A record of high-temperature embrittlement of periodotite in CO/sub 2/ permeated xenoliths from basalt

Journal Article · Mon Mar 10 00:00:00 EST 1986 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB091iB03p03841· OSTI ID:5875667

Rovetta, M R; Delaney, J R; Blacic, J D

Four ultramafic xenoliths recovered from Hawaiian basalts contain CO/sub 2/-fluid inclusion arrays which originated as healed microcracks. These healed microcracks have been used to study the microcracking mechanisms in the xenolith source region. Fluid inclusion arrays in olivine have a preferred crystallographic orientation which is consistent with a hypothesis of microcrack nucleation upon dislocation pileups by the Stroh mechanism on the following olivine slip systems: (0kl)(100), (110)(001), and (010)(001). Previous investigators have shown that all these slip systems of olivine are active at high stress or low temperature. Olivine neoblasts occur as small grains in local shear zones (0.04 mm diameter and less than 3% of total volume) and larger grains which embay porphyroclasts throughout the specimens (0.22-mm diameter and approximately 30% percent of total volume). Olivine neoblast diameters provides estimates of the deviatoric stress of 160--200 MPa using the smaller grains and 50--75 MPa using the larger grains. The absence of clinopyroxene mechanical twinning in the xenoliths provides an independent paleopiezometer that limits the maximum deviatoric stress in the peridotite source region to 200 MPa. Fluid inclusion arrays are parallel to each other, are perpendicular to penetrative foliation planes produced by intragranular plasticity, and have an average spacing between arrays of 0.5--2.0 mm. Recrystallized olivine grains (neoblasts) are free of fluid inclusions. Estimates of the contribution of Stroh cracks to the deformation of the xenolith source region indicate a maximum decrease of a few percent in the net energy required to produce an increment of strain, dependent upon confining pressure.

• Research Organization: School of Oceanography, University of Washington, Seattle
• OSTI ID: 5875667
• Journal Information: J. Geophys. Res.; (United States), Vol. 91:B3
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
PERIDOTITES
MICROSTRUCTURE
BASALT
CARBON DIOXIDE
CRACKING
CRACKS
INCLUSIONS
MAGMA
OLIVINE
TEMPERATURE EFFECTS
ALKALINE EARTH METAL COMPOUNDS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
CRYSTAL STRUCTURE
DECOMPOSITION
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MINERALS
OXIDES
OXYGEN COMPOUNDS
PLUTONIC ROCKS
PYROLYSIS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)