## 7 Discussion
### Implications for Exhunation  
Up-section, the deposition of the Kirthar group and Chitarwatta Formation occurred during the Eocene-Oligocene, in a marine environment [5], which later changed to a continental environment during the Miocene-Pliocene Siwalik's deposition [57]. The Oligocene Chitarwatta Formation has a major increase in input of detrital grains from the younger source (<120 Ma) of KLA and KB of the Eurasian plate. This indicates increased erosion from the collided block. The collision in the SFB has been reported in earlier studies to be at \(\sim\)50 Ma [26], based on the integrated isotopic and detrital zircon U-Pb studies. The earlier sediments, including the Ghazij Formation are considered to have a pre-collisional detrital source, while the post-collisional detritus has been reported to be from the Kirthar and Chitarwatta formations [26,56]. Our data also indicate a similar post collisional provenance for the Chitarwatta Formation (Figure 7A,B). This provenance explains the exhunation of the Himalayan litho-tectonic terranes in response to the continuous India-Asia collision. Initially, following the collision, the foreland basin developed in the footwall of the Indus suture zone. This foreland basin received detritus from the KB, KLA, and ophiolitic sources. This detritus was deposited in the form of the Ghazij, Subathu, and Amile formations [26,58]. As the collision continued, the fold-thrust belt propagated southward, and another fault (MCT), south of the Indus suture zone, was activated, which caused uplifting of the Higher Himalayan block (Figure 7B). With this uplifting, the central part of the Himalaya attained a higher elevation, causing the development of the two major drainage systems that feed the foreland basin to the west and east. These drainage systems are the Indus drainage system and the Bengal drainage system. The Indus drainage system delivered the detritus from the uplifted Higher Himalayan block to the western part of the foreland basin, in the form of deposition of the Chitarwatta Formation and its coeval units (Murree Formation, Dagshai Formation, and Dumre Formation) (Figure 7B). Similarly, the Barail Formation received detritus through the Bengal drainage system, which shows strongly similar detritus [55]. The coeval Dumre Formation detrital age spectrum shows its deposition in the distal part of the basin, which is comparatively far from the major drainage system. Following the model of [PERSON], et al. [59], the India-Eurasia collision occurred in the central segment that uplifted the central part earlier than the west and east. The Indian margin gradually closed towards the west and east, with the development of the Indus drainage system in the west and Bengal drainage system towards the east. The detrital record suggests that the Higher Himalaya were exhumed during the Oligocene-Miocene, and provided the Higher Himalayan detritus to the Chitarwatta Formation through the Indus drainage system. The strong similarity of the detrital record with the coeval Barail Formation (eastern Himalaya) suggests a similar source, which is delivered through the Bengal drainage system, developed to the east during the Oligocene-Miocene time.