Igneous life cycles: geochemistry of magma from mantle to surface and back again

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dc.contributor.advisorLee, Cin-Ty
dc.creatorAllen, Sydney Marie
dc.date.accessioned2023-09-01T21:05:04Z
dc.date.created2023-08
dc.date.issued2023-08-11
dc.date.submittedAugust 2023
dc.date.updated2023-09-01T21:05:05Z
dc.description.abstractMaterial from within the Earth is cycled and recycled from the interior of the Earth to the surface in igneous rocks. The chemistry of igneous rocks record snapshots of this complex history. Here, we use three major projects to assess important processes in this life cycle. Continental arc volcanism generates a wide diversity of magma compositions, but the tempos of compositional variation are unclear. Here, we investigate a 7-million year record of volcanic ash layers in the Cretaceous Eagle Ford Group to investigate temporal changes in ash composition on <100 kyr timescales. We apply an empirical Ti/Zr-SiO2 relationship to Ti/Zr measurements of 52 Eagle Ford bentonites to reconstruct of ash protolith SiO2 of altered bentonites. Ash compositions fluctuate between periods of high and low silica volcanism over ~100 kyr timescales. If the temporal variability of these ashes represents broad snapshots of the Cordilleran continental arc, these results suggest that continental arc systems may undergo episodic changes in the extent of magmatic differentiation or the nature of eruption on rapid (<100 kyr) timescales. Slow-slip megathrust events in the Hikurangi forearc region, New Zealand, may be related to seamount subduction. We examine differences in the clast origins, depositional settings, and diagenetic histories of volcaniclastic units to highlight the heterogeneity of volcanic systems on the Hikurangi Plateau. The presence of voluminous hydrous clays within thick, altered volcaniclastic units provides a ready source for excess pore fluids that may enable slow-slip events along the Hikurangi subduction zone. Alkaline magmatism at Mountain Pass, CA has attracted attention due to its spatial and temporal association with a REE-rich, economically important carbonatite. However, questions remain about the origins of magma here. We present geochemical data for 121 primitive alkaline igneous rocks to allow a more complete picture of these uncommon igneous compositions. Examining primitive magma composition affords a glimpse into the early stages of magma generation to understand the origins and early histories of alkaline magmatism here. We argue for the importance of pyroxenite melting and suggest that metasomatism related to earlier subduction in this region were significant influences on mama compositions.
dc.embargo.lift2024-02-01
dc.embargo.terms2024-02-01
dc.format.mimetypeapplication/pdf
dc.identifier.citationAllen, Sydney Marie. "Igneous life cycles: geochemistry of magma from mantle to surface and back again." (2023) Diss., Rice University. https://hdl.handle.net/1911/115278.
dc.identifier.urihttps://hdl.handle.net/1911/115278
dc.language.isoeng
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.
dc.subjectcontinental arc volcanism
dc.subjectbentonite
dc.subjectEagle Ford Group
dc.subjectvolcanic tempos
dc.subjectvolcaniclastic
dc.subjectHikurangi
dc.subjectslow-slip
dc.subjectdiagenesis
dc.subjectIODP Expedition 375
dc.subjectMountain Pass
dc.subjectultrapotassic magmatism
dc.titleIgneous life cycles: geochemistry of magma from mantle to surface and back again
dc.typeThesis
dc.type.materialText
thesis.degree.departmentEarth Science
thesis.degree.disciplineNatural Sciences
thesis.degree.grantorRice University
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy
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