Quartz and mica fabric control of seismic anisotropy in metamorphic core complexes

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6322675

Szymanski, D L; Ringland, M L; Christensen, N I

Metamorphic core complexes of the Western Cordillera, which likely represent exposures of lower crustal rocks, are typically divided into three domains: 1) an igneous or metamorphic basement protolith; 2) an unmetamorphosed, brittlely deformed cover; and 3) a decollement zone of microbrecciated rock between the basement and cover. The basement protolith grades upward from undeformed rock to a strongly mylonitized zone beneath the decollement. Granite mylonite samples have been collected from the Catalina-Rincon complex near Tucson, Arizona for seismic velocity measurements at pressures to 6 kbar. To investigate anisotropy, velocities were measured in directions normal to foliation and normal and parallel to lineation. Seismically, the mylonites are divided into three types: Type I - isotropic rocks; Type II - anisotropic samples with fast velocities perpendicular to lineation; and Type III - anisotropic samples with fast velocities parallel to lineation. Type I samples contain little mica and petrofabric analyses of quartz show a random c axis orientation. Type II mylonites also contain little mica, but have a strong orientation of quartz c axes perpendicular to lineation. Velocity measurements in single crystal quartz are significantly faster parallel to the c axis than perpendicular to the c axis, thus accounting for the observed anisotropy. The Type III mylonites have similar quartz fabrics to Type II samples, but contain abundant highly anisotropic biotite. Petrofabric analyses of biotite in Type III mylonites show that biotite orientation is responsible for the observed seismic anisotropy.

• Research Organization: Purdue Univ., West Lafayette, IN (USA)
• OSTI ID: 6322675
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580203* -- Geophysics-- Geophysical Survey Methods-- (1980-1989)
ANISOTROPY
ARIZONA
BASEMENT ROCK
CHALCOGENIDES
FEDERAL REGION IX
GEOPHYSICAL SURVEYS
GRANITES
IGNEOUS ROCKS
ISOTROPY
METAMORPHIC ROCKS
MICA
MINERALS
NORTH AMERICA
ORIENTATION
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PLUTONIC ROCKS
QUARTZ
ROCKS
SEISMIC SURVEYS
SEISMIC WAVES
SILICON COMPOUNDS
SILICON OXIDES
SURVEYS
USA
WAVE FORMS
WAVE PROPAGATION