TY - JOUR
T1 - Silica controls on hydration kinetics during serpentinization of olivine
T2 - Insights from hydrothermal experiments and a reactive transport model
AU - Oyanagi, Ryosuke
AU - Okamoto, Atsushi
AU - Tsuchiya, Noriyoshi
N1 - Funding Information:
We are grateful to Koji Hukushima, Tatsu Kuwatani, and Toshiaki Omori for helpful advice on the exchange Monte Carlo method and cross-validation method. We thank Michihiko Nakamura, Takeshi Komai, Kenichi Hoshino, Masaoki Uno, Takayoshi Nagaya, Fumiko Higashino, and Otgonbayar Dandar for valuable discussions. Kenta Yoshida is thanked for his valuable comments on an early version of the manuscript. We thank Satoru Ishikawa and Ryo Yamada for their help with coding using Fortran, and Yusuke Netsu for assisting with the hydrothermal experiments. This manuscript benefited greatly from constructive comments by Benjamin Tutolo, two anonymous reviewers, and the associate editor Frieder Klein. This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Numbers JP18J01649, JP16H06347, JP19K14827, and JP17H02981. The funding sources were not involved in the study design; in the collection, analysis and interpretation of data; in the writing of the report; or in the decision to submit the article for publication.
Funding Information:
This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Numbers JP18J01649 , JP16H06347 , JP19K14827 , and JP17H02981 . The funding sources were not involved in the study design; in the collection, analysis and interpretation of data; in the writing of the report; or in the decision to submit the article for publication. Appendix A
Publisher Copyright:
© 2019 Elsevier Ltd
PY - 2020/2/1
Y1 - 2020/2/1
N2 - Silica activity in fluids is a key factor that controls reaction pathways during the hydrothermal alteration of olivine in the oceanic lithosphere. In this study, we conducted hydrothermal experiments (300 °C, 8.58 MPa) on the olivine (Ol)–quartz (Qtz)–H2O system to understand the coupling between silica transport and olivine alteration. Mineral powders were reacted with 0.5 mol kg−1 NaCl solution in a tube-in-tube type vessel, and the spatial distribution of reactant and product minerals was investigated after the experiments. Alteration zones formed in the Ol-hosted region after 2055 hours of reaction. With increasing distance from the Ol–Qtz boundary these were: talc; talc + serpentine; and serpentine + magnetite + brucite. Talc formed 0–2.3 mm from the Ol–Qtz boundary in the Ol-hosted region, and brucite formed >5 mm from the Ol–Qtz boundary in the Ol-hosted region. No secondary minerals formed in the Qtz-hosted region. The observed mineral distribution was modeled using a reactive transport model that simulated the coupling between SiO2(aq) diffusion and seven silica-controlling reactions. An inverse modeling framework, which combines a reactive transport model with an exchange Monte Carlo method, was used to parameterize the diffusivity of SiO2(aq) and the rate constants of the seven overall reactions. Our model shows that the rate of hydration in the serpentine + metastable talc zone with intermediate silica activity was higher than in the serpentine, serpentine + brucite, and talc zones, suggesting that the silica activity of the reacting fluid has a significant control on the rate of hydrothermal alteration of mantle peridotite by crustal fluids. Moreover, the model suggests that the rate-control process changed from being surface- to transport-controlled over the course of the experiments. We suggest that dynamic changes in rate control process are important contributors to the formation of metasomatic zoning and heterogeneous hydration patterns within the oceanic lithosphere.
AB - Silica activity in fluids is a key factor that controls reaction pathways during the hydrothermal alteration of olivine in the oceanic lithosphere. In this study, we conducted hydrothermal experiments (300 °C, 8.58 MPa) on the olivine (Ol)–quartz (Qtz)–H2O system to understand the coupling between silica transport and olivine alteration. Mineral powders were reacted with 0.5 mol kg−1 NaCl solution in a tube-in-tube type vessel, and the spatial distribution of reactant and product minerals was investigated after the experiments. Alteration zones formed in the Ol-hosted region after 2055 hours of reaction. With increasing distance from the Ol–Qtz boundary these were: talc; talc + serpentine; and serpentine + magnetite + brucite. Talc formed 0–2.3 mm from the Ol–Qtz boundary in the Ol-hosted region, and brucite formed >5 mm from the Ol–Qtz boundary in the Ol-hosted region. No secondary minerals formed in the Qtz-hosted region. The observed mineral distribution was modeled using a reactive transport model that simulated the coupling between SiO2(aq) diffusion and seven silica-controlling reactions. An inverse modeling framework, which combines a reactive transport model with an exchange Monte Carlo method, was used to parameterize the diffusivity of SiO2(aq) and the rate constants of the seven overall reactions. Our model shows that the rate of hydration in the serpentine + metastable talc zone with intermediate silica activity was higher than in the serpentine, serpentine + brucite, and talc zones, suggesting that the silica activity of the reacting fluid has a significant control on the rate of hydrothermal alteration of mantle peridotite by crustal fluids. Moreover, the model suggests that the rate-control process changed from being surface- to transport-controlled over the course of the experiments. We suggest that dynamic changes in rate control process are important contributors to the formation of metasomatic zoning and heterogeneous hydration patterns within the oceanic lithosphere.
KW - Diffusion
KW - Dissolved Si
KW - Markov chain Monte Carlo
KW - Rate-limiting process
KW - Reaction rate
KW - Reactive-transport
KW - Serpentinization
KW - Silica metasomatism
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U2 - 10.1016/j.gca.2019.11.017
DO - 10.1016/j.gca.2019.11.017
M3 - Article
AN - SCOPUS:85075800695
SN - 0016-7037
VL - 270
SP - 21
EP - 42
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -