CHARACTERISTIC OF SUBSTRATE ROCKS OF CAIWEI SEAMOUNTS IN THE WEST PACIFIC OCEAN
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摘要:
对西太平洋采薇海山群基岩的类型、分布及岩石学特征进行了研究，同时对该海山群玄武岩主量元素和微量元素地球化学特征进行了初步分析。研究结果表明，采薇海山群的基岩类型主要为火山碎屑岩、灰岩、玄武岩和磷块岩；海山群的基岩以火山碎屑岩为主，其次为灰岩和玄武岩，磷块岩相对不发育。镜下鉴定结果显示，火山碎屑岩以玄武质火山角砾岩为主，灰岩主要为泥晶生屑灰岩或亮晶生屑灰岩，磷块岩多由生物碎屑灰岩或火山碎屑岩发生磷酸盐化而形成。采薇海山群玄武岩主量元素特征与夏威夷岛碱性玄武岩类似，属碱性玄武岩；微量元素分析结果显示其具有洋岛和碱性玄武岩特征，反映其形成于碱性洋岛构造环境。
Abstract:Lithology and distribution of substrate rocks of the Caiwei Seamount are scrutinized. Results show that the substrate of the Caiwei Seamounts is mainly composed of pyroclastic rock, limestone, basalt and phosphorite. Pyroclastic rock is the most common one, and basalt and limestone are the second. Phosphorite is seldom. Microscopic examination suggests that pyroclastic rocks are dominated by basaltic volcanic breccias, and limestone is dominated by sparry bioclastic limestone or micritic bioclastic limestone. Phosphorite is mainly formed by phosphatization of bioclastic limestone or volcanic breccia. Preliminary study on geochemistry of basalts from the Caiwei Seamounts shows that the major elements contents of basalts from the Caiwei Seamounts are similar to that of Hawaii alkaline basalts. It suggests that the basalt might be formed in a tectonic environment of alkali island.
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Key words:
- geochemistry /
- basalt /
- substrate rock /
- Caiwei Seamounts /
- West Pacific Ocean
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表 1 采薇海山群玄武岩主量元素含量(%)和微量元素含量(μg/g)
Table 1. Major elements(%) and trace elements(μg/g) contents of basalts from Caiwei Seamounts
样品 MASD07[14] MASD12[15] MASD21[15] MASD23[15] MAD23[16] MAD24[15] MASD27[16] MASD31[16] MASD33[16] MASD39[16] SiO2 38.18 45.50 39.83 34.09 39.97 53.75 51.31 48.76 49.58 42.45 Al2O3 18.39 15.76 13.28 13.16 14.14 7.84 18.03 17.81 16.85 16.03 Fe2O3 14.85 14.89 15.36 9.53 17.28 17.23 9.94 12.82 13.20 13.86 MgO 0.06 3.13 1.38 2.46 3.96 1.33 2.31 1.56 2.22 4.13 CaO 9.68 6.22 9.02 16.44 8.32 3.35 5.79 5.26 6.42 8.73 Na2O 2.64 3.55 2.60 1.91 2.60 4.46 3.44 3.25 3.54 1.99 K2O 1.43 1.80 3.61 1.39 1.42 1.94 2.50 2.09 1.73 1.54 MnO 2.27 0.54 1.90 1.25 0.29 0.27 0.16 0.06 0.17 0.16 TiO2 3.40 1.85 2.44 2.58 3.17 2.09 2.51 3.61 2.87 5.41 P2O5 3.35 1.42 5.58 11.95 2.34 0.75 0.78 0.85 1.12 0.41 LOI 5.65 5.09 4.79 5.03 6.19 6.78 2.99 3.65 2.10 5.02 Total 99.90 99.75 99.79 99.79 99.68 99.79 99.76 99.72 99.80 99.73 SI 0.32 13.39 6.01 16.09 15.68 5.33 12.70 7.91 10.73 19.19 Mg# 65.30 68.77 72.94 74.01 62.79 66.83 83.66 56.23 62.65 64.61 Sr 2214 608 1192 12.3 1024 1589 350 252 251 461 Zr 584 112 187 263 218 348 439 344 260 231 Ba 1565 574 2554 1287 71.5 954 982 395 469 590 Rb 33.3 40.5 37.0 25.3 30.2 44.8 78.8 40.5 48.1 33.6 Th 5.58 2.15 4.39 5.63 4.40 6.25 13.5 7.14 5.52 2.74 Ta 9.12 2.28 2.89 11.0 5.05 9.04 24.2 16.7 13.5 16.3 Nb 67.4 30.8 41.1 33.7 231 15.4 80.1 55.1 41.7 49.5 Hf 10.9 1.65 2.75 5.11 2.87 4.94 8.35 6.90 5.25 4.29 Y 36.0 38.9 68.7 149 62.2 49.8 25.9 24.2 21.2 19.5 Ce 93.0 50.8 82.8 67.9 92.4 152 96.7 70.1 55.7 44.6 Sm 7.01 5.37 8.07 10.4 9.82 13.2 8.11 7.30 5.61 6.39 Yb 2.10 2.53 3.32 8.64 3.57 3.59 2.27 2.18 1.75 1.47 
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