Restite Separation and Normal Magmatic Reaction inthe Kashmar granitoid, a typical example of low temperature I-type granites

Category Petrology
Group GSI.IR
Location 20th symposium on geosciences
Holding Date 16 April 2008

     The Kashmar granitoid is the largest plutonic mass occurring in northeastern Central iran. it is cropped out between the two major faults, Doruneh Fault to the south and Rivash Fault to the north, defining the boundaries of the Taknar Zone. it has intruded into andesitic lavas and pvroclastic rocks of Focene age. it comprises several plutons of tonalite, granodiorite, granite and alkali feldspar granite. The first isotopic data (Rh/Sr) on hiotite-whole rock pairs show an age of 43.5 0.4 to 42.4 0.4 Ma for the Kashmar granitoid. Using microscopic and microprobe data, different minerals of the Kashmar granitoid exhibit characteristics of those minerals occurring in metaluminous (ASI<1) i-type granites that formed under low-temperature and high fo2 Similarity in initial87Sr/86Sr (70471-0.70569) and negative values of end(- 0.70 to — 1.86) with a limited range in different samples indicate a homogenous source rock, undergone at least one cycle of fractionation and originated from lower crust or perhaps infracrustal depths. Due to similarity in geochemical and isotopic features, these plutons can be assigned as a simple suite. This simple suite is high in Al2O2, Na2O, K2O, FeO and low in CaO, MnO,P2O5, TiO2 and MgO contents. The composition of inicrogranular enclaves is similar to the composition of the host rocks. This together with linear variations on Harker plots indicate that fractionation and restite separation (unmtlted residual source materials) are two major processes for controlling the variation in
the chemical composition of the Kashmar granitoid. Using tectonic discrimination diagrams. this granitoid and other plutonic rocks of the north Doruneh Fault magmatic arc, plot in the areas of magmas originated in subduction-related zones of continental margins.