Bulletin of the Geological Society of Malaysia, Volume 17, Dec.1984, pp. 79-95
Jabatan Geologi, Universiti Malaya, Kuala Lumpur
Abstract: A regional metamorphic terrane has been mapped in west Kedah covering an area not less than 650 sq. km. The metamorphics in this terrane are called the Patani Metamorphics. The terrane trends NW-SE and is about or more than 30 km wide. At the southeast side the regional metamorphic effects appear to peter out at Lunas-Padang Serai but the northwestern end is truncated by the coast. It is possible that similar metamorphics in southeastern Langkawi group of islands and at Gunung Utan Aji, Perlis may be extensions of the mapped terrane in west Kedah.
The terrane is mostly underlain by slates and phyllites with assemblages such as muscovite+quartz+chlorite±paragonite±pyrophyllite±chloritoid. Higher grade rocks centre around the Jerai granite area developing biotite in pelitic schists and quartzites rocks and calcsilicate minerals such as hornblende, diopside, garnet and epidote in calcareous and amphibolitic rocks. The Jerai granite is believed to superimpose contact metamorphism on the regional metamorphics.
The regional metamorphism is believed to come to an end by Middle Carboniferous followed by the late or post-tectonic emplacement of the Jerai granite in the late or late Middle Carboniferous. The onset of regional metamorphism is believed to be early Devonian or earlier with a probable deformation phase in the Middle or late Devonian.