Crystallization Conditions of Basaltic Lavas Based on Clinopyroxene and Olivine Phenocryst Petrology: A Case Study from the Neogene Lavarab Alkaline Basaltic Lavas (LABL), Eastern Iran

This paper focuses on delineating and charactering of the magma crystallization conditions of the post-collision Lavarab Alkaline Basaltic Lavas in East Iran. The lavas consist mainly of alkali basalt and basanite, with subordinate trachybasalt. Olivine mostly shows forsterite, chrysolite and hyalo-siderite compositions. Clinopyroxenes are diopside and augite, belonging to peralkaline to subalkaline magmatic series within post-collisional tectonic settings. Estimates of temperature and pressure obtained from single clinopyroxene thermobarometers suggest that crystallization temperatures vary between approximately 1110 and 1260 °C, with pressures ranging from about 0.05 to 1.35 GPa, which correspond to depths of roughly 2 to 51 km at high oxygen fugacity in both the lower and upper continental crust. Olivine-liquid thermometry yields temperatures of ~1385 to ~1393 °C for basanites and ~1275 to ~1339 °C for alkali basalts, assuming a constant pressure of 1.4 GPa. The chemical compositions of phenocrysts in the studied basaltic lavas provide evidence of magma recharge, occurring through multiple pulses of new magma injected into the existing reservoir prior to eruptions. Petrographic evidence, including absorption features, rounded crystal morphologies, patchy zones in olivine, and sieve textures in clinopyroxene, support this interpretation. Additionally, microprobe analyses reveal oscillatory variations in crystal composition from core to rim, confirming the hypothesis of dynamic magma replenishment.