Methodology
Electron microprobe mineral analyses
Composition of plagioclase, amphibole and biotite phenocrysts in volcanic rocks were analyzed by wavelength dispersive spectrometry, using a Cameca SX50 electron microprobe (EMPA) at the University of Oklahoma, Norman (USA). Probe conditions were 20 kV accelerating voltage, 20 ηA beam current, a spot size of 3 μm, and measurement times of 30 s per peak for all elements. Analyses were calibrated against appreciate standards before each session. Minimum level of detection (at 3-sigma above mean background) of </= 0.20 wt% of the oxide for all components exept Ba (0.09 wt% BaO), F (0.10 wt%) and Sr (0.03 wt% SrO).
The data for amphibole was then recalculated for Fe+3 using Droop’s (1987) equation. Amphibole, biotite and plagioclase are analyzed as part of this study. Representative analyses are given in Table 1.
Whole rock geochemistry
Samples for geochemical analysis were prepared by crushing in an agat disk mill. Half gram sample leached with 3 milliliter HCl-HNO3-H2O at 95 °C for one hour, diluted to ten milliliter and then analysed by Inductively Coupled Plasma Mass Spectrometer (ICP-MS) for major and trace elements at the ACME analytical laboratories (Vancouver, Canada). Replicate analysis of International Standards indicate accuracy to within 5-10 relative percent of standard values for major and minor elements.
