Four granite provinces have been delineated each with its own distinctive pattern of mineralization. 1. The Main Range Province. Endogenous greisen-bordered vein swarms of cassiterite and wolframite. 2. The Eastern Province. Magnetite–cassiterite skarns ± base metal sulphides with antimony in Thailand. 3. The Western (Peninsular Thailand–Burma) Province. Endogenous greisen-bordered vein swarms and pegmatites of cassiterite and wolframite. 4. The North Thailand Migmatitic Province. Endogenous vein and skarn replacement scheelite and fluorite deposits with some tin and local antimony. In all provinces, but particularly in the Main Range, granitoids designated as two-phase variants have been recognized where xenocrysts and xenoliths of coarse, primary texture granite are enclosed in, and corroded by an invasive, equigranular quartzo–feldspathic matrix. These rocks form an essential part of the granite sequence in all provinces and have probably resulted from the infiltration and disruption of the host granite by late stage magmatic fluids. Whole rock geochemistry from Peninsular Malaysia shows that the granites from the Main Range and Eastern Provinces comprise two contrasted suites which correspond approximately to the I and S-type categories advocated by Chappell & White (1974). In addition it is shown that individual plutons within batholiths in the two provinces have distinctive geochemical parameters. Variation diagrams of plutons having the intrusive sequence primary texture granite—two-phase granite—microgranite show linear trends with increasing SiO 2 , Na 2 O, Rb, W, Sn and U, and decreasing Sr, Ba, Th and all other major elements.

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The Recent volcanic islands of the Red Sea are (1) Jebel at Tair, a single small volcano of tholeiitic basalt lava; (2) the Zubair Islands with pyroclastic cones and flows intermediate between tholeiite and alkali basalt and with picrite basalt and trachybasalt blocks in the agglomerates; (3) the Hanish-Zukur Islands with alkali basalts accompanied by trachybasalts, trachyandesites and trachytes together with pyroclastic rocks. The chemistry of 46 lava specimens indicates that a gradational series exists between the sea-floor basalts (K-poor tholeiites) and the alkali basalts of Hanish-Zukur, with the rocks of Jebel at Tair and Zubair representing intermediate stages. Two alternative petrogenetic models are discussed to account for this gradational behaviour. One derives the parental magma from successively greater depths, the other considers derivation by successively greater fractionation on route to the surface. The relationship of the volcanoes to the opening of the Red Sea is discussed. Possibly, eruptive activity was initiated at the southern end and is migrating northwards in response to the anticlockwise rotation of Arabia relative to Africa. The Red Sea axial trough may die out southwards owing to vocanic fill from the Hanish-Zukur volcanoes.

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The general geology of the New Hebrides is summarized in terms of three volcanic and two main sedimentary episodes. Calc-alkaline volcanics ol the first episode occur on the western islands and accumulated mainly on the submarine slopes below small reef-fringed volcanic islands in Late Oligocene to Middle Miocene times. During the Late Miocene and Early Pliocene wholly submarine tholeiitic or high-Al volcanics accumulated in the eastern and southern part of the New Hebrides while calcareous sediments were forming in the western islands. During the third volcanic phase, of Pliocene to Recent age, regional uplift has led to most of the volcanics being subaerial while extensive flights of limestone terraces occur round the older islands. In consequence the land area of the New Hebrides has increased rapidly during Quaternary times. The landforms produced are briefly described.