Class
Article
College
College of Science
Faculty Mentor
Alexis Ault
Presentation Type
Poster Presentation
Abstract
Transient slow slip events are observed in the shallow portion of faults and are an important part of the earthquake cycle, but the influence of mineralogy on the mechanics of slow slip is poorly constrained. Outcrop to nanoscale structures and mineral textures observed in faults exhumed to the surface record evidence of varying slip rates in the past and may inform ongoing fault slip mechanisms. Hematite, an iron oxide mineral that precipitates in shallow faults, exhibits textures potentially diagnostic of slip rate and is amenable to (U-Th)/He thermochronometry. We report field and scanning electron microscopy (SEM) observations of structures and textures with hematite (U-Th)/He dates from minor fault surfaces in the exhumed damage zone of the Painted Canyon fault zone (PCF) in Mecca Hills, CA, adjacent and parallel to the southern San Andreas fault, to evaluate the rock record of slow slip events. Hematite slip surfaces from the PCF are ubiquitous and occur in association with chlorite-rich gneiss or clay-rich gouge. SEM reveals multiple hematite morphologies including high-aspect ratio plates with rounded or serrated grain boundaries, as well as stubby and euhedral, hexagonal plates. The absence of recrystallization textures likely precludes high temperatures generated along faults due to frictional heating during earthquakes. Hematite-filled injection veins formed during fluid overpressure events and interlayered hematite, calcite, and phyllosilicate and reworked clasts of hematite imply multiple periods of precipitation and deformation. S-C fabrics, folds, and shape preferred orientation in hematite plates suggest ongoing slip at subseismic slip rates. New hematite (U-Th)/He dates (n=37) expand a previously published apatite and hematite (U-Th)/He thermochronometry dataset and document fluid flow and hematite mineralization events during PCF exhumation from ~2.2 to 0.8 Ma and between ~0.8 to 0.5 Ma. Together, these observations support repeated episodes of hematite precipitation and subsequent deformation during slow slip events. Presentation Time: Wednesday, 2-3 p.m. Zoom link: https://usu-edu.zoom.us/j/87892002075?pwd=Ym1Tcy9NOVhaaGZWczZWY1JCL3owUT09
Location
Logan, UT
Start Date
4-11-2021 12:00 AM
Included in
Shallow Slow Slip Events Documented With Hematite Themochronometry and Structural Analysis in an Exhumed Fault Zone in Mecca Hills, CA
Logan, UT
Transient slow slip events are observed in the shallow portion of faults and are an important part of the earthquake cycle, but the influence of mineralogy on the mechanics of slow slip is poorly constrained. Outcrop to nanoscale structures and mineral textures observed in faults exhumed to the surface record evidence of varying slip rates in the past and may inform ongoing fault slip mechanisms. Hematite, an iron oxide mineral that precipitates in shallow faults, exhibits textures potentially diagnostic of slip rate and is amenable to (U-Th)/He thermochronometry. We report field and scanning electron microscopy (SEM) observations of structures and textures with hematite (U-Th)/He dates from minor fault surfaces in the exhumed damage zone of the Painted Canyon fault zone (PCF) in Mecca Hills, CA, adjacent and parallel to the southern San Andreas fault, to evaluate the rock record of slow slip events. Hematite slip surfaces from the PCF are ubiquitous and occur in association with chlorite-rich gneiss or clay-rich gouge. SEM reveals multiple hematite morphologies including high-aspect ratio plates with rounded or serrated grain boundaries, as well as stubby and euhedral, hexagonal plates. The absence of recrystallization textures likely precludes high temperatures generated along faults due to frictional heating during earthquakes. Hematite-filled injection veins formed during fluid overpressure events and interlayered hematite, calcite, and phyllosilicate and reworked clasts of hematite imply multiple periods of precipitation and deformation. S-C fabrics, folds, and shape preferred orientation in hematite plates suggest ongoing slip at subseismic slip rates. New hematite (U-Th)/He dates (n=37) expand a previously published apatite and hematite (U-Th)/He thermochronometry dataset and document fluid flow and hematite mineralization events during PCF exhumation from ~2.2 to 0.8 Ma and between ~0.8 to 0.5 Ma. Together, these observations support repeated episodes of hematite precipitation and subsequent deformation during slow slip events. Presentation Time: Wednesday, 2-3 p.m. Zoom link: https://usu-edu.zoom.us/j/87892002075?pwd=Ym1Tcy9NOVhaaGZWczZWY1JCL3owUT09