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CONTENTS

The term of basement was long, and still is, viewed as a complex of mostly crystalline metamorphic rocks, which underlies a sedimentary basin. The simplistic preoccupation towards the basement was usually perceived them as pre-Tertiary rocks originated in continental environment. The advents of plate tectonics and recent progresses obtained through studies of metamorphic rocks in the country have gradually eliminated such a misleading presumption. The Indonesian archipelago is broadly formed by two continental masses – each corresponds to the amalgamated Eurasian plate in the west and Australian plate in the east, respectively – and the intervening Tertiary collision zone in the middle. Rapid uplift in this Tertiary collision zone has facilitated adequate studies during the last two decades, whereas other investigation in other parts of the continental masses were mostly hindered by extensive coverage of Cenozoic sedimentary and volcanic rocks and logistical problems as well. Three major types of orogenies in Indonesia may be recognized. The Sunda type, representing the narrow and well-defined Late Mesozoic Cordilleran-type Meratus –Karangsambung orogen along the rim of the southeastern Sundaland and the Neogene orogeny stretching across Sumatra, Java and Nusatenggara. Suspected collision of microcontinent occurred in the Meratus-Karangsambung orogen. The Makassar type, which spatially outboards the Meratus-Karangsambung orogen, constitutes Oligocene and Miocene orogenis as a result of consecutive subduction obduction events of the East Arm of Sulawesi and the docking of Australian-derived microcontinents onto Sulawesi The Banda type, which is characterized by repeated pre-collisional obductions of short-lived spreading ridges in front of the Australian passive margins, took place in Oligocene and Miocene, respectively. Understanding the Indonesian orogeny from the perspective of basement geology has not arrived its mature stage, although significant contributions have been documented. With regard to the whole earth tectonics paradigm, further studies, particularly dedicated on the ophiolite emplacement- metamorphism relation, deserve further attention.