Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son-Mae Sariang area, north-west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean-floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana-Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion.

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Petrochemical characteristics of Permo-Triassic granitoids from five regions (i) Mung Loei, (ii) Phu Thap Fah -Phu Thep, (iii) Phetchabun, (iv) Nakon Sawan -Lobburi, and (v) Rayong -Chantaburi along the Loei Fold Belt (LFB), northeastern Thailand were studied. The LFB is a north-south trending 800 km fold belt that hosts several gold and base-metal deposits. The granitoids consist of monzogranite, granodiorite, monzodiorite, tonalite, quartz-syenite, and quartz-rich granitoids. These are composed of quartz, plagioclase, and K-feldspar with mafic minerals such as hornblende and biotite. Accessory minerals, such as titanite, zircon, magnetite, ilmenite, apatite, garnet, rutile, and allanite are also present. Magnetic susceptibilities in the SI unit of granitoids vary from 6.5 × 10 −3 to 15.2 × 10 −3 in Muang Loei, from 0.

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