Elemental dissolution of basalts with ultra-pure water at 340°C and 40 Mpa in a newly developed flow-type hydrothermal apparatus

Abstract

NOTE 89(sea)water that occur in these extreme environments (e.g., Yoshizaki et al., 2009).To date, hydrothermal experiments have been mainly performed using batch-type apparatuses that simulate a closed system (Seyfried, Jr. and Mottl, 1982;Ghiara et al., 1993;Gislason and Arnórsson, 1993). In particular, batch experiments of basalt-seawater reactions have been performed under high temperature (300°C or higher) and high pressure (50 MPa or higher) conditions (e.g., Seyfried, Jr. and Mottl, 1982). In contrast, flowing conditions can occur in open systems (i.e., flow-through systems), where kinetic water-rock reactions and flow rates strongly affect fluid compositions. Here, we developed a new flow-type hydrothermal apparatus to perform experiments in an open system under flowing conditions. This apparatus can reproduce water-rock reactions at elevated temperatures and pressures (up to 500°C, 50 MPa) under flow-through conditions, corresponding to a water-rock reaction zone in the sub-seafloor hydrothermal systems. Furthermore, the apparatus can also reproduce the mixing of hydrothermal fluids with cool seawater. A flow- July 20, 2012; Accepted January 4, 2013) To simulate the discharge zone of hydrothermal systems in the laboratory, we developed a flow-type hydrothermal apparatus that can reproduce water-rock reactions at elevated temperatures and pressures under flow-through conditions and also the mixing of hydrothermal fluids with seawater. Using this apparatus, basaltic rocks were reacted with ultrapure water at 340°C and 40 MPa for 1271 h under flow-through conditions. An increase in Al, Fe, K, Na, P and Si in the reacted water was observed during the experiment, reproducing the process of dissolution from the basaltic rocks. An increase in pH to 9 during the experiment can be attributed to the dissolution of silicate minerals in the basaltic rocks. That the pH in the experiment is higher than the pH observed in natural hydrothermal fluids at mid-ocean ridges is a result of higher Si concentrations observed in the experiment than those of natural hydrothermal fluids.

Hydrogen-rich hydrothermal environments in the Hadean ocean inferred from serpentinization of komatiites at 300 °C and 500 bar

“…Of course, komatiite-associated hydrothermal activity does not occur in the modern ocean; thus, the H 2 generation potential of komatiites during serpentinization can only be experimentally estimated through simulated hydrothermal fluid-rock reactions under high-temperature and high-pressure conditions, as previously conducted to reconstruct modern (Seyfried 1987;Seyfried et al 2007;McCollom et al 2010;Kato et al 2013;Suzuki et al 2015a, b), ancient (Yoshizaki et al 2009;Lazar et al 2012;, and even extraterrestrial subseafloor hydrothermal systems Sekine et al 2015). Yoshizaki et al (2009) confirmed hydrogen generation by a preliminary, ongoing experiment using komatiite and pure water (Yoshizaki et al 2009).…”

Development of Hydrothermal and Frictional Experimental Systems to Simulate Sub-seafloor Water–Rock–Microbe Interactions

“…Kato et al (2013a) reported a flow-type hydrothermal reactor system that can simulate microbial and chemical processes in a deep-sea hydrothermal system. Although the reactor system has not yet been used to reproduce a microbial ecosystem, they successfully investigated the dissolution of major elements (Si, Na, Al, K, Fe, and P) from basaltic rocks at high temperature (340 C) and pressure (40 MPa) under conditions of ultrapure water flow (Kato et al 2013a).…”

“…Kato et al (2013a) reported a flow-type hydrothermal reactor system that can simulate microbial and chemical processes in a deep-sea hydrothermal system. Although the reactor system has not yet been used to reproduce a microbial ecosystem, they successfully investigated the dissolution of major elements (Si, Na, Al, K, Fe, and P) from basaltic rocks at high temperature (340 C) and pressure (40 MPa) under conditions of ultrapure water flow (Kato et al 2013a). Their study was the first to demonstrate dissolution of phosphorus (a major element that is essential for life) from basaltic rocks in a flow-type hydrothermal experiment, thus providing important insights into the sustainability of microbial ecosystems in deep-sea hydrothermal systems.…”

“…Our hydrothermal experiment (described below) provides direct evidence for dissolution of As, Ni, Zn, Rb, V, and Li from basaltic rocks at high temperature (340 C) and pressure (40 MPa). The hydrothermal reactor system we used has been described in detail by Kato et al (2013a). In brief, the reactor system consists of a preheating bath (100 mL), a water-rock reaction bath (390 mL), and a cooling bath (5 L) (Fig.…”

“…The temperature in the cooling bath is maintained at 5 C by a cooling water jacket. Kato et al (2013a) reported the dissolution of major elements from basaltic rocks under the following conditions: fluid pressure of 40 MPa, preheating bath at 250 C, reaction bath at 340 C, and water flow of 6 mL/h. The reactor system was operated for 1,271 h using basalt samples and ultrapure water, and for 1,920 h without basalts (blank test).…”