The south Ardestan region in the Urumieh-Dokhtar arc covers an area of about 250 km2 that is characterized
by plutonic rocks with a compositional spectrum ranging from gabbro, gabbro-norite, gabbroic diorite, diorite,
tonalite to granodiorite. Gabbroic rocks are mainly tholeiitic in character, whereas the diorites, tonalites and
granodiorites show increasingly stronger calc-alkaline affinity. Gradual compositional variation and limited
variation in radiogenic isotopic ratios indicate that these different rock types are petrogenetically related and most
probably are derived from a common primitive source. U-Pb LA-ICP-MS dating of zircon from four granitoids
yielded ages that range from 25 to 24 Ma. For tonalitic rocks, internal Rb-Sr isochron ages (biotite, feldspars)
indicate cooling ages that lie in the range 20.4 +/- 0.1 to 22.1 +/- 0.5 Ma, slightly younger than the zircons’
ages. Their uniform initial Sr-Nd isotopic values imply that the major source component has probably been
an asthenospheric mantle domain. This is further supported by the mantle-derived geochemical affinity of the
plutonic rocks. A geodynamic model is presented in which the asthenospheric upwelling and partial melting in
the south Ardestan has been triggered by Late Oligocene-Miocene rollback of the Neotethyan subducting slab.
These melts were subsequently slightly modified through assimilation, fractional crystallization (AFC) en-route to
the surface (A less than 6%). The trace element rich and high radiogenic Sr signature of some gabbros, this is the
likely perturbation and then mobilization of Sr in the rock system during alteration. 43% fractional crystallization
dominated by plagioclase and orthopyroxene is found responsible for magmatic evolution from gabbro to gabbroic
diorite. Whereas, 44% fractional crystallization of a plagioclase-dominated mineral assemblage that also include
clinopyroxene, titanomagnetite and orthopyroxene is found responsible for the evolutionary path from the gabbroic
diorite to diorite. 22% fractional crystallization of amphibole and plagioclase is calculated as responsible for the
differentiation path from diorite to tonalite. Assuming 6% crustal contamination effect inferred from isotopic
trace elemental modelling by Cadomian crust, the major elemental crustal contamination effect on AFC product is
found to be trivial. That is for K2O it is 10% and for other major elements less than 5%. M-REE abundances of the
tonalites likely imply that a parental melts of these rocks have experienced significant amphibole differentiation
due to a greater depth of magma chamber formation. We do not claim that our petrogenetic model for the south
Ardestan plutonic rocks is representative for the whole UDMA. However, the new isotopic age and bulk rock data
along with the mantle-dominated geochemical characteristics of the studied plutonic rocks open a new window for
geodynamic interpretation and support a model suggesting that subduction still affected the UDMA in Miocene
time
