Description
- Abstract:
- The Andean Transitional Southern Volcanic Zone (34º-38ºS) represents an area of some of the most productive mafic volcanism in South America during the Cenozoic, making it an excellent natural laboratory for investigating the origins of basaltic rocks in a continental subduction zone setting. Basaltic rocks in the back-arc region of the TSVZ display a large chemical and isotopic variability, ranging from intraplate lavas with compositions that resemble ocean island basalts to lavas with compositions that resemble volcanic front lavas. A debate has persisted over the origin of this compositional variability and whether the intraplate signature is derived from an EM-1 type asthenosphere or from the melting of enriched subcontinental lithospheric mantle. The research in this thesis constitutes a new approach to explaining the geochemical diversity observed in the mafic volcanism of the Andean TSVZ over the past 24 million years. Our interpretations integrate previous geochemical datasets with the data reported in this thesis, which constitutes new measurements of the radiometric ages and chemical and isotopic compositions of whole-rock lava samples, the oxygen isotope contents of olivine phenocrysts formed in these lavas, as well as the first dataset to include major, trace, and volatile (H2O, CO2, F, Cl, S) element contents for olivine-hosted melt inclusions from this region. These findings demonstrate that metasomatic cumulates from the SCLM represent a viable source component in mafic TSVZ back-arc lavas. Chapter 1 characterizes the chemical and isotopic composition of mafic lavas from the back-arc Plio-Quaternary Payenia volcanic province and identifies The Payenia melt source consists of three compositional endmembers, of which two are metasomatic cumulates in the SCLM, one with arc signature and one without. Chapter 2 presents the major, trace, and volatile element contents of olivine-hosted melt inclusions from three Plio-Quaternary TSVZ back-arc localities and demonstrates that the volatile contents of melt inclusions with and without arc signature exhibit an influence from metasomatic minerals from the SCLM. Chapter 3 characterizes mafic TSVZ lavas erupted since the Early Miocene and shows that the SCLM melt source has been present in the TSVZ back-arc for at least 24 million years.
- Notes:
- Thesis (Ph. D.)--Brown University, 2019
Access Conditions
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- All rights reserved. Collection is open to the Brown community for research.
Citation
Chilson-Parks, Benjamin H.,
"The Geochemistry of Cenozoic Volcanism in the Andean Southern Volcanic Zone, 34ºS-38ºS: Evaluating the Role of Subcontinental Lithospheric Mantle in Alkali Magma Petrogenesis"
(2019).
Earth, Environmental and Planetary Sciences Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/054h-h397
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Earth, Environmental and Planetary Sciences Theses and Dissertations
Theses and Dissertations for the Earth, Environmental and Planetary Sciences department....