Zircon U-Pb ages, geochemical features and geological implications of Middle Devonian granite in Wulanbaixing area, Qimantag area of East Kunlun Mountains
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摘要:
东昆仑祁漫塔格乌兰拜兴地区花岗岩体由二长花岗岩和花岗闪长岩组成,SiO2含量为67.47%~73.63%,全碱(Na2O+K2O)含量为6.74%~7.89%,K2O/Na2O=0.59~1.30,A/CNK=0.91~1.08,属高钾钙碱性系列和钙碱性系列,准铝质-过铝质岩石。稀土元素总量平均为137.28×10-6,δEu值为0.37~0.89,平均为0.57,(La/Yb)N值为6.72~19.36,平均为10.75。稀土元素球粒陨石标准化配分曲线呈负Eu异常明显的右倾型;岩体明显富集大离子亲石元素Rb、K,不相容元素U和Th,轻稀土元素和Pb;相对亏损高场强元素Nb、Ta、P、Ti,以及大离子亲石元素Ba;岩石Rb/Sr值为0.45~1.17,平均为0.72,介于上地幔值和地壳值之间;Nb/Ta值为5.36~13.90,平均为10.93,比值总体低于地幔平均值,显示壳幔混合的特点。采用锆石U-Pb定年的方法,获得乌兰拜兴花岗闪长岩的206Pb/238U年龄为384.1±2.4Ma,代表该岩体的形成年龄。结合岩石地球化学、构造特征和区域地质背景,认为该岩体形成于中泥盆世晚期后碰撞陆内伸展阶段,并与铁多金属矿成矿密切相关,在矿产勘查中应引起重视。
Abstract:The granite in the study area is composed of monzogranite and granodiorite.Its silicon values are 67.47%~73.63%, alkali values are 6.74%~7.89%, K2O/Na2O values are 0.59~1.30, and A/CNK values are 0.91~1.08, suggesting that the rocks belong to metaluminous to peraluminous rocks of high-K cala-alkaline series and cala-alkaline series.The average values of ∑REE is 137.28×10-6; δEu values vary in the range of 0.37~0.89, with average values of 0.57; (La/Yb)N values vary in the range of 6.72~19.36, with an average value of 10.75.The chondrite-normalized REE patterns of rocks show the right deviation type with obvious negative Eu anomaly.The rocks are significantly enriched in large ion lithophile elements Rb, K and incompatible elements of U and Th as well as LREE and Pb, relatively depleted in high field strength elements Nb, Ta, P, Ti and large ion lithophile element Ba.The Rb/Sr ratios vary in the range of 0.45~1.17, with average value of 0.72, suggesting the upper mantle and the crust.The Nb/Ta ratios vary in the range of 5.36~13.90, with an average value of 10.93, which are overall lower than the average value of the mantle, and exhibit the characteristics of crust-mantle mixture.Using zircon U-Pb dating, the authors obtained the 206Pb/238U age 384.1±2.4Ma (MSWD) of Wulanbaixing granodiorite, which represents the formation age of the rock.In combination with geochemical and structural features and regional geological setting, the authors hold that the intrusive body was formed in an extension environment during post-collisional development stage in the Late Middle Devonian continent and was closely related to the mineralization of the iron-polymetallic deposit.Attentions should be paid to these phenomena in the further mineral exploration.
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Key words:
- granite /
- zircon U-Pb ages /
- geochemical features /
- Qimantag
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表 1 花岗岩主量、微量和稀土元素分析结果
Table 1. Analyses of major, trace and rare earth elements for granites
岩石
名称样品
号主量元素含量/% 总量
/%K2O/
Na2OA/
NKA/CNK K2O+
Na2O/%微量元素含量/10-6 SiO2 Al2O3 TFe2O3 FeO MgO CaO Na2O K2O MnO P2O5 TiO2 烧失量 Sc Cr 花岗闪
长岩B1 72.22 13.39 2.55 2.01 0.52 1.38 4.95 2.94 0.030 0.056 0.259 1.67 99.96 0.59 1.18 0.97 7.89 3.15 410 B2 73.63 12.98 2.56 1.51 0.48 1.54 3.99 3.45 0.028 0.062 0.295 0.98 100.0 0.86 1.26 0.99 7.44 4.40 373 B5 67.47 15.01 3.74 2.27 1.34 3.86 3.35 3.39 0.077 0.104 0.394 1.23 99.97 1.01 1.63 0.93 6.74 7.03 391 B6 72.51 13.60 2.46 1.69 0.53 1.77 4.40 3.24 0.023 0.057 0.266 1.01 99.87 0.74 1.27 0.97 7.64 3.37 588 B7 73.40 13.32 2.49 1.23 0.60 1.13 4.22 3.30 0.023 0.062 0.294 1.13 99.97 0.78 1.27 1.06 7.52 3.88 415 B9 73.49 13.33 2.22 1.29 0.47 1.32 4.17 3.35 0.021 0.057 0.275 1.27 99.97 0.80 1.27 1.03 7.52 4.18 491 二长花
岗岩B3 73.16 14.08 1.79 1.50 0.39 2.22 3.27 4.05 0.032 0.042 0.169 0.79 100.0 1.24 1.44 1.02 7.32 2.31 485 B4 73.40 13.58 2.38 1.93 0.60 1.95 2.96 3.86 0.040 0.079 0.323 0.78 99.96 1.30 1.50 1.08 6.82 2.78 546 B8 73.30 12.94 2.26 1.51 0.41 1.96 3.84 4.00 0.039 0.054 0.255 0.92 99.98 1.04 1.22 0.91 7.84 2.07 375 岩石
名称样品
号微量元素含量/10-6 Ga Rb Sr Y Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb 花岗闪
长岩B1 16.7 93.4 106 25.1 1.60 483 44.2 87.0 9.84 35.6 5.73 0.667 5.18 0.828 4.28 0.863 2.50 0.400 2.68 B2 15.4 101 139 21.6 2.62 468 28.6 55.7 6.34 23.5 4.15 0.551 3.77 0.692 3.72 0.770 2.25 0.364 2.51 B5 15.7 125 278 15.2 5.88 480 34.7 59.7 6.15 21.7 3.53 0.856 3.28 0.523 2.67 0.531 1.61 0.261 1.72 B6 16.4 90.1 150 26.2 1.14 493 38.7 75.9 8.63 31.4 5.42 0.631 4.70 0.814 4.55 0.870 2.60 0.461 3.07 B7 16.4 90.7 154 23.9 2.31 505 32.2 61.9 7.21 26.1 4.63 0.641 4.23 0.733 4.21 0.850 2.53 0.425 2.88 B9 17.9 99.8 149 23.7 2.34 494 36.9 71.5 8.02 29.1 5.18 0.628 4.57 0.775 4.28 0.836 2.46 0.413 2.65 二长花
岗岩B3 14.0 224 192 11.5 11.5 258 16.3 30.4 3.12 11.4 2.08 0.526 1.79 0.306 1.67 0.352 1.09 0.220 1.74 B4 15.8 139 203 8.57 8.82 455 30.5 52.7 5.33 18.4 2.76 0.604 2.38 0.331 1.62 0.287 0.922 0.161 1.13 B8 15.3 107 145 12.4 1.07 716 18.5 33.9 3.84 13.9 2.34 0.657 2.22 0.378 1.99 0.386 1.20 0.203 1.45 岩石
名称样品
号微量元素含量/10-6 LREE/
HREE(La/Yb)N δEu δCe Nb/Ta Rb/Sr La/Nb Ba/Nb Lu Pb Th U Nb Ta Zr Hf ΣREE LREE 花岗闪
长岩B1 0.391 11.1 12.8 1.34 7.49 0.663 72.4 2.67 200.16 183.04 10.69 11.83 0.37 0.98 11.30 0.88 5.90 64.49 B2 0.355 13.1 13.0 1.57 7.71 0.644 79.0 2.70 133.27 118.84 8.24 8.17 0.42 0.97 11.97 0.73 3.71 60.70 B5 0.252 19.7 25.7 2.63 7.30 0.767 76.0 2.28 137.48 126.64 11.67 14.47 0.76 0.92 9.52 0.45 4.75 65.75 B6 0.453 9.13 12.7 1.74 7.25 0.656 74.3 2.55 178.20 160.68 9.17 9.04 0.37 0.98 11.05 0.60 5.34 68.00 B7 0.405 11.6 11.8 1.78 7.95 0.655 73.4 2.64 148.94 132.68 8.16 8.02 0.43 0.96 12.14 0.59 4.05 63.52 B9 0.382 13.3 12.6 1.44 7.88 0.652 77.9 2.69 167.69 151.33 9.25 9.99 0.39 0.97 12.09 0.67 4.68 62.69 二长花
岗岩B3 0.301 27.6 26.1 3.15 7.72 1.44 64.0 2.56 71.30 63.83 8.55 6.72 0.81 0.98 5.36 1.17 2.11 33.42 B4 0.189 24.7 28.3 2.64 9.44 0.856 94.5 3.00 117.31 110.29 15.71 19.36 0.70 0.93 11.03 0.68 3.23 48.20 B8 0.204 16.7 5.39 0.934 4.56 0.328 91.8 2.45 81.17 73.14 9.11 9.15 0.87 0.94 13.90 0.74 4.06 157.02 表 2 乌兰拜兴地区花岗闪长岩锆石U-Th-Pb分析结果
Table 2. U-Th-Pb isotopic data of zircons of granodiorite in Wulanbaixing area
样品号 含量/10-6 Th/
U同位素比值 年龄/Ma Th U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 206Pb/238U 1σ B1-01 365 621 0.587 0.0534 2.9 0.457 3.2 0.0621 1.4 388 5 B1-02 314 484 0.649 0.0551 1.7 0.465 2.3 0.0612 1.7 383 6 B1-03 349 496 0.703 0.0531 1.7 0.462 2.3 0.0631 1.6 394 6 B1-04 499 642 0.777 0.0536 1.6 0.457 2.2 0.0618 1.4 387 5 B1-05 361 770 0.468 0.0548 1.4 0.462 2.0 0.0612 1.4 383 5 B1-06 169 478 0.354 0.0558 1.7 0.466 2.3 0.0605 1.5 379 5 B1-07 199 446 0.445 0.0518 1.9 0.434 2.4 0.0607 1.5 380 6 B1-08 387 727 0.532 0.0541 1.5 0.459 2.1 0.0615 1.5 385 5 B1-09 264 625 0.423 0.0536 1.8 0.451 2.3 0.0610 1.5 382 5 B1-10 149 445 0.335 0.0546 1.9 0.459 2.5 0.0610 1.6 382 6 B1-11 307 564 0.544 0.0529 1.7 0.455 2.3 0.0624 1.5 390 6 B1-12 376 680 0.554 0.0558 1.6 0.473 2.2 0.0614 1.6 384 6 B1-13 165 462 0.358 0.0530 2.0 0.446 2.6 0.0611 1.7 382 6 B1-14 276 484 0.571 0.0579 4.5 0.457 4.7 0.0572 1.6 358 5 B1-15 260 516 0.505 0.0529 2.7 0.444 3.1 0.0608 1.5 380 6 B1-16 494 797 0.619 0.0544 1.5 0.460 2.1 0.0613 1.4 383 5 B1-17 348 496 0.702 0.0537 2.0 0.454 2.5 0.0613 1.6 384 6 B1-18 221 454 0.487 0.0556 6.0 0.466 6.2 0.0609 1.6 381 6 B1-19 530 810 0.654 0.0539 1.6 0.460 2.3 0.0619 1.7 387 6 B1-20 158 407 0.388 0.0557 2.2 0.468 2.7 0.0609 1.7 381 6 B1-21 315 697 0.452 0.0558 1.7 0.475 2.3 0.0617 1.6 386 6 B1-22 182 381 0.478 0.0548 2.3 0.468 2.9 0.0620 1.8 388 7 B1-23 475 643 0.738 0.0565 1.7 0.478 2.3 0.0614 1.5 384 6 -
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