Chemical composition of minerals and genesis of maficmicrogranular enclaves in intermediate - acidic plutonicrocks from Kuh -e- Zar area (southeast of Semnan)

The Kub-e- Zar area is located about 75 Km in southeast of
Semnan. Electron microprobe analyses of plagioclases of mafic
microgranular enclaves and plutonic host rocks from Kuh-e-Zar area display
that they have normal, oscillatory and reverse zoning, so that plagioclase
cores of reverse zoning in enclaves have oligoclase and andesine
compositions and their rims have andesine and laboradorite compositions,
respectively. Investigation of biotite compositions in host rocks show that in
the host granodiorite rocks, there are two types of biotites. The first type has
high Ti02 (mean 4.8%), Alz03 mean 12.84%), MgO (meanI5.38%) and low
Si02 (36.89%), which are similar to mafic microgranular enclaves (mean
Ti02 4.67%, Alz03 13.03%, MgO 15.19% and Si02 37.23%). the second
type is depleted in Ti02 (mean 0.04%) and MgO (mean 0.02%) and enriched
in Al20 3 (mean 18.09%) and Si02 (mean 64.5%). Contents of these elements
in the biotites of host monzodiorite rocks are similar to enclaves. Chemical
compositions of pyroxenes in enclaves are similar in compositions to those
of host rocks. These features, in addition to the patterns and aboundances of
trace elements in enclaves, the presence of inclusions of fine grain biotite
and hornblende in feldspares, synplutonic dykes, the nature of the
plagioclase zoning and etc. display magma mixing and mingling origin for
generation of these enclaves.