The structural evolution of the Qadda area southern Precambrian shield of Saudi Arabia

Abstract EN

The Qadda area in the southern part of the Arabian Shield is composed mainly of metamorphie rocks.

It can he divided into four structural subareas.

1) the Supracustal Syn- form.

2) the Marble Complex.

3) the North West Gneiss Dome, and 4) the North East Gneiss Dome.

Two phases of deformation have effected almost all the rocks exposed throughout these four subareas.

The first phase (/),) is mainly characterised by a strong foliation and line- ation (large-scale tight folding of this age is also recognized in the marble complex subarea).

The second phase (D:) is characterized by doming in the north-western and north-eastern parts, and by large-scale open folding in the areas occupied by rocks of the banded supracrustal sequence.

Some purts of the North-East Gneiss Dome appear to show an older foliation which is refolded by D, and represent the earliest phase of deformation (D(l).

A mechanism for the formation of the domes is suggested.