PALEOMAGNETISM OF THE BALANTAK OPHIOLITE, SULAWESI

Palaeomagnetic data from the East Arm of Sulawesi provide constraints on the Cretaceous and subsequent history of a fragment of the tectonic mosaic of a complex region close to the junction between SE Asia, the Indo-Australian plate and the western Pacific microplates. Primary th ermoremanence has been demonstrated in samples from 23 sites in a tilt ed Cretaceous-Palaeogene lava sequence in the Balantak ophiolite at Ba tusimpang on the eastern tip of the East Arm of Sulawesi. Its directio n (D = 60.5-degrees, I = - 32.1-degrees, alpha95 = 5.5-degrees) indica tes formation at 17 +/- 4-degrees-S and - 60-degrees of subsequent clo ckwise rotation. The primary mode of remanence is deduced from NRM/TRM comparisons; low-temperature cycling and other rock magnetic tests po int to SD magnetite as the principal remanence carrier. Supporting evi dence for the palaeolatitude and northward movement of the East Arm is derived from other lavas at Binsil, and from the Boba Cherts, but lac k of tectonic control limits the interpretation. The contrast between these results and the subequatorial origin of contemporary rocks on ne arly Halmahera is consistent with subduction of Indian Ocean lithosphe re beneath the Sunda margin in the late Mesozoic and early Tertiary. L arge differences in declination of remanence in the E Sulawesi rocks i ndicate large clockwise and anticlockwise rotations of tectonic blocks only tens of kilometres across.