Petrology and provenance of the Neogene fluvial succession in Pishin Belt (Katawaz Basin) western Pakistan: implications for sedimentation in peripheral forelands basins

摘要

Sandstones and conglomerates of the Neogene fluvial succession in Pishin Belt (Katawaz Basin), Pakistan were studied for the first time to understand the composition, provenance and tectonic settings of the source areas. Sandstones of the Miocene Dasht Murgha Group and Pliocene Malthanai Formation are classified as lithic arenites. Modal composition of the Dasht Murgha Group (Qt(61)F(11)L(28)) suggests that sandstone is dominated by quartz with abundant lithic fragments and minor proportions of feldspar. The Malthanai Formation (Qt(60)F(4)L(36)) is comparatively rich in lithic fragments and poor in feldspar. QtFL and QmFLt diagrams show recycled and transitional recycled orogenic source for both the successions. The Dasht Murgha Group is rich in sedimentary and metamorphic lithics and poor in volcanic fragments (Lm(35)Lv(18)Ls(47)). The LmLvLs plot indicate that most of the samples lie in the fields of suture belts and mixed magmatic arc and subduction complexes. Samples of the Malthanai Formation are overwhelmingly rich in sedimentary fragments (Lm(14)Lv(10)Ls(76)), which indicate widespread availability of sedimentary rocks during the Malthanai times. Composition of conglomerates of the Dasht Murgha Group, Malthanai Formation and Pleistocene Bostan formation reveal that the Eocene Nisai Formation and Oligocene Khojak Formation, within the Pishin Belt, were the main source terrains while the Muslim Bagh-Zhob Ophiolite and the Cretaceous and Jurassic succession of the Indian Plate were subordinate source terrains. Sandstone and conglomerate clasts of the Dasht Murgha Group within conglomerate of the Malthanai Formation indicate that the newly uplifted Dasht Murgha Group became an additional source terrain for the Malthanai Formation. Sandstone and conglomerate clasts of the Dasht Murgha Group and Malthanai Formation in conglomerate of the Bostan formation indicate that the Dasht Murgha Group and Malthanai Formation became an additional source terrain as both had been uplifted at the time of deposition of Bostan Formation.