Petrology and Geochemical study of Marri area, volcanic facies with Early Cretaceous

Abstract:

     Marri sheet with the scale of 1:100,000, the southeast of 1:250,000 Khartooran rectangular. The area, is a part of Sabzevar structural zone that is located between the Semnan and Khorasan provinces.                   

     Volcanic horizons are observed as interbedded layers in the early cretaceous limestone and shally layers which are indicators of submarine volcanism. The host sedimentary rocks have marine facies and lavas show the pillow structure.                                                                       

     Andesy Basalt and composition of lava in this period of time is spillitic amigdoidal basalt. The microscopic studies of kind of stones, show the intersertal-amigdoidal and porphiritic texture with the intersertal –amigdoidal matrix. The major mineral is the crystals of plagioclase and minors are sphene, lochocksen and the opaqe minerals. The matrix,  contains the intersected microlites of sodic plagioclase. More over, in the microscopic study of the lava, there are some evidences of Albitization of matrix Feldspars in matrix sphene to lochocksen alteration abundance of chlorite, carbonate patches and the opaque ferroxide minerals with calcite patches that are the evidences of spillitization. Appearance of some texture such as skeleton and so on in the plagioclases, are indication of high speed cooling in matrix environment Cretaceous.                              

    Geochemical diagrams introduce the composition range of Alkakine to calcalkaline with the low content of K. The position of sample in the basic element charts has positive trend toward SiO₂ and shows the magmatic differentiation. Neverthless, it seems that considerable increasing of CaO-SiO₂, Na₂O-SiO₂ in transitional samples indicates the Albitization. In the element charts HFS (Zr, Y), LFS (Sr, Rb) toward SiO₂ aggregation of these elements in basaltic smples introduces the magmatic contamination of  these rock by the crust.