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

Central aims of this project are to delineate and characterize the magma crystallization conditions associated with intra-plate volcanism after collision of the Lavarab Basaltic Lavas (LABL) in East of Iran. Their composition is more basic and includes two principal lithologies: alkali basalt and basanite, and subordinate trachy basalt. The Olivine chemistry indicates forsterite, chrysolite and hyalo-siderite compositions in the study rocks. Clinopyroxene chemistry has been used as the key component of LABL to investigate the nature of magma, tectonic setting, and physicochemical conditions of crystallization (T, P, fO2) in basic-intermediate Lavarab lavas. The clinopyroxenes of these rocks are diopside and augite and belong to peralkaline to subalkaline magmatic series of within plate alkali basalt and volcanic arc basalt settings. Temperature and pressure estimations based on different single clinopyroxene thermobarometers indicate temperatures of ≈1110 to ≈1260 ºC, at pressures of ≈0.05 to ≈1.35 GPa corresponding to pressures equivalent to the depths of ≈2 to ≈51 km for the crystallization of clinopyroxene under the high oxygen fugacity in the lower (>30 Km) to upper (>10 Km) continental crust. Temperature estimations based on olivine-liquid thermometry are calculated temperatures of ≈1380 to ≈1390 ºC for basanites and ≈1299 to ≈1336 ºC for alkali basalts at a constant pressure of 1.4 GPa. The chemical compositions of phenocrysts in the studied basaltic lavas reflect evidence of magma recharge through multi pulses of new magma injected into the existing reservoir prior to eruptions such as petrographic evidence (absorption and rounded-shape and patchy zoned in olivine crystals and sieve texture, absorption, and oscillatory zonation in clinopyroxene crystals) and the oscillatory changes of a crystal's composition from the core to rim in the microprobe data of a crystal.