The Mavuradonha Layered Complex: Neoproterozoic ... - ArchiMeD

2 Geology of the study areas 16
medium-grained and also contain garnet. A common feature is the occurrence of these
leucocratic layers as schlieren. Pegmatites and quartz veins are folded and sheared in the
Ocellar Gneiss.
Intrusive relationships between the granitoid gneisses and the mafic complex have
not been observed. The Ocellar Gneiss and the mafic rocks display the same penetrative
foliation, and the granitoid gneisses and the mafic complex have parallel tectonic contacts
to each other. Field evidence points to thrusting of the mafic complex onto the Ocellar
Gneiss (Bache et al., 1983; Barton et al., 1991; Hargrove et al., 1998). Tectonic movement
of the layered complex to the south is recorded by shear-sense indicators in the
metagabbros (pyroxenes as σ–clasts and s-c fabrics). Shear-sense indicators in the Ocellar
Gneiss show mainly top-to-the-North movement (Plate 1-6). This opposite direction of
movement is probably the result of intense folding after overthrusting that has affected the
gneiss after the development of its foliation, lineation and the shear sense indicators. The
nappe contact is marked by a depression and an increase in deformation within the Ocellar
Gneiss towards the mafic complex. The occurrence of mylonitic rocks at the contact
between the Ocellar Gneiss and amphibolites give further evidence for a tectonic contact
between the two units.
Pegmatites, calc-silicates and marbles are found in the Mavuradonha Layered
Complex as well as in the Ocellar Gneiss. Massive quartzites are restricted to the Ocellar
Gneiss on its southern side near the base of the Mavuradonha Layered Complex. Marbles
and calc-silicates are found only north of the main ridges and occur as lenticular bodies. In
one of the marbles next to the Zambezi Escarpment, fragments of the surrounding host
rocks are found. Pegmatites occur as medium to coarse-grained dykes with varying width.
Commonly these pegmatites are perpendicular to the foliation of the host rocks or crosscut
the foliation or layering of their country rock. One pegmatite sampled in the north of the
Mavuradonha Mountains (sample ZZB 60 in Fig. 2-1) intruded during the last tectonothermal
event. This pegmatite is strongly sheared, and the foliation developed in the
metagabbros is dragged into the crosscutting pegmatite (plate 1-8). The pegmatite is
interpreted as syntectonic-synmetamorphic with respect to the last major tectono-thermal
event.
The observed layering in the Mavuradonha Layered Complex is inclined to the N
with a predominant dip of 40°. The granulites and amphibolites, as well as the Ocellar
Gneiss, show a marked foliation with a NE strike and a dip between 40° to 60° (Fig. 2-1).
This foliation can most likely be correlated with a first deformation event in these rocks. In
addition to the foliation, a lineation is developed. A hornblende mineral lineation in the
case of the amphibolites dips around 40° to the NE. The lineation in the Ocellar Gneiss
dips 10° to 30° N to NW (Fig. 2-1). Recumbent and isoclinal folds mark a second