and island-arc. Such basalts are spatially re- stricted to the northern sector of the arc where
these three components interact. If the Kaourera oceanic within-plate-type metabasalts result from
a similar process, this might account for the re- stricted volume and sporadicinterleaved nature
of these meta-basalts.
5. Discussion
The lithological variation within the Maunde Ophiolite Group can be equated with similar
lithologies taken to represent an ophiolite, i.e. oceanic-type crust. The geochemistry of the
metabasalts indicates that formation of this crust was within a back arc, marginal basin-type envi-
ronment, while the strong arc-type, geochemical signature suggests that the marginal basin was
relatively immature, i.e. was characterised by ju- venile spreading and rifting. The associated is-
land-arc
the Kaourera
Island Arc
Group comprises a range of silica-variable extrusive vol-
canics and contains both arc-type and oceanic within-plate-type meta-basalts. The presence of
all three ophiolite, island-arc and within-plate suites leads to a regional scenario involving
ocean – ocean collision, oceanic subduction, the formation of an island-arc and the initiation of
juvenile back-arc basin spreading Fig. 13. The location of the Ophiolite Terrane between the
Zimbabwe and Congo cratons indicates that these two cratons were at some point in time
separated by an ocean of unknown size but un- doubtedly large enough to develop within-plate
seamounts and induce ocean – ocean collision and subduction. The age of final collision and amal-
gamation
of the
Zimbabwe Kalahari
and Congo Cratons is unknown and is the subject of
much debate Dalziel, 1992; Hanson et al., 1994; Rogers 1996; Unrug, 1997; Weil et al., 1998;
Johnson, 1999, 2000; Kampunzu et al., 1999; Vinyu et al., 1999. Thus, the presence of an
island-arcmarginal basin complex between these two cratons has direct implications for the re-
gional palaeogeographical interpretation at this time and the constraint in the timing of the colli-
sion between these two cratons. Oliver et al. 1998 has obtained a SHRIMP
age for magmatic zircons from a plagiogranite dyke within the Maunde Ophiolite Group of
1393 9 22 Ma, i.e. Kibaran, and have interpreted this to be the age of the ophiolite. Although the
Kaourera Arc is part of the same tectonic frame- work it is not necessarily of the same age, since
when one considers the longevity of the present- day, Circum-Pacific region, the age of an ob-
ductedsubducted ophiolitic fragment need not be the same age as the arc.
Because of its structural and metamorphic complexity, little is known about the southern
portion of the Mesoproterozoic Kibaran Belt of south-eastern and eastern Zambia mapped sim-
ply as ‘Re-mobilised Basement’, see Fig. 1. It is unclear as to whether this region represents Pan
African
aged, tectonised,
Archaean cratonic
basement or whether there is also a Kibaran- aged
crustaltectono-metamorphic component.
The presence and age of the ophiolite indicate that not only does this region contain a Kibaran-
aged crustal component, that this region was subject to crustal growth via arc-accretion. The
two cratons Zimbabwe and Congo must have been separated by oceanic crust at this time. The
age of amalgamation between the cratons can only be constrained to be post 1393 Ma and that
the sedimentary and tectono-metamorphic devel- opment of both cratonic margins cannot be re-
lated
at this
time. The
southern limit
of Kibaran-aged crust must now be drawn at the
position of the present day Chewore Inliers, i.e. the northern margin of the Zimbabwe Craton
and not at the southern margin of the Irumide Belt, which until present has been used by some
authors, Hanson et al., 1994; Shackleton, 1996; Munyanyiwa et al., 1997; Wilson et al., 1997;
Kampunzu et al., 1999 because it aligns neatly with the Choma-Kalomo Block, see Fig. 1 to
infer that the Zambezi Belt cannot be interconti- nental. This line of evidence must now be laid to
rest. The presence of both Kibaran-aged pro- toliths and Kibaran-aged tectono-metamorphism
in the remainder of the Chewore Inlier terranes is confirmed by Johnson 2000 and Goscombe et
al. 1998 and preliminarily from other portions of the belt by John et al. 1999.
Fig. 13. Cartoon style cross sections illustrating the interpreted tectonic relationship between the Ophiolite Terrane groups at ca. 1393 9 22 Ma top and the present day, post Pan African arrangement bottom.
6. Conclusions
