2010 GSA Denver Annual Meeting (31 October 3 November 2010)
Paper No. 271-6
Presentation Time: 8:00 AM-6:00 PM


NACHBOR, Amelia, Department of Geosciences, Univ of Wisconsin-Milwaukee, P.O. Box 413, 366 Lapham Hall, Milwaukee, WI 53201, anachbor@uwm.edu, CZECK, Dyanna, Geosciences, Univ of Wisconsin - Milwaukee, PO Box 413, Milwaukee, WI 53201, YONKEE, Adolph, Department of Geosciences, Weber State University, 2507 University Circle, Ogden, UT 84408, and JOHNSON, Kimberly R., Geosciences, University of Wisconsin - Milwaukee, P. O. Box 413, Milwaukee, WI 53201

Diamictite deformed at greenschist facies within the Willard thrust system of the Sevier orogenic belt, northern Utah, displays varying relations between fluid-rock interaction, volume loss, and strain between the footwall (Antelope Island) and hanging wall (Fremont Island). Diamictite consists of pebble to boulder clasts comprised of red granitic orthogneiss, green paragneiss, and metaquartzite, which sit within a sandy to micaceous matrix. Most gneissic clasts were likely derived from basement of the Farmington Canyon Complex during Neoproterozoic glaciation; these basement rocks were subsequently locally exhumed during Sevier thrusting. By comparing geochemistry of diamictite with basement protoliths, characteristics of fluid-rock interaction across a major thrust can be evaluated.

On Antelope Island (footwall), red orthogneiss clasts and matrix have concentrations of Al2O3 (relatively immobile) that overlap with basement sources, indicating little to no volume change during deformation; SiO2 concentrations also overlap. Green paragneiss clasts, however, display a slight increase in Al2O3 and decrease in SiO2, suggestive of minor volume loss by dissolution of quartz. Strain and microtextural relations also indicate limited volume change. Na2O decreases whereas MgO increases, reflecting alteration of sodic feldspar to phengitic muscovite, with precipitation of quartz in matrix, strain shadows, and microveins. Strain within clasts and matrix increases systematically toward the WNW, with X-Z ratios increasing from ~2:1 to ~10:1. Feldspar is almost completely altered to mica in high-strain samples, and precipitated quartz displays significant plastic deformation. On Fremont Island (hanging wall), significant increases in Al2O3 and decreases in SiO2 of diamictite indicate ~20% volume loss, consistent with strain and microtextural relations. Compared to Antelope Island, Na2O is higher and MgO is lower, reflecting alteration of biotite to Fe-rich chlorite and feldspar to muscovite plus paragonite, with net dissolution of quartz. X-Z strain ratios are overall lower, ranging from ~2:1 to 4:1. Differences in geochemical patterns are interpreted to record up-temperature flow in the footwall and down-temperature flow in the hanging wall, with focused fluid flow along the main fault zone.

2010 GSA Denver Annual Meeting (31 October 3 November 2010)
General Information for this Meeting
Session No. 271--Booth# 329
Coupling of Deformation and Chemical Processes in Earth (Posters)
Colorado Convention Center: Hall D
8:00 AM-6:00 PM, Wednesday, 3 November 2010

Geological Society of America Abstracts with Programs, Vol. 42, No. 5, p. 635

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