Bulletin of the Geological Society of Malaysia, Volume 69, May 2020, pp. 135 – 147

The Ukay Perdana Shear Zone in Kuala Lumpur: A crustal-scale marker of early Jurassic orogenic deformation in Peninsular Malaysia

A. Graham Leslie^1,*, Marcus R. Dobbs², Ng Tham Fatt³, Qalam A’zad Rosle⁴, Muhammad Ramzanee Mohd Noh⁴, Thomas J.H. Dodd¹, Martin R. Gillespie¹
¹ British Geological Survey, the Lyell Centre, Research Avenue South, Edinburgh, EH14 4AP, UK
2 British Geological Survey, Environmental Science Centre, Keyworth, Nottingham, NG12 5GG, UK
3 Department of Geology, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
4 Dept. of Mineral & Geoscience Malaysia, Selangor & W. Persekutuan, 6th & 7th Floor,
Bangunan Darul Ehsan, No.3, Jln. Indah, Section 14, 40000 Shah Alam, Selangor D.E., Malaysia
* Corresponding author email address: agle@bgs.ac.uk

Abstract: A ‘top-to-the-east’ ultramylonite zone is identified in north-eastern Kuala Lumpur and named here as the ‘Ukay Perdana Shear Zone (UPSZ). The UPSZ is at least 250–300 m thick, east-verging, and superimposed on the later stages of assembly of the c. 200 Ma S-type ‘Western Belt’ granite plutons generated by crustal thickening and assigned to the Main Range Granite Province. Younger bodies of S-type granitic rocks cut the shear zone. These intensely deformed quartzofeldspathic rocks contain distinctive relict porphyroclasts of perthitic K-feldspar (microcline), oligoclase and quartz, entrained within the ultramylonitic fabric. Migrating sub-grain boundaries in quartz indicate deformation occurred under moderate to high temperature conditions during ductile deformation (c. 500–600°C); undulose extinction suggests down-temperature evolution of the deformation history. This deformation event implies that the final stages of collisional interaction between Sibumasu and the Sukhothai Arc would have involved now east-directed (080°N, then generally northward) over-thrusting of the leading edge of Sibumasu onto the Sukhothai Arc/Indochina-East Malaya margin after
198 ±2 Ma. Kenny Hill Formation strata in Kuala Lumpur preserve widespread evidence of a dominant phase of E- or ENE-verging, upward-facing fabrics and folds; that deformation is judged to be a hanging wall response to deformation in the UPSZ. This early-Mesozoic structural framework is significant during assembly of the Peninsular Malaysia region of Sundaland; evidence form Kuala Lumpur is combined with new published Singapore data. Dextral strike-slip tectonics is superimposed on this collisional framework in the later Mesozoic and Cenozoic; subsurface development across Peninsular Malaysia, and in Kuala Lumpur and Singapore in particular, should account for deformation structures linked with this expanded record of Mesozoic tectonics.

Keywords: Ultramylonite, E-verging, granite protolith, Main Range Province, Kenny Hill Formation, Sibumasu, Sukhothai Arc, urban geology

DOI: https://doi.org/10.7186/bgsm69202012