Mineral Chemistry and Whole Rock Isotope Chemistry: an aperture to petrogenesis of the Abbasabad basaltic- andesitic rocks, east of Shahrood

The Abbasabad Eocene volcano-sedimentary belt in the east of Shahrood includes of basaltic-andesitic rocks and related pyroclastics along with interlayers of sedimentary rocks. The volcanic rocks include olivine basalt, trachybasalt, trachy andesybasalt, trachyandesite and andesite with various textures such as hyallomicrolitic porphyry, microlitic porphyry, glomeroporphyry, trachytic and sieve textures. The main minerals of the rocks are clinopyroxene and feldspar. Pyroxene composition ranges from diopside to augite and feldspar composition is in the ranges of orthoclase and oligoclase to bytownite. The 87Sr/86Sr(Initial) and 143Nd/144Nd(Initial) ratios of these rocks, taking into account the age of 40 Ma for them, range from 0.7042 to 0.7047 and 0.5127 to 0.5130 respectively. Also, the values of ԐNd(0) and ԐNd(t=40Ma) of them range between 2.67 to 7.72 and 3.8 to 8.8, respectively, indicate an enriched mantle source for them. Whole rock, isotopic and clinopyroxene chemistry indicate arc-related calc-alkaline-alkaline nature and basaltic composition of the parental magma originated from partial melting of an enriched OIB source in an extensional intra-arc setting. Geothermobarometry calculations on clinopyroxene indicate a temperature range of 1100-1150 Cº and pressures of 2-13 kb for crystallization of the magma.