Stress variations in space and time within the mantle section of an oceanic transform zone; evidence for the seismic cycle

The Bogota Peninsula shear zone in New Caledonia (southwest Pacific Ocean) is the exhumed mantle section of an oceanic transform zone. Ductile fabrics in this zone formed at temperatures >820°C, and differential stresses estimated from microstructures vary spatially and temporally. Along a transf...

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Bibliographic Details
Published in:Geology (Boulder) 2020-06, Vol.48 (6), p.569-573
Main Authors: Chatzaras, Vasileios, Tikoff, Basil, Kruckenberg, Seth C, Titus, Sarah J, Teyssier, Christian, Drury, Martyn R
Format: Article
Language:English
Subjects:
Bogota Peninsula
Crack propagation
Deformation
Deformation mechanisms
ductile deformation
Earth mantle
Earthquakes
EBSD data
electron diffraction data
exhumation
Fabrics
faults
Fracture mechanics
Geology
Geophysics
harzburgite
igneous and metamorphic rocks
igneous rocks
Lithosphere
Localization
mantle
Melanesia
microstructure
New Caledonia
Oceania
ophiolite complexes
peridotites
petrofabrics
Petrology
plutonic rocks
preferred orientation
Seismic activity
Shear zone
shear zones
solid Earth (tectonophysics)
Strain
Strain localization
Strain rate
stress
Stresses
strike-slip faults
structural analysis
Temporal variations
transform faults
ultramafics
Upper mantle
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Summary:The Bogota Peninsula shear zone in New Caledonia (southwest Pacific Ocean) is the exhumed mantle section of an oceanic transform zone. Ductile fabrics in this zone formed at temperatures >820°C, and differential stresses estimated from microstructures vary spatially and temporally. Along a transform-perpendicular transect, stresses increase toward the high-strain areas. We attribute this stress gradient to an increase in strain rate caused by imposed rather than intrinsic strain localization. Temporal stress variations are indicated by the formation of fine-grained microdeformation zones (MDZs) that truncate and offset coarser grains. We interpret the MDZs to result from zones of brittle deformation caused by earthquake fracture propagation downward in the upper mantle, which are in turn overprinted by ductile deformation at stresses 2-6 times higher (22-81 MPa) than their surrounding steady-state fabrics. We interpret the spatial and temporal variations in microstructures and stresses as reflecting different stages of the seismic cycle in oceanic lithosphere.
ISSN:0091-7613
1943-2682
DOI:10.1130/G47137.1