The plate-tectonic evolution of a region can be deduced by following the assumptions that (1) subduction zones are characterized by ophiolite, melange, wildflysch, and blueschist; (2) intermediate and silicic calc-alkaline igneous rocks form above Benioff zones; and (3) truncations of orogenic belts indicate rifting. Interrelations provide cross checks, as do marine geophysical data.

Southeast Asia and "Sundaland" are an aggregate of small continental fragments. Late Paleozoic subduction westward beneath Malaya and Thailand (recorded by granites in eastern Malaya, and by melanges in western Laos and Cambodia) ended when Indochina collided with them. Early and Middle Triassic subduction was eastward, beneath the west side of the aggregate. Late Triassic and Jurassic subduction from the north ended in collision of the aggregate with China. Early Cretaceous subduction was also from the west. Late Cretaceous subduction was beneath the east side of the aggregate and followed continental rifting there. Cenozoic subduction, from the west once more, ended in the north when the aggregate collided with India, but subduction still continues in the south. Borneo similarly ref ects changing subduction patterns.

The Philippines, Sulawesi, and Halmahera consist wholly of upper Mesozoic(?) and Cenozoic island-arc subduction and magmatic complexes and lack old continental foundations. The scrambled fragments of the Philippines came from several arc systems, including 2 extending to Borneo. Sulawesi and Halmahera record primarily subduction from the east and may be rifted and contorted fragments initially continuous with southeast Borneo and central Java.

In the early Tertiary, Australia and New Guinea, which then had a stable-shelf northern margin, moved northward until they collided with a southward-migrating island arc, behind which had formed the Caroline oceanic plate. Late Cenozoic tectonics in New Guinea have been dominated by southward subduction of the Caroline oceanic plate beneath the Australian-New Guinea continent, and by left-lateral strike-slip faulting. Such faulting tore the Sula Islands from northwest New Guinea and carried them to Sulawesi.

The islands of the outer Banda arc are formed of melanges of the shallow-water sediments of the New Guinea and Australian continental shelf, which is now disappearing beneath the active arc.

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