Gravity modelling of extensional basins in Southeast Asia

702001-101015-812-B
Author : Steven H. Harder, Steven J. Mauri & Susan Marshall-Arrazola
Publication : Bulletin of the Geological Society of Malaysia
Page : 153-162
Volume Number : 33
DOI : https://doi.org/10.7186/bgsm33199312

Bulletin of the Geological Society of Malaysia, Volume 33, Nov. 1993, pp. 153-162

 

Gravity modelling of extensional basins in Southeast Asia

STEVEN H. HARDER1, STEVEN J. MAURI2 AND SUSAN MARSHALL-ARRAZOLA3

1Dept. of Geophysics and Geodynamics Research Institute, Texas A&M University College Station, TX 77843, USA

2Dept. of Geophysics, Texas A&M University, College Station, TX 77843, USA

3Exxon, P.O. Box 4279, Houston, TX 77210, USA

 

Abstract: Comparison of free-air gravity over sedimentary basins in Southeast Asia with sediment accumulations in the basins indicates no correlation between gravity and sediment thickness. This is due to differences in crustal structure under basins in extensional versus convergent regimes. In convergent regimes, thickened crust creates negative gravity anomalies. In extensional regimes, the crust is thinned creating both positive and negative gravity anomalies. We examine the problem of gravity modelling in extensional regimes, using the Malay basin as an example. We find:

1.         while gravity modelling is a non-unique process, the use of a priori knowledge (i.e., prior information derived from other sources) in gravity models greatly reduces the range of possible models. In the Malay basin, a priori knowledge indicates the basin should have a -100 mGal anomaly. However, only a -20 mGal anomaly is seen over the basin. This suggests there is a high density intrusion at the base of the crust, producing an offsetting positive anomaly.

2.         the gravity field is only a minor constraint in gravity modelling over extensional basins. This is due to the almost complete cancellation of the positive anomaly associated with the high density intrusion at the base of the crust and the negative anomaly associated with the sedimentary basin in the upper crust.

3.         gravity modelling can produce useful geologic information if deep crustal structure is accounted for before attempting to model shallow crustal features. This can best be accomplished with the use of a priori knowledge in the modelling process. 

https://doi.org/10.7186/bgsm33199312