Publication Date

Summer 2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

Advisor

Ellen Metzger

Keywords

contact metamorphism, fluid flow, May Lake, skarn, stable isotope, Yosemite

Subject Areas

Geochemistry; Mineralogy

Abstract

The May Lake interpluton screen is a 4 km long, ~0.5 km wide swath of metamorphic rock cropping out between plutons of the ~103 Ma Yosemite Valley Intrusive Suite and the ~93-85 Ma Tuolumne Intrusive Suite in Yosemite National Park, California. Metasomatic alteration and recrystallization due to contact metamorphism and fluid infiltration resulted from the emplacement of the Cretaceous plutons. Mineral assemblages are consistent with metamorphism to hornblende-hornfels and amphibolite facies. The presence of sillimanite-bearing metapelite and more Mg-rich clinopyroxene in calc-silicate assemblages of the northeast section of the screen than the southwest suggest higher grade metamorphism was experienced to the northeast. Pseudosection diagrams created from whole rock chemical analyses of three metapelite rocks also indicate higher temperatures in the northeastern section of the screen with minimum temperatures estimated from ~540-617°C. Based on petrographic analysis of andalusite- and sillimanite-bearing metapelite, it is likely that the screen experienced two stages of contact metamorphism: relatively lower temperature metamorphism during intrusion of the Yosemite Valley Intrusive Suite followed by relatively higher temperature contact metamorphism during intrusion of the more mafic Tuolumne Intrusive Suite. Stable isotope data suggest that rock permeability and preexisting structures were the strongest factors controlling fluid infiltration through the contact aureole.

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