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Trace Element Geochemistry and Petrology of Aden Crater and the Albuquerque Volcanoes

by Butler, Daniel Jay

Abstract

Aden Crater and the Albuquerque volcanoes are spatter and cinder cone systems with minor lava flows. They developed within the Rio Grande rift, a wedge shaped extensional feature in the southwestern United States, in the late Tertiary. Both systems are thus hypothesized to have a similar geochemistry that reflects upon comparable tectonic processes, settings, and time periods of eruption. The Aden volcanic field is a <80 Ka volcanic system in southern New Mexico, situated within the Rio Grande rift, approximately 25 miles north of the Mexican border. The eleven samples collected at the Aden system are from the spatter wall, lava lake feeder vent, and flow features. In thin section, plagioclase composition of An60 occurs alongside olivine crystals without reaction rims in a plagioclase, clinopyroxene, brown glass, and olivine groundmass. Major element geochemistry, determined by X-ray fluorescence (XRF), reveals an SiO2 content of 50-55% and an MgO content of 10-11%. The Aden basalts are classified as alkaline, within-rift basalts on IgPet classification diagrams. In-depth geochemical study, focusing on trace element geochemistry, reveals a close match on spider-type plots with Ocean Island Basalt and internal variation in heavy rare earth element (HREE) contents. Ytterbium divides the Aden basalts into three groups on rare earth element (REE) plots based on location, but there is not enough evidence in other elements or classification diagrams to support differentiation. There are no distinct differentiation or fractionation trends on SiO2 vs. V or Ni vs. Rb diagrams. The unusually high magnesium content and the pattern of spider diagrams suggest the presence of garnet in the source melt retaining these HREEs. Furthermore, the lack of distinguishable trends indicates a relatively short eruption from a single source without time for fractionation. The Albuquerque volcanoes lie eight kilometers to the southwest of Albuquerque, New Mexico, situated near the Albuquerque basin, within the Rio Grande rift. The volcanoes are situated in the center of the Rio Grande rift both from a north to south and east to west perspective. The eight samples collected at the Albuquerque volcanoes are include three from surrounding flows and five samples from the three main volcanoes: JA cone, Black Cone, and Vulcan. Phenocrysts of plagioclase (An69-65) and olivine occur in a grey groundmass. The basalts are classified as subalkaline, and their geochemical data plots most similarly to Enriched Mid Ocean Ridge Basalt (EMORB). Interpreting these data with relation to the geochemistry of the Albuquerque volcanoes, and other volcanic fields in the Rio Grande rift area, suggests that Aden Crater is not representative of central Rio Grande rift geochemistry. The geochemistry of the Albuquerque volcanoes is similar to the Servilleta Basalt and Taos Volcanic field, both within the Rio Grande rift, while the Aden basalts are most similar to the Ocate volcanic field and the Zuni-Bandera volcanic field, both outside the boundaries of the Rio Grande rift. This difference in classification reflects differences in levels of crustal trace elements like Zr, Nb, and K, yet Aden Crater and the Albuquerque volcanoes have a similar overlying crustal thickness. I believe that Aden Crater was sourced from a metasomatized garnet bearing mantle, such metasomatism caused by overlying remnants of the Farallon plate enriching Aden Crater in crustal trace elements not seen in other within-rift basalts.

Note

The author has given permission for this work to be deposited in the Digital Archive of Colorado College.

Colorado College Honor Code upheld.

Includes bibliographical references.

Administrative Notes

The author has given permission for this work to be deposited in the Digital Archive of Colorado College.

Colorado College Honor Code upheld.

Copyright
Copyright restrictions apply.
Publisher
Colorado College
PID
coccc:11233
Digital Origin
born digital
Extent
64 pages : illustrations, map(s)
Thesis
Senior Thesis -- Colorado College
Thesis Advisor
Noblett, Jeff
Department/Program
Geology
Degree Name
Bachelor of Arts
Degree Type
bachelor
Degree Grantor
Colorado College
Date Issued
2015-05