Using Numerical Modeling for Estimation of Rate of Nucleation and Growth Time of Plagioclase Microlites from Quaternary Gandom Beriyan Basaltic Flows, NE of Kerman

Gandom Beriyan, as a part of Quaternary volcanism of Iran, is a kind of messa which is covered by very dark lava flows. The flows are generally fresh to rarely altered alkali olivine basalts and cover an area around 480 km2 in southern part of the Lut desert in northeast of Kerman. The common textures of basaltic lava flows are porphyry to glomeroporphyry with an intersertal to intergranular groundmass. Their major minerals are olivine and clinopyroxene phenocrysts along with plagioclase microlites. Plagioclase microlites are recognized as the major silicate phase in these rocks. Three-dimensional shape of plagioclase crystals and also rate of nucleation and growth time was estimated by thin section image processing and using crystal size distribution (CSD) method. Based on this, it is revealed that the shape of plagioclase microlites is tablet with aspect ratio of 1:10:10 for short: intermediate: long axes, respectively. The uniformity of CSD graph and its constant slope show that the effect of physical processes such as magma mixing was limited during ascent of basaltic magma toward the surface. Based on these calculations, growth time (t) and rate of nucleation (J) were estimated 2.53 to 3.21 years and 10.17×10-9 to 9.53×10-9 mm-3/s-1, respectively. The results are completely matched with nature of alkali basalt magmas.