The geochemical characteristics of rare earth elements rich deep sea deposit of Core GC11 in central Indian Ocean Basin
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摘要: 对中印度洋洋盆的沉积GC11岩心开展了主量元素、微量元素和稀土元素分析研究,根据主微量元素相关性特征、稀土元素富集程度以及澳大利亚后太古代平均页岩归一化模式特征,初步探讨了GC11岩心的沉积地球化学特征,以及影响稀土元素富集的可能因素。研究表明,GC11岩心稀土元素总量在400.64×10−6~742.74×10−6,平均值为658.41×10−6,略低于邻近海域的GC02岩心,与沃顿海盆DSDP213岩心中含沸石型深海粘土层位中的稀土元素含量相当。δCe负异常明显,(La/Yb)N为0.42,显示重稀土相对富集的特点。稀土元素与P2O5呈显著正相关性,CaO/P2O5的平均值为2.3,表明生物钙磷灰石可能是稀土元素的主要载体矿物,而铁锰水合物可能对富集稀土元素有一定的促进作用,但影响不大;GC11岩心中δCe负异常程度远低于GC02岩心,略低于DSDP213岩心,中稀土富集特征与GC02和DSDP213岩心基本一致。不同程度陆源物质的混入可能是导致以上不同岩心中稀土元素富集程度和分馏特征的主要原因。Abstract: Measurement of major elements, trace elements and rare earth elements (REY) for sediment Core GC11 collected in the central Indian Ocean Basin were performed. Based on the analysis of interelemental correlation, REY enrichment and post-Archean Australian Shale (PAAS) normalization style, the factors impacting the REY enrichment are discussed. The study suggests that: the total amount of REY varies from 400.64×10−6 to 742.74×10−6, with an average of 658.41×10−6, which is slightly lower than that of Core GC02, however, is equivalent to that of the zeolite-bearing rich deep-sea deposit in the Core DSDP213 . The sediment exhibits distinct negative abnormal δCe and lower (La/Yb)N为0.42, with obvious positive correlation between REY and P2O5. The average value of CaO/P2O5 ratio is 2.3, demonstrating that the bio-apatite may be the main host mineral of REY. Although there is positive correlation between REY and Fe and Mn, hydroxyl hydrate of Fe and Mn have low impact to the enrichment of REY for the distinct negative abnormal δCe. The mixture with the terregeneous materials maybe the main cause inducing the differences of REY enrichment degree, δCe and PAAS normalization style.
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图 6 样品稀土元素相对澳大利亚后太古代平均页岩(PAAS)归一化配分模式及与其他区域富稀土深海黏土的比较
GC11不包括H2和H5层位;GC02位于中印度洋洋盆;DSDP213位于东印度洋沃顿海盆;以上数据均为沉积岩心的平均值, 见参考文献[5, 12]
Fig. 6 Sample vs. post-Archean Australian Shale (PAAS) normalized partitioning pattern of rare earth elements and comparison with other regions of rare earth-rich deep sea clay
GC11 does not include H2 and H5 horizons; GC02 is located in the central Indian Ocean Basin;DSDP213 is located in the Wharton Basin of the east Indian Ocean;the above data are average values of sedimentary cores, see references [5, 12]
表 1 GC11岩心沉积物涂片鉴定结果
Tab. 1 The results of smear identification of sediments in Core GC11
序号 岩心深度/cm 镜下图片 放大倍数 描述 定名 01 1~2 10×10 镜下见大量生物碎片,主要为放射虫,以及少量球状硅藻,同时可见大量的鱼牙骨和长条状沸石,几乎未见有孔虫等钙质生物,硅质生物占了视域的50%~60% 黏土质放射虫软泥 02 14~15 10×5 镜下见大量生物碎片,主要为有孔虫壳体,同时见有放射虫碎体,亦见少量硅藻,鱼牙骨及沸石,有孔虫壳较为完整,钙质生物占视域的15%~25%, 硅质生物占视域的10%~15% 含硅质和钙质黏土 03 24~25 10×10 镜下见大量的生物碎片,主要为放射虫壳体及鱼牙骨屑,偶见有孔虫碎体,硅质生物占视域的50%以上 放射虫软泥 04 54~55 10×20 镜下可见大量鱼牙骨及沸石颗粒,少量的放射虫壳体(约5%),钙质生物几乎难以见到 沸石黏土 05 80~81 10×20 镜下可见大量鱼牙骨及沸石颗粒,少量放射虫(不大于5%),钙质生物难以见到 沸石黏土 06 119~120 10×50 镜下可见较多的沸石颗粒,鱼牙骨难以见到,偶见少量放射虫(不大于5%),钙质生物难以见到 沸石黏土 07 159~160 10×20 镜下可见较多的沸石颗粒,鱼牙骨难以见到,偶见少量放射虫(不大于5%),钙质生物难以见到 沸石黏土 08 199~200 10×10 镜下多见沸石颗粒,可见有少量的鱼牙骨,硅质生物及钙质生物几乎不可见 沸石黏土 表 2 澳大利亚后太古代平均页岩的稀土元素含量[10]
Tab. 2 Rare earth element content of the post-Athena average shale in Australia[10]
元素 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y 含量/10–6 38.2 79.6 8.83 33.9 5.55 1.08 4.66 0.774 4.68 0.991 2.85 0.405 2.82 0.433 27 表 3 主量元素特征值(wt%)
Tab. 3 Characteristic values of main elements (wt%)
Al2O3 CaO TFe2O3 K2O MgO MnO Na2O P2O5 SiO2 TiO2 LOI 平均值 16.40 1.32 8.90 2.53 3.06 2.53 3.31 0.56 49.60 0.71 10.48 最大值 16.95 1.40 9.20 2.80 3.22 2.63 4.02 0.60 50.78 0.75 11.27 最小值 15.42 1.24 8.52 2.39 2.80 2.37 2.46 0.51 48.91 0.66 9.72 标准差 0.42 0.03 0.20 0.14 0.12 0.08 0.35 0.03 0.43 0.03 0.37 H2 12.32 1.04 5.95 2.52 2.25 1.58 5.51 0.30 56.26 0.46 11.37 H5 13.57 1.09 6.16 2.97 2.02 1.62 4.04 0.32 58.04 0.47 9.55 注:LOI为烧失量。H2层位孔深为15 cm;H5层位孔深为55 cm。TFe2O3代表总铁含量。 表 4 GC11岩心微量元素和稀土元素含量(10-6)
Tab. 4 Contents of trace elements and rare earth elements in the Core GC11 (10-6)
Ba Co Cr Cs Cu Ga Hf In Li Mo Nb Ni 平均值 1 631 205.67 41.06 5.16 441.72 24.09 5.01 0.14 59.54 57.01 13.12 516.67 最大值 2 250 224.00 51.00 5.49 474.00 25.50 5.40 0.16 71.20 68.20 14.30 556.00 最小值 1 200 182.50 38.00 4.77 386.00 22.20 4.50 0.13 51.20 33.00 11.80 467.00 标准差 267 9.15 2.69 0.19 22.77 0.94 0.23 0.01 5.67 7.76 0.64 24.14 H2 1 480 136.50 27.00 4.39 286.00 16.70 3.50 0.10 38.60 20.40 9.90 342.00 H5 1 205 136.50 27.00 5.50 293.00 18.70 4.20 0.11 42.90 20.60 11.40 323.00 Pb Rb Sc Sr Ta Th U V W Zn Zr 平均值 80.39 83.04 25.89 202.78 0.92 19.81 2.27 125.61 9.19 146.39 194.39 最大值 89.30 90.60 27.90 215.00 1.09 22.30 2.46 133.00 10.10 152.00 211.00 最小值 72.70 78.60 23.40 190.00 0.77 17.70 1.98 115.00 8.20 137.00 177.00 标准差 4.56 3.09 1.35 7.09 0.10 1.52 0.14 4.97 0.60 4.82 9.25 H2 65.80 83.30 19.20 162.00 0.79 17.75 2.03 84.00 9.10 112.00 129.00 H5 69.10 107.50 18.50 159.50 0.94 21.70 2.58 82.00 9.00 106.00 145.00 注:H2层位孔深为15 cm;H5层位孔深为55 cm。 表 5 稀土元素特征值(澳大利亚后太古代平均页岩(PAAS)归一化,PAAS数据参考文献[10])
Tab. 5 Rare earth elements characteristic values (post-Archean Australian Shale (PAAS) normalized, PAAS data refer to reference[10])
层位/cm ∑REY/10 – 6 δCe δEu (La/Gd)N (La/Yb)N LREE/MREE LREE/HREE MREE/HREE H1 0~10 735.56 0.87 1.08 0.40 0.53 4.25 13.07 3.07 H2 10~20 400.64 1.06 1.04 0.41 0.58 4.85 15.64 3.23 H3 20~30 679.22 0.89 1.07 0.39 0.52 4.33 13.24 3.06 H4 30~40 711.97 0.88 1.10 0.43 0.56 4.44 13.77 3.10 H5 40~50 457.12 1.06 1.02 0.43 0.58 4.92 15.31 3.11 H6 50~60 647.70 0.88 1.07 0.40 0.55 4.36 13.65 3.13 H7 60~70 636.13 0.91 1.08 0.40 0.56 4.45 14.23 3.20 H8 70~80 619.32 0.93 1.11 0.40 0.59 4.45 14.57 3.27 H9 80~90 707.86 0.85 1.08 0.41 0.54 4.25 13.16 3.09 H10 90~100 680.30 0.89 1.06 0.41 0.55 4.37 13.62 3.12 H11 100~110 682.17 0.83 1.07 0.39 0.51 4.12 12.70 3.09 H12 110~120 742.74 0.84 1.08 0.40 0.57 4.24 13.75 3.24 H13 120~130 651.93 0.89 1.08 0.38 0.51 4.20 12.97 3.09 H14 130~140 738.42 0.84 1.12 0.40 0.55 4.26 13.48 3.16 H15 140~150 635.25 0.88 1.10 0.40 0.52 4.36 13.29 3.04 H16 150~160 705.34 0.80 1.07 0.39 0.53 4.14 12.96 3.13 H17 160~170 691.36 0.85 1.11 0.41 0.56 4.26 13.46 3.16 H18 170~180 692.79 0.86 1.10 0.42 0.58 4.44 14.05 3.16 H19 180~190 707.43 0.85 1.13 0.42 0.58 4.38 13.92 3.18 H20 190~200 644.98 0.85 1.07 0.39 0.53 4.18 13.13 3.14 Min / 400.64 0.80 1.02 0.38 0.51 4.12 12.70 3.04 Max / 742.74 1.06 1.13 0.43 0.59 4.92 15.64 3.27 Ave / 658.41 0.89 1.08 0.40 0.55 4.36 13.70 3.14 GC02 / 1072.17 0.56 1.13 0.42 0.63 3.72 12.02 3.24 DSDP213 / 628.22 0.81 1.08 0.41 0.49 4.21 11.60 2.77 -
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