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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研究区位于兴蒙造山带东段，由北向南依次为额尔古纳地块、兴安地块和松嫩地块，经历了古生代多块体拼合作用过程和中生代陆内演化过程的叠加，地壳结构、构造相对复杂[1-2]。大兴安岭北段发育大面积的晚中生代火山岩，由于研究区内火山岩研究对象不同，众多学者对火山岩期次的划分与厘定存在分歧。关于火山岩形成的构造环境问题存在争议，先后有地幔柱成因[3-4]、板内成因[5]、蒙古-鄂霍茨克洋俯冲成因[6-8]、古太平洋俯冲成因[9-10]等多种观点。另一方面，大兴安岭北段的中西部地区目前有较多的年代学资料，但东部地区火山岩年代学及火山岩构造背景的研究较滞后。因此，本文对研究区不同期次火山岩开展详细的研究工作，进一步划分火山岩浆活动期次，讨论火山岩的成因及形成的构造环境，为晚中生代火山岩的构造环境提供依据。
1. 地质背景及岩石学特征
龙江盆地位于黑龙江省龙江县境内，内蒙古自治区东部，所在区域为古生代陆壳侧向增生区，亦为兴安地块和松嫩地块的缝合区（图 1-a）。在地质特征上，龙江盆地是由多个发育在海西褶皱基底上，以早白垩世为主体的一群中小规模的断陷湖盆组合而成，形成条件相近的断陷，具有各自独立的沉积体系。
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图 1 大兴安岭北部构造单元划分[11]（a）和龙江盆地地质简图（b）Figure 1. Tectonic setting map of the northern Da Hinggan Mountains (a) and simplified geological map of Longjiang basin(b)区内出露的地质体主要包括晚古生代大石寨组、花岗岩体及晚中生代火山岩。其中，大石寨组为一套经过低级变质作用改造的火山-沉积岩系[12]，其形成环境为浅海并伴随较强烈的火山活动；花岗岩主要由花岗闪长岩和二长花岗岩组成，为一套高钾钙碱性系列岩石。盆地内出露的晚中生代地层自下而上为下白垩统龙江组、光华组和甘河组，是大兴安岭北段火山盆地的基本类型。龙江组为偏中性火山岩，以安山岩、安山质凝灰岩、火山角砾岩、凝灰质细-粉砂岩夹少量英安岩、英安质凝灰岩为主，与下伏二叠系和侵入岩呈角度不整合接触。光华组为偏酸性火山岩，以流纹岩、碱流岩、流纹质凝灰岩、流纹质沉凝灰岩夹薄层凝灰质细-粉砂岩为主，灰白色粘土岩及沉凝灰岩中富产叶肢介、介形虫、淡水双壳类、腹足类、昆虫及植物化石，属于中期热河生物群。甘河组为偏中基性火山岩，以玄武岩、橄榄玄武岩和玄武安山岩为主，厚度大于82.6m，喷发覆盖于下伏地层之上。
本文涉及的光华组在光华村—兴义村一带分布，出露面积约89km2，碱流岩出露于大景星山附近（图 1-b），沿新兴村-大景星山-东临山进行地层剖面实测和采样，详细考察了龙江盆地碱流岩的野外产状、空间分布特征和野外地质关系。大景星山呈椭圆形，长轴方向为北北东向，与区域构造（断裂）走向一致，地貌表现为中央山峰高耸，周围是阶梯状下降的多轮环状山。碱流岩以大景星山为中心向四周溢流（图 2-a），覆盖于下部流纹质-英安质火山碎屑岩之上，流面发育（图 2-b），岩性稳定。本次研究的样品（PM412TW25）采自大景星山碱流岩中心部位，即北纬47°09′28″、东经122°56′27″。
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图 2 大景星山碱流岩野外照片（a、b）和显微照片（c、d）a—碱流岩宏观照片；b—流面发育；c—透长石斑晶裂纹发育；d—正长石流状定向；San—透长石；Or—正长石Figure 2. Field photographs (a, b) and microphotographs (c, d) for the pantellerite in Dajingxing Mountain碱流岩呈灰白色-灰紫色，斑状结构，基质具有球粒-显微嵌晶结构。斑晶成分为透长石（10%~ 15%），半自形板状，局部聚斑状，发育横向裂纹（图 2-c），卡氏双晶，粒径0.4~3.0mm。基质以长英质放射状、扇形球粒为主，球粒之间可见少量他形粒状石英中嵌有自形长柱状正长石微晶。正长石呈半自形板状，卡氏双晶，近平行消光，表面较洁净，可见流状定向（图 2-d），粒径均小于0.1mm。
2. 锆石U-Pb分析方法及结果
样品破碎和锆石分选由河北省廊坊市科大矿物分选技术股份有限公司完成。锆石阴极发光（CL）照相在中国地质科学院北京离子探针中心完成。锆石激光剥蚀等离子体质谱（LA-ICP-MS）U-Pb同位素分析在中国地质科学院国家地质实验测试中心完成。试验中采用高纯氦作为剥蚀物质载气，用标准参考物质NIST SRM610进行仪器最佳化，样品测定时用哈佛大学标准锆石91500作为外部校正。本次实验采用的激光斑束直径为30μm，激光脉冲为10Hz，能量密度为16~ 17 J/cm2。普通铅校正采用Anderson的方法，详细实验测试过程可参见文献[13]。锆石U-Pb同位素分析结果见表 1，代表性的锆石阴极发光图像见图 3，年龄加权平均值计算和U-Pb谐和图（图 4）由3.0版本的Isoplot程序完成[14]。
表 1 大景星山碱流岩（PM412TW25）LA-ICP-MS锆石U-Th-Pb同位素测试结果Table 1. LA-ICP-MS data of zircons from the pantellerite (PM412TW25) in Dajingxing Mountain测点号 组成/10-6 Th/U 同位素比值 年龄/Ma Th U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 1 38 56 0.68 0.0500 0.0021 0.1376 0.0062 0.0198 0.0006 195.9 95 130.9 5.6 126.5 3.7 2 40 63 0.64 0.0508 0.0023 0.1352 0.0067 0.0200 0.0006 229.7 103 128.8 6.0 127.5 3.9 5 32 53 0.62 0.0499 0.0035 0.1300 0.0096 0.0198 0.0007 188.1 154 124.1 8.6 126.2 4.3 6 46 74 0.63 0.0484 0.0018 0.1247 0.0051 0.0184 0.0005 119.2 87 119.3 4.6 117.5 3.4 8 180 127 1.41 0.0549 0.0020 0.1497 0.0059 0.0195 0.0006 408.4 79 141.6 5.2 124.6 3.6 9 38 63 0.61 0.0510 0.0036 0.1326 0.0099 0.0196 0.0007 240.2 155 126.4 8.9 125.2 4.3 10 29 61 0.48 0.0491 0.0025 0.1339 0.0072 0.0196 0.0006 150.9 114 127.6 6.4 125.1 3.8 12 47 73 0.63 0.0495 0.0022 0.1305 0.0062 0.0188 0.0006 171.9 101 124.5 5.6 120.1 3.6 13 35 63 0.55 0.0507 0.0030 0.1259 0.0078 0.0187 0.0006 227.9 130 120.4 7.1 119.6 3.8 14 31 57 0.54 0.0491 0.0028 0.1273 0.0076 0.0191 0.0006 154.4 128 121.6 6.9 121.8 3.8 16 105 103 1.02 0.0534 0.0020 0.1389 0.0056 0.0189 0.0006 344.7 83 132 5.0 120.4 3.5 17 28 50 0.56 0.0473 0.0025 0.1257 0.0069 0.0190 0.0006 61.2 120 120.2 6.2 121.6 3.7 18 248 174 1.43 0.0496 0.0017 0.1340 0.0050 0.0195 0.0006 175.5 79 127.6 4.5 124.4 3.6 19 32 50 0.65 0.0496 0.0021 0.1365 0.0060 0.0198 0.0006 178.3 94 129.9 5.4 126.5 3.7 22 33 62 0.53 0.0482 0.0022 0.1306 0.0062 0.0188 0.0006 111 102 124.6 5.5 120.1 3.5 23 20 42 0.47 0.0475 0.0050 0.1239 0.0138 0.0182 0.0007 73.1 235 118.6 12 116.3 4.5 25 26 45 0.58 0.0548 0.0037 0.1427 0.0102 0.0196 0.0007 403 144 135.4 9.0 125.4 4.2 28 38 68 0.56 0.0472 0.0025 0.1264 0.0071 0.0188 0.0006 56.3 123 120.9 6.4 119.8 3.6 29 81 85 0.95 0.0505 0.0019 0.1312 0.0054 0.0188 0.0006 217.6 87 125.2 4.8 120.1 3.5 ![]()
图 3 大景星山碱流岩锆石阴极发光图像、测点编号及 206Pb/238U年龄Figure 3. Cathodoluminescence images of typical single-crystal zircons and their apparent ages from the pantellerite in Dajingxing Mountain![]()
图 4 大景星山碱流岩锆石U-Pb谐和图Figure 4. U-Pb concordia diagram of zircons from the pantellerite in Dajingxing Mountain锆石阴极发光图像显示，碱流岩样品中大多数锆石晶体多呈短柱状，部分长柱状，晶轴比为1：1~1：3，柱面和锥面较发育，韵律环带不很发育，Th/U值介于0.48~1.43之间，反映岩浆成因锆石的特点。对80粒锆石中的30颗锆石进行了测试分析，其中11个测点由于Pb丢失而偏离谐和曲线，无年龄意义。其余数据分布在谐和线上及其附近，206Pb/238U年龄加权平均值为122.4±1.7Ma（n= 19，MSWD=0.77）。该年龄与光华村光华组火山-沉积碎屑岩中的双壳类、叶肢介、三尾拟蜉蝣等热河生物群化石组合所属时代早白垩世相符合，代表火山岩的喷发年龄。
3. 岩石地球化学特征
本文对7件火山岩样品进行了主量、微量元素测试，结果见表 2。样品测试在国土资源部东北矿产资源监督检测中心完成，整个过程均在无污染设备中进行。主量元素采用X射线荧光光谱法(XRF)，微量元素分析采用电感耦合等离子质谱法(ICP-MS)完成。主量元素分析精度和准确度优于5%，微量元素分析精度和准确度优于10%。
表 2 大景星山碱流岩主量、微量及稀土元素分析结果Table 2. Major, trace and rare earth elements compositions of the pantellerite in Dajingxing Mountain样品号 SiO2 Al2O3 Fe2O3 FeO TiO2 K2O Na2O CaO MgO MnO P2O5 烧失量 总量 AR DI PM412YQ7 73.32 14.04 0.63 0.54 0.2 5 4.84 0.15 0.23 0.003 0.03 0.24 99.23 5.51 96.75 PM412YQ9 73.29 13.82 0.16 0.54 0.2 5.25 4.65 0.52 0.49 0.01 0.03 0.29 99.23 5.45 95.65 PM412YQ10-1 73.85 13.41 0.74 0.54 0.2 5.3 3.95 0.29 0.73 0.034 0.03 0.17 99.24 5.15 94.42 PM412YQ10-2 72.94 13.35 1.28 0.4 0.19 5.44 4.21 0.21 0.54 0.044 0.05 0.43 99.1 5.93 95.39 PM412YQ23 74.16 12.76 1.18 0.56 0.17 4.72 4.64 0.28 0.63 0.01 0.04 0.33 99.47 6.09 95.71 PM412YQ25 75.64 12.96 0.3 0.4 0.16 4.54 4.54 0.13 0.18 0.004 0.04 0.19 99.09 5.53 97.54 PM412YQ27 73.14 13.85 0.58 0.45 0.2 4.92 4.9 0.21 0.54 0.004 0.04 0.29 99.14 5.64 96.21 A型花岗岩 73.81 12.4 1.24 1.58 0.26 4.65 4.07 0.75 0.2 0.06 0.04 样品号 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y PM412YQ7 74.0 151 19.8 75.1 13.7 0.51 10.14 1.71 9.60 1.82 4.64 0.75 5.10 0.74 47.4 PM412YQ9 71.1 163 19.4 74.9 14.2 0.44 10.78 1.77 10.05 1.92 4.90 0.79 5.34 0.78 59.5 PM412YQ10-1 75.3 166 20.2 80.0 15.1 0.51 10.95 1.77 9.35 1.73 4.26 0.69 4.66 0.67 35.3 PM412YQ10-2 60.6 120 15.8 61.6 11.6 0.57 8.62 1.44 8.50 1.64 4.19 0.69 4.60 0.67 48.1 PM412YQ23 72.2 161 18.9 71.8 13.3 0.65 9.94 1.66 9.51 1.83 4.80 0.78 5.20 0.76 46.7 PM412YQ25 57.9 162 16.5 60.7 11.9 0.51 9.02 1.54 9.21 1.80 4.57 0.76 5.17 0.75 45.2 PM412YQ27 74.8 152 20.2 76.0 14.2 0.42 10.33 1.76 9.99 1.89 4.86 0.80 5.36 0.79 46.6 样品号 Sr Rb Ba Th Ta Nb Zr Hf Sc Cr Ni Cs ΣREE δEu (La/Yb)N PM412YQ7 13.2 141 25.7 6.25 1.09 37.0 765 13.9 6.66 11.4 2.36 0.83 369 0.13 9.79 PM412YQ9 14.2 146 33.2 6.16 0.54 35.2 776 14.3 6.57 14.2 1.95 1.12 379 0.11 8.97 PM412YQ10-1 13.1 150 26.5 6.51 0.77 36.0 708 13.6 5.14 16.6 4.32 1.57 391 0.12 10.91 PM412YQ10-2 11.5 151 40.3 6.87 0.86 37.9 724 10.4 6.02 8.7 3.60 1.24 301 0.17 8.89 PM412YQ23 13.2 144 42.7 6.41 0.84 39.9 627 12.2 4.92 17.2 5.59 0.69 372 0.16 9.35 PM412YQ25 11.6 137 24.0 6.68 1.29 38.1 667 11.7 4.26 20.5 2.67 0.35 343 0.15 7.55 PM412YQ27 12.8 140 25.6 6.59 1.24 36.6 759 14.5 6.53 15.4 2.23 0.77 374 0.10 9.40 注：主量元素含量单位为%，微量和稀土元素为10-6；A型花岗岩数据据参考文献[15] 3.1 主量元素
大景星山碱流岩具有以下特征：①富Si（SiO2= 72.94%~75.64%），贫Mg（MgO=0.18%~0.73%）和Ca（CaO=0.13%~0.52%）, 在TAS图解（图 5-a）中，所有样品点均落在流纹岩区，分异指数高（DI=94.42~ 97.54）, 表现出高分异演化的特征。②碱含量高，全碱（K2O+Na2O）=9.08%~9.89%，碱度指数（AR）为5.15~ 6.09，且相对富钾，K2O/Na2O值为1.00~1.34，在Nb/Y-Zr/TiO2分类图解（图 5-b）中全部落在碱流岩区域。③准铝质-弱过铝质，A/CNK值变化范围为0.96~1.05。④低TiO2（0.16%~0.2%）和P2O5（0.03%~ 0.05%），显示岩浆经历了钛铁矿、磷灰石等矿物的分离结晶作用。上述主量元素特征与A型花岗岩平均值一致[15]。
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图 5 大景星山碱流岩TAS图解(a)和Nb/Y-Zr/TiO2图解(b)Figure 5. TAS(a)and Nb/Y-Zr/TiO2(b)diagrams of the pantellerite in Dajingxing Mountain3.2 微量元素
大景星山碱流岩稀土元素总量（ΣREE）在301 × 10-6~391 × 10-6范围内, 轻、重稀土元素比值（LREE/HREE）在8.91~10.47之间，(La/Yb)N=7.55~ 10.91，轻、重稀土元素分馏程度中等，轻稀土元素分馏较明显，（La/Sm)N值为3.06~3.49，重稀土元素分馏不显著。岩石的球粒陨石标准化稀土元素配分曲线呈明显的右倾“V”字形特征（图 6-a），并显示较明显的负Eu异常（δEu=0.1~0.17）。微量元素蛛网图（图 6-b）显示，大景星山碱流岩富集Rb、Th、U、Zr和轻稀土元素，如La、Ce、Nd和Sm，明显亏损Ba、Sr、P、Ti等元素。Nb和Ta具有中等-弱亏损。在Whalen等[15]提出的分类图（图 7）上，该区流纹岩与高度分异的I、S型花岗岩明显不同，所有样品点都落在A型花岗岩区。在花岗岩的微量元素构造判别图解（图 8）中，大景星山碱流岩全部落入板内花岗岩区。
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图 7 Zr（a），Nb（c）与10000×Ga/Al判别图和（K2O+Na2O）/CaO（b），TFeO/MgO（d）与Zr+Nb+Ce+Y判别图[15]FG—分异的I、S型花岗岩；OTG—未分异的I、S、M型花岗岩；I、S、A—I、S、A型花岗岩Figure 7. Zr(a), Nb(c)versus 10000×Ga/Al and (K2O+Na2O)/CaO(b), TFeO/MgO versus Zr+Nb+Ce+Y discrimination diagrams![]()
图 8 (Y+Nb)-Rb（a）和Y-Nb（b）图解[18]WPG—板内花岗岩；VAG—火山弧花岗岩；syn-COLG—同碰撞花岗岩；ORG—洋脊花岗岩Figure 8. (Y+Nb)-Rb(a) and Y-Nb(b) discrimination diagrams4. 讨论
4.1 岩石成因
自1979年Loiselle等[19]提出以碱性、无水、非造山为特征的A型花岗岩以来，许多学者对A型花岗岩的岩石地球化学、岩石成因及构造背景进行了研究。目前认为，A型花岗岩不局限于非造山，也可以形成于不同的构造背景；在成分上，既可以是过碱的，也可以是准铝质或过铝质的[20-21]；在岩石学上，包括石英正长岩、亚碱性-碱性花岗岩、流纹岩、碱流岩等[22-23]。大景星山碱流岩岩石富硅、富碱，贫Mg、Ca；稀土元素配分曲线呈现右倾“V”字形特征，显示强烈的负Eu异常；微量元素显示较低的Sr和Ba丰度，以及较高的Rb、Th、U、Zr等特点。其地球化学特征类似于A型花岗岩。
目前认为，碱性长英质岩石的成因模式有：①幔源岩浆与深熔形成的壳源岩浆的混合和交代作用[24-25]；②富F、Cl麻粒岩高温部分熔融作用[26]；③碱性岩浆的分离结晶作用[27-28]；④在挥发组分作用下下地壳岩石部分熔融[29]。首先，由于研究区和相邻地区缺乏同时代的镁铁质岩石，可以排除大景星山碱流岩是幔源岩浆分离结晶作用产物的可能。其次，大景星山碱流岩富硅及贫Mg、Ca的特征可以排除幔源岩浆与深熔形成的壳源岩浆混合的成因机制。第三，岩石的高硅、相对富Na、贫Mg、贫Ca及强烈的负Eu异常等特征, 与下地壳麻粒岩物质部分熔融的成因模式并不吻合。
King等[20]认为，铝质A型花岗岩岩浆源于长英质地壳的部分熔融，而碱性花岗岩浆则为幔源镁铁质岩浆分异的产物。研究区大景星山碱流岩A/CNK值介于0.96~1.05之间，属于准铝质-弱过铝质，Si2O含量高、变化范围较小，含有低Al2O3、FeO和MgO含量，以及明显的Ba、P、Sr、Eu及Ti负异常特征，指示长英质成分的源岩在低压下发生部分熔融，其中斜长石、磷灰石及Ti、Fe氧化物在源岩中残留。综合上述特征可以判定，长英质地壳部分熔融及其后的分异作用可能为大景星山碱流岩形成的重要机制。
4.2 构造背景
1992年，Eby[22]把A型花岗岩分为A1型花岗岩（非造山花岗岩拉张环境）、A2型花岗岩（后造山环境）。在Nb-Y-Ce图解（图 9-a）中，大景星山碱流岩主要落在A1、A2的分界线上，而在Y/Nb-Rb/Nb判别图（图 9-b）中，样品点全部落入A1型花岗岩区，指示了一种非造山拉张环境。
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图 9 大景星山碱流岩Nb-Y-Ce（a）和Y/Nb-Rb/Nb（b）图解[22]Figure 9. Nb-Y-Ce(a)and Y/Nb-Rb/Nb(b)diagrams of the pantellerite in Dajingxing Mountain兴蒙造山带东部的大兴安岭地区从晚古生代—早中生代经历了古亚洲洋、蒙古-鄂霍次克洋的闭合及区内多块体的拼贴过程[30]。早—中三叠世兴蒙造山带南缘碰撞型花岗岩的发现标志着古亚洲洋的最终闭合[31]；早—中侏罗世，古太平洋板块开始向欧亚大陆俯冲，在吉黑东部（东宁—晖春）、小兴安岭—张广才岭地区形成大陆弧岩浆作用[32-34]，而在西部额尔古纳—根河地区出露的钙碱性火山岩组合[35]则反映了活动陆缘的构造背景，引起该期岩浆事件的区域动力应来自于蒙古-鄂霍芡克大洋板块向额尔古纳地块下的俯冲作用。中侏罗世晚期—早白垩世早期阶段，古太平洋板块进入了间歇期[36]，而在大兴安岭西坡—辽西地区存在一次重要的陆壳加厚过程[37-38]，与该区构造推覆使地壳增厚的伸展环境有关[35]，与蒙古-鄂霍芡克缝合带闭合时间一致。
早白垩世晚期火山岩（114 Ma ~131Ma，峰值年龄为125Ma）在大兴安岭地区广泛分布，北部以上库力组流纹岩和伊列克得组玄武岩为代表[39-40]，南部以白音高老组流纹岩和梅勒图组玄武岩为代表[41]，翼北—辽西地区，以义县组火山岩为代表，形成年龄为120~126Ma[42]。该期火山岩岩石组合为典型的双峰式火山岩，是早白垩世晚期区域性伸展的直接反映。同时，早白垩世晚期A型花岗岩的广泛分布[43]、变质核杂岩的产出[44]及同期沉积盆地的形成[45]都指示了伸展背景。大兴安岭巴尔哲碱性花岗岩和碾子山A型花岗岩（年龄为125Ma）是张性构造体制背景下的产物[46]。大景星山碱流岩的产出指示，大兴安岭北段龙江盆地在122.4Ma已经进入板内拉张环境，该期火山事件既与环太平洋构造体系有关，又与蒙古-鄂霍茨克构造带相联系，从大兴安岭地区中生代火山岩的空间展布可以判断，位于松辽盆地以西的龙江盆地碱流岩的形成与后者的联系更密切。
5. 结论
(1) 龙江盆地光华组碱流岩中的锆石为岩浆成因，LA-ICP-MS U-Pb定年结果为122.4±1.7Ma，表明其形成时代为早白垩世。
(2) 龙江盆地光华组碱流岩具有富硅、富碱、贫Mg、Ca的特征，具有显著的负Eu异常、低Sr和Ba丰度，以及较高的Rb、Th、U、Zr和轻稀土元素，说明其岩浆源区有斜长石、磷灰石及Ti、Fe氧化物残留，为长英质地壳部分熔融的产物。
(3) 龙江盆地光华组碱流岩的特征类似于铝质A1型花岗岩，形成于板内拉张环境，代表了伸展的大地构造背景。
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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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