The evolution of Sumba Island (Indonesia) revisited in the light of new data on the geochronology and geochemistry of the magmatic rocks

The island of Sumba, presently located in the southern row of islands of th e Eastern Nusa Tenggara province of Eastern Indonesia, has a unique positio n, being part of the Sunda-Banda magmatic are and subduction system. It rep resents a continental crustal fragment located at the boundary between the Sunda oceanic subduction system and the Australian arc-continent collision system, separating the Savu Basin from the Lombok Basin. New data on magmat ic rocks collected From Sumba are presented in this paper, including bulk r ock major and trace element chemistry, petrography and whole rock and miner al K-40-Ar-40 ages. Three distinct calc-alkaline magmatic episodes have been recorded during Cr etaceous-Paleogene: all of them characterized by similar rock assemblages ( i.e, pyroclastic rocks, basaltic-andesitic lava flows and granodioritic int rusions). They are: (i) the Santonian-Campanian episode (86-77 hla) represe nted by volcanic and plutonic rock exposures in the Masu Complex in Eastern Sumba: (ii) the Maastrichtian-Thanetian episode (71-56 Ma) represented by the volcanic and plutonic units of Sendikari Bay, Tengairi Bay and the Tana daro Complex in Central Sumba; and (iii) the Lutetian-Rupelian episode (42- 31 Ma) of which the products are exposed at Lamboya and Jawila in the weste rn part of Sumba. No Neogene magmatic activity has been recorded. (C) 2000 Elsevier Science Ltd. All rights reserved.