DECIPHERING THE SPATIO-TEMPORAL EVOLUTION OF OF KIRTHAR FOLD-THRUST BELT AND FORELAND BASIN,WESTERN PAKISTAN

In this study, we investigate the spatiotemporal structural evolution of the Western Indian plate region i.e Kirthar FTB, Foreland and adjoining Pashin Basin, Pakistan. We are using balanced cross-sections, alongside apatite (U- Th-Sm)/He (AHe), and fission track (AFT) age data from 8 samples collected from the Northern-, Central-, Southern Kirthar FTB and Pashin Basin. The preliminary AHe ages for the Oligocene Khojak Formation from the northern part of the Pashin Basin ranges from ~9.8 Ma to ~10.8 Ma with an average of ~10.3 Ma, the AHe are interpreted to be reset after deposition. While AHe ages from the Oligocene Khojak Formation from the southern part of the Pashin Basin shows partial reset ages ranging from ~8.4 Ma to ~23.9 Ma. The AHe ages from the Eocene Ghazij Formation of Northern Kirthar FTB ranges from ~16.4 to ~38.3 Ma that show partial resetting suggesting shallow burial <2-3 km after deposition. In the Central Kirthar, the Paleocene Thar Formation from the western part of the fold and thrust belt displays reset ages ranging from ~7.3 to ~8.7 Ma with an average of ~8 Ma. The Oligocene Nari Formation from the eastern frontal region shows reset AHe ages from ~5.9 to ~8.5 Ma that are similar with previously published AHe around ~6 Ma (Ghani, et al, 2023). In the Southern Kirthar FTB, the Oligocene Nari Formation shows partially reset ages ranging from ~6.5 to ~21.2 Ma and the Miocene Gaj Formation displays non-reset ages ranging from ~17.5 to ~19.3 Ma suggesting a shallow post Oligocene burial in comparison to Northern Kirthar FTB. In the foreland region, the sample data from 04 subsurface wells yielded a total of 22 sample for apatite fission track dating, suggest that south of Jacobabad high, a recent cooling episode of around 5 Ma was recorded while northern kirthar has preserved a cooling event of 20 Ma.

In summary, the preliminary data from the Pashin Basin suggest that the northern part of the basin had experienced deeper paleo-burial compared to the southern part of the basin. In the Kirthar FTB, the Central Kirthar has experienced deeper paleo-burial compared to the Northern and Southern Kirthar FTB, which most likely indicates controls of paleogeography on the basin-filling process.In foreland basin, the region north of Jacobad is supposed to experienced shallow deposition as compared to norther forland basin.