DISTRIBUTION, ORIGIN AND MINERALIZATION OF TWO TYPES OF CENOZOIC ADAKITE AND ADAKITE-LIKE ROCKS IN SOUTHEASTERN ASIA

The Sunda Islands of southeastern Asia is an area where Cenozoic adakite and adakite-like rocks are well developed.These intermediate-acid magmatic rocks are widespread in Guinea Island, Sulawesi (Indonesia), Papua New Guinea, and scattered in Sumatra western Java, Banda island arc and Central Kalimantan.The adakite and adakite-like rocks of the area belong respectively to island-arc tholeiitic /calc-alkaline series and high-potassium calc-alkaline series and are characterized by low HREE contents such as Y and Yb (Y ≤19 ×10^-6 and Yb ≤1.8 ×10^-6 respectively)and high Sr content (> 355 ×10^-6).The spider diagrams show strongly positive anomalies of Ba, K and Sr and relatively negative anomalies of Th and Nb.The adakite and adakite-like rocks show enrichments in large-ion lithophitic element (LILE)and high-field strength elements (HFSE).The adakite and adakite-like rocks of Sunda Islands are tectonically distributed near the Cenozoic sutures, and can be divided into two types of origin.The first one, called oceanic type (O-type)of adakites, belongs to tholeiitic calcalk aline series with REE pattern of oceanic island arcs, and is seen at the oceanic island.The second type, named continental type (C-type)of adakites, belongs to high-potassium calc-alkaline series with REE patterns of continental type, often occurs in continental margin orogenic zone of continental plate and is originally related to arc-continent collision zone or post-collision.Our result reveals that the our research works reveals that the continental-type (C-type)adakite and adakite-like rocks have a similar distribution to the world-class porphyry copper-gold deposits, whereas the oceanic island arc type (Otyp e)adakite and adakite-like rocks are related in origin with epithermal hot-spring gold zones and ehalation ore deposits.