GEOCHEMICAL CHARACTERISTICS OF THE YOUHULUGOU BASALTS IN THE SUTURE ZONE OF THE NORTH QILIAN MOUNTAIN
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摘要: 对油葫芦沟蛇绿岩中玄武岩进行了地球化学研究, 以探讨其形成环境。油葫芦沟蛇绿岩中玄武岩的主量和微量元素具有低钾富钠的特征, 属低钾(拉斑)系列。玄武岩的球粒陨石标准化稀土元素分配模式图表现为近平坦型, 轻重稀土富集不明显, 属于亏损地幔(N型)。大离子亲石元素(LILE)Rb、K和Sr出现负异常, 高场强元素(HFSE)Nb、Ta、Hf、Zr无负异常, 表现出大洋中脊幔源岩浆作用的特征。构造环境判别图显示, 油葫芦沟玄武岩属于典型的亏损型大洋中脊玄武岩(MORB)。研究结果表明油葫芦沟蛇绿岩中玄武岩为北祁连洋洋壳的组成部分, 北祁连洋在晚元古代—晚寒武世为典型的大洋中脊环境。Abstract: Geochemical study for the basalt of Youhulugou ophiolite was carried out and discussed its genesis environment. Major and trace element in basalt is one of the representative ophiolite fragments in the suture zone of the North Qilian Mountain. In this study, geochemical study and indicates that the basalts from the Youhulugou ophiolite have N-MORB type characteristics. And according to the REE distribution patterns with no anomaly, the basalts are also similar to mid-ocean ridge basalt. Meanwhile, these basalts are generally depleted in large ion lithophile elements (LILE) of Rb、K and Sr, and high field strength elements (HFSE) are normal, indicating the characteristics of mantle-derived magma from mid oceanic ridge. Tectonic environment discrimination diagrams also suggest that these basalts are typical mid oceanic ridge basalts (MORB). Combined with regional geological characters and geochemical data, we conclude that the Youhulugou basalts represents a part of the dismembered North Qianlian oceanic crust of the era. And the tectonic setting of the North Qilian Ocean was mid-ocean ridge during the late Proterozoic to late Cambrian.
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Key words:
- North Qilian suture zone /
- Youhulugou basalts /
- geochemical characteristics /
- MOR /
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图 4 油葫芦沟地区玄武岩岩性判别图
a—(Na2O+K2O)-SiO2分类图(原图据文献[21];Pc—苦橄玄武岩;B—玄武岩;O1—玄武安山岩;O2—安山岩;O3—英安岩;R—流纹岩;S1—粗面玄武岩;S2—玄武质粗面安山岩;S3—粗面安山岩;T—粗面岩、粗面英安岩;F—副长石岩;U1—碱玄岩、碧玄岩;U2—响岩质碱玄岩;U3—碱玄质响岩;Ph—响岩;Ir—Irvine分界线,上方为碱性,下方为亚碱性);b—K2O-SiO2分类图(实线据文献[22],虚线据文献[23])
Figure 4. Discrimination diagrams of basalt in Youhulugou area
图 5 油葫芦沟地区玄武岩类构造环境判别图
a—Zr/Y-Zr分类图(原图据文献[24]);b—TiO2-Zr分类图(原图据文献[25]);c—P2O5-TiO2分类图(原图据文献[26]);d—Th/Yb-Ta/Yb分类图(原图据文献[25]);IAB—岛弧玄武岩;IAT—岛弧拉斑系列;ICA—岛弧钙碱系列;SHO—岛弧橄榄玄粗岩系列;WPB—板内玄武岩;MORB—洋中脊玄武岩;TH—拉斑玄武岩;TR—过渡玄武岩;ALK—碱性玄武岩
Figure 5. Tectonic environment discrimination diagrams of basalts from Youhulugou area
表 1 油葫芦沟玄武岩主量元素分析结果
Table 1. Major elements of basalts in Youhulugou area%
% 样品号 SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2O K2O P2O5 CO2 H2O+ TOTAL B063-1 48.32 1.50 13.09 5.82 5.34 0.15 5.05 7.08 4.63 0.03 0.14 5.14 3.34 99.63 B063-2 45.73 1.51 13.03 3.69 7.38 0.16 5.68 8.26 3.75 0.04 0.12 6.26 3.68 99.29 B063-3 46.07 1.38 12.06 5.21 5.35 0.17 4.11 9.90 4.39 0.02 0.13 7.20 3.30 99.29 B063-4 46.47 1.58 13.13 2.99 7.35 0.16 5.99 7.77 3.77 0.02 0.13 6.17 4.04 99.57 B063-6 47.64 1.77 15.10 5.89 6.41 0.14 6.25 5.06 4.61 0.14 0.15 2.49 3.88 99.53 表 2 油葫芦沟玄武岩微量元素分析结果
Table 2. Trace elements of basalts in Youhulugou areaμg/g
μg/g 样品号 Sr Rb Ba Th Ta Nb Zr Hf Sc Cr Ni Co V U La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y B063-1 127 0.59 45.6 0.34 0.25 3.56 83.9 2.77 45.2 172 60.1 39.8 297 0.25 3.04 8.57 1.35 7.94 2.79 0.84 4.03 0.87 4.92 1.28 3.24 0.61 3.26 0.53 40.0 B063-2 126 1.11 29.5 0.35 0.26 3.58 83.5 2.69 45.2 163 62.1 46.9 329 0.14 3.82 10.6 1.69 9.35 2.89 1.03 4.09 0.85 4.68 1.18 3.09 0.58 3.12 0.51 36.0 B063-3 133 0.49 31.5 0.33 0.25 3.44 80.2 2.61 42.4 144 49.8 36.9 294 0.28 3.51 9.45 1.54 8.74 2.80 1.03 3.73 0.79 4.66 1.15 3.02 0.57 3.01 0.49 37.0 B063-4 98.6 0.46 16.2 0.38 0.29 3.79 91.8 2.96 47.0 158 68.1 46.4 322 0.29 4.01 11.5 1.86 10.4 3.17 1.07 3.93 0.93 5.37 1.32 3.40 0.66 3.41 0.55 41.1 B063-6 98.3 3.65 56.0 0.41 0.29 4.23 97.2 3.03 39.3 29.4 31.5 49.2 367 0.14 5.89 15.7 2.29 11.3 3.08 1.17 4.38 0.85 4.91 1.22 3.14 0.59 3.16 0.51 36.7 -
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