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Journal of African Earth Sciences 40 (2004) 219–244
Petrography, geochemistry, and geochronology of granitoid rocksin the Neoproterozoic-Paleozoic Lufilian–Zambezi belt, Zambia:
Implications for tectonic setting and regional correlation
Crispin Katongo a, Friedrich Koller a, Urs Kloetzli a, Christian Koeberl a,*,Francis Tembo b, Bert De Waele c
a University of Vienna, Department of Geological Sciences, Althanstrasse 14, 1090 Vienna, Austriab University of Zambia, School of Mines, Geology Department, P.O. Box 32379, Lusaka, Zambia
c Curtin University of Technology, Tectonics Special Research Centre, Department of Applied Geology, GPO Box U1987, Perth, WA 6845, Australia
Received 13 November 2003; received in revised form 21 December 2004; accepted 23 December 2004
Abstract
There are several pre-orogenic Neoproterozoic granitoid and metavolcanic rocks in the Lufilian–Zambezi belt in Zambia and Zim-
babwe that are interpreted to have been emplaced in a continental-rift setting that is linked to the break-up of the Rodinia supercon-
tinent. However, no geochemical data were previously available for these rocks in the Zambian part of the belt to support this model.
We conducted petrographic and whole-rock chemical analyses of the Neoproterozoic Nchanga Granite, Lusaka Granite, Ngoma
Gneiss and felsic metavolcanic rocks from the Lufilian–Zambezi belt in Zambian, in order to evaluate their chemical characteristics
and tectonic settings. Other magmatic rocks of importance for understanding the evolution of the belt in Zambia, included in this
study, are theMesoproterozoicMunali Hills Granite and associated amphibolites and theMpande Gneiss. The Neoproterozoic rocks
have monzogranitic compositions, aluminum-saturation indices (ASI) < 1.1, and high contents of high field strength elements
(HFSE) and rare earth elements (REE). The chondrite-normalised spider diagrams are similar to those of A-type granites from
the Lachlan fold belt and show negative Sr, P, and Ti anomalies. On various tectonic discrimination diagrams the Neoproterozoic
rocks plot mainly in A-type granite fields. These petrographic and trace element compositions indicate that these rocks are A-type
felsic rocks, but they do not have features of granites and rhyolites emplaced in true continental-rift settings, as previously suggested.
On the basis of the A-type features and independent regional geological and geochronological data, we suggest that the Neoprote-
rozoic granitoid and felsic metavolcanic rocks were emplaced during the earliest extensional stages of continental rifting in the Luf-
ilian–Zambezi belt. The apparent continental-arc like chemistry of the granitoid and felsic metavolcanic rocks is thus inferred to be
inherited from calcalkaline sources. The Mesoproterozoic Munali Hills Granite and Mpande Gneiss have trace element features e.g.,
Nb–Ta depletions, which indicate that that these gneisses were emplaced in a convergent-margin setting. The MORB-normalised spi-
der diagram of co-magmatic amphibolites exhibit a fractionated LILE/HFSE pattern recognized in subduction zones. This inference
is consistent with remnants of ocean crust, juvenile Island arcs and ophiolites elsewhere in the Mesoproterozoic Irumide belt in
Zambia and Zimbabwe. In addition, we report the first U–Pb zircon age of 1090.1 ± 1.3 Ma for the Munali Hills Granite. The
age for the Munali Hills Granite provides new constraints on correlation and tectono-thermal activity in the Lufilian–Zambezi belt.
The age of the Munali Hills Granite indicates that some supracrustal rocks in the Zambezi belt of Zambia, which were previously
thought to be Neoproterozoic and correlated with the Katanga Supergroup in the Lufilian belt, are Mesoproterozoic or older.
Consequently, previous regional lithostratigraphic correlations in the Lufilian–Zambezi belt would require revision.
� 2005 Elsevier Ltd. All rights reserved.
Keywords: Lufilian–Zambezi belt; Geochemistry; Munali Hills Granite; U–Pb zircon age; Tectonic setting; A-type granite
0899-5362/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jafrearsci.2004.12.007
* Corresponding author. Tel.: +43 1 4277 53110; fax: +43 1 4277 9531.
E-mail address: [email protected] (C. Koeberl).
220 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
1. Introduction
Until recently, the Lufilian and the Zambezi belts
were believed to form discrete orogenic belts separated
by the Mwembeshi dislocation zone (MDZ, Fig. 1a),
on the basis of presumed marked differences in meta-morphic grade, structural vergence, and orogenic histo-
ries (De Swardt and Drysdall, 1964; Unrug, 1983;
Coward and Daly, 1984; Hanson et al., 1993). The
MDZ is a prominent, crustal-scale ENE-trending shear
zone extending across Central Zambia, which is believed
to continue to the northeast into Malawi and to the
southwest into Namibia (De Swardt and Drysdall,
1964; Coward and Daly, 1984; Daly, 1986; Porada,1989; Kampunzu and Cailteux, 1999). Isotopic age data
of key lithotectonic units, coupled with re-interpreta-
tions of the geology in the belts in Zambia and Zimba-
bwe, have shown that the two belts are coeval and
form part of a network of Neoproterozoic-early Paleo-
zoic orogenic belts in Central-southern Africa that also
includes the Damara belt (e.g., Hanson et al., 1993;
Dirks et al., 1999; Kampunzu and Cailteux, 1999; Vinyuet al., 1999; Porada and Berhorst, 2000). The Damara–
Lufilian–Zambezi transcontinental network separates
the Congo and Kalahari cratons (Coward and Daly,
Fig. 1. (a) Geological map of the Lufilian–Zambezi belt showing the region
dislocation zone; I = external fold and thrust belt; II = Domes region; III =
shows relationship between Congo and Kalahari cratons, and the Damara (D
et al., 1988b) of the area outlined in Fig. 1a showing sample locations in th
NGG = Ngoma Gneiss.
1984; Unrug, 1983) and formed during the assembly of
the Gondwana supercontinent (Unrug, 1996; Weil
et al., 1998). The disposition and composition of metase-
dimentary rocks in the belt are inferred to indicate depo-
sition in a rift basin (Wilson et al., 1993; Hanson et al.,
1994; Porada and Berhorst, 2000). Geochemical charac-teristics of metagabbros and eclogites in the belt suggest
that ocean crust was generated during continental rifting
beginning at ca. 880 Ma and subsequently subducted
during the amalgamation of Gondwana ca. 550 Ma.
(Vrana et al., 1975; Dirks and Sithole, 1999; Tembo
et al., 1999; John et al., 2003, 2004). Some workers
attributed the rifting in the belt to the break-up of the
Rodinia supercontinent (e.g., Unrug, 1992; Kampunzu,2001; Porada and Berhorst, 2000), whereas others argue
that South-central Africa did not form part of the Rodi-
nia supercontinent (Kroner and Cordani, 2003). A suite
of Neoproterozoic granitoids and felsic metavolcanic
rocks in the belt is considered to have been emplaced
during this episode of continental rifting around
880 Ma (Porada and Berhorst, 2000). Kampunzu
(2001) proposed a similar evolution for these granitoids,but suggested that these rocks were emplaced as a result
of extensional collapse of continental crust thickened
during the assembly of the Rodinia supercontinent. In
al setting of the study area (after Porada, 1989). MDZ = Mwembeshi
synclinoria belt; IV = Katanga high; NG = Nchanga Granite. Insert
B)–Lufilian (LB)–Zambezi (ZB) belt. (b) Geological map (after Hanson
e Zambezi belt. LG = Lusaka Granite; MHG =Munali Hills Granite;
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 221
this model, the collapse took place about 120 million
years after the collision ca. 1000 Ma. However, in most
well-documented examples of extensional collapse of
thickened orogenic crust, the collapse begins soon
after, or even during collision (e.g., the present-day
Himalayas, Edwards and Harrison, 1997; Jinjiang etal., 2000).
In the Zambian part of the Lufilian–Zambezi belt,
there are several magmatic rocks that have been dated
by the U–Pb zircon method. These include the Nchanga
Granite (ca. 877 Ma, Armstrong et al., 1999), Lusaka
Granite (ca. 865 Ma, Barr et al., 1978), Hook Granite
(ca. 570–530 Ma, Hanson et al., 1993), mafic metavolca-
nic rocks (ca. 765 Ma, Key et al., 2001) (Fig. 1a), Kafuemetavolcanic rocks (ca. 879 Ma, Wardlaw quoted in
Wilson et al., 1993) (Fig. 1b) and Ngoma Gneiss (ca.
820 Ma, Hanson et al., 1988b). Other important mag-
matic rocks in the understanding of the evolution of
the belt in Zambia are the Mpande Gneiss (ca.
1100 Ma, Hanson et al., 1988b) and the Munali Hills
Granite (not dated). However, no geochemical data
were previously available for the granitoids and Kafuemetavolcanic rocks in the Zambian part of the belt.
Neoproterozoic magmatic rocks in the same age range
as those in Zambia have been dated and also chemically
characterized in the Zimbabwean part of the Zambezi
belt (e.g., Dirks et al., 1999; Vinyu et al., 1999; Hargrove
et al., 2003). Here, we present results of petrographic
studies and reconnaissance whole-rock chemical analy-
ses from the Lufilian–Zambezi belt in Zambia for theNchanga Granite, Lusaka Granite, Munali Hills Gran-
ite, Mpande and Ngoma Gneisses, and Kafue metavol-
canic rocks in order to evaluate chemical characteristics
and tectonic settings of these rocks. Additionally, we
present the first U–Pb zircon age data for the Munali
Hills Granite, which places new constraints on the tim-
ing of tectono-thermal events and correlation within
the belt.
2. Regional geological framework of the Lufilian–
Zambezi belt
A detailed review of previous work and synthesis of
the evolutionary history for much of the Lufilian–
Zambezi belt was provided by Porada and Berhorst(2000). Key et al. (2001) presented the most recent
comprehensive interpretation of the tectono-thermal
evolution of the Lufilian belt based on their work in
NW Zambia. An overview of the structure and geology
of the Zambezi belt was given by Hanson et al. (1994).
Here, we summarise previous work on the Lufilian
and Zambezi belts in order to provide a regional geolo-
gical framework for the discussion of our results.The Lufilian belt (Fig. 1a) is a large arcuate structure
covering eastern Angola, the southern Democratic
Republic of Congo (DRC) and northwestern Zambia
and is well known for its world-class copper-cobalt
deposits (Mendelsohn, 1961; Unrug, 1983). The southern
boundary of the Lufilian belt is marked by the MDZ. In
the Copperbelt region, the basement is composed of Luf-
ubu schists and gneisses (Mendelsohn, 1961) that are in-truded by Eburnian (ca. 2200–1800 Ma) granites (Cahen
et al., 1984; Key et al., 2001). Overlying the Lufubu
schists and gneisses is a sequence of schists and quartzites
of the Muva Supergroup, which are in turn intruded by
early Neoproterozoic granites (e.g., Nchanga Granite).
Key et al. (2001) dated basement rocks of Archean age
(ca. 2.6 Ga) in the western arm of the Lufilian belt, where
they are unconformably overlain by metasediments ofthe Neoproterozoic Katanga Supergroup. The revised
lithostratigraphy of the Katanga Supergroup (Porada
and Berhorst, 2000) consists, in stratigraphic succession,
of the arenaceous Roan Group, carbonaceous Mwashia
Group with metavolcanic interbeds, and the conglomer-
atic, arenaceous and pelitic Kundelungu Group. In NW
Zambia, Angola and the DRC, the Mwashia Group con-
tains mafic volcanic rocks (Key et al., 2001). Metamor-phic assemblages in the Lufilian belt are principally in
the greenschist facies, but higher grades up to eclogite fa-
cies have been locally recorded (Cosi et al., 1992; John
et al., 2003). Deformation in the Lufilian belt mainly in-
volved thin-skinned tectonics with northerly directed
thrusting (Coward and Daly, 1984; Daly, 1986; Kampu-
nzu and Cailteux, 1999; Porada and Berhorst, 2000; Key
et al., 2001).The east–west-trending Zambezi belt stretches from
Central Zambia into northern Zimbabwe where it is as-
sumed to merge with the north–south-trending Mozam-
bique belt (Fig. 1a). In Zambia, the Zambezi belt
consists of wide zones of remobilized crystalline base-
ment, unconformably overlain by Neoproterozoic supra-
crustal rocks (Hanson et al., 1988b; Wilson et al.,
1993). The basement is partly composed of the MpandeGneiss, a megacrystic, K-feldspar- and biotite-bearing
augen gneiss. The Ngoma Gneiss (Fig. 1b) is a protom-
ylonitic to mylonitic gneiss that is inferred to be intru-
sive into the supracrustal sequence (Hanson et al.,
1988b). The two gneiss units form extensive gneissic
terranes in the central parts of the belt. The Munali Hills
Granite is a small lensoidal body that is intrusive into
the Mpande Gneiss (Smith, 1963; Hanson et al.,1988b). At the structural base of the supracrustal
sequence is a thick, rift-related bimodal metaryholite-
metabasalt unit (ca. 879 Ma), comprising the Kafue
Rhyolite and Nazingwe Formations. The bimodal meta-
volcanic unit is structurally overlain by a thick sequence
of psammites and pelites, which are in turn succeeded by
an extensive unit of marbles and calc-silicate rocks (De
Swardt and Drysdall, 1964; Wilson et al., 1993; Hansonet al., 1994). Metamorphic assemblages in the Zambezi
belt are primarily in the amphibolite facies (Barton
222 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
et al., 1991; Hanson et al., 1994; Hargrove et al., 2003),
but locally there are occurrences of tectonically ex-
humed high-pressure rocks comprising eclogites and
whiteschists in Zambia and northwest Zimbabwe
(Vrana et al., 1975; Johnson and Oliver, 2000; Dirks
and Sithole, 1999; John et al., 2004). In contrast to theLufilian belt, deformation in the Zambezi belt is charac-
terised by thick-skinned tectonics, involving both supra-
crustal and basement rocks (Coward and Daly, 1984).
The supracrustal sequence in the Zambezi belt in Zam-
bia has been correlated, based on structural continuity
and broad lithological similarities, with the Makuti
Group (Broderick, 1976, 1981) and Rushinga Group
(Barton et al., 1991) in Zimbabwe.
3. Field relations and petrography of granitoids and
associated rocks
Mineralogical compositions of the granitoids and
felsic metavolcanic rocks studied are summarised in
Table 1.
3.1. Munali hills granite
Although this unit is gneissic and has undergone
metamorphism up to amphibolite facies, we maintain
usage of the term ‘‘Munali Hills Granite’’ for it, which
is well established in the literature, to avoid confusion.
The Munali Hills Granite, centred at 028� 10 0E, 15�53 0S, forms a small part of the Munali Hills, a WNW
trending, elongate ridge, underlain mainly by the
Mpande Gneiss (Smith, 1963; Mallick, 1966). It is a
small elongate pluton that is best exposed at the Munali
Table 1
Summary of indicator mineralogical compositions of granitoids and associa
Granite type MHG LG NG
Samples MHG2, LG2. LG4 NG
MHG4, LG5, LG6 NG
MHG7, NG
MHG10, NG
MHG9 NG
Biotite xxx xxx xxx
Muscovite o ±x xx
Hornblende o ±x o
Apatite xx xx xx
Zircon xx xx xx
Monazite ±x ±x ±x
Garnet o o ±x
Tourmaline xx xx xx
Allanite ±x ±x ±x
Titanite ± x xx
Fluorite ±x o o
Fe-oxides xx xx xx
MHG—Munali Hills Granite; LG—Lusaka Granite; NG—Nchanga Granite
Gneiss. xxx: abundant; xx: common; x: rare; o: absent.
Pass (Fig. 2, location MHG9) and Munali Quarry (Fig.
2, location MHG1-10). In an effort to confirm the intru-
sive character of the Munali Hills Granite, we mapped
along the southern boundary and made several traverses
across the width of the pluton. We found neither intru-
sive contacts with surrounding rocks nor xenoliths thatwere reported by Hanson et al. (1988b). We, therefore,
can neither dispute nor confirm those observations.
The southern boundary of the granite is marked by an
alternating sequence of kyanite schist, quartzite, and
marbles, which constitute the Nega Formation in the
Kafue area (Smith, 1963).
The Munali Hills Granite has been mapped as a small
intrusion into the Mesoproterozoic Mpande Gneiss(Mallick, 1966; Smith, 1963; Hanson et al., 1988b;
Wilson et al., 1993; Hanson et al., 1994). The granite
was described as having intrusive relations with both
supracrustal rocks and the Mpande Gneiss (Smith,
1963; Hanson et al., 1988b, 1994). On this basis, the Mu-
nali Hills Granite had been regarded as younger than
both the host ca. 1100 Ma Mpande Gneiss and the ca.
879 Ma felsic metavolcanic unit that forms the struc-tural base of the Zambezi supracrustal sequence. The
Munali Hills Granite was considered to represent pre
or syn-tectonic Neoproterozoic plutonic activity accom-
panying orogenesis in the Zambezi belt (Hanson et al.,
1994). The granite was inferred to contain xenoliths of
country rocks (Hanson et al., 1988b), which had previ-
ously been broadly correlated with Neoproterozoic
Katanga Supergroup metasediments in the Lufilian belt.A reliable age estimate for the Munali Hills Granite is
therefore critical in the evaluation of the tectono-
thermal history and regional correlation of supracrustal
rocks in the Lufilian–Zambezi belt.
ted rocks from the Lufilian–Zambezi belt
NGG MPD MVR
2, NGG3, MPD1 CR1, CR2,
3, NGG4, MPD2 KGR2,
4, NGG5 KGR3,
5, KGR4,
6 KGR5
xxx xxx xxx
xx xx ±x
o o o
xx xx ±x
xx xx xx
±x ±x ±x
±x o o
±x ±x o
±x ±x o
xx xx ±x
±x o o
xx xx xx
, MVR—Metavolcanic rocks; MPD—Mpande Gneiss; NGG—Ngoma
Fig. 2. Detailed geological map of the Kafue area (after Smith, 1963 and Thieme, 1984) outlined in Fig. 1b, showing sample locations. Maz.
Rd = Mazabuka Road; Kf. Rd = Kafue Gorge Road; Ch. Rd = Chirundu Road. MHG =Munali Hills Granite; MPD =Mpande Gneiss; CR and
KGR = Chirundu and Kafue Gorge Road felsic metavolcanic rocks, respectively; MPD =Mpande Gneiss; SDA = metabasalt.
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 223
The Munali Hills Granite is generally described as
strongly foliated biotite granite rich in K-feldspar mega-
crysts and resembles the adjacent Mpande Gneiss in
lithology (Smith, 1963; Hanson et al., 1988b). Our field
and petrographic studies show that the granite is less de-
formed and finer grained than the typical MpandeGneiss. The Munali Hills Granite is a porphyritic K-
feldspar-rich granite gneiss composed of a range of fine-
to coarse-grained varieties, varying from leucocratic to
melanocratic depending on the abundance of biotite,
and displaying varying degrees of deformation. There
are two main varieties of Munali Hills Granite: grey
and pink granite gneiss.
3.1.1. Grey mesocratic, megacrystic biotite granite gneiss
This variety is exposed at the Munali Pass (location
MHG9) and contains coarse-grained pink microcline
porphyroclasts set in a finer grained mesocratic ground-
mass. Isolated dark, fine-grained, irregularly shaped bio-
tite-rich enclaves are common (Fig. 3a). Deformation is
generally weak, and exhibited by a crude foliation de-
fined by aligned biotite wrapping around slightly elon-gated porphyroclasts of feldspar and quartz aggregates.
The granite is composed of microcline, quartz, pla-
gioclase, and biotite ± muscovite. The microcline crys-
tals are generally poikiloblastic, hosting smaller grains
of other mineral constituents, and are non-perthitic
and slightly kaolinised. Accessory minerals include
sphene, epidote, apatite, zircon, and less commonly
tourmaline. The granite displays varying degrees of
alteration, including chloritisation of biotite and
replacement of plagioclase by sericite and scapolite. In
some cases, scapolite displays myrmekite-like inter-growths with quartz, suggesting replacement of plagio-
clase on a fine scale. Undulose extinction in quartz,
kink bands in biotite and deformation twins in plagio-
clase indicate weak deformation in the granite.
3.1.2. Pink-grey, leucocratic, fine- to medium-grained
porphyritic granite gneiss
There are several varieties of fine- to medium-grainedgranite gneisses at the Munali Quarry (location MHG1-
10). They range from grey to pink, and are invariably
porphyritic, although they contain less microcline por-
phyroclasts than at the Munali Pass. The granites have
a heterogeneous composition, consisting of pink micro-
cline porphyroclasts 1–2 cm long and biotite clots
(aggregates) 0.5–1 cm long embedded in a fine- to med-
ium-grained granoblastic intergrowth of quartz, micro-cline, plagioclase and biotite. The microcline is
subhedral to anhedral, randomly oriented and hosts
smaller grains of quartz, plagioclase, and biotite. Biotite
clots are irregularly shaped and unevenly distributed in
the rock (Fig. 3b).
Fig. 3. Field photographs of granitoid rocks in the Kafue area. (a) Mesocratic medium-coarse grained seriate variety of Munali Hills Granite. Dark
enclave composed mainly of biotite. Scale: one division on scale-card = 1 cm (Munali Pass, MHG9). (b) Leucocratic fine-medium grained varieties of
the Munali Hills Granite. Dark spots are biotite-rich clots, which are more abundant in the dark bands than in the light bands (Munali Quarry,
MHG1-10). (c) Deformed amphibolitic dykes intrusive into Munali Hills Granite. (d) Megacrystic K-feldspar augen gneiss (Mpande Gneiss, MPD1).
(e) Banded felsic metavolcanic rock with en echelon array of scapolite-filled white vein-lets aligned subparallel to schistosity (Chirundu Road,
CR1-2).
224 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
The microcline porphyroclasts have moderately tur-
bid altered surfaces and exhibit vein- to flame-type
perthite. Plagioclase occurs mainly in the groundmass
as anhedral to subhedral grains, most of which show
deformation twinning, moderate sericitisation and par-
tial replacement by scapolite. The replacement is mainlyalong cleavage planes or in cores of the plagioclase.
Myrmekitic intergrowth between plagioclase and quartz
is common, where the former is adjacent to microcline.
In most samples, muscovite occurs as sericite, but in
one sample (MHG7), it occurs as large apparently pri-
mary igneous crystals associated with biotite. All the
samples contain minor amounts of interstitial carbonate
minerals. Accessory minerals include zircon, epidote,
apatite, rutile, tourmaline, carbonates, sphene, metamict
allanite and opaque minerals.
Amphibolitic and gabbroic bodies are aligned along
WNW-trends in the Munali Hills Granite and Mpande
Gneiss (Fig. 2). At the Munali Quarry, there are several
steep, WNW-trending amphibolitic dykes, measuring upto 5 m in width that appear intrusive into the Munali
Hills Granite (Fig. 3c) and in some case appear to be
coeval with the granite due to the absence of contact
metamorphism. The amphibolitic dykes do not exhibit
contact metamorphic relations with the host granite
and some dykes have strong shear fabrics. The amphib-
olites (samples MHG5a-c) are dark green and
fine-grained, with or without white relict plagioclase
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 225
phenocrysts. They are composed mainly of blue-green
hornblende and subordinate biotite with plagioclase.
Scapolite occurs as a secondary mineral replacing pla-
gioclase, and in one sample the scapolite is in textural
equilibrium with the hornblende. Accessory minerals
include epidote, sphene chalcopyrite and pyrite.
3.2. Mpande Gneiss
3.2.1. Biotite-rich megacrystic K-feldspar augen gneiss
The Mpande Gneiss is generally weathered and best
exposed as loose boulders along the Kafue–Gorge road.
Fresh exposures occur in roadcuts near the gorge (Fig.
2, location MPD1). The unit is a dark grey, megacrysticaugen gneiss, composed of large augen-shaped micro-
cline, set within a relatively fine-grained protomylonitic,
biotite-rich quartzofeldspathic groundmass. Biotite
aggregates and quartz ribbons wrap around the micro-
cline augen (Fig. 3d). Detailed geology and structural
evaluation of the Mpande Gneiss are presented by
Wilson et al. (1993) and Hanson et al. (1994). We only
studied the best outcrops for comparison with theMunali Hills Granite. The protomylonitic fabric is par-
allel to that in the adjacent supracrustal rocks and is
attributed to Neoproterozoic orogenesis on the basis
of its parallelism with the regional structural grain in
the Zambezi belt, suggesting that the gneiss was first de-
formed during Pan-African orogenesis (Wilson et al.,
1993; Hanson et al., 1994). Because of the coarse texture
of the rock, no petrographic analyses were conducted.
3.2.2. Pink porphyritic megacrystic K-feldspar-rich
granite gneiss
The rock is best exposed at a roadcut on the Maza-
buka road (Fig. 2, location MPD2). The rock is much
coarser grained than the Munali Hills Granite but con-
tains much lower amounts of biotite. It is composed
mainly of megacrystic, euhedral to subhedral pinkmicrocline porphyroclasts set in a medium- to coarse-
grained matrix of granoblastic quartz, feldspars and
minor biotite. The microcline megacrysts are randomly
oriented and enclose smaller grains of all the other
major minerals. Biotite in the matrix occurs as irregular
dark clusters. Interstitial polycrystalline quartz is, in
some places, stretched into quartz ribbons. Pervasive
millimeter-scale anastomosing shear zones indicate thatthe outcrop is located close to or within a shear zone.
The microcline megacrysts display crosshatch twining
and are non-perthitic. All the megacrysts are surrounded
by a highly strained, relatively fine-grained mylonitic
matrix composed mainly of microcline. The fine-grained
zones around the megacrysts form an anastomozing net-
work characterised by sericitised plagioclase, chlorite,
and sericite. Myrmekitic intergrowths of plagioclasewith quartz are common. Muscovite occurs in minor
amounts and is mainly associated with plagioclase as
inclusions and in some cases is intergrown with biotite.
Accessory minerals include epidote, sphene, zircon and
opaque minerals.
3.3. Ngoma Gneiss
Detailed geology and structural evaluation of the
Ngoma Gneiss are also presented by Wilson et al.
(1993) and Hanson et al. (1994). The texture of the
Ngoma Gneiss varies from strongly sheared mylonitic
rocks to relatively less sheared gneissic rocks. The
outcrops are generally small and isolated, except in river
exposures. The sheared derivatives are greyish musco-
vite-rich mylonites, whereas the less sheared types areprotomylonitic in texture and medium-grained. Micro-
cline porphyroclasts are embedded in a relatively fine-
grained mylonitic matrix of quartz, microcline, plagio-
clase, and biotite ± muscovite, ±garnet (NGG3 and
NGG5). Accessory minerals include epidote, zircon,
allanite, sphene, and opaques. The mylonite is
composed of fine- to medium-grained microcline augen
set in a fine-grained micaceous matrix. Micas and quartzribbons define the mylonitic foliation. The structure and
strong shear fabric displayed by the Ngoma Gneiss are
attributed to shear deformation during emplacement in
a crustal-scale extensional shear zone (Wilson et al.,
1993; Hanson et al., 1994).
3.4. Metavolcanic rocks
Metavolcanic rocks of the Kafue Rhyolite and
Nazingwe Formations (Smith, 1963; Mallick, 1966),
crop out in a belt trending NW–SE for about 35 km
south of the Mpande Dome (Fig. 2). They form the
structurally lowest part of the Zambezi supracrustal
sequence in the area (Hanson et al., 1988b). We have
studied two types of metavolcanic rocks, felsic metavol-
canic rocks in the Kafue Rhyolite Formation andmetabasalt in the Nazingwe Formation (Smith, 1963;
Mallick, 1966). The felsic metavolcanic rocks are moder-
ately weathered and best exposed along the Kafue
Gorge road (KGR2-6) and in streambeds (CR1-2).
There are dark and light grey varieties, which range in
texture from schistose to massive. They are porphyritic,
consisting of relict, fine- to medium-grained phenocrysts
of opalescent pale blue quartz and subhedral laths ofplagioclase set in a fine-grained, recrystallised mica-rich
groundmass. In places, the light grey felsic metavolcanic
variety is intruded by an array of en echelon veins filled
with scapolite, resulting in a banded appearance (Fig.
3e). Aligned micas define a foliation in the schistose vari-
ety. In the dark grey variety (KGR2-5) mica is chiefly
biotite, whereas white mica is predominant in the light
grey variety (CR 1, 2). Plagioclase is moderately alteredto sericite in both types; however, in the light grey vari-
ety, it was subsequently partially replaced by scapolite.
226 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
Accessory minerals include opaque minerals, tourma-
line, epidote, and carbonate.
The metabasalt is represented by one sample of chlo-
rite-biotite schist (Fig. 2, SDA1). The outcrops are mod-
erately weathered and fresh samples are difficult to find.
The schist possesses an S2 crenulation cleavage. Unlikethe felsic metavolcanic rocks, volcanic textures of the
presumed basaltic precursor rock are not preserved.
The interpretation that the chlorite-biotite schists are
metabasalts is based on their close association with the
felsic metavolcanic rocks (Smith, 1963).
3.5. Lusaka Granite
The Lusaka Granite is considered to form basement
to the supracrustal sequence in the Zambezi belt (Pora-
da and Berhorst, 2000). It forms a prominent EW-trend-
ing ridge measuring about 4 · 12 km2 (Fig. 1, locationLG). Detailed geology and petrographic descriptions
of Lusaka Granite are provided by Thieme (1968) and
Simpson et al. (1965). There are several varieties of gran-
ites, but samples for this study were taken from two dis-tinct dominant varieties i.e., pink and grey granites.
Both granites are porphyritic and have a medium- to
coarse-grained seriate texture. The granites display a
crude east–west striking foliation, which is continuous
with the country rocks. The foliation is defined by cru-
dely aligned biotite. The granites contain coarse por-
phyroclasts of microcline set in a medium-grained
granoblastic matrix of quartz, microcline, plagioclase,and biotite.
The microcline displays vein-perthite. Some porphyr-
oclasts of microcline host smaller grains of quartz, bio-
tite, and plagioclase. The plagioclase is anhedral to
subhedral, generally shows albite twinning and is
slightly altered to saussurite. Most plagioclase grains
are inclusion free, but a few host small crystals of quartz
and biotite, and display myrmekitic texture. Quartz oc-curs in coarse recrystallised polycrystalline aggregates,
which are intergrown with the microcline, biotite, and
plagioclase. Biotite occurs in clusters, which measure
up to 3 cm in size, and as interstitial flakes. The biotite
is closely associated with sphene and opaque minerals.
Some of the biotite flakes are partly replaced by chlorite.
Muscovite is present in the grey granites (LG1, 5) but is
absent in the pink granite (LG2, 6). In the grey granite,it occurs in minor amounts and is intimately associated
with biotite. Accessory minerals in both the granite
types include zircon, sphene, epidote and opaque
minerals.
3.6. Nchanga Granite
Detailed descriptions of different varieties of theNchanga Granite are presented in Mendelsohn (1961).
There are two main varieties: grey granite and red gran-
ite. The grey granite (NG2, 4, 6) is equigranular, with
grain sizes of 0.5–4 cm, and is composed of white micro-
cline, quartz, plagioclase, and biotite ± garnet. The red
granite (NG3, 5) is generally equigranular with grain
sizes of 0.5–3 cm. It is composed chiefly of an inter-
growth of anhedral pink microcline, subordinate quartz,plagioclase, and minor biotite.
In both granites, microcline is slightly turbid and
most grains contain inclusions of quartz, biotite, and
plagioclase. Plagioclase exhibits polysynthetic deforma-
tion twins and shows different degrees of alteration to
sericite, especially in the grain cores. The plagioclase in
the grey granite hosts inclusions of euhedral garnet
and biotite. Quartz occurs as large, polycrystalline,irregularly shaped aggregates. Individual quartz grains
are medium- to coarse-grained and show undulose
extinction, subgrains and irregular grain boundaries.
Biotite occurs both as coarse flakes and medium-grained
aggregates. Muscovite occurs in minor amounts and is
generally associated with biotite but also occurs in pla-
gioclase as secondary inclusions. Accessory minerals
include zircon, epidote, allanite, sphene, opaques and,in some samples, fluorite.
4. Analytical methods
A total of 31 representative samples were collected
for whole-rock chemical analysis. Samples of coarse-
grained granitoid rocks weighed between 25–40 kg,and samples of fine-grained metavolcanic rocks and
amphibolites ranged in weight from 5–10 kg. The sam-
ples were crushed in a steel jaw crusher to 3-cm-sized
pieces. Fresh pieces were selected, cleaned and crushed
again to 3-mm pieces. The products of the secondary
crushing were then split and a representative sample pul-
verised in an agate mill.
Concentrations of whole-rock major and some traceelements (Co, Cu, Zn, Sr, Y, Ga, and Nb) were
determined by standard X-ray fluorescence (XRF) pro-
cedures on a Phillips PW2400 spectrometer at the Uni-
versity of Vienna, Department of Geological Sciences.
Loss on ignition (LOI) was determined by heating pow-
dered samples at 850 �C for 3 h. The major and minor
elements were determined on fused glass discs, whereas
trace elements were analyzed on pressed pellet powders.Accuracy and precision are better than 5% RSD (% rel-
ative standard deviation). Geostandards used in the
analyses are UB-N and GSR1 to 6, consisting of granite,
shale, gabbro, and limestone.
Rare earth elements (REE) and other trace elements
(Sc, V, Cr, Ni, Rb, Ta, Hf and W) were analysed by
instrumental neutron activation analysis (INAA) at the
University of Vienna, Department of GeologicalSciences. Several international rock standards, such as
ACE (C.R.P.G-Nancy Granite), Allende (Carbonaceous
Table 2
Results of major, minor, and trace element compositions, together with selected CIPW-normative mineral compositions of granitoids and associated rocks from the Lufilian–Zambezi belt
Sample Munali Hills Granite Mpande Gneiss Lusaka Granite Nchanga Granite
MHG1 MHG2 MHG3 MHG4 MHG9 MHG10 MPD1 MPD2 LG1 LG2 LG5 LG6 NG2 NG3 NG4 NG5 NG6
SiO2 71.80 69.80 71.22 72.92 66.93 73.21 71.36 71.53 73.24 73.55 73.95 73.15 74.62 74.24 74.42 75.49 71.75
TiO2 0.40 0.59 0.53 0.38 0.93 0.32 0.40 0.44 0.36 0.37 0.33 0.35 0.10 0.16 0.21 0.14 0.29
Al2O3 12.91 12.99 12.95 12.37 13.09 12.35 13.51 12.83 12.59 12.05 12.14 12.50 12.18 12.42 12.27 12.21 13.25
Fe2O3 2.94 4.48 3.44 2.74 6.12 2.40 2.59 3.25 2.35 2.64 2.40 2.52 0.93 2.13 2.14 1.77 2.69
MnO 0.02 0.03 0.03 0.02 0.03 0.02 0.04 0.03 0.03 0.05 0.03 0.04 0.01 0.05 0.05 0.02 0.07
MgO 0.41 0.58 0.63 0.35 1.08 0.35 0.80 0.50 0.37 0.38 0.35 0.37 0.70 0.10 0.16 0.13 0.24
CaO 1.10 1.43 1.43 1.00 2.71 0.71 1.05 1.11 1.40 1.26 1.23 1.27 0.07 0.91 1.10 0.71 1.23
Na2O 2.23 2.31 2.43 2.02 2.27 2.19 2.62 2.65 3.13 2.93 2.97 3.02 0.73 3.23 3.08 3.30 3.14
K2O 6.56 5.76 5.38 6.38 4.63 6.71 5.70 5.53 5.01 4.98 5.00 5.17 8.45 5.37 5.11 5.17 5.54
P2O5 0.14 0.15 0.13 0.12 0.27 0.11 0.14 0.11 0.06 0.06 0.06 0.06 0.02 0.03 0.06 0.02 0.08
LOI 0.43 0.67 0.65 0.93 0.53 0.66 0.57 0.58 0.25 0.41 0.28 0.36 0.87 0.46 0.38 0.51 0.42
Total 98.94 98.79 98.82 99.23 98.59 99.03 98.78 98.56 98.79 98.68 98.74 98.81 98.68 99.10 98.98 99.47 98.70
CIA 50.2 50.7 51.0 50.6 48.9 50.4 52.1 50.9 48.9 49.0 49.2 49.2 53.7 49.2 49.3 49.8 49.7
A/CNK 1.01 1.03 1.04 1.03 0.96 1.02 1.09 1.04 0.96 0.96 0.97 0.97 1.16 0.97 0.97 0.99 0.99
A/NK 1.20 1.29 1.32 1.21 1.50 1.14 1.29 1.24 1.19 1.17 1.18 1.18 1.18 1.12 1.16 1.11 1.19
CIPW norm
Qtz 31.15 30.81 32.86 34.43 29.35 33.06 31.26 32.14 32.70 34.53 34.70 32.83 36.90 33.05 34.63 34.88 29.51
Or 38.77 34.04 31.79 37.70 27.36 39.65 33.69 32.68 29.61 29.43 29.55 30.55 49.94 31.74 30.20 30.55 32.74
Ab 18.87 19.55 20.56 17.09 19.21 18.53 22.17 22.42 26.49 24.79 25.13 25.55 6.18 27.33 26.06 27.92 26.57
An 4.54 6.11 6.25 4.18 11.68 2.80 4.29 4.79 5.51 5.02 5.03 5.28 0.22 3.53 4.56 3.24 5.58
C 0.48 0.71 0.84 0.61 0.06 0.46 1.46 0.73 - - - - 1.75 - - - 0.04
Hy 1.02 1.44 1.57 0.87 2.69 0.87 1.99 1.25 0.92 0.95 0.87 0.92 1.74 0.10 0.40 0.32 0.60
Sc 6.53 7.54 7.64 6.40 14.7 5.87 6.17 8.77 5.05 5.67 5.33 5.01 1.25 2.47 3.56 0.28 6.82
V 24.8 36.5 35.5 17.3 82.2 17.7 30.1 25.9 13.4 16.0 15.7 15.5 3.30 < 3 4.90 < 3 6.6
Cr 17.3 16.8 13.1 16.0 22.4 7.19 9.77 17.3 14.0 24.4 16.4 19.5 1.78 7.72 2.33 8.31 8.65
Co 7.51 10.5 8.24 6.19 14.2 5.75 6.12 7.16 4.67 5.97 5.64 5.11 26.2 3.14 3.71 5.69 4.24
Ni 25.6 30.4 24.8 24.6 37.3 11.7 20.2 23.4 12.6 14.6 3.46 20.7 27.7 23.8 18.1 17.7 22.9
Cu 12.2 24.6 10.9 62.8 54.7 14.5 24.3 20.4 < 3 6.30 3.80 3.90 660 4.70 7.00 43.0 4.10
Zn 15.6 32.6 25.1 15.5 23.7 18.5 36.3 23.1 24.7 34.4 26.9 30.1 33.6 94.8 66.1 53.7 67.5
Ga 16.7 18.8 17.8 14.4 21 15.4 17.6 18.6 15.0 15.0 15.3 14.6 20.5 20.9 18.7 21.0 19.3
Rb 293 339 214 271 200 290 293 369 264 256 286 233 501 334 278 357 287
Sr 99.3 102 113 85 153 92.9 105 91.1 64.9 56.4 58.3 62.1 39.3 37.7 67.8 309 90.2
Y 51.2 112 56.5 35.2 57.3 45.5 53.9 105 44.5 44.7 45.4 39.5 75.7 159 88.7 105 79.1
Zr 214 280 279 235 317 193 164 254 182 211 201 190 136 191 211 148 227
Nb 11.5 20.0 17.1 9.80 21.8 10.5 18.1 16.5 22.4 23.6 22.7 20.2 92.0 94.2 51.4 111 36.4
Sb 0.15 0.18 0.12 0.10 0.12 0.17 0.03 0.14 0.19 0.55 0.22 0.52 0.11 0.11 0.08 0.05 0.09
Cs 3.59 5.31 3.58 3.52 3.76 3.94 3.37 5.26 5.59 8.88 6.4 7.78 2.99 3.71 2.72 1.93 3.27
Ba 677 628 658 644 987 598 600 532 450 451 435 472 831 263 483 207 795
La 104 126 107 111 72 117 94.0 148 49.8 58.8 68.4 47.2 45.3 91.9 103 75.6 138
Ce 204 258 218 224 142 235 185 234 98.7 115 125 91.9 100 196 203 203 268
Nd 83.6 119 82.2 89.2 70.2 94.1 79.1 112 41.1 44.3 55.6 36.5 55.0 95.7 94.5 76.2 116
Sm 16.7 21.5 15.5 18.5 14.2 19.8 15.4 26 7.8 9.22 9.81 7.48 12.2 20.6 17.0 15.3 20.6
Eu 1.79 1.60 1.67 1.53 2.33 1.54 1.86 2.09 1.04 1.22 1.09 0.95 0.75 0.99 1.42 0.75 2.02
Gd 15.5 19.6 11.3 17.6 14.4 19.6 13.1 24.7 7.98 9.91 8.42 6.25 11.2 19.0 18.0 14.8 17.2
C.Katongoetal./JournalofAfricanEarthSciences40(2004)219–244
227
Table 2 (continued)
Sample Munali Hills Granite Mpande Gneiss Lusaka Granite Nchanga Granite
MHG1 MHG2 MHG3 MHG4 MHG9 MHG10 MPD1 MPD2 LG1 LG2 LG5 LG6 NG2 NG3 NG4 NG5 NG6
Tb 2.24 3.10 1.74 2.21 2.09 2.70 1.98 3.50 1.55 1.67 1.45 1.07 1.85 3.18 2.88 2.32 2.73
Tm 0.71 1.09 0.77 0.74 0.80 0.79 0.72 1.33 0.77 0.88 0.82 0.60 1.05 1.67 1.33 1.22 1.36
Yb 3.72 7.69 5.46 4.40 4.86 3.97 4.52 9.02 5.37 5.30 5.48 4.00 7.97 11.4 9.27 8.66 8.03
Lu 0.53 0.88 0.82 0.55 0.71 0.49 0.64 1.21 0.84 0.76 0.85 0.61 1.34 2.07 1.36 1.60 1.16
Hf 8.88 10.2 9.43 10.2 11.1 8.76 10.4 12.9 7.62 8.68 8.49 6.96 7.66 9.12 8.89 7.22 9.82
Ta 1.10 2.83 1.57 0.59 1.89 1.12 2.29 2.13 2.62 2.31 3.45 2.19 7.39 4.30 3.83 4.36 2.93
Th 57.3 71.1 70.4 99.9 30.7 71.2 54.1 93.0 30.3 35.0 38.5 27.2 78.5 89.1 83.6 102 66.5
U 3.98 3.24 4.82 9.32 2.13 5.03 8.99 7.39 6.23 6.61 7.50 6.18 14.2 12.7 11.7 16.9 9.13
Y/Nb 4.45 5.60 3.30 3.59 2.63 4.33 2.98 6.36 1.99 1.89 2.00 1.96 0.82 1.69 1.73 0.95 2.17
LaN/SmN 3.92 3.69 4.35 3.78 3.19 3.72 3.84 3.58 4.02 4.01 4.39 3.97 2.34 2.81 3.81 3.11 4.22
LaN/YbN 18.89 11.07 13.24 17.05 10.01 19.92 14.05 11.09 6.27 7.50 8.43 7.97 3.84 5.45 7.51 5.90 11.61
GdN/YbN 3.38 2.07 1.68 3.24 2.40 4.00 2.35 2.22 1.20 1.52 1.25 1.27 1.14 1.35 1.57 1.39 1.74
Eu/Eu*N 0.34 0.24 0.39 0.26 0.50 0.24 0.40 0.25 0.40 0.39 0.37 0.42 0.20 0.15 0.25 0.15 0.33
Sample Ngoma Gneiss Metavolcanic rocks Amphibolites
NGG3 NGG4 NGG5 KGR2 KGR3 KGR4 KGR5 CR1 CR2 SDA1 MHG5a MHG5b MHG5c
SiO2 73.88 74.19 71.55 69.13 68.44 68.85 70.57 69.06 71.89 48.74 48.16 50.19 47.17
TiO2 0.23 0.22 0.42 0.79 0.81 0.79 0.76 0.57 0.53 1.37 1.22 2.49 2.05
Al2O3 12.53 12.38 12.78 13.06 13.08 12.98 12.74 12.78 12.71 14.19 14.28 15.23 14.32
Fe2O3 2.48 2.07 3.10 4.58 4.92 4.36 3.01 4.40 3.13 16.11 13.61 13.55 14.57
MnO 0.03 0.03 0.09 0.08 0.07 0.09 0.10 0.02 0.01 0.07 0.15 0.13 0.10
MgO 0.15 0.16 0.19 0.99 1.03 0.92 0.90 1.34 1.18 11.20 6.84 3.59 6.88
CaO 0.82 1.46 0.99 1.39 1.58 1.72 2.26 3.26 1.49 0.34 6.48 8.09 6.68
Na2O 3.64 3.50 3.44 2.97 3.30 2.70 5.08 2.09 1.36 0.52 1.89 2.38 1.74
K2O 4.87 4.59 5.56 4.76 4.40 5.06 1.83 3.89 4.57 1.20 4.26 2.57 4.36
P2O5 0.03 0.03 0.04 0.18 0.17 0.18 0.19 0.13 0.10 0.19 0.09 0.34 0.22
LOI 0.42 0.67 0.42 0.88 0.97 1.36 1.54 1.08 1.61 5.15 1.59 0.44 0.52
Total 99.08 99.30 98.58 98.81 98.77 99.01 98.98 98.62 98.58 99.08 98.57 99.00 98.61
CIA 49.5 48.0 48.6 50.9 50.0 49.8 46.8 48.5 56.2 83.6 42.2 41.5 42.0
A/CNK 0.98 0.93 0.95 1.03 1.00 0.99 0.88 0.94 1.28 5.12 0.73 0.71 0.73
A/NK 1.11 1.15 1.09 1.29 1.28 1.31 1.23 1.67 1.77 6.59 1.85 2.27 1.89
CIPW norm
Qtz 32.26 33.53 28.32 29.69 27.96 29.23 29.11 33.68 41.82 n.c n.c n.c n.c
Or 28.78 27.13 32.86 28.13 26.00 29.90 10.81 22.99 27.01 n.c n.c n.c n.c
Ab 30.80 29.62 29.11 25.13 27.92 22.85 42.99 17.69 11.51 n.c n.c n.c n.c
An 3.47 4.51 3.01 5.72 6.73 7.36 6.56 14.00 6.74 n.c n.c n.c n.c
C – – – 0.93 0.42 0.37 – – 3.06 n.c n.c n.c n.c
Hy 0.37 0.00 0.28 2.47 2.57 2.29 1.82 3.34 2.94 n.c n.c n.c n.c
Sc 1.77 1.80 3.18 8.99 9.12 8.44 7.10 7.19 6.57 30.5 33.1 27.5 26.5
V 4..9 4.40 5.50 13.0 13.9 12.1 10.3 12.8 10.8 279 260 265 257
Cr 5.90 2.67 16.7 14.2 <3 9.56 3.08 4.64 3.47 75.9 93.9 62.9 213
Co 4.03 3.46 3.45 6.77 7.51 5.94 5.01 7.81 7.60 51.5 46.6 44.1 52.5
Ni 16.7 8.56 21.8 26.8 30.0 38.3 24.6 28.4 6.25 88.8 122 68.0 142
228
C.Katongoetal./JournalofAfricanEarthSciences40(2004)219–244
Cu 5.10 4.30 4.60 69.2 13.3 8.80 3.50 3.40 3.20 15.8 123 73.8 212
Zn 80.2 69.2 68.0 35.2 36.0 39.5 30.4 7.20 7.84 36.7 62.4 60 55.1
Ga 30.5 29.3 25.0 23.9 25.0 24.4 17.6 18.8 22.8 25.8 22.1 27.3 25.1
Rb 109 114 144 188 191 180 90.3 213 188 72.9 315 134 316
Sr 70.7 104 87.8 129 109 172.3 93.2 33.2 27.2 32.2 122 342 125
Y 122 125 84.9 72.9 69.4 75.5 64.0 67.7 72.6 25.1 29.9 39.7 29.2
Zr 394 363 447 601 618 592 566 521.7 471 146 70.0 258 138
Nb 92.4 88.8 77.2 50.1 49.6 49.2 46.5 46.4 48.0 8.80 7.90 28.8 16.2
Sb 0.03 <0.04 0.03 0.09 0.05 0.05 0.06 0.08 0.05 0.04 0.16 0.33 0.08
Cs 0.58 0.52 0.37 1.88 1.92 2.12 1.86 4.58 2.64 2.01 5.44 3.21 5.40
Ba 421 390 1135 934 751 963 325 595 626 158 510 739 422
La 93 97.5 133 78.4 76.5 76.4 66.2 89.2 89.4 38.5 10.6 42.8 17.7
Ce 188 207 269 166 161 160 143 182 183 73.0 22.8 86.8 37.5
Nd 90.5 91.8 119 78.4 78.6 75.1 70.2 84.8 84.2 41.1 13.8 44.3 21.2
Sm 20.2 21.4 21.3 16.1 16.6 16.5 14.2 17.4 17.2 7.80 3.21 8.59 4.88
Eu 1.69 1.55 2.87 3.54 3.63 3.75 2.87 3.54 3.6 1.04 0.85 2.36 1.55
Gd 25.3 19.4 18.6 15.6 15.7 15.5 14.9 15.2 16.6 7.98 3.52 7.79 4.48
Tb 3.94 3.50 2.92 2.42 2.46 2.35 2.35 2.55 2.46 1.55 0.67 1.23 0.79
Tm 1.59 1.67 1.19 1.05 1.03 1.18 0.98 1.04 1.10 0.77 0.4 0.61 0.37
Yb 11.6 11.3 8.22 7.25 7.31 7.40 6.53 6.49 6.63 5.37 2.96 3.65 1.90
Lu 1.62 1.64 1.25 0.99 0.94 0.92 0.91 0.93 0.97 0.84 0.36 0.54 0.29
Hf 17.9 14.4 14.8 16.0 16.3 14.6 14.3 14.6 13.6 7.62 2.55 6.78 3.53
Ta 5.94 6.22 4.79 3.26 3.62 3.62 3.62 3.0 3.31 2.62 0.42 1.61 1.09
Th 22.7 25.7 29.2 24.8 24.7 24.8 24.0 27.0 28.0 8.69 2.89 7.94 2.80
U 3.63 3.67 3.85 6.65 6.29 5.72 5.62 6.72 8.32 1.88 0.68 1.62 0.64
Y/Nb 1.32 1.41 1.10 1.46 1.40 1.53 1.38 1.46 1.51 2.85 3.78 1.38 1.80
LaN/SmN 2.90 2.87 3.93 3.07 2.90 2.91 2.93 3.23 3.27 3.11 2.08 3.14 2.28
LaN/YbN 5.42 5.83 10.93 7.31 7.07 6.98 6.85 9.29 9.11 4.84 2.42 7.92 6.30
GdN/YbN 1.77 1.39 1.83 1.74 1.74 1.70 1.85 1.90 2.03 1.20 0.96 1.73 1.91
Eu/Eu*N 0.23 0.23 0.44 0.68 0.69 0.72 0.60 0.67 0.65 0.40 0.77 0.88 1.01
Major and minor elements in wt%; trace elements in ppm; total iron as Fe2O3; Eu/Eu* = EuN/(SmN ·GdN)1/2; molar CIA = 100*(Al2O3/A O3 + CaO + K2O + N2O), A/CNK = molar Al2O3/
(CaO + Na2O + K2O); A/NK = molar Al2O3/(Na2O + K2O); LOI: loss on ignition. n.c.: not calculated.
C.Katongoetal./JournalofAfricanEarthSciences40(2004)219–244
229
l2
230 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
chondrite) and G-2 (U.S.G.S Granite) (Govindaraju,
1989) were used. Analytical methods, including informa-
tion on instrumentation, correction procedures, and pre-
cision and accuracy of the INAA method are described
by Koeberl (1993). Results of whole-rock compositions
and selected CIPW normative mineral compositionsare given in Table 2.
Single zircon U–Pb age determinations were
conducted by thermal ionisation mass spectrometry
(TIMS) at the University of Vienna, Department of
Geological Sciences (Geochronology laboratory), and
by in-situ secondary ionisation mass spectrometry
(SIMS), at Curtin University of Technology, Perth,
Australia. Large samples ranging in weight from 25to 40 kg were prepared by standard crushing, heavy
mineral, and magnetic separation techniques. With the
aid of a binocular microscope, euhedral clear and un-
cracked zircon crystals, with no visible inherited cores
and virtually no inclusions, were hand-picked for the
analyses.
Seven zircons from two samples (MHG2 and MHG9)
for TIMS analyses were air-abraded following proce-dures described by Krogh (1982). The abraded zircons
were cleaned by leaching with 8 N HNO3 and 6 N
HCL at 80 �C for 24 h in Teflon vessels. A known
amount of 205Pb–233U–235U mixed spike was added to
each vessel and the zircons were digested using a mixture
Table 3a
TIMS analytical data for the Munali Hills Granite, samples MHG2 and MH
Zircon %206Pbc U ppm Pb ppm 207Pb*/206Pb* age ±2r 206Pb*
MHG2A 9.566 331.8 68.3 1115.9 35.9 0.18436
MHG2B 0.718 189.0 38.8 1115.6 28.9 0.18606
MHG2C 0.420 275.3 51.5 1120.8 20.8 0.18882
MHG2E 1.541 290.4 54.2 1116.0 21.0 0.18606
MHG9A 1.068 205.6 46.9 1122.0 13.4 0.18464
MHG9B 0.581 227.4 51.8 1114.9 12.4 0.18919
MHG9D 0.429 152.7 30.1 1142.4 13.9 0.18936
Errors are 2r; Pbc and Pb* indicate the common and radiogenic portions, rCommon Pb corrected using blank and spike corrected 204Pb.
Common Pb composition calculated after Stacey and Kramers (1975) using
%C denotes percent concordance.
Table 3b
SHRIMP-II ion microprobe analytical data for the Munali Hills Granite, sa
Spot %206Pbc U
ppm
Th
ppm
232Th/238U
206Pb*/238U age
±1r 207Pb*/206Pb* age
MHG1-1 0.298 55.2 84.9 1.59 1063 15 1123
MHG1-2 <0.001 156.3 123.1 0.81 1060 12 1163
MHG1-3 <0.001 121.0 88.2 0.75 1061 15 1146
MHG1-4 0.237 190.7 159.4 0.86 1045 11 1064
MHG1-5 <0.001 132.5 114.0 0.89 1054 12 1135
MHG1-6 1.176 60.1 51.6 0.89 1064 16 1115
MHG1-7 0.740 69.8 84.1 1.24 1074 14 1159
Errors are 1r; Pbc and Pb* indicate the common and radiogenic portions, rCommon Pb corrected using measured 204 Pb.
Common Pb composition calculated after Stacey and Kramers (1975) using
%C denotes percent concordance.
of HF and HNO4. The total procedural Pb and U-
blanks were 2 pg and 0.1 pg, respectively. Common Pb
correction was made using Stacey and Kramers (1975)
model parameters at the apparent 207Pb/206Pb age. Anal-
yses were carried out on a Finningan MAT 262 mass
spectrometer, equipped with a secondary electron multi-plier-ion counter system.
Another seven clear and uncracked zircons from one
sample (MHG1) for SIMS analyses were polished to-
gether with the CZ3 zircon standard and imaged by
cathodoluminescence (CL). The mounted zircons were
analysed by SHRIMP-II ion microprobe under standard
operating conditions i.e., 6-scan cycle, 2 nA primary
O2� beam, 25 lm analytical spot size and mass resolu-tion of ca. 5000. The data processing procedure was sim-
ilar to that described by Nelson (1997). Errors on
individual analyses are given at the 1-r level based oncounting statistics, whereas errors on pooled analyses
are at 2-r level. Sample U/Pb ratios were corrected bynormalising to the CZ3 zircon standard, which has a
conventionally determined 206Pb/238U ratio of 0.0914,
corresponding to an age of 564 Ma (Pidgeon et al.,1994). The ages for both methods were calculated at
2r standard deviation, with the Isoplot/Ex program,
version 2.10, of Ludwig (1999). Results of the first age
determination of the Munali Hills Granite are presented
in Table 3a and 3b.
G9
/238U ±2r% 207Pb*/235U ±2r% 207Pb*/206Pb* ±2r% %C
7 0.52 1.952204 4.63 0.076796 1.80 97.7
1 0.46 1.969809 4.48 0.076784 1.44 98.6
4 0.44 2.004300 2.87 0.076985 1.04 99.5
1 0.44 1.970235 2.87 0.076800 1.05 98.6
5 0.45 1.961104 4.41 0.077030 0.67 97.4
3 0.44 2.002240 3.93 0.076756 0.63 100
4 0.45 2.031982 5.25 0.077826 0.70 97.9
espectively.
calculated apparent 207Pb/206Pb ages.
mple MHG1
±1r 207Pb*/235U ±1r% 206Pb*/238U
±1r% 207Pb*/206Pb*
±1r% %C
44 1.906 2.7 0.1793 1.5 0.0771 0.0017 94.7
28 1.939 1.9 0.1788 1.2 0.0787 0.0011 91.2
30 1.923 2.2 0.1789 1.5 0.0780 0.0012 92.6
35 1.815 2.1 0.1759 1.2 0.0748 0.0013 98.2
23 1.899 1.7 0.1776 1.2 0.07753 0.0009 92.9
190 1.900 9.6 0.1795 1.7 0.0768 0.0072 95.4
67 1.962 3.7 0.1813 1.5 0.0785 0.0027 92.7
espectively.
calculated apparent 207Pb/206Pb ages.
A
"" "
Q
P
Syenogranite Monzogranite Granodiorite
10 35 65 90Normative %
5
20
60
90
Fig. 4. Normative compositions of granitoids plotted on the classifi-
cation diagram of Streckeisen (1976). Q = quartz; A = (Or);
P = (Ab + An). Symbols: (�) = Munali Hills Granite; (�) = MpandeGneiss; (j) = Lusaka Granite; (m) = Nchanga Granite; (d) = Ngoma
Gneiss; (�) = felsic metavolcanic rocks. Q = quartz; A = Alkali feld-spar; P = plagioclase.
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 231
5. Results
5.1. Geochemical alteration
Because the samples analysed in this study have
undergone various degrees of metamorphism, mobileelements such as alkalies (K2O, Na2O), CaO, and large
ion lithophile elements (LILE: e.g., Rb, Sr, Ba, Th) have
been mobilised and thus may not represent original pre-
metamorphic concentrations. The chemical indices of
alteration (CIA, Table 2) of 49–54, and 42, are compa-
rable to those of unaltered granite and mafic rocks (50
and 42, respectively; Nesbitt and Young, 1982). How-
ever, inspection of Table 2 reveals that several sampleshave Na/K ratios atypical for normal felsic igneous
rocks, suggesting significant mobilisation of the alkalies.
The metabasite sample (SDA1) shows a high CIA value
of 84, indicating extreme alteration of the purported
basaltic parent rock (Smith, 1963; Mallick, 1966). All
the samples have low levels of loss on ignition
(LOI < 1 wt%) except the metabasite sample, which
has a relatively high value at 5.51 wt%. Most of theNchanga and Lusaka Granite samples have undergone
very low alteration and thus their element contents re-
flect, to a large extent, the original magmatic
concentrations.
In this study, geochemical characterisation and dis-
crimination of the granitoids and associated rocks were
based on rare earth elements (REE) and high field
strength elements (HFSE: e.g., Nb, Ta, Zr, Hf, Ti, P,Y) that are generally considered to be relatively immo-
bile during metamorphism (Rollinson, 1993; and refer-
ences therein). Geochemical characterisation schemes
that use mobile major element contents were employed
with caution especially for the most metamorphosed
samples.
5.2. Modal classification of analysed granitoids and
metavolcanic rocks
According to the classification of Chappell and White
(1974) and revised by Barbarin (1999), most granitoids
have mineralogical compositions (Table 1) compatible
with I-type granites, which share many chemical charac-
teristics with A-type granites. Accessory muscovite and
garnet are present in Nchanga Granite (NG4) andNgoma Gneiss (NGG3 and NGG5).
Point counting results plotted on the Q-A-P Streckei-
sen diagram (Streckeisen, 1976) show that all the grani-
toids are granite in composition. However, because the
granitoids are coarse-grained and, porphyritic, and only
one thin section per sample was counted, the counts
were biased towards compositions dominated by the
coarse-grained minerals, especially microcline. CIPW-normative compositions indicate that the granitoids
have compositions similar to monzogranite (Fig. 4).
5.3. Major and minor elements
The major-element contents of the granitoids andassociated rock samples show slight variations within
the same sample suite. The SiO2 content in all the grani-
toids and felsic metavolcanic rocks ranges from
67–76 wt%, with lower contents in the felsic metavolca-
nic rocks (68–72 wt%) and higher contents in the
Nchanga Granite (72–76 wt%). The variations of SiO2with other major elements are illustrated in the Harker
diagrams (Fig. 5a–h). Because data points represent dif-ferent granitoids, which are separated in space and time,
the plots are not intended to show magmatic evolution-
ary trends. In general, Fe2O3, TiO2, and P2O5, show a
coherent negative correlation with SiO2. CaO and to a
lesser extent MgO also show a negative correlation with
SiO2. K2O and Na2O, in contrast, show considerable
scatter, indicative of major element mobility during
metamorphism. Large ion lithophile elements such asRb, Th, and to a lesser extent Ba show poor correlation
with SiO2, indicating that the original contents of these
elements have also been modified by metamorphism
(Fig. 6a–d). High field strength elements (HFSE) repre-
sented by Zr show linear coherent trends. The Zr–SiO2diagram shows that the felsic metavolcanic and Ngoma
Gneiss samples have higher contents of Zr than the rest
of the samples. On the Zr/TiO2–Nb/Y diagram (Fig. 7a),most of the granitoids and felsic metavolcanic rocks plot
in fields ranging from rhyolite to rhyodacite (equivalent
to granitic compositions for plutonic rocks), whereas the
amphibolites and metabasite plot in the sub-alkaline
basalt field. The felsic metavolcanic rocks and metaba-
site plot in two chemically distinct compositional fields
(b)(a)
66 68 70 72 74 7666 68 70 72 74 76
SiO
2
2
012345678
1
2
3
4
0
0
1
2
3
4
5
SiO (wt %)2 SiO (wt %)2
PO
(wt%
)2
5N
aO
(wt %
)2
MgO
(wt%
)Ti
O(w
t%)
2Fe
O(w
t%)
23
KO
(wt%
)2
AlO
(wt%
)2
3 CaO
( wt%
)
(c) (d)
(e) (f)
(g) (h)
0.2
0.1
0.0
14
13
12
11
6
4
2
0
0.8
0.6
0.4
0.2
0.0
1.41.2
1.0
0.80.6
0.40.2
0.0
Fig. 5. Harker variation diagrams for major element oxides for the granitoid and felsic metavolcanic rocks. Symbols: (�) = Munali Hills Granite;
(�) = Mpande Gneiss; (j) = Lusaka Granite; (m) = Nchanga Granite; (�) = Ngoma Gneiss; (�) = felsic metavolcanic rocks.
232 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
with no intermediate (andesite) composition, in keeping
with the bimodal nature of these rocks inferred from
general lithological characteristics. On the SiO2–K2Odiagram (Fig. 7b), the Lusaka and Nchanga Granites,
which are less metamorphosed, compared to other
sample suites, plot in the high-K calcalkaline series field.
Although the rest of the samples are highly metamor-
phosed and deformed they also plot in the same field,
except for some Munali Hills Granite samples, which
plot in the shoshonitic series field, but we place no
significance on this discrimination due to the apparentdisturbance of K contents in most of these samples
(Table 2).
Granitoids were previously commonly classified into
three main types: I-S- and A-type (Chappell and White,
1974); however, this classification has evolved substan-
tially from the original use. Originally the S-type
granites were considered to result from partial melting
of metasedimentary source rocks; I-types from source
rocks of igneous origin that have not gone through the
surface weathering processes; and A-type or anorogenicgranites from rocks emplaced in settings that are far
from an orogenic belt. It is now known that the
I-S- and A-types can be generated in various ways and
settings (Barbarin, 1999). The aluminum saturation in-
dex (ASI: molar Al2O3/(CaO + Na2O + K2O)) (Zen,
1986) is used to distinguish between S-, and I-type gran-
ites (Chappell, 1999). We employed the ASI classifica-
tion scheme, keeping in mind its short-comings andapparent disturbance of CaO, Na2O and K2O in some
of our samples. On the SiO2–A/CNK diagram (Clarke,
1992) all the samples, except for the garnet-bearing
Nchanga Granite sample (NG 4), which falls in the
S-type granite field (A/CNK > 1.1), plot in the I-type
granite field (A/CNK < 1.1) (Fig. 7c). On the A/NK–
A/CNK diagram (Fig. 7d), the Munali Hills Granite
0.5 1.0 1.5
2.0
1.5
1.0
0.5
A/N
K
A/CNK
Peralkaline
Metaluminous Peraluminous
(a)
0.001 0.1 1 10
5
1
0.1
0.01
0.001
Rhyolite
Com/PantPhonolite
Trachyte
TrachyAnd
Alk-Bas Bsn/NphSub-Alkaline Basalt
Andesite
Andesite/Basalt
Rhyodacite/Dacite
Nb/Y
Zr/T
iO*0
.000
12
SiO (wt %)2
0
1
2
3
4
5
6
7
CALCALKALINE SERIES
HIGH K-CALCALKALINE SERIES
SHOSHONITIC SERIES
ARC THOLEITIITIC SERIES
KO
(wt%
)2
45 50 55 60 65 70 75
(b)
(d)
I-Type
S-TypePeraluminous
Metaluminous
SiO (wt %)2
65 70 75 80
2.0
1.5
1.0
0.5
A/C
NK
(c)
Fig. 7. Various chemical classification diagrams. (a) Zr/TiO2–Nb/Y diagram (Winchester and Floyd, 1977). (b) SiO2–K2O diagram (Gill, 1981). (c)
SiO2–A/CNK diagram (Clarke, 1992), where A/CNK = molar Al2O3/(CaO + Na2O + K2O), aluminum saturation index (ASI). (d) A/CNK–A/NK
diagram (Zen, 1986), where A/NK = molar Al2O3/(Na2O + K2O). Symbols: (}) = Munali Hills Granite; (�) = Mpande Gneiss; (j) = LusakaGranite; (m) = Nchanga Granite; (�) = Ngoma Gneiss (�) = felsic metavolcanics rocks; (h) = amphibolite; (�) = metabasalt.
Th(p
pm)
Rb
(ppm
)
Zr(p
pm)
Ba(p
pm)
66 68 70 72 74 76 66 68 70 72 74 76
SiO (wt %)2SiO (wt %)2
600
500
400
300
200
100
1250
1000
750
500
250
0
600
500
400
300
200
100
0
(a) (b)
100
80
60
40
20
0
(c)
0
(d)
Fig. 6. Harker variation diagrams for selected trace elements; Sr, Rb, Th, and Zr. Symbols: (}) = Munali Hills Granite; (�) = Mpande Gneiss;(j) = Lusaka Granite; (m) = Nchanga Granite; (�) = Ngoma Gneiss; (�) = felsic metavolcanic rocks.
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 233
and Mpande Gneiss samples and one garnet-bearing
Nchanga Granite sample plots in the peraluminous field
(A/CNK > 1), whereas the rest of the Nchanga and Lu-
saka Granites, Ngoma Gneiss, and felsic metavolcanic
rock samples plot in the metaluminous field (A/
CNK < 1). The garnet-bearing Ngoma Gneiss samples
do not plot in the peraluminous field as one would ex-
pect. The garnet is thus inferred to be metamorphic in
origin and to have formed during extensive recrystallisa-
tion and shearing of the gneiss. The lack of peralumi-
nous compositions in the garnet-bearing gneiss
samples implies that there has been further modification
of the bulk-rock major element chemistry subsequent to
garnet growth.
234 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
5.4. Rare earth element (REE) patterns
Chondrite-normalised REE distribution patterns for
all the granitoids and associated rocks are presented in
Fig. 8a–f. Samples in each suite show similar parallel,
conformable and strongly fractionated patterns ((La/Yb)N = 5–19). The granitoid rocks are enriched in light
rare earth elements (LREE) ((La/Sm)N = 2.34–4.39)
and relatively depleted in heavy rare earth elements
(HREE) ((Gd/Yb)N = 1.14–3.38), and exhibit weak to
moderate negative Eu-anomalies (Eu/Eu* = 0.15–0.77).
The Nchanga and Lusaka Granites have relatively flat
HREE patterns ((Gd/Yb)N = 1.14–1.71) compared to
the Munali Hills Granites and the Mpande and NgomaGneisses, which have slightly more depleted HREE
((Gd/Yb)N = 1.68–3.24). The LREE distribution pat-
terns for the felsic metavolcanic rocks (CR1, 2 and
KGR 2–5) and the metabasalt (SDA1) are parallel but
that for the metabasalt is more depleted in HREE and
lacks a negative Eu-anomaly. The amphibolites are
NG2
NG3
NG4
NG5
NG6
(c)
KGR2KGR3KGR4KGR5CR1CR2SDA 1
(e) Felsic metavolcanic rocksand metabasalt
Sam
ple/
Cho
ndrit
eSa
mpl
e/C
hond
rite
Sam
ple/
Cho
ndrit
e
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Nchanga Granite
MHG1MHG2MHG3MHG4MHG9MHG10MPD1MPD2
1
1
1
10
10
10
100
100
100
1000
1000
1000
(a) Munali Hills Granite and Mpande Gneiss
Fig. 8. Chondrite-normalised REE patterns (normalis
enriched in LREE (((La/Sm)N = 2.08–3.14) and rela-
tively depleted in HREE ((Gd/Yb)N = 0.96–1.91) and
also lack a Eu-anomaly.
5.5. Incompatible multi-element patterns
Chondrite-normalised incompatible multi-element
spider diagrams for the various granitoid suites and asso-
ciated rocks (Fig. 9a–f) exhibit generally similar con-
formable parallel patterns. The contents of LILE (Rb,
K, Sr and Ba) show coherent uniform patterns in all
the sample suites, in spite of evident petrographic alter-
ation and mobility of these elements. All the granitoids
and felsic metavolcanic rocks are enriched in Th andweakly depleted in Zr. The Munali Hills Granite,
Mpande Gneiss and to a lesser extent Lusaka Granite
samples exhibit relatively strong depletions in contents
of Nb and in some cases Ta, whereas the Ngoma Gneiss,
Nchanga Granite and felsic metavolcanic rocks show rel-
atively weak depletions in these elements. Compositional
LG1
LG2
LG5
LG6
(b)
(d)
MHG5cMHG5bMHG5a
(f) Amphibolites
Lusaka Granite
Sam
ple/
Cho
ndrit
eSa
mpl
e/C
hond
rite
Sam
ple/
Cho
ndrit
e
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Ngoma Gneiss
1
1
1
10
10
10
100
100
100
1000
1000
1000
NGG3NGG4NGG5
ation values from Taylor and McLennan, 1985).
KGR2KGR3KGR4KGR5CR1CR2I-typeA-t
Sam
ple/
Cho
ndrit
eSa
mpl
e/C
hond
rite
Sam
ple/
Cho
ndrit
e
0.1
1
10
100
1000
Sample/M
OR B
Amphibolites and metabasalt(f)
1
10
100
1000
(e) Felsic metavolcanic rocksMHG5aMHG5bMHG5cSDA1
1
10
100
1000
NGG3NGG4NGG5I-typeA-type
(d) Ngoma Gneiss
Ba Rb Th K Nb Ta La Ce Sr Nd P Sm Zr Hf Ti Tb Y
Ba Rb Th K Nb Ta La Ce Sr Nd P Sm Zr Hf Ti Tb Y
Ba Rb Th K Nb Ta La Ce Sr Nd P Sm Zr Hf Ti Tb Y
Ba Rb Th K Nb Ta La Ce Sr Nd P Sm Zr Hf Ti Tb Y
Ba Rb Th K Nb Ta La Ce Sr Nd P Sm Zr Hf Ti Tb Y
Sr K Rb Ba Th Ta Nb Ce P Zr Hf Sm Ti Y
0.1
1
10
100
1000
10000
NG2NG3NG4NG5NG6I-type
A-type
(c) Nchanga Granite
1
10
100
1000
LG1LG2LG5LG6I-typeA-type
Lusaka Granite(b)
1
10
100
1000
10000MHG1
MHG2
MHG3
MHG4
MHG8MHG10
MPD1
I-type
A-type
Munali Hills Granite and Mpande Gneiss(a)
MPD2
ype
Fig. 9. Chondrite-normalised incompatible multi-element spider diagrams (a) to (e) for granitoid and felsic metavolcanic rocks (normalisation values
from Thompson, 1982; Rb, K, P, from primitive mantle values of Sun, 1980). Compositional data for I-type granites (Chappell and White, 1992) and
A-type granites (Whalen et al., 1987) from Lachlan fold belt are plotted for comparison. (f) MORB-normalised diagram of ampbibolites and
metabasalt (normalisation values from Pearce, 1983).
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 235
data for continental-arc I-type granites (Chappell and
White, 1992) and A-type granites (Whalen et al., 1987)
from the Lachlan fold Belt are shown for comparison.The pronounced negative Nb-anomaly in the patterns
for the Munali Hills Granite and Mpande Gneiss resem-
ble those of I-type granites, whereas the rest of the grani-
toids and felsic metavolcanic rocks show patterns
comparable to those of A-type granites.
The mid-ocean ridge basalt (MORB)-normalised spi-
der diagrams for amphibolite and metabasalt samples
exhibit enrichments in contents of LILE and depletionsin HFSE. The contents of LILE in the amphibolites
have certainly been modified by amphibolite facies
metamorphism. The HFSE are flat and show nearly
MORB-like concentrations (HFSE/MORB � 1). The
fractionated LILE/HFSE pattern is generally recognized
as a distinct feature of subduction zone magmatism
(Winter, 2001; and references therein). The lack of a
negative anomaly in the HREE concentrations suggeststhat the magma source was not deep and garnet-bearing.
5.6. High field strength elements (HFSE)
Chemical compositions of granitoid rocks are com-monly used to provide information about tectonic set-
tings and source rock characteristics (Pearce et al.,
1984; Harris et al., 1986; Whalen et al., 1987; Eby,
1990, 1992). Geological interpretations have previ-
ously been used in evaluating the tectonic setting of
the granitoid rocks in the Lufilian–Zambezi belt. Here,
we employ various tectonic discrimination diagrams to
evaluate the tectonic settings or source rocks of thegranitoids in the belt (Fig. 10a–d). On the Nb–Y and
Ta–Yb diagrams of Pearce et al. (1984), practically all
data points plot in the attenuated continental litho-
sphere region of the within plate granite (WPG) field,
except for some Munali Hills Granite samples, which
plot in the volcanic arc granite (VAG) field (Fig. 10a
and b). On the Zr–Ga/Al diagram of Whalen et al.
(1987), the felsic metavolcanic rocks and Ngoma Gneissplot in the A-type field and the rest of the samples plot in
(a) (b)
Zr(p
pm)
(c)
Nb
(ppm
)
Ta(p
p m)
10000*Ga/Al
100
101
1000
10
I & S-Type A-Type
Y (ppm)
syn-COLG
WPG
VAG +
ORG
1000
100
10
1
1 10 100 1000Yb (ppm)
syn-COLG
WPG
VAGORG
100
10
1
0.1
0.1 1 10 100
Y
(d)
3*Ga
Nb
A1
A2
Fig. 10. Trace element discrimination diagrams for the granitoid and associated rocks. (a) Nb–Y and (b) Ta–Yb) diagrams (Pearce et al. (1984). (c)
Zr–Ga/Al diagram (Whalen et al., 1987). (d) Y–Nb–Ga diagram (Eby, 1992). WPG = within plate granites; VAG = volcanic arc granite; syn-
COLG = syn-collision granite; ORG = ocean ridge granite; A1 = continental rift or intraplate granitoids; A2 = continent-continent collision or
island-arc granitoids. Symbols: (�) = Munali Hills Granite; (�) = Mpande Gneiss; (j) = Lusaka Granite; (m) = Nchanga Granite; (�) = NgomaGneiss (�) = felsic metavolcanic rocks.
236 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
and close to the I-S type field (Fig. 10c). Eby (1992) di-
vided A-type granitoids (WPG) into two main groups.
One group, the A1-subtype, represents ‘‘true’’ anoro-
genic WPG emplaced in continental rifts. The other
group, the A2-subtype, is associated with convergent
plate-tectonic settings, i.e., emplaced during extensional
collapse of an orogenic belt. On the Nb–Y–Ga diagramof Eby (1992), most of the data points plot in the A2-
subtype field (Y/Nb > 1.2), except for three samples,
i.e., Nchanga Granite (NG2, 5) and Ngoma Gneiss
(NGG5), which plot in the A1-subtype (Y/Nb < 1.2)
(Fig. 10d).
The amphibolite and metabasite samples plot in di-
verse fields on various tectonic discrimination diagrams
(Fig. 11a–d). On the Zr/Y–Zr diagram (Fig. 11a) ofPearce and Norry (1979), two amphibolite samples
(MHG5a, b) and the metabasite sample plot in the with-
in plate basalt (WPB) field, whereas one sample
(MHG5c) plots in the overlap region between island
arc basalts (IAB) and MORB fields. On the Hf–Th–
Nb diagram (Fig. 11b) of Wood (1980), all the samples
plot in the continental arc basalt (CAB) field, whereas
the data points are scattered on the Nb–Zr–Y diagram
(Fig. 11c) of Meschede (1986) and Ti–Zr–Y diagram
(Fig. 11d) of Pearce and Cann (1973).
5.7. U–Pb zircon geochronology
5.7.1. TIMS zircon results
U–Pb data were obtained from two varieties of theMunali Hills Granite: samples MHG2 and MHG9.
Sample MHG9 is dark grey weakly foliated granite
gneiss, whereas MHG2 is a pink unfoliated, leucocratic
granite gneiss. In both samples, prismatic, clear to trans-
lucent, idiomorphic zircons with the least number of
inclusions and no visible inherited cores were selected
for analysis (Fig. 12a). All the seven TIMS analyses
are >97% concordant and show three distinct concor-dant age populations; three grains (MHG2C, 2B and
9D) = 1116.2 ± 1.0 Ma (MSWD = 1.9); two grains
(MHG2B and 2E) = 1098.9 ± 1.2 Ma (MSWD = 0.90)
and two grains (MHG2A and 9A) = 1090.1 ± 1.3 Ma
(MSWD = 1.4). Regression of all the seven data points
through the origin yielded an upper intercept age of
1119 ± 24 Ma (MSWD = 0.04) (Fig. 13a). Because of
the high concordance of all the three zircon populations,
10 100 10001
10
20
Zr (ppm)
Zr/Y A
CB
A: Within plate basalts B: Island arc basaltsC: Mid-ocean ridge basalts (MORB)
(a) (b)
Hf/3
Nb/16Th
Nb*2
YZr/4
AI
AIIB
D
C
B
A
D
C
Zr Y*3
Ti/100
CB
AD
(c) (d) A-B: Low-K tholeiitesB: Ocean floor basaltsB-C: Calcalkaline basaltsC: Continental arc basaltsD: Within plate basalts
A: N-tpye MORBB: E-type MORBC: Within plate basaltsD: Destructive plate- margin basalts
AI, AII: Within plate alkaline basaltsAII, C: Within plate tholeiitesB: P-MORBC-D: Volcanic arc basaltsD: N-MORB
Fig. 11. Various tectonic discrimination diagrams for basaltic rocks. (a) Zr/Y–Zr diagram (Pearce and Norry, 1979). (b) Hf–Th–Nb diagram (Wood,
1980). (c) Nb–Zr–Y diagram (Meschede, 1986). (d) Ti–Zr–Y diagram (Pearce and Cann, 1973). Symbols: (h) = amphibolite; (r) = metabasalt.
Fig. 12. Images of zircons used in the U–Pb zircon age determination. Photomicrographs of (a) zircons from sample MHG2 and (b) zircons from
sample MHG9. The photomicrographs were taken in transmitted light under cross-polars. The zircons are 200–250 lm in length. (c) and (d) are
cathodoluminescence images of zircons from MHG1 showing spots analyzed by SHRIMP-II ion probe.
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 237
we consider the two older populations of 1116.2 ±
1.0 Ma and 1098.9 ± 1.2 Ma to reflect inherited xeno-
crysts from the host Mpande Gneiss, which has a U–
Pb zircon age of 1106 ± 19 Ma (Hanson et al., 1994)
207Pb/235U
1140
1100
1060
1020
980
0.155
0.165
0.175
0.185
0.195
1.5 1.6 1.7 1.8 1.9 2.0 2.1
206 Pb
/238 U
Intercepts at0 ± 0 and 1129 ± 34 Ma(MSWD = 2.0)
(b) Sample MHG1
1130
1120
110
1100
1090
10800.182
0.184
0.186
0.188
0.190
0.192
1.8 1.9 2.0 2.1 2.2207Pb/235U
Intercepts at0 ± 0 and 1119 ± 24 Ma(MSWD= 0.04)
(a)
206 Pb
/238 U
1110
1100
1000
Samples MHG2 and 9 MHG2C, 9B and 9D= 1116.2 ± 1.0 Ma (MSWD = 1.9)
MHG2B and 2E= 1098.9 ± 1.2 Ma(MSWD = 0.90)
MHG2A and 9A= 1090.1 ± 1.3 Ma(MSWD = 1.4)
Fig. 13. U–Pb Concordia diagrams (a) TIMS data form MHG2 and 9
showing three distinct highly concordant zircon populations (b)
SHRIMP data for sample MHG1 yielded an upper intercept age of
1129 ± 34 Ma (MSWD = 2.0). Error ellipses are at 2r level.
238 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
and interpret the youngest population of 1090.1 ±
1.3 Ma to represent the igneous crystallisation age of
the Munali Hills Granite. The data show that the
Mpande Gneiss and Munali Hills Granite form part of
a multi-phase intrusion in which at least three separate
magmatic pulses are recorded.
5.7.2. SHRIMP-II zircon results
Cathodoluminescence (CL) imaging of the selected
zircons from sample MHG1, which is similar to sample
MHG2, revealed broad zoning patterns, consistent with
magmatic growth (Fig. 12c, d). In some cases, medium
to low reflectance zones truncate the oscillatory pat-
terns, possibly indicating post-crystallisation distur-
bance of the crystal structure. Wherever possible,
regions selected for analysis, were located within themagmatic crystal domains. Seven analyses were con-
ducted on seven zircon grains. Common Pb was gener-
ally low and ranges from 0% to 1.18%. Contents of U
and Th range from 55–191 ppm and 52–159 ppm,
respectively, resulting in Th/U ratios in the range 0.75–
1.59, typical for magmatic zircon. The data vary from
98% to 91% concordant, and define a cluster with
weighted mean 207Pb/206Pb age of 1133 ± 26 Ma
(MSWD = 0.90). Because of the generally low U content
of the zircons, the analytical errors on each individualdata point are quite large. Moreover, the common Pb
correction, which is based on the relatively low counts
on 204Pb, is apparently inaccurate. On the Concordia
diagram, linear regression of data points through the
origin yielded an upper intercept age of 1129 ± 34 Ma
(MSWD = 2.0) (Fig. 12c), which is, within error, similar
to the age obtained by TIMS.
In view of the large errors associated with SHRIMPanalyses due to low concentrations of U in the zircons,
we have adopted the more accurate TIMS results to
represent the crystallisation age of the Munali Hills
Granite. It is noteworthy, however, that all the 14 zir-
cons analyzed by TIMS and SHRIMP methods yielded
ages older than 1000 Ma, strengthening our case for the
Mesoproterozoic age of the Munali Hills Granite.
6. Discussion
6.1. Bulk composition of source rock(s) for the
granitoids and associated rocks
Because the contents of CaO, K2O and Na2O have
clearly been affected by secondary alteration and meta-morphism, the K2O–SiO2 and ASI discrimination dia-
grams (Fig. 7b–d) are only potentially useful for
weakly metamorphosed samples such as those for the
Lusaka and Nchanga Granites. Both the Lusaka and
Nchanga Granite samples have high-K calcalkaline,
metaluminous, and I-type compositions. We infer that
these compositional features are primary, suggesting
that the granites were derived from mixed crustalsources that were previously emplaced in a continental
convergent plate setting (Barbarin, 1999). One peralumi-
nous Nchanga Granite sample (NG4) contains garnet,
which is inferred to be of restitic origin. This inference
is supported by lack of metamorphic growth of other
minerals e.g., feldspars, to suggest that the garnet is of
in-situ metamorphic origin. In contrast, the garnet in
Ngoma Gneiss samples is most likely metamorphic be-cause the rock has been strongly metamorphosed and
sheared.
The fractionated REE and incompatible multi-
element patterns of all the granitoids and felsic metavol-
canic rocks are typical of felsic continental crust. The
Eu-anomalies in the chondrite-normalised REE dia-
grams indicate a plagioclase-depleted crustal source or
fractionation during magmatic differentiation. Thechondrite-normalised REE patterns of amphibolites
lack a Eu-anomaly and exhibit enrichments in LREE
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 239
with respect to HREE. The pattern is similar to enriched
MORB or MORB contaminated with continental crust.
6.2. Tectonic setting
The Neoproterozoic granitoids and felsic metavolca-nic rocks generally exhibit WPG (A-type granite) affini-
ties. A-type granites are characterised by high contents
of (Na2O + K2O), Ga/Al, Zr, Y, Nb and low abun-
dances of CaO and MgO, and contain one or more fer-
romagnesium minerals such as annite-rich biotite,
ferrohastingsite, alkali amphibole and sodic pyroxene
(e.g., Collins et al., 1982; Whalen et al., 1987; Eby,
1990). The mineralogical and trace element composi-tions of all the Neoproterozoic granitoids and felsic
metavolcanic rocks are not consistent with ‘‘true’’ conti-
nental-rift settings as previously suggested (cf. Fig. 10d;
Eby, 1992). The felsic metavolcanic rocks and Ngoma
Gneisses have WPG affinities in keeping with previous
interpretations (Wilson et al., 1993; Hanson et al.,
1994; Munyanyiwa et al., 1997; Vinyu et al., 1999;
Porada and Berhorst, 2000). The felsic metavolcanicrocks (ca. 880 Ma) and Ngoma Gneiss (ca. 820 Ma)
have been correlated with broadly coeval peralkaline
metavolcanics in the Makuti Group (ca. 854 Ma) and
with granites of the Basal Rushinga Intrusive Complex
(BRIC, ca. 804 Ma) in the Zambezi belt of Zimbabwe
(Munyanyiwa et al., 1997; Dirks et al., 1999; Hanson
et al., 1994; Vinyu et al., 1999; Porada and Berhorst,
2000). However, mineralogical and chemical composi-tions indicate that the correlatives in Zambia are not
peralkaline.
Porada and Berhorst (2000) proposed that continen-
tal rifting in the Lufilian–Zambezi belt started at ca.
880 Ma, resulting in the formation of the Katanga rift
basin. Tembo et al. (1999) concluded from the geochem-
istry of metagabbros in the Lufilian belt that rifting did
not progress beyond the continental stage. However,John et al. (2003) interpreted the MORB-like trace
element contents of eclogites, metagabbros and gabbros
as evidence of the existence of ocean crust in the
Lufilian–Zambezi belt, which was subducted at about
595 Ma during the amalgamation of the Gondwana
supercontinent. The felsic metavolcanic rocks (879 Ma)
were interpreted to mark the beginning of continental
rifting in the Zambezi belt (Hanson et al., 1994). Mostauthors (e.g., Porada and Berhorst, 2000; John et al.,
2003) have suggested that continental rifting in the
Lufilian–Zambezi belt was associated with the break-
up of the Rodinia supercontinent at ca. 900 Ma. Porada
and Berhorst (2000) linked the formation of the Neopro-
terozoic granitoids and felsic metavolcanic rocks in the
belt to the break-up of the Rodinia supercontinent.
However, Kroner and Cordani (2003) have argued thatthis part of Africa did not form part of the Rodinia
supercontinent.
Most authors argue that felsic granitoid chemistry re-
flects the tectonic settings of the source rocks (e.g.,
Whalen et al., 1987; Forster et al., 1997). On the basis
of mineralogical, HFSE and REE contents, and regional
geological data, we infer that the Ngoma Gneiss, felsic
metavolcanics rocks, and Nchanga and Lusaka Graniteswere emplaced in an extensional WPG setting. The high-
K calcalkaline, metaluminous and I-type compositions
of the Lusaka and Nchanga Granites indicate that these
rocks were derived from sources emplaced in a continen-
tal convergent plate setting. However, most studies have
shown that A-type granitoids exhibit heterogeneous
chemistry (Forster et al., 1997). In the Lufilian belt there
is no evidence of the existence of a continental arcaround 880 Ma. Dirks and Sithole (1999) interpreted
the P–T and age data of eclogites in the Zimbabwean
part of the Zambezi belt to be related a major a colli-
sional event associated with the assembly of the Rodinia
supercontinent. In contrast, based on a Sm–Nd age of
595 Ma and P–T data, John et al. (2003) concluded that
the eclogites in the Zambian part of the belt were formed
during subduction of oceanic crust during the assemblyof the Gondwana supercontinent. Although the studied
Neoproterozoic felsic rocks in the Lufilian–Zambezi belt
exhibit strong A-type granite features, they lack evi-
dence of generation in a ‘‘true’’ continental-rift setting
as previously suggested. On the basis of the A-type gran-
ite features and independent regional geological and
geochronological data, we suggest that the Neoprotero-
zoic granitoids and felsic metavolcanic rocks wereemplaced during the earliest extensional stages of conti-
nental rifting in the Lufilian–Zambezi belt. The apparent
continental-arc like chemistry of the granitoids and fel-
sic metavolcanic rocks is thus derived from older calcal-
kaline rocks in the region, which were previously
affected by continental arc magmatism.
The variable geochemical compositions of granitoids
and felsic metavolcanic rocks, and Neoproterozoicmafic volcanic activity in the Lufilian–Zambezi belt indi-
cate a more complex, possibly progressively evolving
extensional regime than previously suggested. Clearly
much more geochronological and geochemical data are
required to fully understand the precise tectonic and
magmatic evolution of the felsic igneous rocks.
The Mesoproterozoic Munali Hills Granite and
Mpande Gneiss exhibit geochemical characteristics,particularly the Nb–Ta depletions relative to LILE,
indicating that these granitoids were emplaced in a con-
vergent-margin setting or derived from a source previ-
ously affected by subduction. The regional setting,
chemistry, and Mesoproterozoic ages suggest that these
granitoids were emplaced during the Irumide orogeny in
a convergent-margin setting, and were subsequently re-
worked by the Neoproterozoic Lufilian–Zambezi oro-geny. The trace element contents of amphibolites that
are associated with the Munali Hills Granite fall in
240 C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244
diverse fields on tectonic discrimination diagrams (Fig.
11), including that of continental arc basalts (CAB),
but show a distinct LILE/HFSE pattern generally recog-
nized in subduction zones. Field relations between the
Munali Hills Granite and the amphibolites suggest that
the two units are probably co-magmatic. This bimodal,coeval relationship is common in continental magmatic
arcs and a good example is from Central Madagascar
(Handle et al., 1999; McMillan et al., 2003). The conti-
nental-arc setting for the Munali Hills Granite-amphib-
olite suite is supported by remnants of Mesoproterozoic
ocean crust, juvenile island arcs and ophiolites elsewhere
in the region (Johnson and Oliver, 2000, 2004; Tembo
et al., 2000).
6.3. Regional correlation
The new age of 1090.1 ± 1.3 Ma for the Munali Hills
Granite provides new constraints on correlation and tec-
tono-thermal activity in the Lufilian–Zambezi belt. The
age of the Munali Hills Granite also has regional signif-
icance because it is similar to the 1088 Ma continentalarc granite gneisses and granulites in the Chewore inliers
in Zimbabwe (Goscombe et al., 2000; Johnson and
Oliver, 2004).
The Zambezi belt supracrustal rocks are generally
correlated with the Katanga supracrustal rocks in the
Lufilian belt based on broad lithological similarities
(De Swardt and Drysdall, 1964; Moore, 1964; Unrug,
1983; Coward and Daly, 1984; Wilson et al., 1993).The Nchanga Granite and Lusaka Granite are both in-
ferred to be unconformably overlain by supracrustal
rocks, which have been correlated across the MDZ
(Moore, 1964; Simpson et al., 1965; Porada and
Berhorst, 2000). The maximum age of the supracrustal
rocks in the Zambezi belt is constrained by the age of
the felsic metavolcanic rocks (ca. 879 Ma), which occur
at the structural base of the succession.The U–Pb zircon age of the Munali Hills Granite
determined in this study is not consistent with the previ-
ous suggestions, which are based on geological interpre-
tations (Hanson et al., 1994; Porada and Berhorst,
2000), that the pluton could be pre- to syn-tectonic with
respect to the Zambezi orogeny (ca. 550 Ma). Instead,
the new age supports earlier interpretations (Smith,
1963; Mallick, 1966; Hanson et al., 1988b) that theMunali Hills Granite is a younger phase of the Mpande
Gneiss and, therefore, constitutes part of the Mesopro-
terozoic basement.
The new age of the Munali Hills Granite does not
seem to help resolve correlation problems in the Lufil-
ian–Zambezi belt in Zambia either. Hanson et al.
(1988b) provided a detailed map (their Fig. 3) that
shows inferred xenoliths of adjacent metasedimentsin the Munali Hills Granite. The strike of the foliation
in the xenoliths is shown to be similar to that of the
country rocks. These field observations were interpreted
to indicate intrusive relations between the Munali Hills
Granite and the adjacent country rocks. Our zircon
age conflicts with the earlier interpretation that the
supracrustal rocks intruded by the Munali Hills Granite
belong to the Neoproterozoic supracrustal succession inthe Zambezi belt (Smith, 1963; Mallick, 1966; Hanson
et al., 1988b). If the inferred xenoliths are of the Neo-
proterozoic Nega Formation, as Fig. 3 of Hanson
et al. (1988b) suggests, then these rocks are not xenoliths
but instead represent outliers of the Nega Formation,
which unconformably overlie the Munali Hills Granite
and Mpande Gneiss as earlier suggested by Smith
(1963). If we accept that an intrusive relation exists be-tween the Munali Hills Granite and the supracrustals,
as suggested by Hanson et al. (1988b), then the regional
lithostratigraphy requires that we re-assign some units
of the Zambezi supracrustals such as those composing
xenoliths in the Munali Hills Granite to an older se-
quence and others to the Neoproterozoic Katanga
Supergroup (Fig. 2). A likely candidate for regional cor-
relation of these older successions within the Zambezibelt would be the Paleoproterozoic Muva Supergroup,
which occurs in the Irumide belt to the northeast (De
Waele and Mapani, 2002; De Waele et al., 2003). How-
ever, the carbonate or calc-silicate sequences in the
Zambezi belt most likely belong to the Katangan Super-
group rather than the Muva Supergroup, which lacks
extensive carbonate or calc-silicate rocks (De Waele
and Mapani, 2002).Porada and Berhorst (2000) reviewed in detail poten-
tial problems in any attempts to correlate the entire se-
quence of Zambezi supracrustals with the Katanga
Supergroup. On the basis of inverted stratigraphies in
the area (Mallick, 1966), and the fact that the Zambezi
belt abuts against the Choma-Kalomo batholith
(1345–1200 Ma, Hanson et al., 1988a) to the south
and Irumide belt (ca. 1020 Ma, De Waele et al., 2003)to the north, Porada and Berhorst (2000) argued that
there could be some vestiges of older metasediments in
the Zambezi belt, which are now intersliced with the
younger Neoproterozoic Zambezi supracrustal rocks.
One other possible candidate that may belong to the
older succession is the Mulola Formation (Porada and
Berhorst, 2000), a sequence of quartzites, schists and
phyllites in the vicinity of the Mpande Dome (Smith,1963; Mallick, 1966). Similar lithologies are reported
in the Paleoproterozoic succession in the Irumide belt
(De Waele and Mapani, 2002). The Mulola Formation
was interpreted by Porada and Berhorst (2000) to have
originally been stratigraphically located below the Zam-
bezi supracrustal succession-implying that it is Meso-
proterozoic or older- and, in this interpretation, was
thrusted onto the Kafue metavolcanic rocks and inters-liced with younger units that belong to the Neoprotero-
zoic Katanga Supergroup. In this scenario, the Munali
C. Katongo et al. / Journal of African Earth Sciences 40 (2004) 219–244 241
Hills Granite would have intruded during the Irumide
orogeny and the date for it provides the minimum age
of the metasediments in the area.
7. Conclusions
We conducted fieldwork and collected samples of
granitoids, metavolcanic rocks and amphibolites in the
Lufilian–Zambezi belt of Zambia, and carried out
reconnaissance whole-rock chemical analyses in order
to evaluate their chemical characteristics and possible
regional tectonic settings. In addition, we have obtained
a new U–Pb zircon age for the Munali Hills Granite,which places new constraints on regional correlations
and tectono-thermal activity in the Lufilian–Zambezi
belt. The following conclusions have been drawn from
the results of this study:
(1) Mineralogical features, immobile element contents
and CIPW normative compositions of all the grani-
toids and felsic metavolcanic rocks indicate that
these rocks are of granitic composition. The amphibo-lites and metabasalt have sub-alkaline basalt com-
positions.
(2) Because most samples are metamorphosed, con-
tents of mobile major elements such as CaO, K2O, and
Na2O were disturbed. The geochemical classification
schemes based on these major elements were employed
for classifying and interpreting only the least deformed
and metamorphosed Lusaka and Nchanga Granites.These granites have high-K calcalkaline, metaluminous
and I-type characteristics. The rest of the granitoids
and felsic metavolcanic rocks exhibit similar features
but we place no significance on these results.
(3) Although the studied Neoproterozoic granitoids
and felsic metavolcanic rocks, in the Lufilian–Zambezi
belt, exhibit A-type granite trace element features, there
is no geological and geochronological evidence in sup-port of the previous suggestion that they were emplaced
in a ‘‘true’’ continental-rift setting. We suggest that the
Neoproterozoic granitoids and felsic metavolcanic rocks
were emplaced during the earliest extensional stages of
continental rifting in the Lufilian–Zambezi belt. The
apparent continental-arc like chemistry of the granitoids
and felsic metavolcanic rocks thus reflect the presence of
calcalkaline rocks in the region, which were influencedby continental arc processes.
(4) The tectonic discrimination diagrams did not un-
iquely characterise the tectonic setting for the Munali
Hills Granite and the Mpande Gneiss. The chondrite-
normalised spider diagrams for the Munali Hills Granite
and Mpande Gneiss exhibit Nb and Ta depletions rela-
tive to LILE (including Th), indicating that these grani-
toids were emplaced in a convergent-margin setting.Similarly, MORB-normalised spider diagrams for
coeval amphibolites exhibit a fractionated LILE/HFSE
pattern recognized in subduction zones. The continen-
tal-arc setting for the Munali Hills Granite-amphibolite
suite is supported by remnants of Mesoproterozoic
ocean crust, juvenile island arcs and ophiolites elsewhere
in Irumide belt in Zambia and Zimbabwe.
(5) The Munali Hills Granite yielded a concordantU–Pb zircon igneous crystallisation age of 1090.1 ±
1.3 Ma, which is consistent with the age of the host
Mpande Gneiss, but much older than previously consid-
ered. The new age indicates that the entire Zambezi
belt supracrustal rocks cannot be correlated with the
Katanga Supergroup in the Lufilian belt. We propose
that some lithologies previously thought to be Neopro-
terozoic in age, e.g., the Nega Formation (if the intrusiverelations with the Munali Hills Granite are accepted)
and the Mulola Formation, be re-assigned to an succes-
sion, pre-dating �1.1 Ga, possibly the PaleoproterozoicMuva Supergroup.
Acknowledgments
We thank the Austrian Academic Exchange Service
(OAD) for a PhD stipend and financial support for both
fieldwork and analyses (to C. Katongo). The Geology
Department, University of Zambia, is gratefully
thanked for logistical support and use of facilities for
sample preparation. Laboratory work in Vienna was
supported by the Austrian FWF grant Y58-GEO (to
C. Koeberl). We are grateful to Mr. P. Nagl (Universityof Vienna, Department of Geological Sciences) for help
with the XRF analyses. The authors acknowledge finan-
cial support for SHRIMP-II U–Pb zircon analyses from
the Australian Research Council through the Tectonic
Special Research Centre, and a Curtin University Inter-
national Postgraduate Research Scholarship (to B. De
Waele). We thank the Associate Editor Prof. A.B Kam-
punzu, and two reviewers; Prof. R.E. Hanson and Dr. S.Johnson for very constructive and helpful comments,
which greatly improved the original version of the
manuscript.
The co-authors would like to dedicate this paper to
the first author, Crispin Katongo, who passed away
after a short illness on July 18, 2004, at the age of 38,
shortly after completing his PhD at the University of
Vienna. We are mourning the loss of a promising col-league and a fine human being.
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