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2.4.4 Eastern Central Africa
rocks and its overlying Cryogenian sequences (Poidevin
1985
;
Toteu et al.
2001
,
2006
,and
2014
, in preparation). Farther
south scarce Archean dates mark the diffuse tectonic transition
between the northern margin of the Archean Bouca and
Mboumou Cratons and the allochthonous southern margin of
the Oubanguides (Cahen et al.
1984
;Poidevin
1985
;Toteu
et al.
2014
, in preparation). Apart from its western extension in
Cameroon (e.g. Nkoumbou et al.
2013
), this tectonic transition
has not been studied with modern structural and radiometric
analysis in the central section of the belt.
In Cameroon and western CAR, the Oubanguides com-
prise both Eburnian and Pan-African thrust sheets with high
grade allochthons of Archean (e.g. 3072 Ma), Eburnian
(2372 Ma) and Pan-African juvenile volcanogenic rocks
(1100-625 Ma; Nkoumbou et al.
2013
; Toteu et al.
2006
;
Toteu et al.
2014
, in preparation; de Wit et al.
2014
under
review) emplaced across a ~3 km thick Neoproterozoic
platform sequences known as the Lindian Supergroup
(Lepersonne
1974
; Poidevin
1985
). Pan-African tectonism
has been dated, for example at Akwa at 756
Along the eastern margin of the CB, the 300 km wide, NNE-
trending Kibaran Belt (s.s.) separates the Tanzanian Craton
from the CS (Figs.
2.2
,
2.3
and
2.5
), and is tectonically
overlain to the south by the late Neoproterozoic (Pan
African) Lufilian-Damara Belts.
2.4.4.1 The Tanzanian Craton (TC)
The Tanzanian Craton (
3.8-2.6 Ga) comprises a complex
amalgamation of Archean blocks (seven super-terranes and
twelve or so terranes as defined by Kabette et al.
2012a
)in
which Neoarchean granitic gneisses and a number of classic
greenstone belts predominate; but Mesoarchean dates have
also been sporadically reported (Borg and Shackleton, 1997;
Kabette et al.
2012a
,
b
; Kasanzu
2014
).
In the northern section of the Tanzanian Craton (TC),
volcanics of the Nyanzian and Kavirodian Supergroups
have been dated, for example at Homolo (2808
>
3 Ma)
and at Geita (2699
9 Ma; U-Pb zircon dates; Borg and
Krogh
1999
; Fig.
2.5
), and near Mpampa at 2742
40 Ma, at
Boukouma at 708
11 Ma (Rb/Sr whole-rock dates, in
Poidevin
1985
), near Sidut at 639
27 Ma
(Sm/Nd whole-rock date; Manya and Maboko
2008
). These
dates represent a significant episode of volcanism within the
TC that clearly differs from that of all Congolese Cratons.
In the central TC, Meso- to Paleoarchean TTG gneisses
have been reported (Kabette et al.
2012a
), and basement to
juvenile greenstone rocks in the Central Tanzania Region
includes orthogneisses with enclaves of
3 Ma (U-Pb zircon
dates, in Rolin
1995
) and in southwestern Cameroon
between 640-600 Ma (Nkoumbou et al.
2013
). This is
comparable with gabbros (c. Lomie) dated at 666
26 Ma
in the western part of the belt, and slightly younger
monzodiorites in western Cameroon (c. West of Bafia)
dated at 619
4 Ma (U-Pb zircon dates, Toteu et al.
2006
). More recent dates from western and central CAR
includes extensive granite activity between 640-660 Ma,
with magmas derived from melting of Kibaran crust
(1020 Ma), as well as Archean granitoids with Neoprotero-
zoic overprints; and ca. 800 Ma metasediments with meta-
morphic overprints at ca. 650 Ma (LA-ICP-MS; K. Drost
and M. de Wit, unpublished; Toteu et al.
2014
in prepa-
ration). In general, the Pan-African dates of this northern
region of central Africa seems to represent orogenic events
that apparently young westward across this vast and
understudied belt; but this is poorly constrained.
The deformed Lindian Supergroup comprises carbonate
metasediments (the Ituri and Lokoma Groups) including
dolomites with spectacular stromatolites (Plate 5; Robert
1946
). This sequence is dated at 730-755 Ma (Rb/Sr dates,
Poidevin
2007
) and includes a tillite (the Akwokwo Tillite)
that may represents either the Sturtian or Marinoan glaci-
ation. These sequences are overlain by about 1,500 m thick
red quartzites, schists, and arkoses (the Galamboge, Alolo,
and Banalia Formations) of the late Neoproterozoic-lower
Paleozoic Aruwimi Group (Lepersonne
1974
). Based on
lithostratigraphy, the uppermost Banalia Redbeds unit is
now considered to be Cambrian in age (Tait et al.
2011
).
3600 Ma
fuchsitic quartzite with detrital zircons as old as 4013 Ma
(Kalsbeek et al.
2013
).
In the south, the TC includes late Neoarchean gneisses
and migmatites of
the Dodoman Complex dated at
2573
34 Ma (Rb/Sr whole-rock date; in Cahen et al.
1984
), and granites (e.g. Singida) dated at 2535
30 Ma
(Rb/Sr whole-rock date; Bell and Dodson
1981
), and
between 2660 to 2850 (U/Pb Zircon SHRIMP, Kabette
et al.
2012a
).
The southern and western margins of the TC are poorly
defined and includes a number of remobilized Archean
endogenous and exogenous terranes within a broad zone,
known as the Ubendian-Usagaran Belt, of long-lived Prote-
rozoic tectonism that lasted over a period of ca. 300 million
years between 2.1-1.8 Ga (Boniface et al.
2012
; Lawley
et al.
2013
,
2014
). The zone includes sheared Paleopro-
terozoic (Eburnian) metasediments of the Rusizian Super-
group dated between 1.9 and 2.1 Ga, and younger granitoids
dated around 1.7-1.8 Ga, that form the Ubendian Belt
(Cahen et al.
1984
; Lenoir et al.
1995
; Lawley et al.
2013
,
2014
and references therein). The complex series of
allochthonous terranes of the Ubendian Belt are in turn
overlain by Mesoproterozoic metasediments that, in turn,
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