HR: 1330h
AN: V12A-0568    [PDF]
TI: Contrasting fabrics produced during magmatic slumping and compaction of gabbroic cumulates from the Stillwater complex, Montana
AU: * Meurer, W P
EM: wpmeurer@mail.uh.edu
AF: University of Houston, Dept. of Geosciences 312 Sci. & Res. Bldg. 1, Houston, TX 77204 United States
AU: Gee, J S
EM: jsgee@ucsd.edu
AF: Scripps Inst. Oceanography, UCSD, San Diego, CA 92037 United States
AU: Selkin, P A
EM: pselkin@ucsd.edu
AF: Scripps Inst. Oceanography, UCSD, San Diego, CA 92037 United States
AU: Cheadle, M
AF: University of Wyoming, Dept of Geology, Laramie, WY 86574 United States
AB: We conducted a detailed study of the textures of a 70 m stratigraphic section of gabbroic cumulates in the Upper Banded Series of the Stillwater complex, Montana. The lower cumulates have a variably developed and locally strong foliation and fine-scale modal layering alternating on scales as small as 10 cm and are interpreted to have compaction as their main fabric forming process. They are overlain by a modally uniform gabbronorite that hosts anorthositic and pyroxenitic lenses whose fabric is believed to be related to slumping of a crystal mush. This gabbronorite lacks any continuous modal layering and while it has a well-developed foliation the orientation of this fabric is not as uniform as in the lower cumulates. We characterized the fabrics of the cumulates by measuring (1) the silicate fabric on orthogonal sections of 18 oriented blocks and (2) the Anisotropy of Magnetic Susceptibility (AMS) and Anisotropy of Anhysteretic Remanence (AARM) on minicores from the blocks and from sites spaced an average of 50 cm apart. Fabric data from the blocks agrees with the AMS and AARM of their minicores. The foliation planes and lineation directions indicated by the stratigraphic sampling, show good serial correlation and provide insight into where fabric-forming processes differed. The AMS data reveal a strong change in the magnetic character of the cumulates that corresponds with the transition from modally layered to modally uniform cumulates. Samples from the upper section are more magnetically anisotropic than would be inferred from their silicate fabrics. This difference may be related to textural variations present at scales too large to be sampled by minicores.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1527 Paleomagnetism applied to geologic processes
DE: 3640 Igneous petrology
DE: 3694 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting