Research Training Program

Douglas Edmonds
St. Louis University
St. Louis, Missouri

Dr. James F. Luhr, Ph.D.
Supervising Scientist
Department of Mineral Sciences

"The chance to do research in one of the nation’s premier institutions is something I can’t get anywhere else. This has been an awesome experience."

Controls on K2O Contents in Three Cross-arc Volcanic Chains of the Mexican Volcanic Belt (MVB)

Research has shown that some subduction-related volcanic arcs demonstrate an increase in potassium (expressed as K2O) content as distance from the trench increases. Geologists have proposed two different mechanisms that may act additively to explain these trends: 1) the degree of partial melting of the mantle decreases as trench distance increases, and 2) crustal contamination of the ascending magma increases with trench distance. Insight into these hypotheses can be gained by studying the Mexican Volcanic Belt (MVB), which is unique among the world’s subduction-related volcanic arcs because it is not parallel to the associated trench; instead, the E-W trend of the MVB forms a 15-degree angle with the N-W-trending Middle America Trench. Crustal thickness increases eastward along the MVB, and over the past several million years the locus of activity in the MVB has migrated southward toward the trench. Accordingly, it should be possible to isolate the contribution of the first mechanism within the MVB by focusing on N-S-trending volcanic chains that have migrated southward over crust of relatively constant thickness. For this project, three such volcanic chains from the MVB were examined by using a chemical database of 444 volcanic rock samples and focusing on variations of K2O contents versus a variety of other parameters. To aid in the research GIS (geographical information system) images of each of the three chains were prepared. The results of this research show that K2O concentrations for each chain decrease significantly from N to S, supporting the role of decreasing partial melting with increased trench distance in the N-S direction but not in the E-W direction, implying that the trend is related to the distance from the trench or partial melting.

This research was supported by a grant from the National Science Foundation Research Experiences for Undergraduates program, Award Number DBI 9820303.

Letter of Gratitude