Carbonation of Serpentinite in Creeping Faults of California. Issue 15 (11th August 2022)

• Record Type: Journal Article
• Authors: Klein, Frieder; Goldsby, David L.; Lin, Jian; Andreani, Muriel
• Is Part Of: Geophysical research letters. Volume 49:Issue 15(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-11
• Subjects: mineral carbonation -- serpentinite -- talc -- CO2 -- aseismic creep -- San Andreas Fault; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL099185
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Several large strike slip faults in central and northern California accommodate plate motions through aseismic creep. Although there is no consensus regarding the underlying cause of aseismic creep, aqueous fluids and mechanically weak, velocity‐strengthening minerals appear to play a central role. This study integrates field observations and thermodynamic modeling to examine possible relationships between the occurrence of serpentinite, silica‐carbonate rock, and CO2 ‐rich aqueous fluids in creeping faults of California. Our models predict that carbonation of serpentinite leads to the formation of talc and magnesite, followed by silica‐carbonate rock. While abundant exposures of silica‐carbonate rock indicate complete carbonation, serpentinite‐hosted CO2 ‐rich spring fluids are strongly supersaturated with talc at elevated temperatures. Hence, carbonation of serpentinite is likely ongoing in parts of the San Andres Fault system and operates in conjunction with other modes of talc formation that may further enhance the potential for aseismic creep, thereby limiting the potential for large earthquakes. Plain Language Summary: Constraining the relationships between the mechanical properties of rocks and lubricating fluids in tectonic fault zones is critical to understanding their seismogenic potential. We examined the distribution of exhumed mantle rocks and CO2 ‐rich springs in the San Andreas Fault area and find ubiquitous evidence for carbonate alteration in the creeping sections. Although carbonate alteration has gone to completion in exposed silica‐carbonate rocks, thermodynamic calculations suggest that CO2 ‐rich spring fluids are supersaturated with talc and magnesite at greater depth where temperatures are high. Because wet talc is a mechanically weak mineral, its formation through carbonation promotes tectonic movements without large earthquakes. Key Points: Carbonate‐altered mantle rocks and CO2 ‐rich springs are ubiquitous in the creeping section of the San Andreas Fault system CO2 ‐rich spring fluids are saturated with talc and magnesite at seismogenic depths where mineral carbonation is likely ongoing today The formation of talc facilitates aseismic creep in wet faults and promotes tectonic movements without large earthquakes