SHRIMP U-Pb and Sm-Nd dating of the gabbro and syenite from the Hongge ore district in western Panzhihua and its geological significance
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摘要:
用SHRIMP U-Pb和Sm-Nd定年技术，对攀西红格矿区含矿层状辉长岩、碱性正长岩进行了年龄测定。获得红格辉长岩中3种不同晶形锆石的U-Pb年龄分别为258.4±4.1Ma、1841±34Ma、2487±12Ma，由辉长岩、辉石和磷灰石所构成的Sm-Nd等时线年龄为253±14Ma；碱性正长岩中锆石的U-Pb年龄为257.2±1.5Ma。结果表明，红格辉长岩中具有典型基性岩锆石特征的锆石U-Pb年龄（258Ma）与同一地质样品的Sm-Nd年龄（全岩+矿物内部等时线年龄），以及同一矿区的正长岩锆石U-Pb年龄在测定误差范围内一致。鉴于层状辉长岩和碱性正长岩在空间上密切共生，在形成时间上一致，可以认为它们都属于晚二叠世末岩浆活动的产物；而1841Ma和2487Ma的锆石，可能是在基性-超基性岩浆的上侵过程中，从基底所捕获的岩浆锆石和继承锆石，其年龄信息，揭示了康滇地轴岩浆岩带的下部或结晶基底存在元古代甚至新太古代末期的岩石或物质。
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关键词:
- 攀西红格矿区 /
- 辉长岩 /
- 正长岩 /
- SHRIMP锆石U-Pb定年 /
- Sm-Nd等时线
Abstract:Adopting the SHRIMP U-Pb and Sm-Nd method, this paper reported the dating results of the bedded ore-bearing gab-bros and alkaline syenites from the Hongge ore district in western Panzhihua area.The results show that the zircons from gabbro in Hongge have ages of 258.4±4.1Ma, 1841±34Ma and 2487±12Ma, the Sm-Nd isochron age of the gabbro, pyroxene and apatite sam-ples is 253±14Ma, while the zircon U-Pb age of alkaline syenite is 257.2±1.5Ma.These data show that the zircon U-Pb age (258Ma) of the typical mafic rock is similar to the Sm-Nd isochron age of the same samples, and also similar to the zircon U-Pb age of syenite.Considering the close relationship between layered gabbro and alkaline syenite rock in space and in time, it is suggested that both of them resulted from Permian Magmatism, but 1841Ma and 2487Ma zircon might have been magmatic zircon and inherit-ed zircons, which originated from the basement.These data imply the existence of Paleo-Petrozoic or even Archean materials in the lower part of Kangdian axis magmatic rock belt or the crystalline basement.
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致谢: 野外采样过程中得到中国地质调查局成都地质调查中心齐先茂研究员、四川省地质矿产勘查开发局一〇六地质队田小林总工程师和蒋先忠副总工程师的大力支持，并协助完成采样工作，SHRIMP锆石定年得到北京离子探针中心车晓超助理研究员的帮助，在锆石年龄数据的解释方面与万渝生研究员进行了有益的讨论，在此一并表示衷心的感谢。
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图 1 攀西红格矿区地质简图[5]
Q—第四系；N2x—新近系昔格达组；Pt1h—下元古界河口群；CN—正长岩；ν—基性-超基性岩；1—含矿岩体；2—断层
Figure 1. Geological sketch map of the Hongge ore district in the Panxi area
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图 2 红格矿区含矿辉长岩显微镜下照片
Pl—斜长石；Px—辉石；Hbl—角闪石；Spl—尖晶石；Ap—磷灰石
Figure 2. Microscope photos showing the features of the ore-bearing gabbro from the Hongge ore district
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图 3 红格矿区闪石正长岩岩石薄片显微镜下特征
Kfs—钾长石；Hbl—角闪石；Px—辉石；Qtz—石英；Pl—斜长石
Figure 3. Microscope photos showing the features of the ore-bearing mafic-ultramafic rocks from the Hongge ore district
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图 4 红格矿区辉长岩体代表性锆石的阴极发光图像、分析点位及206Pb/238U年龄
Figure 4. Cathodoluminescence (CL) image of zircons from the Hongge ore district and 206Pb/238U age of the measuring points
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图 5 红格矿区辉长岩体的锆石U-Pb谐和图
Figure 5. Concordia diagram of zircon SHRIMP U-Pb data from gabbro in the Hongge ore district
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图 6 红格矿区辉长岩体全岩+矿物及全岩分相Sm-Nd内部等时线图
Figure 6. Sm-Nd isochron age of gabbro and mineral samples from the Hongge ore district
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图 7 红格矿区碱性正长岩体中部分锆石的阴极发光图像、分析点位及206Pb/238U视年龄
Figure 7. Cathodoluminescence (CL) image of zircons from syenite in the Hongge ore district and 206Pb/238U age of the measuring points
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图 8 红格矿区闪石碱性正长岩体锆石U-Pb谐和图
Figure 8. Concordia diagram of SHRIMP U-Pb data of zircon from syenite in the Hongge ore district
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图 9 红格矿区碱性正长岩体锆石206Pb/238U年龄加权平均图
Figure 9. 206Pb/238U weighted average age of zircons from the syenite in the Hongge ore district
表 1 红格矿区辉长岩锆石U-Th-Pb年龄测定结果
Table 1 Zircon U-Th-Pb age determination results of the gabbro from the Hongge ore district
分析点 206Pbc/% U/10-6 Th/10-6 232Th/238U 206Pb*/10-6 206Pb/238U年龄/Ma 207Pb/206Pb年龄/Ma 208Pb/232Th年龄/Ma 207Pb/235U ±/% 206Pb/238U ±/% Rho HGH-1.1 -- 1017 919 0.93 35.4 256.16 ±0.98 277 ±30 240.3 ±2.5 0.2896 1.4 0.04054 0.39 0.286 HGH-2.1 0.05 256 45 0.18 72.6 1, 836.0 ±8.8 1, 840 ±12 1, 723 ±30 5.109 0.84 0.3295 0.55 0.651 HGH-3.1 0.00 256 136 0.55 9.12 262.0 ±1.9 363 ±55 253.3 ±5.4 0.3077 2.6 0.04147 0.73 0.284 HGH-4.1 0.28 630 392 0.64 22.0 255.5 ±1.4 223 ±60 252.7 ±4.7 0.2821 2.7 0.04043 0.55 0.205 HGH-7.1 0.04 102 130 1.32 41.2 2, 489 ±18 2, 492 ±13 2, 479 ±28 10.62 1.1 0.4712 0.86 0.755 HGH-9.1 0.32 698 330 0.49 25.0 262.2 ±1.2 235 ±51 224.4 ±4.8 0.2912 2.3 0.04151 0.47 0.206 HGH-10.1 0.11 448 51 0.12 136 1, 955.6 ±7.9 1, 862 ±14 1, 850 ±78 5.564 0.93 0.3544 0.47 0.507 HGH-11.1 1.66 379 198 0.54 96.5 1, 646.7 ±8.3 1, 862 ±90 1, 728 ±150 4.57 5.0 0.2910 0.60 0.119 HGH-12.1 0.13 585 290 0.51 245 2, 551.4 ±8.6 2, 484.7 ±7.2 2, 898 ±26 10.897 0.59 0.4855 0.41 0.694 HGH-14.1 0.32 117 71 0.63 36.4 1, 979 ±19 1, 867 ±22 1, 938 ±44 5.656 1.7 0.3593 1.1 0.667 HGH15.1 3.30 421 623 1.53 15.3 259.4 ±3.1 -252 ±590 244 ±15 0.235 23 0.04106 1.2 0.053 HGH16.1 1.71 939 466 0.51 244 1, 675.1 ±7.4 1, 793 ±17 1, 604 ±50 4.485 1.1 0.2967 0.50 0.463 注：误差为1σ；Pbc和Pb*分别代表普通铅和放射性成因铅，应用实测204Pb校正普通铅；Rho为误差相关系数 
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表 2 红格矿区辉长岩全岩分相组分及矿物Sm-Nd年龄测定结果
Table 2 Sm-Nd age determination results of gabbro and mineral samples from the Hongge ore district
实验室编号 原送样号 样品名称 Sm/10-6 Nd/10-6 147Sm/144Nd 143Nd/144Nd 9015003 HGH 红格矿区辉长岩 15.8 75.21 0.1271 0.512535±0.000004 9015001 HGH-辉长 红格矿区辉长岩中辉石 8.692 31.21 0.1737 0.512610±0.000006 9015008 HGH-磷灰石 红格矿区辉长岩中磷灰石 128.1 649.4 0.1193 0.512522±0.000007 3c HGH-可溶相 辉长岩王水可溶相 32.16 149.1 0.1305 0.512537±0.000006 3c HGH-王水可溶相 辉长岩王水可溶相 36.95 172.6 0.1295 0.512535±0.000010 3f HGH-残留相 辉长岩残留相 1.54 5.786 0.1610 0.512590±.000004 3f HGH-残留相 辉长岩残留相 3.919 13.93 0.1702 0.512605±.000009
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表 3 红格矿区碱性正长岩锆石U-Th-Pb年龄测定结果
Table 3 U-Th-Pb age determination results of zircon from the syenite in the the Hongge ore district
分析点 206Pbc/% U/10-6 Th/10-6 232Th/238U 206Pb*/10-6 206Pb/238U年龄/Ma 207Pb/206Pb年龄/Ma 208Pb/232Th年龄/Ma 207Pb/235U ±/% 206Pb/238U ±/% Rho HGZ-1.1 0.06 1756 1058 0.62 61.8 258.8 ±1.9 243 ±25 246.6 ±2.7 0.2883 1.3 0.04097 0.75 0.572 HGZ-2.1 0.19 1284 1042 0.84 44.8 255.9 ±1.9 241 ±36 243.8 ±2.9 0.2847 1.7 0.04049 0.75 0.440 HGZ-3.1 0.14 499 381 0.79 17.4 255.9 ±2.1 311 ±43 241.0 ±3.7 0.2936 2.1 0.04050 0.86 0.412 HGZ-4.1 0.18 930 974 1.08 32.1 253.6 ±1.9 235 ±32 240.8 ±2.7 0.2815 1.6 0.04012 0.78 0.487 HGZ-5.1 0.51 361 484 1.39 12.6 254.9 ±2.4 232 ±100 246.1 ±4.7 0.283 4.5 0.04034 0.96 0.213 HGZ-6.1 -- 582 622 1.10 20.2 254.9 ±2.1 316 ±39 243.2 ±3.2 0.2932 1.9 0.04034 0.84 0.441 HGZ-7.1 -- 924 956 1.07 32.2 256.1 ±2.6 317 ±31 244.9 ±3.2 0.2947 1.7 0.04053 1.0 0.601 HGZ-8.1 0.13 1988 1425 0.74 70.2 259.1 ±1.9 175 土49 243.4 ±2.8 0.2804 2.2 0.04102 0.73 0.331 HGZ-9.1 -- 1362 1071 0.81 47.5 256.7 ±2.1 228 ±26 243.6 ±2.7 0.2841 1.4 0.04063 0.82 0.596 HGZ-10.1 0.10 2047 1284 0.65 73.0 261.8 ±1.9 227 ±33 246.0 ±3.1 0.2897 1.6 0.04144 0.72 0.452 HGZ-11.1 0.11 1297 1028 0.82 45.4 257.3 ±1.9 218 ±37 240.4 ±2.9 0.2836 1.8 0.04072 0.75 0.425 HGZ-12.1 -- 1399 1291 0.95 49.2 258.9 ±1.9 224 ±25 244.8 ±2.5 0.2861 1.3 0.04098 0.76 0.579 注：误差为1σ；Pbc和Pb*分别代表普通铅和放射性成因铅，应用实测204Pb校正普通铅；Rho为误差相关系数
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