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早中三叠世金沙江缝合带碰撞造山过程岩浆作用响应

杨礼创, 唐渊, 祝向平, 李勇, 吴昊, 吴波

杨礼创,唐渊,祝向平,等,2025. 早中三叠世金沙江缝合带碰撞造山过程岩浆作用响应[J]. 沉积与特提斯地质,45(1):168−186. DOI: 10.19826/j.cnki.1009-3850.2024.04008
引用本文: 杨礼创,唐渊,祝向平,等,2025. 早中三叠世金沙江缝合带碰撞造山过程岩浆作用响应[J]. 沉积与特提斯地质,45(1):168−186. DOI: 10.19826/j.cnki.1009-3850.2024.04008
YANG L C,TANG Y,ZHU X P,et al.,2025. Magmatism during collisional orogenic processes in Early–Middle Triassic Jinsha River suture zone[J]. Sedimentary Geology and Tethyan Geology,45(1):168−186. DOI: 10.19826/j.cnki.1009-3850.2024.04008
Citation: YANG L C,TANG Y,ZHU X P,et al.,2025. Magmatism during collisional orogenic processes in Early–Middle Triassic Jinsha River suture zone[J]. Sedimentary Geology and Tethyan Geology,45(1):168−186. DOI: 10.19826/j.cnki.1009-3850.2024.04008

早中三叠世金沙江缝合带碰撞造山过程岩浆作用响应

基金项目: 中国地质调查局项目(DD20240026,DD20221635)
详细信息
    作者简介:

    杨礼创(1997—),男,矿物学、岩石学、矿床学专业硕士研究生。E-mail:903646335@qq.com

    通讯作者:

    唐渊(1985—),女,正高级工程师,主要从事构造地质学研究。E-mail:tyvienna@163.com

  • 中图分类号: P588.1

Magmatism during collisional orogenic processes in Early–Middle Triassic Jinsha River suture zone

  • 摘要:

    金沙江缝合带内地质构造单元组成多样,岩浆作用复杂,关于其初始碰撞时间和碰撞后伸展时限还存在较大的争议。本文利用锆石U-Pb年代学和岩石地球化学分析方法,选取金沙江缝合带中北段贡觉地区二长岩和花岗斑岩进行研究,分析岩体的形成时代、岩石成因、物质来源以及构造背景。研究表明,贡觉二长岩属于钾玄岩系列的I型花岗岩,成岩年龄为(250±1)Ma;岩体富集轻稀土元素,Mg#值为28~30,Rb/Sr比值为0.07~0.11,Nb/La比值为0.43~0.49,为下地壳基性变火成岩物质发生部分熔融形成的产物;成岩环境为俯冲末期至碰撞早期地壳隆升增厚的环境。贡觉花岗斑岩属于中钾钙碱性系列的S型花岗岩,成岩年龄为(244±2)Ma;岩体Mg#值介于26~29,FeOT/MgO比值为4.43~4.98,Al2O3/TiO2比值为47.57~51.12,CaO/Na2O比值为0.28~0.49,为地壳变杂砂岩部分熔融形成的产物;成岩环境为碰撞后的伸展环境。综合分析金沙江缝合带内二叠纪—中三叠世的花岗岩类的年代学、Hf同位素及地球化学数据,并结合前人研究成果,认为金沙江缝合带俯冲—碰撞—伸展的构造–岩浆作用过程中,地壳物质越来越多地参与到了岩浆源区。

    Abstract:

    The Jinsha River suture zone is characterized by diverse geological structures and complex magmatic processes. There are considerable controversies about the timing of its initial collision and subsequent extension time limit. This paper uses zircon U-Pb dating and rock geochemical analysis methods to study the monzonite and granite porphyry in the Gonjo area in the mid-north section of the Jinsha River suture zone, analyzing the formation age, rock origin, material source, and tectonic setting of the rock mass. Research shows that Gonjo monzonite belongs to the shoshonite series and is classified as I-type granite, with a diagenetic age of (250±1) Ma. The rock mass is enriched in light rare earth elements, with Mg# values ranging from 28 to 30, Rb/Sr ratios from 0.07 to 0.11, and Nb/La ratios from 0.43 to 0.49, indicating that it is the product of partial melting of basic metavolcanic materials in the lower crust. The diagenetic environment is a tectonic environment in which the crust uplifts and thickens during the end of subduction to the early collision period. Gonjo granite porphyry belongs to the medium-potassium calc-alkaline series of S-type granite, with a crystallization age of (244±2) Ma. The Mg# values of the rock range from 26 to 29, with FeOT/MgO ratios between 4.43 and 4.98, Al2O3/TiO2 ratios of 47.57~51.12, and CaO/Na2O ratios between 0.28 and 0.49, indicating that it is the product of partial melting of the crustal metasandstone. The diagenetic environment is an extensional tectonic environment after collision. Based on the geochronological data, Hf isotope, and geochemical data of the Permian–Middle Triassic granitic rocks within the Jinsha River suture zone, and in combination with previous research results, it is believed that during the process of subduction, collision, and extension of the Jinsha River orogenic belt, more and more crustal materials participated in the magma source region.

  • 西南三江造山带位于喜马拉雅东构造结东侧,北与华北克拉通相连,西与青藏高原相接,经历了晚古生代—早中生代的古特提斯演化,并受新生代以来印度板块与欧亚板块碰撞聚合事件的影响,是特提斯构造域的重要组成部分(闫国川等, 2021; 许王等, 2021; 王立全等, 2021)。金沙江缝合带是三江地区古特提斯洋的分支洋盆,缝合带内保存着断续出露的代表着古洋壳的蛇绿混杂岩、碰撞挤压形成的变形变质构造、洋壳俯冲–碰撞过程中形成的大量二叠纪—三叠纪岩浆岩以及大地构造演化过程伴生形成的多种矿产资源(葛孟春等, 2002; Wang et al., 2017; 李旭拓, 2018; 杨天南等, 2019; Tang et al., 2023),因此,受到了地质学家的广泛关注。众多学者对金沙江缝合带的地层、岩浆岩、蛇绿混杂岩和构造演化进行了大量的研究, 认为其大致经历了裂(陷)谷盆地(D)、洋盆扩张(C1—P1)、洋壳俯冲消减(P1—P3)、弧陆碰撞造山(T1—T2),以及上叠火山裂谷盆地阶段(T2—T3)(王立全等, 1999; Jian et al., 2009; 王保弟等, 2021; 唐渊等, 2022a, 2022b)。两个不同大陆块体的初始碰撞,代表了地球上新生大陆地壳的形成(杨文采和于常青, 2014),碰撞后伸展环境则为火山成因块状硫化物矿床的形成提供了重要条件。因此,精确厘定金沙江古特提斯弧陆碰撞闭合以及碰撞后伸展的时限具有重要意义。然而,金沙江缝合带内地质构造单元组成多样,且岩浆作用复杂,关于金沙江古特提斯弧陆碰撞闭合以及碰撞后伸展的准确时限目前还存在较多的争议,如莫宣学和潘桂棠(2006)根据弧岩浆岩和碰撞型岩浆岩的时空分布认为,金沙江–哀牢山洋板块于早二叠世开始向西俯冲,弧陆碰撞发生于早三叠世至晚三叠世(T1—T3)。张万平等(2011)利用LA-ICP-MS锆石U-Pb测年技术,获得德钦岩体的寄主岩石——花岗闪长岩及其镁铁质微粒包体(MME)闪长岩年龄分别为(254±1)Ma和(253±1)Ma,认为金沙江缝合带在约255 Ma(晚二叠世)已经进入了弧陆碰撞—后碰撞的地质时期。李旭拓(2018)对金沙江缝合带中段的混杂岩、侵入岩和角度不整合事件进行研究,通过构造解析、锆石微量元素分析以及综合前人研究成果,认为金沙江缝合带在269~259 Ma处于碰撞造山阶段,而258~220 Ma处于后碰撞伸展阶段。

    本文对金沙江缝合带贡觉地区出露的早中三叠世花岗质岩浆岩开展了LA-ICP-MS锆石U-Pb定年和全岩主、微量元素地球化学特征分析,研究其岩浆性质、岩石成因及其形成的大地构造背景,并结合金沙江缝合带内岩浆作用研究取得了一系列的成果,探讨金沙江古特提斯构造–岩浆演化过程。

    金沙江缝合带位于其西侧的昌都–思茅地块和东侧的中咱地块之间(图1a),北起青海玉树,向南可延伸至哀牢山缝合带,代表了一个泥盆纪—三叠纪重要的古特提斯洋盆。江达–维西陆缘弧位于金沙江缝合带西侧,长约500 km,沟—弧—盆的空间配置和火成岩成分的穿弧极性说明其是由金沙江洋盆向西俯冲至昌都–思茅地块之下形成的(刘增乾等, 1993)。弧内岩浆活动频繁,与俯冲–碰撞相关的喷出岩,主要分布在二叠系—三叠系吉东龙组(P1jd)、禺功组(P2y)、沙木组(P3sm)、普水桥组(T1p)、马拉松多组(T1-2m)、攀天阁组(T2-3p)、歪古村组(T3w)中,岩性从基性岩到酸性岩均有发育,岩石类型包括玄武岩、玄武安山岩、安山岩、英安岩、流纹岩、火山角砾凝灰岩等(王立全等, 2013)。弧内侵入岩浆活动明显弱于火山岩浆活动,以中酸性岩为主,二叠纪侵入岩体分布广泛,但岩体规模都较小,以江达县附近冬普和测侠弄等地区出露的石英闪长岩、二长花岗岩为代表,被中三叠世普水桥组砾岩不整合覆盖。三叠纪侵入岩体主要在巴塘—德钦—鲁甸一带分布,呈岩基或小岩株产出,以鲁甸和德钦花岗岩岩体规模较大,鲁甸岩体出露面积约为600 km2,德钦岩体面积约为134.5 km2

    图  1  西南三江造山带大地构造位置图(a, 据李兴振等, 1999)及藏东贡觉地区地质简图(b, 据1∶5万江达幅、贡觉幅区域地质图修改)
    Figure  1.  Simplified tectonic map of the Sanjiang tectonic belt (a, after Li et al., 1999) and geological map of the Gonjo, eastern Tibet (b, modified from 1∶50 000 Jiangda, Gonjo regional geological map)

    本文样品采自金沙江缝合带中北段贡觉县附近,该地区三叠纪岩浆岩大面积侵入到宁多变质岩群、马拉松多组、洞卡组以及混杂岩基质中,岩石类型以二长花岗岩、二长岩、花岗闪长岩、石英闪长岩为主,区域内还发育了一系列韧性剪切带及断层(图1b, 图2)。贡觉二长岩(D3016-1)呈灰色,具伟晶结构,块状构造,主要矿物为钾长石(50%~55%),斜长石(30%~35%),角闪石(约10%),单斜辉石(约5%)等。钾长石粒径为10~20 mm,呈半自形板状,发育卡式双晶及环带结构;斜长石粒径为0.5~1 mm,呈半自形板状,常呈包体状分布钾长石内;角闪石呈半自形—他形柱状,单斜辉石呈半自形柱状(图3a, 3c, 3d)。

    图  2  金沙江缝合带贡觉地区地质剖面图
    Figure  2.  Geological profile of the Gonjo areas in the Jinsha River suture zone
    图  3  贡觉二长岩、花岗斑岩野外和镜下照片
    a. 贡觉二长岩; b. 贡觉花岗斑岩; c、d. 贡觉二长岩镜下照片,正交偏光; e、f. 贡觉花岗斑岩镜下照片,正交偏光。K—钾长石; Pl—斜长石;Hb—角闪石;Cpx—单斜辉石;Q—石英
    Figure  3.  Field photographs and photomicrographs of the Gonjo monzonite and granite porphyry

    贡觉花岗斑岩(D5008-1)呈肉红色、灰白色,似斑状结构,块状构造,斑晶主要为斜长石(20%~25%)、石英(15%~20%)和钾长石(约5%)。石英斑晶呈半自形粒状,粒径1~3 mm,裂隙较少,表面平整光滑;斜长石斑晶自形程度较高,粒径0.5~3 mm,可见聚片双晶,发育明显的环带结构;基质含量大于50%,主要为斜长石、石英、钾长石等矿物微晶(图3b, 3e, 3f)。样品中副矿物包括磷灰石、锆石、磁铁矿等。

    本次研究在贡觉地区共采集了8件新鲜的早中三叠世岩浆岩样品进行全岩主量和微量元素分析,分析单位为中国地质调查局成都地质调查中心(西南地质科技创新中心),每件样品同时配套手标本进行薄片鉴定。将样品进行淘洗并切除表面,选取中心新鲜无污染的部分进行粗碎,然后细碎至200目以上。对需要进行全岩主量和微量元素分析的样品进行预处理,岩石主量元素分析采用XRF玻璃熔饼法完成,仪器型号为Rigaku RIX 2100型,元素分析误差小于4%。稀土元素和微量元素采用电感耦合等离子质谱仪(ICP-MS)进行测试,分析误差小于5%,详细分析过程见参考文献(Huang et al., 2017)。

    共采集了2件样品进行锆石U-Pb定年,锆石分选在河北区域地质矿产调查研究所实验室完成,原岩样品按常规方法进行粉碎、淘洗去除轻矿物部分,将得到的重砂矿物经过电磁选后,获得锆石精矿,最后在双目显微镜下选取晶型较好,无裂隙、无包裹体的锆石颗粒用于定年分析。CL 照相和U-Pb 年龄测定均委托武汉上谱分析科技有限责任公司完成,首先将锆石样品进行打磨、抛光,制成样品靶,然后进行阴极发光(CL)图像拍照,锆石阴极发光图像拍摄使用仪器为配备有GATAN MINICL系统的高真空扫描电子显微镜(JSM-IT100),电场电压10~13 kV,钨灯丝电流80~85µA,最后选定在反射光、透反射光和阴极发光(CL)图像中晶型表现较完整,颗粒形状较规则的锆石颗粒作为测定对象。

    贡觉二长岩(D3016-1)的锆石颗粒形态受到了一定程度的破坏,呈他形不规则状,直径为50~150 μm,长宽比为1∶1~1∶2,在CL图像中大多数无明显振荡环带和核边结构,且透明度较差,指示后期可能受到了热液作用的影响。锆石的Th和U含量变化均较大,U含量为365×10-61906×10-6,Th含量为173×10-62976×10-6,Th/U值介于0.47~1.84(表1,均大于0.4),为典型的岩浆锆石特征(Claesson et al., 2000)。样品22个分析点均位于谐和线上,206Pb/238U年龄介于257~247 Ma,加权平均年龄为(250±1)Ma(MSWD=0.4, n=22),代表了贡觉二长岩的结晶年龄(图4a-b)。

    表  1  贡觉二长岩、花岗斑岩LA-ICP-MS锆石U-Pb数据
    Table  1.  LA-ICP-MS zircon U-Pb data of monzonite and granite porphyry samples in the Gonjo area
    测点号含量/×10-6Th/U同位素比值年龄/Ma
    ThU207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238U
    D3016 -1 二长岩
    16035501.100.05290.00230.28800.01210.03950.000432494257102503
    23925060.770.05040.00230.27640.01210.03970.0006217106248102513
    36886841.010.05010.00170.27520.00920.03970.00041988024772512
    45805870.990.04810.00190.26200.01070.03940.00051069623692493
    5178211951.490.04960.00180.27520.01010.04000.00041767924782532
    6174613181.320.05010.00190.27220.01020.03920.00051988724482483
    7143913701.050.05100.00180.28040.00970.03980.00052397525182523
    8141811121.280.05140.00180.28230.00950.03980.00052578425282523
    910458501.230.04800.00170.26360.00930.03970.00051028523872513
    10180812931.400.04830.00150.26600.00830.03960.00041227424072503
    111733650.470.04940.00220.27450.01320.03960.0006165138246102514
    12158614521.090.04830.00170.26580.00870.03980.00051228123972513
    136846801.010.05030.00190.27840.01070.03980.00052098924992523
    14297616141.840.04890.00140.26880.00790.03950.00041466724262503
    15196519061.030.05000.00140.27130.00710.03920.00031956324462482
    16111510211.090.04960.00180.26890.00950.03920.00041768524282483
    179969801.020.05080.00170.27550.00940.03920.00042327824772482
    18117810011.180.04950.00170.27070.00960.03940.00041728124382493
    19111712150.920.05130.00150.27970.00860.03940.00052546625072493
    20112711610.970.04870.00150.26410.00880.03910.00042007623872473
    216856701.020.05160.00190.28590.01110.03990.00052658725592523
    227009680.720.04980.00200.27710.01160.04000.00051839424892533
    D5008 -1 花岗斑岩
    11513610.420.05740.00320.29610.01560.03790.0007506129263122404
    22236760.330.05380.00260.27750.01300.03760.0006365114249102384
    34738070.590.05100.00230.27300.01200.03900.000624371245102474
    41453950.370.05420.00270.28660.01410.03850.000738977256112444
    53527610.460.05530.00240.29240.01360.03830.000743398260112424
    63308530.390.05150.00200.28140.01200.03960.00072658925292504
    72916170.470.05020.00270.25070.01300.03640.0006211122227112304
    863511400.560.05280.00210.28520.01160.03930.00063209125592484
    93127000.450.05330.00220.27650.01110.03800.00063399424892414
    104367590.570.05140.00250.26980.01270.03850.0006257111243102434
    111915740.330.05390.00260.29310.01480.03930.0007365109261122494
    122715510.490.05260.00260.27210.01360.03790.0006309115244112404
    132806410.440.05260.00250.28340.01320.03950.0008309109253102505
    142063890.530.04800.00340.24860.01650.03890.000898159225132465
    153105960.520.05450.00270.28560.01390.03840.0007391113255112434
    161814490.400.05230.00270.28740.01460.04030.0006298119256112544
    171864630.400.05150.00270.27810.01510.03900.000726594249122474
    186169700.640.05530.00230.30000.01260.03940.000643397266102494
    192266190.370.05010.00230.26700.01210.03900.000719899240102474
    202866870.420.05000.00260.26890.01430.03930.0007195122242112495
    21112513820.810.05250.00180.28580.01020.03920.00063097625582483
    222166150.350.04770.00240.25700.01300.03930.000783115232112484
    232656420.410.04780.00230.25120.01210.03810.000687111228102413
    242166320.340.05560.00270.29570.01410.03910.0007435109263112474
    251644090.400.05270.00280.27810.01560.03770.0007317120249122394
    262586430.400.05070.00240.27810.01320.03980.0007228111249102524
    下载: 导出CSV 
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    图  4  贡觉二长岩、花岗斑岩锆石CL图像(a、c)及U-Pb年龄谐和图(b、d)
    Figure  4.  CL images (a, c) and U-Pb concordia diagrams (b, d) of the Gonjo monzonite and granite porphyry

    贡觉花岗斑岩(D5008-1)的锆石大部分呈自形的长—短柱状,长度在50~200 μm,长宽比为1∶1~1∶3,具有清晰的内部结构以及岩浆振荡环带,锆石中U含量为360×10-61382×10-6,Th含量为145×10-61125×10-6,Th/U值介于0.33~0.81,绝大部分大于0.4,表明其为岩浆成因(表1)。样品26个分析点均位于谐和线上及附近,206Pb/238U年龄介于254~230 Ma,加权平均年龄为(244±2)Ma(MSWD=3.8, n=26),代表了贡觉花岗斑岩的结晶年龄(图4c- d)。

    贡觉二长岩和花岗斑岩地球化学测试数据见表2由分析结果可知,二长岩样品的SiO2含量为56.70%~57.66%,TiO2含量为0.71%~0.85%,MgO含量为1.04%~1.23%,全碱(K2O+Na2O)含量为6.26%~10.83%,K2O/Na2O为2.28~2.43,Mg#值为28~30。样品烧失量较低,在TAS图解中,样品数据点基本落入了二长岩区域(图5a);在K2O–SiO2关系图中显示为钾玄岩系列(图5b),SiO2–AR图解中显示为碱性系列(图5c);样品铝饱和指数介于0.80~0.83,在A/NK–A/CNK关系图中(图5d),数据点落在准铝质区域;二长岩稀土元素总含量为155.90×10-6~194.58×10-6,平均值为176.93×10-6,总体变化范围不大。LREE/HREE值为3.64~4.66,平均值为4.39,(La/Yb)N值为12.04~16.06,平均值为14.82,属于轻稀土元素富集型。稀土配分曲线图上,样品曲线较为一致,表现为右倾型(图6a)。δEu值为0.96~1.23,平均值为1.09,不存在明显的Eu异常。在原始地幔微量元素蛛网图中,富集Ba、U、K和Sr等大离子亲石元素,明显亏损Nb、Ta、Ti和Y等高场强元素(图6b)。

    表  2  贡觉二长岩、花岗斑岩全岩主量、微量和稀土元素成分
    Table  2.  Major, trace, and rare earth element concentrations of the Gonjo monzonite and granite porphyry
    样品号 D3016-H1 D3016-H2 D3016-H3 D3016-H4 D5008-H1 D5008-H2 D5008-H3 D5008-H4
    岩性 二长岩 花岗斑岩
    SiO2 57.66 57.03 57.47 56.70 73.78 75.17 74.52 74.59
    TiO2 0.80 0.78 0.71 0.85 0.28 0.26 0.28 0.27
    Al2O3 18.12 18.40 18.42 17.87 13.43 13.29 13.32 13.60
    TFe2O3 5.66 5.68 5.08 6.12 2.71 2.42 2.74 2.61
    MnO 0.12 0.12 0.11 0.13 0.043 0.031 0.044 0.024
    MgO 1.20 1.12 1.04 1.23 0.49 0.47 0.50 0.53
    CaO 4.62 5.03 4.90 5.15 1.74 1.09 1.69 0.88
    Na2O 3.13 3.14 3.18 3.07 3.53 3.35 3.57 3.12
    K2O 7.61 7.15 7.37 7.26 2.65 2.93 2.64 2.94
    P2O5 0.24 0.24 0.21 0.26 0.053 0.054 0.056 0.051
    烧失量 0.90 1.08 1.12 1.11 0.84 1.11 0.84 1.52
    总量 100.06 99.77 99.61 99.75 99.546 100.17 100.20 100.135
    Rb 72.4 108 112 115 49.6 44.3 52.4 49.7
    Ba 2300 2740 2370 2570 731 637 718 610
    Th 6.02 11.8 11.1 12.7 6.87 7.45 7.18 7.99
    U 1.01 2.04 1.78 2.13 1.22 1.3 1.26 1.37
    Nb 19 18.6 16.6 21 5.32 5.11 5.44 5.13
    Ta 0.84 0.97 1.2 0.95 0.41 0.49 0.42 0.44
    La 39.1 43.6 38.8 47.6 19.6 17.5 20 18.8
    Ce 56.2 58.9 52 64.9 34.2 35.8 35.6 35.1
    Pb 17.4 19.7 19.9 21.7 8.48 8.77 28.2 7.79
    Pr 9.30 9.32 7.99 10.2 4.02 3.55 4.14 3.78
    Sr 1040 1140 1090 1080 177 122 176 112
    Nd 29.00 27.2 23.60 29.90 11.40 9.84 11.8 10.4
    Sm 5.47 4.84 4.05 5.13 2.04 1.73 2.12 1.80
    Zr 152 162 150 181 116 122 120 130
    Hf 19.9 4.11 3.49 5.31 3.84 3.06 4.24 4.33
    Ga 12.3 13.5 12.9 13.4 9.16 8.71 9.55 9.15
    Eu 2.04 2.1 1.94 2.08 0.6 0.46 0.62 0.45
    Gd 7.7 6.66 5.73 7.24 3.09 2.66 3.18 2.76
    Tb 0.98 0.81 0.68 0.87 0.42 0.34 0.44 0.37
    Dy 5.35 4.25 3.63 4.64 2.56 2.00 2.64 2.21
    Ho 0.96 0.76 0.66 0.83 0.51 0.40 0.53 0.45
    Y 18.2 14.4 12.8 16.1 9.94 7.69 10.3 8.56
    Er 2.66 2.15 1.85 2.36 1.55 1.28 1.6 1.42
    Tm 0.36 0.29 0.26 0.33 0.23 0.2 0.24 0.22
    Yb 2.19 1.83 1.66 2.08 1.6 1.46 1.66 1.57
    Lu 0.34 0.28 0.25 0.32 0.25 0.24 0.26 0.26
     注:主量元素含量单位为%,微量和稀土元素含量单位为10-6
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    图  5  金沙江缝合带贡觉岩浆岩(Na2O+K2O) – SiO2岩石分类图解(a, 据Middlemost, 1994),K2O–SiO2图(b, 据Streckeisen, 1976),SiO2–AR图(c, 据Wright, 1969),A/NK–A/CNK图解(d, 据Maniar and Piccoli,1989
    数据来源:晚二叠世—早三叠世花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020; 吴喆, 2022; 中三叠世花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等; 2019; 闫国川等, 2021; 吴喆, 2022
    Figure  5.  Diagrams of total alkali (Na2O+K2O) vs. SiO2 (a, after Middlemost, 1994), K2O vs. SiO2 (b, after Streckeisen, 1976), SiO2 vs. AR (c, after Wright, 1969), A/NK vs. A/CNK (d, after Maniar and Piccoli, 1989) for the Gonjo magmatites in the Jinsha River suture zone
    图  6  金沙江缝合带贡觉岩浆岩球粒陨石标准化稀土元素配分图(a)和原始地幔标准化微量元素蛛网图(b)(标准化值据Sun and McDonough, 1989
    数据来源:晚二叠世—早三叠世花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020; 吴喆, 2022; 中三叠世花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等; 2019; 闫国川等, 2021; 吴喆, 2022
    Figure  6.  Chrondrite–normalized REE patterns (a) and primitive mantle–normalized trace element spider diagram (b) for the Gonjo magmatites in the Jinsha River suture zone (normalization values after Sun and McDonough, 1989 )

    花岗斑岩样品的SiO2含量为74.52%~75.17%,TiO2含量为0.26%~0.28%,MgO含量为0.47%~0.53%,全碱(K2O+Na2O)含量为6.15%~6.34%,K2O/Na2O为0.74~0.94,Mg#值为26~29。样品烧失量较低,表明样品在后期并没有遭受明显蚀变作用。在TAS图解中,数据点全都落入了花岗岩区域(图5a),在SiO2–K2O关系图中显示为中钾钙碱性系列(图5b),SiO2–AR图解中显示为钙碱性–碱性系列(图5c);样品铝饱和指数介于1.13~1.37,A/NK–A/CNK关系图中(图5d),样品数据点落在过铝质区域。花岗斑岩稀土元素总含量为88.15×10-6~95.13×10-6,平均值为90.11×10-6,总体变化范围不大。LREE/HREE值为3.56~4.23,平均值为3.83,(La/Yb)N值为8.07~8.26,平均值为8.13,属于轻稀土元素富集型。稀土配分曲线图上,样品曲线较为一致,表现为右倾型(图6a)。δEu值为0.62~0.73,平均值为0.68,存在中等的负Eu异常。在原始地幔微量元素蛛网图中,富集Ba、Th、U和K等大离子亲石元素,明显亏损Nb、Ta、Ti和Y等高场强元素(图6b)。

    目前常见的花岗岩成因分类方案是根据原岩类型和构造环境把花岗岩划分为I型、S型和A型(吴福元等, 2007)。贡觉二长岩和花岗斑岩FeOT/MgO比值较低(4.24~4.98),不同于A型花岗岩显著富铁的特征(FeOT/MgO>10),且在薄片中也没有观察到霓石–霓辉石、铁橄榄石等A型花岗岩标志性碱性铁镁矿物的存在。同时,在(Na2O+K2O)/CaO–(Zr+Nb+Ce+Y)和Zr–10000 Ga/Al判别图解中(图7a-b),贡觉二长岩和花岗斑岩的数据点也并非落在A型花岗岩类的范围中,而是落在了I型或S型花岗岩区域。由此,可以判断贡觉二长岩和花岗斑岩并不属于A型花岗岩,而是I型或S型花岗岩。

    图  7  金沙江缝合带贡觉岩浆岩成因判别图解(a、b据Whalen et al., 1987; c据Chappell and White, 1992 ; d据Nakada and Takahashi, 1979
    Figure  7.  Genesis discrimination diagrams (a and b, after Whalen et al., 1987; c, after Chappell and White, 1992; d, after Nakada and Takahashi, 1979) for the Gonjo magmatites in the Jinsha River suture zone

    贡觉二长岩具有准铝质特性,A/CNK值均小于1,CIPW标准矿物计算显示刚玉成分含量在1%以下,镜下薄片鉴定中未见富铝矿物(如白云母、堇青石等),明显不同于S型花岗岩的强过铝质特性。Chappell(1999) 认为部分 S 型花岗岩 A/ CNK值也可能小于1.1,因此我们判别花岗岩成因类型还需结合其他特征。近年来,实验岩石学发现,磷灰石在I型和S型花岗岩中具有不同的地球化学行为,在I型花岗岩中,磷灰石具有较低的溶解度,结晶分异过程中,P2O5含量总是随着SiO2含量的升高而降低;而在S型花岗岩中,P2O5含量总是随着SiO2含量的升高而升高,或保持不变(Li et al., 2007; 朱弟成等, 2009; Chappell et al., 2012)。贡觉二长岩样品中的P2O5 含量随着SiO2含量的增加而明显减少(图7c),与I型花岗岩的演化趋势一致;在ACF图解中,样品点也均落在了I型花岗岩区域(图7d)。上述特征表明贡觉二长岩应为I型花岗岩。

    贡觉花岗斑岩具有高硅[w(SiO2)为73.78%~75.17%]、高铝[w(Al2O3)为13.29%~13.60%]、低镁[w(MgO)为0.47%~0.53%]的特点,A/CNK值均大于1.1,所有CIPW标准矿物计算样品刚玉分子介于1.62%~2.74%之间,具有S型花岗岩的一般特征。研究表明,Sr/Ba比值对区分S型和I型花岗岩具有指示意义,S型花岗岩一般贫Sr,Sr/Ba比值小于0.5,I型花岗岩则相反(刘振声和王洁明, 1994)。贡觉花岗斑岩Sr/Ba比值为0.18~0.24,平均值为0.21,与S型花岗岩一致。在P2O5–SiO2图解(图7c)中,由于花岗斑岩样品点太过密集,并没有表现出明显的趋势,但在ACF图解中(图7d),样品点均落在了S型花岗岩区域。综上所述,本文认为贡觉花岗斑岩应为S型花岗岩。

    前人研究认为,I型花岗岩的成因主要有三种:(1)幔源的基性岩浆发生分离结晶(Soesoo, 2000; Wyborn et al., 2001);(2)来自幔源的基性岩浆与壳源长英质岩浆发生混合(赵姣龙等, 2012; 陈沐龙等, 2024);(3)幔源分异的基性岩浆底侵,使下地壳物质部分熔融(Richards, 2011; 马鹏飞等, 2021)。自然界中由幔源岩浆直接分离结晶形成的酸性岩浆较为稀少,即使存在这种情况,也需要巨量的基性岩浆与之互补。然而,根据野外观察以及前人资料,贡觉及邻近地区并未发现大规模基性岩浆岩,并且贡觉二长岩Mg#值为28~30,明显低于幔源岩浆(Mg#>45, Rapp et al., 1995),说明它们不可能是幔源基性岩浆分离结晶形成的。岩浆混合作用通常具有较明显特征,表现为不平衡的矿物共生组合、矿物的反环带结构以及某些矿物成分呈双峰式分布(Feeley et al., 2008; 郝彬等, 2016; 郝晓伟等, 2021)。但是,根据岩石地球化学分析以及显微镜下薄片观察结果,贡觉二长岩并没有上述这些特征,表明贡觉二长岩也并不是岩浆混合的产物。贡觉二长岩LREE/HREE值为3.56~4.23,(La/Yb)N值为8.07~8.26,呈现轻稀土元素富集的特征,MgO含量较低,Rb/Sr比值介于0.07~0.11,Nb/La比值介于0.43~0.49,类似于加厚镁铁质下地壳部分熔融形成的岩石(Rb/Sr=0.01~0.40, Nb/La≈0.60, Mg#<40, Sun and McDonough, 1989; Rapp and Watson, 1995; Rapp et al., 2002)。在岩石成因判别图解中(图8a- b),样品数据点主要也落入了玄武质岩派生熔体和角闪岩熔体区域。综上所述,贡觉二长岩应为幔源分异的玄武质岩浆底侵,使下地壳基性变火成岩物质发生部分熔融形成的产物。

    图  8  金沙江缝合带贡觉岩浆岩源区判别图解(a,据Sylvester, 1998; b,据Douce, 1999
    数据来源:晚二叠世—早三叠世I型花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020;中三叠世S型花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等, 2019; 闫国川等, 2021; 吴喆, 2022
    Figure  8.  Source discrimination diagrams (a, after Sylvester, 1998; b, after Douce, 1999) for the Gonjo magmatites in the Jinsha River suture zone

    S型花岗岩一般认为是经过风化的沉积岩或变沉积岩部分熔融形成的(Chappell and White, 1992; Sylvester, 1998)。贡觉花岗斑岩MgO含量较低,Mg#值介于26~29,Nb/Ta比值为10.43~12.98,平均值为12.00,与地壳平均值一致(Nb/Ta=12~13, Barth et al., 2000)。岩石FeOT/MgO比值为4.43~4.98,Al2O3/TiO2比值为47.57~51.12,CaO/Na2O比值为0.28~0.49,这些地球化学特征与地壳沉积岩部分熔融形成的强过铝质花岗岩类似(Chappell et al., 1999; 路凤香和桑隆康, 2002)。并且,据前人研究可知,昌都地块的结晶基底为一套变沉积岩,包含变泥岩、变杂砂岩等(杜德勋等,1997),这类岩石部分熔融很可能形成贡觉地区强过铝质花岗岩(吴喆等,2021)。CaO/Na2O比值可以有效区分S型花岗岩岩浆源区的物质成分为变泥岩或变杂砂岩,变泥岩部分熔融产生的S型花岗岩CaO/Na2O一般小于0.3,变杂砂岩部分熔融产生的S型花岗岩CaO/Na2O比值一般为0.3~0.5,贡觉花岗斑岩CaO/Na2O比值为0.28~0.49,表明其岩浆源区物质成分应为变杂砂岩(Chappell and White, 1992)。通过Rb/Ba–Rb/Sr图解(图8a)以及Al2O3/(FeOT+MgO+TiO2)–(Al2O3+FeOT+MgO+TiO2)图解(图8b)可以看出,样品数据点也均落在黏土含量较少的杂砂岩熔体的范围内。所以,本文认为该套贡觉花岗斑岩的源岩应为地壳变杂砂岩。

    前人已经对俯冲过程中岛弧岩浆岩的岩石性质变化规律做了很好的总结,岛弧岩浆组合在俯冲早期以发育低钾拉斑玄武岩系列为主,随着俯冲的进行,岛弧岩浆岩钾质不断增加,到了俯冲末期,以发育钾玄岩系列为主(莫宣学等, 2009)。贡觉二长岩富集大离子亲石元素(例如Ba、U和Sr),亏损高场强元素(例如Nb、Ta和Ti),具有岛弧岩浆岩的特征,且其K2O含量介于7.24%~7.67%,在Si2O–K2O图解中投入了钾玄岩区域,暗示其可能形成于俯冲末期阶段。张旗等(2006, 2010, 2023)对花岗岩的地球化学性质与源区深度之间的关系进行了深入的研究,认为Sr、Yb两种元素可以很好地指示花岗岩源区残留相的特征。高Sr[w(Sr)>300×10-6]低Yb[w(Yb)<2.5×10-6],代表源区存在石榴石,无斜长石,属于一种高压环境,地壳厚度大于50 km;低Sr[w(Sr)<400×10-6]低Yb[w(Yb)<2×10-6],代表源区存在石榴石和斜长石,由于斜长石在压力大于1.0 GPa情况下并不稳定,所以这种元素特征指示了一种中高压环境,地壳厚度介于40~50 km之间;低Sr[w(Sr)<400×10-6]高Yb[w(Yb)>1.5×10-6],代表源区残留相有斜长石,无石榴石,属于一种中压环境,地壳厚度介于30~40 km;极低Sr[w(Sr)<100×10-6]与极高Yb[w(Yb)>2×10-6],代表其形成与辉长岩部分熔融有关,地壳厚度小于30 km。贡觉二长岩Sr含量源区深度大于50 km。一般情况下,克拉通地区地壳厚度在30 km左右,而贡觉二长岩形成岩浆源区大于50 km,说明其应该是在碰撞造山情况下地壳急剧变厚的环境中形成的。在Rb/(Y+Nb)和Ta/Yb图解中(图9),贡觉二长岩样品数据点也同样分别落入了同碰撞花岗岩区域和火山弧花岗岩区域中。综上所述,本文认为贡觉二长岩形成于俯冲到碰撞的转换阶段,指示了金沙江缝合带贡觉地区的弧陆初始碰撞时间在250 Ma。

    图  9  金沙江缝合带贡觉岩浆岩构造环境判别图解(a、b据Pearce et al., 1984
    Syn-CLOG—同碰撞花岗岩;VAG—火山弧花岗岩;WPG—板内花岗岩;ORG—洋中脊花岗岩。数据来源:晚二叠世—早三叠世花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020; 吴喆, 2022; 中三叠世花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等, 2019; 闫国川等, 2021; 吴喆, 2022
    Figure  9.  Tectonic discrimination diagrams (a and b, after Pearce et al., 1984) for the Gonjo magmatites in the Jinsha River suture zone

    贡觉花岗斑岩在Rb/(Y+Nb)和Ta/Yb图解(图9)中,数据投点均落入了火山弧花岗岩区域,说明其具有弧性质。然而,据前人研究,在同碰撞阶段和后碰撞伸展阶段中,火山弧同样可以产出具有弧性质的岩浆岩(吴才来等, 2004; 李宁波等, 2012 )。因此,判别贡觉花岗斑岩的形成构造背景,还需要结合其他证据。贡觉花岗斑岩Sr含量介于112×10-6~177×10-6,Yb含量介于1.46×10-6~1.66×10-6,具有低Sr[w(Sr)<400×10-6]高Yb[w(Yb)>1.5×10-6]的特征,指示源区存在斜长石,无石榴石,为一种中压环境(张旗等,2006, 2010, 2023),地壳厚度介于30~40 km(图10),与贡觉二长岩源区的地壳厚度(>50 km)相比,已经明显减薄。同时,研究表明,高压变质岩的折返与俯冲板块的断离有着密切的关系,随着俯冲–碰撞作用的进行,被拖拽部分在深部发生高压变质作用形成榴辉岩,并随着深俯冲板片的断离而折返发生退变质,软流圈从板片断离窗口中上涌,使岩石圈发生伸展减薄,部分地幔衍生熔体与地壳部分熔融形成的酸性岩浆岩共同组成了双峰式火山岩(Davies and von Blanckenberg, 1995)。Tang et al.(2020)在贡觉地区获得的榴辉岩的变质年龄在245~240 Ma,可能代表了榴辉岩从深部折返发生退变质作用的时间,闫国川(2021)获得的金沙江南段维西地区催依比组双峰式火山岩中的流纹岩年龄为244 Ma,代表了流纹岩的喷发时间,均暗示了金沙江地区在中三叠世已经进入碰撞后伸展阶段。综上所述,结合本文获得的贡觉花岗斑岩年龄(244±2) Ma,本文认为,金沙江缝合带贡觉地区在244 Ma已经进入了后碰撞伸展时期。

    图  10  金沙江缝合带中二叠世—中三叠世花岗岩形成深度(据张旗等, 2006, 2010, 2023
    ①—高Sr低Yb型;②—低Sr低Yb型;③—低Sr高Yb型;④—极低Sr极高Yb型;横纵坐标数据单位为10-6。数据来源:中二叠世花岗质岩体数据引自吴涛等, 2013; 杨喜安等, 2013; He et al., 2020; 晚二叠世—早三叠世花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020; 吴喆, 2022; 中三叠世花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等, 2019; 闫国川等, 2021; 吴喆, 2022
    Figure  10.  Formation depth diagrams of the Middle Permian–Middle Triassic granitic rocks along the Jinsha River suture zone (after Zhang et al., 2006, 2010, 2023)

    本文系统收集了金沙江缝合带内二叠纪—中三叠世的花岗质岩的年代学及Hf同位素数据(表3),并结合地球化学特征及前人研究成果,将该时期构造–岩浆演化过程分为三个阶段。第一阶段(300~261 Ma),为洋内俯冲及洋陆俯冲阶段,该时期主要产出与俯冲洋壳部分熔融有关的具有埃达克岩性质的岩浆岩以及部分具有岛弧性质的I型、S型花岗岩;有限的Hf同位素资料显示,该时期εHf(t)值介于-5.0~+11.0,结合地球化学特征,指示岩浆来源主要与俯冲洋壳部分熔融有关;将该时期陆壳源区的花岗质岩投入Sr–Yb图解中(图10),显示该时期地壳厚度差异较大,但主要介于30~40 km,可能暗示了俯冲阶段金沙江缝合带不同地区地壳厚度的不均一性。

    表  3  金沙江缝合带二叠纪—中三叠世花岗质岩年龄及Hf同位素组成
    Table  3.  The reported ages and Hf isotopic results for the Permian–Middle Triassic granitic rocks along the Jinsha River suture zone
    采样位置 样品号 岩性 测试方法 年龄/Ma εHf(t) 岩石类型 数据来源
    第一阶段(300~262 Ma)
    同普 JD-19N 含黑云母花岗岩 锆石U-Pb 263 S型花岗岩 吴涛等,2013
    同普 JD-35N 花岗闪长岩 锆石U-Pb 263 S型花岗岩 吴涛等,2013
    鲁春 LC34 流纹岩 锆石U-Pb 270 S型花岗岩 杨喜安等,2013
    同普 JD-42N 石英闪长岩 锆石U-Pb 262 I型花岗岩 吴涛等,2013
    鲁甸 D2666 花岗岩 锆石U-Pb 271 -5.0~+0.6 I型花岗岩 He et al., 2020
    羊拉 YL1 二长花岗岩 锆石U-Pb 261 埃达克质岩 高睿等,2010
    雪堆 012-3 斜长花岗岩 锆石U-Pb 300 埃达克质岩 简平等,2003
    娘九丁 007-4 斜长花岗岩 锆石U-Pb 285 埃达克质岩 简平等,2003
    吉义独 002-1 花岗闪长岩 锆石U-Pb 263 埃达克质岩 Jian et al., 2008
    吉义独 SJ-101 英云闪长岩 锆石U-Pb 283 -4.5~+11.0 埃达克质岩 Zi et al., 2012a
    第二阶段(254~250 Ma)
    贡觉 20 LMC 英安岩−流纹岩 锆石U-Pb 251 -12.51~-1.56 S型花岗岩 吴喆, 2022
    德钦 01-1a 花岗闪长岩 锆石U-Pb 254 -9.56~-7.04 I型花岗岩 张万平等, 2011
    鲁甸 D2660 二长岩 锆石U-Pb 250 -7.9~-6.6 I型花岗岩 He et al., 2020
    鲁甸 D2665 二长花岗岩 锆石U-Pb 252 -4.1~-1.7 I型花岗岩 He et al., 2020
    鲁甸 D2660u1 石英闪长玢岩 锆石U-Pb 250 I型花岗岩 蒋勇, 2020
    第三阶段(247~242 Ma)
    贡觉 20HJ-01 英安岩−流纹岩 锆石U-Pb 246 -3.56~+5.50 S型花岗岩 吴喆, 2022
    贡觉 20HJ-02 英安岩−流纹岩 锆石U-Pb 246 -22.50~-7.36 S型花岗岩 吴喆, 2022
    贡觉 20HJ-03 英安岩−流纹岩 锆石U-Pb 246 -17.30~-8.54 S型花岗岩 吴喆, 2022
    日扎山 LW-01 流纹岩 锆石U-Pb 244 S型花岗岩 于远山等,2019
    鲁春 LCTK0-1 流纹岩 锆石U-Pb 245 -14.5~-8.3 S型花岗岩 Wang et al., 2014
    几家顶 JJD03-2 流纹岩 锆石U-Pb 244 -13.7~-8.2 S型花岗岩 Wang et al., 2014
    几家顶 JJD03-9 流纹岩 锆石U-Pb 246 -14.1~-9.1 S型花岗岩 Wang et al., 2014
    叶枝 YZ01-1 流纹岩 锆石U-Pb 247 S型花岗岩 Wang et al., 2014
    攀天阁 SJ33 流纹岩 锆石U-Pb 246 S型花岗岩 Zi et al., 2012b
    攀天阁 SJ22 流纹岩 锆石U-Pb 247 S型花岗岩 Zi et al., 2012b
    维西 PM03-59 流纹岩 锆石U-Pb 244 S型花岗岩 闫国川等, 2021
    催依比 SJ04 流纹岩 锆石U-Pb 242 I型花岗岩 Zi et al., 2012b
    下载: 导出CSV 
    | 显示表格

    第二阶段(254~250 Ma),为弧陆碰撞阶段,该时期主要产出高钾钙碱性I型花岗岩;Hf同位素资料显示,该时期εHf(t)值介于-12.5~-1.7,指示其相比于俯冲阶段,岩浆物质更多地来源于地壳;将该时期的I型花岗岩地球化学数据投入Rb/Ba–Rb/Sr和Al2O3/(FeOT+MgO+TiO2)–(Al2O3+FeOT+MgO+TiO2)岩浆源区判别图解中(图8a-b),指示其主要来源于角闪岩熔体和杂砂岩熔体;再将该时期的花岗质岩投入Sr–Yb图解中(图10),数据点大多投入高Sr低Yb区域,表明该时期地壳厚度大于50 km,与俯冲阶段相比,地壳厚度急剧变厚,指示已经进入同碰撞阶段。

    第三阶段(247~242 Ma),为碰撞后伸展阶段,该时期主要产出高钾钙碱性S型花岗岩;Hf同位素资料显示,该时期εHf(t)值介于-22.5~+5.5,指示相比于碰撞阶段,古老地壳物质更多地参与到了岩浆源区;将该时期的S型花岗岩地球化学数据投入Rb/Ba–Rb/Sr以及Al2O3/(FeOT+MgO+TiO2)–(Al2O3+FeOT+MgO+TiO2)岩浆源区判别图解中(图8a-b),主要落入了杂砂岩熔体和泥质岩熔体区域。在Sr–Yb图解中(图10),数据点大多投入极低Sr极高Yb区域,表明该时期地壳厚度小于30 km,相比于碰撞阶段,地壳厚度急剧减薄,暗示已经进入碰撞后伸展阶段。

    综上所述,俯冲阶段到碰撞阶段再到后碰撞伸展阶段,地壳厚度经历了由正常到增厚再到减薄的过程,Sr–Yb图解将这一过程很好地表现了出来(图10)。同时,随着俯冲—碰撞—伸展这一过程的进行,岩石的主要类型也由俯冲洋壳板片部分熔融形成的埃达克质岩变成了下地壳变基性岩部分熔融形成的I型花岗岩,再到古老地壳部分熔融形成的S形花岗岩,εHf(t)的值整体呈变小的趋势(表3),暗示了在金沙江俯冲—碰撞—伸展的构造–岩浆作用过程中,地壳物质越来越多地参与到了岩浆源区。

    (1)贡觉二长岩和花岗斑岩锆石U-Pb年龄分别为(250±1)Ma、(244±2)Ma,属于早中三叠世岩浆作用的产物。矿物组成和地球化学特征表明贡觉二长岩为I型花岗岩,花岗斑岩为S型花岗岩。

    (2)贡觉二长岩呈现轻稀土元素富集的特征,Mg#值为28~30,Rb/Sr比值介于0.07~0.11,Nb/La比值介于0.43~0.49,为下地壳基性变火成岩物质发生部分熔融形成的产物。花岗斑岩FeOT/MgO比值为4.43~4.98,Al2O3/TiO2比值为47.57~51.12,CaO/Na2O比值为0.28~0.49,说明该岩石岩浆源区为地壳变杂砂岩。

    (3)贡觉二长岩和花岗斑岩岩石地球化学特征分别具有碰撞造山和地壳伸展减薄环境的特点,表示贡觉地区在250 Ma的时候进入俯冲到碰撞的转换阶段,在244 Ma已经进入碰撞后伸展阶段。

    (4)综合分析金沙江缝合带内二叠纪—中三叠世的花岗岩类的年代学、Hf同位素及地球化学数据,并结合前人研究成果,认为金沙江俯冲—碰撞—伸展的构造–岩浆作用过程中,地壳物质越来越多地参与到了岩浆源区。

    致谢:成都地质调查中心项目团队的老师、同学们在野外地质调查和样品采集等方面给予了大力支持与帮助,两位匿名审稿人和责任编辑对本文提出的宝贵修改意见,使得文章质量有了大幅度的提升,在此一并致以衷心感谢!

  • 图  1   西南三江造山带大地构造位置图(a, 据李兴振等, 1999)及藏东贡觉地区地质简图(b, 据1∶5万江达幅、贡觉幅区域地质图修改)

    Figure  1.   Simplified tectonic map of the Sanjiang tectonic belt (a, after Li et al., 1999) and geological map of the Gonjo, eastern Tibet (b, modified from 1∶50 000 Jiangda, Gonjo regional geological map)

    图  2   金沙江缝合带贡觉地区地质剖面图

    Figure  2.   Geological profile of the Gonjo areas in the Jinsha River suture zone

    图  3   贡觉二长岩、花岗斑岩野外和镜下照片

    a. 贡觉二长岩; b. 贡觉花岗斑岩; c、d. 贡觉二长岩镜下照片,正交偏光; e、f. 贡觉花岗斑岩镜下照片,正交偏光。K—钾长石; Pl—斜长石;Hb—角闪石;Cpx—单斜辉石;Q—石英

    Figure  3.   Field photographs and photomicrographs of the Gonjo monzonite and granite porphyry

    图  4   贡觉二长岩、花岗斑岩锆石CL图像(a、c)及U-Pb年龄谐和图(b、d)

    Figure  4.   CL images (a, c) and U-Pb concordia diagrams (b, d) of the Gonjo monzonite and granite porphyry

    图  5   金沙江缝合带贡觉岩浆岩(Na2O+K2O) – SiO2岩石分类图解(a, 据Middlemost, 1994),K2O–SiO2图(b, 据Streckeisen, 1976),SiO2–AR图(c, 据Wright, 1969),A/NK–A/CNK图解(d, 据Maniar and Piccoli,1989

    数据来源:晚二叠世—早三叠世花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020; 吴喆, 2022; 中三叠世花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等; 2019; 闫国川等, 2021; 吴喆, 2022

    Figure  5.   Diagrams of total alkali (Na2O+K2O) vs. SiO2 (a, after Middlemost, 1994), K2O vs. SiO2 (b, after Streckeisen, 1976), SiO2 vs. AR (c, after Wright, 1969), A/NK vs. A/CNK (d, after Maniar and Piccoli, 1989) for the Gonjo magmatites in the Jinsha River suture zone

    图  6   金沙江缝合带贡觉岩浆岩球粒陨石标准化稀土元素配分图(a)和原始地幔标准化微量元素蛛网图(b)(标准化值据Sun and McDonough, 1989

    数据来源:晚二叠世—早三叠世花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020; 吴喆, 2022; 中三叠世花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等; 2019; 闫国川等, 2021; 吴喆, 2022

    Figure  6.   Chrondrite–normalized REE patterns (a) and primitive mantle–normalized trace element spider diagram (b) for the Gonjo magmatites in the Jinsha River suture zone (normalization values after Sun and McDonough, 1989 )

    图  7   金沙江缝合带贡觉岩浆岩成因判别图解(a、b据Whalen et al., 1987; c据Chappell and White, 1992 ; d据Nakada and Takahashi, 1979

    Figure  7.   Genesis discrimination diagrams (a and b, after Whalen et al., 1987; c, after Chappell and White, 1992; d, after Nakada and Takahashi, 1979) for the Gonjo magmatites in the Jinsha River suture zone

    图  8   金沙江缝合带贡觉岩浆岩源区判别图解(a,据Sylvester, 1998; b,据Douce, 1999

    数据来源:晚二叠世—早三叠世I型花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020;中三叠世S型花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等, 2019; 闫国川等, 2021; 吴喆, 2022

    Figure  8.   Source discrimination diagrams (a, after Sylvester, 1998; b, after Douce, 1999) for the Gonjo magmatites in the Jinsha River suture zone

    图  9   金沙江缝合带贡觉岩浆岩构造环境判别图解(a、b据Pearce et al., 1984

    Syn-CLOG—同碰撞花岗岩;VAG—火山弧花岗岩;WPG—板内花岗岩;ORG—洋中脊花岗岩。数据来源:晚二叠世—早三叠世花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020; 吴喆, 2022; 中三叠世花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等, 2019; 闫国川等, 2021; 吴喆, 2022

    Figure  9.   Tectonic discrimination diagrams (a and b, after Pearce et al., 1984) for the Gonjo magmatites in the Jinsha River suture zone

    图  10   金沙江缝合带中二叠世—中三叠世花岗岩形成深度(据张旗等, 2006, 2010, 2023

    ①—高Sr低Yb型;②—低Sr低Yb型;③—低Sr高Yb型;④—极低Sr极高Yb型;横纵坐标数据单位为10-6。数据来源:中二叠世花岗质岩体数据引自吴涛等, 2013; 杨喜安等, 2013; He et al., 2020; 晚二叠世—早三叠世花岗质岩体数据引自张万平等, 2011; 蒋勇, 2020; He et al., 2020; 吴喆, 2022; 中三叠世花岗质岩体数据引自Zi et al., 2012b; Wang et al., 2014; 于远山等, 2019; 闫国川等, 2021; 吴喆, 2022

    Figure  10.   Formation depth diagrams of the Middle Permian–Middle Triassic granitic rocks along the Jinsha River suture zone (after Zhang et al., 2006, 2010, 2023)

    表  1   贡觉二长岩、花岗斑岩LA-ICP-MS锆石U-Pb数据

    Table  1   LA-ICP-MS zircon U-Pb data of monzonite and granite porphyry samples in the Gonjo area

    测点号含量/×10-6Th/U同位素比值年龄/Ma
    ThU207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238U
    D3016 -1 二长岩
    16035501.100.05290.00230.28800.01210.03950.000432494257102503
    23925060.770.05040.00230.27640.01210.03970.0006217106248102513
    36886841.010.05010.00170.27520.00920.03970.00041988024772512
    45805870.990.04810.00190.26200.01070.03940.00051069623692493
    5178211951.490.04960.00180.27520.01010.04000.00041767924782532
    6174613181.320.05010.00190.27220.01020.03920.00051988724482483
    7143913701.050.05100.00180.28040.00970.03980.00052397525182523
    8141811121.280.05140.00180.28230.00950.03980.00052578425282523
    910458501.230.04800.00170.26360.00930.03970.00051028523872513
    10180812931.400.04830.00150.26600.00830.03960.00041227424072503
    111733650.470.04940.00220.27450.01320.03960.0006165138246102514
    12158614521.090.04830.00170.26580.00870.03980.00051228123972513
    136846801.010.05030.00190.27840.01070.03980.00052098924992523
    14297616141.840.04890.00140.26880.00790.03950.00041466724262503
    15196519061.030.05000.00140.27130.00710.03920.00031956324462482
    16111510211.090.04960.00180.26890.00950.03920.00041768524282483
    179969801.020.05080.00170.27550.00940.03920.00042327824772482
    18117810011.180.04950.00170.27070.00960.03940.00041728124382493
    19111712150.920.05130.00150.27970.00860.03940.00052546625072493
    20112711610.970.04870.00150.26410.00880.03910.00042007623872473
    216856701.020.05160.00190.28590.01110.03990.00052658725592523
    227009680.720.04980.00200.27710.01160.04000.00051839424892533
    D5008 -1 花岗斑岩
    11513610.420.05740.00320.29610.01560.03790.0007506129263122404
    22236760.330.05380.00260.27750.01300.03760.0006365114249102384
    34738070.590.05100.00230.27300.01200.03900.000624371245102474
    41453950.370.05420.00270.28660.01410.03850.000738977256112444
    53527610.460.05530.00240.29240.01360.03830.000743398260112424
    63308530.390.05150.00200.28140.01200.03960.00072658925292504
    72916170.470.05020.00270.25070.01300.03640.0006211122227112304
    863511400.560.05280.00210.28520.01160.03930.00063209125592484
    93127000.450.05330.00220.27650.01110.03800.00063399424892414
    104367590.570.05140.00250.26980.01270.03850.0006257111243102434
    111915740.330.05390.00260.29310.01480.03930.0007365109261122494
    122715510.490.05260.00260.27210.01360.03790.0006309115244112404
    132806410.440.05260.00250.28340.01320.03950.0008309109253102505
    142063890.530.04800.00340.24860.01650.03890.000898159225132465
    153105960.520.05450.00270.28560.01390.03840.0007391113255112434
    161814490.400.05230.00270.28740.01460.04030.0006298119256112544
    171864630.400.05150.00270.27810.01510.03900.000726594249122474
    186169700.640.05530.00230.30000.01260.03940.000643397266102494
    192266190.370.05010.00230.26700.01210.03900.000719899240102474
    202866870.420.05000.00260.26890.01430.03930.0007195122242112495
    21112513820.810.05250.00180.28580.01020.03920.00063097625582483
    222166150.350.04770.00240.25700.01300.03930.000783115232112484
    232656420.410.04780.00230.25120.01210.03810.000687111228102413
    242166320.340.05560.00270.29570.01410.03910.0007435109263112474
    251644090.400.05270.00280.27810.01560.03770.0007317120249122394
    262586430.400.05070.00240.27810.01320.03980.0007228111249102524
    下载: 导出CSV

    表  2   贡觉二长岩、花岗斑岩全岩主量、微量和稀土元素成分

    Table  2   Major, trace, and rare earth element concentrations of the Gonjo monzonite and granite porphyry

    样品号 D3016-H1 D3016-H2 D3016-H3 D3016-H4 D5008-H1 D5008-H2 D5008-H3 D5008-H4
    岩性 二长岩 花岗斑岩
    SiO2 57.66 57.03 57.47 56.70 73.78 75.17 74.52 74.59
    TiO2 0.80 0.78 0.71 0.85 0.28 0.26 0.28 0.27
    Al2O3 18.12 18.40 18.42 17.87 13.43 13.29 13.32 13.60
    TFe2O3 5.66 5.68 5.08 6.12 2.71 2.42 2.74 2.61
    MnO 0.12 0.12 0.11 0.13 0.043 0.031 0.044 0.024
    MgO 1.20 1.12 1.04 1.23 0.49 0.47 0.50 0.53
    CaO 4.62 5.03 4.90 5.15 1.74 1.09 1.69 0.88
    Na2O 3.13 3.14 3.18 3.07 3.53 3.35 3.57 3.12
    K2O 7.61 7.15 7.37 7.26 2.65 2.93 2.64 2.94
    P2O5 0.24 0.24 0.21 0.26 0.053 0.054 0.056 0.051
    烧失量 0.90 1.08 1.12 1.11 0.84 1.11 0.84 1.52
    总量 100.06 99.77 99.61 99.75 99.546 100.17 100.20 100.135
    Rb 72.4 108 112 115 49.6 44.3 52.4 49.7
    Ba 2300 2740 2370 2570 731 637 718 610
    Th 6.02 11.8 11.1 12.7 6.87 7.45 7.18 7.99
    U 1.01 2.04 1.78 2.13 1.22 1.3 1.26 1.37
    Nb 19 18.6 16.6 21 5.32 5.11 5.44 5.13
    Ta 0.84 0.97 1.2 0.95 0.41 0.49 0.42 0.44
    La 39.1 43.6 38.8 47.6 19.6 17.5 20 18.8
    Ce 56.2 58.9 52 64.9 34.2 35.8 35.6 35.1
    Pb 17.4 19.7 19.9 21.7 8.48 8.77 28.2 7.79
    Pr 9.30 9.32 7.99 10.2 4.02 3.55 4.14 3.78
    Sr 1040 1140 1090 1080 177 122 176 112
    Nd 29.00 27.2 23.60 29.90 11.40 9.84 11.8 10.4
    Sm 5.47 4.84 4.05 5.13 2.04 1.73 2.12 1.80
    Zr 152 162 150 181 116 122 120 130
    Hf 19.9 4.11 3.49 5.31 3.84 3.06 4.24 4.33
    Ga 12.3 13.5 12.9 13.4 9.16 8.71 9.55 9.15
    Eu 2.04 2.1 1.94 2.08 0.6 0.46 0.62 0.45
    Gd 7.7 6.66 5.73 7.24 3.09 2.66 3.18 2.76
    Tb 0.98 0.81 0.68 0.87 0.42 0.34 0.44 0.37
    Dy 5.35 4.25 3.63 4.64 2.56 2.00 2.64 2.21
    Ho 0.96 0.76 0.66 0.83 0.51 0.40 0.53 0.45
    Y 18.2 14.4 12.8 16.1 9.94 7.69 10.3 8.56
    Er 2.66 2.15 1.85 2.36 1.55 1.28 1.6 1.42
    Tm 0.36 0.29 0.26 0.33 0.23 0.2 0.24 0.22
    Yb 2.19 1.83 1.66 2.08 1.6 1.46 1.66 1.57
    Lu 0.34 0.28 0.25 0.32 0.25 0.24 0.26 0.26
     注:主量元素含量单位为%,微量和稀土元素含量单位为10-6
    下载: 导出CSV

    表  3   金沙江缝合带二叠纪—中三叠世花岗质岩年龄及Hf同位素组成

    Table  3   The reported ages and Hf isotopic results for the Permian–Middle Triassic granitic rocks along the Jinsha River suture zone

    采样位置 样品号 岩性 测试方法 年龄/Ma εHf(t) 岩石类型 数据来源
    第一阶段(300~262 Ma)
    同普 JD-19N 含黑云母花岗岩 锆石U-Pb 263 S型花岗岩 吴涛等,2013
    同普 JD-35N 花岗闪长岩 锆石U-Pb 263 S型花岗岩 吴涛等,2013
    鲁春 LC34 流纹岩 锆石U-Pb 270 S型花岗岩 杨喜安等,2013
    同普 JD-42N 石英闪长岩 锆石U-Pb 262 I型花岗岩 吴涛等,2013
    鲁甸 D2666 花岗岩 锆石U-Pb 271 -5.0~+0.6 I型花岗岩 He et al., 2020
    羊拉 YL1 二长花岗岩 锆石U-Pb 261 埃达克质岩 高睿等,2010
    雪堆 012-3 斜长花岗岩 锆石U-Pb 300 埃达克质岩 简平等,2003
    娘九丁 007-4 斜长花岗岩 锆石U-Pb 285 埃达克质岩 简平等,2003
    吉义独 002-1 花岗闪长岩 锆石U-Pb 263 埃达克质岩 Jian et al., 2008
    吉义独 SJ-101 英云闪长岩 锆石U-Pb 283 -4.5~+11.0 埃达克质岩 Zi et al., 2012a
    第二阶段(254~250 Ma)
    贡觉 20 LMC 英安岩−流纹岩 锆石U-Pb 251 -12.51~-1.56 S型花岗岩 吴喆, 2022
    德钦 01-1a 花岗闪长岩 锆石U-Pb 254 -9.56~-7.04 I型花岗岩 张万平等, 2011
    鲁甸 D2660 二长岩 锆石U-Pb 250 -7.9~-6.6 I型花岗岩 He et al., 2020
    鲁甸 D2665 二长花岗岩 锆石U-Pb 252 -4.1~-1.7 I型花岗岩 He et al., 2020
    鲁甸 D2660u1 石英闪长玢岩 锆石U-Pb 250 I型花岗岩 蒋勇, 2020
    第三阶段(247~242 Ma)
    贡觉 20HJ-01 英安岩−流纹岩 锆石U-Pb 246 -3.56~+5.50 S型花岗岩 吴喆, 2022
    贡觉 20HJ-02 英安岩−流纹岩 锆石U-Pb 246 -22.50~-7.36 S型花岗岩 吴喆, 2022
    贡觉 20HJ-03 英安岩−流纹岩 锆石U-Pb 246 -17.30~-8.54 S型花岗岩 吴喆, 2022
    日扎山 LW-01 流纹岩 锆石U-Pb 244 S型花岗岩 于远山等,2019
    鲁春 LCTK0-1 流纹岩 锆石U-Pb 245 -14.5~-8.3 S型花岗岩 Wang et al., 2014
    几家顶 JJD03-2 流纹岩 锆石U-Pb 244 -13.7~-8.2 S型花岗岩 Wang et al., 2014
    几家顶 JJD03-9 流纹岩 锆石U-Pb 246 -14.1~-9.1 S型花岗岩 Wang et al., 2014
    叶枝 YZ01-1 流纹岩 锆石U-Pb 247 S型花岗岩 Wang et al., 2014
    攀天阁 SJ33 流纹岩 锆石U-Pb 246 S型花岗岩 Zi et al., 2012b
    攀天阁 SJ22 流纹岩 锆石U-Pb 247 S型花岗岩 Zi et al., 2012b
    维西 PM03-59 流纹岩 锆石U-Pb 244 S型花岗岩 闫国川等, 2021
    催依比 SJ04 流纹岩 锆石U-Pb 242 I型花岗岩 Zi et al., 2012b
    下载: 导出CSV
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出版历程
  • 收稿日期:  2023-08-31
  • 修回日期:  2024-02-24
  • 录用日期:  2024-03-03
  • 刊出日期:  2025-03-19

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