Petrography, geochemistry, and geochronology of granitoid rocks in the Neoproterozoic-Paleozoic...

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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).

mailto:[email protected]

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


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.


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).


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


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.


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


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.


229

l2


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.


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.


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.


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.


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



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




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





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).


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.


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.


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.


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


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


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


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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Petrography, geochemistry, and geochronology of granitoid rocks in the Neoproterozoic-Paleozoic...

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