Dr. Frank Ramos offers "Insights from Radium Isotopes"

  • Jan 26, 2019

EES welcomes Dr. Frank Ramos, New Mexico State University, as out Distinguished Speaker this week.

"Dating Young Volcanic Rocks at Changbaishan Volcano:  Insights from Radium Isotopes"

Radium isotope dating is becoming more popular for constraining the crystallization and residence ages of young crystals in volcanic rocks erupted in the recent past (<8000 years).  Plagioclase and potassium feldspar are usually targeted where resulting ages are highly dependent on radium partition coefficients derived from experimental or theoretical methods.  It is very difficult to obtain direct empirical measurements for feldspars because the most accurate estimates originate from rare, zero-aged volcanic crystals (free of melt inclusions or other materials that might retain Ra) with minimal or no residence prior to eruption.  We determine Ra and Ba partition coefficients and calculate ages for potassium feldspars from extremely young, alkali-rich trachytes where the melt component (represented by crystal-free pumice) is subtracted from the whole rock  (melt plus crystals) to obtain average DRa and DBa values of “bulk” feldspar.  We also isolate rim and core portions of potassium feldspars to determine crystal ages using theoretically determined DRa derived from measured crystal DCa, DBa, and DSr and compare theoretical values to experimentally determined values. Partition coefficients and ages are variable with empirical results derived from mass balance determinations offering minimum DRa and DBa for all theoretical and experimental determinations for Or42 sanidine (and resulting ages).  We review results and uncertainties regarding calculated ages (and other geochronological constraints) and their implications for crystallization and residence ages of ~Or42 sanidine in Changbaishan trachytes or other young volcanic systems.

Join us for more on Friday, February 2, 2019 at 12:30 PM in Room 204, Natural Science Buidling on the East Lansing Campus.