Sulfur mineralogy and geochemistry of serpentinites and gabbros of the Atlantis Massif (IODP Site U1309)
Sulfur mineralogy and geochemistry of serpentinites and gabbros of the Atlantis Massif (IODP Site U1309)
复制标题
DOI：
10.1016/j.gca.2008.07.018
复制
发表时间：
2008-10-15
影响因子：
5
通讯作者：
Bernasconi, Stefano M.
中科院分区：
文献类型：
--
作者：
Delacour, Adelie;Frueh-Green, Gretchen L.;Bernasconi, Stefano M.
在综合大洋钻探计划(IODP)第304次和第305次探险期间，在亚特兰蒂斯地块(大西洋中脊，北纬30度)中央穹顶的就地洋壳隆起部分进行了钻探，并发现了1.4公里的以辉长岩为主的岩石和少量夹层的超镁铁质岩石。在这里，我们描述了从1309D孔中回收的蛇纹岩橄榄岩、富橄榄橄榄岩和各种辉长岩的精选样品的硫矿物学和地球化学变化。这些数据被用来约束蚀变过程和氧化还原条件，并与亚特兰蒂斯地块南墙的基岩进行比较，亚特兰蒂斯地块位于南部5公里处，是Lost City热液田的所在地。中央穹隆的洋壳以富镍硫化物为特征，反映了还原条件和有限的海水循环。辉长岩和富橄榄橄榄岩的均一类地幔硫含量和同位素组成表明，在抬升和折返过程中，辉长岩为主的区域内的海水相互作用有限。地幔成分的局部变化与岩浆的可变性或与沿断裂带输送的海水流体的相互作用有关。富含橄榄石的榴辉岩中伴生的Mackinawite和辉长岩中的硬石脉为700米以下局部脆性断层的晚期循环流体提供了150-200摄氏度的温度限制。相反，中央穹隆的超镁铁质岩性代表了海水通量和蚀变程度较高的区域，并显示出明显的硫地球化学变化。孔上部蛇纹岩具有全硫化物含量高、S-34(硫化物)值高、S-34(硫酸盐)值低的特点，反映了一个主要受海水-辉长岩相互作用和随后的蛇纹岩作用控制的多阶段历史。与失落城市热液系统的蛇纹岩和辉长岩相比，中央穹顶的基底岩石记录了较低的氧逸度和更有限的流体通量。我们的研究与前人的结果一致，表明蚀变洋幔序列的硫形态和硫同位素组成通常会随着时间的推移而演化。硫地球化学的不均一性反映了蛇纹岩对流体通量、温度、氧逸度和硫逸度以及微生物活动的局部变化高度敏感的事实。(C)2008爱思唯尔有限公司。保留所有权利。
In-situ uplifted portions of oceanic crust at the central dome of the Atlantis Massif (Mid-Atlantic Ridge, 30 degrees N) were drilled during Expeditions 304 and 305 of the Integrated Ocean Drilling Program (IODP) and a 1.4 km section of predominantly gabbroic rocks with minor intercalated ultramafic rocks were recovered. Here we characterize variations in sulfur mineralogy and geochemistry of selected samples of serpentinized peridotites, olivine-rich troctolites and diverse gabbroic rocks recovered from Hole 1309D. These data are used to constrain alteration processes and redox conditions and are compared with the basement rocks of the southern wall of the Atlantis Massif, which hosts the Lost City Hydrothermal Field, 5 km to the south. The oceanic crust at the central dome is characterized by Ni-rich sulfides reflecting reducing conditions and limited seawater circulation. During uplift and exhumation, seawater interaction in gabbroic-dominated domains was limited, as indicated by homogeneous mantle-like sulfur contents and isotope compositions of gabbroic rocks and olivine-rich troctolites. Local variations from mantle compositions are related to magmatic variability or to interaction with seawater-derived fluids channeled along fault zones. The concomitant occurrence of mackinawite in olivine-rich troctolites and an anhydrite vein in a gabbro provide temperature constraints of 150-200 degrees C for late circulating fluids along local brittle faults below 700 m depth. In contrast, the ultramafic lithologies at the central dome represent domains with higher seawater fluxes and higher degrees of alteration and show distinct changes in sulfur geochemistry. The serpentinites in the upper part of the hole are characterized by high total sulfide contents, high delta S-34(sulfide) values and low delta S-34(sulfate) values, which reflect a multistage history primarily controlled by seawater-gabbro interaction and subsequent serpentinization. The basement rocks at the central dome record lower oxygen fugacities and more limited fluid fluxes compared with the serpentinites and gabbros of the Lost City hydrothermal system. Our studies are consistent with previous results and indicate that sulfur speciation and sulfur isotope compositions of altered oceanic mantle sequences commonly evolve over time. Heterogeneities in sulfur geochemistry reflect the fact that serpentinites are highly sensitive to local variations in fluid fluxes, temperature, oxygen and sulfur fugacities, and microbial activity. (C) 2008 Elsevier Ltd. All rights reserved.