Sains Malaysiana 52(2)(2023): 417-430

http://doi.org/10.17576/jsm-2023-5202-08

Structural Analysis of Kirthar Fold Belt, Lower Indus Basin, Balochistan, Pakistan; Implications from Compression and Inversion Tectonics

(Analisis Struktur Jalur Lipatan Kirthar, Lembangan Indus Awal, Balochistan, Pakistan; Implikasi daripada Tektonik Mampatan dan Penyongsangan)

ADNAN KHALID¹,*, SAJJAD AHMAD¹, ASGHAR ALI¹, GOHAR REHMAN¹ & MUHAMMAD YASEEN²

¹Department of Geology, University of Peshawar, 25120, Peshawar Pakistan

²Department of Geology, Abdul Wali Khan University Mardan, 23200, Pakistan

Diserahkan: 1 Jun 2022/Diterima: 21 November 2022

Abstract

The current research work mainly focuses on tectonic evolution of the Central Kirthar Fold Belt. It also deals with the structural impact of the Late Cretaceous/Paleocene, Indian-Eurasian collision on the Central Kirthar Fold Belt which is situated in the western shear zone of Indian Plate. The Kirthar Fold Belt is different from the rest of western shear zone because it is mainly deformed by compressional tectonics which has created wide anticlines, narrow synclines and overturned folds as shown by geological mapping. It has been observed that thin-skinned deformation has played a major role in structural disharmony which is mainly seen in the Early Eocene Ghazij and Oligocene Nari formations. Seismic data shows thick-skinned deformation because the faults seem to penetrate deeper stratigraphic levels. Involvement of the basal decollement and the penetration of the interpreted faults to the level of basement rocks is also evident from the exposure of Jurassic/Cretaceous rocks at surface on the western part of the mapped area. Cross sections data shows that Kirthar Thrust Fault has a structural throw around 3-4 km in the Kirthar Folded Zone featuring deformational front while the seismic data and well data shows that this intensity decreases in the Kirthar Foredeep Zone towards east where the structural throw is about 2-3 km. Restoration of cross sections show an overall 17.3% shortening which shows that the area is under influence of compressional stresses.

Keywords: Inversion; Kirthar Fold Belt; thick-skinned deformation; thin-skinned deformation; thrust kinematics

Abstrak

Penyelidikan ini tertumpu terutamanya pada evolusi tektonik Jalur Lipatan Kirthar Tengah. Ia juga berkaitan dengan kesan struktur perlanggaran Akhir Kapur/Paleosen, India-Eurasia pada Jalur Lipatan Kirthar Tengah yang terletak di zon ricih barat Plat India. Jalur Lipatan Kirthar berbeza daripada zon ricih barat yang lain kerana ia dicangga terutamanya oleh tektonik mampatan yang telah mencipta antiklin lebar, sinklin sempit dan lipatan terbalik seperti yang ditunjukkan oleh pemetaan geologi. Telah diperhatikan bahawa canggaan kulit nipis telah memainkan peranan utama dalam ketidakharmonian struktur terutamanya yang dilihat dalam pembentukan Ghazij Eosen Awal dan Nari Oligosen. Data seismik menunjukkan canggaan kulit tebal kerana sesar kelihatan menembusi tahap stratigrafi yang lebih dalam. Penglibatan dekolemen basal dan penembusan sesar yang ditafsirkan ke tahap batuan bawah tanah juga jelas daripada pendedahan batuan usia Jura/Kapur pada permukaan di bahagian barat kawasan yang dipetakan. Data keratan rentas menunjukkan bahawa sesar sungkup Kirthar mempunyai lontaran struktur sekitar 3-4 km di Zon Lipatan Kirthar yang menunjukkan canggaan hadapan manakala data seismik dan data telaga menunjukkan bahawa keamatan ini berkurangan di Zon Lembangan Depan Kirthar ke arah timur dengan lontaran struktur adalah kira-kira 2-3 km. Pemulihan keratan rentas menunjukkan keseluruhan 17.3% pemendekan yang menunjukkan bahawa kawasan itu berada di bawah pengaruh tegasan mampatan.

Kata kunci: Canggaan kulit nipis; canggaan kulit tebal; jalur lipatan Kirthar; kinematik tujahan;  penyongsangan

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^*Pengarang untuk surat-menyurat; email: adnan.khalid@uop.edu.pk