شواهد بافتي -كاني شناسي حاكي از وقوع اختلاط ماگمايي در گدازه هاي تراكي آندزيتي پاليوژن منطقه آبترش ، غرب قزوين

Textural and mineralogical evidences of magma mixing in the trachyandesitic lava flows in the Ab-e-Torsh district, Western Qazvin, Iran

Trachyandesitic rocks in the Ab-e-Torsh region, western Qazvin, have considerable thickness and extensive outcrops (>200 Km2) that form parts of the Alborz Paleogene volcanic belt. These rocks that can be correlated with the upper member of the Karaj formation, are subaerial eruptions with lava flows and some lava domes. Geochemically, these are classified as shoshonitic series. Occurrence of some textural evidences (e.g., reaction rims, sieve textures and oscillatory zoning in feldspars and augites phenocrysts) and coexistence of inequilibriurn plagioclase phonocrysts (An5.20, An36-61, An77-93), as well as compositional differences between phenocrysts and their surrounded mesostasis, all suggest that the magmatic evolutionary processes could have been occurred in an open system. On the other hand, existence of some alterations such as opacitization in phlogopitic biotites and paragasitic hornblende might be related to the late stages of the magmatic evolution with high fO2 and PHZO. Considering textural and mineralogical observations, as well as dispersion of the whole rock geochemical data, one may conclude that the magmatic evolution have been occurred by periodic refreshment of alkaline and basic magma by a more acidic intrusion.