Geochemistry and provenance of the sediment core from the rift valley of the Southwest Indian Ridge(49.58°E)
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摘要:
目前有关西南印度洋中脊沉积物的研究多集中在洋脊翼表层沉积物，对洋脊轴部裂谷沉积物的研究较匮乏，制约了对该区沉积物物质来源和沉积环境的深入认识。针对大洋49航次在洋脊轴部裂谷（东经49.58°）获取的沉积物岩心（GC03）进行了全岩样品主量、微量、稀土元素和Y（REY）含量测试分析，探讨研究区沉积物的物质来源和沉积环境。结果表明，GC03岩心样品富CaO、LOI（烧失量）和Sr，指示以钙质生物沉积占主导，并混有玄武岩碎屑。稀土元素总量（ΣREY）低，平均为54.3×10-6，稀土元素球粒陨石标准化配分图显示轻稀土元素富集，Ce和Eu显著负异常特征。其中L2层（83~87 cmbsf）富集Cu、Zn、Fe、Co等金属元素及较低的100*Al/（Al+Fe+Mn）值，揭示存在热液组分输入。Ceanom值与微量元素V/（V+Ni）-U/Th判别指标指示，研究区总体为偏氧化环境，部分层位显示还原特征。
Abstract:The current research on the sediments of the Southwest Indian Ridge(SWIR) mainly focuses on the surface sediments of the flank of the ridge, but lack of research on its ridge axis restricts the in-depth understanding of the sediment sources and sedimentary environment in this area.Based on the major element, trace element, REE and Y assay of a sediment core(GC03) collected from SWIR 49.58°E during Chinese DY-49 Cruise, the material source and sedimentary environment of the sediments in the study area were discussed.The results show that the bulk samples are enriched in CaO, LOI and Sr, indicating that calcareous biodeposition is dominant and mixed with basalt debris.The content of the ΣREY is low, with average value of 54.3×10-6, and the chondrite-nomalized REY distribution patterns show the enrichment of LREE compared to HREE and significant negative Ce and Eu anomaly.The enrichment of metal elements such as Cu、Zn、Fe and Co, and low 100*Al/(Al+Fe+Mn)value characterizing samples from Layer L2(83-87 cmbsf)reveals the presence of a hydrothermal component input.The Ceanom value and V/(V+Ni)-U/Th discriminant diagram indicate that the study area is generally a stable oxidized environment except for reduction characteristics exhibited from partial samples.
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Key words:
- Southwest Indian Ridge /
- sediment core /
- geochemistry /
- provenance /
- sedimentary environment
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表 1 GC03岩心样品主量、微量和稀土元素测试结果
Table 1. Assay results of major, trace elements and REE of the sediment core GC03
元素 GC03(n=80) BGS[13](n=4) 最小值 最大值 平均值 中位数 标准差 最小值 最大值 平均值 中位数 标准差 CaO 37.80 47.50 45.03 45.30 2.00 50.53 51.46 50.97 50.94 0.39 SiO2 5.95 15.82 7.54 7.24 1.62 2.51 3.71 3.12 3.13 0.62 Al2O3 1.42 5.28 1.83 1.73 0.53 0.68 0.99 0.81 0.79 0.13 TFe2O3 0.89 3.40 1.42 1.30 0.48 0.44 0.62 0.55 0.56 0.08 K2O 0.28 0.42 0.33 0.32 0.03 0.16 0.19 0.18 0.18 0.02 MgO 0.62 5.09 1.08 0.85 0.70 0.37 0.42 0.38 0.37 0.03 MnO 0.02 0.08 0.05 0.05 0.01 0.04 0.05 0.04 0.04 0.01 Na2O 1.28 2.22 1.58 1.56 0.19 0.97 1.66 1.24 1.17 0.31 P2O5 0.04 0.08 0.06 0.06 0.01 0.02 0.13 0.06 0.05 0.05 TiO2 0.07 0.25 0.09 0.09 0.03 0.03 0.05 0.04 0.04 0.01 Mo 0.06 0.41 0.21 0.20 0.08 0.35 0.44 0.40 0.40 0.04 Bi 0.06 0.11 0.09 0.09 0.01 0.04 0.07 0.06 0.06 0.01 Cu 35.60 344.00 75.59 64.80 41.62 11.60 21.60 18.05 19.50 4.58 Pb 3.50 7.50 5.08 4.90 0.76 3.20 8.70 4.70 3.45 2.67 Zn 22.00 56.00 27.20 26.00 6.31 13.00 15.00 14.25 14.50 0.96 Ag 0.01 0.11 0.03 0.02 0.02 0.01 0.02 0.01 0.01 0.01 As 7.70 13.90 10.87 10.85 1.32 1.70 2.10 1.90 1.90 0.18 Sb 0.16 0.45 0.26 0.24 0.08 0.13 0.17 0.15 0.15 0.02 Co 4.80 20.50 8.04 7.45 2.62 4.70 9.20 6.58 6.20 2.00 Ni 15.60 149.50 30.31 23.60 21.28 11.40 20.60 14.33 12.65 4.23 Cr 13.00 100.00 24.38 19.50 16.39 5.00 6.00 5.50 5.50 0.58 V 16.00 55.00 22.34 20.00 6.59 4.00 7.00 5.50 5.50 1.29 Y 12.80 17.40 14.57 14.20 1.04 9.00 15.60 11.75 11.20 2.91 Sr 1140.00 1800.00 1659.88 1675.00 106.34 - - - - - Th 0.97 1.90 1.42 1.41 0.14 - - - - - U 0.30 3.70 0.98 0.70 0.78 - - - - - ∑REY 47.83 66.16 54.31 53.01 4.60 34.94 54.07 43.37 42.24 9.12 LREE 26.85 40.56 32.64 32.17 3.14 21.15 31.13 25.67 25.21 5.05 HREE 6.24 8.82 7.10 6.93 0.64 13.79 22.94 17.70 17.04 4.13 LREE/HREE 3.48 5.14 4.61 4.59 0.29 1.36 1.53 1.46 1.47 0.08 δEu* 0.61 0.73 0.66 0.66 0.03 0.67 0.75 0.71 0.70 0.03 δCe* 0.55 0.65 0.58 0.58 0.02 0.52 0.65 0.57 0.56 0.06 Ceanom* -0.27 -0.19 -0.25 -0.25 0.02 -0.31 -0.21 -0.27 -0.27 0.04 注：主量元素含量单位为%，微量和稀土元素含量单位为10-6；δEu=2×(Eu/EuN)/(Sm/SmN+Gd/GdN)，δCe=2×(Ce/CeN)/(La/LaN+Pr/PrN)，Ceanom=lg(3CeN/(2LaN+NdN))，“*”表示采用球粒陨石标准化；“-”表示数据缺失；BGS—西南印度洋表层背景沉积物，离洋中脊大于60 km，代表洋盆附近沉积 
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表 2 GC03岩心主量和微量元素相关系数(n=80)
Table 2. The correlated coefficient of major and trace elements in GC03 core
CaO SiO2 Al2O3 TFe2O3 K2O MgO MnO Na2O P2O5 TiO2 LOI Mo V Cr Co Ni Cu Zn Pb As Sb Ba Sr Zr Hf Th U ∑REY CaO 1 SiO2 -0.857 1 Al2O3 -0.678 0.917 1 TFe2O3 -0.816 0.938 0.810 1 K2O -0.401 0.192 0.016 0.239 1 MgO -0.734 0.810 0.633 0.838 -0.057 1 MnO -0.081 0.348 0.383 0.392 -0.338 0.382 1 Na2O -0.774 0.533 0.443 0.508 0.629 0.266 -0.228 1 P2O5 0.043 -0.159 -0.245 -0.166 0.477 -0.335 -0.131 0.142 1 TiO2 -0.732 0.924 0.955 0.865 0.123 0.672 0.365 0.508 -0.178 1 LOI 0.612 -0.917 -0.932 -0.870 0.070 -0.774 -0.494 -0.262 0.324 -0.902 1 Mo -0.190 0.282 0.387 0.265 -0.130 0.179 0.413 0.157 -0.212 0.432 -0.327 1 V -0.746 0.866 0.854 0.829 0.200 0.632 0.262 0.594 -0.133 0.850 -0.804 0.246 1 Cr -0.767 0.901 0.797 0.872 -0.086 0.960 0.386 0.329 -0.368 0.809 -0.878 0.273 0.742 1 Co -0.726 0.740 0.556 0.837 0.149 0.828 0.321 0.415 -0.266 0.582 -0.673 0.143 0.663 0.779 1 Ni -0.682 0.746 0.551 0.780 -0.095 0.985 0.376 0.197 -0.351 0.578 -0.718 0.142 0.570 0.925 0.842 1 Cu -0.160 0.260 0.209 0.343 -0.094 0.340 0.222 0.041 -0.147 0.187 -0.304 0.088 0.436 0.304 0.531 0.384 1 Zn -0.843 0.894 0.703 0.896 0.200 0.916 0.286 0.473 -0.175 0.762 -0.794 0.125 0.762 0.908 0.817 0.883 0.334 1 Pb -0.283 0.056 -0.096 0.017 0.745 -0.197 -0.326 0.532 0.563 -0.046 0.207 -0.283 0.110 -0.206 -0.085 -0.240 -0.259 0.076 1 As -0.221 0.032 -0.109 -0.027 0.143 0.036 -0.106 0.245 0.193 -0.157 0.134 -0.329 0.057 -0.029 0.172 0.086 0.210 0.105 0.310 1 Sb -0.167 0.095 0.104 0.057 0.293 -0.075 -0.269 0.301 0.186 0.073 -0.047 -0.026 0.384 -0.052 0.155 -0.050 0.319 0.087 0.299 0.265 1 Ba -0.139 -0.139 -0.355 -0.131 0.702 -0.193 -0.505 0.320 0.404 -0.315 0.363 -0.426 -0.150 -0.289 -0.020 -0.172 -0.088 0.005 0.716 0.291 0.334 1 Sr 0.689 -0.903 -0.898 -0.834 -0.085 -0.677 -0.404 -0.388 0.220 -0.919 0.884 -0.474 -0.780 -0.809 -0.558 -0.598 -0.178 -0.720 0.098 0.195 0.011 0.335 1 Zr -0.743 0.772 0.728 0.685 0.578 0.389 0.028 0.704 0.038 0.774 -0.612 0.191 0.746 0.504 0.442 0.305 0.038 0.638 0.410 0.041 0.301 0.194 -0.685 1 Hf -0.569 0.612 0.609 0.542 0.447 0.291 0.072 0.542 -0.030 0.643 -0.499 0.186 0.612 0.402 0.339 0.217 -0.080 0.486 0.324 -0.012 0.167 0.109 -0.554 0.834 1 Th 0.173 -0.307 -0.409 -0.348 0.663 -0.501 -0.323 0.029 0.651 -0.361 0.468 -0.336 -0.315 -0.544 -0.395 -0.487 -0.328 -0.312 0.664 0.123 0.176 0.619 0.310 0.110 0.110 1 U 0.121 -0.175 -0.119 -0.259 0.112 -0.199 -0.311 0.011 0.090 -0.166 0.143 -0.145 0.104 -0.207 -0.132 -0.161 0.063 -0.084 0.159 0.125 0.734 0.274 0.219 0.051 0.018 0.227 1 ∑REY -0.239 0.060 -0.074 0.024 0.808 -0.243 -0.306 0.436 0.561 0.007 0.178 -0.268 0.090 -0.237 -0.132 -0.288 -0.310 0.028 0.869 0.173 0.270 0.656 -0.008 0.494 0.446 0.806 0.143 1
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