Mexico

I hope to continue exploring questions about the evolution of continental magmatic systems and the origin of continental crust.  My research is field-based research in Mexico, and uses analytical tools such as geochronology, GIS, and geochemistry to address first order questions.  One of the most intriguing ideas that arose from my graduate research is the time-scale over which stratocones develop and erupt.  Detailed 40Ar/39Ar geochronology allows us to date individual cone-building events and suggests that stratocones grow in spurts, with productivity separated by a hiatus of 10,000-100,000 years.  Is this voluminous, episodic stratocone growth unique to the tectonic setting of western Mexico?  What is the cause of the observed hiatus? Are magma chambers beneath stratocones ephemeral or are the magmas slowly undergoing differentiation?  How does the geochemistry of the lavas change over time and what constraints does that place on petrogenetic models? 

Plagioclase hygrometer

The role of water is important in the generation of andesites, the most voluminous lavas at volcanic arcs.  I have developed a new plagioclase hygrometer, a thermodynamically derived, experimentally calibrated model which predicts the water content of the magma based on the composition of plagioclase and the co-existing liquid.  The model has been used to explain the existence of a wide range of plagioclase compositions in crystal-poor melts, through degassing-induced crystallization.  This idea is contrary to the published literature, which typically invokes magma mixing processes for compositional variation.  I would like to apply the plagioclase hygrometer to samples in which water contents have been independently determined by analysis of melt inclusions by FTIR or SIMS.  If the water contents are comparable, petrologists would be able to use the hygrometer and plagioclase compositions as a proxy for water in magmas.

Publications

Frey, H.M., Lange, R.A., Hall, C.M., and Delgado-Granados, H. (2004) Magma eruption rates constrained by 40Ar/39Ar chronology and GIS for the Ceboruco-San Pedro volcanic field, western Mexico: Geological Society of America Bulletin, v. 166, p. 259-276.

deWet, C.B., Frey, H.M., Gaswirth, S.B., Mora, C.L., Rahnis, M., and Bruno, C.R. (2004) Origin of meter-scale submarine cavities and herringbone calcite cement in a Cambrian microbial reef, Ledger Formation (U.S.A.): Journal of Sedimentary Research, v. 74, p. 914-923.

Carmichael, I.S.E., Frey, H.M., Lange, R.A., and Hall, C.M. (2007)The Pleistocene-Holocene cinder cones surrounding Volcan Colima, Mexico re-visited: 40Ar/39Ar ages, cone and lava volumes, oxidation states and sulfur content; Bulletin of Volcanology

Frey, H.M., Lange, R.A., Hall, C.M., and Delgado-Granados, H. (2007) A voluminous ignimbrite flare-up in the Tepic-Zacoalco Rift at 5-3 Ma: possible evidence for an aborted transfer of the Jalisco Block (and Rivera Plate) to the Pacific Plate (submitted to Geological Society of America Bulletin)

Wiebe, R.A., Frey, H.M., and Hawkins, D.P. (2001) Basaltic pillow mounds in the Vinalhaven intrusion, Maine, Journal of Volcanology and Geothermal Research, vol.107, no.1-3, p.171-184.

deWet, C.B., Dickson, J.A.D., Wood, R.A., Gaswirth, S.B., and Frey, H.M. (1999)  A new type of shelf margin deposit; rigid microbial sheets and unconsolidated grainstones riddled with meter-scale cavities.  Sedimentary Geology, vol.128, no.1-2, p.13-21.