Combination of geochemical- statistical- petrological and crystal size distribution (CSD) as a new confidence in determination of magmatic processes in Kodegan Area (South Khorasan)

Eocene volcanic and plutonic rocks exposed in the 90 km south of Khusf, south Khorasan Province. The texture of these rocks is porphyritic, glomeroporphyritic, seriate and poikilitic. Plagioclase, Alkali feldspar, quartz, pyroxene and hornblende are abundant mineral in these rocks. Plagioclase crystals show sieve texture and zoning. These rocks are calc-alkaline to tholeiiti. They characterized by enrichment of LREE and LILE, depletion of HREE and HFSE. Negative anomalies of Ti, Nb, P, Zr, and positive anomalies of Pb, K, U reflect emplacement of volcanic rocks in an active continental margin. In order to investigation of magma crystallization, crystal size distribution (CSD) technique also used for 10 andesite and basalt rock samples. Increasing of plagioclase crystal size in a semi-logarithmic plot which demonstrate population density versus size, represents fractional crystallization. Concavity of the CSD diagrams resulting from combination of two populations of crystals, that one of them formed during slow cooling and the other formed during a period of pressure reduction and rapid cooling. Additionally, chemical features such as variation trends of Nb/Y vs. Nb and MgO vs. Fe2O3 and two different trends of volcanic and plutonic samples in Harker and dendrogram diagram, regarded as an indicator of magma mixing processes.