HR: 0800h
AN: V41A-1366    [Abstracts]
TI: ``Sedimentary'' Structures in a Layered Granodiorite: A Window Into Physical Conditions Present During the Development of the Tuolumne Intrusive Suite, Sierra Nevada California
AU: * Loetterle, J
EM: jloetter@u.washington.edu
AF: University of Washington- Department of Earth and Space Sciences, 310 Condon Hall Box 35310, Seattle, WA 98105-1310 United States
AU: Bergantz, G
EM: bergantz@u.washington.edu
AF: University of Washington- Department of Earth and Space Sciences, 310 Condon Hall Box 35310, Seattle, WA 98105-1310 United States
AB: The presence of sedimentary-type features exposed in layered Tuolumne Intrusive Suite (TIS) outcrops provides a unique opportunity to assess fluid dynamic processes associated with both pluton assembly and magma chamber processes. Previous analyses of layered mafic intrusions, experimental and mathematical modeling of igneous layering, analogs in sedimentary rocks, and layering in granitic intrusions, have not defined a set of physical conditions that exist during intermediate granitic pluton development. Using constraints provided by field, petrographic, and geochemical relations among the layered outcrops in the TIS field area, both the dynamic conditions and rheological state necessary to form these "sedimentary" structures can be identified. Similar layer orientations at many different outcrops and sharp upper and lower layer/host rock contacts suggest that the layers occupy shallowly dipping, near-planar, "slot-like" openings in the outer members of the TIS. The TIS layers appear to originate by a combination of flow sorting and crystal settling due to the modal grading of the cm-scale layers, cumulate mineral textures, and mafic glomercrysts. Groups of layers with similar features demonstrate the repetition of this process. Examination of reoriented hornblende crystals along fault surfaces shows that slumps form due to the addition of overlying layers when the melt fraction is between 20 and 50%. Given the presence of (1) dikes full of K-feldspar megacrysts that cross-cut the layers but not the host rock, (2) resorbed crystal edges, (3) zoned hornblende crystals with pyroxene cores and (4) adjacent groups of layers that have features different from one another; the layering conditions such as magmatic temperature, water content, and direction of layer deposition must change periodically.
UR: http://www.ess.washington.edu/Program/physpet/personal\_page-sierra.html
DE: 8439 Physics and chemistry of magma bodies
DE: 8035 Pluton emplacement
DE: 5104 Fracture and flow
DE: 5139 Transport properties
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting