PETROLOGY AND GEOCHEMISTRY OF THE OLIGOCENE-EARLY MIOCENE PANJGUR FORMATION AND PALEOCENE ISPIKAN FORMATION AND WAKAI MÉLANGE IN THE MAKRAN ACCRETIONARY BELT, SOUTHWEST PAKISTAN

Oligocene-Early Miocene Panjgur Formation, comprised of abyssal plain turbidites, is widely exposed in the vast area of the Makran accretionary wedge in southwest Pakistan. Isolated wedge-shaped slivers of the Ispikan Formation and Wakai mélange also outcrop in the study area. Sandstones of the Panjgur Formation have an average grain composition of Qt₆₅F₁₀L₂₅ and indicate a transitional to quartzose-recycled origin. Sandstones of the Ispikan formation have an average composition of Qt₅₂F₃₃L₁₅ with the source ranging from dissected arc to recycled origin and sandstones of the Wakai mélange have an average grain composition of Qt₁₉F₁₁L₇₀ suggesting an undissected to transitional arc source.

Major and trace element analysis illustrate similar element composition for the Panjgur Formation and sandstones of the Wakai mélange. These sandstones classify as wackes to albitized or Fe-bearing sandstones and fall into the active continental margin field based on the bivariate K₂O/Na₂O-SiO₂ plot. A mafic to ultramafic component is suggested based on high mean abundances of Co (14 ppm), Cr (148 ppm), and Ni (56 ppm). Although the sandstones of the Ispikan formation plot in the same active continental margin field, the Co (5 ppm), Cr (22 ppm), and Ni (3 ppm) mean abundances are much lower suggesting less influence from mafic to ultramafic sources.

Preliminary results suggest that the Panjgur and Ispikan detritus was transported from the Himalayan collisional orogen southward and deposited as a submarine-fan system in the Katawaz Ocean. The Bela-Muslimbagh ophiolites and associated mélanges to the east and the Chaghai-Raskoh volcanic arc to the west shed mafic to ultramafic detritus that is preserved in the Panjgur sediments. Sandstones of the Wakai mélange, rich in mafic volcanic fragments and associated with sheared mafic volcanic rocks, purple colored shales, cherts, marbles, and pelagic limestones, suggest that they were possibly derived from the ophiolitic mélanges obducted during the subduction of the oceanic crust of the Gulf of Oman.