FLUID MIXING AND ANHYDRITE PRECIPITATION WITHIN THE TAG MOUND
FLUID MIXING AND ANHYDRITE PRECIPITATION WITHIN THE TAG MOUND
复制标题
Tag Mound 内的流体混合和硬石膏沉淀
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
M. Tivey
中科院分区：
文献类型：
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作者：
R. Mills;D. Teagle;M. Tivey
硫化物体低温循环过程中硫化物物质的再加工和区域精炼是洋中脊扩张中心丘状增生的重要过程。其中，位于北纬26°的大西洋中脊的跨大西洋地质导线（TAG）已经通过潜水器和钻井进行了详细研究。水携入和流体在丘内循环的重要性已被认为是控制塔卡丘结构和组成的主要因素。由于硬石膏成分记录了海水-热液混合过程，因此可以通过分析Ocean Drill gram （ODP）取样中回收的硬石膏来监测海水夹带的后果。本文利用所选硬石矿样品的Sr、Ca、Mg和Sr同位素组成作为土丘环流过程中流体混合和演化的地球化学示踪剂。锶和镁在硬石膏中的分配主要受晶格应变的晶体学控制，尽管在表面硬石膏中观察到高分配系数，这被推断是由细粒含镁滑石相的存在引起的。现有白色流体资料与黑烟液资料对比表明，TAG m内硬石膏沉淀的Sr分配系数≤1，导致流体演化为高Sr/Ca值，并持续循环沉淀。温度变化对D - Sr值的影响不大，持续的海水夹带和anh - drite降水引起的流体演化是控制固相地球化学的主要因素。这些结果通过评估海水进入土丘的夹带和环流过程中的流体演化，为研究地下环流提供了新的思路。广泛的海水夹带进入土丘，再加上混合物的导电加热，必须发生，以解释TAG硬石膏的地球化学分布。
Reworking of sulfide material and zone-refining during lower temperature circulation within sulfide bodies has been identified as an important process in mound accretion at mid-ocean ridge spreading centers. One site, the Trans-Atlantic Geotraverse (TAG), at 26°N on the Mid-Atlantic Ridge has been studied in detail by submersible and by drilling. The importance of se ter entrainment into, and fluid circulation within, the mound has been recognized as a major control on the TAG mound ture and composition. Because anhydrite composition records the seawater-hydrothermal fluid mixing process, the nat consequences of seawater entrainment can be monitored through analysis of anhydrite recovered from the Ocean Drill gram (ODP) sampling. Sr, Ca, Mg, and the Sr-isotopic composition of selected anhy rite samples are used here as geochemic tracers of fluid mixing and evolution during mound circulation. Sr and Mg partitioning into anhydrite is largely controlled crystallographic controls imposed by lattice strain, though high partition coefficients are observed in surface anhydrite s e, which are inferred to be caused by the presence of a fine-grained Mg-bearing talc phase. Comparison of existing white fluid data to black smoker fluid data suggests that the Sr partition coefficient for anhydrite precipitation within the TAG m nd is ≤1, which results in fluid evolution to high Sr/Ca values with ongoing circulation and precipitation. Temperature varia through the mound have little effect on D Sr values, and fluid evolution arising from ongoing seawater entrainment and anh drite precipitation is the dominant control on solid phase geochemistry. These results give new insights into subsurfac circulation by evaluating seawater entrainment into the mound and fluid evolution during circulation. Extensive sea entrainment into the mound, coupled with conductive heating of the mixture, must be occurring to explain the distributio geochemistry of TAG anhydrite.