Poster Number 106
Dokhan Volcanics range from basalt to rhyolite (45 to 79% SiO2) and, although typically regarded as andesitic, according to a TAS classification they are 29% rhyolite but only 19% andesite sensu stricto. Wt% SiO2 is mildly bimodally peaked at ~62% and ~74% both regionally and for several individual suites. On an AFM diagram the data plot in a tholeiitic trajectory. Harker diagrams exhibit well-correlated trends with similar negative slopes, displaced in a vertical sense (i.e., at a specified value of SiO2, values of TiO2, MgO, CaO, or P2O5 differ according to local suite). Planes whose axes are SiO2 (felsic index) vs. MgO (mafic index) vs. TiO2, P2O5, FeO*, etc. are fitted to chemical data. Within one standard deviation, best-fit planes accommodate a remarkable 90% of the total range of coordinated variations among SiO2, MgO (>1 wt%), TiO2, P2O5, and FeO*. Dokhan Volcanics are a vast unified chemical system, created from melting and differentiation of a uniform source. Following deep erosion, rocks in various stages of differentiation progress are preserved in local eruptive centers. N-MORB-normalized trace element plots for basaltic samples exhibit negative-slope arrays. According to the Ce/Y indicator, contemporary crustal thickness was ≥40 km.