Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Geosciences

First Advisor's Name

Rosemary Hickey-Vargas

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Guatam Sen

Third Advisor's Name

Andrew McFarlane

Date of Defense

7-10-2001

Abstract

Subduction zone magmatism is an important and extensively studied topic in igneous geochemistry. Recent studies focus on from where arc magmas are generated, how subduction components (fluids or melts) are fluxed into the source of the magmas, and whether or how the subduction components affect partial melting processes beneath volcanic arcs at convergent boundaries.

At 39.5°S in the Central Southern Volcanic Zone of the Andes, Volcano Villarrica is surrounded by a suite of Small Eruptive Centers (SEC). The SECs are located mostly to the east and northeast of the stratovolcano and aligned along the Liquine - Ofqui Fault Zone, the major fracture system in this area. Former studies observed the geochemical patterns of the SECs differ distinctively from those of V.Villarrica and suggested there may be a relationship between the compositions of the volcanic units and their edifice sizes. This work is a comprehensive geochemical study on the SECs near V.Villarrica, using a variety of geochemical tracers and tools including major, trace and REE elements, Li - Be - B elements, Sr - Nd - Pb isotopes and short - lived isotopes such as U - series and 10Be. In this work, systematic differences between the elemental and isotopic compositions of the SECs and those of V.Villarrica are revealed and more importantly, modeled in terms of magmatic processes occurring at continental arc margins. Detailed modeling calculations in this work reconstruct chemical compositions of the primary magmas, source compositions, compositions and percentages of different subduction endmembers mixed into the source, degrees of partial melting and different time scales of the SECs and V.Villarrica, respectively. Geochemical characteristics and possible origins of the two special SECs - andesitic Llizan, with crustal signatures, and Rucapillan, to the northwest toward the trench, are also discussed in this work.

Identifier

FI15071601

Comments

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