Major deformation events

Caledonian (Silurian) Deformation

The Basement is strongly folded and pelitic rocks have a well-developed axial planar cleavage. Isoclinal folds with east-striking axial planes overturned to the north have been described (e.g. Kotov and Poritskaya, 1992). Such isoclinal folding is interpreted to have occurred prior to deposition of Cover Sequence 1, which exhibits open folds with vertical axial planes. The east-west trending fold visible west of Muruntau (Fig. 3) is believed to be of Caledonian age.

Metamorphic grade of the Basement did not exceed greenschist facies over much of the region. Rb - Sr dating of metamorphic micas has yielded a Caledonian (Early Devonian) cooling age of 401 ± 11 million years (Kostitsyn, 1996). This age is consistent with the unmetamorphosed nature of unconformable Cover Sequence 1.

Hercynian (Late Carboniferous) Deformation

There is evidence of a deformation event during the Hercynian (late Carboniferous) in this region. North of Muruntau, Devonian and Carboniferous carbonate rocks are thrust over the top of the older basement rocks ( Fig. 3; Drew et al., 1996). The age of this thrusting is therefore Carboniferous or younger. Drew et al., (1996) consider that the contact between the Besopan 3 and 4 is marked by a Carboniferous shear zone, the Sangruntau-Tamdytau shear zone.

A thrusting event at this time helps to explain the change at the top of the Carboniferous (in the Karatau range) from shallow marine to terrestrial. T h e widespread intrusion of granitic intrusions also occurred at this time, possibly in response to crustal thickening by thrusting.

Permo-Triassic Deformation

Alexeiev et al., (1997) have documented a major Permo-Triassic deformation event in the Karatau Range, north of Muruntau (Fig. 1). This event is synchronous with the major unconformity between Cover Sequences 1 and 2. The main manifestation of this event is the giant Karatau Fault (Fig. 1) which has right-lateral displacement of 150 km and related steeply-plunging Z-shaped folds (Alexeiev et al., 1997). A parallel structure occurs about 50 km south of Muruntau (Fig. 1). Outcrops of the basement and Cover Sequence 1 throughout the region are elongate in the direction of strike-slip faulting (i.e. NW) as are the principal magnetic trends.

A second set of faults trends NE and ENE (Fig. 3). A fault of this orientation, the Muruntau-Daugyztau fault, is spatially and probably temporally associated with mineralisation at Muruntau (Fig. 3). The age of this and parallel structures is clearly Carboniferous or later.

Figure 3 shows NE-trending anticlinal and synclinal axes paralleling, and probably related to, major strike-slip faults. These folds are open with a wavelength of approximately 1 km and the axes plunge shallowly north-eastwards. Much of the gold at Muruntau is located within the axial zone of the syncline.