Paleomagnetism of younger volcanics from Western Timor, Indonesia

Abstract

Paleomagnetic research has been carried out on volcanic rocks from two formations exposed in Western Timor, Indonesia: i.e., the Metan Formation of Eocene age, and the Manamas Formation of Late Miocene age. Because of the chaotic tectonic setting of the rocks at the Metan Formation it was the inclination data from five lavas only that could be interpreted in the final analysis of the characteristic remanence directions (ChRM) with I = 33.6°, a 95 = 4.1°. The Metan volcanics most probably extruded originally in the northern hemisphere at a latitude of about 17°. The volcanics may have extruded on a crustal unit which includes a continental fragment that became detached from Gondwana in Mesozoic times and subsequently shifted to the southeast Asian continent. This crustal unit broke away from southeast Asia in Eocene times, moved towards the south and collided 3 Ma ago with the frontal part of the Australian continental margin. The Manamas Formation of Late Miocene age includes obducted volcanics consisting of both deep-sea pillow lavas and island arc volcanics with ChRM directions of D = 132.6°, I = 15.8°, no a 95, because 2 sites only, and D = 295.9°, I = −26.3°, a 95 = 2.8°, respectively. The declinations of the ChRM directions, derived from the rocks from two localities, show counterclockwise deviations of approximately 45 and 60°, respectively, relative to the present earth's field direction. The deviating directions can be explained in terms of a counterclockwise rotation of Timor which may have begun as early as 3 Ma ago, and which could be a result of the obliquely northward protruding Australian continent, where the originally west-east directed Banda Arc rotated in a counterclockwise sense. It is also possible that during the obduction the lava piles performed counterclockwise rotations. Rock magnetic analyses show that magnetite or/and titanomagnetite is the main carrier of remanence.