Peninsular Malaysia consists of three terranes, a western Gondwanan affinity terrane (Sibumasu), an eastern Cathaysian affinity terrane (Indochina/East Malaya) and an accretionary complex terrane (the Palaeo-Tethyan Bentong-Raub suture zone) which contains fault-bounded blocks and clasts of radiolarian-bearing chert and argillite. ... The representation of the Palaeo-Tethyan suture zone of Peninsular Malaysia as a narrow zone (13 - 18 km wide) is not favoured in this study. The Gondwanan affinity Sibumasu terrane is narrower than presently defined and includes only passive margin continental sequences. All radiolarian-bearing chert and argillite, belts of mélange and imbricate thrust slices of marine sedimentary rocks characteristic of accretionary complexes are not part of the Sibumasu or Indochina/East Malaya terranes, but are of Palaeo-Tethyan origin, and form a distinct accretionary complex terrane which has been thrust westwards over the eastwards-dipping Sibumasu terrane. The Bentong-Raub suture zone of Peninsular Malaysia, the Uttaradit-Nan/Sra Kaeo suture zone of Thailand and the Changning-Menglian suture zone of South China have yielded radiolarian faunas of similar biostratigraphic ages, ranging from Upper Devonian (Famennian), through Middle Triassic (Ladinian). These ages suggest that the Palaeo-Tethys ocean existed between the Sibumasu and Indochina terranes from at least Late Devonian through to Middle Triassic (Ladinian) time. Results of this thesis support tectonic models that propose Late Silurian - Early Devonian rifting of continental fragments from the Gondwanan margin, Devonian opening of the Palaeo-Tethys, and subsequent closure of the ocean in Peninsular Malaysia and Southeast Asia during the Late Triassic.