The importance of cooling regime in the formation of melt inclusions in olivine crystals in haplobasaltic melts

Experiments using synthetic mafic liquids of compsoition Fo(30)Di(30)An(40) and Fo(22)Di(28)An(20) (wt.%) were condUcted to constrain the range of cooling regimes over Which melt inclusions form in Olivine crystals, In one set of experiments, batches of melt were cooled at rates of 1, 7, 10, 50, 100, and 250 degrees C/h from superliquidus temperatures to 1350 or 1300 degrees C, below the liquidus temperature (1450 degrees C) ofboth bulk compositions. In it second set ofexperiments, samples were cooled at rates of 100 degrees C/h and 250 degrees C/h to temperatures of 1300, 1350, or 1400 degrees C, where they were held isothermally for six hours before quenching. Melt inclusions form at cooling rates between 7 degrees C/h and 250 degrees C/h in experiments with no isothermal period More abundant inclusions formed in the second set ofexperiments. with an isothermal period. In some cases, melt inclusions form by the simultaneous growth or oriented agglomeration of neighboring platy crystals. This mechanism is consistent with observations of linear trends of inclusions and re-entrants, its well as the composite appearance of platy crystals and long narrow re-entrants between plates.