TY - JOUR
T1 - Fluid Infiltration Through Oceanic Lower Crust in Response to Reaction-Induced Fracturing
T2 - Insights From Serpentinized Troctolite and Numerical Models
AU - Oman Drilling Project Phase 2 Science Party
AU - Yoshida, Kazuki
AU - Okamoto, Atsushi
AU - Shimizu, Hiroyuki
AU - Oyanagi, Ryosuke
AU - Tsuchiya, Noriyoshi
N1 - Funding Information:
The authors thank Masaoki Uno for valuable discussions. This work was financially supported by the Japan Society for the Promotion of Science (KAKENHI Grant Numbers JP16H06347, JP17H02981, JP18K18778, and JP18KK0376) and the Cooperative Research Program of the Earthquake Research Institute, University of Tokyo (Grant Number ERI JURP 2018-B-01).
Funding Information:
The authors thank Masaoki Uno for valuable discussions. This work was financially supported by the Japan Society for the Promotion of Science (KAKENHI Grant Numbers JP16H06347, JP17H02981, JP18K18778, and JP18KK0376) and the Cooperative Research Program of the Earthquake Research Institute, University of Tokyo (Grant Number ERI JURP 2018‐B‐01).
Publisher Copyright:
©2020. American Geophysical Union. All Rights Reserved.
PY - 2020/11
Y1 - 2020/11
N2 - The mechanisms of fluid penetration through the gabbroic lower crust are important for the hydration of oceanic lithosphere. In the Oman ophiolite, which preserves an entire sequence of oceanic lithosphere formed at a fast-spreading ridge, the layered gabbros and dunites are extensively serpentinized. In this paper, we describe the characteristic textures of serpentinized troctolite and olivine gabbros recovered from the CM1A site of the Oman Drilling Project. In the troctolite, an olivine mesh texture is pervasively developed and is characterized by two types of veins: early lizardite + brucite + magnetite and late Al-rich lizardite + magnetite. These veins suggest the initiation of serpentinization at <350°C and a supply of Si and Al from plagioclase during the later stages of serpentinization. Plagioclase surrounding serpentinized olivine grains commonly shows radial fracturing. Numerical simulations using the discrete element method applied to coupled fluid flow, reaction, and fracturing reveal that volume expansion of olivine grains during serpentinization results in the simultaneous fracturing of olivine and surrounding plagioclase, and that the thermal stress during cooling of oceanic lithosphere might also cause preferential olivine fracturing prior to serpentinization. The simulations also predict a self-organizing fracture network that connects the olivine grains and passes through both olivine-rich and olivine-poor layers, resulting in permeability enhancement during serpentinization. Our results suggest that reaction-induced fracturing plays an essential role in the infiltration of seawater through the lower crust and into the mantle within oceanic lithosphere.
AB - The mechanisms of fluid penetration through the gabbroic lower crust are important for the hydration of oceanic lithosphere. In the Oman ophiolite, which preserves an entire sequence of oceanic lithosphere formed at a fast-spreading ridge, the layered gabbros and dunites are extensively serpentinized. In this paper, we describe the characteristic textures of serpentinized troctolite and olivine gabbros recovered from the CM1A site of the Oman Drilling Project. In the troctolite, an olivine mesh texture is pervasively developed and is characterized by two types of veins: early lizardite + brucite + magnetite and late Al-rich lizardite + magnetite. These veins suggest the initiation of serpentinization at <350°C and a supply of Si and Al from plagioclase during the later stages of serpentinization. Plagioclase surrounding serpentinized olivine grains commonly shows radial fracturing. Numerical simulations using the discrete element method applied to coupled fluid flow, reaction, and fracturing reveal that volume expansion of olivine grains during serpentinization results in the simultaneous fracturing of olivine and surrounding plagioclase, and that the thermal stress during cooling of oceanic lithosphere might also cause preferential olivine fracturing prior to serpentinization. The simulations also predict a self-organizing fracture network that connects the olivine grains and passes through both olivine-rich and olivine-poor layers, resulting in permeability enhancement during serpentinization. Our results suggest that reaction-induced fracturing plays an essential role in the infiltration of seawater through the lower crust and into the mantle within oceanic lithosphere.
KW - alteration and weathering processes
KW - discrete element method
KW - hydrothermal system
KW - mid-ocean ridge processes
KW - oceanic crust
UR - http://www.scopus.com/inward/record.url?scp=85096565951&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85096565951&partnerID=8YFLogxK
U2 - 10.1029/2020JB020268
DO - 10.1029/2020JB020268
M3 - Article
AN - SCOPUS:85096565951
VL - 125
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
SN - 2169-9313
IS - 11
M1 - e2020JB020268
ER -