Differentiation regimes in the Central Andean magma systems: case studies of Taapaca and Parinacota volcanoes, Northern Chile

by Magdalena Banaszak
Doctoral thesis
Date of Examination:2014-04-23
Date of issue:2014-10-29
Advisor:Prof. Dr. Gerhard Wörner
Referee:Prof. Dr. Gerhard Wörner
Referee:Prof. Dr. François Holtz
Persistent Address: http://dx.doi.org/10.53846/goediss-4748

 

 

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Abstract

English

Volcanoes have shaped the Earth’s surface and are nature’s most awesome manifestation of the power within our planet (Rosaly M. Lopes). Compositional and mineralogical diversity of erupted lavas reflects distinct magma differentiation paths, resulting from magmatic processes controlled by magma sources and architecture of the Earth's crust. A differentiation regime is a concept encompassing different magmatic conditions and mechanisms operating in subvolcanic plumbing systems during magma evolution. This study addresses the compositional and mineralogical variability of magmas erupted in the Andean Central Volcanic Zone (14°-27°S). Taapaca and Parinacota located in the Central Andes (18°S), are composite stratovolcanoes distinctive in their morphology: Taapaca represents a dacitic dome complex; Parinacota forms a symmetrical stratocone. These two characteristic effusive end-member types of the arc volcanism reflect two different magma evolutionary paths. Taapaca has erupted compositionally and mineralogically uniform dacites. In contrast, Parinacota demonstrates a large compositional variability of the erupted lavas, from basaltic andesite to rhyolite. Moreover, Parinacota experienced an edifice sector collapse, which punctuates changes in the composition of prevailing Fe-Mg silicates in the andesite lavas. Although both volcanos appear to be completely different, Taapaca and Parinacota share several characteristics such as trace element and isotopic composition, mineral chemistry, and a range of physical parameter P-T-ƒO2 during magma crystallization. Geochemical, geochemical-statistical and petrological investigations presented in this study in a connection with experimental constraints reveal one principal mechanism operating in the subvolcanic Taapaca and Parinacota systems: two-stage magma mixing between magmas generated in the mantle wedge, lithospheric mantle and the continental crust is responsible for the varying compositions of the erupted Taapaca and Parinacota lavas. Proportions of the mafic and silicic magmas, simultaneously present in the subvolcanic plumbing system constitute mineralogy of the hybrid lavas. This study shows that the proportions of the compositionally and physically contrasting magmas define the distinct differentiation regimes of the calc-alkaline magmas in the volcanic systems, controlled by input rates from the mantle and the deep crust. 
Keywords: magmatic processes; magmatic differentiation; differentiation regime; magma mixing; Polytopic Vector Analysis; Central Andes; Central Volcanic Zone (CVZ); Taapaca Volcanic Complex; Parinacota Volcano
 
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