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Show 53 college of mines & earth sciences Metamorphism of the siliceous dolomites surrounding the mid-Tertiary Alta stock has produced a ther-mal contact aureole, defined by a series of reactions (isograds) with increasing metamorphic tempera-ture, resulting in the formation of: talc, tremolite, forsterite, clinohumite, and periclase. The dolomites in the outermost part of the Alta aureole commonly contain dolomite veins and chert nodules. Reac-tion rims of talc and calcite form by the reaction of these nodules with the surrounding dolomite by the reaction: 3 dolomite + 4 quartz +H2O = talc + 3 calcite + 3 CO2 . Isograds within the inner aureole are parallel to the igneous contact; however the distribution of talc in the outer aureole is irregular and strongly controlled by stratigraphy. This irregular distribution of talc may be produced by variations in rock permeability; the talc-bearing layers are more permeable than the talc-absent layers. If so, the talc-bearing layers should contain greater abundances of dolomite veins. The hypothesis is being tested by documenting the number of generations of dolomite vein sets, their orientation and abundances in the talc-bearing vs. talc-absent layers. Within talc-bearing layers, it will be important to establish the timing of vein formation rela-tive to development of talc reaction rims. Field measurements suggest that there are two main vein generations: a NW-SE trending vein set that accounts for about 43% of the vein sets, and a younger NE-SW cross-cutting generation that accounts for about 57% of the veins. Preliminary measurements establish that in one section, a talc-bearing interval has significantly higher abundances of veins than the adjacent talc-absent interval. Documentation of dolomite vein generations and abundances will lead to a better understanding of the physical and thermodynamic processes responsible for development of these veins in the Alta aureole. If formation of the dolomite veins is contemporaneous with the talc and calcite reaction rims, then vein formation sheds light on the physical-chemical processes controlling the onset of metamor-phism in carbonate rocks. If the veins are later than the formation of talc, then these veins will provide more information on regional tectonics, including the uplift history of the Wasatch Mountains. MAPPING GENERATIONS OF DOLOMITE VEINS WITHIN THE ALTA STOCK AUREOLE, ALTA, UTAH Kathryn A. Bradbury (John R. Bowman) Department of Geology and Geophysics, The University of Utah UNDERGRADUATE RESEARCH ABSTRACTS Kathryn A. Bradbury John R. Bowman |
