Zircon SHRIMP U-Pb age of the layered mafic rock mass in Panxi area, Sichuan Province, and its geological significance
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摘要:
应用SHRIMP锆石U-Pb测年，对攀西地区白马和太和含矿层状基性-超基性岩体的年龄进行研究，获得白马层状辉长岩体锆石U-Pb年龄为258±2Ma（95%可信度），太和层状辉长岩体锆石U-Pb年龄为262±2Ma（95%可信度）。结果表明，攀西地区的白马和太和含矿层状辉长岩体均形成于二叠纪晚期。该年龄信息显示了从层状辉长岩体的侵入到峨眉山玄武岩的喷发高峰期（250Ma）仅距5~10Ma，二者应属于同期不同阶段岩浆活动的产物。鉴于空间上层状辉长岩体与峨眉山玄武岩密切相关，基性-超基性岩体和玄武岩的形成均与晚古生代末期峨眉地幔柱活动有关。
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关键词:
- 攀西地区 /
- 峨眉地幔柱 /
- 基性-超基性岩体 /
- SHRIMP锆石U-Pb定年 /
- 白马和太和层状侵入体
Abstract:In this paper, based on the application of SHRIMP zircon U-Pb dating method, the authors studied the age of the orecontaining layered basic-ultrabasic rocks in western Panzhihua area, with the U-Pb ages of zircons from the Baima layered gabbro body being 258±2Ma (95% confidence) and those of zircons from the Taihe layered gabbro body being 262±2Ma (95% confidence).These data show that both Baima and Taihe ore-bearing gabbros in western Panzihua metallognetic belt were formed in Late Perm-ian.The age information also suggests that the time gap between the intrusion of the layered gabbro body and the eruption of the Emeishan basalt (peak at 250Ma) was only about 5~10Ma, and both the intrusive rocks and the basalts should have resulted from mag-matic activities at different stages.Considering the spatial relationship between the layered gabbro body and the Emeishan basalt and consulting the above age dating results, it is suggested that both the mafic ultramafic rocks and the basalts were formed at the end of the late Paleozoic period and associated with the Emei mantle plume activity.
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表 1 白马岩体的锆石U-Th-Pb定年结果
Table 1. Zircon U-Th-Pb dating results of the Baima intrusive body
测点 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 BM-1.1 0.02 611 376 0.64 21.3 256.4 ±2.1 244 ±42 245.4 ±3.9 0.2858 2.0 0.04058 0.82 0.409 BM-2.1 0.08 1249 194 0.16 43.3 254.6 ±1.9 293 ±27 252.2 ±5.1 0.2898 1.4 0.04028 0.75 0.529 BM-3.1 -- 912 716 0.81 31.5 253.7 ±1.9 254 ±50 245.4 ±2.9 0.2839 2.3 0.04014 0.78 0.337 BM-4.1 -- 603 538 0.92 21.4 261.2 ±2.1 260 ±39 246.1 ±3.3 0.2932 1.9 0.04135 0.82 0.432 BM-6.1 0.14 362 232 0.66 12.7 257.5 ±2.5 257 ±100 254.6 ±8.0 0.289 4.6 0.04076 10 0.217 BM-7.1 0.15 528 630 1.23 18.4 256.3 ±2.1 278 ±50 249.1 ±3.4 0.2899 2.3 0.04056 0.84 0.361 BM-8.1 -- 702 533 0.78 24.9 261.0 ±2.0 306 ±39 252.0 ±3.5 0.2989 1.9 0.04131 0.80 0.426 BM-9.1 -- 836 1032 1.27 29.4 259.1 ±2.0 296 ±35 245.4 ±2.7 0.2953 1.7 0.04100 0.78 0.452 BM-10.1 0.28 460 291 0.65 16.4 260.7 ±2.2 195 ±51 241.3 ±4.3 0.2845 2.4 0.04127 0.86 0.362 BM-11.1 -- 614 725 1.22 21.5 257.3 ±2.7 300 ±38 242.7 ±3.4 0.2938 2.0 0.04072 1.1 0.546 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 太和岩体的锆石U-Th-Pb定年结果
Table 2. Zircon U-Th-Pb dating results of the Taihe intrusive body
测点 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 TH-1.1 0.17 495 404 0.84 17.8 264.1 ±2.2 204 ±44 252.9 ±4.7 0.2895 2.1 0.04183 0.84 0.406 TH-2.1 0.42 646 221 0.35 23.0 260.6 ±2.1 119 ±71 236.8 ±8.1 0.2753 3.1 0.04126 0.82 0.264 TH-3.1 0.00 101 63 0.65 3.51 256.4 ±3.6 235 ±110 255.7 ±9.4 0.285 4.8 0.04058 1.4 0.296 TH-4.1 0.01 273 289 1.09 9.61 259.0 ±2.5 257 ±97 242.6 ±5.4 0.290 4.3 0.04099 0.97 0.224 TH-5.1 -- 371 259 0.72 13.1 261.0 ±2.3 356 ±70 260.5 ±5.8 0.3055 3.2 0.04131 0.90 0.280 TH-6.1 -- 210 167 0.82 7.43 260.8 ±2.6 340 ±92 266.8 ±7.0 0.303 4.2 0.04128 1.0 0.246 TH-7.1 0.11 949 488 0.53 33.5 259.2 ±1.9 238 ±36 253.1 ±3.7 0.2882 1.8 0.04103 0.76 0.435 TH-8.1 0.22 773 728 0.97 27L9 264.8 ±2.0 320 ±58 247.6 ±3.5 0.3053 2.7 0.04193 0.79 0.294 TH-9.1 0.14 693 667 0.99 24.6 260.6 ±2.1 251 ±56 249.9 ±3.6 0.2914 2.6 0.04125 0.80 0.312 TH-12.1 -- 830 416 0.52 29.8 264.5 ±2.0 290 ±30 259.9 ±4.9 0.3009 1.5 0.04188 0.77 0.504 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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