The Zimbabwe Craton in Mozambique: A brief review of its geochronological pattern and its relation to the Mozambique Belt

Accepted Manuscript The Zimbabwe Craton in Mozambique: A brief review of its geochronological pattern and its relation to the Mozambique Belt F.R. Chaúque, U.G. Cordani, D.L. Jamal, A.T. Onoe PII:

S1464-343X(17)30026-2

DOI:

10.1016/j.jafrearsci.2017.01.021

Reference:

AES 2787

To appear in:

Journal of African Earth Sciences

Received Date: 25 May 2016 Revised Date:

15 January 2017

Accepted Date: 16 January 2017

Please cite this article as: Chaúque, F.R., Cordani, U.G., Jamal, D.L., Onoe, A.T., The Zimbabwe Craton in Mozambique: A brief review of its geochronological pattern and its relation to the Mozambique Belt, Journal of African Earth Sciences (2017), doi: 10.1016/j.jafrearsci.2017.01.021. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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THE ZIMBABWE CRATON IN MOZAMBIQUE: A BRIEF REVIEW OF ITS

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GEOCHRONOLOGICAL PATTERN AND ITS RELATION TO THE MOZAMBIQUE

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BELT

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Chaúque, F.R.1; Cordani, U.G.2; Jamal, D.L3; Onoe, A.T.2. 1.

National Institute for Mines, Praça 25 de Junho, 380, CP.4605, Maputo, Mozambique.

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Institute for Geosciences, University of São Paulo, Brazil.

Departament of Geology, Eduardo Mondlane University, Maputo, Mozambique.

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E-mail: [email protected]

ABSTRACT

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The eastern margin of the Zimbabwe Craton, along the Mozambique-Zimbabwe border, includes

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the oldest rocks of west-central Mozambique constituting a large terrain of granite-greenstone

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type dated between 3000 and 2500 Ma. These rocks consist mainly of gneisses and granitoid

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rocks of tonalitic-trondhjemitic-granodioritic composition belonging to the Mudzi Metamorphic

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Complex in the northern part and to the Mavonde Complex in the southern part. The latter is

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associated with a granite-greenstone terrain, which includes the eastern part of Mutare-Odzi-

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Manica greenstone belt. A volcano-sedimentary sequences cover, belonging to the apparently

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Mesoproterozoic and Paleoproterozoic Umkondo and Gairezi groups respectively was deposited

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along the eastern margin of the craton and is exposed in the territory of Mozambique. The

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Umkondo minimum age is marked by intrusive dolerite in Zimbabwe dated at 1100 Ma while for

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the Ghairezi it is still not well established. The Gairezi Group was subjected to progressive

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metamorphism of Pan-African age. At the margin of the Zimbabwe Craton, in its northern part,

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metasedimentary units occur representing a passive margin of Neoproterozoic age. They make

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up the Rushinga Group, which includes felsic metavolcanic rocks dated at ca.800 Ma.

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Granulites and medium- to high-grade paragneisses, and migmatites of the Chimoio, Macossa

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and Mungari Groups of Neoproterozoic metamorphic age, overly the ortho-metamorphic pre-

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existing rock of ca. 1100 Ma, which belongs to the Báruè Magmatic Arc. They characterise the

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N-S trend Mozambique Belt, which appears to the east of the craton tectonically juxtaposed on

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the Archean rocks. The maximum age of deposition of these rocks, indicated by U-Pb dating of

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detrital zircons, is ca. 700 Ma and their minimum age is limited by a few monzonitic Cambrian

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intrusions dated at ca. 500 Ma.

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The Neoproterozoic bimodal Guro Suite, dated at ca. 850 Ma and composed of felsic and mafic

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members characterizes the east-dipping outer rim of the craton margin in the north. The felsic

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member comprises the Serra Banguatere aplitic granite gneiss-migmatite and the mafic member

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consists of the Magasso metagabbro and mafic gneiss-migmatite. The geochemical signature and

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bimodality are all characteristics of anorogenic, A-type granites.

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The tectono-thermal effects of the Pan-African orogenic event, of approximately 500 Ma, are

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visible along the margin of the Zimbabwe Craton. Deformation and metamorphism are

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progressive from the craton towards the belt, from greenschist facies to granulite facies. The

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main suture in the study area shall be placed along the frontal thrusts of the Mungari and

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Macossa/Chimoio nappes of Neoproterozoic to Cambrian age. To the west of the suture the

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rejuvenated margin of the craton occurs, indicated by K-Ar dating. To the east, the Mozambique

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Belt occurs with its paragneisses of the Neoproterozoic overlaying the Mesoproterozoic

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granitoids of the Báruè magmatic arc.

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Keyword: Geochronology, tectonic evolution, Mozambique belt, Zimbabwe craton

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INTRODUCTION

The study area is located at the west-central region of Mozambique and corresponds to the

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southern end of the Mozambique Belt. At a regional scale, it is part of the north-eastern

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boundary of the Neoproterozoic Kalahari Craton (Fig.1). This is a very complex area in which

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several intricate tectonic and structural features occur, including collisional closures of different

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ages. The tectonic history of these components is still disputed, so a good correlation between

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the tectonic units depends on an adequate coverage of robust geochronological data. In the study

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area, geological control data are available from the work of the Geological Survey of Finland-

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GTK consortium (GTK, 2006), but the number of available rock ages is still very small and, as a

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result, the geochronological control remains insufficient. On the other hand, the region is of great

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geotectonic importance and trying to ascertain the extent and characteristics of the Pan-African

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orogeny in the southern part of the Mozambique Belt is of significant interest.

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The Neoproterozoic Kalahari Craton, along the border between Zimbabwe and Mozambique,

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includes the Archaean Zimbabwe cratonic nucleus, which has remained tectonically stable since

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the end of the Paleoproterozoic orogenies at ca. 2000 Ma. The Zimbabwe Craton is one of the

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three major crustal domains of the proto-Kalahari. The two other are the Kaapvaal Craton in the

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southern part and the Limpopo Belt located between the Zimbabwe and Kaapvaal cratons. Each

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of these main domains is a complex geotectonic unit with distinctive tectono-stratigraphic

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characteristics with a long Archean history and is separated by the two other domains by means

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of mega-shear zones (Fig. 2).

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In the south-eastern part of the Zimbabwe Craton, along its eastern margin, the Umkondo Group

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characterized by Nyanga facies, from Zimbabwe, whose Mesoproterozoic age is established by

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the mafic magmatism of Umkondo at ca.1100 Ma that crosscut the sequence, was deposited.

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Along the eastern part of the Umkondo Group, there are the Paleoproterozoic Gairezi facies,

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Figure 1.Gondwana reconstruction (after Lawver et al. 1998). The model assumes the collision and amalgamation of three major lithospheric plates: East, West and South Gondwana. Key: PC = Palgat-Cauvery Shear Zone; RC = Rayner Complex; A = Achankovil Shear Zone; GC = Grunehogna cratonic fragment; H = Heimefrontflella; RF = Ranotsara Shear Zone; U = Urfjell; N = Namama Shear Belt; O = Orvinfjella Shear Zone; M = Manica Shear Zone (adapted from Grantham et al. 2003). The study area shown in Figure 2 is here marked as a rectangular box.

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whose depositional age is dated at ca. 2000 Ma, from Mozambique. Farther north, along the

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north-eastern border of the craton, another sedimentary sequence, the Rushinga Group, also

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occurs, which is considered to be a marginal basin. The age and genetic relationships of these

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lithological units are not resolved and GTK (2006) suggested a similar depositional age for both

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the Gairezi and Rushinga sequences, at ca. 2000 Ma, based on preliminary U-Pb data on detrital

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zircons.

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This paper discusses the geotectonic relations between the Zimbabwe Craton, its covers and the

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Mozambique Belt. The main purpose of the study is to establish the boundaries of the Zimbabwe

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Craton with the Pan-African mobile belt, making use of an updated compilation of existing

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geochronological data, with the addition of some original U-Pb, K-Ar and Sm-Nd data

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Figure 2. Geological map of the study area (C). In inserting on map B shows the location and tectonic framework.

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on single zircons, biotite concentrate and whole rock respectively to better contextualise the

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tectonic setting.

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2. REGIONAL GEOLOGY A common feature of the three afore mentioned proto-Kalahari crustal areas is that all contain

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Paleoarchean crust older than 3.2 Ga (Armin et al., 2009). The Zimbabwe Craton comprises of a

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crustal core of Archean age, bordered to the south and west by the Paleoproterozoic belts of

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Limpopo and Magondi, respectively. The Neoproterozoic belts of the Zambezi (to the north) and

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the Mozambique (to the east) were added along the cratonic margins, as shown in Figure 2.

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Largely based on Rb-Sr isotopic analyses (and now supported by U-Pb and Sm-Nd data), Armin

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et al. (2009) divided the Archean crustal core of the Zimbabwe Craton into four tectonic

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domains. Three of them are granite-greenstone terrains formed at ca. 3.5 Ga, 2.9 Ga and 2.7 Ga,

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associated to tonalitic-trondhjemitic-granodioritic (TTG) type granitoid rocks. The fourth

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domain comprises the granitic suite of Chilimanzi-Razi, dated at ca. 2.6 Ga, which was followed

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by a relative quiescence and the intrusion of the Great Dyke at ca. 2.5 Ga. A high-grade terrain

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with a similar age of 2.60 to 2.56 Ga occurs at the northern margin of the craton and can be

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followed along the border zone between Zimbabwe and Mozambique. In Mozambique, the

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Archean nucleus is flanked by the Mozambique belt and affected by the Neoproterozoic Pan-

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African orogeny.

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In Mozambique, the rocks in the northern part of the Zimbabwe Craton are assigned to the

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Metamorphic Complex of Mudzi, which exhibits Mesoarchean metamorphism in continuity with

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the corresponding unit in Zimbabwe. The rocks of the Mudzi Complex are usually ortho-derived

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and include TTG-type associations and foliated granitoids (GTK, 2006); however, garnet-

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paragneisses are also present. Further south, the cratonic margin comprises of "granite-

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greenstone" terrain, which includes the eastern part of the greenstone belt of Mutare-Manica-

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Odzi whose lithologies are ascribed to the Manica Group on the Mozambican side.

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The Manica Group is subdivided into two main sequences. The lower one, the Macequece

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Formation, is made up of meta-volcanic ultramafic to mafic rocks interlayered with banded

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ferruginous rocks and metacherts. The upper unit, the Vengo Formation, is meta-sedimentary,

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consisting of a band of meta-conglomerates containing Archean granitoid pebbles, underlying

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sericite-chlorite schists and phyllite units, which include black shales and small marble bands

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(Grantham et al., 2008). On the other hand, a series of felsic granitoid rocks, associated with the

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greenstone belt, are assigned to the Mavonde Complex (Koistinen et al., 2008).

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In the Zimbabwe Craton there is evidence for very old early crustal components, indicated by

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detrital zircon dated ca. 3.8 Ga, as well as Re-Os isotopic data suggesting that at that time the

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lithospheric mantle was separated from the asthenospheric convective mantle (Armin et al.,

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2009). The tectonic setting responsible for the formation of the granite-greenstone terrains is a

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subject of debate. Two types of geotectonic settings are present. The first one is made up of

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tholeiitic basalt piles and ultramafic lavas overlying the older granitic terrains, suggesting that

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the greenstone belts were formed unconformably covering the existing basement in a continental

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rift environment. The second comprises of a series of calc-alkaline lavas and meta-sediments

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intruded by syn-volcanic plutons. Kusky (1998) suggested the existence of major structural

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feature and described the granite-greenstone terrains as possible tectonic relicts of collisions

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along active oceanic margins. Alternatively, Armin et al. (2009) suggested that their formation

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would have started with flows and intrusions of mafic magma, followed by the intrusion of TTG-

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type plutonic bodies, sodic granites and sanukitoids and would have finished with the intrusion

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of potassium granites.

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The Umkondo and Gairezi that form volcano-sedimentary sequences rest discordantly on the

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lithologies of the Limpopo Belt and the Zimbabwe Craton. It is exposed along the eastern border

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of Zimbabwe and extends into Mozambique (Gaireizi facies). The Umkondo represents

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autochthonous Nyanga facies in Zimbabwe (western facies) and the Gairezi facies in

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Mozambique (eastern facies). The Nyanga facies is described as a flat-lying, non- to weakly

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deformed, mostly unmetamorphosed sequence composed of basal arkoses, stromatolitic

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limestone, chert, mudrock and ortho-sandstone and amygdaloidal lavas appear in the uppermost

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section of the preserved part of the sequence. The deformed and metamorphosed lithologies have

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been incorporated into the Gairezi Group which consists predominantly of pelitic schists and

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white to greyish orthoquartzites and quartzites (GTK Consortium 2006). The rock sources of the

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sediments, with strong participation of Archean material, are certainly located within the

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Zimbabwe Craton.

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At Nyanga, Umkondo sediments apparently uncoformably overlie a thin sill of porphyritic

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dolerite, typical of the Mashonaland Dolerite group, samples of which give a Rb-Sr age of

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1850±20 Ma (Hunter, 1981). Marschall et al., 2006 correlates the Nyanga sequence, with the ca.

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1130 Ma Ahlmannryggen Group of East Antarctica, suggesting a Mesoproterozoic maximum

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age of Umkondo. On the other hand, the sequence is invaded by huge volumes of mafic tholeiitic

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magma, as dykes and sills, characterising the igneous Umkondo Province precisely dated at ca.

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1100 Ma (Hanson et al., 2006; Wingate, 2001), thereby establishing a minimum

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Mesoproterozoic age for the Umkondo Group. GTK Consortium (2006) and data from this

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paper, based on the accurate age determinations of detrital zircon from the Gairezi Group

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metasediments, point the age values of 2040 Ma and ca. 2000 Ma respectively, as maximum

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depositional ages of the Gairezi Group. In addition, Vail (1965) showed that this

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lithostratigraphic unit in Mozambique was metamorphosed from low- to high-grade at a distance

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of around 50 km from the craton margin. Barton et al. (1991) indicated that the northern margin

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of the Zimbabwe craton contained south-directed thrusts, including Archean and Proterozoic

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basement components. However, in Mozambique, at the eastern border of the craton, the

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Archaean granitoid rocks are tectonically superimposed by the supracrustal rocks of the

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Mozambique Belt. These were structurally thrusted to the west towards the cratonic area and

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were affected by the Neoproterozoic to Cambrian Pan-African orogeny.

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At the north-easternmost part of the cratonic area the metasedimentary units of the Rushinga

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Group occur, which may represent a passive margin of Neoproterozoic age. It is made up of

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meta-sediments of low to medium grade, including quartzite, schist, marble, calc-silicate rocks,

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paragneisses and interbedded bands of amphibolite (Barton et al., 1991, GTK Consortium 2006).

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The Rushinga Group in Mozambique also includes felsic metavolcanic rocks dated in Zimbabwe

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at ca. 800 Ma (Hargrove et al., 2003). To the south, in the west-central part of Mozambique, the

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Archean rocks are in direct tectonic contact with the frontal nappes of Chimoio-Macossa and

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Mungari (Chaúque, 2012), consisting of low- to high-grade paragneisses, including granulites

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and migmatites, associated with the pre-existing orthomagmatic rocks related to the ca. 1100 Ma

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old Báruè magmatic arc. GTK Consortium (2006) indicates that both Umkondo Group and the

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Rushinga Group are Paleoproterozoic in age; however, Chaúque (2012) considered the latter to

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be Neoproterozoic in age and a possible passive margin of the Zimbabwe Craton.

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Abundant Neoproterozoic felsic-mafic intrusive association belonging to the Guro Suite,

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characterize the east-dipping outer rim of the craton margin in the north, where eastwards they

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gradually take all space from the Palaeoproterozoic metasediments overlying the basement. The

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felsic component consists of fine-grained, foliated aplitic granites, occasionally injected by

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pegmatite veins to make a migmatitic aspect. The mafic component is represented by

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metagabbro, locally deformed into mafic gneiss or schist with intruding pegmatite. The chemical

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characteristics, bimodality, high values of Fe# and high contents of Ba, Rb and Zr are all

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characteristics of anorogenic, A-type granites (GTK Consortium 2006).

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Zircons from 9

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aplogranites were dated ca. 850 Ma and ɛNd values suggest an important contribution from the

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mantle (Mäntäri, 2008; Chauque, 2012 ). This magmatic age is also recorded from Zimbabwe,

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Malawi, Madagascar, Tanzania and other Eastern African Orogen areas which is considered

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extensional type and possibly associated to Rodinia breackup.

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The Pan African orogenic event, occurring around 550-500 Ma, affected the old cratonic border

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(Vail, 1965; Vail and Dodson, 1969) and is recorded in all meta-sedimentary units. Its thermal

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effects partially or totally disturbed the isotopic systems, as reflected by K-Ar ages in mica, by

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lower intersections in many of the U-Pb Concordia diagrams and as U-Pb dates on zircon rims

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(Chauque, 2012). Vail and Dodson (1969) proposed a geographic limit for the region heated

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above at least 250–300 oC during the Pan-African event and discussed in Section 4.4 (Fig. 8).

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The Cambrian post-orogenic magmatism marked in the study area by the Mount Chissui

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nepheline syenite intrusion (U-Pb zircon 498 ± 3 Ma), south of Chimoio, is a reflection of the

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final stages of the Pan-African Orogeny (Chauque, 2012). In addition, according to GTK

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Consortium (2006), several alkali and syenogranitic suites of Cambrian age in north-eastern

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Mozambique, such as Murrupula, Niassa, Malema, Sinda and the weakly deformed Macanga

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granite, intrude the regional gneissic rocks of the Mozambique Belt.

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3. ANALYTICAL METHODS

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This study aims to compile and re-interpret the previously existing geochronological data of the

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Zimbabwe Craton in Mozambique. This shall include the works of Vail and Dodson (1969),

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Manhiça et al. (2001), Mäntäri (2008) and Sumburane (2011). Descriptions of the employed

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methods can be found in each of these references. In this paper, we report the analytical methods

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employed by Chaúque (2012) in the central and western region of Mozambique. In the study

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area, a significant amount of precise U-Pb Sensitive High Resolution Ion Microrobe (SHRIMP)

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zircon data for rock crystallization ages is available from the Archean rocks (Mäntäri, 2008; 10

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Sumburane, 2011). In this study, additional age data is presented (Chauque, 2012) that could be

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relevant for determining the regional tectonic history. Chauque (2012) produced K-Ar ages for

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the determination of the final regional cooling, Sm-Nd isochron calculations for the age of

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igneous or metamorphic episodes and U-Pb Laser Ablation Inductively Coupled Plasma Mass

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Spectrometry (LA-ICP-MS) ages on detrital zircons, to obtain some clues on the age of the

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source rocks. This analytical work was conducted at the Geochronological Research Center

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(CPGeo) of the Institute of Geosciences at University of São Paulo, Brazil.

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For the K-Ar method, the age analyses were made using high purity concentrates of micas and

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the analytical results are presented in Table 5. The internal CPGeo standard of biotite SJ-1 was

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used and the experimental accuracy was 0.01 ppm for the potassium analysis and between 2 and

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4 % for argon, depending on the ratio of radiogenic argon present in each sample in relation to

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the contaminant atmospheric argon. A detailed description of the methodology employed, as

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well as the quantitative data on the accuracy of the K-Ar analysis, can be found in Amaral et al.

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(1966).

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For the Sm-Nd method, the experimental error (2δ level) is 0.003 % and the isotopic

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composition of Nd is fixed to a mass normalisation by fractionation to a value of 0.72190 for

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146

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depleted mantle (DM), according to the equations presented by De Paolo (1988). The constants

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used in the calculations were

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0.1967. The analytical data are included in Table 2.

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Zircon crystals were extracted from the chosen samples and mounted in epoxy mounts for LA-

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ICP-MS analysis. Cathodoluminescence images (CL) were produced by Scanning Electron

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Microscope. The images served to help interpret the internal structure of the crystals and select

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the best areas for the isotopic analyses. The U-Pb isotopic ratios were determined using the

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Nd/144Nd (Sato et al., 1995). Model ages (TDM) and εNd(T) values were calculated for the

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Nd/144Nd (CHUR) = 0.512638 and

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Sm /144Nd (CHUR)0 =

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NEPTUNE-ICP-MS instrument at the CPGeo, coupled to a laser ablation system. The settings

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used for data acquisition and a detailed description of the applied methodology are found in Sato

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et al. (1995). For the normalisation of the

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NIST 610) and external standards was used and the normalisation of the

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based on an external zircon standard. The GJ-1 standard zircon was used to estimate the

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necessary corrections for the external corrections and the internal instrumental fractionation.

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Diagrams and age calculations of isotopic data were made using the software Isoplot 4 (Ludwig

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2012). For the interpretations only values with a concordance level greater than 95% were used.

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Details of the analytical procedures and the calibration methods employed are reported in

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Williams (1998) and Stern (1994). The analytical results of the new measurements are shown in

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Tables 3 and 4.

Pb/206Pb ratio, a combination of internal (glass 206

Pb/238U ratio was

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4. RESULTS

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4.1.The Archean nucleus

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According to the U-Pb zircon data compiled from several studies (Table 1), the magmatic

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crystallisation ages at the eastern border of the Zimbabwe Craton in Mozambique vary between

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ca. 3.0 and 2.5 Ga.

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For a few TTG-type granitoids belonging to the Mavonde Complex, the obtained ages imply at

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least three phases of magmatism:

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tonalitic magmatism older than 3000 Ma (Manuel, 1992);

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ii.

tonalitic magmatism of ca. 2900 Ma (Manuel, 1992; Mäntäri, 2008;Sumburane, 2011));

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iii.

granitic to granodiorite magmatism between ca. 2500 and 2700 Ma (Chenjerai et al.,

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1993 ; Manhiça et al., 2001; Mantari, 2008; Sumburane, 2011) ).

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Within the Metamorphic Complex of Mudzi, Mäntäri (2008), obtained magmatic U-Pb zircon

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ages between ca. 2600 and 2700 Ma. For the same Mudzi Complex in Zimbabwe, near the 12

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Mozambique border. Barton et al. (1991) presented some very inaccurate Rb-Sr ages in whole-

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rock samples: tonalitic gneisses with ages of 3247 ± 627 Ma and mesocratic orthogneisses with

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ages of 2494 ± 194 and 2937 ± 178 Ma.

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The granodioritic intrusion of Penhalonga, dated 2741 ± 3 Ma by Chenjerai et al. (1993) sets a

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precise minimum age for the greenstone belt of Mutare-Odzi-Manica. This age is additionally

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supported by a U-Pb Thermal Ionisation Mass Spectrometric (TIMS) determination in zircon of

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2990 ± 33 Ma (Sumburane, 2011) and a whole-rock Rb-Sr age of 2800 ± 41 Ma (Manuel, 1992)

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from metavolcanic rocks of the Manica greenstone belt in Mozambique.

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In this study a few Sm-Nd whole-rock isotopic data were obtained from three granitoid samples

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of the Mavonde Complex and the results are given in Table 2. Figure 3 shows the Sm-Nd whole-

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rock isochron, which produced an apparent age of 2409 ± 78 Ma. Manhiça et al. (2001) obtained

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a similar age (2353 ± 175 Ma) for the Messica granite-gneiss, using the whole-rock Rb-Sr

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isochron of five samples and thus considered it as belonging to the Neoarchean-Lower

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Proterozoic. This possibly correlates with the Chilimanzi Granitic Suite of Zimbabwe with an

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age of 2601 ± 14 Ma estimated by conventional U-Pb TIMS analysis of zircon (Armin et al.,

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2009). For the same Messica granite-gneiss, Sumburane (2011) obtained a U-Pb zircon age of

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2661 ± 46 by SHRIMP and a U-Pb TIMS age of 2471 ± 93, which were very inaccurate but

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nevertheless consistent with the age of the Chilimanzi granites.

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In conclusion, from the data presented above, a few different periods of Archaean magmatic

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activity are reported along the eastern border of the Zimbabwe Craton, close to Mozambique.

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Armin et al. (2009) defined three generations of granite-greenstone terrains for the Zimbabwe

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Craton, (~3.5, 2.9 and 2.7 Ga) and the two younger are present in the Mozambique portion of the

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cratonic area. The Mutare-Odzi-Manica greenstone belt, like many others in Zimbabwe, may

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have unconformably covered one of the granitic terrains around 2.9 to 2.8 Ga. In addition, the

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younger series of magmatic episodes, which occurred roughly between 2.6 and 2.5 Ga could be

2

equivalent to the age of intrusion of the Chilimanzi-Razi suite, followed by some quiescence,

3

crustal relaxation and the intrusion of the Great Dike in Zimbabwe at about 2.5 Ga.

4 5 6 7

Table 1- Summary of the geochronological previous U-Pb data from zircon of rocks of the eastern margin of the Zimbabwe craton, in the midwestern region of Mozambique, extracted from Mantari, 2008 (1), Sumburane 2011 (2) and Manhiça et al. 200 (3). Method TIM

Mos-7N Mos-7B Mos-21 Mos-23 Mos-30 99MS01 09MS13 09MS13 09MS17 09MS70 99MS21 99MS26

Gneisse

Mudzi

SHRIMP

Mudzi Mavonde Mavonde Mavonde Mavonde Mavonde Mavonde Mavonde Mavonde Manica Chilimanzi

SHRIMP SHRIMP TIM SHRIMP SHRIMP TIM TIM SHRIMP TIM TIM TIM

M AN U

Gneisse Tonalite Granodiorite granitoid Granite Granite granitoid Granitoid Granitoid Volcanic acid Granite

Age (Ma) 2632±3 554±33 2713± 22 520±16 2593±22 2907±16 ~2500 (?) 2898±20 2661±46 2471±93 2902±28 2815±35 2715±26 2990±33 2601±14

Meaning Upper intercept Lower intercept Upper intercept Concord Upper intercept Upper intercept Reference line intercept Upper intercept Upper intercept Upper intercept Upper intercept Upper intercept Upper intercept Upper intercept

RI PT

Compl/Group Mudzi

Ref.

(1)

SC

Rock Gneisse

(2)

(3)

Tabela 2 -Sm and Nd isotope data from Precambrian rocks of the Midwestern region of Mozambique Sumple

Sm

Nd

147

Sm/

Error

TE D

Unit

144

143

Nd/

Error

fSm/Nd TDePaolo T1

144

Mavonde 5bFR09 13.977 88.320 07aFR09 3.733 22.247

0.0957 0.0006 0.510827 0.000013 -0.51 2.9 0.1015 0.0006 0.510956 0.000009 -0.48 2.9

(Ga) 2.6 -24.26 2.6 -36.77 2.6 -35.32 2.6 -32.81

Mudzi

0.1269 0.0007 0.511127 0.000011 -0.35 3.4

2.6

04FR09 5aFR09

1.135

5.409

EP

24FR09

(ppm) (ppm) Nd Nd (Ga) 5.316 24.581 0.1308 0.0008 0.511394 0.000014 -0.34 3.1 22.096 148.005 0.0903 0.0006 0.510753 0.000006 -0.54 2.9

ԐNd (T0) ԐNd(T1) ԐNd(TDM)

-29.47

-2.22 -1.18

1.90 2.35

-1.54 -0.95

2.28 2.30

-6.17

1.49

AC C

8 9 10

Sample Mos-6

14

RI PT

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4

Figure 3. 147Sm/144Nd vs 143Nd/144Nd isotope diagram of granitoids of the Mavonde metamorphic complex

4.2. Paleo to Mesoproterozoic metasedimentary rocks

M AN U

2 3

SC

1

Two samples of meta-sediments: Schist (19MZ10) and a quartzite (27MZ10), most likely

6

belonging to the Gairezi Group, were collected in the region affected by the Pan-African

7

deformation and metamorphism, in the vicinity of Nyanga, Mozambique, to investigate their

8

possible rock sources. In Figure 4, the CL images show rims of metamorphic overgrowth in a

9

few of 30 and 32 detrital zircons from 19MZ10 and 27MZ10 respectively. Table 3 displays the

10

analytical data of the LA-ICP-MS measurements in the zircon grains and Figure 5 shows the

11

histogram of the concordant (100 ± 10%) age values obtained in rims and nuclei of the crystals.

12

For the nuclei, two peaks at ca. 2000 and ca. 2600 Ma were obtained. The apparent maximum

13

depositional age is ca. 2000 Ma and two of the ages for sample 19MZ10 were older than 3000

14

Ma. Moreover, Figure 5 shows clearly that all overgrowth rims indicate the same metamorphic

15

age at about 500 Ma.

AC C

EP

TE D

5

15

RI PT

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1

Fig. 4. cathodeluminescence selected images of the samples dated by U-Pb LA-ICP-MS. The analyzed spots and the numbers of corresponding analysis are indicated (see table 3). 19MZ10: Ages of detrital zircons between ~20002900 Ma. 27MZ10: Ages of detrital zircons between 2000-2700 Ma. In both samples, the overgrowing metamorphic edges gave ~ 500 Ma. The scale bar corresponds to 50µm.

6

The apparent Paleoproterozoic depositional age for the Gairezi Group is confirmed by the U-Pb

7

SHRIMP dating done by Mäntäri (2008) in the detrital zircons of garnet-kyanite schist, whose

8

minimum age value was 2040 Ma. The minimum age is still not well established.

EP

TE D

M AN U

SC

2 3 4 5

Fig.5. Histograms showing isotopic U-Pb data from zircon by LA-ICP-MS. The two samples show a similar evolutionary nature. The peak of ~500 Ma observed in the histograms represents the metamorphic ages obtained from the overgrowth rims.

13

The Ar-Ar thermochronology on mica by Manhiça et al. (2001) suggests that the Kalahari Craton

14

lithologies have experienced heating above at least c. 300°C during the c.1100 Ma Grenville age

15

orogeny. According to the SHRIMP zircon data from the vein phase which is oriented parallel to

16

localized but intense N-S oriented shearing along the Kalahari Craton/Mozambique Belt

17

boundary zone, the high strain along the eastern margin of the Kalahari Craton in the Manica

18

area, occurred at ca. 1000 Ma (Grantham et al., 2011). The superposition of the Pan-African

AC C

9 10 11 12

16

ACCEPTED MANUSCRIPT

tectono-thermal episode, indicated by overgrowth rims in the two samples studied, is fully

2

confirmed by K-Ar and Ar-Ar datings around 465 to 470 Ma in moscovites, reported by Vail

3

(1965) and more recently by Manhiça et al. (2001) and Grantham et al. (2011).

4

The provenance of the Gairezi Group metasediments is bracketed between ca. 3000 and ca 2700

5

Ma, clearly revealing the Zimbabwe Craton as a source of the sediments. The detrital zircons

6

aged at ca. 2000 Ma could come from the Magondi Belt, which belongs to the western part of the

7

same cratonic region. In central and southern Africa the Paleoproterozoic Eburnean Orogenic

8

Cycle, between 2200 and 1800 Ma, is not that widespread. Zircons of that age could come from

9

some faraway region of the Congo and the Kalahari cratons, or additionally from the Limpopo

10

Belt, not very far from the study area where the Archean substrate was affected and rejuvenated

11

by the Eburnean orogeny (Jacobs et al., 2003).

AC C

EP

TE D

M AN U

SC

RI PT

1

17

ACCEPTED MANUSCRIPT Table 3- U-Pb LA-ICP-MS date, sample 19MZ10 Sample: 19MZ10 Schist

Ratio 207Pb/235U

1sigma

206Pb/238U

1 sigma

Spot

Correc.

238U/206Pb

Age (Ga) 1 sigma

207Pb/206Pb

1 sigma

208Pb/206Pb

1 sigma

206Pb/238U

1 sigma

207Pb/235Pb

Conc.(%) 1 sigma

207Pb/206Pb

1 sigma

error

206Pb/238U 207Pb/206Pb

0.7151

0.0739

0.0873

0.0024

0.27

11.4544

0.3170

0.0585

0.0064

0.0838

0.0487

0.540

0.014

0.548

0.043

0.542

0.225

100

2.1

7.3168

0.0767

0.3212

0.0027

0.79

3.1138

0.0257

0.1621

0.0020

0.1470

0.0506

1.795

0.013

2.151

0.009

2.475

0.021

73

3.1

1.2256

0.0249

0.1031

0.0013

0.61

9.7019

0.1201

0.0867

0.0014

0.0377

0.0131

0.632

0.007

0.812

0.011

1.359

0.031

47

4.1

12.0957

0.3901

0.4859

0.0135

0.86

2.0580

0.0571

0.1790

0.0024

0.7088

0.2426

2.553

0.058

2.612

0.030

2.645

0.023

97

5.1

5.8806

0.0495

0.3411

0.0023

0.80

2.9319

0.0196

0.1261

0.0015

0.0775

0.0265

1.892

0.011

1.958

0.007

2.043

0.021

93

6.1

7.5277

0.3287

0.3992

0.0239

0.99

2.5049

0.1498

0.1353

0.0041

0.5180

0.1798

2.165

0.109

2.176

0.038

2.164

0.051

100

7.1

13.2833

0.2423

0.5221

0.0080

0.84

1.9154

0.0293

0.1866

0.0024

0.1497

0.0509

2.708

0.034

2.700

0.017

2.715

0.022

100

8.1

6.0109

0.0643

0.3467

0.0032

0.87

2.8844

0.0267

0.1265

0.0015

0.0852

0.0289

1.919

0.015

1.977

0.009

2.048

0.021

94

9.1

11.9177

0.0894

0.4897

0.0029

0.79

2.0422

0.0121

0.1779

0.0021

0.0749

0.0253

2.569

0.013

2.598

0.007

2.634

0.020

98

10.1

13.2557

0.1641

0.5199

0.0046

0.71

1.9234

0.0169

0.1858

11.1

11.8153

0.1700

0.4966

0.0056

0.79

2.0135

0.0228

0.1767

11.2

11.6651

0.1707

0.4932

0.0065

0.90

2.0277

0.0269

0.1738

12.1

13.6373

0.1948

0.5404

0.0061

0.79

1.8504

0.0210

0.1982

13.1

12.1348

0.1263

0.5006

0.0055

0.99

1.9976

0.0218

0.1769

14.1

6.7313

0.1785

0.3815

0.0091

0.90

2.6214

0.0628

0.1503

15.1

15.4291

0.2120

0.5558

0.0074

0.97

1.7992

0.0239

0.2049

16.1

11.3689

0.1256

0.4808

0.0053

1.00

2.0799

0.0229

0.1779

0.0012

17.1 18.1

17.7462 12.8035

0.3409 0.1457

0.5195 0.4752

0.0059 0.0054

0.59 0.99

1.9250 2.1043

0.0219 0.0240

0.2570 0.1960

0.0032 0.0013

19.1

10.6475

0.1756

0.4740

0.0075

0.96

2.1099

0.0335

0.1653

0.0013

0.4340

0.1378

2.501

0.033

2.493

0.015

2.508

0.014

100

20.1

6.0543

0.0683

0.3432

0.0038

0.99

2.9141

0.0326

0.1254

0.0008

0.4778

0.1509

1.902

0.018

1.984

0.010

2.033

0.011

94

21.1

11.5729

0.1792

0.4824

0.0061

0.81

2.0732

0.0260

0.1745

0.0020

0.2394

0.0755

2.538

0.026

2.570

0.014

2.601

0.019

98

22.1

11.5797

0.2033

0.4909

0.0066

0.76

2.0371

0.0273

0.1780

0.0023

0.3870

0.1216

2.575

0.028

2.571

0.016

2.636

0.022

98

23.1

5.9708

0.0662

0.3522

0.0040

0.99

2.8393

0.0325

0.1238

0.0008

0.1387

0.0434

1.945

0.019

1.972

0.010

2.011

0.011

97

24.1

10.1315

0.1079

0.4619

0.0052

25.1

4.3441

0.0488

0.2650

0.0030

26.2

15.8322

0.5506

0.5522

0.0142

27.1

7.8004

0.2707

0.4108

0.0106

28.1

11.6835

0.3899

0.4917

0.0110

28.2

13.6587

0.4238

0.5296

0.0117

29.1

22.3580

0.6644

0.6388

0.2483

0.4053

30.1

7.6140

SC

M AN U 0.0024

0.5368

0.1809

2.699

0.019

2.698

0.012

2.708

0.021

100

0.0022

0.5006

0.1683

2.599

0.024

2.590

0.013

2.623

0.021

99

0.0021

0.4163

0.1397

2.584

0.028

2.578

0.014

2.594

0.021

100

0.0027

0.2945

0.0985

2.785

0.026

2.725

0.013

2.817

0.022

99

0.0011

0.4615

0.1485

2.616

0.023

2.615

0.010

2.625

0.011

100

0.0020

0.2477

0.0799

2.083

0.043

2.077

0.023

2.345

0.023

89

0.0016

0.0084

0.0028

2.849

0.030

2.842

0.013

2.872

0.013

99

0.5144

0.1642

2.531

0.023

2.554

0.010

2.634

0.011

96

0.2923 0.3949

0.0933 0.1258

2.697 2.506

0.025 0.024

2.976 2.665

0.018 0.011

3.226 2.798

0.019 0.011

84 90

TE D

EP

AC C

RI PT

1.1

0.99

2.1650

0.0243

0.1654

0.0011

0.6202

0.1938

2.448

0.023

2.447

0.010

2.510

0.012

98

0.99

3.7737

0.0432

0.1179

0.0008

0.2359

0.0736

1.515

0.015

1.702

0.009

1.925

0.011

79

0.74

1.8108

0.0467

0.2100

0.0026

0.3065

0.0681

2.834

0.059

2.867

0.033

2.912

0.020

97

0.74

2.4343

0.0629

0.1468

0.0022

0.1087

0.0245

2.219

0.048

2.208

0.031

2.305

0.025

96

0.67

2.0339

0.0454

0.1725

0.0029

0.3396

0.0747

2.578

0.047

2.579

0.031

2.581

0.029

100

0.71

1.8883

0.0417

0.1859

0.0021

0.7691

0.1670

2.740

0.049

2.726

0.029

2.709

0.019

101

0.0132

0.69

1.5655

0.0323

0.2542

0.0029

0.2730

0.0597

3.184

0.052

3.199

0.028

3.210

0.017

99

0.0098

0.74

2.4671

0.0598

0.1401

0.0018

0.5761

0.1242

2.194

0.045

2.187

0.029

2.224

0.021

99

18

ACCEPTED MANUSCRIPT

Table 3- U-Pb LA-ICP-MS data, sample 19MZ10 (cont) Schist

Ratio 207Pb/235U

1sigma

206Pb/238U

1 sigma

Spot

Correc.

238U/206Pb

Age (Ga) 1 sigma

207Pb/206Pb

1 sigma

208Pb/206Pb

error

1 sigma

206Pb/238U

1 sigma

RI PT

Sample: 19MZ10

207Pb/235U

Conc.(%) 1 sigma

207Pb/206Pb

1 sigma

206Pb/238U 207Pb/206Pb

31.1

11.3601

0.3291

0.4260

0.0085

0.69

2.3475

0.0468

0.1946

0.0022

0.3063

0.0656

2.288

0.038

2.553

0.027

2.786

0.019

82

33.1

9.3649

0.2705

0.4098

0.0082

0.69

2.4404

0.0487

0.1664

0.0019

0.2342

0.0494

2.214

0.037

2.374

0.026

2.520

0.019

88

34.1

13.1266

0.3838

0.5152

0.0106

0.70

1.9409

0.0399

0.2003

0.0024

0.4580

0.0960

2.679

0.045

2.689

0.027

2.834

0.020

95

6.3972

0.1866

0.3718

0.0076

0.70

2.6896

0.0550

0.1236

0.0014

0.5171

0.1077

2.038

0.036

2.032

0.025

2.008

0.019

101

9.7403

0.0730

0.4546

0.0025

0.72

2.1999

0.0119

0.1723

0.0011

0.2229

0.0872

2.416

0.011

2.411

0.007

2.580

0.011

94

37.1

0.6582

0.0024

0.0826

0.0004

0.99

12.1133

0.0654

0.0571

0.0003

0.0073

0.0030

0.511

0.003

0.513

0.001

0.491

0.013

104

37.2

4.4286

0.0333

0.2627

0.0020

0.99

3.8066

0.0297

0.1228

0.0008

0.2657

0.1032

1.504

0.010

1.718

0.006

1.997

0.011

75

38.1

0.7730

0.0024

0.0846

0.0004

0.99

11.8142

0.0605

0.0663

0.0004

0.0317

0.0123

0.524

0.003

0.581

0.001

0.811

0.013

65

38.2

12.6443

0.1256

0.5110

0.0048

0.94

1.9570

0.0183

0.1815

0.0012

0.3520

0.1357

2.661

0.020

2.654

0.009

2.668

0.011

100

39.1

17.9083

0.1362

0.5569

0.0055

0.99

1.7958

0.0178

0.2337

0.0014

0.2639

0.1014

2.854

0.023

2.985

0.007

3.082

0.009

93

40.1

11.5436

0.2546

0.4752

0.0110

0.99

2.1044

0.0488

0.1765

0.0008

0.9202

0.9229

2.506

0.048

2.568

0.020

2.620

0.007

96

41.1

5.6638

0.1211

0.3382

0.0077

0.99

2.9564

0.0669

0.1218

0.0005

1.0462

1.1104

1.878

0.037

1.926

0.018

1.983

0.008

95

42.1

0.6330

0.0136

0.0807

0.0018

0.99

12.3969

0.2799

0.0570

0.0003

0.0175

0.0199

0.500

0.011

0.498

0.008

0.484

0.011

103

42.2

15.9154

0.3482

0.5617

0.0127

0.99

1.7803

0.0403

0.2137

0.0010

0.6950

0.8353

2.874

0.052

2.872

0.021

2.940

0.007

98

0.0780

0.1208

0.0007

0.4391

0.5650

1.702

0.035

1.837

0.020

1.968

0.010

87

0.2698

0.0609

0.0003

0.0096

0.0134

0.534

0.012

0.556

0.010

0.628

0.011

85

0.0546

0.1835

0.0028

0.3110

0.5581

2.650

0.060

2.640

0.030

2.687

0.026

99

0.0573

0.1906

0.0014

0.2843

0.7244

2.718

0.066

2.729

0.030

2.751

0.012

99

TE D

M AN U

SC

35.1 36.1

5.1073

0.1197

0.3023

0.0071

0.99

3.3084

0.7295

0.0170

0.0864

0.0020

0.99

11.5787

45.1

12.4657

0.4036

0.5085

0.0141

0.86

1.9664

48.1

13.7014

0.4359

0.5243

0.0158

0.94

1.9072

46.1

7.2842

0.1700

0.3176

0.0073

0.99

3.1487

0.0726

0.1684

0.0014

0.0325

0.0646

1.778

0.036

2.147

0.021

2.540

0.014

70

EP

43.1 43.2

6.1407

0.1379

0.2904

0.0067

0.99

3.4439

0.0789

0.1542

0.0008

0.1734

0.3877

1.643

0.033

1.996

0.019

2.389

0.009

69

0.7044

0.1642

0.0873

0.0063

0.31

11.4587

0.8282

0.0627

0.0026

0.0176

0.0530

0.539

0.037

0.541

0.093

0.692

0.088

78

AC C

47.1 48.2

19

ACCEPTED MANUSCRIPT

Table 3- U-Pb LA- ICP-MS data, sample 27MZ10 (cont.) Sample: 27MZ10

Ratio

7.1194 10.8225 6.4236 6.4743

0.0557 0.0849 0.0507 0.0521

0.3921 0.4683 0.3708 0.3731

0.0059 0.0070 0.0056 0.0056

0.99 0.99 0.99 0.99

2.5507 2.1353 2.6967 2.6800

0.0384 0.0321 0.0405 0.0405

0.1323 0.1677 0.1261 0.1263

0.0015 0.0020 0.0015 0.0015

1.1680 0.6020 0.4581 0.4171

0.1817 0.0946 0.0727 0.0669

2.132 2.476 2.033 2.044

0.027 0.031 0.026 0.026

2.126 2.508 2.036 2.042

0.007 0.007 0.007 0.007

2.125 2.534 2.042 2.045

0.020 0.020 0.020 0.020

100 98 100 100

5.1 5.2 6.1 7.1 8.1 9.1 9.2 10.1 11.1 12.1 12.2 13.1 14.1

2.0319 0.6300 7.3090 6.4275 6.6187 5.7388 1.7558 0.6384 0.7112 6.1308 0.6489 6.0718 8.3868

0.0316 0.0051 0.0752 0.0537 0.0537 0.0461 0.0523 0.0053 0.0074 0.0535 0.0072 0.0600 0.0758

0.1519 0.0802 0.3974 0.3714 0.3773 0.3445 0.1538 0.0808 0.0892 0.3607 0.0818 0.3572 0.4174

0.0027 0.0012 0.0064 0.0056 0.0057 0.0052 0.0033 0.0012 0.0015 0.0045 0.0011 0.0046 0.0052

0.99 0.99 0.99 0.99 0.99 0.99 0.72 0.99 0.99 0.99 0.99 0.99 0.99

6.5849 12.4668 2.5161 2.6922 2.6505 2.9024 6.5027 12.3701 11.2122 2.7728 12.2203 2.7998 2.3960

0.1187 0.1854 0.0403 0.0405 0.0399 0.0434 0.1387 0.1851 0.1830 0.0343 0.1697 0.0363 0.0299

0.1040 0.0573 0.1342 0.1249 0.1269 0.1221 0.0878 0.0571 0.0581 0.1239 0.0573 0.1214 0.1468

0.0012 0.0007 0.0016 0.0015 0.0015 0.0014 0.0012 0.0007 0.0008 0.0012 0.0006 0.0012 0.0015

0.2225 0.0015 0.5934 0.3090 0.3514 0.1406 0.1077 0.0049 -0.0038 0.3080 0.0091 0.4183 0.5701

0.0362 0.0009 0.0972 0.0512 0.0588 0.0238 0.0187 0.0012 0.0112 0.4632 0.0126 0.5316 0.6724

0.911 0.497 2.157 2.036 2.064 1.908 0.922 0.501 0.551 1.985 0.507 1.969 2.248

0.015 0.007 0.029 0.026 0.027 0.025 0.018 0.007 0.009 0.021 0.007 0.022 0.024

1.126 0.496 2.150 2.036 2.062 1.937 1.029 0.501 0.545 1.995 0.508 1.986 2.274

0.011 0.003 0.009 0.007 0.007 0.007 0.019 0.003 0.004 0.008 0.004 0.009 0.008

1.701 0.496 2.150 2.026 2.054 1.986 1.384 0.489 0.528 2.012 0.498 1.977 2.304

0.021 0.026 0.020 0.020 0.020 0.020 0.027 0.026 0.028 0.017 0.022 0.018 0.017

54 100 100 100 100 96 67 102 104 99 102 100 98

14.2 15.1

0.6155 5.8472

0.0062 0.0524

0.0780 0.3339

0.0010 0.0042

0.99 0.99

12.8270 2.9947

0.1643 0.0375

0.0570 0.1283

0.0006 0.0013

0.0056 0.7972

0.0068 0.8221

0.484 1.857

0.006 0.020

0.487 1.953

0.004 0.008

0.487 2.073

0.023 0.017

99 90

16.1 16.2 17.1 18.1 19.1 19.2 20.1 21.1 22.1 23.1 24.1 25.1 25.2 26.1 27.1

6.2478 0.7254 5.1871 12.1455 6.5150 1.6317 2.2563 6.5122 4.7133 5.5469 6.1833 0.6266 12.2012 4.5881 12.9389

0.0555 0.0085 0.0627 0.1114 0.0692 0.0562 0.0732 0.0899 0.0655 0.0766 0.1114 0.0160 0.1684 0.0734 0.1779

0.3623 0.0905 0.3050 0.4793 0.3759 0.1392 0.1824 0.3634 0.3044 0.3289 0.3537 0.0759 0.4873 0.2790 0.5066

0.0045 0.0012 0.0041 0.0061 0.0051 0.0032 0.0054 0.0034 0.0029 0.0031 0.0044 0.0010 0.0047 0.0030 0.0048

0.99 0.99 0.99 0.99 0.99 0.67 0.91 0.69 0.69 0.69 0.68 0.50 0.69 0.68 0.69

2.7604 11.0498 3.2792 2.0862 2.6601 7.1834 5.4813 2.7516 3.2849 3.0408 2.8275 13.1676 2.0522 3.5842 1.9741

0.0345 0.1476 0.0443 0.0264 0.0363 0.1659 0.1612 0.0261 0.0316 0.0290 0.0348 0.1686 0.0196 0.0388 0.0188

0.1257 0.0586 0.1215 0.1846 0.1269 0.1026 0.0894 0.1304 0.1131 0.1230 0.1261 0.0568 0.1826 0.1242 0.1858

0.0012 0.0008 0.0012 0.0018 0.0013 0.0011 0.0011 0.0007 0.0006 0.0006 0.0008 0.0013 0.0010 0.0009 0.0010

0.6273 -0.0393 0.3691 4.7656 0.8211 0.5869 0.2233 0.5812 1.2953 0.7266 0.8553 0.0399 0.3595 0.8423 0.4419

0.6137 0.0403 0.3202 3.9266 0.6442 0.4395 0.1605 0.6181 1.4403 0.8465 1.0463 0.0573 0.4887 1.2027 0.6760

1.993 0.558 1.716 2.524 2.057 0.840 1.080 1.998 1.713 1.833 1.952 0.472 2.559 1.586 2.642

0.021 0.007 0.020 0.026 0.024 0.018 0.029 0.016 0.014 0.015 0.021 0.006 0.020 0.015 0.021

2.011 0.554 1.851 2.616 2.048 0.983 1.199 2.048 1.770 1.908 2.002 0.494 2.620 1.747 2.675

0.008 0.005 0.010 0.009 0.009 0.021 0.023 0.012 0.012 0.012 0.016 0.010 0.013 0.013 0.013

2.037 0.548 1.978 2.697 2.053 1.676 1.418 2.100 1.851 2.000 2.042 0.476 2.679 2.015 2.708

0.017 0.029 0.018 0.017 0.017 0.020 0.023 0.009 0.009 0.009 0.011 0.048 0.009 0.012 0.009

98 102 87 94 100 50 76 95 93 92 96 99 96 79 98

28.1

6.7510

0.1109

0.3796

0.0047

0.76

2.6346

0.0327

0.1289

0.0007

0.6551

1.0690

2.074

0.022

2.079

0.014

2.080

0.010

100

29.1

5.8584

0.0836

0.3510

0.0034

0.69

2.8493

0.0279

0.1207

0.0007

0.3164

0.5533

1.939

0.016

1.955

0.012

1.966

0.010

99

30.1

11.4021

0.1624

0.4652

0.0046

0.70

2.1498

0.0214

0.1779

0.0010

0.4716

0.8881

2.462

0.020

2.557

0.013

2.635

0.009

93

31.1

0.6449

0.0091

0.0813

0.0008

0.68

12.3037

0.1180

0.0575

0.0004

-0.0001

0.0035

0.504

0.005

0.505

0.006

0.504

0.014

100

32.1

6.4665

0.0958

0.3710

0.0037

0.67

2.6952

0.0267

0.1270

0.0007

0.4502

1.0023

2.034

0.017

2.041

0.013

2.055

0.010

99

1 sigma

207

Pb/206Pb

1 sigma

208

Pb/206Pb

1 sigma

206

Pb/238U

1 sigma

207

RI PT

1.1 2.1 3.1 4.1

U/206Pb

Pb/235U

Conc.(%)

238

1 sigma

SC

Pb/238U

M AN U

206

Idade (Ga)

Correc. error

1sigma

TE D

Pb/235U

EP

207

AC C

Quartzite Spot

1 sigma

207

Pb/206Pb

1 sigma

206

Pb/238U 206 Pb/ Pb

207

20

ACCEPTED MANUSCRIPT 1

4.3. Neoproterozoic meta-sedimentary rocks A population of about 40 detrital zircon grains from a sample of feldspathic quartzite (21MZ10)

3

attributed to the Rushinga Group, which is in juxtaposition with the cratonic border near

4

Catandica, was dated by U-Pb dating using the LA-ICP-MS instrument at the CPGeo. Only

5

Neoproterozoic ages were obtained from the nuclei of the detrital zircon grains (Fig. 6A).

6

Moreover, in this figure the concordant points (100 ± 10%) corresponding to the crystallisation

7

ages of the source rocks plot between 750 and 890 Ma. Therefore the maximum age of

8

sedimentation is approximately 750 Ma and the peak of the frequency histogram (Fig. 6B) is

9

located around 850 Ma. Nevertheless, the concordant points obtained from overgrowth rims of

10

some of the same zircons yielded much younger U-Pb ages, close to 500 or 600 Ma, indicating

11

recrystallisation during the medium- to high-grade Pan-African metamorphism. Sample

12

21MZ10, which produced Neoproterozoic maximum ages, does not include older zircons, in

13

great contrast with the meta-sediments of the Umkondo Group (samples 19MZ10 and 27MZ10),

14

whose detrital zircons are at least Paleoproterozoic and include a great deal of archean grains.

15 16 17 18 19

Figure 6. Concord Diagram and histogram showing U-Pb isotopic data from detrital zircons by LA-ICP-MS. Histogram (B) shows the peak of ~850 Ma. The peak of ~500 Ma observed in the histogram and reflected by the concordant points in concord diagram (A) represents the metamorphic ages obtained from metamorphic overgrowth rims.

20

These data are contrary to the ideas of Mantari (2008), which considered Umkondo and

21

Rushinga as contemporaneous. If sample 21MZ10 indeed belongs to the Rushinga Group, the

AC C

EP

TE D

M AN U

SC

RI PT

2

21

ACCEPTED MANUSCRIPT

analysis presented here implies that the granitoids of the Guro Suite are the possible source of its

2

zircons. The Guro Suite, which extends from northern Zimbabwe to Mozambique along the

3

Zambezi Belt, consists of an early-Neoproterozoic intrusive activity dated ca. 850 Ma. Moreover,

4

in sample 21MZ10 many of the detrital zircons exhibit oscillatory zoning in the CL images very

5

similar to those of zircon crystals presented by Chauque (2012) and Mantari (2008) for a aplite

6

granite-gneiss of the Guro Suite from Cuchamane and Changara areas, with magmatic

7

crystallisation nuclei c. 850 Ma and metamorphic overgrowth rims c. 500 Ma.

RI PT

1

SC

8

M AN U

9

10

11

15

16

17

EP

14

AC C

13

TE D

12

18

19

20

22

ACCEPTED MANUSCRIPT

Table 4- U-Pb LA- ICP-MS date, sample 21MZ10

Quartzite

Ratio 207Pb/235U

1sigma

206Pb/238U

1 sigma

Age (Ga)

238U/206Pb

1 sigma

207Pb/206Pb

1 sigma

208Pb/206Pb

error

1 sigma

206Pb/238U

1 sigma

1.2973

0.0255

0.1437

0.0029

0.99

6.9590

0.1428

0.0664

0.0005

0.2281

2.1

1.3560

0.0234

0.1445

0.0028

0.99

6.9189

0.1339

0.0680

0.0003

0.1682

3.1

1.3429

0.0228

0.1434

0.0028

0.99

6.9737

0.1345

0.0680

0.0002

0.1957

3.2

1.3298

0.0230

0.1419

0.0027

0.99

7.0454

0.1357

0.0675

0.0003

0.2173

4.1

1.3413

0.0236

0.1433

0.0028

0.99

6.9785

0.1350

0.0679

0.0004

0.3643

5.1

1.1469

0.0199

0.1260

0.0024

0.99

7.9394

0.1542

0.0665

0.0002

0.1998

0.0771

0.765

0.014

5.2

0.7345

0.0129

0.0887

0.0017

0.99

11.2785

0.2188

0.0603

0.0003

0.0625

0.0236

0.548

0.010

6.1

1.3721

0.0240

0.1460

0.0029

0.99

6.8483

0.1356

0.0685

0.0003

0.2091

0.0762

0.879

0.016

6.2

0.4982

0.0124

0.0661

0.0015

0.90

15.1367

0.3398

0.0561

0.0003

-0.0528

0.0189

0.412

7.1

1.2743

0.0223

0.1383

0.0027

0.99

7.2294

0.1416

0.0671

0.0004

0.2216

0.0766

0.835

7.2

1.3107

0.0227

0.1409

0.0027

0.99

7.0985

0.1352

0.0675

0.0003

0.3789

0.1275

8.1

1.3123

0.0219

0.1405

0.0027

0.99

7.1180

0.1347

0.0682

0.0002

0.3306

0.1084

8.2

0.6120

0.0108

0.0783

0.0015

0.99

12.7752

0.2471

0.0574

0.0003

-0.0197

9.1

1.3364

0.0238

0.1427

0.0016

0.62

7.0087

0.0767

0.0678

0.0004

0.4316

9.2

1.1531

0.0222

0.1287

0.0015

0.62

7.7697

0.0932

0.0654

0.0004

0.2580

0.0818

0.780

0.009

10.1

1.1541

0.0222

0.1288

0.0015

0.62

7.7616

0.0930

0.0654

0.0004

0.2529

0.0818

0.781

0.009

11.1

0.6968

0.0145

0.0873

0.0011

0.63

11.4567

11.2

1.3150

0.0236

0.1413

0.0015

0.61

7.0794

12.1

0.7504

0.0144

0.0918

0.0011

0.62

10.8899

13.1

1.3091

0.0229

0.1410

0.0015

0.62

14.1

1.2665

0.0224

0.1376

0.0015

0.62

15.1

1.3698

0.0241

0.1450

0.0016

0.62

16.1

1.3367

0.0236

0.1418

0.0015

0.62

7.0507

16.2

0.8037

0.0143

0.0971

0.0011

0.62

17.1

0.7075

0.0129

0.0872

0.0010

17.2

1.0014

0.0175

0.1128

18.1

0.9287

0.0146

18.2

1.2465

0.0189

19.1

1.3540

20.1

1.2794

M AN U

TE D

207Pb/235U

1 sigma

Conc.(%) 207Pb/206Pb

1 sigma

206Pb/238U 207Pb/206Pb

0.1032

0.866

0.017

0.845

0.011

0.814

0.016

106

0.0735

0.870

0.016

0.870

0.010

0.866

0.009

100

0.0827

0.864

0.016

0.864

0.010

0.865

0.007

100

0.0890

0.856

0.015

0.859

0.010

0.851

0.009

100

0.1447

0.863

0.016

0.864

0.010

0.864

0.011

100

0.776

0.009

0.817

0.008

94

0.559

0.008

0.608

0.009

90

0.877

0.010

0.881

0.010

100

0.009

0.411

0.008

0.451

0.012

91

0.015

0.834

0.010

0.837

0.011

100

0.850

0.015

0.850

0.010

0.849

0.011

100

0.847

0.015

0.851

0.010

0.872

0.007

97

0.0071

0.486

0.009

0.485

0.007

0.502

0.011

97

0.1344

0.860

0.009

0.862

0.010

0.859

0.011

100

0.779

0.010

0.783

0.013

100

0.779

0.010

0.782

0.013

100

SC

1.1

EP

Spot

Correc.

RI PT

Sample: 21MZ10

0.1493

0.0589

0.0004

0.0915

0.0304

0.539

0.007

0.537

0.009

0.558

0.016

97

0.0770

0.0676

0.0004

0.3547

0.1194

0.852

0.009

0.852

0.010

0.853

0.012

100

0.0003

0.0889

0.0307

0.566

0.006

0.568

0.008

0.623

0.012

91

0.0769

0.0676

0.0003

0.3167

0.1108

0.851

0.009

0.850

0.010

0.854

0.011

100

7.2699

0.0792

0.0673

0.0004

0.3580

0.1284

0.831

0.008

0.831

0.010

0.843

0.011

99

6.8987

0.0755

0.0681

0.0003

0.3024

0.1109

0.873

0.009

0.876

0.010

0.869

0.011

100

0.0767

0.0677

0.0004

0.3999

0.1500

0.855

0.009

0.862

0.010

0.857

0.013

100

10.2988

0.1136

0.0606

0.0003

0.0534

0.0206

0.597

0.006

0.599

0.008

0.619

0.011

97

0.61

11.4627

0.1261

0.0585

0.0004

0.0284

0.0117

0.539

0.006

0.543

0.008

0.542

0.014

100

0.0012

0.62

8.8617

0.0961

0.0640

0.0003

0.1498

0.0604

0.689

0.007

0.705

0.009

0.737

0.011

94

0.1052

0.0009

0.56

9.5048

0.0844

0.0637

0.0006

0.1971

0.0997

0.645

0.005

0.667

0.008

0.728

0.019

89

0.1360

0.0012

0.56

7.3508

0.0628

0.0665

0.0006

0.3101

0.1535

0.822

0.007

0.822

0.008

0.820

0.019

100

0.0208

0.1438

0.0013

0.58

6.9555

0.0624

0.0676

0.0006

0.3798

0.1842

0.866

0.007

0.869

0.009

0.854

0.018

101

0.0188

0.1385

0.0011

0.53

7.2191

0.0557

0.0672

0.0006

0.3076

0.1462

0.836

0.006

0.837

0.008

0.840

0.019

100

AC C

0.0607

7.0899

0.1305

23

ACCEPTED MANUSCRIPT

Table 4- U-Pb LA- ICP-MS date, sample 21MZ10 (cont.)

Quartzite

Ratio 207Pb/235U

1sigma

206Pb/238U

1 sigma

Spot

Correc.

Age (Ga)

238U/206Pb

1 sigma

207Pb/206Pb

1 sigma

RI PT

Sample: 21MZ10

208Pb/206Pb

error 1.2894

0.0194

0.1389

0.0011

0.52

7.1988

0.0561

0.0671

0.0006

0.3790

22.1

1.3355

0.0193

0.1434

0.0011

0.53

6.9745

0.0531

0.0678

0.0006

0.4497

23.1

1.2748

0.0189

0.1375

0.0011

0.52

7.2713

0.0562

0.0672

0.0006

0.4609

1 sigma

207Pb/235Pb

1 sigma

Conc.(%) 207Pb/206Pb

1 sigma

206Pb/238U 207Pb/206Pb

0.1765

0.839

0.006

0.841

0.009

0.837

0.020

0.2053

0.864

0.006

0.861

0.008

0.860

0.018

100 100

0.2070

0.831

0.006

0.835

0.008

0.840

0.018

99

25.1

1.2783

0.0190

0.1368

0.0011

0.53

7.3112

0.0578

0.0669

0.0006

SC

21.1

1 sigma

206Pb/238U

0.2950

0.1252

0.826

0.006

0.836

0.008

0.830

0.019

26.1

0.6450

0.0097

0.0808

0.0006

0.53

12.3779

0.0986

0.0574

0.0005

0.0068

0.0036

0.501

0.004

0.505

0.006

0.502

0.020

100

26.2

1.3013

0.0198

0.1405

0.0011

0.51

7.1199

0.0558

0.0674

0.0006

0.2620

0.1071

0.847

0.006

0.846

0.009

0.847

0.020

100

0.9324

0.0151

0.1061

0.0010

0.57

9.4272

0.0877

0.0639

0.0006

1.3140

0.0205

0.1419

0.0012

0.55

7.0461

0.0608

0.0679

0.0007

0.1623

0.0714

0.650

0.006

0.669

0.008

0.732

0.020

89

0.3725

0.1607

0.856

0.007

0.852

0.009

0.862

0.020

99 100

M AN U

24.1 24.2

27.1

1.2847

0.0186

0.1389

0.0011

0.52

7.1984

0.0544

0.0672

0.0006

0.4137

0.1663

0.839

0.006

0.839

0.008

0.841

0.018

100

28.1

1.3281

0.0079

0.1419

0.0008

0.96

7.0454

0.0404

0.0676

0.0005

0.4523

0.2194

0.856

0.005

0.858

0.003

0.852

0.015

100

29.1

1.3153

0.0079

0.1407

0.0008

0.97

7.1072

0.0412

0.0674

0.0005

0.3748

0.1842

0.849

0.005

0.852

0.003

0.846

0.015

100

30.1

1.2879

0.0068

0.1389

0.0008

0.99

7.1974

0.0397

0.0672

0.0005

0.4095

0.2039

0.839

0.004

0.840

0.003

0.840

0.015

100

31.1

0.5900

0.0050

0.0754

0.0005

0.80

13.2603

32.1

1.2673

0.0067

0.1373

0.0008

0.99

7.2837

1.2525

0.0068

0.1362

0.0008

0.99

7.3425

1.2802

0.0071

0.1386

0.0008

0.99

7.2132

0.0565

TE D

33.1 34.1

0.0904 0.0399

0.0669

0.0006

0.0117

0.0085

0.469

0.003

0.471

0.003

0.466

0.022

101

0.0005

0.3284

0.1681

0.829

0.004

0.831

0.003

0.832

0.015

100

0.0417

0.0663

0.0005

0.1985

0.1030

0.823

0.004

0.825

0.003

0.812

0.015

101

0.0411

0.0671

0.0005

0.2717

0.1427

0.837

0.004

0.837

0.003

0.839

0.015

100

1.2804

0.0067

0.1387

0.0008

0.99

7.2099

0.0395

0.0672

0.0005

0.2604

0.1390

0.837

0.004

0.837

0.003

0.841

0.014

100

1.0956

0.0072

0.1236

0.0009

0.99

8.0920

0.0565

0.0645

0.0004

0.4409

0.2388

0.751

0.005

0.751

0.003

0.752

0.015

100

37.1

1.2358

0.0066

0.1340

0.0007

0.99

7.4637

0.0417

0.0671

0.0005

0.4335

0.2382

0.811

0.004

0.817

0.003

0.837

0.015

97

EP

35.1 36.1

1.0125

0.0078

0.1166

0.0009

0.99

8.5741

0.0665

0.0642

0.0005

0.2083

0.1163

0.711

0.005

0.710

0.004

0.744

0.016

96

1.1512

0.0087

0.1265

0.0009

0.92

7.9025

0.0547

0.0665

0.0005

0.1930

0.1093

0.768

0.005

0.778

0.004

0.819

0.016

94

39.1

1.1742

0.0066

0.1299

0.0007

0.99

7.6984

0.0442

0.0656

0.0005

0.2458

0.1413

0.787

0.004

0.789

0.003

0.789

0.015

100

AC C

37.2 38.1

24

1 2 3

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Figure 7. Map of U-Pb magmatic cristalization ages in single zircon of rock from eastern border of Zimbabwe craton.

4.4. K-Ar ages and Pan-African regional rejuvenation.

4

At the eastern margin of the Zimbabwe Craton the Archean and Paleoproterozoic rocks

5

experienced partial or total loss of argon in their isotopic systems, as reflected in the K-Ar data

6

in Table 5 and plotted in Figure 8. The K-Ar Pan-African ages are also confirmed by U-Pb data

7

from overgrowth zircon rims of the meta-sediments of Umkondo and Rushinga produced in this 25

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work. Chauque (2012) produced similar ages from U-Pb zircon rims and from WR-garnet Sm-

2

Nd isochrones obtained from paragneisses belonging to the Macossa, Chimoio and Mungari

3

groups forming nappes which are in tectonic juxtaposition to the Zimbabwe Craton border. In

4

addition, in a few granitoids of the Archean Metamorphic Complex of Mudzi, Mantari (2008)

5

also obtained U-Pb SHRIMP zircon rim ages of 520 ± 16 Ma, with a lower intercept of 554 ± 33

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1

Tabela 5- K-Ar data of Precambrian rocks of midwestern region of Mozambique, incluinding pre-existing data of Vail & Dodson, 1969 (1) and of Sumburane, 2011 (2). Complex/ Suite

Rock

Sample

Material

40

Error Ar Rad (%) ccSTP/g

K (%)

40

Ar Atm (%)

Age (Ma)

Ref.

-6

Granite

02FR09

1.2

159.18

7.9

480±13

Granodiorite

7.3251

0.8

584.70

3.6

1372±23

Botite

7.9553

0.5

Mavonde

Granitoid

5aFR09

Mavonde

Granitoid

5bFR09

Mavonde

Amphibolite

07bFR09

Báruè

Granite

01FR09

Granitóide

15FR09

Guro

Granitóide

19FR09

Guro

Granitóide

19FR09

Guro

Granite

21bFR09

Chimoio

Granulite

09aFR09

Mungari

Paraneisse

Sohwe

Pelite

174.64

7.3

492±10

Botite

7.8494

1.5

164.56

4.4

472±14

Amphibole Botite

1.3836

0.5

32.31

10.1

519±13

7.6148

0.5

141.09

6.1

423±8

Botite

4.6108

0.5

104.58

6.6

506±10

Botite

5.6183

0.5

113.89

6.4

458±9

Amphibole

1.3825

0.6

27.42

11.4

450±10

Botite

7.9048

0.5

161.75

4.9

462±9

Botite

7.6664

0.5

135.76

5.6

406±8

7.8205

0.5

209.02

4.7

583±11

TE D

Báruè

18aFR09

Botite Botite

465±20

Botite

510±25

Muscovite

460±20

Botite

595±25 450±20

Pelite Pegmatite

Bangawia

Granite

Mina Benson

Pegmatite

Nyapanani

Gneisse

Muscovite Biotite

R. Gairezi

Pelite

Botite

525±25

Mashonaland

Dolorite

Whole rock

1400

Umkondo

Dolorite

Whole rock

640±20

Umkondo

Dolorite

Whole rock

1136±9

Umkondo

Dolorite

757±20

Mavonde

Granitoid

07MS12

Whole rock Botite

4.598

0.5

429.58

1.35

1529±21

09MS19

Botite

7.441

0.5

394.51

2.07

1016±16

7.440

0.5

173.89

3.13

519±10

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Mina Idol Mina Idol

Mavonde

Granitoid

615±30

Mavonde

Granitoid

09MS69

Botite

Mavonde

Granitoid

09MS15

Botite

7.677

1.3

180.46

3.74

522±13

09MS70

Botite

4.687

2.2

137.51

4.78

631±21

Mavonde

6

7.4553

04FR09

Botite Botite

M AN U

Mavonde Mavonde

SC

(*10 )

Granitoid

(1)

(2)

Ma in a Discordia produced by U-Pb TIMS (Table 3).

26

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2 3 4 5 6

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1

Figure 8. Map of k-Ar cooling ages in mica, whole rock (wr) and an amphibole (An); metamorphic recrystallization ages by U-Pb from overgrowth rims of zircon (Zr) and Sm-Nd from garnet (Grt), both reflecting the Pan-African event. CIBR= Basal Intrusive Complex of Ruchinga. (after Chaúque, 2012).

5. CONCLUSIONS

7

The review of the geochronological pattern related to the Zimbabwe Craton in Mozambique is

8

now very clear. The unit was formed during Archean tectonic episodes in which various granite27

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greenstone terrains were developed. Proterozoic events were only registered, up to now, in

2

detrital zircons from meta-sedimentary rocks whose sources may have been elsewhere in

3

Zimbabwe, Zambia or South Africa. Moreover, the Pan-African orogenic event, dated at about

4

500 to 600 Ma, is imprinted in all tectonic units and recorded, for example, in the U-Pb ages of

5

metamorphic recrystallization encountered in the rims of zircon crystals and in the K-Ar cooling

6

ages in mineral concentrates.

7

In Mozambique, the collisional Neoproterozoic to Cambrian Pan-African orogeny was the only

8

important tectonic event recognised in the Zimbabwe Craton. The intensity of deformation at the

9

cratonic margins is clearly associated with the progressive west-to-east increase of regional

10

metamorphic conditions, from greenschist to granulite facies. Over the cratonic area, the Paleo to

11

Mesoproterozoic sedimentary cover of Umkondo and Gairezi occur and other allochthonous

12

terranes, such as the Rushinga Group and other sequences.

13

This work corroborates that of Chauque (2012) in that the main suture of the Zimbabwe Craton

14

with the Mozambique Belt in the study area is marked by the frontal thrusts of two large nappes,

15

tentatively named Mungari and Macossa-Chimoio. The first nappe, to the north, would include

16

the Guro granitoid rocks of about 850 Ma. The second, to the south, would include the Baruè

17

magmatic arc, formed by orthomagmatic rocks of about 1100 Ma, overlaid by supracrustal rocks

18

with Neoproterozoic detrital zircons.

19

At the western side of the suture is the Zimbabwe Craton with its rejuvenated margin indicated

20

by the K-Ar age determinations with Neoproterozoic or Cambrian apparent ages. To the eastern

21

side the Mozambique belt appears containing paragneisses, which bring Neoproterozoic detrital

22

zircons and the Mesoproterozoic Báruè granitoids whose metamorphic rims yielded Cambrian

23

U-Pb ages.

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24

28

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ACKNOWLEDGEMENTS

This work results from the PhD research, whose project involved the cooperation of institutions

3

and individuals, provided in the form of financial aid and services. The scholarship was awarded

4

by the National Council for Scientific and Technological Development-CNPq of Brazil,

5

including financial aid for research by PRO-AFRICA program. The Ministry of Mineral

6

Resources, through the National Directorate of Geology and the University Eduardo Mondlane,

7

Mozambique, provided all technical and logistical support in carrying out the fieldwork.

8

Geosciences Institute of the University of São Paulo provided the academic qualification and

9

logistic support of their laboratory structure. We thank Filmão Catuane for their valuable

10

language reviews of earlier versions of the manuscript and the reviewers of the Journal of

11

African Earth Sciences, Geoff Grantham, Alfredo Kroner and Ruy Paulo Philipp.

SC

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WILLIAMS, I. S. (1998). U-Th-Pb Geochronology by Ion Microprobe. In: McKibben, M.A., Shanks III, W.C. and Ridley, W.I. (eds.), Applications of microanalytical techniques to understanding mineralizing processes, Reviews in Economic Geology, 7, 1-35.

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ACCEPTED MANUSCRIPT Highlights 

The magmatic ages at the eastern border of the Zimbabwe Craton vary between ca. 3.0 and 2.5 Ga.



Umkondo maximum depositional age is ~1800 Ma and Zimbabwe Craton is the



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main provenance source.

Over the border of the craton the metasedimentary rocks are Neoproterozoic of Mozambique belt.

The suture is marked by the frontal thrust of two nappes, Mungari and Macossa-

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

Chimoio

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Pan-African orogenic event is imprinted in all tectonic units.

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