PALEOMAGNETIC EVIDENCE FOR ROTATION AND NORTHWARD DRIFT OF SUMATRA

The rocks sampled include ?Permian, Upper Triassic, Lower Cretaceous, and Lower Tertiary, with rocks at 2 sites being of uncertain age, probably Mesozoic. A total of 137 orientated samples was collected at 25 sites from 13 localities in N and central Sumatra. 2 Loer Teriary sites (Geunteut & Breueh Island) yield magnetic directions of D = 8, I = 11 and D = 34, I = 3 respectively, equivalent to apparent palaeomagnetic poles at 82oN 183oE, and 56o 190oE. An Upper Triassic site gives D = 220, I = 26, equivalent to a pole at 49oN 210oE, assuming, as seems likely, that the field was reversed. These results indicate a probable northward drift of 12o since the late Triassic, accompanied by a clockwise rotation of 40o. -Author