Geochemical characteristics and zircon U-Pb ages of the Kuoyitasi complex body from Mayileshan area in western Junggar, Xinjiang
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摘要: 新疆西准噶尔北部广泛发育中酸性侵入岩,其形成时代为晚石炭世-早二叠世,岩石类型为辉石闪长岩、石英闪长岩和花岗闪长岩。阔依塔斯杂岩体的形成年龄为(297±2)Ma,SiO2为52.40%~67.53%;高Al2O3,14.92%~17.85%;里特曼指数(δ)小于3.3,介于1.47~1.98;富钠贫钾,K2O/Na2O为0.15~0.49;铁高而镁低,FeOT/MgO为1.01~1.69。其稀土配分模式右倾,轻重稀土分馏明显,具有微弱铕正异常。地球化学和年代学特征表明:岩体形成于后碰撞演化的晚期阶段,这一时间早于东准噶尔后碰撞的时间(二叠纪末)。该杂岩体主体可能为幔源岩浆底侵镁铁质下地壳,导致发生部分熔融的产物。
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关键词:
- 西准噶尔 /
- 晚石炭世-早二叠世 /
- 后碰撞 /
- 岩石成因 /
- LA-ICP-MS锆石定年
Abstract: There are large-scale intermediate-acid intrusive rocks distributed in the north of western Junggar, Xinjiang. The rocks formed during late Carboniferous to early Permian. The typical plutons include pyroxene diorite, quartz diorite and granodiorite. The Kuoyitasi intrusion is among one of them. It has SiO2 values of 52.40%-67.53%, high Al2O3 content (14.92%-17.85%) and Na content, and low K and MgO content. Rittman values (δ) of the samples vary from 1.47 to 1.98, and the FeOT/MgO values are between 1.01 and 1.69. The REE patterns are characterized by LREE enrichment and slight Eu anomalies with obvious fractionation between LREE and HREE. The geochemical characteristics suggest that the Kuoyitasi intrusion formed in a post-collisional extensional tectonic environment, and should be formed earlier than the collision time of east Junggar terrain. The rocks were probably derived from partial melting of the lower crust which was intruded by mafic magmas.-
Keywords:
- western Junggar /
- Late-Early Pamir /
- Carboniferous /
- post-collision /
- petrogenesis
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图 2 阔依塔斯杂岩体岩石学特征
a—石英闪长岩中含大量角闪闪长岩包体,同时可见大量后期钾长石细脉;b—花岗闪长岩内各类包体;c—花岗闪长岩中辉石闪长岩包体(内又有角闪闪长岩包体);d—角闪岩包体;e—花岗闪长岩与辉长闪长岩间脉动接触;f—辉长闪长岩镜下照片;g—石英闪长岩镜下照片;h—花岗闪长岩镜下照片
Figure 2. Petrologic characteristics of Kuoyitasi complex body
a-Plenty of amphibole diorite inclusions in quartz diorite, with large quantities of late K-feldspar veinlits; b-Various inclusions in granodiorite; c- Gabbro diorite inclusions in granodiorite (with amphibole diorite inclusions); d-Diorite inclusion; e-Pulsation contact between granodiorite and gabbro diorite; f-Microphotograph of gabbro diorite; g- Microphotograph of quartz diorite; h- Microphotograph of granodiorite
表 1 西准噶尔阔依塔斯杂岩体主量元素(%)、微量和稀土元素(10-6)分析结果
Table 1 Analyses of major elements, trace elements and REE from Kuoyitasi complex body in west Junggar
样品号 P10YQ1 P10YQ2 P10YQ4 TP11YQ3 P10YQ3 岩性 辉长闪长岩 辉长闪长岩 辉长闪长岩 石英闪长岩 花岗闪长岩 SiO2 52.4 52.76 54.6 61.64 67.53 TiO2 0.76 0.85 0.8 0.55 0.46 Al2O3 15.88 17.85 17.45 16.4 14.92 Fe2O3 4.82 2.4 6.1 1.11 1.74 FeO 2.18 4.72 2.11 3.95 1.76 MnO 0.11 0.12 0.14 0.1 0.05 MgO 7.14 5.68 5.82 3.26 2.17 CaO 6.74 8.71 7.82 3.59 3.56 Na2O 3.66 3.85 3.69 5.15 4.05 K2O 1.25 0.58 0.61 1.04 1.99 P2O5 0.18 0.25 0.2 0.14 0.13 烧失量 1.36 1.53 0.7 2.15 1.37 H2O+ 0.94 0.93 0.59 1.72 1.06 H2O- 0.18 0.21 0.17 0.15 0.2 Total 99.48 99.29 100.04 100.95 99.73 K2H2O+/Na2H2O+ 0.34 0.15 0.17 0.2 0.49 Na2H2O++K2H2O+ 4.91 4.43 4.3 6.19 6.04 A/NK 2.15 2.56 2.59 1.71 1.69 A/CKN 0.81 0.78 0.83 1.02 0.98 δ 1.76 1.87 1.55 1.98 1.47 Rb 26.9 9 10.3 32.24 68.06 Ba 444 282 347 496 643 Th 2.4 1.3 1.1 9.49 9.42 Nb 2.9 3.1 2.5 12.54 11.66 Ta 0.24 0.22 0.2 0.98 0.91 Sr 635 840 703 226 189 Zr 92 86 94 357.7 336.14 Hf 4.9 3.6 4.1 8.7 8.21 Y 14.4 14.6 13.8 24.4 22.54 Sc 20.8 26.1 22.7 4.36 4.26 Cr 192 142 206 29.2 49.2 Co 29 30 32 P 949 1263 1052 685 770 La 9.86 8.24 9.28 22.09 25.87 Ce 20.9 18.6 20.2 47.43 51.06 Pr 2.95 2.74 3.01 7.16 7.08 Nd 13.4 14 14.2 27.34 25.77 Sm 2.92 3.26 3.13 4.98 5.49 Eu 0.96 1.08 1.17 1.2 1.18 Gd 2.72 3.13 2.96 4.55 4.29 Tb 0.48 0.54 0.49 0.78 0.73 Dy 2.72 3.08 2.86 4.66 4.22 Ho 0.54 0.57 0.542 0.9 0.81 Er 1.5 1.6 1.44 2.57 2.33 Tm 0.23 0.23 0.23 0.46 0.42 Yb 1.43 1.43 1.4 3.04 2.86 Lu 0.21 0.23 0.23 0.43 0.4 ΣREE 60.73 58.67 61.14 127.6 132.52 LREE/HREE 5.18 4.43 5.03 6.34 7.25 δEu 1.03 1.02 1.15 0.76 0.72 (La/Yb)N 4.95 4.13 4.75 5.22 6.49 (La/Sm)N 2.18 1.63 1.91 2.86 3.04 (Gd/Yb)N 1.57 1.81 1.75 1.24 1.24 表 2 阔依塔斯杂岩体CIPW标准矿物及岩石化学参数一览表
Table 2 Analyses of CIPW and chemical parameters of rock from Kuoyitasi complex body
样品号 P10YQ1 P10YQ2 P10YQ4 TP11YQ3 P10YQ3 岩性 辉长闪长岩 辉长闪长岩 辉长闪长岩 石英闪长岩 花岗闪长岩 Q 5.41 1.71 4.76 13.4 25.37 Au 23.47 30.39 29.55 17.43 16.94 Ab 31.32 33.33 31.55 44.96 34.85 Or 7.47 3.51 3.64 6.34 11.96 Ne 0 0 0 0 0 C 0 0 0 0.63 0 Di 7.32 9.77 6.72 0 0.13 Hy 19.73 15.63 18.06 14.17 7.56 Ol 0 0 0 0 0 Cs 0 0 0 0 0 Il 1.46 1.65 1.54 1.08 0.89 Mt 3.39 3.42 3.72 1.66 2 Ap 0.42 0.59 0.47 0.33 0.31 Zr 0 0 0 0 0 合计 100 100 100.01 100 100.01 DI 44.2 38.55 39.95 64.7 72.18 A/CNK 0.809 0.783 0.833 1.017 0.976 SI 37.98 32.98 32.38 22.47 18.59 A.R 1.55 1.4 1.41 1.9 1.97 σ 1.76 1.87 1.55 1.98 1.47 R1 1986 1839 1971 1941 2532 R2 1403 1600 1483 895 795 F1 0.54 0.5 0.53 0.62 0.66 F2 -1.49 -1.55 -1.53 -1.48 -1.34 F3 -2.54 -2.56 -2.53 -2.6 -2.56 A/MF 0.58 0.74 0.68 1.07 1.46 C/MF 0.45 0.66 0.56 0.43 0.63 表 3 西准噶尔阔依塔斯杂岩体LA-ICP-MS锆石U-Pb同位素测试结果
Table 3 Zircon U-Pb isotopic data obtained by LA-ICP-MS from Kuoyitasi complex body in west Junggar
测点号 含量/10-6 Th/U 同位素比值 表面年龄/Ma 207Pb/206Pb lσ 207Pb/235U lσ 238Pb/238U lσ 207Pb/206Pb lσ 207Pb/235U lσ 238Pb/238U lσ 01 3 38 45 0.84 0.0546 0.0017 0.3617 0.0059 0.0481 0.0006 395 71 314 5 303 4 02 5 65 80 0.82 0.0514 0.0009 0.3397 0.0036 0.0480 0.0006 257 41 297 3 302 4 03 3 41 49 0.82 0.0513 0.0012 0.3304 0.0050 0.0467 0.0005 256 55 290 4 294 3 04 4 25 52 0.49 0.0525 0.0010 0.3398 0.0038 0.0470 0.0009 306 44 297 3 296 6 05 7 80 109 0.74 0.0527 0.0012 0.3524 0.0033 0.0485 0.0009 318 51 307 3 305 5 06 4 33 61 0.54 0.0524 0.0012 0.3468 0.0039 0.0480 0.0009 304 50 302 3 302 5 07 4 49 62 0.78 0.0530 0.0010 0.3470 0.0040 0.0475 0.0006 330 44 302 4 299 4 08 4 47 60 0.78 0.0537 0.0015 0.3508 0.0046 0.0474 0.0006 359 62 305 4 298 4 09 4 38 61 0.63 0.0541 0.0014 0.3430 0.0040 0.0460 0.0006 376 57 299 3 290 4 10 4 33 57 0.57 0.0541 0.0011 0.3448 0.0040 0.0462 0.0009 377 47 301 3 291 6 11 5 56 80 0.71 0.0547 0.0011 0.3505 0.0038 0.0465 0.0008 399 43 305 3 293 5 12 5 58 86 0.67 0.0510 0.0012 0.3273 0.0053 0.0466 0.0006 240 56 288 5 293 4 13 6 93 109 0.86 0.0543 0.0009 0.3507 0.0031 0.0469 0.0005 381 38 305 3 295 3 14 5 22 56 0.38 0.0512 0.0015 0.3378 0.0043 0.0479 0.0006 249 69 295 4 301 4 15 9 113 155 0.73 0.0532 0.0016 0.3491 0.0027 0.0476 0.0010 339 66 304 2 299 6 16 5 47 76 0.61 0.0525 0.0012 0.3423 0.0041 0.0473 0.0007 307 54 299 4 298 4 17 5 38 72 0.53 0.0530 0.0012 0.3356 0.0038 0.0459 0.0005 327 51 294 3 290 3 18 5 39 75 0.53 0.0527 0.0012 0.3451 0.0042 0.0475 0.0009 315 52 301 4 299 5 -
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