LA-ICP-MS zircon U-Pb dating of the Chongshan Group in the Xiaowan area along the southern section of the Lancang River in western Yunnan and its geological significance
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摘要:
滇西崇山岩群一直被认为是元古宙的大陆地壳-结晶基底,但至今无精确的年龄依据。对滇西澜沧江南段小湾地区崇山岩群的5件样品(糜棱岩化斜长变粒岩、黑云斜长角闪岩、片麻岩、糜棱岩化花岗质片麻岩、糜棱岩化黑云斜长变粒岩)进行锆石U-Pb定年。5件样品的锆石阴极发光图像显示,锆石有明显的生长振荡环带,指示岩浆成因。5件样品锆石的206Pb/238U年龄加权平均值分别为239.4±3.8Ma、248.4±4.3Ma、237.1±5.7Ma、268.7±3.2Ma、238.4±5.5Ma。根据野外地质特征和年龄数据,认为滇西澜沧江南段小湾地区崇山岩群是不同时代、不同岩性的岩体/地层(二叠系、三叠系)经后期变质作用形成的一套正变质岩,并不全是古老基底岩石出露。
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关键词:
- 崇山岩群 /
- LA-ICP-MS锆石U-Pb定年 /
- 小湾 /
- 澜沧江南段 /
- 滇西
Abstract:This paper focuses on the LA-ICP-MS U-Pb ages of the zircons of five samples(mylonitization plagioclase leptynite, bio-tite amphibolites, gneiss, mylonitization granitic gneiss, and mylonitization biotite amphibolites)from the Chongshan Group in the Xiaowan area along the southern section of Lancang River of western Yunnan.Cathodoluminescence images of five samples reveal that these zircon crystals generally have oscillatory zoning, implying their magatic genesis.One hundred and two analyses of five sam-ples yielded concordance, with their weighted average ages being 239.4±3.8Ma, 248.4±4.3Ma, 237.1±5.7Ma, 268.7±3.2Ma, and 238.4±5.5Ma.According to geological characteristics and available age data, it is considered that the so-called Chongshan Group in the Xiaowan area is orthometamorphite composed of various parent components with different ages rather than entirely Proterozoic crystalline basement rocks as previously considered.
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表 1 测年样品LA-ICP-MS锆石U-Th-Pb同位素分析数据
Table 1. LA-ICP-MS zircons U-Th-Pb data
点号 含量/10-6 Th/U 同位素比值 同位素年龄值/Ma Pb Th U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 糜棱岩化斜长变粒岩(D0006-1) 1 31.3 158 282 0.56 0.0525 0.0023 0.2763 0.0110 0.0384 0.0006 309 100 248 9 243 3 2 67.5 352 622 0.56 0.0526 0.0016 0.2711 0.0083 0.0374 0.0004 309 69 244 7 237 3 3 58.6 358 397 0.90 0.0562 0.0021 0.2762 0.0104 0.0357 0.0005 461 83 248 8 226 3 4 57.8 323 472 0.68 0.0536 0.0020 0.2685 0.0095 0.0363 0.0004 367 53 241 8 230 3 5 44.8 259 347 0.75 0.0538 0.0023 0.2811 0.0123 0.0380 0.0006 365 96 252 10 241 4 6 47.7 241 398 0.61 0.0533 0.0021 0.2847 0.0111 0.0388 0.0005 343 89 254 9 245 3 7 31.2 184 237 0.78 0.0520 0.0028 0.2669 0.0140 0.0373 0.0005 283 150 240 11 236 3 8 70.2 406 491 0.83 0.0505 0.0019 0.2663 0.0105 0.0381 0.0006 217 85 240 8 241 4 9 56.6 313 406 0.77 0.0503 0.0022 0.2639 0.0119 0.0380 0.0006 209 102 238 10 240 4 10 47.2 273 373 0.73 0.0476 0.0023 0.2437 0.0108 0.0372 0.0005 83 107 221 9 235 3 11 36.5 221 262 0.84 0.0509 0.0029 0.2606 0.0137 0.0373 0.0005 235 133 235 11 236 3 12 85.1 522 567 0.92 0.0566 0.0024 0.2868 0.0122 0.0367 0.0006 476 90 256 10 232 4 13 54.9 252 412 0.61 0.0620 0.0029 0.3648 0.0202 0.0418 0.0008 674 98 316 15 264 5 14 46.9 259 248 1.05 0.0566 0.0026 0.3173 0.0142 0.0406 0.0006 476 102 280 11 256 4 15 57.7 282 505 0.56 0.0493 0.0019 0.2642 0.0084 0.0388 0.0005 165 86 238 7 245 3 16 59.8 312 448 0.70 0.0523 0.0019 0.3080 0.0109 0.0426 0.0006 298 88 273 8 269 4 17 38.0 212 279 0.76 0.0524 0.0028 0.2774 0.0152 0.0385 0.0008 306 129 249 12 244 5 18 71.0 403 568 0.71 0.0520 0.0017 0.2697 0.0091 0.0373 0.0005 287 77 242 7 236 3 19 58.1 347 394 0.88 0.0550 0.0020 0.2826 0.0102 0.0373 0.0006 413 88 253 8 236 4 20 39.1 190 254 0.75 0.0594 0.0026 0.3379 0.0144 0.0413 0.0006 583 94 296 11 261 4 21 61.8 344 486 0.71 0.0512 0.0019 0.2729 0.0100 0.0386 0.0005 254 90 245 8 244 3 22 29.9 178 187 0.96 0.0510 0.0024 0.2648 0.0118 0.0381 0.0006 239 107 238 9 241 4 23 60.6 378 360 1.05 0.0510 0.0021 0.2597 0.0103 0.0368 0.0005 243 93 234 8 233 3 24 37.1 206 252 0.82 0.0521 0.0024 0.2791 0.0135 0.0389 0.0006 300 101 250 11 246 4 黑云斜长角闪岩(D0007-1) 1 92.1 427 754 0.57 0.0550 0.0015 0.2955 0.0091 0.0388 0.0005 413 63 263 7 245 3 2 77.0 434 445 0.98 0.0660 0.0024 0.3417 0.0121 0.0375 0.0004 809 74 298 9 237 3 3 44.9 224 395 0.57 0.0521 0.0021 0.2697 0.0107 0.0375 0.0005 287 91 242 9 238 3 4 68.1 287 439 0.65 0.0535 0.0016 0.3220 0.0097 0.0437 0.0007 350 69 283 7 276 4 5 57.3 246 541 0.45 0.0560 0.0020 0.3036 0.0127 0.0392 0.0010 450 80 269 10 248 6 6 47.5 243 341 0.71 0.0537 0.0022 0.2818 0.0115 0.0381 0.0005 367 94 252 9 241 3 7 53.4 270 299 0.90 0.0625 0.0024 0.3376 0.0138 0.0390 0.0006 694 83 295 10 247 4 8 44.5 226 334 0.68 0.0543 0.0026 0.2853 0.0128 0.0387 0.0011 383 114 255 10 245 7 9 72.7 381 470 0.81 0.0516 0.0018 0.2743 0.0105 0.0385 0.0009 333 81 246 8 244 5 10 57.8 261 398 0.66 0.0574 0.0022 0.3296 0.0139 0.0413 0.0006 509 85 289 11 261 4 11 80.3 407 562 0.72 0.0534 0.0018 0.2891 0.0110 0.0392 0.0009 343 78 258 9 248 6 12 48.5 226 394 0.57 0.0520 0.0021 0.2805 0.0133 0.0390 0.0010 283 94 251 11 246 6 13 67.0 342 488 0.70 0.0577 0.0020 0.3157 0.0113 0.0395 0.0005 520 76 279 9 250 3 14 52.3 236 286 0.83 0.0623 0.0031 0.3352 0.0152 0.0394 0.0006 687 106 294 12 249 4 15 45.1 243 330 0.74 0.0510 0.0021 0.2554 0.0107 0.0365 0.0007 239 94 231 9 231 4 16 60.1 349 261 1.33 0.0571 0.0024 0.3004 0.0140 0.0385 0.0011 494 94 267 11 243 7 17 62.9 288 612 0.47 0.0516 0.0016 0.2684 0.0097 0.0377 0.0008 265 77 241 8 238 5 18 51.5 244 469 0.52 0.0531 0.0019 0.2727 0.0099 0.0376 0.0009 345 80 245 8 238 6 19 45.8 215 335 0.64 0.0500 0.0017 0.2718 0.0111 0.0391 0.0008 195 75 244 9 247 5 20 86.1 502 475 1.06 0.0617 0.0024 0.3215 0.0141 0.0377 0.0009 665 85 283 11 238 5 21 29.9 113 344 0.33 0.0541 0.0024 0.2924 0.0119 0.0402 0.0011 376 100 260 9 254 7 22 70.0 339 408 0.83 0.0589 0.0021 0.3324 0.0125 0.0407 0.0007 561 76 291 10 257 4 23 55.1 226 488 0.46 0.0532 0.0019 0.3066 0.0127 0.0422 0.0012 345 83 272 10 267 7 24 101.7 505 492 1.03 0.0570 0.0017 0.3398 0.0106 0.0432 0.0007 500 67 297 8 273 5 25 61.2 229 501 0.46 0.0535 0.0019 0.2990 0.0115 0.0402 0.0006 350 81 266 9 254 4 26 40.4 197 161 1.22 0.0602 0.0038 0.3395 0.0227 0.0403 0.0009 609 139 297 17 255 6 27 53.8 248 242 1.03 0.0600 0.0029 0.3189 0.0163 0.0383 0.0008 606 104 281 13 242 5 28 83.1 416 488 0.85 0.0520 0.0020 0.2685 0.0122 0.0371 0.0009 283 89 241 10 235 6 29 100.8 405 667 0.61 0.0599 0.0025 0.3231 0.0150 0.0388 0.0008 611 91 284 12 246 5 30 33.9 150 217 0.69 0.0499 0.0030 0.2762 0.0169 0.0400 0.0008 191 143 248 13 253 5 31 51.5 228 248 0.92 0.0506 0.0032 0.2934 0.0204 0.0419 0.0012 233 144 261 16 265 7 32 73.5 365 397 0.92 0.0526 0.0022 0.2803 0.0126 0.0385 0.0010 309 96 251 10 244 6 33 36.2 179 218 0.82 0.0540 0.0032 0.2915 0.0197 0.0385 0.0011 372 135 260 16 243 7 34 63.6 308 475 0.65 0.0564 0.0027 0.2930 0.0134 0.0380 0.0008 478 103 261 11 241 5 35 70.3 272 676 0.40 0.0591 0.0023 0.3212 0.0142 0.0397 0.0011 569 87 283 11 251 7 36 71.7 304 567 0.54 0.0572 0.0022 0.3171 0.0128 0.0405 0.0008 502 85 280 10 256 5 37 23.9 118 128 0.92 0.0591 0.0040 0.3284 0.0211 0.0413 0.0009 572 151 288 16 261 6 38 62.5 330 319 1.03 0.0501 0.0027 0.2683 0.0148 0.0393 0.0008 198 121 241 12 248 5 39 41.1 190 272 0.70 0.0555 0.0031 0.2945 0.0148 0.0401 0.0007 432 124 262 12 253 5 40 153.8 871 827 1.05 0.0530 0.0018 0.2772 0.0089 0.0391 0.0006 328 108 248 7 247 4 片麻岩(D1050-1) 1 67.4 2957 4838 0.61 0.0686 0.0028 0.3694 0.0159 0.0379 0.0006 887 83 319 12 240 3 2 63.7 2109 4885 0.43 0.0775 0.0034 0.3913 0.0159 0.0372 0.0006 1133 88 335 12 236 4 3 43.4 1690 3700 0.46 0.0539 0.0021 0.2752 0.0099 0.0370 0.0005 369 87 247 8 234 3 4 99.0 5508 7302 0.75 0.0500 0.0015 0.2579 0.0074 0.0372 0.0005 195 69 233 6 235 3 5 42.2 2395 2996 0.80 0.0534 0.0024 0.2704 0.0120 0.0368 0.0006 346 106 243 10 233 4 6 135.8 7757 9722 0.80 0.0526 0.0015 0.2728 0.0079 0.0370 0.0005 322 60 245 6 234 3 7 131.2 7728 9357 0.83 0.0495 0.0013 0.2541 0.0065 0.0368 0.0004 169 63 230 5 233 3 8 118.4 4452 9092 0.49 0.0678 0.0021 0.3735 0.0142 0.0384 0.0006 865 65 322 11 243 4 9 73.0 2845 5024 0.57 0.0769 0.0029 0.4258 0.0162 0.0393 0.0006 1120 74 360 12 248 4 10 99.3 3359 6027 0.56 0.0988 0.0059 0.5971 0.0425 0.0394 0.0007 2000 112 475 27 249 4 11 53.6 2454 4347 0.56 0.0524 0.0024 0.2658 0.0122 0.0367 0.0005 306 104 239 10 232 3 12 127.3 7152 9617 0.74 0.0515 0.0015 0.2641 0.0078 0.0366 0.0004 265 67 238 6 232 2 13 278.0 18013 20447 0.88 0.0557 0.0016 0.2845 0.0089 0.0363 0.0004 439 65 254 7 230 2 14 121.4 5053 10302 0.49 0.0500 0.0015 0.2530 0.0072 0.0365 0.0005 195 70 229 6 231 3 15 142.7 6831 11466 0.60 0.0538 0.0015 0.2765 0.0070 0.0371 0.0004 365 65 248 6 235 3 16 66.2 2851 5551 0.51 0.0503 0.0018 0.2568 0.0088 0.0370 0.0005 209 90 232 7 234 3 17 141.9 7962 11082 0.72 0.0497 0.0014 0.2568 0.0071 0.0369 0.0004 189 67 232 6 234 3 18 71.4 4470 5258 0.85 0.0534 0.0022 0.2732 0.0110 0.0367 0.0006 346 91 245 9 232 4 19 97.7 3800 8731 0.44 0.0650 0.0020 0.3143 0.0094 0.0347 0.0004 776 66 278 7 220 3 20 96.5 3484 8149 0.43 0.0535 0.0018 0.2928 0.0093 0.0394 0.0005 350 81 261 7 249 3 21 87.5 3967 7095 0.56 0.0534 0.0019 0.2886 0.0096 0.0390 0.0005 346 86 257 8 246 3 22 163.6 7742 13557 0.57 0.0570 0.0016 0.2979 0.0080 0.0374 0.0004 500 63 265 6 237 2 23 118.8 5369 8151 0.66 0.0502 0.0016 0.3041 0.0095 0.0436 0.0006 206 76 270 7 275 4 24 57.1 2184 4297 0.51 0.0601 0.0026 0.3435 0.0139 0.0414 0.0007 609 88 300 10 262 4 糜棱岩化花岗质片麻岩(D1051-1) 1 144.1 5029 11501 0.44 0.0486 0.0015 0.3053 0.0094 0.0453 0.0007 128 70 271 7 286 4 2 161.4 7705 11691 0.66 0.0513 0.0015 0.2997 0.0085 0.0421 0.0005 254 70 266 7 266 3 3 73.9 3899 5290 0.74 0.0489 0.0019 0.2847 0.0108 0.0422 0.0006 143 90 254 9 266 3 4 79.0 4859 4722 1.03 0.0549 0.0020 0.3436 0.0118 0.0455 0.0006 409 88 300 9 287 4 5 72.2 3848 4921 0.78 0.0547 0.0021 0.3199 0.0118 0.0424 0.0006 398 79 282 9 268 4 6 143.2 8376 9719 0.86 0.0514 0.0017 0.2973 0.0094 0.0421 0.0005 257 71 264 7 266 3 7 152.7 6692 11965 0.56 0.0505 0.0014 0.2948 0.0077 0.0422 0.0005 220 56 262 6 266 3 8 181.5 10767 11953 0.90 0.0526 0.0015 0.3068 0.0083 0.0423 0.0005 322 67 272 6 267 3 9 216.4 11007 16874 0.65 0.0561 0.0014 0.3286 0.0085 0.0422 0.0005 457 62 289 6 267 3 10 151.5 5109 9236 0.55 0.0994 0.0038 0.6497 0.0293 0.0453 0.0007 1614 70 508 18 285 4 11 172.3 7372 13152 0.56 0.0549 0.0015 0.3231 0.0085 0.0426 0.0006 406 66 284 6 269 4 12 201.2 8974 14189 0.63 0.0633 0.0019 0.3729 0.0114 0.0424 0.0005 720 65 322 8 267 3 13 111.3 6481 7388 0.88 0.0554 0.0022 0.3226 0.0122 0.0426 0.0006 428 89 284 9 269 4 14 243.0 13122 17844 0.74 0.0596 0.0015 0.3440 0.0092 0.0415 0.0005 587 56 300 7 262 3 15 182.5 10581 12476 0.85 0.0519 0.0015 0.3047 0.0084 0.0422 0.0004 283 65 270 7 266 3 16 117.8 5406 9067 0.60 0.0537 0.0016 0.3178 0.0097 0.0426 0.0006 367 73 280 8 269 4 17 103.6 5415 7616 0.71 0.0542 0.0019 0.3155 0.0104 0.0423 0.0005 389 80 278 8 267 3 18 92.0 4449 6691 0.66 0.0593 0.0030 0.3484 0.0189 0.0420 0.0006 576 109 304 14 265 4 19 75.8 3494 5542 0.63 0.0534 0.0019 0.3103 0.0106 0.0421 0.0006 346 84 274 8 266 4 20 92.7 4238 6859 0.62 0.0633 0.0087 0.3932 0.0735 0.0424 0.0006 717 296 337 54 268 4 21 152.2 8546 8602 0.99 0.0795 0.0023 0.4696 0.0135 0.0422 0.0005 1187 56 391 9 266 3 糜棱岩化黑云斜长变粒岩(D6714-1) 1 40.6 179 198 0.90 0.0386 0.0066 0.2075 0.0261 0.0384 0.0015 191 22 243 9 2 63.5 292 303 0.97 0.0460 0.0056 0.2156 0.0201 0.0353 0.0010 -- -- 198 17 223 6 3 85.1 280 258 1.09 0.0718 0.0084 0.4866 0.0437 0.0495 0.0023 989 273 403 30 311 14 4 53.4 248 246 1.01 0.0493 0.0076 0.2409 0.0293 0.0366 0.0014 161 326 219 24 232 8 5 108.7 439 591 0.74 0.0454 0.0041 0.2494 0.0197 0.0394 0.0010 -- -- 226 16 249 6 6 76.4 361 314 1.15 0.0501 0.0060 0.2312 0.0258 0.0357 0.0012 198 259 211 21 226 8 7 70.1 343 324 1.06 0.0506 0.0059 0.2665 0.0268 0.0383 0.0012 233 239 240 21 243 8 8 125.4 597 516 1.16 0.0502 0.0057 0.2352 0.0223 0.0364 0.0014 211 244 215 18 230 8 9 86.7 446 314 1.42 0.0578 0.0063 0.2932 0.0287 0.0374 0.0010 520 243 261 23 236 6 10 43.1 193 244 0.79 0.0516 0.0068 0.2659 0.0293 0.0376 0.0013 265 281 239 23 238 8 11 46.3 219 250 0.88 0.0511 0.0056 0.2701 0.0225 0.0383 0.0015 243 233 243 18 242 9 12 113.5 554 476 1.16 0.0586 0.0054 0.2832 0.0232 0.0355 0.0010 554 199 253 18 225 6 13 60.6 286 293 0.98 0.0682 0.0088 0.3468 0.0398 0.0377 0.0011 876 269 302 30 239 7 14 87.4 402 445 0.90 0.0512 0.0053 0.2618 0.0237 0.0373 0.0011 256 217 236 19 236 7 15 187.3 650 1555 0.42 0.0570 0.0032 0.2958 0.0161 0.0377 0.0008 500 124 263 13 238 5 16 41.5 203 220 0.92 0.0559 0.0079 0.2590 0.0292 0.0358 0.0014 450 321 234 24 227 9 17 42.2 179 230 0.77 0.0585 0.0072 0.2967 0.0328 0.0373 0.0011 550 270 264 26 236 7 18 63.7 325 296 1.10 0.0552 0.0075 0.2720 0.0300 0.0378 0.0012 420 309 244 24 239 7 19 89.1 341 318 1.07 0.0634 0.0060 0.3514 0.0284 0.0408 0.0012 720 202 306 21 258 7 20 29.6 129 155 0.83 0.0589 0.0097 0.3012 0.0377 0.0394 0.0016 565 360 267 29 249 10 21 141.3 649 612 1.06 0.0637 0.0057 0.3000 0.0247 0.0338 0.0009 731 189 266 19 214 6 22 117.6 555 427 1.30 0.0506 0.0057 0.2618 0.0245 0.0383 0.0011 220 244 236 20 242 7 23 73.8 317 310 1.02 0.0513 0.0058 0.2636 0.0222 0.0390 0.0012 254 241 238 18 247 7 24 98.3 482 415 1.16 0.0518 0.0055 0.2742 0.0238 0.0392 0.0011 280 244 246 19 248 7 25 171.4 816 738 1.11 0.0571 0.0051 0.2630 0.0199 0.0345 0.0009 494 196 237 16 219 5 26 94.3 375 498 0.75 0.0546 0.0048 0.3317 0.0275 0.0446 0.0015 398 198 291 21 281 9 27 51.0 218 240 0.91 0.0519 0.0067 0.2624 0.0306 0.0367 0.0013 280 274 237 25 232 8 28 66.1 309 294 1.05 0.0533 0.0066 0.2607 0.0254 0.0355 0.0010 343 288 235 20 225 7 29 47.9 192 250 0.77 0.0523 0.0075 0.2696 0.0330 0.0402 0.0013 298 300 242 26 254 8 30 113.2 434 597 0.73 0.0659 0.0060 0.3225 0.0261 0.0356 0.0013 806 186 284 20 225 8 -
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