Paleomagnetism of rocks from Sumba: tectonic implications since the late Cretaceous

Abstract

The island of Sumba (Southeast Indonesia) is a continental fragment that is situated in the transition zone from the Sunda Arc to the Banda Arc, between the active volcanic inner arc to the north and the locally less well developed outer arc to the south. On Sumba, rock samples for paleomagnetic research have been collected from three formations: (a) the late Cretaceous Lasipu Formation; (b) the Paleocene Massu Formation; (c) the early Miocene Jawila Formation. The sediments of the Lasipu Formation revealed a mean ChRM direction with Declination (D)= 226.8 °, Inclination (1)= 33.5 °, a95 = 7.6 ° with a paleolatitude of 18.3°; the volcanics of the Massu Formation gave a mean ChRM direction with D = 275.6 °, I = 14.6 °, a95 = 9.4 ° with a paleolatitude of 7.4°; the volcanics of the Jawila Formation presented a mean ChRM with D = 357.1 °, I = - 19.3 ° with a paleolatitude of 9.9 °. These paleomagnetic data have been interpreted in terms of an original position of the Sumba fragment in the northern hemisphere in late Cretaceous time. Between the late Cretaceous and Paleocene, Sumba performed a counterclockwise (CCW) rotation of 50 ° and a drift of 11 ° to the south; between the Paleocene and early Miocene the fragment moved a CCW rotation of 85 ° and a drift of 17 ° to the south. Since the early Miocene, Sumba has occupied its present position. The significance of this interpretation for the tectonic evolution of Southeast Asia is discussed.