Calculation and inversion of two-dimensional gravity in the vicinity of Lake Tuz, Turkey

An example of gravity inversion and interpretation is presented which demonstrates how a priori information can be used to derive reliable, though complex models. In this case, the geometry of the studied model profile has been constructed on the basis of seismic and geological data. The densities used in the forward calculations were obtained from laboratory measurements of drill cores, from density-velocity relationships, and from Nettleton's method of fitting gravity and topography. In the seismic section 21 'formations' are distinguished leading to a very complex gravity model. What is called 'formations' here, are two-dimensional bodies which are distinguished from each other seismically and perhaps partly by a priori knowledge. Some of the formations have approximately the same densities and could thus be treated as single masses. On the other hand, the same formation may have a complex form and may consist of separate bodies, e.g. as a consequence of faulting; they are still treated as single bodies. Accordingly, the number of bodies of constant density could be reduced to eight. The gravity effect calculated for the model with the initial density assumptions regionally clearly deviated from the observed anomaly. More probable densities were then determined for the formations with inversion calculations in an attempt to optimally fit the calculations to the observations. Always, a better fit could be obtained. In one case about 5 g/cm(3) density was calculated for a single small formation. The proposal is to either investigate whether or not there may exist an ore-body worthwhile for further exploration or to change the seismic section on a limited scale. If the high density is not accepted, compatibility between observed and calculated gravity and plausible densities can be achieved by changing the formation volume (thickness). Other formational densities down to the depth of 32 km have been found to be between 2 and 2.7 g/cm(3). (C) 1999 Elsevier Science Ltd. All rights reserved.