Michigan Technological University and the University of Wisconsin-Madison have initiated a collaborative research project to test the hypothesis that the lava flows exposed in the crater wall of Santa Maria Volcano record a geomagnetic excursion known as the Mono Lake Event and that this event is global in extent. The Mono Lake is one of many proposed short-lived periods of geomagnetic instability that riddle Earth's geomagnetic field within longer intervals of constant normal or reversed polarity. Some of these short-lived instabilities affect the geomagnetic field globally whereas others are more local in extent. In either case, these periods of instability or excursions of the geomagnetic field are generally expressed in the rock record by paleomagnetic directions whose variation is outside the normal bounds of secular variation to the point of being almost fully reversed. Excursions which are global and have been dated precisely are important stratigraphic markers and are critical to understanding geodynamo processes. To date, there remains considerable debate as to whether the Mono Lake excursion is a global event as previous studies either are from sediments where dating is problematic and directional data not as reliable as from volcanic rocks or are from studies on volcanic rocks which either lack precise radioisotopic ages, or are based on incomplete paleomagnetic data. Therefore, the objective of this research is to fully characterize the geomagnetic variations (and therefore the Mono Lake Event) recorded by the lava flows exposed in the crater wall of Santa Maria Volcano using paleomagnetic techniques and to precisely determine age of the geomagnetic event using the 40Ar/39Ar incremental heating method. If the 40Ar/39Ar ages bear out the hypothesis that the Santa Maria lava flows record the Mono Lake event, then there is unequivocal evidence that this geomagnetic excursion is global in extent. An addition, well-defined 40Ar/39Ar ages for the lava flows at Santa Maria will place important boundary conditions on the volcanic flux for the latter stages of growth of the Santa Maria's cone.
As for broader aspects of this research, Michigan Tech has worked closely with Guatemalan volcanologists at monitoring and hazards agencies (INSIVUMEH and CONRED) for more than 35 years, developing a synergistic relationship where the University has provided access to advanced laboratory and research applications and these volcanologists supply strong field context for obtaining relevant samples. In recent years, several Central American volcanologists have obtained degrees at Michigan Tech. This research will continue that tradition bringing a Guatemalan volcanologist to the United States to study both in the paleomagnetism laboratory at Michigan Tech and to participate in the dating of the Santa Maria lava flows at the University of Wisconsin-Madison. After completing his MS degree, this volcanologist will return to Guatemala where he is expected to provide leadership in important volcanic hazards work for decades.
