CHEMICAL EXCHANGE DURING HYDROTHERMAL ALTERATION OF BASALT BY SEAWATER .1. EXPERIMENTAL RESULTS FOR MAJOR AND MINOR COMPONENTS OF SEAWATER
CHEMICAL EXCHANGE DURING HYDROTHERMAL ALTERATION OF BASALT BY SEAWATER .1. EXPERIMENTAL RESULTS FOR MAJOR AND MINOR COMPONENTS OF SEAWATER
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DOI：
10.1016/0016-7037(78)90107-2
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发表时间：
1978-01-01
影响因子：
5
通讯作者：
HOLLAND, HD
中科院分区：
文献类型：
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作者：
MOTTL, MJ;HOLLAND, HD
不同结晶度的新鲜洋中脊玄武岩被磨成粉末，并在密封的金胶囊中与海水和人造Na-K-Ca-Cl溶液在200-500°C和500-1000 bar下反应。水/岩体比为1-3，持续时间为2 - 20个月，这些时间足以使大多数元素在溶液中达到稳定状态浓度，该浓度由与蚀变矿物（Mg、SiO 2、SO 4）的平衡、这些矿物（Na、Ca）的形成速率或岩石中的贫化（K、B、Ba）决定。由此产生的溶液非常类似于冰岛雷克雅未克玄武岩-海水地热系统的盐水。镁几乎完全从海水中转移到蚀变产物蒙皂石，透闪石阳起石，或滑石。硫酸盐也被去除到低浓度，无论是通过沉淀的无水石膏和还原硫化物。在大多数实验中，钠从海水中净转移到固体中是通过形成钠长石和方沸石来实现的。在一些实验中，从海水中去除锶，但在其他实验中没有变化或略有增加。SiO2、Ca、K、Ba、B、CO2等元素从玄武岩中被淋溶并富集。SiO2浓度通过在300°C及以上用石英饱和来控制。形成的主要含钙相是硬石膏，水化钙硅酸盐truscottite，透闪石阳起石，并可能wairakite。没有富钾相形成。对于某些矿物来说，初始玄武岩的结晶度会影响形成的量。海水中的镁迅速转移到固体蚀变产物中，并且在很大程度上通过玄武岩中钙的浸出来平衡。钠从海水到固体的净转移发生得更慢，主要是通过从玄武岩中浸出额外的钙来平衡。因此，海水与玄武岩在低水/岩比下的反应可以被认为包括两个交换：Mg交换Ca，Na交换Ca。
Fresh mid-ocean ridge basalt of varying crystallinity has been powdered and reacted with seawater and an artificial Na-K-Ca-Cl solution at 200–500°C and 500–1000 bar in sealed gold capsules. Water/rock mass ratios of 1–3 were used and durations ranged from 2 to 20 months.These time periods were sufficient for most elements to approach a steady-state concentration in solution which was determined by equilibrium with alteration minerals (Mg, SiO2, SO4), by rate of formation of these minerals (Na, Ca), or by depletion from the rock (K, B, Ba). The resulting solutions closely resemble the brines from the basalt-seawater geothermal system at Reykjanes, Iceland. Mg was almost completely removed from seawater into the alteration products smectite, tremolite-actinolite, or talc. Sulfate also was removed to low concentrations, both by precipitation of anyhydrite and by reduction to sulfide. Net transfer of Na from seawater into solids occurred in most experiments by formation of sodic feldspar and possibly analcime. Sr was removed from seawater in some experiments but showed no change or a small gain in others. SiO2, Ca, K, Ba, B and CO2were leached from basalt and enriched in solution. SiO2concentrations were controlled by saturation with quartz at 300°C and above. The principal Ca-bearing phases which formed were anhydrite, the hydrated Ca-silicate truscottite, tremolite-actinolite, and possibly wairakite. No K-rich phases formed. For some minerals the crystallinity of the starting basalt affected the amount which formed.Removal of Mg from seawater into solid alteration products occurred rapidly and was balanced largely by leaching of Ca from basalt. Net transfer of Na from seawater into solids occurred more slowly and was balanced mainly by leaching of additional Ca from basalt. Thus, reaction between seawater and basalt at low water/rock ratios can be considered to consist of two exchanges: Mg for Ca, and Na for Ca.