Petrography and mineral chemistry of zeolite in pillow lavas and diabasic dykes, southwest of Aleshtar (north of Lorestan)

The Pillow lava and diabase dykes of the southwestern region of Aleshtar are host different species of zeolites and secondary minerals. Zeolites are formed by the cavities and veins and decomposed from primary minerals. Based on field studies, X-ray diffraction (XRD) and Electron Microprobe Analysis (EPMA), natrolite zeolites (most abundant zeolites), mesolite, scolecite and analcime have been identified in the pillow lava and diabase dykes in the study area. The average Si/Al ratios for natrolite, mesolite, scolecite and analcim are 1.46, 1.49, 1.62 and 2.29, respectively. These zeolites are formed during two stages of metamorphic hydrothermal fluids, during fractures and in the cavities of host rocks and at temperatures below 250 °C. The investigation of the geochemical properties of zeolites host rocks, shows that their magmatic series is calc-alkaline to tholeiitic and their tectonic environment depends on the mid-ocean ridges (MORB).