Geochemistry and U-series dating of Holocene and fossil marinehydrothermal manganese deposits from the Izu-Ogasawara arc
Geochemistry and U-series dating of Holocene and fossil marinehydrothermal manganese deposits from the Izu-Ogasawara arc
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伊豆-小笠原弧全新世和化石海洋热液锰矿床的地球化学和U系列测年
DOI：
10.1016/j.oregeorev.2016.07.025
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发表时间：
2016
影响因子：
3.3
通讯作者：
A.
中科院分区：
文献类型：
--
作者：
Yamaoka;K.;Ma;L. Hishikawa;K.;Usui;A.
这项研究调查了伊豆-小笠原岛弧的全新世和化石热液锰矿床。从矿物学角度来看，这些矿床包含 10 Å 和 7 Å 锰酸盐矿物，化石样本显示出更高的 10 Å 稳定性。全新世样品的化学成分是其他热液锰矿床的典型化学成分，包括低铁锰比、低痕量金属和低稀土元素。尽管化石样品通常具有相似的化学特征，但它们在 Ni、Cu、Zn、Cd、Ba、REE、Tl 和 Pb 含量方面表现出显着富集。此外，球粒陨石归一化的稀土元素模式显示出更轻的稀土元素富集趋势。这些化学特征表明这些金属是在沉积后从海水中吸收的。对凯卡塔海山全新世热液锰矿床进行 U-Th 测年表明，最上层的温度为 8.8 ± 0.94 ka，并且在海底下方向下生长，生长速率约为 1.5 倍。 2 毫米/凯尔。这比氢化铁锰结壳快大约三个数量级。西上京海山热液锰矿床化石的 U-Pb 年龄显示为 4.4 ± 1.6 Ma，与玄武岩火山活动 (5.8 ± 0.3 Ma) 处于同一时代。热液锰矿床含有高浓度的高价值锰，但仅含有少量有价值的稀有金属；它们的年龄限制了过去热液活动的时期，并为勘探多金属硫化物矿床提供了载体。
This study investigated Holocene and fossil hydrothermal manganese deposits in the Izu-Ogasawara arc. Mineralogically, these deposits comprise 10 Å and 7 Å manganate minerals, and the fossil samples showed higher 10 Å stabilities. Chemical compositions of the Holocene samples are typical of other hydrothermal manganese deposits, including low Fe/Mn ratios, low trace metals, and low rare earth elements. Although the fossil samples generally have similar chemical characteristics, they exhibit significant enrichment in Ni, Cu, Zn, Cd, Ba, REE, Tl, and Pb contents. Furthermore, the chondrite-normalized REE patterns showed more light REE enrichment trends. These chemical characteristics suggest post-depositional uptake of these metals from seawater. U-Th dating of a Holocene hydrothermal manganese deposit from the Kaikata Seamount indicated 8.8 ± 0.94 ka for the uppermost layer and downward growth beneath the seafloor with a growth rate of ca. 2 mm/kyr. This is approximately three orders of magnitude faster than that of hydrogenetic ferromanganese crusts. U-Pb age of a fossil hydrothermal manganese deposit from the Nishi-Jokyo Seamount showed 4.4 ± 1.6 Ma, which was contemporary with basaltic volcanism (5.8 ± 0.3 Ma). Hydrothermal manganese deposits contain high concentrations of high value Mn, but only small amounts of valuable minor metals; their ages constrain the periods of past hydrothermal activity and provide a vector to explore for polymetallic sulfide deposits.