.612.6213.03.4
    GB040.24420.01170.03240.0005221.99.6205.33.0
    GB050.22870.01850.03300.0006209.115.3209.13.4
    GB060.22930.01370.03340.0005209.611.3212.03.3
    GB070.24050.01130.03390.0005218.89.2215.03.2
    GB080.21650.01410.03270.0005199.011.8207.13.2
    GB090.22950.01560.03410.0006209.812.9216.43.5
    GB100.24700.01810.03420.0006224.214.7216.73.6
    GB110.22810.02210.03510.0006208.618.3222.34.0
    GB120.26190.02010.03540.0006236.216.2224.23.9
    GB130.23130.03440.03550.0008211.328.3225.14.8
    GB140.28610.02520.03470.0007255.519.9219.94.3
    GB150.29210.03130.03220.0007260.224.6204.14.4
    GB160.21230.01640.03490.0006195.513.7221.03.5
    GB170.24760.02120.03530.0006224.617.2223.74.0
    GB180.26590.02830.03420.0007239.422.7217.04.5
    GB190.20330.02640.03380.0007187.922.3214.54.1
    GB200.27170.02320.03310.0007244.018.5210.14.2
    GB210.26730.02190.03340.0006240.517.6212.03.9
    GB220.10760.02820.03410.0006103.825.8216.14.0
    GB230.26600.01570.03450.0005239.512.6218.83.4
    GB240.23700.01760.03600.0006216.014.4227.83.6
    GB250.24130.01330.03350.0005219.410.9212.13.3
    D2615N=25(有效点17个)
    GC010.25920.01620.03380.0005234.113.0214.63.3
    GC020.20180.01210.03290.0005186.610.2208.93.0
    GC030.21010.01350.03250.0005193.611.3205.93.1
    GC040.28770.01640.03280.0005256.712.9207.83.3
    GC050.23000.01230.03390.0005210.210.2215.13.2
    GC060.29520.01730.03300.0005262.713.6209.13.4
    GC070.22250.02120.03370.0006204.017.6213.44.0
    GC080.26570.02680.03530.0007239.221.5223.64.3
    GC090.17770.02360.03420.0006166.120.4216.73.9
    GC100.22050.01790.03410.0006202.314.9216.03.7
    下载: 导出CSV
    续表2
    测点207Pb/235U206Pb/238U207Pb/235U206Pb/238U
    同位素比值同位素比值年龄(Ma)年龄(Ma)
    GC110.28800.02240.03310.0007257.017.7209.64.3
    GC120.06450.03410.03620.000763.532.5229.14.3
    GC130.37170.04120.03370.0009320.930.5213.35.5
    GC140.31550.02540.03540.0007278.519.6224.54.1
    GC150.32910.03280.03510.0008288.925.1222.34.9
    GC160.22510.01810.03440.0006206.215.0217.73.6
    GC170.21050.01730.03350.0006194.014.5212.53.6
    GC180.32040.02880.03560.0007282.222.1225.54.5
    GC190.24370.02080.03350.0006221.417.0212.33.6
    GC200.24910.02840.03280.0007225.923.1208.24.3
    GC210.30010.02250.03300.0006266.517.6209.23.9
    GC220.10110.02860.03370.000697.826.4213.93.9
    GC230.22720.01410.03400.0005207.911.7215.43.2
    GC240.22810.01870.03290.0005208.715.5208.43.4
    GC250.23780.01120.03330.0005216.69.2211.13.1
    D1710N=25(有效点19个)
    GD010.71070.022910.03500.00057545.113.6222.23.5
    GD020.28870.020590.03370.00058257.616.2213.83.6
    GD030.24820.015280.03390.00054225.112.4215.33.3
    GD040.23230.016680.03320.00055212.113.7210.63.4
    GD050.27600.015740.03430.00055247.412.5217.83.4
    GD060.23560.016220.03390.00056214.813.3215.53.5
    GD070.27850.023840.03290.00071249.518.9208.74.4
    GD080.27940.019280.03390.00060250.215.3215.13.7
    GD090.34400.024230.03400.00065300.218.3215.54.0
    GD100.94480.029600.03650.00060675.415.4231.53.8
    GD110.20610.028700.03510.00071190.324.1222.44.4
    GD120.27810.021800.03470.00068249.117.3220.44.2
    GD130.25650.019180.03490.00064231.815.5221.23.9
    GD140.23930.021950.03460.00066217.817.9219.54.1
    GD150.21750.017690.03330.00059199.814.7211.73.7
    GD160.26980.029210.03390.00067242.623.3215.34.2
    GD170.25090.015610.03370.00056227.312.6213.73.5
    GD180.31580.017610.03480.00059278.713.5220.83.7
    GD190.53700.027100.03730.00065436.417.9236.64.1
    GD200.21940.017170.03510.00057201.414.3222.53.6
    GD210.25540.009640.03430.00048230.97.8217.73.0
    GD220.28130.023270.03470.00070251.718.42204.3
    GD230.14340.023780.03480.00056136.121.1220.83.5
    GD240.27470.011800.03460.00050246.49.4219.43.2
    GD250.24520.012620.03510.00052222.710.3222.73.2
    下载: 导出CSV

    表  3   巴颜喀拉山和达日地区花岗质岩石主量元素(%)和微量元素数据(10 −6)结果表

    Table  3   Major (%) and trace element contents (10−6) of granitoids in Bayankala and Dari area

    样品号巴颜喀拉山样品达日地区样品
    357358359363D2902D2610D2615D2409D2410D1710
    岩性花岗闪长岩闪长岩花岗闪长岩花岗闪长岩二长岩石英二长岩石英二长岩石英二长岩石英二长岩花岗岩
    SiO265.0959.0565.5963.3458.5865.4567.7066.3765.2873.77
    TiO20.600.820.690.731.040.730.540.540.650.17
    Al2O315.9514.6814.2614.1116.9015.0415.5614.7415.6413.69
    Fe2O30.921.580.852.611.490.910.720.490.801.93
    FeO3.374.833.794.124.243.082.182.883.100.28
    MnO0.110.140.100.0980.0990.0640.0480.0590.0730.065
    MgO1.694.402.862.873.141.791.241.191.450.11
    CaO3.365.354.114.544.923.012.602.333.030.28
    Na2O3.103.863.432.933.052.872.993.113.073.24
    K2O2.952.052.462.614.534.725.445.275.015.42
    P2O50.150.180.140.180.310.160.140.150.190.041
    LOI4.244.831.952.742.942.701.184.292.581.44
    Total101.53101.77100.23100.88101.24100.52100.34101.42100.87100.44
    K2O+Na2O6.055.915.895.547.587.598.438.388.088.66
    CaO/Na2O1.082.611.671.741.611.050.870.750.990.09
    K2O/Na2O0.951.881.391.121.491.641.821.691.631.67
    A/CNK1.411.01.181.201.171.201.181.141.181.20
    A/NK1.921.711.721.851.701.531.441.361.491.22
    Rb94.3225129120220262297306262263
    Ba880397696695901647538635747229
    Th12.821.118.429.818.728.743.732.231.928.8
    U2.955.823.071.942.92.633.374.475.324.91
    Nb15.715.618.750.530.230.526.023.927.742.3
    Ta1.531.431.761.42.312.082.182.162.054.14
    La29.9032.0034.9089.3047.8050.8084.7046.8059.6076.00
    Ce62.5075.8075.80272.00103.00114.00156.00100.00126.00142.00
    Pr7.388.678.0845.4011.9012.3016.3010.8013.6015.60
    Sr27425228031138925020216324354.5
    Nd26.4032.8029.80204.0043.2042.5054.3038.1047.0056.00
    Zr175172168170251283278226244236
    Hf4.916.754.996.688.346.794.745.015.425.08
    Sm4.916.335.4618.007.787.418.817.188.0510.20
    Eu1.361.371.322.831.821.331.291.121.350.69
    Gd4.155.374.8812.206.946.678.156.757.289.25
    Tb0.550.860.731.351.000.951.091.061.041.46
    Dy2.474.543.794.185.134.865.415.805.227.77
    Ho0.430.950.780.801.030.971.081.231.071.57
    Y13.7024.5020.8021.8026.0025.7027.8032.3027.5039.60
    Er1.172.712.222.902.852.753.083.553.024.47
    Tm0.170.440.350.340.460.430.480.610.500.73
    Yb1.092.942.342.192.932.723.094.123.154.97
    Lu0.160.460.360.330.450.400.460.630.480.76
    ∑REE56.5683.2772.83270.9299.5996.69115.04102.45105.66137.47
    (La/Sm) N6.095.066.394.966.146.869.616.527.407.45
    (La/Yb) N19.687.8110.7029.2511.7013.4019.668.1513.5710.97
    Eu/Eu0.300.230.260.190.250.190.150.160.180.07
    下载: 导出CSV
    续表3
    达日地区样品
    样品号D1604D1608D1610D1611D0114D0114360361362D2313
    岩性花岗岩花岗闪长岩花岗闪长岩二长岩花岗岩花岗岩花岗岩花岗岩石英二长岩石英二长岩
    SiO267.6865.5066.8460.8171.7971.0870.5969.0265.8965.81
    TiO20.510.760.710.940.240.280.280.330.660.66
    Al2O314.8415.8215.5716.7714.2514.5614.7415.5915.6215.34
    Fe2O30.800.991.181.410.640.510.500.560.850.71
    FeO2.093.422.934.071.641.801.831.922.983.17
    MnO0.0570.0860.0780.100.0420.0480.0490.0520.0610.070
    MgO1.121.681.592.640.540.910.921.151.391.58
    CaO2.493.162.233.431.812.302.152.572.762.81
    Na2O2.633.072.903.073.493.613.684.033.043.01
    K2O3.984.264.124.704.533.653.722.945.315.18
    P2O50.120.170.160.220.0830.0970.0950.110.190.19
    LOI5.171.542.862.741.351.742.082.651.791.91
    Total101.49100.46101.17100.90100.41100.59100.63100.92100.54100.44
    K2O+Na2O6.617.337.027.778.027.267.406.978.358.19
    CaO/Na2O0.951.030.771.120.520.640.580.640.910.93
    K2O/Na2O1.511.391.421.531.301.011.010.731.751.72
    A/CNK1.361.261.381.271.161.221.221.281.181.17
    A/NK1.721.641.691.651.341.471.461.591.451.45
    Rb187200210237187155161147301286
    Ba554663526653432572610792687634
    Th22.0019.9021.3024.4024.6013.7014.0012.435.338.7
    U3.873.343.633.052.764.282.663.205.155.57
    Nb21.227.523.732.227.821.423.221.827.930.5
    Ta2.132.432.082.922.962.022.762.272.212.79
    La36.2039.2041.5048.6037.1030.2029.2027.5071.3072.40
    Ce78.8089.6094.20106.0084.4057.7054.8047.50134.00137.00
    Pr8.569.8810.0011.909.567.196.945.8614.7015.20
    Sr131254200301171305301470219208
    Nd30.9034.8036.0042.9035.6026.0025.9020.9052.3051.90
    Zr185232225292190177173198290268
    Hf3.445.925.338.324.353.643.985.016.705.78
    Sm5.686.716.878.437.375.305.373.938.828.85
    Eu1.171.391.201.430.921.001.001.121.381.30
    Gd5.476.516.337.496.824.784.893.657.968.36
    Tb0.891.030.981.191.070.750.800.561.141.19
    Dy4.945.695.376.265.733.934.292.935.816.10
    Ho1.001.171.151.261.110.770.820.571.171.25
    Y27.6030.1029.1032.4029.2021.1022.3017.2032.2031.50
    Er2.963.243.313.623.022.082.281.523.313.50
    Tm0.490.530.540.590.470.320.350.250.530.56
    Yb3.353.433.523.773.042.062.281.693.453.65
    Lu0.510.520.550.560.460.310.340.260.530.57
    ∑REE84.9695.1294.92109.9094.8168.4070.6254.58125.30118.73
    ( La/Sm) N6.375.846.045.775.035.705.447.008.088.18
    ( La/Yb) N7.758.208.469.258.7510.529.1911.6714.8214.23
    Eu/Eu0.210.210.180.180.130.200.190.300.160.15
     注:Eu/Eu= 2×EuN/(SmN+ GdN);A/CNK= (2×Al2O3/101.96)/(CaO/56.08+2×Na2O/61.98+2×K2O/94.2)。
    下载: 导出CSV

    表  4   巴颜喀拉山地区花岗质岩石锆石Hf同位素统计表

    Table  4   Zircon Hf isotopic data of granitoids in Bayankala

    点号176Yb/177Hf176Lu/177Hf176Hf/177Hf±2σεHf(t)±1σtDM1(Ma)tDM2(Ma)
    样号359(N=25)t=215 Ma
    10.0350930.0009920.2826630.0000250.750.8686958321207
    20.0318250.0013070.2826840.0000251.500.8884088011159
    30.0353190.00060.2826710.0000271.020.9504268231190
    40.0447790.0007960.2826740.0000251.060.8733998271187
    50.0219610.000690.2826390.000029−0.081.0136658601260
    60.0267090.0006920.2825540.000028−3.100.9898649831451
    70.0248280.0012080.2826220.000026−0.680.9266118851298
    80.0235070.0014350.2826240.000037−0.611.3004288831293
    90.0393560.0006690.2826210.000031−0.781.096098991304
    100.0519670.0008210.2827270.0000282.920.9804837531069
    110.0232060.0005270.2826520.0000260.380.9121938431230
    120.0291540.0011150.2826020.000032−1.411.1307279171344
    130.0176740.0009730.2826460.0000260.190.9005528481243
    140.0372240.0005610.2827050.0000262.200.9116387781114
    150.0326880.0005730.2826250.000027−0.610.9589718871293
    160.0193920.0003770.2825410.000024−3.520.8350799951478
    170.0190880.000690.2825850.000025−1.980.8864569341380
    180.0133010.0007050.2825580.000027−2.900.9476279671438
    190.0236230.0005920.2825620.000027−2.800.9546759691432
    200.0246320.0006260.2826190.000025−0.800.8584468901305
    210.020760.0006250.282640.000027−0.030.9564518581257
    220.0216550.0006440.2825960.000026−1.600.9194859211356
    230.0211390.0006160.2826280.000025−0.450.878358751283
    240.0246040.0014350.2826830.0000231.470.8192538001161
    250.0222380.0003770.2825390.000025−3.620.87545610001484
     注:εHft)的计算采用球粒陨石现今的176Hf/177Hf =0.282772和176Lu/177Hf=0.0332(据Blichert et al.,1997);Hf同位素二阶段模式年龄(tDM2 )分别采用平均下地壳176Lu/177Hf =0.022(据Altherr et al.,2000)和平均大陆壳176Lu/177Hf =0.015(据Griffin et al.,2002)。
    下载: 导出CSV
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  • 收稿日期:  2021-10-19
  • 修回日期:  2022-01-23
  • 网络出版日期:  2023-05-21
  • 刊出日期:  2023-10-19

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