Abstract

A high temperature spreading centre has been subducted beneath Sumatra. As a result, a normally cool area has been made warmer. This raises the exploration potential of the area. The evolution of the Indian ocean has resulted in variations in crustal thickness, created by the thickening away from spreading centres. These variations affect the thermal regimes of the Sunda Craton as these spreading centres collided with the craton. Between the Ninety East Ridge and the Investigator Fracture Zone is a palaeo-spreading centre, known as the Wharton Ridge, which separates the Sino-Burmalayasian plate from the Australian plate. This spreading centre collided with the Sumatran subduction zone and created a ridge/trench triple junction. California offers a well documented analogy, where the ridge separating the Farallon Plate and the Pacific Plate collided with the North American Plate.

Another example can be seen in the Gulf of Alaska with the subduction of the spreading centre separating the Kula Plate and the Pacific Plate. The Californian collision is documented by Tanya Atwater. Using the results of her work and applying this concept to the Sumatran collision, the thermal history of Western Sumatra can be reconstructed.

The collision of the Sunda Craton and the West Sumatran Spreading Centre results in various parts of the trench having thinner crust. This causes certain locations to be hotter than others. Outer arc basins are usually considered to be non-prospective due to their low thermal gradients caused by the extra thickness of crust. This extra thickness is created by a combination of the subducting oceanic plate and the over-riding continental plate. The areas where the spreading centre collides with the trench will only be slightly greater than one plate thick and are warmer, therefore increasing the petroleum potential.