Evolution of textures, crystal size distributions and growth rates of plagioclase, clinopyroxene and spinel crystallized at variable cooling rates from a mid-ocean ridge basaltic melt

摘要

Mid-ocean ridge basalts (MORBs) are the most abundant eruptive tholeiitic products on Earth. Many experiments have been performed to investigate the solidification of basalts but under limited thermal ranges of cooling (Delta Tc) and cooling rates (Delta T/Delta t). We analyze the experimental charges solidified from previous studies: the BIR1A basalt from USGS was solidified using Delta T/Delta t of 1, 7, 60, 180, 1800 and 9000 degrees C/h, in the Delta Tc between 1300 and 800 degrees C, at atmospheric conditions. The previous studies allowed determining the glass-forming ability (GFA) of sub-alkaline silicate liquids, but do not give information on their textures. Here, we quantify the evolution of sizes, shapes, number of crystals per area (/A), CSDs and growth rates (Gs) of plg (plagioclase), cpx (dinopyroxene) and sp. (spinel). Textures were investigated by image analysis on thousands of crystals and are one of the most complete datasets ever obtained from laboratory studies: they reflect rapid, intermediate and sluggish cooled parts of MORB from liquidus to solidus.