海山当地物源和南极底层水对富钴结壳成矿作用的影响——来自海山周围水柱化学分析的证据

A local metal sources and the influence of the Antarctic Bottom Water on the cobalt-rich crust formatim—New evidence from the data of seawater column chemistry around a seamount

为了了解海山富钴结壳中金属元素的来源及其形成环境,对中太平洋某海山周围两个站位(一个位于海山斜坡上部,另一个位于海山外围较远处)进行了海水水柱综合水化学分析,发现两个站位溶解氧、pH及营养盐的分布是一致的,反映了两个站位海水化学环境的相似性,而剖面上金属元素含量却存在很大差异,位于海山斜坡上部站位的金属元素含量明显高于离海山较远的站位,说明海山结壳的主要金属来源于海山当地的水岩反应甚至低温热液活动。尽管存在差异,但在两个不同站位均存在近底层金属元素含量高,这印证了通过势温分布推断的本区存在南极底层水(AABW)影响的判断,说明AABW在本研究区确实存在,并且是维持海山斜坡强氧化环境的主要因素,AABW可能同时起着输运部分成矿元素的作用,但两个站位水柱金属元素含量的差异主要揭示了海山区存在水岩反应或者低温热液等当地物质的输入。

In order to probe seamount Co-rich crusts＇ metal sources and their ore-forming environment, water column chemistry analyses were done at two sites （one site is just on the seamount slope and the another is relative far away the seamount） around a seamount in the central Pacific Ocean. The results reveal that the water chemical environments of the two sites are similar because of the similar distributions of dissolved oxygen concentration, pH and nutrients concentrations of these sites, two. but the metal element concentrations from the water column are obvious difference between the two sites, and the metal element concentrations at the site on the seamount slope are obvious higher than those of the site relative far away the seamount; the main metal is from the local seamount rocks, maybe related to the low temperature hydrothermal activity and the water-rock reaction. There are relative high metal concentrations in the bottom water near the seafloor at the two sites although there is the above-mentioned difference. This condition confirms the influence of the Antarctic Bottom Water（AABW） on this area, which is confirmed by the local distributions of the Seawater potential temperatures, and shows that the AABW is a main factor to keep the relative strong oxidizing environment in the seawater on the seamount slope and has the ability of transporting partial ore-forming elements. The difference of the two sites maybe hints that there is a local metal source such as low temperature hydrothermal activity in this seamount area.