Formation mechanism of the Chengba high Sr/Y granodiorite and enclaves in southern Gangdise region, southern Tibet
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摘要:
程巴岩体位于藏南冈底斯岩基东段南缘, 由花岗闪长岩、细粒闪长质包体等组成。测得的锆石U-Pb年龄可以代表岩石的形成年龄, 即花岗闪长岩形成年龄为29.40±0.18Ma与29.42±0.25Ma, 细粒闪长质捕虏体形成年龄为30.02±0.15Ma。花岗闪长岩具有较高的SiO2(65.2%~66.2%)、K2O(3.2%~4.0%), 较低的铁(TFeO=3.2%~4.0%)和MgO(约2%), 同时具有高Sr(774×10-6~813×10-6)、低Y(9.9×10-6~11.2×10-6)、高Sr/Y值(63.4~82.2)等特征; 闪长质包体表现出较低的SiO2(53%~56.1%)和K2O(1.5%~3.2%), 较高的铁(TFeO=6.1%~8.1%)、MgO(4.0%~6.2%)和Na2O/K2O≥2, 同时具有负Eu异常(Eu/Eu*=0.432~0.804)。2种岩性都富集LREE及LILE, 亏损HREE及HFSE, 具有较高且一致的εHf(t)值(+1.1~+6.2)和全岩εNd(t)值(-2.9~-5.9)。以上数据表明, 花岗闪长岩与细粒闪长质包体由同一岩浆分离结晶形成, 花岗闪长岩经历磷灰石和角闪石的分离结晶, 其高Sr/Y值为岩浆分离结晶的结果, 并不代表原始岩浆组分
Abstract:The Chengba Complex on the southern margin of the Gangdise batholiths in southern Tibet comprises mainly granodio-rite and subordinately dioritic enclaves and leucogabbro. Zircon U-Pb analytical results demonstrate that the granodiorites formed at 29.40±0.18Ma to 29.42±0.25Ma, whereas the fine-grained dioritic enclaves formed at 30.02±0.15Ma. Bulk-rock major and trace el-ement and isotope(Sr-Nd-Hf) analyses indicate that the granodiorites are characterized by relatively high SiO2(65.2%~66.2%) and K2O(3.2%~4.0%) but low FeO and MgO, and high Sr(774×10-6~813×10-6), low Y(9.9×10-6~11.2×10-6), and hence high Sr/Y ratios(>60 and up to 82). In contrast, the dioritic enclaves are relatively low in SiO2(53%~56.1%) and K2O(1.5%~3.2%), but high in MgO and FeO with relatively high Na/K ratios(≥2). Both are enriched in LREE and LILE and depleted in HREE and HFSE and have similar relatively high zircon εHf(t) values(+1.1~+6.2) as well as negative whole-rock εNd(t) values(-2.9~-5.9). Combined with data available, the new results obtained by the authors suggest that the Chengba granodiorite and dioritic enclaves were formed within a time span of ca.1Ma. Similar isotopic characteristics imply that they were derived from similar sources. The high Sr/Y ratios in Chengba granodiorite, in contrast to low Sr/Y ratios in the mafic enclaves, possibly do not represent primary magma composition. Instead, the high Sr/Y and high Ba characteristics of the Chengba granodiorite might have resulted from fractional crystallization of parent magmas with low Sr/Y ratios and low Ba content like those mafic enclaves.
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Keywords:
- Gangdise batholith /
- Chengba rock mass /
- granodiorite /
- high Sr/Y /
- dioritic enclaves /
- LA-ICP-MS zircon U-Pb ages
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冈底斯岩基位于拉萨地块南部，由不同时代和地球化学性质各异的岩浆岩组成[1-8]，可与美国西部的内华达岩基相媲美[9]。这些花岗质岩石为细致刻画拉萨地体的起源和构造演化过程提供了重要的记录，为理解大陆岩石圈的分异、演化和再造的动力学机理提供了良好的野外实验室。冈底斯带经历了与印度-亚洲碰撞造山作用相关的构造与岩浆作用，发育了大量小于40Ma的岩浆岩，为解译陆陆碰撞造山带上盘岩石如何响应碰撞造山过程提供了良好的记录。在冈底斯岩基中，随着特提斯洋的北向俯冲、消减和闭合，印度-亚洲碰撞的开启，伴随大量的岩浆作用（图 1-a），主要包括：①碰撞前的大陆弧和洋内弧岩浆作用，表现为中侏罗世叶巴组火山岩及晚侏罗世—早白垩世桑日群火山岩[10]和侵入岩[6, 11-15]；②同碰撞阶段(65~45Ma)岩浆作用，形成大量的侵入岩[12, 16-17]和东西走向绵延超过1000km的林子宗火山岩[18-19]。③后碰撞阶段岩浆作用，持续时间为37~8Ma，包括高Sr/Y值的花岗岩岩类[4-5, 12, 20-26]和钾质-超钾质火山岩[27-32]。
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图 1 藏南新生代岩浆分布图（a）（据参考文献[4]修改）与程巴岩体地质图（b）MCT—主中央逆冲断裂；STDS—藏南拆离系；ITS—雅鲁藏布江缝合带；BNS—班公湖怒江缝合带Figure 1. Geological map showing the distribution of Cenozoic magmatic rocks in southern Tibet (a) and geological map of the Chengba Complex (b)埃达克岩自提出之后被广大学者关注，高Sr（> 400×10-6）、低Y（小于20×10-6）是埃达克岩的主要地球化学特征[33]。在世界上，众多花岗岩体中都伴生类似的花岗质岩石，其形成机制存在重大分歧。由于地球化学特征的相似性，埃达克岩或高Sr、Y岩石的形成环境存在重大争议，越来越多的研究表明，高Sr/Y值岩浆岩的形成机制较复杂，存在多种成因，主要包括：①年轻俯冲洋壳的部分熔融[33]；②不同类型岩浆（主要为基性岩浆）的分离结晶与混染作用[14, 34-35]；③增厚下地壳或拆沉下地壳的部分熔融[4-5, 11, 24, 26, 36-40]；④经历流体或熔体交代俯冲带上盘地幔楔的部分熔融[41]；⑤长英质岩浆与玄武质岩浆的混合作用[23, 42-43]。高Sr/Y值的岩浆岩可形成于不同的构造环境，如洋壳俯冲带、陆壳内部伸展环境，陆陆碰撞带、其他原因的岩浆底侵环境等。因此，要确定高Sr/Y值岩浆岩的成因，需要详细分析其地球化学特征和地质构造环境。
明则-程巴-冲木达岩体（Yajia）位于冈底斯东段南缘，紧邻雅鲁藏布江缝合带。最早由Harrison等[44]发现并报道了该岩体的形成时代（30.4±0.2Ma, 锆石U-Pb年龄）和全岩地球化学数据。Chung等[30]在重新审视该岩体的全岩地球化学数据后，认为由于该岩体具有高Sr、低Y的地球化学特征，应为埃达克岩。由于该岩体在形成时代和地球化学特征上具有特殊性，许多学者开展了跟进的研究，试图确定该岩体的形成机理及其构造动力学意义。这些研究表明：①主体岩石的形成时代为28.4~ 31.0Ma[13, 20, 44-47]，岩体中的暗色包体的形成时代约为31.0Ma[46]；程巴矿区辉钼矿Re-Os年龄为30.2±0.9Ma[47], 与程巴岩体的形成时代相近，角闪石K-Ar年龄和白云母40Ar/39Ar年龄分别为21.4±1.9Ma和28.9±1.4Ma[48-49]，预示该岩体在结晶后，经历了快速剥露的过程（表 1）；②除了具有高Sr/Y值特征外，该岩体具有较高的87Sr/86Sr值（0.07057~0.7062）和较低的εNd(t)值（-2.5~-5.9），锆石具有较高的εHf(t)值（+2.0~+8.0）同位素组成[20, 45-47]，反映其源区可能是富集大陆岩石圈地幔或新生下地壳。此外，对于程巴岩体形成机理的认识存在较大的分歧, 包括以下3种模型：①增厚下地壳部分熔融作用[20, 30, 45]；②熔体-地幔楔交代反应和部分熔融作用，俯冲印度大陆地壳的部分熔融作用形成的熔体交代上盘地幔楔，随后发生部分熔融作用[46]；③上述2种模型的混搭[47, 50]。最近的地质调查发现，程巴岩体的组成较先前报道的复杂，除花岗闪长岩外，还包含至少2种细粒包体和浅色辉长岩，为进一步解译程巴岩体的形成机理提供了新证据。
表 1 西藏南部冈底斯岩基程巴-冲木达岩体年龄Table 1. Summary of previous dating results for the Chengba-Chongmuda Complex, southern Tibet采样区域及样品 测试对象及方法 年龄/Ma 数据来源 程巴(Yaja)岩体花岗闪长岩 锆石U-Pb 30.42±0.21 Harrison[44] 冲木达矿区花岗闪长质围岩 角闪石K-Ar 21.5±1.9 李光明等[48] 程巴岩体花岗闪长岩 锆石U-Pb 30.3±0.6, 31.0±0.5 Chung[30] 冲木达矿区花岗闪长质围岩 黑云母40Ar/39Ar 28.9±1.4 李光明等[49] 冲木达岩体花岗闪长岩与喑色包体 锆石U-Pb 30.2±0.7, 31.0±0.5 姜子琦等[46] 程巴-冲木达岩体花岗闪长岩等 锆石U-Pb 29.82±0.27 侯增谦[20] 程巴矿区辉钼矿 辉钼矿Re-Os 30.2±0.9 孙祥等[47] 程巴岩体花岗闪长岩与明则岩体二长岩 锆石U-Pb 28.4±0.4, 30.4±0.6 孙祥等[47] 在前人研究和详细的野外地质调查的基础上，通过岩相学、元素和放射性同位素地球化学及地质年代学测试，限定程巴岩体中花岗闪长岩与细粒闪长质包体的形成机制及岩浆过程。
1. 区域地质背景与样品描述
程巴岩体位于冈底斯东段南缘，山南地区泽当镇以东约15km处，紧邻雅鲁藏布江河谷，出露面积约8km2。区域构造线主要为北部的北倾冈底斯逆冲断裂带和南部的南倾仁布-泽当逆冲断裂带，冈底斯逆冲断裂带以北大面积出露古生代—中生代地层及侵入其中的白垩纪—新近纪花岗岩类岩石，仁布-泽当逆冲断裂带以南大面积出露晚三叠世砂岩和千枚岩，2条逆冲断裂带之间分布晚白垩世和古近纪—新近纪正长岩、古近纪—新近纪砾岩及基性-超基性岩[47]。程巴岩体产出于冈底斯逆冲断裂系的上盘，侵入到古—中生代沉积岩中，底部被逆冲断层截断，发育靡棱岩化剪切带[44]。在大地构造位置上，程巴岩体处于拉萨地块冈底斯岩基最南缘，紧接喜马拉雅造山带，形成时代处于印度-亚洲陆陆碰撞的后碰撞阶段（约30Ma），即印度-欧亚大陆碰撞造山作用的关键转换期。
程巴岩体主要出露花岗闪长岩、淡色辉长岩及不同性质的包体和脉体（图 2-a）。本文以花岗闪长岩（样品T0911-A和T0911-J）与细粒闪长质包体（T0911-C）为研究对象（图 1-b）。花岗闪长岩与细粒闪长质包体之间界线明显（图 2-b），花岗闪长岩呈灰白色，主要矿物为斜长石（45%~55%）、钾长石（20%~25%）、角闪石（15%~20%）、黑云母（5%）和石英（10%~15%），含有少量的磁铁矿、榍石、磷灰石等副矿物（图 2-c），长石与角闪石多为自形-半自形，出现钾长石斑晶。细粒闪长质包体呈灰黑色，主要矿物为斜长石（35%~45%）、角闪石（30%~35%）、钾长石（15%~25%）、黑云母（5%）和少量石英（5%），副矿物包括榍石、磁铁矿、针状磷灰石等，斜长石和角闪石颗粒较大，多为自形（图 2-d）。
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图 2 程巴花岗闪长岩及细粒闪长质包体野外和镜下照片a—野外露头；b—花岗闪长岩及细粒闪长质包体；c—花岗闪长岩镜下照片（单偏光）；d—细粒闪长质包体镜下照片（单偏光）。Amp—角闪石；Bt—黑云母；Pl—斜长石；Tnt—榍石；Kf—钾长石；Ap—磷灰石；Qtz—石英Figure 2. Field photographs and microphotographs of granodiorite and dioritic enclaves from the Chengba Complex2. 分析方法
2.1 LA-ICP-MS锆石U-Pb定年
为了限定程巴岩体中花岗闪长岩与细粒闪长质包体的形成时代，分别从2种岩石中分选出锆石，制成样品靶，并进行阴极发光（CL）和扫描电镜背散射（BSE）成像观察。阴极发光成像在北京离子探针中心进行。在中国地质科学院地质研究所，利用扫描电子显微镜进行了BSE图像和锆石内部包裹体的成分测试。根据阴极发光和BSE图像，确定锆石U-Pb年龄测定的选点位置。LA-ICP-MS锆石U-Pb定年在中国地质科学院矿产资源研究所成矿作用与资源评价重点实验室进行，所用仪器为德国Finnigan公司生产的Neptune型激光多接收等离子体质谱（LA-MC-ICP-MS），并结合美国New Wave公司生产的UP213nm激光剥蚀系统，激光剥蚀束斑直径为25μm，频率为10Hz，能量密度约为2.5J/cm2，以氦为载气。U、Th含量以锆石M127（U为923×10-6，Th为439×10-6，Th/U值为0.475）为外标进行校正。测试过程中，每测定10个样品点测量2次锆石标样GJ1和1次锆石标样Plesovice。对分析数据的离线处理（包括对样品和空白信号的选择、仪器灵敏度漂移校正、元素含量及U-ThPb同位素比值和年龄计算）采用软件ICPMSData-Cal完成[51]，锆石U-Pb谐和图用Isoplot 3.0程序获得，测试结果见表 2。
表 2 程巴花岗闪长岩与细粒闪长质包体LA-ICP-MS锆石U-Th-Pb定年数据Table 2. LA-ICP-MS zircon U-Th-Pb isotopic analyses of granodiorite and dioritic enclaves from the Chengba Complex测点号 元素含量/10-6 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ Th/U 年龄/Ma
206Pb/238U1σ Pb(Total) 232Th 238U T0911-A花岗闪长岩 01 58.6 599 442 0.0968 0.00117 0.06757 0.00178 0.00505 0.00011 1.35 32.5 0.7 02 38.2 650 490 0.04906 0.00049 0.03054 0.00042 0.00452 0.00005 1.33 29.1 0.3 03 48.4 818 495 0.04924 0.00076 0.0312 0.00077 0.00456 0.00006 1.65 29.4 0.4 04 41.8 667 1106 0.04706 0.00029 0.02979 0.00046 0.00458 0.00006 0.60 29.5 0.4 05 99.9 1713 1499 0.04668 0.00028 0.02928 0.00041 0.00455 0.00005 1.14 29.2 0.3 06 74.9 1269 1559 0.04726 0.00028 0.02991 0.00038 0.00459 0.00005 0.81 29.5 0.3 07 35.6 625 587 0.04696 0.00036 0.02921 0.00039 0.00452 0.00005 1.07 29.1 0.3 08 14.6 256 219 0.04759 0.00055 0.02989 0.00048 0.00456 0.00005 1.17 29.3 0.3 09 39.8 658 506 0.04702 0.0004 0.02976 0.00045 0.00460 0.00006 1.30 29.6 0.4 10 74.1 1357 765 0.04694 0.00036 0.03 0.00059 0.00462 0.00007 1.77 29.7 0.5 11 41.7 696 1062 0.0467 0.00029 0.02925 0.00055 0.00454 0.00008 0.66 29.2 0.5 12 36.6 599 435 0.05075 0.00054 0.0321 0.00051 0.00459 0.00006 1.38 29.6 0.4 13 96.1 651 426 0.16179 0.0066 0.12426 0.00683 0.00538 0.00014 1.53 34.6 0.9 14 27.4 545 392 0.0486 0.00059 0.03047 0.00049 0.00453 0.00002 1.39 29.1 0.1 15 114.1 2245 1664 0.04773 0.00055 0.03108 0.00066 0.00469 0.00004 1.35 30.1 0.3 16 46.4 862 527 0.05104 0.00041 0.03195 0.00028 0.00454 0.00002 1.64 29.2 0.1 17 56.9 744 381 0.08921 0.00125 0.05831 0.00085 0.00474 0.00002 1.95 30.5 0.1 18 28.2 612 402 0.04765 0.00049 0.0301 0.00031 0.00459 0.00002 1.52 29.5 0.1 19 54.8 1018 1239 0.04691 0.00042 0.0299 0.00056 0.00459 0.00004 0.82 29.5 0.2 20 35.7 735 395 0.04814 0.00054 0.03021 0.00042 0.00454 0.00003 1.86 29.2 0.2 21 37.6 731 497 0.04817 0.00037 0.0304 0.00025 0.00458 0.00002 1.47 29.5 0.1 22 30.1 582 803 0.04671 0.00028 0.02914 0.00021 0.00453 0.00002 0.73 29.1 0.1 23 47 935 1263 0.04741 0.00024 0.03023 0.00018 0.00463 0.00002 0.74 29.8 0.1 24 29.2 551 410 0.04794 0.00062 0.03045 0.00075 0.00455 0.00004 1.35 29.3 0.2 25 38.9 691 1289 0.04727 0.0004 0.03043 0.00057 0.00466 0.00007 0.54 29.9 0.4 26 52.3 880 1526 0.04661 0.00033 0.03034 0.00048 0.00471 0.00006 0.58 30.3 0.4 27 46.5 773 1158 0.04696 0.00098 0.03031 0.00078 0.00469 0.0001 0.67 30.1 0.7 28 30.8 527 413 0.04723 0.00048 0.02991 0.00031 0.00460 0.00003 1.28 29.6 0.2 29 47.7 834 1222 0.04663 0.00025 0.03 0.00023 0.00467 0.00003 0.68 30 0.2 30 44.5 770 498 0.04702 0.00045 0.03001 0.00036 0.00463 0.00003 1.55 29.8 0.2 T0911-C细粒闪长质包体 01 180.5 4711 3457 0.04633 0.00015 0.03744 0.00036 0.00586 0.00005 1.36 37.7 0.4 02 10.4 232 234 0.05143 0.00056 0.03844 0.0007 0.00541 0.00007 0.99 34.8 0.5 03 204.6 4298 2585 0.05817 0.00402 0.09564 0.02193 0.00888 0.00153 1.66 57 9.8 04 440 9093 4047 0.04662 0.00035 0.03018 0.0009 0.00468 0.00012 2.25 30.1 0.8 05 143.4 2821 1418 0.04669 0.00024 0.02972 0.00037 0.00462 0.00006 1.99 29.7 0.4 06 206.5 4064 2122 0.04701 0.00029 0.03052 0.00058 0.00469 0.00006 1.92 30.1 0.4 07 1611.8 32032 7447 0.04868 0.00013 0.031 0.00033 0.00462 0.00005 4.30 29.7 0.3 08 75 1345 1682 0.04714 0.0002 0.03051 0.00027 0.00470 0.00004 0.80 30.2 0.2 09 81.2 1555 564 0.05203 0.0008 0.03217 0.00067 0.00450 0.00007 2.76 28.9 0.5 10 275.3 5305 1841 0.04657 0.00027 0.03024 0.00042 0.00470 0.00005 2.88 30.2 0.3 11 264.7 5217 2895 0.04778 0.00031 0.03076 0.00045 0.00466 0.00005 1.80 29.9 0.3 12 23.6 442 538 0.04822 0.00065 0.03075 0.00088 0.00457 0.00006 0.82 29.4 0.4 13 148.6 2852 962 0.05054 0.00038 0.03258 0.00043 0.00468 0.00005 2.96 30.1 0.3 14 203.5 2826 980 0.09401 0.00145 0.05959 0.00153 0.00458 0.00009 2.88 29.5 0.6 15 92.2 1800 1866 0.04678 0.0002 0.02994 0.00048 0.00464 0.00007 0.96 29.8 0.4 16 4.5 62 458 0.04877 0.00053 0.03027 0.00046 0.00451 0.00005 0.14 29.0 0.3 17 135.1 2034 863 0.06677 0.00081 0.04219 0.00166 0.00457 0.00016 2.36 29.4 1 18 19.9 430 341 0.05102 0.00075 0.03845 0.00088 0.00546 0.00009 1.26 35.1 0.6 19 142.3 2530 910 0.04931 0.00089 0.0316 0.00092 0.00459 0.00006 2.78 29.6 0.4 20 8.5 143 530 0.04749 0.00037 0.03101 0.00039 0.00473 0.00005 0.27 30.4 0.3 21 89.6 1726 610 0.04668 0.00035 0.0296 0.00036 0.00460 0.00004 2.83 29.6 0.3 22 46.2 896 415 0.07911 0.01214 0.34549 0.19212 0.00797 0.00188 2.16 51.2 12 23 7.4 170 335 0.04962 0.00111 0.02844 0.00062 0.00416 0.00004 0.51 26.8 0.2 24 65.2 1070 835 0.04665 0.00038 0.03051 0.00038 0.00474 0.00003 1.28 30.5 0.2 25 121.5 2282 713 0.04684 0.00033 0.03017 0.00024 0.00467 0.00002 3.20 30.1 0.1 26 73.8 1364 1433 0.04789 0.00056 0.03029 0.0004 0.00459 0.00002 0.95 29.5 0.1 27 104.2 2084 694 0.04666 0.00048 0.0297 0.00033 0.00462 0.00003 3.00 29.7 0.2 28 150.7 3354 1014 0.04683 0.00028 0.02984 0.00021 0.00462 0.00002 3.31 29.7 0.1 29 52.6 1085 1270 0.04688 0.00025 0.02981 0.00028 0.00461 0.00004 0.85 29.7 0.2 30 34.8 724 881 0.04804 0.00039 0.0309 0.00036 0.00467 0.00004 0.82 30.0 0.3 T0911-J花岗闪长岩 01 95.5 1263 1177 0.06400 0.00141 0.04186 0.00098 0.00475 0.00005 1.07 30.6 0.3 02 51.9 904 558 0.04665 0.00049 0.02927 0.00042 0.00455 0.00005 1.62 29.3 0.3 03 64.9 1104 591 0.04966 0.00052 0.03138 0.00043 0.00458 0.00004 1.87 29.5 0.2 04 47.1 855 499 0.04695 0.00048 0.02937 0.00034 0.00454 0.00002 1.71 29.2 0.2 05 55.3 873 523 0.04775 0.00046 0.03033 0.00030 0.00461 0.00002 1.67 29.6 0.1 06 66.0 1101 526 0.04778 0.00039 0.02997 0.00026 0.00455 0.00002 2.09 29.3 0.1 07 85.5 1383 655 0.04685 0.00034 0.02951 0.00023 0.00457 0.00002 2.11 29.4 0.1 08 175.9 2292 2079 0.05600 0.00036 0.03746 0.00031 0.00485 0.00003 1.10 31.2 0.2 09 52.9 830 498 0.05089 0.00042 0.03217 0.00030 0.00458 0.00002 1.67 29.5 0.1 10 33.2 445 344 0.04810 0.00047 0.03049 0.00030 0.00460 0.00002 1.29 29.6 0.1 11 991.1 608 391 0.59600 0.00213 1.29868 0.01251 0.01577 0.00011 1.55 100.8 0.7 12 45.4 447 334 0.07900 0.00216 0.05261 0.00164 0.00476 0.00003 1.34 30.6 0.2 13 66.2 997 566 0.04801 0.00040 0.03047 0.00027 0.00461 0.00002 1.76 29.6 0.1 14 33.3 471 346 0.04832 0.00044 0.03029 0.00029 0.00455 0.00002 1.36 29.3 0.1 15 47.2 766 437 0.04781 0.00065 0.03028 0.00042 0.00460 0.00002 1.75 29.6 0.1 16 54.7 720 418 0.05640 0.00086 0.03693 0.00058 0.00475 0.00002 1.72 30.6 0.1 17 67.0 984 520 0.04734 0.00051 0.03003 0.00033 0.00460 0.00002 1.89 29.6 0.1 18 57.8 885 513 0.04785 0.00045 0.03022 0.00028 0.00459 0.00002 1.73 29.5 0.1 19 52.0 832 484 0.04818 0.00049 0.03046 0.00034 0.00459 0.00003 1.72 29.5 0.2 20 70.4 992 554 0.04705 0.00049 0.02981 0.00036 0.00459 0.00003 1.79 29.5 0.2 21 512.4 1678 428 0.04888 0.00019 0.14765 0.00078 0.02191 0.00008 3.92 139.7 0.5 22 79.4 1168 639 0.05110 0.00040 0.03248 0.00030 0.00461 0.00002 1.83 29.6 0.1 23 43.8 655 407 0.04808 0.00053 0.03027 0.00039 0.00457 0.00003 1.61 29.4 0.2 24 54.9 742 518 0.04850 0.00047 0.03050 0.00036 0.00456 0.00004 1.43 29.4 0.2 25 57.4 715 1136 0.05209 0.00035 0.03431 0.00028 0.00478 0.00003 0.63 30.7 0.2 2.2 全岩地球化学测试
主量及微量元素测试在国土资源部国家地质实验测试中心进行。主量元素通过XRF（X荧光光谱仪3080E）方法测试，分析精度为5%。微量和稀土元素（REE）通过等离子质谱仪（ICP-MS-Excell）分析，含量大于10×10-6的元素测试精度为5%，小于10×10-6的元素测试精度为10%。样品中含量低的个别元素，测试误差大于10%，分析结果见表 3。
表 3 冈底斯程巴岩体花岗闪长岩和细粒闪长质包体元素和Rb-Sr、Sm-Nd同位素组成Table 3. Major and trace element and Sr-Nd isotopic compositions of granodiorite and dioritic enclaves from the Chengba Complex样品原号 T0911-A1 T0911-A2 T0911-A3 T0911-A4 T0911-A5 T0911-J1 T0911-J2 T0911-C1 T0911-C2 T0911-C3 T0911-C4 T0911-C5 岩性 花岗闪长岩 花岗闪长岩 细粒闪长质包体 SiO2 65.62 65.74 65.24 65.43 66.16 64.94 64.13 56.15 54.37 54.05 55.47 53.02 TiO2 0.53 0.51 0.49 0.52 0.45 0.49 0.53 0.79 0.94 0.89 0.87 1.03 Al2O3 15.30 15.09 15.25 15.29 15.68 15.47 15.46 15.99 15.58 17.30 16.93 17.62 FeO 1.53 1.67 1.45 1.38 1.49 1.42 1.92 3.43 3.93 3.86 3.29 3.97 Fe2O3 2.45 2.15 2.36 2.45 1.80 2.22 1.91 2.80 2.96 4.24 2.86 3.19 MnO 0.07 0.07 0.07 0.06 0.06 0.06 0.07 0.14 0.20 0.15 0.13 0.14 MgO 2.06 2.01 2.02 2.02 1.75 2.04 2.26 5.20 6.15 4.42 4.07 5.03 CaO 3.74 3.49 3.49 3.49 3.35 3.50 3.99 6.55 7.24 5.93 5.82 5.97 Na2O 4.17 3.94 3.94 3.94 4.11 3.98 4.24 4.39 4.67 5.32 4.44 4.73 K2O 3.32 3.72 3.77 3.89 4.03 4.28 3.38 2.18 1.53 1.77 3.55 2.44 P2O3 0.28 0.28 0.27 0.27 0.24 0.26 0.29 0.32 0.50 0.47 0.77 0.61 Mg# 49.58 49.85 50.19 50.11 50.08 51.55 52.54 60.91 62.44 50.65 55.30 56.72 Na2O/K2O 1.26 1.06 1.05 1.01 1.02 0.93 1.25 2.01 3.05 3.01 1.25 1.94 TFeO 3.74 3.61 3.57 3.59 3.11 3.42 3.64 5.95 6.59 7.68 5.86 6.84 烧失量 0.56 0.49 0.46 0.58 0.43 0.64 0.61 1.25 0.99 0.92 0.84 0.98 总量 99.63 99.16 98.81 99.32 99.55 99.30 98.79 99.19 99.06 99.32 99.04 98.73 Sc 6.94 6.50 6.97 6.16 5.89 6.75 7.86 20.50 17.80 18.80 14.50 14.30 V 81.40 79.10 81.40 79.80 69.70 75.60 83.20 141.00 150.00 200.00 137.00 164.00 Cr 34.50 30.10 71.70 30.80 24.80 31.20 31.20 112.00 191.00 28.40 49.10 33.00 Ni 20.50 19.70 40.30 19.60 15.70 19.00 20.40 38.50 67.20 26.90 39.30 50.30 Co 10.40 10.40 11.00 10.80 8.87 10.20 11.50 21.30 25.70 23.50 20.20 26.40 Cu 17.40 20.30 819.00 262.00 14.20 19.40 15.80 79.30 40.30 47.00 30.10 71.10 Zn 56.20 53.50 53.50 54.00 49.40 45.90 44.70 81.60 112.00 111.00 97.00 115.00 Ga 18.30 17.80 18.90 18.70 18.00 17.70 18.70 17.60 20.30 24.30 21.90 23.00 Rb 130.00 146.00 140.00 154.00 154.00 156.00 142.00 130.00 107.00 153.00 194.00 251.00 Sr 785.00 769.00 774.00 782.00 813.00 838.00 860.00 626.00 545.00 677.00 695.00 676.00 Y 12.00 11.20 12.20 11.60 9.89 10.10 11.50 12.70 18.60 15.00 18.10 14.70 Zr 183.00 176.00 172.00 188.00 155.00 164.00 203.00 110.00 160.00 181.00 116.00 238.00 Nb 14.70 13.20 14.50 14.30 12.20 12.20 12.60 10.10 15.30 12.00 14.70 11.60 Mo 1.54 1.40 49.70 1.96 1.14 1.41 1.42 1.82 1.05 1.08 0.86 0.66 Sn 1.30 1.21 1.37 1.43 1.05 1.21 1.35 1.75 2.43 1.86 1.31 1.67 Cs 8.13 8.13 8.03 8.60 8.28 7.83 7.97 12.70 15.80 18.60 13.70 29.20 Ba 793.00 970.00 1, 013.00 1, 120.00 1, 238.00 1, 520.00 902.00 432.00 274.00 300.00 895.00 438.00 Hf 5.08 4.78 4.66 5.05 4.27 4.35 5.39 3.84 4.50 4.91 2.78 6.26 Ta 1.47 1.30 1.50 1.34 1.16 1.04 1.12 0.59 0.89 0.52 0.87 0.46 W 5.88 6.57 3.58 7.30 3.06 3.83 2.45 9.23 0.95 2.70 0.70 0.94 Tl 0.90 1.03 1.02 1.05 1.05 0.95 0.80 0.99 0.84 1.14 1.26 1.80 Pb 30.30 32.30 30.90 32.80 34.80 29.00 25.40 27.50 19.90 23.20 32.60 19.90 Th 35.80 38.50 36.50 37.00 37.50 38.90 33.80 20.10 40.70 12.80 65.80 29.30 U 7.46 8.15 8.33 9.49 8.16 9.15 9.45 7.75 8.09 5.52 10.10 7.97 La 62.40 59.50 59.10 60.00 53.80 68.20 58.50 54.70 84.00 69.20 157.00 87.70 Ce 116.00 111.00 110.00 111.00 98.90 111.00 112.00 96.80 161.00 112.00 282.00 146.00 Pr 13.00 12.10 12.60 12.40 11.00 11.80 12.80 10.80 19.40 12.50 31.30 16.10 Nd 45.30 43.10 43.90 44.60 38.50 41.10 45.30 40.80 75.90 48.00 111.00 60.90 Sm 6.79 6.35 6.83 6.46 5.74 5.93 6.75 6.71 12.80 8.40 16.30 10.00 Eu 1.47 1.43 1.47 1.41 1.38 1.48 1.63 1.43 1.75 1.20 1.68 1.35 Gd 4.05 3.82 3.92 3.67 3.49 3.66 4.02 4.52 7.14 5.23 8.90 6.70 Tb 0.68 0.62 0.68 0.67 0.56 0.58 0.67 0.71 1.15 0.88 1.39 0.97 Dy 2.52 2.55 2.71 2.48 2.20 2.26 2.49 2.92 4.52 3.46 4.46 3.49 Ho 0.48 0.42 0.48 0.43 0.40 0.40 0.45 0.57 0.79 0.63 0.70 0.62 Er 1.45 1.38 1.49 1.40 1.19 1.33 1.47 1.63 2.33 1.88 2.31 1.84 Tm 0.17 0.16 0.17 0.17 0.12 0.14 0.16 0.20 0.26 0.21 0.21 0.19 Yb 1.15 1.11 1.13 1.15 0.97 1.02 1.02 1.28 1.81 1.29 1.45 1.26 Lu 0.17 0.16 0.17 0.16 0.14 0.15 0.18 0.20 0.26 0.19 0.20 0.17 Sr/Y 65.42 68.66 63.44 67.41 82.20 82.97 74.78 49.29 29.30 45.13 38.40 45.99 Nb/Ta 10.00 10.15 9.67 10.67 10.52 11.73 11.25 17.12 17.19 23.08 16.90 25.22 La/Sm 9.19 9.37 8.65 9.29 9.37 11.50 8.67 8.15 6.56 8.24 9.63 8.77 Rb/Sr 0.17 0.19 0.18 0.20 0.19 0.19 0.17 0.21 0.20 0.23 0.28 0.37 Sm/Nd 0.15 0.15 0.16 0.14 0.15 0.14 0.15 0.16 0.17 0.18 0.15 0.16 87Rb/86Sr 0.479 0.549 0.523 0.569 0.548 0.539 0.478 0.601 0.568 0.654 0.807 1.074 87Sr/86Sr 0.706423 0.706431 0.706447 0.706458 0.706465 0.706430 0.706392 0.706533 0.706522 0.706535 0.706671 0.706771 l47Sm/l44Nd 0.091 0.089 0.094 0.088 0.090 0.087 0.090 0.099 0.102 0.106 0.089 0.099 l43Nd/l44Nd 0.512470 0.512466 0.512460 0.512437 0.512480 0.512456 0.512395 0.512428 0.512415 0.512483 0.512327 0.512383 εNd(t) -3.10 -3.17 -3.32 -3.73 -2.90 -3.35 -4.56 -3.97 -4.24 -2.94 -5.88 -4.85 注：主量元素含量单位为%，微量和稀土元素含量为10-6；T0911-A（A1-A5）系列与T0911-J（J1-J5）系列岩性为花岗闪长岩，T0911-C系列岩性为细粒闪长质包体；Mg#=100×Mg2+/(Mg2++Fe2+)；TFeO=FeO+Fe2O3×0.899；Eu/Eu*=EuN/(SmN×GdN)1/2；87Sr/86Sr(i)=87Sr/ 86Sr-87Rb/86Sr(eλt-1)，其中λ=1.42×10-11a-1, t=30Ma; 143Nd/ 144Nd(i)=143Nd/ 144Nd-147Sm/ 144Nd(eλt-1), 143Nd/ 144Nd (CHUR)=143Nd/ 144Nd-147Sm/ 144Nd(eλt-1)，其中143Nd/144Nd=0.512638, 147Sm/144Nd=0.1967, 其中λ=6.54×10-11a-1, t=35Ma, εNd(i)=[143Nd144Nd(i)143Nd144Nd(i)143Nd144Nd(CHUR)−1]×104 2.3 锆石Hf同位素测试
锆石Hf同位素测试在中国地质科学院矿产资源研究所成矿作用与资源评价重点实验室进行，所用仪器为Neptune多接收等离子质谱和Newwave UP213紫外激光剥蚀系统（LA-MC-ICP-MS），采用氦作为剥蚀物质载气，根据锆石大小，剥蚀直径采用55μm或40μm，测定时使用锆石标样GJ1和Plesovice作为参考物质，分析点与U-Pb年龄分析点相同或尽可能接近，分析结果见表 4。
表 4 程巴花岗闪长岩与细粒闪长质包体锆石Hf同位素数据Table 4. Zircon Hf isotopic data of granodiorite and dioritic enclaves from the Chengba Complex测点号 206Pb/238U年龄/Ma 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf 2σ 176Hf/177Hfi εHf（0） εHf（t） tDM/Ma tDMC/Ma fs T0911-A花岗闪长岩 03 29.4 0.018918 0.000895 0.282916 0.000017 0.28292 +5.10 +5.73 475 743 -0.97 04 29.5 0.018866 0.000908 0.282832 0.000016 0.28283 +2.13 +2.76 594 933 -0.97 05 29.2 0.019544 0.000827 0.282827 0.000019 0.28283 +1.95 +2.58 599 945 -0.98 06 29.5 0.024496 0.001041 0.282895 0.000019 0.28289 +4.35 +4.97 507 791 -0.97 07 29.1 0.013533 0.000681 0.282889 0.000016 0.28289 +4.13 +4.76 510 805 -0.98 08 29.3 0.018845 0.000797 0.282881 0.000019 0.28288 +3.86 +4.49 523 822 -0.98 10 29.7 0.020933 0.000978 0.282927 0.000016 0.28293 +5.49 +6.12 460 718 -0.97 12 29.6 0.014562 0.000637 0.282871 0.000018 0.28287 +3.50 +4.14 535 845 -0.98 13 34.6 0.012880 0.000568 0.282827 0.000019 0.28283 +1.94 +2.68 596 942 -0.98 16 29.2 0.012264 0.000571 0.282911 0.000017 0.28291 +4.92 +5.55 478 754 -0.98 17 30.5 0.013923 0.000647 0.282841 0.000018 0.28284 +2.43 +3.09 578 913 -0.98 19 29.5 0.016271 0.000770 0.282828 0.000017 0.28283 +1.98 +2.62 597 942 -0.98 20 29.2 0.018459 0.000782 0.282845 0.000019 0.28284 +2.59 +3.21 573 904 -0.98 21 29.5 0.016038 0.000688 0.282839 0.000018 0.28284 +2.38 +3.02 580 917 -0.98 22 29.1 0.022745 0.001068 0.282930 0.000017 0.28293 +5.59 +6.20 457 712 -0.97 23 29.8 0.023771 0.000970 0.282870 0.000017 0.28287 +3.48 +4.11 541 847 -0.97 24 29.3 0.011723 0.000513 0.282858 0.000019 0.28286 +3.04 +3.68 551 874 -0.98 25 29.9 0.018906 0.000886 0.282886 0.000018 0.28289 +4.03 +4.66 517 811 -0.97 26 30.3 0.014694 0.000692 0.282880 0.000014 0.28288 +3.83 +4.48 522 823 -0.98 30 29.8 0.012670 0.000560 0.282837 0.000018 0.28284 +2.29 +2.93 582 923 -0.98 T0911-C细粒闪长质包体 01 37.7 0.025078 0.001108 0.282823 0.000020 0.28282 +1.79 +2.59 610 950 -0.97 02 34.8 0.008204 0.000372 0.282841 0.000018 0.28284 +2.45 +3.21 573 909 -0.99 04 30.1 0.045735 0.001747 0.282883 0.000022 0.28288 +3.93 +4.56 533 818 -0.95 06 30.1 0.013025 0.000574 0.282738 0.000024 0.28274 -1.20 -0.55 720 1145 -0.98 08 30.2 0.020508 0.000944 0.282834 0.000019 0.28283 +2.20 +2.84 591 928 -0.97 09 28.9 0.024164 0.001066 0.282787 0.000020 0.28279 +0.54 +1.15 660 1035 -0.97 12 29.4 0.007083 0.000333 0.282847 0.000019 0.28285 +2.65 +3.29 564 899 -0.99 13 30.1 0.014520 0.000645 0.282787 0.000017 0.28279 +0.52 +1.17 653 1035 -0.98 15 29.8 0.011797 0.000586 0.282904 0.000018 0.2829 +4.65 +5.30 488 771 -0.98 16 29.0 0.007162 0.000344 0.282867 0.000020 0.28287 +3.36 +3.99 537 854 -0.99 17 29.4 0.016739 0.000765 0.282909 0.000016 0.28291 +4.83 +5.46 484 760 -0.98 18 35.1 0.013234 0.000603 0.282813 0.000017 0.28281 +1.44 +2.19 616 974 -0.98 20 30.4 0.010235 0.000421 0.282873 0.000019 0.28287 +3.55 +4.21 530 841 -0.99 21 29.6 0.024794 0.001104 0.282852 0.000020 0.28285 +2.83 +3.46 568 888 -0.97 23 26.8 0.014253 0.000638 0.282831 0.000020 0.28283 +2.08 +2.65 591 938 -0.98 24 30.5 0.018135 0.000831 0.282855 0.000020 0.28285 +2.95 +3.60 560 880 -0.97 26 29.5 0.014894 0.000724 0.282859 0.000016 0.28286 +3.06 +3.69 554 873 -0.98 28 29.7 0.039738 0.001742 0.282813 0.000021 0.28281 +1.46 +2.07 634 977 -0.95 29 29.7 0.014810 0.000728 0.282866 0.000017 0.28287 +3.33 +3.96 543 856 -0.98 注：εHf(t)=10000×{[(176Hf/177Hf)s-(176Lu/177Hf)s×(eλt-1)]/[(176Hf/177Hf)CHUR, 0-(176Lu/177Hf)CHUR×(eλt-1)]-1}；tDM=1/λ×ln{1+ [(176Hf/177Hf)s-(176Hf/177Hf)DM]/[(176Lu/177Hf)s-(176Lu/177Hf)DM]}.tDMC=tDM-(tDM-t)×[(fcc-fs)/(fcc-fDM)]. fLu/Hf=(176Hf/177Hf)s /(176Lu/ 177Hf)CHUR-1。λ=1.867×10-11a-1；(176Lu/177Hf)s和176Hf/177Hf)s是样品标准值；(176Lu/177Hf)CHUR=0.0332；(176Hf/177 Hf)CHUR, 0=0.282772；(176Lu/177Hf)DM=0.28325; (176Lu/177Hf)平均地壳=0.015；fcc=[(176Lu/177Hf)平均地壳/(176Lu/177Hf)CHUR]-1；fs=fLu/Hf；fDM=[(176Lu/177Hf)DM/(176Lu/177Hf)CHUR]-1；t为锆石结晶时间 2.4 全岩Sr和Nd同位素测试
Rb-Sr和Sm-Nd同位素分析在中国科技大学地球与空间科学院学院进行。使用Finnigan MAT262热离子质谱仪测得Sr同位素组成，采用同位素稀释法，用同一仪器获得Rb、Sr、Sm、Nd的浓度。利用Nu PlasamHR MC-ICP-MS多接收等离子质谱仪（Nu Instruments）进行Nd同位素分析。Nd、Sr分析结果通过标准化到146Nd/142Nd=0.7219和86Sr/88Sr=0.1194进行质量分馏校正。在分析样品期间，Sr同位素测试标准为NBS987，测试值为0.710247±12(2σ)。Nd同位素标准为JMC Nd，测试值为0.511127±12(2σ)。Sr、Nd同位素的测试精度分别为±0.000010(n=18)和±0.000011(n=18)，根据本次所得的LA-MC-ICP-MS锆石U-Pb年龄，程巴岩体花岗岩和包体形成于约30Ma。样品的Sr和Nd同位素初始值按t=30Ma计算。分析结果见表 3。
3. 测定结果
3.1 花岗闪长岩及其包体的形成时代
在花岗闪长岩样品（T0911-A和T0911-J）中，大部分锆石为无色透明，自形-半自形长柱状，棱角清晰，长度在100~200mm之间，个别达250mm，长宽比一般为2:1，个别达3:1。在阴极发光图像（图 3）上，锆石均呈现典型的韵律生长环带，为岩浆成因锆石。锆石的U、Th含量变化较大，分别为218×10-6~1664×10-6和255×10-6~2245×10-6，Th/U值为0.54~1.86。206Pb/238U年龄值变化较小，在29.1~30.3Ma之间。T0911-A除去谐和度较差（＜95%）及离群值的5个测点外，25个测点的年龄加权平均值为29.40±0.18Ma（图 4-a、b）；样品T0911-J除去谐和度较差（＜95%）及离群值的8个测点外，17个测点的年龄加权平均值为29.42±0.25Ma（图 4-e、f）。2件样品给出的U-Pb年龄相似，典型的韵律生长环带和较高的Th/U值都表明，程巴复合岩体中的主体花岗闪长岩形成于约29.4Ma。
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图 3 程巴花岗闪长岩与细粒闪长质包体锆石阴极发光（CL）图像和206Pb/238U年龄a—花岗闪长岩样品T0911-A；b—细粒闪长质包体样品T0911-C；c—花岗闪长岩样品T0911-JFigure 3. Cathodoluminescence (CL) images showing the texture and respective spots for U-Pb analysis of zircon grains from the Chengba Complex在细粒闪长质包体样品（T0911-C）中，锆石分为2类。第一类为短柱状，中心由于Th含量较高呈黑色，结构均匀，边部发育紧密韵律环带（图 3-b），颗粒较小，粒度在50~80μm之间；第二类为长板状，灰白色，长度在80~150mm之间，长宽比2.5~4。两者具有明显的韵律环带，为岩浆成因锆石，两类锆石形态虽有差异，但在元素组成上较一致，锆石的U、Th含量分别为530×10-6~7446×10-6和143×10-6~32032×10-6，Th/U值为0.27~4.3。除去谐和度较差（＜95%）的U-Pb测点外，206Pb/238U年龄变化较大，在29.0~30.6Ma之间，集中在谐和线附近，除去谐和度较差（＜95%）及离群值的11个U-Pb测点外，19个测点的年龄加权平均值为30.03±0.15Ma （图 4-c、d）。典型的韵律生长环带和较高的Th/U值表明，该年龄为细粒闪长质包体的结晶年龄。
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图 4 程巴花花岗闪长岩与细粒闪长质包体的锆石U-Pb谐和图和206Pb/238U年龄图a、b—样品T0911-A (花岗闪长岩)；c、d—样品T0911-C (细粒闪长质包体)；e、f—样品T0911-J (花岗闪长岩)Figure 4. U-Pb concordia diagram and 206Pb/238U age plot of the zircons in samples from the Chengba granodiorite and dioritic enclaves上述数据表明，在程巴复合岩体中，主体花岗闪长岩形成于约29.4Ma，但其中的细粒闪长质包体形成时间明显较早，早于花岗闪长岩0.6Ma，与姜子琦等[46]、孙祥等[47]的结果相似。
3.2 锆石Hf同位素组成
利用MC-ICP-MS对花岗闪长岩与细粒闪长质包体的锆石进行原位Hf同位素测试。花岗闪长岩与闪长质包体的锆石Hf同位素特征较一致（表 4），测试结果表明：①除个别锆石具有负εHf(t)外，花岗闪长岩和细粒闪长质包体的εHf(t)均为正值，在+1.1~+6.2之间；②176Lu/177Hf值变化较大，花岗闪长岩176Lu/177Hf值为0.00056~0.00107，细粒闪长质包体176Lu/177Hf值变化范围更大，在0.00037~0.00174之间；③锆石Hf同位素亏损地幔模式年龄（TDM）较年轻，为475~720Ma。
3.3 全岩元素地球化学特征
在主量元素组成特征上（表 3；图 5），程巴花岗闪长岩表现出以下特征：①较高的SiO2（65.2%~ 66.2%）、Al2O3（15.1% ~15.7%）含量，A/CNK较低（0.88~0.91）, 属于准铝质系列；②TFeO（3.3% ~ 4.0%）、MgO（1.8%~2.1%）、TiO2（0.5%左右）、CaO （3.4%~3.7%）含量较低；③K2O（3.2%~4.0%）和Na2O （3.9%~4.2%）含量较高，Na2O/K2O=1.0~1.3，表明该套岩石为富钠高钾钙碱性系列岩石；④Mg#变化范围小，为49.6~50.2。与花岗闪长岩相比，闪长质细粒包体表现出以下特征：①SiO2（53.0%~58.0%）含量较低；②Al2O3（15.6%~17.6%）、TFeO（36.2%~8.1%）、MgO（4.0%~6.2%）、TiO2（0.8%~1.0%）和CaO（5.8%~ 7.2%）含量都较高；③K2O（1.53%~3.55%）含量较低，但Na2O（4.4%~5.3%）含量和Na2O/K2O值（1.3~3.0）较高，该套岩石总体属于高钾钙碱性系列，个别属于钾玄岩系列（图 5）；④Mg#较高，变化范围较大，为50.7~62.4，类似于高镁安山岩-闪长岩的特征。花岗闪长岩与细粒闪长质包体的Ca、Fe、Mg、Mn、P、Ba等元素随SiO2含量变化呈线性关系（图 5）。
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图 5 程巴花岗闪长岩与细粒闪长质包体的主量元素地球化学特征Figure 5. Covariation diagram of selected major oxides of Al2O3, TFeO, CaO, MgO, K2O and Na2O versus SiO2 in the Chengba granodiorite and dioritic enclaves在微量元素组成特征上（表 3；图 6），程巴岩体花岗闪长岩与细粒闪长质包体表现出类似的特征：①轻、重稀土元素明显分馏明显，富集轻稀土元素，相对亏损重稀土元素，均表现为较高的(La/ Yb)N值，花岗闪长岩为36.7~39.0，细粒闪长质包体为30.0~76.2；②微弱负Eu异常，花岗闪长岩的Eu/ Eu ∗=0.87~0.95，细粒闪长质包体的Eu/Eu ∗=0.43~ 0.80；③富集大离子亲石元素，亏损Nb、Ta、Ti，但Zr、Hf亏损不明显。在这两类岩石中，花岗闪长岩具有高Sr（774×10-6~813×10-6）、低Y（9.9×10-6~ 11.2×10-6）、低Yb（1.0×10-6~1.2×10-6），高Sr/Y值（63.4~82.2）的特征，为埃达克质岩石。但细粒闪长质包体的Sr含量明显较低，Y含量较高，Sr/Y值（29.3~49.3）也较低（图 7），细粒闪长质包体中轻稀土元素和稀土元素总量都高于花岗闪长岩（图 6-a）。随SiO2和K2O含量的升高，Ba含量也升高（图 8），说明在程巴复合岩体中，较基性岩浆的Ba含量较低（274×10-6~895×10-6），较酸性岩浆的Ba含量的升高（790×10-6~1520×10-6）可能与后期的岩浆过程相关。
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图 6 程巴花岗闪长岩与细粒闪长质包体稀土及微量元素地球化学特征（标准化值据参考文献[52]）Figure 6. Rare earth element and trace element distribution diagram for the Chengba granodiorite and dioritic enclaves3.4 全岩Sr和Nd同位素特征
程巴复合岩体的花岗闪长岩与细粒闪长质包体具有较一致的Sr、Nd同位素组成。细粒闪长质包体具有较高的Rb、Sm、Nd和较低的Sr。花岗闪长岩Rb/Sr值变化范围为0.1651~0.1969，Sm/Nd值变化范围为0.1448~0.1556，初始87Sr/86Sr值变化范围为0.706392~0.706465，初始143Nd/144Nd值变化范围为0.512395~0.512480，εNd(t)变化范围为-2.90~-4.56。细粒闪长质包体Rb/Sr值变化范围为0.1963~0.3713，Sm/Nd值变化范围为0.1468~0.1750，初始87Sr/86Sr值变化范围为0.706522~0.706771，初始143Nd/144Nd值变化范围为0.512327~0.512483，εNd(t)变化范围为-2.94~-5.88 （表 3；图 9）。
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图 9 程巴岩体143Nd/144Nd-87Sr/86Sr (a)和SiO2-εNd(t)(b)关系Figure 9. Co-variation diagrams showing the relationship of 143Nd/144Nd-87Sr/86Sr (a) and SiO2-εNd(t)(b)4. 讨论
上述数据表明：①程巴复合岩体的花岗闪长岩与细粒闪长质包体形成于29.4~30.2Ma，与前人的地质年代学结果[12, 20, 44-47]相似；②这2种岩石的锆石Hf同位素及全岩Sr、Nd同位素特征差别很小；③花岗闪长岩与细粒闪长质包体的Ca、Fe、Mg、Mn、P等元素随SiO2含量变化呈线性关系；④花岗闪长岩Sr/Y值（63.4~82.2）高（图 7-a），Mg#和Na/K值均较高，与冈底斯中带古近纪—新近纪高Sr/Y值的埃达克质岩石地球化学特征相似。
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图 7 程巴岩体Y-Sr/Y与La-La/Sm图解Figure 7. Discrimination diagrams of Sr/Y ratios versus Y and La/Sm ratios versus La values for the Chengba Complex西藏渐新世—中新世冈底斯岩基高Sr/Y值的岩浆岩被认为形成于相同的大地构造背景，但对其形成机理存在不同的认识。主要模型包括：①古老增厚基性下地壳的部分熔融作用[4, 24]；②新生铁镁质下地壳部分熔融形成[5, 45]；③俯冲过程中，洋壳板片部分熔融释放的熔体或流体交代上地幔形成[22, 53-54]。程巴岩体位于冈底斯岩基南缘，冈底斯逆冲推覆带的上盘，紧接喜马拉雅造山带，在形成时间节点上，处于印度-欧亚大陆碰撞造山作用的关键转换期，无论在构造位置上，还是在碰撞造山作用时段上，都处于关键位置，是研究探讨大陆碰撞造山作用的深部岩石圈构造动力学过程与高Sr/Y值的岩浆岩形成机理重要的野外实验室。
4.1 程巴岩体的源区特征
在微量地球化学元素组成上，程巴花岗闪长岩与细粒闪长质包体的特征相似（图 6-b），均表现出富集大离子亲石元素（Rb、Ba、Th、U、K和Pb）, 亏损高场强元素（Nb、Ta和Ti），具有类似岛弧岩浆岩的特征，但Zr、Hf亏损不明显，说明锆石等矿物在岩浆中溶解度较高。这些特征说明，形成程巴花岗闪长岩和闪长质包体需要富集组分的加入。在岩浆岩中，导致Nb、Ta和Ti强烈亏损的因素主要有2种：①在洋壳俯冲过程中，俯冲板片发生脱水或部分熔融作用，残留富钛矿物相，产生的流体或熔体亏损Nb、Ta和Ti。这种熔/流体交代上覆地幔楔[55-56]，导致源区亏损Nb、Ta和Ti；②在增厚下地壳或俯冲带环境下，基性物质部分熔融过程中，残留大量金红石等含钛矿物，导致派生熔体亏损Nb、Ta和Ti[5, 29]。实验岩石学数据表明，在15~25kbar和850~1050℃条件下，玄武质下地壳或榴辉岩发生部分熔融，在形成亏损Nb、Ta、Ti硅酸质岩浆的同时，形成含金红石的榴辉质残留物[57-59]。上述2种过程都可能导致冈底斯岩基高Sr/Y值的岩浆岩强烈亏损高场强元素Nb、Ta和Ti。
与亏损地幔相比，程巴岩体高Sr/Y值的花岗闪长岩与细粒闪长质包体均具有较高的Sr（87Sr/86Sr(t) > 0.7060），较低的Nd（εNd(t) <-2.0)和Hf(εHf(t) < +7.0)同位素组成，可以排除其为亏损地幔直接部分熔融的产物。上述特征也表明，形成程巴花岗闪长岩和闪长质包体需要富集组分的加入，来源可能是：①古老基性下地壳；②新生下地壳；③经过流体或熔体交代的岩石圈地幔。与喜马拉雅地块相似，拉萨地块来源于冈瓦那大陆北缘，在新特提斯洋俯冲之前，其下地壳物质应与喜马拉雅相似，基性下地壳应表现为高度富集的Nd（εNd <-10.0）和Hf（εHf <-12.0）同位素组成特征[6, 13, 39-40, 60]。如果是直接来源于古老基性下地壳的部分熔融，产生的熔体应具有类似的高度富集的Nd和Hf同位素组成，这与程巴岩浆岩的特征相悖，因此可以排除该套岩浆岩是古老下地壳部分熔融的产物。
程巴岩体高Sr/Y值的花岗闪长岩与细粒闪长质包体全岩Nd同位素组成一致，两者εNd(t)=-2.9~-5.9，都具有负的εNd(t)值，初始143Nd/144Nd值变化范围为0.512327~0.512483，低于上地幔的εNd(t)=+13~+18及143Nd/144Nd值（0.51315）。从锆石Hf同位素分析，除个别锆石具有负的εHf(t)外，花岗闪长岩和细粒闪长质包体的εHf(t)均为正值，在+1.1~+6.2之间，也低于上地幔的εHf(t)=+15~+20。相较上地幔，花岗闪长岩与闪长质包体较低的εNd(t)与εHf(t)都表明有富集组分的加入，且两者较一致的εNd(t)与εHf(t)并不随SiO2含量的增加而变化（图 9），说明富集组分并未在岩浆演化过程中加入，并不是岩浆混合或后期混染作用造成的，而是源区有富集组分的加入。如果是新生下地壳的部分熔融，可以形成同位素特征类似于程巴岩体的酸性岩浆，但不能解释玄武安山质-安山质的包体，在Ba-Si和Ba-K关系图上（图 8），随SiO2和K2O含量的升高，Ba含量随之升高，说明花岗闪长岩的包体更接近于原始岩浆，但基性下地壳的部分熔融较难于形成安山质的熔体[61-62]，需要超镁铁质岩石的部分熔融。上述分析表明，程巴岩浆岩的源区应是具有富集组分的岩石圈地幔。
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图 8 程巴岩体SiO2-Ba(a)和K2O-Ba（b）关系Figure 8. Co-variation diagrams showing the relationship between SiO2 and Ba (a) and between K2O and Ba (b)4.2 程巴岩体高Sr/Y值花岗闪长岩的成因机制
在程巴岩体中，主体花岗闪长岩表现出明显的高Sr、低Y和高Sr/Y值的特征，但其中包含的细粒闪长质包体并未表现出类似的特征。较高的Mg#、较低的SiO2和较早的形成时代表明，细粒闪长质包体可能是较原始的岩浆。程巴岩体花岗闪长岩形成时间为29.40±0.18Ma和29.42±0.25Ma，细粒闪长质包体形成时间为30.02±0.15Ma，两者形成时间在误差范围内一致，表明花岗闪长岩和细粒闪长质包体是近同时形成的。在全岩微量元素（图 6-b）、锆石Hf同位素及全岩Sr和Nd同位素组成上，两者的地球化学特征较一致，说明两者源区可能相同，是经历了同种岩浆的分离结晶作用形成的。与花岗闪长岩相比，细粒闪长质包体更富集LREE（图 6-a），Sr/Y值较低，且两者的主量元素特征差异较大。La/Sm-La演化关系显示，两者之间存在明显的分离结晶关系（图 7-b），同时细粒闪长质包体含有大量针状磷灰石，磷灰石含量明显高于花岗闪长岩。以上特征表明，花岗闪长岩可能经历了磷灰石分离结晶作用，Harrison等[63]通过实验指出，磷在熔体中的溶解行为表明，SiO2含量与磷的溶解度呈负相关，岩相学特征也表明细粒闪长质包体含有大量针状磷灰石，而花岗闪长岩具有少量较大颗粒的磷灰石，以上证据都符合花岗闪长岩经历了磷灰石的分离结晶作用，从而导致LREE与磷含量的降低（图 10）。但磷灰石的分离结晶作用并不能解释两者其他主、微量元素的明显差异，细粒闪长质包体具有较高的Ca、Fe、Mg和Mn（图 5、图 11），如果以细粒闪长质包体为原始岩浆，那么角闪石的分离结晶能解释上述特征，因为角闪石中具有较高的Mg#值、Cr、Ni、Y及较低的SiO2、K、Ba、Sr，角闪石的分离结晶会使花岗闪长岩具有向高Si，高K、高Sr/Y值，低Mg#，以及较低的Cr、Ni、Y等微量元素特征演化。此外，实验岩石学表明，角闪石中的DNb > DTa [58]，角闪石的分离结晶或残留会导致熔体的Nb/Ta值降低，与细粒闪长质包体相比，花岗闪长岩具有较低的Nb/Ta值符合上述结论（图 11）。大量研究和实验也表明，角闪石从钙碱性及饱和水原始安山岩浆中分离结晶[64-67]。综上所述，程巴岩体花岗闪长岩与细粒闪长质包体在形成时间、锆石Hf同位素、全岩Sr、Nd同位素等方面差别甚微，但在元素地球化学特征上具有明显的差异，可能表明花岗闪长岩与细粒闪长质包体由同一岩浆分离结晶形成，花岗闪长岩经历较高程度的磷灰石和角闪石的分离结晶。
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图 10 磷灰石分离结晶所导致的P2O5-La(a)及SiO2-P2O5(b)关系Figure 10. Co-variation diagrams showing the relationship of P2O5-La (a) and SiO2-P2O5 (b)![]()
图 11 角闪石分离结晶导致的SiO2-MnO(a)和Mg#-Nb/Ta(b)关系Figure 11. Co-variation diagrams showing the relationship of SiO2-MnO (a) and Mg#-Nb/Ta (b)上述分析表明，程巴岩浆岩的源区应该是具有富集组分的岩石圈地幔，可能是俯冲板片脱水释放流体交代过的SCLM（陆下岩石圈地幔）。渐新世—中新世，冈底斯高Sr/Y值的岩浆岩形成于后碰撞阶段，此阶段已不存在洋壳俯冲作用，不可能是洋壳俯冲的直接结果。在印度-欧亚大陆碰撞前，位于俯冲带上盘的拉萨地块的岩石圈经历了长期俯冲的新特提斯洋板片释放的熔体或流体交代作用，形成富集岩石圈地幔。在65~45Ma期间，印度与亚洲发生陆陆碰撞[67-74]及俯冲特提斯洋壳板片断离作用[12, 45, 75]，导致软流圈地幔的上涌和诱发岩石圈地幔或基性下地壳部分熔融作用，富集岩石圈部分熔融，形成类似程巴闪长质包体的高镁安山质熔体，在上侵过程中发生分离结晶作用形成程巴花岗闪长岩，而基性下地壳的部分熔融，形成富钠、高Sr/Y值的花岗质岩浆[26, 76]。
孙祥等[47]指出，位于程巴岩体东侧附近的明则岩体二长岩与程巴岩体细粒闪长质包体的地球化学特征和形成时间一致，两者为同一机制形成的。因此表明，形成程巴岩体及明则岩体的原始岩浆至少分离结晶形成花岗闪长岩与闪长质包体2种岩性，更加接近原始岩浆的细粒闪长质包体虽具有较高的（La/Yb）N值，但其较低的Sr/Y值并不符合埃达克岩特征；符合埃达克质岩石地球化学特征的花岗闪长岩虽具有高的Sr/Y值（图 7），但与闪长质包体相比，其明显经历了磷灰石、角闪石等矿物的分离结晶作用，并不代表原始熔体，不能反映源区的地球化学特征。高Sr/Y值等地球化学特征是岩浆分离结晶的结果。虽然程巴高镁闪长质包体具有接近于原始岩浆的特征，但是否还存在更原始的岩浆，还需进一步的地质调查和地球化学研究。
5. 结论
通过对程巴岩体花岗闪长岩与细粒闪长质包体的年代学、岩相学和地球化学研究，结合前人的数据获得以下认识。
（1）程巴岩体花岗闪长岩与细粒闪长岩具有较一致的年龄、微量元素特征、锆石Hf同位素（εHf(t)=+ 1.1~ + 6.2）和全岩Sr、Nd同位素特征（εNd(t)=-2.9~-5.9）。
（2）程巴岩体花岗闪长岩与细粒闪长岩源区为具有富集组分的岩石圈地幔，为同源岩浆经历分离结晶形成的，与具有接近于原始岩浆特征的细粒闪长质包体相比，花岗闪长岩经历了磷灰石、角闪石等矿物的分离结晶，高Sr/Y值是岩浆分离结晶的结果，并不代表原始岩浆的地球化学特征。
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图 1 藏南新生代岩浆分布图（a）（据参考文献[4]修改）与程巴岩体地质图（b）
MCT—主中央逆冲断裂；STDS—藏南拆离系；ITS—雅鲁藏布江缝合带；BNS—班公湖怒江缝合带
Figure 1. Geological map showing the distribution of Cenozoic magmatic rocks in southern Tibet (a) and geological map of the Chengba Complex (b)
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图 2 程巴花岗闪长岩及细粒闪长质包体野外和镜下照片
a—野外露头；b—花岗闪长岩及细粒闪长质包体；c—花岗闪长岩镜下照片（单偏光）；d—细粒闪长质包体镜下照片（单偏光）。Amp—角闪石；Bt—黑云母；Pl—斜长石；Tnt—榍石；Kf—钾长石；Ap—磷灰石；Qtz—石英
Figure 2. Field photographs and microphotographs of granodiorite and dioritic enclaves from the Chengba Complex
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图 3 程巴花岗闪长岩与细粒闪长质包体锆石阴极发光（CL）图像和206Pb/238U年龄
a—花岗闪长岩样品T0911-A；b—细粒闪长质包体样品T0911-C；c—花岗闪长岩样品T0911-J
Figure 3. Cathodoluminescence (CL) images showing the texture and respective spots for U-Pb analysis of zircon grains from the Chengba Complex
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图 4 程巴花花岗闪长岩与细粒闪长质包体的锆石U-Pb谐和图和206Pb/238U年龄图
a、b—样品T0911-A (花岗闪长岩)；c、d—样品T0911-C (细粒闪长质包体)；e、f—样品T0911-J (花岗闪长岩)
Figure 4. U-Pb concordia diagram and 206Pb/238U age plot of the zircons in samples from the Chengba granodiorite and dioritic enclaves
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图 5 程巴花岗闪长岩与细粒闪长质包体的主量元素地球化学特征
Figure 5. Covariation diagram of selected major oxides of Al2O3, TFeO, CaO, MgO, K2O and Na2O versus SiO2 in the Chengba granodiorite and dioritic enclaves
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图 6 程巴花岗闪长岩与细粒闪长质包体稀土及微量元素地球化学特征（标准化值据参考文献[52]）
Figure 6. Rare earth element and trace element distribution diagram for the Chengba granodiorite and dioritic enclaves
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图 9 程巴岩体143Nd/144Nd-87Sr/86Sr (a)和SiO2-εNd(t)(b)关系
Figure 9. Co-variation diagrams showing the relationship of 143Nd/144Nd-87Sr/86Sr (a) and SiO2-εNd(t)(b)
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图 7 程巴岩体Y-Sr/Y与La-La/Sm图解
Figure 7. Discrimination diagrams of Sr/Y ratios versus Y and La/Sm ratios versus La values for the Chengba Complex
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图 8 程巴岩体SiO2-Ba(a)和K2O-Ba（b）关系
Figure 8. Co-variation diagrams showing the relationship between SiO2 and Ba (a) and between K2O and Ba (b)
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图 10 磷灰石分离结晶所导致的P2O5-La(a)及SiO2-P2O5(b)关系
Figure 10. Co-variation diagrams showing the relationship of P2O5-La (a) and SiO2-P2O5 (b)
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图 11 角闪石分离结晶导致的SiO2-MnO(a)和Mg#-Nb/Ta(b)关系
Figure 11. Co-variation diagrams showing the relationship of SiO2-MnO (a) and Mg#-Nb/Ta (b)
表 1 西藏南部冈底斯岩基程巴-冲木达岩体年龄
Table 1 Summary of previous dating results for the Chengba-Chongmuda Complex, southern Tibet
采样区域及样品 测试对象及方法 年龄/Ma 数据来源 程巴(Yaja)岩体花岗闪长岩 锆石U-Pb 30.42±0.21 Harrison[44] 冲木达矿区花岗闪长质围岩 角闪石K-Ar 21.5±1.9 李光明等[48] 程巴岩体花岗闪长岩 锆石U-Pb 30.3±0.6, 31.0±0.5 Chung[30] 冲木达矿区花岗闪长质围岩 黑云母40Ar/39Ar 28.9±1.4 李光明等[49] 冲木达岩体花岗闪长岩与喑色包体 锆石U-Pb 30.2±0.7, 31.0±0.5 姜子琦等[46] 程巴-冲木达岩体花岗闪长岩等 锆石U-Pb 29.82±0.27 侯增谦[20] 程巴矿区辉钼矿 辉钼矿Re-Os 30.2±0.9 孙祥等[47] 程巴岩体花岗闪长岩与明则岩体二长岩 锆石U-Pb 28.4±0.4, 30.4±0.6 孙祥等[47] 
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表 2 程巴花岗闪长岩与细粒闪长质包体LA-ICP-MS锆石U-Th-Pb定年数据
Table 2 LA-ICP-MS zircon U-Th-Pb isotopic analyses of granodiorite and dioritic enclaves from the Chengba Complex
测点号 元素含量/10-6 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ Th/U 年龄/Ma
206Pb/238U1σ Pb(Total) 232Th 238U T0911-A花岗闪长岩 01 58.6 599 442 0.0968 0.00117 0.06757 0.00178 0.00505 0.00011 1.35 32.5 0.7 02 38.2 650 490 0.04906 0.00049 0.03054 0.00042 0.00452 0.00005 1.33 29.1 0.3 03 48.4 818 495 0.04924 0.00076 0.0312 0.00077 0.00456 0.00006 1.65 29.4 0.4 04 41.8 667 1106 0.04706 0.00029 0.02979 0.00046 0.00458 0.00006 0.60 29.5 0.4 05 99.9 1713 1499 0.04668 0.00028 0.02928 0.00041 0.00455 0.00005 1.14 29.2 0.3 06 74.9 1269 1559 0.04726 0.00028 0.02991 0.00038 0.00459 0.00005 0.81 29.5 0.3 07 35.6 625 587 0.04696 0.00036 0.02921 0.00039 0.00452 0.00005 1.07 29.1 0.3 08 14.6 256 219 0.04759 0.00055 0.02989 0.00048 0.00456 0.00005 1.17 29.3 0.3 09 39.8 658 506 0.04702 0.0004 0.02976 0.00045 0.00460 0.00006 1.30 29.6 0.4 10 74.1 1357 765 0.04694 0.00036 0.03 0.00059 0.00462 0.00007 1.77 29.7 0.5 11 41.7 696 1062 0.0467 0.00029 0.02925 0.00055 0.00454 0.00008 0.66 29.2 0.5 12 36.6 599 435 0.05075 0.00054 0.0321 0.00051 0.00459 0.00006 1.38 29.6 0.4 13 96.1 651 426 0.16179 0.0066 0.12426 0.00683 0.00538 0.00014 1.53 34.6 0.9 14 27.4 545 392 0.0486 0.00059 0.03047 0.00049 0.00453 0.00002 1.39 29.1 0.1 15 114.1 2245 1664 0.04773 0.00055 0.03108 0.00066 0.00469 0.00004 1.35 30.1 0.3 16 46.4 862 527 0.05104 0.00041 0.03195 0.00028 0.00454 0.00002 1.64 29.2 0.1 17 56.9 744 381 0.08921 0.00125 0.05831 0.00085 0.00474 0.00002 1.95 30.5 0.1 18 28.2 612 402 0.04765 0.00049 0.0301 0.00031 0.00459 0.00002 1.52 29.5 0.1 19 54.8 1018 1239 0.04691 0.00042 0.0299 0.00056 0.00459 0.00004 0.82 29.5 0.2 20 35.7 735 395 0.04814 0.00054 0.03021 0.00042 0.00454 0.00003 1.86 29.2 0.2 21 37.6 731 497 0.04817 0.00037 0.0304 0.00025 0.00458 0.00002 1.47 29.5 0.1 22 30.1 582 803 0.04671 0.00028 0.02914 0.00021 0.00453 0.00002 0.73 29.1 0.1 23 47 935 1263 0.04741 0.00024 0.03023 0.00018 0.00463 0.00002 0.74 29.8 0.1 24 29.2 551 410 0.04794 0.00062 0.03045 0.00075 0.00455 0.00004 1.35 29.3 0.2 25 38.9 691 1289 0.04727 0.0004 0.03043 0.00057 0.00466 0.00007 0.54 29.9 0.4 26 52.3 880 1526 0.04661 0.00033 0.03034 0.00048 0.00471 0.00006 0.58 30.3 0.4 27 46.5 773 1158 0.04696 0.00098 0.03031 0.00078 0.00469 0.0001 0.67 30.1 0.7 28 30.8 527 413 0.04723 0.00048 0.02991 0.00031 0.00460 0.00003 1.28 29.6 0.2 29 47.7 834 1222 0.04663 0.00025 0.03 0.00023 0.00467 0.00003 0.68 30 0.2 30 44.5 770 498 0.04702 0.00045 0.03001 0.00036 0.00463 0.00003 1.55 29.8 0.2 T0911-C细粒闪长质包体 01 180.5 4711 3457 0.04633 0.00015 0.03744 0.00036 0.00586 0.00005 1.36 37.7 0.4 02 10.4 232 234 0.05143 0.00056 0.03844 0.0007 0.00541 0.00007 0.99 34.8 0.5 03 204.6 4298 2585 0.05817 0.00402 0.09564 0.02193 0.00888 0.00153 1.66 57 9.8 04 440 9093 4047 0.04662 0.00035 0.03018 0.0009 0.00468 0.00012 2.25 30.1 0.8 05 143.4 2821 1418 0.04669 0.00024 0.02972 0.00037 0.00462 0.00006 1.99 29.7 0.4 06 206.5 4064 2122 0.04701 0.00029 0.03052 0.00058 0.00469 0.00006 1.92 30.1 0.4 07 1611.8 32032 7447 0.04868 0.00013 0.031 0.00033 0.00462 0.00005 4.30 29.7 0.3 08 75 1345 1682 0.04714 0.0002 0.03051 0.00027 0.00470 0.00004 0.80 30.2 0.2 09 81.2 1555 564 0.05203 0.0008 0.03217 0.00067 0.00450 0.00007 2.76 28.9 0.5 10 275.3 5305 1841 0.04657 0.00027 0.03024 0.00042 0.00470 0.00005 2.88 30.2 0.3 11 264.7 5217 2895 0.04778 0.00031 0.03076 0.00045 0.00466 0.00005 1.80 29.9 0.3 12 23.6 442 538 0.04822 0.00065 0.03075 0.00088 0.00457 0.00006 0.82 29.4 0.4 13 148.6 2852 962 0.05054 0.00038 0.03258 0.00043 0.00468 0.00005 2.96 30.1 0.3 14 203.5 2826 980 0.09401 0.00145 0.05959 0.00153 0.00458 0.00009 2.88 29.5 0.6 15 92.2 1800 1866 0.04678 0.0002 0.02994 0.00048 0.00464 0.00007 0.96 29.8 0.4 16 4.5 62 458 0.04877 0.00053 0.03027 0.00046 0.00451 0.00005 0.14 29.0 0.3 17 135.1 2034 863 0.06677 0.00081 0.04219 0.00166 0.00457 0.00016 2.36 29.4 1 18 19.9 430 341 0.05102 0.00075 0.03845 0.00088 0.00546 0.00009 1.26 35.1 0.6 19 142.3 2530 910 0.04931 0.00089 0.0316 0.00092 0.00459 0.00006 2.78 29.6 0.4 20 8.5 143 530 0.04749 0.00037 0.03101 0.00039 0.00473 0.00005 0.27 30.4 0.3 21 89.6 1726 610 0.04668 0.00035 0.0296 0.00036 0.00460 0.00004 2.83 29.6 0.3 22 46.2 896 415 0.07911 0.01214 0.34549 0.19212 0.00797 0.00188 2.16 51.2 12 23 7.4 170 335 0.04962 0.00111 0.02844 0.00062 0.00416 0.00004 0.51 26.8 0.2 24 65.2 1070 835 0.04665 0.00038 0.03051 0.00038 0.00474 0.00003 1.28 30.5 0.2 25 121.5 2282 713 0.04684 0.00033 0.03017 0.00024 0.00467 0.00002 3.20 30.1 0.1 26 73.8 1364 1433 0.04789 0.00056 0.03029 0.0004 0.00459 0.00002 0.95 29.5 0.1 27 104.2 2084 694 0.04666 0.00048 0.0297 0.00033 0.00462 0.00003 3.00 29.7 0.2 28 150.7 3354 1014 0.04683 0.00028 0.02984 0.00021 0.00462 0.00002 3.31 29.7 0.1 29 52.6 1085 1270 0.04688 0.00025 0.02981 0.00028 0.00461 0.00004 0.85 29.7 0.2 30 34.8 724 881 0.04804 0.00039 0.0309 0.00036 0.00467 0.00004 0.82 30.0 0.3 T0911-J花岗闪长岩 01 95.5 1263 1177 0.06400 0.00141 0.04186 0.00098 0.00475 0.00005 1.07 30.6 0.3 02 51.9 904 558 0.04665 0.00049 0.02927 0.00042 0.00455 0.00005 1.62 29.3 0.3 03 64.9 1104 591 0.04966 0.00052 0.03138 0.00043 0.00458 0.00004 1.87 29.5 0.2 04 47.1 855 499 0.04695 0.00048 0.02937 0.00034 0.00454 0.00002 1.71 29.2 0.2 05 55.3 873 523 0.04775 0.00046 0.03033 0.00030 0.00461 0.00002 1.67 29.6 0.1 06 66.0 1101 526 0.04778 0.00039 0.02997 0.00026 0.00455 0.00002 2.09 29.3 0.1 07 85.5 1383 655 0.04685 0.00034 0.02951 0.00023 0.00457 0.00002 2.11 29.4 0.1 08 175.9 2292 2079 0.05600 0.00036 0.03746 0.00031 0.00485 0.00003 1.10 31.2 0.2 09 52.9 830 498 0.05089 0.00042 0.03217 0.00030 0.00458 0.00002 1.67 29.5 0.1 10 33.2 445 344 0.04810 0.00047 0.03049 0.00030 0.00460 0.00002 1.29 29.6 0.1 11 991.1 608 391 0.59600 0.00213 1.29868 0.01251 0.01577 0.00011 1.55 100.8 0.7 12 45.4 447 334 0.07900 0.00216 0.05261 0.00164 0.00476 0.00003 1.34 30.6 0.2 13 66.2 997 566 0.04801 0.00040 0.03047 0.00027 0.00461 0.00002 1.76 29.6 0.1 14 33.3 471 346 0.04832 0.00044 0.03029 0.00029 0.00455 0.00002 1.36 29.3 0.1 15 47.2 766 437 0.04781 0.00065 0.03028 0.00042 0.00460 0.00002 1.75 29.6 0.1 16 54.7 720 418 0.05640 0.00086 0.03693 0.00058 0.00475 0.00002 1.72 30.6 0.1 17 67.0 984 520 0.04734 0.00051 0.03003 0.00033 0.00460 0.00002 1.89 29.6 0.1 18 57.8 885 513 0.04785 0.00045 0.03022 0.00028 0.00459 0.00002 1.73 29.5 0.1 19 52.0 832 484 0.04818 0.00049 0.03046 0.00034 0.00459 0.00003 1.72 29.5 0.2 20 70.4 992 554 0.04705 0.00049 0.02981 0.00036 0.00459 0.00003 1.79 29.5 0.2 21 512.4 1678 428 0.04888 0.00019 0.14765 0.00078 0.02191 0.00008 3.92 139.7 0.5 22 79.4 1168 639 0.05110 0.00040 0.03248 0.00030 0.00461 0.00002 1.83 29.6 0.1 23 43.8 655 407 0.04808 0.00053 0.03027 0.00039 0.00457 0.00003 1.61 29.4 0.2 24 54.9 742 518 0.04850 0.00047 0.03050 0.00036 0.00456 0.00004 1.43 29.4 0.2 25 57.4 715 1136 0.05209 0.00035 0.03431 0.00028 0.00478 0.00003 0.63 30.7 0.2
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表 3 冈底斯程巴岩体花岗闪长岩和细粒闪长质包体元素和Rb-Sr、Sm-Nd同位素组成
Table 3 Major and trace element and Sr-Nd isotopic compositions of granodiorite and dioritic enclaves from the Chengba Complex
样品原号 T0911-A1 T0911-A2 T0911-A3 T0911-A4 T0911-A5 T0911-J1 T0911-J2 T0911-C1 T0911-C2 T0911-C3 T0911-C4 T0911-C5 岩性 花岗闪长岩 花岗闪长岩 细粒闪长质包体 SiO2 65.62 65.74 65.24 65.43 66.16 64.94 64.13 56.15 54.37 54.05 55.47 53.02 TiO2 0.53 0.51 0.49 0.52 0.45 0.49 0.53 0.79 0.94 0.89 0.87 1.03 Al2O3 15.30 15.09 15.25 15.29 15.68 15.47 15.46 15.99 15.58 17.30 16.93 17.62 FeO 1.53 1.67 1.45 1.38 1.49 1.42 1.92 3.43 3.93 3.86 3.29 3.97 Fe2O3 2.45 2.15 2.36 2.45 1.80 2.22 1.91 2.80 2.96 4.24 2.86 3.19 MnO 0.07 0.07 0.07 0.06 0.06 0.06 0.07 0.14 0.20 0.15 0.13 0.14 MgO 2.06 2.01 2.02 2.02 1.75 2.04 2.26 5.20 6.15 4.42 4.07 5.03 CaO 3.74 3.49 3.49 3.49 3.35 3.50 3.99 6.55 7.24 5.93 5.82 5.97 Na2O 4.17 3.94 3.94 3.94 4.11 3.98 4.24 4.39 4.67 5.32 4.44 4.73 K2O 3.32 3.72 3.77 3.89 4.03 4.28 3.38 2.18 1.53 1.77 3.55 2.44 P2O3 0.28 0.28 0.27 0.27 0.24 0.26 0.29 0.32 0.50 0.47 0.77 0.61 Mg# 49.58 49.85 50.19 50.11 50.08 51.55 52.54 60.91 62.44 50.65 55.30 56.72 Na2O/K2O 1.26 1.06 1.05 1.01 1.02 0.93 1.25 2.01 3.05 3.01 1.25 1.94 TFeO 3.74 3.61 3.57 3.59 3.11 3.42 3.64 5.95 6.59 7.68 5.86 6.84 烧失量 0.56 0.49 0.46 0.58 0.43 0.64 0.61 1.25 0.99 0.92 0.84 0.98 总量 99.63 99.16 98.81 99.32 99.55 99.30 98.79 99.19 99.06 99.32 99.04 98.73 Sc 6.94 6.50 6.97 6.16 5.89 6.75 7.86 20.50 17.80 18.80 14.50 14.30 V 81.40 79.10 81.40 79.80 69.70 75.60 83.20 141.00 150.00 200.00 137.00 164.00 Cr 34.50 30.10 71.70 30.80 24.80 31.20 31.20 112.00 191.00 28.40 49.10 33.00 Ni 20.50 19.70 40.30 19.60 15.70 19.00 20.40 38.50 67.20 26.90 39.30 50.30 Co 10.40 10.40 11.00 10.80 8.87 10.20 11.50 21.30 25.70 23.50 20.20 26.40 Cu 17.40 20.30 819.00 262.00 14.20 19.40 15.80 79.30 40.30 47.00 30.10 71.10 Zn 56.20 53.50 53.50 54.00 49.40 45.90 44.70 81.60 112.00 111.00 97.00 115.00 Ga 18.30 17.80 18.90 18.70 18.00 17.70 18.70 17.60 20.30 24.30 21.90 23.00 Rb 130.00 146.00 140.00 154.00 154.00 156.00 142.00 130.00 107.00 153.00 194.00 251.00 Sr 785.00 769.00 774.00 782.00 813.00 838.00 860.00 626.00 545.00 677.00 695.00 676.00 Y 12.00 11.20 12.20 11.60 9.89 10.10 11.50 12.70 18.60 15.00 18.10 14.70 Zr 183.00 176.00 172.00 188.00 155.00 164.00 203.00 110.00 160.00 181.00 116.00 238.00 Nb 14.70 13.20 14.50 14.30 12.20 12.20 12.60 10.10 15.30 12.00 14.70 11.60 Mo 1.54 1.40 49.70 1.96 1.14 1.41 1.42 1.82 1.05 1.08 0.86 0.66 Sn 1.30 1.21 1.37 1.43 1.05 1.21 1.35 1.75 2.43 1.86 1.31 1.67 Cs 8.13 8.13 8.03 8.60 8.28 7.83 7.97 12.70 15.80 18.60 13.70 29.20 Ba 793.00 970.00 1, 013.00 1, 120.00 1, 238.00 1, 520.00 902.00 432.00 274.00 300.00 895.00 438.00 Hf 5.08 4.78 4.66 5.05 4.27 4.35 5.39 3.84 4.50 4.91 2.78 6.26 Ta 1.47 1.30 1.50 1.34 1.16 1.04 1.12 0.59 0.89 0.52 0.87 0.46 W 5.88 6.57 3.58 7.30 3.06 3.83 2.45 9.23 0.95 2.70 0.70 0.94 Tl 0.90 1.03 1.02 1.05 1.05 0.95 0.80 0.99 0.84 1.14 1.26 1.80 Pb 30.30 32.30 30.90 32.80 34.80 29.00 25.40 27.50 19.90 23.20 32.60 19.90 Th 35.80 38.50 36.50 37.00 37.50 38.90 33.80 20.10 40.70 12.80 65.80 29.30 U 7.46 8.15 8.33 9.49 8.16 9.15 9.45 7.75 8.09 5.52 10.10 7.97 La 62.40 59.50 59.10 60.00 53.80 68.20 58.50 54.70 84.00 69.20 157.00 87.70 Ce 116.00 111.00 110.00 111.00 98.90 111.00 112.00 96.80 161.00 112.00 282.00 146.00 Pr 13.00 12.10 12.60 12.40 11.00 11.80 12.80 10.80 19.40 12.50 31.30 16.10 Nd 45.30 43.10 43.90 44.60 38.50 41.10 45.30 40.80 75.90 48.00 111.00 60.90 Sm 6.79 6.35 6.83 6.46 5.74 5.93 6.75 6.71 12.80 8.40 16.30 10.00 Eu 1.47 1.43 1.47 1.41 1.38 1.48 1.63 1.43 1.75 1.20 1.68 1.35 Gd 4.05 3.82 3.92 3.67 3.49 3.66 4.02 4.52 7.14 5.23 8.90 6.70 Tb 0.68 0.62 0.68 0.67 0.56 0.58 0.67 0.71 1.15 0.88 1.39 0.97 Dy 2.52 2.55 2.71 2.48 2.20 2.26 2.49 2.92 4.52 3.46 4.46 3.49 Ho 0.48 0.42 0.48 0.43 0.40 0.40 0.45 0.57 0.79 0.63 0.70 0.62 Er 1.45 1.38 1.49 1.40 1.19 1.33 1.47 1.63 2.33 1.88 2.31 1.84 Tm 0.17 0.16 0.17 0.17 0.12 0.14 0.16 0.20 0.26 0.21 0.21 0.19 Yb 1.15 1.11 1.13 1.15 0.97 1.02 1.02 1.28 1.81 1.29 1.45 1.26 Lu 0.17 0.16 0.17 0.16 0.14 0.15 0.18 0.20 0.26 0.19 0.20 0.17 Sr/Y 65.42 68.66 63.44 67.41 82.20 82.97 74.78 49.29 29.30 45.13 38.40 45.99 Nb/Ta 10.00 10.15 9.67 10.67 10.52 11.73 11.25 17.12 17.19 23.08 16.90 25.22 La/Sm 9.19 9.37 8.65 9.29 9.37 11.50 8.67 8.15 6.56 8.24 9.63 8.77 Rb/Sr 0.17 0.19 0.18 0.20 0.19 0.19 0.17 0.21 0.20 0.23 0.28 0.37 Sm/Nd 0.15 0.15 0.16 0.14 0.15 0.14 0.15 0.16 0.17 0.18 0.15 0.16 87Rb/86Sr 0.479 0.549 0.523 0.569 0.548 0.539 0.478 0.601 0.568 0.654 0.807 1.074 87Sr/86Sr 0.706423 0.706431 0.706447 0.706458 0.706465 0.706430 0.706392 0.706533 0.706522 0.706535 0.706671 0.706771 l47Sm/l44Nd 0.091 0.089 0.094 0.088 0.090 0.087 0.090 0.099 0.102 0.106 0.089 0.099 l43Nd/l44Nd 0.512470 0.512466 0.512460 0.512437 0.512480 0.512456 0.512395 0.512428 0.512415 0.512483 0.512327 0.512383 εNd(t) -3.10 -3.17 -3.32 -3.73 -2.90 -3.35 -4.56 -3.97 -4.24 -2.94 -5.88 -4.85 注：主量元素含量单位为%，微量和稀土元素含量为10-6；T0911-A（A1-A5）系列与T0911-J（J1-J5）系列岩性为花岗闪长岩，T0911-C系列岩性为细粒闪长质包体；Mg#=100×Mg2+/(Mg2++Fe2+)；TFeO=FeO+Fe2O3×0.899；Eu/Eu*=EuN/(SmN×GdN)1/2；87Sr/86Sr(i)=87Sr/ 86Sr-87Rb/86Sr(eλt-1)，其中λ=1.42×10-11a-1, t=30Ma; 143Nd/ 144Nd(i)=143Nd/ 144Nd-147Sm/ 144Nd(eλt-1), 143Nd/ 144Nd (CHUR)=143Nd/ 144Nd-147Sm/ 144Nd(eλt-1)，其中143Nd/144Nd=0.512638, 147Sm/144Nd=0.1967, 其中λ=6.54×10-11a-1, t=35Ma, εNd(i)=[143Nd144Nd(i)143Nd144Nd(i)143Nd144Nd(CHUR)−1]×104
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表 4 程巴花岗闪长岩与细粒闪长质包体锆石Hf同位素数据
Table 4 Zircon Hf isotopic data of granodiorite and dioritic enclaves from the Chengba Complex
测点号 206Pb/238U年龄/Ma 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf 2σ 176Hf/177Hfi εHf（0） εHf（t） tDM/Ma tDMC/Ma fs T0911-A花岗闪长岩 03 29.4 0.018918 0.000895 0.282916 0.000017 0.28292 +5.10 +5.73 475 743 -0.97 04 29.5 0.018866 0.000908 0.282832 0.000016 0.28283 +2.13 +2.76 594 933 -0.97 05 29.2 0.019544 0.000827 0.282827 0.000019 0.28283 +1.95 +2.58 599 945 -0.98 06 29.5 0.024496 0.001041 0.282895 0.000019 0.28289 +4.35 +4.97 507 791 -0.97 07 29.1 0.013533 0.000681 0.282889 0.000016 0.28289 +4.13 +4.76 510 805 -0.98 08 29.3 0.018845 0.000797 0.282881 0.000019 0.28288 +3.86 +4.49 523 822 -0.98 10 29.7 0.020933 0.000978 0.282927 0.000016 0.28293 +5.49 +6.12 460 718 -0.97 12 29.6 0.014562 0.000637 0.282871 0.000018 0.28287 +3.50 +4.14 535 845 -0.98 13 34.6 0.012880 0.000568 0.282827 0.000019 0.28283 +1.94 +2.68 596 942 -0.98 16 29.2 0.012264 0.000571 0.282911 0.000017 0.28291 +4.92 +5.55 478 754 -0.98 17 30.5 0.013923 0.000647 0.282841 0.000018 0.28284 +2.43 +3.09 578 913 -0.98 19 29.5 0.016271 0.000770 0.282828 0.000017 0.28283 +1.98 +2.62 597 942 -0.98 20 29.2 0.018459 0.000782 0.282845 0.000019 0.28284 +2.59 +3.21 573 904 -0.98 21 29.5 0.016038 0.000688 0.282839 0.000018 0.28284 +2.38 +3.02 580 917 -0.98 22 29.1 0.022745 0.001068 0.282930 0.000017 0.28293 +5.59 +6.20 457 712 -0.97 23 29.8 0.023771 0.000970 0.282870 0.000017 0.28287 +3.48 +4.11 541 847 -0.97 24 29.3 0.011723 0.000513 0.282858 0.000019 0.28286 +3.04 +3.68 551 874 -0.98 25 29.9 0.018906 0.000886 0.282886 0.000018 0.28289 +4.03 +4.66 517 811 -0.97 26 30.3 0.014694 0.000692 0.282880 0.000014 0.28288 +3.83 +4.48 522 823 -0.98 30 29.8 0.012670 0.000560 0.282837 0.000018 0.28284 +2.29 +2.93 582 923 -0.98 T0911-C细粒闪长质包体 01 37.7 0.025078 0.001108 0.282823 0.000020 0.28282 +1.79 +2.59 610 950 -0.97 02 34.8 0.008204 0.000372 0.282841 0.000018 0.28284 +2.45 +3.21 573 909 -0.99 04 30.1 0.045735 0.001747 0.282883 0.000022 0.28288 +3.93 +4.56 533 818 -0.95 06 30.1 0.013025 0.000574 0.282738 0.000024 0.28274 -1.20 -0.55 720 1145 -0.98 08 30.2 0.020508 0.000944 0.282834 0.000019 0.28283 +2.20 +2.84 591 928 -0.97 09 28.9 0.024164 0.001066 0.282787 0.000020 0.28279 +0.54 +1.15 660 1035 -0.97 12 29.4 0.007083 0.000333 0.282847 0.000019 0.28285 +2.65 +3.29 564 899 -0.99 13 30.1 0.014520 0.000645 0.282787 0.000017 0.28279 +0.52 +1.17 653 1035 -0.98 15 29.8 0.011797 0.000586 0.282904 0.000018 0.2829 +4.65 +5.30 488 771 -0.98 16 29.0 0.007162 0.000344 0.282867 0.000020 0.28287 +3.36 +3.99 537 854 -0.99 17 29.4 0.016739 0.000765 0.282909 0.000016 0.28291 +4.83 +5.46 484 760 -0.98 18 35.1 0.013234 0.000603 0.282813 0.000017 0.28281 +1.44 +2.19 616 974 -0.98 20 30.4 0.010235 0.000421 0.282873 0.000019 0.28287 +3.55 +4.21 530 841 -0.99 21 29.6 0.024794 0.001104 0.282852 0.000020 0.28285 +2.83 +3.46 568 888 -0.97 23 26.8 0.014253 0.000638 0.282831 0.000020 0.28283 +2.08 +2.65 591 938 -0.98 24 30.5 0.018135 0.000831 0.282855 0.000020 0.28285 +2.95 +3.60 560 880 -0.97 26 29.5 0.014894 0.000724 0.282859 0.000016 0.28286 +3.06 +3.69 554 873 -0.98 28 29.7 0.039738 0.001742 0.282813 0.000021 0.28281 +1.46 +2.07 634 977 -0.95 29 29.7 0.014810 0.000728 0.282866 0.000017 0.28287 +3.33 +3.96 543 856 -0.98 注：εHf(t)=10000×{[(176Hf/177Hf)s-(176Lu/177Hf)s×(eλt-1)]/[(176Hf/177Hf)CHUR, 0-(176Lu/177Hf)CHUR×(eλt-1)]-1}；tDM=1/λ×ln{1+ [(176Hf/177Hf)s-(176Hf/177Hf)DM]/[(176Lu/177Hf)s-(176Lu/177Hf)DM]}.tDMC=tDM-(tDM-t)×[(fcc-fs)/(fcc-fDM)]. fLu/Hf=(176Hf/177Hf)s /(176Lu/ 177Hf)CHUR-1。λ=1.867×10-11a-1；(176Lu/177Hf)s和176Hf/177Hf)s是样品标准值；(176Lu/177Hf)CHUR=0.0332；(176Hf/177 Hf)CHUR, 0=0.282772；(176Lu/177Hf)DM=0.28325; (176Lu/177Hf)平均地壳=0.015；fcc=[(176Lu/177Hf)平均地壳/(176Lu/177Hf)CHUR]-1；fs=fLu/Hf；fDM=[(176Lu/177Hf)DM/(176Lu/177Hf)CHUR]-1；t为锆石结晶时间
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