Dwayne Beattie

B. Sc. Honours Thesis

Gravity Modeling of a Mafic-Ultramafic Association Darvel Bay, Sabah, Northern Borneo.

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The association of Pre-Tertiary mafic and ultramafic rocks exposed at Darvel Bay, East Sabah, is believed to form an ophiolite suite. These outcrops are believed to provide evidence for a Middle Tertiary island arc-continent collision zone, which forms an apparently continuous arcuate line from southeastern to northwestern Sabah.

This area was the site of a gravity survey conducted by Dr. P. J. C. Ryall in 1977. The results of the survey are summarized in a Bouguer contour map of the area, which shows a positive gravity anomaly of 70 mgal associated with the out-croping mafic and ultramafic rocks.

Structural features in the area are dominated by broad open folds and extensive faulting. Structural and gravity data have been combined to produce computer aided two dimensional models of the subsurface structure.

Models produced indicate subsurface geometry consistent with post emplacement tectonic activity, rather than over thrusting associated with a Middle Tertiary emplacement.

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Pages: 57
Supervisor: Patrick J. C. Ryall