The Mavuradonha Layered Complex: Neoproterozoic ... - ArchiMeD

2 Geology of the study areas 12
2 Geology of the study areas
The Zambezi belt of NE-Zimbabwe contains several large mafic masses that consist
of amphibolite- to granulite-facies metagabbroic rocks (Leitner & Phaup, 1974; Bache et
al., 1983, 1984; Barton et al., 1991, 1993; Carney et al., 1991; Hargrove et al. 1998, 2003;
Mariga et al., 1998). The largest block, with an extent of ~60 km, occurs in the
Mavuradonha Mountain range, where a layered mafic complex is exposed. Another mafic
block is exposed near the township of Dotito, some 20 km to the NE of Mt. Darwin in the
Nyamhanda Inlier. The metagabbros in the Nyamhanda Inlier are exposed in a circular
structure, surrounded by quartzo-feldspathic gneisses. A smaller metagabbro crops out in
the Chimwaya Hill Inlier, which is part of the Mavuradonha Mountain range farther to the
west. The Chimwaya Hill Inlier is located 10 km to the N of the Nyamhanda Inlier. The
geology of the inliers is only briefly summarized, detailed descriptions are given in Leitner
& Phaup (1974) and Bache et al. (1983).
2.1 Geology of the Mavuradonha Mountain range
The Mavuradonha Mts. are bounded to the north by the Zambezi Escarpment and
form WNW trending ridges. The highest peak of 1511 m above sea level rises some 600 m
(in the S) above the surrounding plains and up to 900 m (in the N) higher than the Zambezi
Valley (see cross-section in Appendix I). The most common rock types in the
Mavuradonha Mts. (Fig. 2-1) are garnet-bearing amphibolites and metagabbros.
Metapyroxenites, meta-anorthosites and garnet-bearing metagabbros occur to a minor
extent. The granitoid Ocellar Gneiss crops out at the base of the mountains in the south and
is also exposed west of the Mavuradonha Mission. In the valley west of the Mavuradonha
Mission the gneisses taper off into a band which is ~100 m wide (see Fig. 2-1 and crosssection
in Appendix I).
The formation of steep cliffs in meta-anorthosites and corona-textured
metagabbros, low hills in amphibolites, and plains in the Ocellar Gneiss (Plate 1-1) are
common characteristic features on the southern side of the Mavuradonha Mts. An increase
in metamorphic grade was observed within the mountain range. In the southern part, the
Ocellar Gneiss, the metagabbroic rocks and amphibolites are exposed under mid- to upper
amphibolite-facies conditions, whereas in the northern part of the study area, near the
Zambezi Escarpment, the rocks preserve the assemblage garnet, clinopyroxene and
plagioclase which is interpreted as a granulite-facies assemblage (Bache et al. 1983;
Makanza, 1993; Hargrove et al. 1998, 2003).