MINERALOGICAL AND GEOCHEMICAL COMPOSITION OF THE OLIGOCENE DIZ FORMATION (KHOJAK FORMATION), MAKRAN FLYSCH BELT, PAKISTAN: IMPLICATIONS FOR PROVENANCE AND TECTONIC SETTINGS

The petrography and whole rock geochemistry of medium- to very fine-grained sandstone and mudstone samples (N=35) of Oligocene Diz formation (now part of Khojak Formation) of Makran Flysch Belt, were determined to report, for the first time, the geochemical and mineralogical composition. The point count data of framework grains were plotted in QFL diagrams whereas the geochemical results were compared with NASC, PAAS, GLOSS, Upper Continental Crust and Indus Fan sediments.

Using Dickinson's QFL ternary plots the Diz formation is divided into Upper and Lower Diz. In the QFL plot the Lower Diz samples indicate Basement Uplift (n=7) and Transitional Continental (n=9) provenance, whereas the Upper Diz sediment indicate Transitional Continental (n=12) and Recycled Orogen (n=7) provenance. On the other hand, in the QmFL plots the Lower Diz sediment indicate Dissected Arc (n=9), Basement Uplift (n=4), and Transitional Continental (n=3) provenance whereas the Upper Diz sediments indicate Transitional Continental (n=7), Quartzose Recycled (n=4) Transitional Recycled (n=4) and Craton Interior (n=2) provenance.

Using geochemical parameters (log SiO2/Al2O3 and log Fe2O3/K2O), the Diz sediment are classified as litharenite and Fe-sand. Geochemical results show that K2O is positively correlated with Al2O3(r=0.86) and Rb (r=0.66), Hf with Zr (r=0.999), Nb with Ta (r=.971), Rb with Cs (r=0.951), U with Th (r=0.926), Sr with CaO (r=0.674), and Nb with TiO2 (r=0.514). Little or no correlation exist between other major oxides or trace elements. The average concentration of K2O and Ba in the Diz sediment is considerably less and the average concentration of CaO is slightly more than in Upper Crust, GLOSS, PAAS, NASC, and Indus Fan sediments.

In one of the discriminant function diagrams, the Diz samples plot in the intermediate igneous and felsic igneous provenance, whereas in the other diagram the same samples plot in the quartzose sedimentary and intermediate igneous provenance fields. In the tectonic discrimination diagrams using Al2O3/(CaO+Na2O) vs Fe2O3+MgO, and SiO2 vs K2O/Na2O most of the Diz samples plot in Active Continental Margin. A few samples plot in the Island arc field.