to the Shan-Thai. The seamount limestones were interpreted by some authors, based on pure limestone quality and stratigraphy overlying oceanic basalt. However, this interpretation is still controversial. Evidences from Lower Devonian black shale bearing graptolite, north of Chiang Mai, overlain conformably by radiolarian chert not only indicate its Early Devonian rifted age from the Gondwana, but also argue against as fragment of the Indochina and the South China. Occurrence of Devonian to Triassic radiolarian cherts were regarded as major Paleotethys ocean. Shan-Thai terrane Lower Paleozoic sequences of the Shan-Thai terrane (also called Sibumasu) commence with Upper Cambrian shallow marine siliciclastics with Trilobite, cropped out only at Tarutao island, whereas on the mainland consists mainly of quartzite. They were conformably overlain by Ordovician shallow marine carbonates, changing upward to Silurian-Devonian deep marine fine-grained sediments with graptolite and tentaculite, and Lower Carboniferous shallow marine sediments containing Posidonomya sp. There was a hiatus during Late Carboniferous in the Shan-Thai terrane. Lower Permian diamictite was taken as evidence for rifted age away from the Gondwana. It changes upward to Middle to Upper Permian epieric carbonate platform. Fauna are rich in brachiopods and bryozoans, but low diversity. Coral is mainly tabulata and solitary; Sinopora sp. with rare compound rugosa. Fusulinid genera, are of low diversity, occurring locally such as Pseudofusulina sp., Yangchienia sp, Eopolydiexodina sp, Polydiexodina sp. Shanita sp. Faunal evidences indicated that during Middle Permian, the Shan-Thai terrane moved northward to a warm-temperate area between Gondwana and Cathaysia. During Late Permian, it still remained at a distance from the Indochina terrane. In some places, carbonate continued to Triassic. Magmatism Granites in Thailand were lineated in 3 major belts with ages seem younging to the west: the Eastern belt consists mainly of I-type Triassic granite; the central belt consists of S-type Triassic granite, and the Western belt consists of I- and S-type Cretaceous granites. Devonian basalt in Loei- Phetchabun- Phai Sali vocanic belt is interpreted as MORB and arc related volcanics (Panjasawatwong et al., 2006). Nan-Uttraradit and Sa Kaeo sutures contained Permian ocean basalts of the Ocean Plate Stratigraphy, while Triassic Lampang volcanic of the Chiang Khong-Tak volcanic belt belonged to subduction related volcanics (Bunopas, 1981; Barr et al., 2000). Permian MORB and ocean island basalt are interpreted from Chiang Rai-Chiang Mai volcanic belt
(Phajuy et al., 2005).
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