TY - JOUR
T1 - Experimental constraints on the serpentinization rate of fore-arc peridotites
T2 - Implications for the upwelling condition of the slab-derived fluid
AU - Nakatani, T.
AU - Nakamura, M.
N1 - Publisher Copyright:
© 2016. American Geophysical Union. All Rights Reserved.
PY - 2016/8/1
Y1 - 2016/8/1
N2 - To constrain the water circulation in subduction zones, the hydration rates of peridotites were investigated experimentally in fore-arc mantle conditions. Experiments were conducted at 400–580°C and 1.3 and 1.8 GPa, where antigorite is expected to form as a stable serpentine phase. Crushed powders of olivine ± orthopyroxene and orthopyroxene + clinopyroxene were reacted with 15 wt % distilled water for 4–19 days. The synthesized serpentine varieties were lizardite and aluminous lizardite (Al-lizardite) in all experimental conditions except those of 1.8 GPa and 580°C in the olivine + orthopyroxene system, in which antigorite was formed. In the olivine + orthopyroxene system, the reactions were interface-controlled except for the reaction at 400°C, which was transport-controlled. The corresponding reaction rates were 7.0 × 10−12 to 1.5 × 10−11 m s−1 at 500–580°C and 7.5 × 10−16 m2 s−1 at 400°C for the interface and transport-controlled reactions, respectively. Based on a simple reaction-transport model including these hydration rates, we infer that penetration of the slab-derived fluid all the way through a water-unsaturated fore-arc mantle is allowed only when focused flow occurs with a spacing larger than 77–229 km in hot subduction zones such as Nankai and Cascadia. However, the necessary spacing is only 2.3–4.6 m in intermediate-temperature subduction zones such as Kyushu and Costa Rica. These calculations imply that fluid leakage in hot subduction zones may occur after the fore-arc mantle is totally hydrated, whereas in intermediate-temperature subduction zones, leakage through a water-unsaturated fore-arc mantle may be facilitated.
AB - To constrain the water circulation in subduction zones, the hydration rates of peridotites were investigated experimentally in fore-arc mantle conditions. Experiments were conducted at 400–580°C and 1.3 and 1.8 GPa, where antigorite is expected to form as a stable serpentine phase. Crushed powders of olivine ± orthopyroxene and orthopyroxene + clinopyroxene were reacted with 15 wt % distilled water for 4–19 days. The synthesized serpentine varieties were lizardite and aluminous lizardite (Al-lizardite) in all experimental conditions except those of 1.8 GPa and 580°C in the olivine + orthopyroxene system, in which antigorite was formed. In the olivine + orthopyroxene system, the reactions were interface-controlled except for the reaction at 400°C, which was transport-controlled. The corresponding reaction rates were 7.0 × 10−12 to 1.5 × 10−11 m s−1 at 500–580°C and 7.5 × 10−16 m2 s−1 at 400°C for the interface and transport-controlled reactions, respectively. Based on a simple reaction-transport model including these hydration rates, we infer that penetration of the slab-derived fluid all the way through a water-unsaturated fore-arc mantle is allowed only when focused flow occurs with a spacing larger than 77–229 km in hot subduction zones such as Nankai and Cascadia. However, the necessary spacing is only 2.3–4.6 m in intermediate-temperature subduction zones such as Kyushu and Costa Rica. These calculations imply that fluid leakage in hot subduction zones may occur after the fore-arc mantle is totally hydrated, whereas in intermediate-temperature subduction zones, leakage through a water-unsaturated fore-arc mantle may be facilitated.
KW - Arima-type fluid
KW - fore-arc
KW - hydration reaction
KW - serpentine
KW - slab fluid
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U2 - 10.1002/2016GC006295
DO - 10.1002/2016GC006295
M3 - Article
AN - SCOPUS:84982225568
VL - 17
SP - 3393
EP - 3419
JO - Geochemistry, Geophysics, Geosystems
JF - Geochemistry, Geophysics, Geosystems
SN - 1525-2027
IS - 8
ER -