Geochemical and petrological reconstruction of the Talle-Pahlevani mafic-ultramafic intrusions Shahre-Babak, Iran

The Talle-Pahlevani mafic-ultramafic intrusions located in northwest and south of leuco-quartz dioritic and anorthositic batholiths developed in the southwestern Sanandaj-Sirjan zone (173 Ma). These intrusions consist primarily of gabbro in association with veins and lenses of anorthosite, trectolite, clinopyroxenite, and wehrlite which show gradual and sometimes sharp boundaries with the gabbro. In the gradual boundaries, the gabbro are mineralogically transformed into anorthosites and wehrlites. On the other hand, in the sharp boundaries, the mineral assemblages in two sides are different. There is no clear deformation in the Talle-Pahlevani mafic-ultramafic intrusions. Hence, the changes in mineral compositions are the result of crystallization processes in the magma chamber. The chemical changes, especially for REE, from anorthosite and wehrlite veins and lenses toward gabbro in the gradual boundaries are continuous. The changes are presumably resulted from different crystallization processes in the different parts of the intrusions that cause crystallization of anorthosite, clinopyroxenite, and wehrlite cumulates in the intrusions. Rocks of the sharp boundaries show sudden chemical changes, but the changes exhibit the same patterns of increasing and decreasing of the elements, especially for REE. Therefore, it is possible that all parts of the intrusions were formed from the same parental magma. Parts with unequilibrium crystallization in the form of cumulus and sub-solidification, underwent fractures, and were interspersed throughout the magma chamber due to late injection pulses or mechanical movements. The geological and age data show that the intrusions generated from an Al2O3, Sr-, and FeO-enriched and K- and Nb-depleted tholeiitic basaltic magma likely partial melting 5-30 wt. % of the spinel-peridotite mantle within an incipient rift system. Then, the magma was crystallized in lower crust (relatively high P.) magma chamber.