West Greenland Glass in Picrite – Low-pressure Cotectic Differentiates or Independent Compositions?

The title of Larsen & Pedersen (2009) speaks to the tug that picrites have on the petrological conscience, extant at least since O’Hara (1968), but perhaps even before (Drever & Johnston, 1957), namely that all picrites represent great heat and high temperature. This idea today is rather entrenched. However, Clague et al. (1995) proposed that most picritic basalt from Kilauea volcano and offshore Puna Ridge resulted from mixing between crystal-rich sludges with abundant accumulated olivine and strongly differentiated liquids that had evolved by crystallization of plagioclase, clinopyroxene and olivine along a low-pressure cotectic. The picrites, then, erupted at temperatures of host liquids (glasses), far along a multi-phase liquid line of descent, and Clague et al. (1995) calculated these temperatures using geothermometry. I advocate this mechanism for Baffi n Bay and West Greenland for exactly the same reasons.The disposition of melt and magma chambers was considered by Clague et al. (1995) and it is no different, no less complex a problem, than it is now; any solution to it must be contrived.