Pre-Paleocene Kohistan–Karakoram Amalgamation: Evidence from the Detrital Zircon Provenance of the Baraul Banda Formation, Pakistan

The Baraul Banda Formation preserves an important Paleocene–Eocene sedimentary record within the western Kohistan–Ladakh Arc (KLA) and provides new constraints on sediment provenance and tectonic evolution during the final stages of Neo-Tethyan closure. This study integrates stratigraphic observations, detrital zircon U-Pb geochronology, and quantitative provenance analyses to investigate sediment sources and basin development within the western India–Eurasia collision zone. The formation comprises a thick marine siliciclastic succession of conglomerate, sandstone, siltstone, mudstone, and slate deposited in a tectonically active forearc basin. Detrital zircon age spectra are dominated by Mesozoic–Cenozoic populations (48%) with major peaks at ~57–61 Ma, ~70 Ma, ~85–90 Ma, and ~114–115 Ma, accompanied by subordinate Neoproterozoic, Mesoproterozoic, Paleoproterozoic, and minor Archean populations. These age components closely resemble those of the KLA, Karakoram Block, and Lhasa Block. Statistical provenance analyses indicate the strongest affinity with Eurasian arc-related terranes and contemporaneous forearc basin deposits of the Tar and Indus groups, whereas affinity with Indian Plate sources is minor. The provenance record indicates that sediment supply was dominated by erosion of the KLA and the adjacent Karakoram–Lhasa continental margin, with only minor recycled contributions from Indian-derived sources. The youngest zircon populations constrain deposition to the Paleocene–Early Eocene and record rapid erosion of active arc terranes immediately prior to the India–KLA collision. Placed within the regional magmatic chronology, these results support initiation of the KLA by ca. 155 Ma, Late Cretaceous amalgamation with the Karakoram–Lhasa margin at ca. 80–70 Ma, and subsequent collision with India at ca. 60–55 Ma. The KLA therefore remained an active pre-India-collision arc system for approximately 95–100 Myr, whereas collision-related magmatism continued until ca. 40 Ma, extending its complete magmatic history to approximately 115 Myr.