Degree Year

2013

Document Type

Thesis

Degree Name

Bachelor of Arts

Department

Geology

Advisor(s)

F. Zeb Page

Keywords

Santa Catalina Island, Thermobarometry, Amphibolite, Melange, Subduction, Theriak Domino, Pseudosection, Restite, Partial melt, Melt extraction, Garnet hornblendite

Abstract

On Santa Catalina Island, Ca high-grade amphibolite units overlie progressively lower- grade blueschist units in an inverted stack structure. This juxtaposition of high grade and low-grade metamorphic units has long been the subject of much debate as to the tectonic origins of the formation and how it relates to California's tectonic evolution. Previous petrography and thermobaromety of blocks in the amphibolite unit estimate pressures and temperatures of ~8-11 kbar and ~640-750 °C (Platt, 1975; Sorensen and Barton 1987). These estimates were calculated before many of the computational advances in modern thermobarometry. Using Equilibrium Assemblage Diagrams (EAD) calculated with Theriak Domino, this study estimates the peak of metamorphism at temperatures between 700 °C and 750 °C and pressures above 15kbar. Interpretation of textural features from a clinopyroxene bearing block previously studied by Sorensen (1988) and Sorensen and Grossman (1989) suggest the sample followed a near isothermal decompression path from 50km to 21 km of depth. EAD analysis also provides additional support for claims that large metamafic blocks in the Amphibolite unit melange were residua of Fe-Ti rich mafic rocks after extraction of an albite rich partial melt.

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Geology Commons

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