DEPTH PROFILES OF TH-230(EXCESS), TRANSITION-METALS AND MINERALOGY OF FERROMANGANESE CRUSTS OF THE CENTRAL INDIAN BASIN AND IMPLICATIONS FOR PALAEOCEANOGRAPHIC INFLUENCE ON CRUST GENESIS
DEPTH PROFILES OF TH-230(EXCESS), TRANSITION-METALS AND MINERALOGY OF FERROMANGANESE CRUSTS OF THE CENTRAL INDIAN BASIN AND IMPLICATIONS FOR PALAEOCEANOGRAPHIC INFLUENCE ON CRUST GENESIS
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DOI：
10.1016/0168-9622(91)90038-x
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发表时间：
1991-11-01
期刊：
影响因子：
3.9
通讯作者：
BOROLE, DV
中科院分区：
文献类型：
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作者：
BANAKAR, VK;BOROLE, DV
使用 U-Th 系列同位素和过渡金属通量研究了来自印度中部盆地海山区域 CCD（碳酸盐补偿深度）以下水深的两种氢铁壳的生长速率。 在一个地壳（F-380）上相距几厘米的深度剖面中，Th-230（过量）库存和过渡金属通量显示出不显着的变化。 在另一个地壳 (SS-663X) 中，这种变化在 2 倍以内，而太平洋地壳中的变化则为 5 倍。 单个地壳以及两个相邻地壳内的生长速率、Th-230 和过渡金属通量的微小变化表明，它们是由于增生地壳表面与沉积物在空间和时间上的动态表层的接触所致。几乎均匀的 Mn/Fe 比率 (1-1.6)，sigma-MnO2 作为主要 Mn 矿物相以及 Th-230（过量）和平滑的指数衰减模式Th-230（过量）/Th-232 活动的深度表明这些地壳没有记录过去约 0.4 Ma 的任何古海洋事件。 这些地壳的插值年龄在 10 至 13 Ma 之间，与中新世中期 AABW（南极底水）流活动增强导致碳酸盐溶解增加的时期相当。 中新世中期的海洋条件可能与碳酸盐溶解的增加有关，可能引发了印度中部盆地地壳的形成。
Two ferromanganese encrustations of hydrogenetic origin from water depths well below the CCD (carbonate compensation depth) from a seamount zone in the Central Indian basin were studied for growth rates using U-Th series isotopes and transition-metal fluxes. The Th-230(excess) inventories and transition-metal fluxes in depth profiles separated by a few cm on one crust (F-380) show insignificant variations. In another crust (SS-663X) this variation is within a factor of 2 as compared to variations by a factor of 5 in the Pacific crusts. The minor variations in growth rates, Th-230 and transition-metal fluxes within a single crust as well as two adjacent crusts suggest that they are due to the contact of the accreting crust surface with a dynamic veneer of sediment in space and time.Nearly uniform Mn/Fe ratios (1-1.6), sigma-MnO2 as the main Mn mineral phase and a smooth exponential decay pattern of Th-230(excess) and Th-230(excess)/Th-232 activities with depth indicate that these crusts have not recorded any palaeoceanographic events of the past approximately 0.4 Ma. The interpolated age of these crusts is between 10 and 13 Ma which is comparable to the period of increased carbonate dissolution due to enhanced activity of AABW (Antartic Bottom Water) currents during the middle Miocene. Probably the middle Miocene oceanographic conditions, which were associated with increased carbonate dissolution, might have initiated the formation of crusts in the Central Indian basin.