Detrital modes and provenance of the Paleogene Khojak Formation in Pakistan: Implications for early Himalayan orogeny and unroofing

Different tectonic settings have characteristic detrital modes and sediment-dispersal patterns. Detrital modes and sediment-dispersal patterns of the siliciclastic Khojak Formation in the Katawaz basin, Pakistan, suggest that its sand was derived from the early Himalayan orogen and longitudinally transported to the Katawaz remnant ocean, where it was deposited as a delta−submarine-fan complex. Modal analysis of the Khojak Formation suggests composition that is dominated by subangular quartz with abundant lithic fragments and minor feldspar, i.e., Qt 60 F 9 L 31 (Qt, total quartz; F, feldspar; L, lithic fragments). The predominance of quartz, sedimentary, and low-grade metamorphic lithic fragments suggests early derivation from a collision orogen; scarcity of detrital feldspar and volcanic lithic fragments precludes a magmatic arc as the main source. The decrease in monocrystalline quartz, concomitant increase in total lithic percentages, and relative abundance of low-grade metamorphic lithic fragments from the bottom to the top of the Khojak Formation reflect progressive erosional history of the early Himalaya. This history is part of a previously known major unroofing trend collectively depicted by the detrital modes of the Murree Formation, Siwalik Group, and the modern Indus fan in the Indian Ocean. These detrital modes are also related in time and space.