# Mesoproterozoic orogeny in Malawi, part 1: Irumide Domain

Thomas Fullgraf, Steven Boger, Robert J. Thomas, Alexis Plunder, Kondwani Dombola

► To cite this version:

Thomas Fullgraf, Steven Boger, Robert J. Thomas, Alexis Plunder, Kondwani Dombola. Mesoproterozoic orogeny in Malawi, part 1: Irumide Domain. Journal of African Earth Sciences, 2026, 235, pp.105982. 10.1016/j.jafrearsci.2025.105982. hal-05442283

HAL Id: hal-05442283

https://brgm.hal.science/hal-05442283v1

Submitted on 5 Jan 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
<figure><img src="image_2.png" /></figure>

# Mesoproterozoic orogeny in Malawi, part 1: Irumide Domain

Thomas Fullgraf<sup>a, *</sup>, Steven D. Boger<sup>b</sup>, Robert J. Thomas<sup>c</sup>, Alexis Plunder<sup>a</sup>, Kondwani Dombola<sup>d</sup>

## ARTICLE INFO

Handling Editor: M Mapeo

### Keywords:

Malawi
Irumide
Mesoproterozoic
Orogeny

## ABSTRACT

The Mesoproterozoic Irumide belt is a paired orogen comprising two contrasting segments. The northerly, Irumide Domain, is composed of reworked Palaeoproterozoic crust and Mesoproterozoic igneous rocks. To the south, the South Irumide Domain consists of an assembly of juvenile Mesoproterozoic arc-related crustal blocks. The suture between the two domains is a sharp tectonic contact marked by a sudden change in lithologies, magmatism and isotopic signature. This paper describes the northern segment where recent geological mapping and laboratory studies allow its precise delineation in Malawi, building upon the definitions established in adjacent Zambia and Mozambique. The Irumide Domain has been subdivided into the Mzimba, Kasungu and Mchinji subdomains. Each contains high-grade paragneisses that post-date the ~2 Ga Ubendian orogeny. Two age-sequences are recognized; an older assemblage of paragneisses and quartzites considered to be high-grade metamorphic equivalents of the Muva Supergroup in Zambia, and including the Mafingi Group in Malawi. Detrital zircon data show that the other paragneiss sequence also contains significant contributions of ~1100 Ma source rocks currently unknown from Zambia. These younger paragneisses, together with a suite of granitoid orthogneisses dated at ~1080 Ma, provide evidence for a short-lived Mesoproterozoic active continental margin along the southern edge of the Congo-BaNy (combined Bangweulu Block-Nyika Subdomain) Craton. The first phase of the Irumide orogeny, resulting from arc accretion of the Irumide and South Irumide Domains to the Congo Craton, is dated at 1069 ± 9 Ma by local syntectonic anatectic melting in the suture between them. This was followed by closure of the Irumide Ocean and docking of the Proto-Kalahari craton from the south at c. 1045 Ma, which represents the main Irumide tectono-metamorphic event. Voluminous, syn-collision magmatism at c. 1040 Ma resulted from melting and assimilation of Ubendian-age continental crust from the Irumide Domain mixed with mantle-derived juvenile crust of the South Irumide Domain. Structural observations show that the Irumide Domain is sandwiched between South Irumide Domain rocks at the base of the tectonic pile and Congo Craton on top. This suggests that N-directed subduction of the Irumide Ocean beneath the Irumide Domain was followed by south-directed nappe transport during the collision phase. Our revised model of the Irumide Orogeny suggests that the main crustal architecture of southern Africa was established at the end of the Mesoproterozoic and is not just the result of the Neoproterozoic Pan-African, East African orogeny as advanced by some researchers.

## 1. Introduction

The Precambrian to early Palaeozoic geology of Malawi has attracted little attention in recent years, despite its critical position at the junction of several orogenic belts in SE Africa. Fig. 1 is a compilation of the basic crustal building blocks of southern East Africa, stripped of its zones of

variable later Neoproterozoic ("Pan-African") reworking which is locally intense throughout the area, especially in the south and east. Prior to the current survey, geological mapping of Malawi at 1:100k scale in the 1970s by the British Geological Survey (BGS), grouped the Precambrian rocks into the "Malawi Basement Complex" of the "Mozambique Belt" in the absence of radiometric ages (e.g. Bloomfield,

<footnote><sup>a</sup> Bureau de Recherches Géologiques et Minières, Orléans, 45060, France</footnote>

<footnote><sup>b</sup> Geological Survey of Victoria, Melbourne, Australia</footnote>

<footnote><sup>c</sup> Council for Geoscience, Bellville, Western Cape, 7535, South Africa</footnote>

<footnote><sup>d</sup> Geological Survey Department, Zomba, Malawi</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: T.Fullgraf@brgm.fr (T. Fullgraf).</footnote>
1966). The BGS maps show considerable accurate detail of rock types and structures but lithostratigraphic/lithodemic classification is lacking and, for example, ortho- and paragneisses were generally classified singly as vast areas of "biotite gneisses".

The Geological Mapping and Mineral Assessment Program (GEM-MAP) which ran from 2016 to 2021 involved the complete geological mapping of Malawi at a scale of 1:100,000, complemented by airborne geophysical data and by a comprehensive analytical program. The basic Precambrian geology of Malawi can be summarized as follows (Fullgraf et al., 2026).

1) The Palaeoproterozoic Ubendian Domain in the north, subdivided into three subdomains. Of these, the southernmost, Nyika Subdomain has been re-interprted to form part of a contiguous c. 2 Ga crustal entity with the Bangweulu Block of Zambia and termed the "BaNy Block" (Thomas et al., 2023a);

2) The Mesoproterozoic "Irumide Belt (IB)", comprising two major parts:

* **The Irumide Domain (IRD)** central Malawi, defined by Palaeoproterozoic rocks which underwent intense Mesoproterozoic orogeny;

* **The South Irumide Domain (SID)** in the south, composed of stacked juvenile Mesoproterozoic rocks (De Waele et al., 2006a, 2006b; Johnson et al., 2004, 2005; Westerhof et al., 2008; Boyd et al., 2010; Macey et al., 2010); also subdivided into three subdomains. Similarly, we use the term "SID-type crust" outside of Malawi in this paper.

We employ the terms Irumide **Domain** and South Irumide **Domain** as the two major crustal components of the IB/orogen, each subdivided

into **Subdomains**. The non-genetic terms "Domain" and "Subdomain" are used in favour of looser terms like "belt" or more genetic terms such as "terrane". Because the terms IRD and SID are not used in the published literature, the term "IRD/SID-type crust" is used outside of Malawi in this paper. When referring to both domains in a regional context, in this paper we use the informal terms "Irumide Belt/orogen", or "Irumides".

The three major tectonostratigraphic domains in Malawi were variably reworked during the Neoproterozoic to lower Palaeozoic ("Pan-African") East African orogen. In this paper, which constitutes Part 1 of our contribution to the Irumides in Malawi, we describe the geological evolution of the Irumide Domain (Fig. 1). A separate contribution to the Special Issue, Part 2, on the South Irumide Domain, also provides a regional synthesis of both Irumide domains in Malawi and the wider southern African region.

The Irumides were first described by Ackermann (1936, 1950, 1960) in Zambia and studied subsequently in numerous studies, reviews of which are given in De Waele (2009), De Waele et al. (2006a), Westerhof et al. (2008) and Goscombe et al. (2020).

## 2. Geological setting

### 2.1. Regional geology

The NE-trending Mesoproterozoic (~1.1 Ga) Irumide orogeny covers most of central and eastern Zambia and extends over 1500 km into northern Mozambique, Malawi and southern Tanzania, where it terminates just east of Lake Malawi (Thomas et al., 2016) (Fig. 1).

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Tectonic map of central/southern Africa showing the main Precambrian crustal domains with their protolith ages and demonstrating the importance of Mesoproterozoic terranes (modified after Fullgraf et al., 2026, this volume).</figcaption></figure>
### 2.1.1. *Irumide Belt rocks in surrounding countries*

Almost 100 published studies of the Irumides in Zambia and Tanzania have addressed the tectonic and metamorphic features, the age and composition of intrusive rocks and the geodynamic interpretation of the belt, outlining its evolution between c. 1400 and 1000 Ma.

#### 2.1.1.1. Zambia.
By far the largest part of the IB and its northern cratonic foreland outcrops in NW Zambia. The detailed geology and evolution of the area was established by the Zambian Geological Survey in the mid to late 20th century and detailed in a series of publications in the international geoscience literature (e.g. De Waele and Mapani, 2002; De Waele and Fitzsimons, 2007; De Waele, 2009; De Waele et al., 2003, 2005, 2006a, b, 2008; Johnson et al., 2004, 2005; Alessio et al., 2019a, b and their included references to the pioneering early work). The main features of the IB are.

(1) Palaeoproterozoic (c. 2.0 Ga) volcano-plutonic complexes and gneisses grouped as the "Bangweulu Block" (now BaNy Block) forming the cratonic basement and representing the eastern part of the Congo Craton;

(2) The craton is overlain by an extensive c. 1.85 Ga cover sequence of quartzite, metapelite and minor carbonate termed the Muva Supergroup;

(3) Kibaran-related events comprise a phase of NE-SW extension in the Palaeoproterozoic BaNy Block at around 1400 Ma, when the sediments of the Kasama Group were deposited in the NE part of the belt (Daly and Unrug, 1982; De Waele et al., 2006a), closely followed by a minor suite of anorogenic plutons (nepheline syenite and biotite granite), dated at 1.36-1.33 Ga (Vrána et al., 2004).

(4) Between 1150 and 1040 Ma the southern margin of the BaNy Block has been interpreted as either a passive (De Waele et al., 2005; De Waele et al., 2006a, b) or active (Johnson and Oliver, 2004; Johnson et al. 2005, 2007a, 2007b) continental margin, with the "Irumide Ocean" lying to the south

(5) Island arcs which formed in the Irumide Ocean south of the margin, and now constituting the SID, were accreted between 1070 and 1040 Ma and accompanied by high-temperature, low-pressure metamorphism and voluminous syn-to post-collisional Irumide granitoids emplaced between 1.05 and 1.02 Ma (Westerhof et al., 2008; Fullgraf et al., 2026).

Note that points 1 to 4 refer to IRD-type crust (i.e. Irumide-reworked Palaeoproterozoic crust), while point 5 refers to SID-type crust (i.e. juvenile c. 1 Ga crust).

The metamorphic gradient over the contact between the IB and the BaNy Block is very high, increasing over only c.100 km from sub-greenschist facies in the NW foreland to granulite facies in the central zone of the orogen (Ramsay and Ridgway, 1977; Karmakar and Schenk, 2016; Sakuwaha and Tsunogae, 2024, Wakabayashi et al., 2024).

#### 2.1.1.2. SW Tanzania.
Close to the eastern shore of Lake Malawi in the extreme SW of Tanzania a small area of IRD rocks outcrops in the Mgazini area (Thomas et al., 2016). The rocks exposed gave Ubendian protolith ages of ca. 1980–1800 Ma, but underwent high-grade metamorphism between 1015 and 1040 Ma and were intruded by granitoid at c. 1080 Ma. The area is also noteworthy in that it contains young quartzites that were deposited around 1.1 Ga.

#### 2.1.1.3. Mozambique.
There is very little IRD-type crust in Mozambique. In the far NW of NE Mozambique, the Ubendian-aged Ponte Messuli Complex is intruded by Irumide-age granites, but there is little evidence of pervasive Mesoproterozoic tectono-metamorphic reworking (Bingen et al., 2009). Geophysial data of Malawi suggest, however, the continuation of the IRD east of Lake Malawi (Fig. 1).

Island arc related rocks south of the IRD are subdivided into the Marrupa, Unango and Nampula metamorphic complexes and form part of the SID (Bingen et al., 2009; Boyd et al., 2010; Macey et al., 2010).

### 2.1.2. *Boundaries of the Irumide Belt*

In Malawi, the boundary of the IB with the Palaeoproterozoic Ubendian belt to the north has been interpreted as the NW- trending Mugesse Shear Zone (MuSZ) (Ring, 1993). This runs counter to our findings, which shows the Irumide-Ubendian contact in Malawi to be an arcuate thrust zone, ca. 100 km south of, and unrelated to, the MuSZ.

To the south, the IB was sutured against the Archaean-Palaeoproterozoic Proto-Kalahari craton (sensu Jacobs et al., 2008) along the Sanangoè shear zone (SSZ) (Westerhof et al., 2008). While the precise position and trend of the SSZ is not very well documented in NW Mozambique, in Malawi it is steep SE trending structure which follows the Shire River valley. The collision between the Irumides and Proto-Kalahari is widely thought to be Pan-African in age and coeval with the Damara-Lufilian-Zambezi belt system, more recently included in the "Kuunga orogen" by Goscombe et al. (2020), with the Irumides transported to the SE over the Proto-Kalahari craton (Westerhof et al., 2008). While we agree with the general geometry of this collision, we do believe it was originally a Mesoproterozoic (Irumide) collision zone, and rejuvenated during the Pan-African event.

To the east the IB is overlain by Pan-African nappes of the East African orogen (Bingen et al., 2009; Fritz et al., 2013).

## 3. Results

### 3.1. *Geology of the Irumide Domain in Malawi*

The IRD in Malawi covers an area of c. 21,200 km². It has been subdivided by crustal-scale shear zones and thrusts into the Mzimba (NW), Kasungu (SE) and Mchinji (SW) subdomains (Fig. 2). The rocks are of Palaeoproterozoic protolith age, but have been pervasively overprinted by Mesoproterozoic (Irumide) high-grade metamorphism and ductile deformation and intruded by ~1 Ga plutonic rocks. The largest Mzimba (c. 4600 km²) and Kasungu (c. 15,800 km²) subdomains are separated by a ~30 km wide, NW-trending, complex thrust zone that forms the NE extremity of the trans-continental Mwembesi Shear Zone (MwSZ). To the south, the Kasungu SD overlies the Lilongwe SD along a sharp tectonic contact that forms the suture between the SID and IRD (Fullgraf et al., 2026). To the west, the Lilongwe SD has been thrust over the Mchinji SD, obscuring the contact between the Mchinji and Kasungu SDs.

The Mzimba and Kasungu subdomains share similar rock types, tectonic styles and metamorphism, as well as predominantly Archaean to Palaeoproterozoic (Ubendian) Nd$_{Tdm}$ protolith ages (Fullgraf et al., 2026). The absence of Palaeoproterozoic orthogneiss and a systematic southward younging of Nd$_{Tdm}$ model ages in the Kasungu SD, up to 1.45 Ga indicates post-Ubendian deposition of the paragneiss precursor sediments and increasing influence of Mesoproterozoic juvenile sources. It also implies the post-Ubendian age of metamorphism and deformation in these subdomains.

Detailed field descriptions of all rock types of the IRD and their petrography are given in the explanatory notes to the 1:100,000 scale geological map series of Malawi produced by BGS geologists (Thatcher and Wilderspin, 1968; Peters, 1969, 1975; Walter, 1972; Bellingham and Bromley, 1973; Gaskell, 1973) and by GEMMAP (Boger et al., 2021 a,b; Fullgraf et al., 2021 a-d). Because there are an enormous number of lithodemic units defined and described in the many GEMMAP sheet explanations, they cannot each be described in this paper, so summary descriptions of all units (supracrystal and igneous rocks), together with illustrative photographs is given in Appendix 1. Due to generally poor outcrop conditions in Malawi, the spatial distributions of all the supra-crystal units were defined by their geophysical characteristics, with actual lithologies ascertained wherever outcrops occur.
<figure><img src="image_4.png" /><figcaption>Fig. 2. Simplified geological map of central Malawi. The supracrustal rocks of the IRD are shown at the subgroup level (this study).</figcaption></figure>

### 3.1.1. Supracrustal rocks

The Mzimba SD comprises high-grade supracrustal gneisses known as the Mzimba Group, subdivided into three lithodemic subgroups based mainly on their geophysical character (Table 1). The mineral parageneses of the Mzimba Group gneisses (e.g. garnet-sillimanite ± cordierite-biotite gneiss (locally with spinel) indicate Mesoproterozoic peak metamorphic conditions of granulite facies. They have been determined as 6–9.5 kbar at 900–1000 °C in cordierite gneiss of the Champira Dome in Malawi and dated by U-Pb monazite at 1047 ± 47 Ma (Hieber, 2021). Similar data were obtained from the western extension of the dome in Zambia (Sakuwaha and Tsunogae, 2024).

The Kasungu SD is poorly exposed in the western highlands of the Lilongwe-Kasungu Plain, but good outcrops are found along the eastern escarpment west of Lake Malawi. The supracrustal rocks (Kasungu Group) are a similar package to the Mzimba Group, characterised by garnet-biotite-sillimanite gneiss and sillimanite-bearing quartzite, along with layered leucogneiss, amphibolite and quartzite. In the NE part of the Kasungu SD, metamorphic peak conditions of 5.1–7.2 kbar/ 730–770 °C dated at 1038 ± 36 Ma have been determined (Böhme, 2021).

In contrast, the Mchinji SD is of markedly lithologically different. It occupies a small area of about 800 km² in the border area with Zambia in the SW (Fig. 2). Ferruginous quartzite, banded iron formation, massive quartzite and metapelitic paragneiss of the Mchinji Group underwent granulite facies metamorphism at c. 5–7 kbar at 800–950 °C dated at 1013 ± 4 and 1021 ± 4 Ma (Karmakar and Schenck, 2016).

### 3.1.2. Plutonic rocks

The supracrustal rocks of the IRD were intruded by widespread,

typically sheet-like, late Mesoproterozoic granitoids, between 1060 and 1020 Ma. They are grouped into the Mkanda Suite which covers about one third of the surface area of the domain (c. 7200 km²; Fig. 2). The suite ranges from deformed, locally migmatised orthogneisses (Euthini facies), to less deformed, locally megacrystic granitoids. The Mkanda Suite was intruded by the metamorphosed sub-alkaline mafic rocks of the Bua Suite (Thatcher and Wilderspin, 1968) that form numerous small plugs, stocks and dykes in the Kasungu SD (and the northern part of the SID). Their emplacement post-dates the juxtaposition of the IRD with the SID but predates regional medium-to high-grade regional metamorphism, making the suite a valuable time marker. Most common are rocks with clinopyroxene, plagioclase (andesine), hornblende and garnet as major components. A relict, sub-ophitic (plagioclase-clino-pyroxene) magmatic texture is preserved in most samples. The minimum age of regional high-grade tectono-metamorphism is constrained by the Neoproterozoic alkaline Nyassa Suite, occurring as intrusions in the Irumide gneisses.

### 3.1.3. Structural geology

The structural map of Fig. 3 illustrates the larger scale tectonic elements (contacts, shear zones, folds, faults), with stereogram plots illustrating the variation in orientation of the small-scale planar and linear elements (Fig. 4). The statistics of the stereograms are presented in Table 2.

### 3.1.4. Mzimba SD

The boundary between the Mzimba SD and the Ubendian Nyika SD is marked by a major change in tectonic style and magmatism but appears to be gradual over a transition zone several kilometres wide. Where
<caption>**Table 1**</caption>

The main characteristics of each subdomain with the surface area, percentage of sediment cover, the abundance of observed rock types, and principal geophysical features.

<table><thead><tr><th rowspan="2">Subdomain/Group</th><th colspan="4">Mchinji (Imc)</th><th colspan="2">Kasungu</th><th colspan="3">Mzimba</th></tr><tr><th>Imc1</th><th>Imc2</th><th>Imc3</th><th>Imc4</th><th>Ika1</th><th>Ika2</th><th>Imz1</th><th>Imz2</th><th>Imz3</th></tr></thead><tbody><tr><td>Subgroup</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Total surface area of unit [km2]</td><td>52</td><td>142</td><td>423</td><td>0.8</td><td>8355</td><td>2238</td><td>843</td><td>1870</td><td>1225</td></tr><tr><td>Sediment cover [%]</td><td>79.0</td><td>81.0</td><td>78.0</td><td>100.0</td><td>55.0</td><td>48.0</td><td>99.0</td><td>67.0</td><td>8.8</td></tr><tr><td>Rock Type</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(gt) bt gneiss</td><td>+</td><td>++</td><td>++</td><td></td><td>++</td><td>++</td><td>++</td><td>++</td><td>++</td></tr><tr><td>leucogneiss</td><td></td><td></td><td>+</td><td></td><td>+//++</td><td>+//O</td><td>+//++</td><td>++</td><td>O</td></tr><tr><td>quartzite</td><td>+//++</td><td>+//++</td><td>++</td><td></td><td></td><td>+</td><td></td><td>+</td><td>O</td></tr><tr><td>sl-ms-quartzite/schist</td><td></td><td>++</td><td>+</td><td></td><td></td><td>O</td><td></td><td></td><td></td></tr><tr><td>bt-ms gneiss/schist</td><td></td><td></td><td></td><td></td><td></td><td>+</td><td></td><td>+//++</td><td></td></tr><tr><td>(gt) ms schist</td><td></td><td></td><td>++</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>qz-ms schist/phyllonite</td><td></td><td></td><td>++</td><td></td><td></td><td></td><td></td><td>+</td><td>+</td></tr><tr><td>(banded) bt-hb gneiss, amphibolite</td><td></td><td></td><td></td><td></td><td>++</td><td></td><td></td><td>+//++</td><td></td></tr><tr><td>calc-silicate gneiss</td><td></td><td></td><td></td><td></td><td>+//O</td><td></td><td></td><td>O</td><td></td></tr><tr><td>gt-hb-gneiss</td><td></td><td></td><td></td><td></td><td></td><td></td><td>+//++</td><td>+//++</td><td></td></tr><tr><td>(sp) gt-bt-sl gneiss/schist</td><td>++</td><td></td><td></td><td></td><td></td><td>+//++</td><td></td><td></td><td></td></tr><tr><td>cd-gt-bt-sl gneiss (granulite)</td><td>++</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>++</td></tr><tr><td>(gt, bt)-mt-sl-qz gneiss (granulite)</td><td>++</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>sp-mt-(px)-sl-cd gneiss (granulite)</td><td>++</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>banded iron formation (BIF)</td><td>O</td><td></td><td></td><td>++</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>ferruginous quartzite</td><td></td><td></td><td>O</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(Mn) ferruginous schist</td><td></td><td></td><td>O</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>greenschist</td><td></td><td></td><td></td><td>++</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Geophysics</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Potassium</td><td>-</td><td>-</td><td>-/o</td><td>-</td><td>-//++</td><td>o//++</td><td>-</td><td>o//++</td><td>-</td></tr><tr><td>Thorium</td><td>+</td><td>+</td><td>o</td><td>+</td><td>-/o</td><td>+//++</td><td>o//+</td><td>o//++</td><td>o</td></tr><tr><td>Uranium</td><td>-</td><td>o</td><td>o//++</td><td>+</td><td>-/o</td><td>+//++</td><td>o//+</td><td>+//++</td><td>o</td></tr><tr><td>RTP_TMF</td><td>++</td><td>o</td><td>-/+</td><td>o</td><td>-</td><td>-//++</td><td>o//++</td><td>-/o</td><td>++</td></tr><tr><td>Magnetic texture</td><td>L</td><td>S</td><td>S/M</td><td>M</td><td>S/M</td><td>S/M</td><td>L</td><td>M/L</td><td>M</td></tr><tr><td>Representative HCA cluster</td><td>11, 12</td><td>4, 11</td><td>4, 11 (5, 9)</td><td>4</td><td>1, 5, 3, 4, 11 (7)</td><td>10, 14, 8, (3)</td><td>10 (8)</td><td>7, 9 (8, 10)</td><td>12, 10</td></tr></tbody></table><table><thead><tr><th colspan="2">Legend</th></tr><tr><th>Rock type</th><th>Geophysics</th></tr></thead><tbody><tr><td>major</td><td>low</td></tr><tr><td>minor</td><td>moderate</td></tr><tr><td>rare</td><td>elevated</td></tr><tr><td></td><td>high</td></tr></tbody></table>

bt = biotite, L = layered, cd = cordierite, S = smooth, gt = garnet, M = Mottled, hb = hornblende, ms = muscovite, mt = magnetite, px = pyroxene, sl = sillimanite, sp = spinel.

unaffected by later Pan-African deformation (see Fullgraf et al., 2026), foliations and lineations in the Nyika SD are steep (Fig. 4, NY-4), whereas in the Mzimba SD foliations dip moderately/shallowly to the east or west (MZ-1, MZ-2) with shallow N-plunging lineations. The transition between the two subdomains is recorded in area NY-3, where the foliations dip steeply (Ubendian trend) and both steep (Ubendian) and shallow (Irumide) lineations occur. In the north, N- and NE-dipping foliations indicate the underlying position of the Mzimba SD with respect to the Nyika SD. In the east and south, the contact was reactivated during the Pan-African event, which transformed the rocks into mylonitic gneisses and schists (Fig. 3). The outlines of individual units on the geological and structural maps of the Mzimba SD (Figs. 2 and 3) illustrate regional polyphase deformation with three fold phases recognized (Fullgraf et al., 2022). F1 folds are the most common, being marked by narrow to closed fold hinges, N-S trending axial planes and shallow N- or S-plunging axes; at regional scale they correspond to the F2 folds in the Kasungu SD. The final phase of gentle, large-scale F3 folds have WNW-ESE trending axial planes, so that interference with F1 folds resulted in the regional domes and basins seen. The most dominant F3 structure is the 50 × 20 km, elliptical N-S trending northern dome, within which polyphase deformation resulted in several smaller dome and basin structures at the ~10 km scale. Pan-African F4 structures refold the F3 domes and basins in the SE part of the Mzimba SD around N-S trending axes.

### 3.1.5. Mwembeshi SZ

In the south, the Mzimba SD is truncated by the c. 30 km wide, NE-SW trending Pan-African MwSZ which forms the northern boundary of

the Kasungu SD to the south (Fig. 2). The main shear sense is dextral, as inferred from the geometry of the N-S trending older gneissic fabrics and fold axial traces that rotate clockwise into the structure on either side and by the right-facing asymmetrical rhombohedral-shape of the Champira dome mega-boudin, which measures 50 × 15 km. The northern half of the MwSZ forms a several kilometers wide schist belt, while the southern contact is characterised by an anastomosing system of discrete mylonite zones. All structures in the schist belt are transposed towards the MwSZ trend (Fig. 4, MwSZ-2). The poles of the planar structures define a NE plunging fold axis, parallel to the maximum of lineations (Table 2). In contrast, planar structures in the Champira dome are often highly oblique (Fig. 4; MwSZ-1) which are interpreted as preserved older Mesoproterozoic structures.

### 3.1.6. Kasungu SD

The northern boundary of the Kasungu SD is the MwSZ, as described above. In the south, the sharp boundary between the Kasungu and Lilongwe SDs represents the suture between the IRD and SID. It is characterised by a sudden change in radiometric and magnetic signals, lithology, metamorphism and Nd isotope composition. The structurally overlying position of the Kasungu SD was observed in the area between Ntchisi and Dowa (Fig. 3; Fullgraf et al., 2026).

The Kasungu SD is structurally characterized by flat-lying foliations, N-plunging lineations and polyphase folding where unaffected by Pan-African deformation. Three generations of Irumide folding are recognized (Fig. 3). Large-scale F1 isoclinal folds were traced mainly in the eastern Kasungu SD, but they are common at outcrop scale across the IRD (Fullgraf et al., 2022). NW- to N-trending, open to closed F2 folds
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Structural map of northern to central Malawi illustrating the main geological units and structural elements. The three Irumide subdomains are shown in different shades of green.</figcaption></figure>

are the most common, occurring throughout the subdomain, particu-
larly in the west where they are the most prominent structures, being up
to tens of kilometres in wavelength. The F2 folds deform the
Kasungu-Lilongwe SD contact in the south and are transposed into the
MwSZ in the northern part of the SD. E-W trending, open F3 folds in the
eastern Kasungu SD result in similar basin and dome geometries as in the
Mzimba SD. NW-SE trending Panafrican F4 folds in the eastern part of
the subdomain add additional interference folding patterns to the earlier
generations. F5 folds are limited to the SE corner of the Kasungu SD
where they transpose the older structures into the final NE-trend.

Six stereograms illustrate the regional changes in orientation of
gneissic foliations and lineations in the IRD and adjacent areas (Figs. 4
and 5, and Table 2). Gneissic foliations in KA1, KA2 and KA3 are rotated

around shallow SW plunging axes, parallel to the measured NE and SW
plunging lineations. NW-SE shortening and parallelism with the MwSZ
suggest that their final orientation is strongly influenced by dextral
transpression. Lineations of subset KA3 have in contrast low multidi-
rectional plunges, illustrating polyphase deformation, so no unique so-
lution explains the data distribution. The distribution of gneissic
foliations in KA4 with relatively few data differs considerably from that
of subsets KA-1 to 3, even though shallow to moderate dips predominate
again. Two density maxima correspond to moderately SE and WNW
dipping planes whereas fold axes plunge at low angle SSE. Subset KA-5
in the central eastern part of the Kasungu SD is almost unaffected by the
MwSZ. Gneissic foliations dip mostly shallowly south and SE; their wide
scatter indicates fold interference structures. Lineations plunge at low to
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Stereograms of gneissic foliations (and minor mylonitic fabrics, schistosity) and simplified structures indicating the area for each stereogram (7712 data points).</figcaption></figure>

moderate angles in almost all directions with the majority clustering from the S to the SW, similar to KA3. The orientation of planar and linear data in KA6 differs from all other subsets, which is attributed to the uplift of the adjacent Unango SD. Gneissic foliations and associated down-dip lineations dip in NW directions, away from the rising dome. The remainder of the data is scattered over a broad NW-SE belt, suggesting additional interference folding. The influence of the Unango metamorphic dome is also evident in subset NC-1 of the Lilongwe SD, which envelops the NW part of the structure.

In summary, the orientation of tectonic structures in the Kasungu SD is influenced by the MwSZ in the north, by the Unango metamorphic dome in the SE and in the other parts characterized by flat foliations and

polyphase or non-coaxial deformation.

### 3.1.7. Mchinji SD

The Mchinji SD is bounded in the east by the Lilongwe SD (SID). The contact generally dips east, implying that the latter was thrust over the former. This is confirmed by SC fabrics and asymmetric sigma clasts in orthogneiss near the contact, suggesting westward tectonic transport, but which could be either of Irumide and/or Pan-African in age. Discrete steep shear zones of mylonitic quartzite and orthogneiss with prominent down-dip lineations close to, and at, the boundary record subsequent top-to-the-east normal movements which may be associated with late-Pan-African extension. In the south, the domain boundary links with
<caption>**Table 2**</caption>

Statistical data of the stereograms of the IRD and adjacent areas (from north to south). n = number of data; ρ = data density at maximum (multiples of random distribution); Max1-3 = direction of calculated local maximum; R1, 2 = calculated rotation axis 1, 2 (in blue); AC = perpendicular plane to fold axis. The structural symbols illustrate graphically the calculated dip/plunge direction to their left.

<table><thead><tr><th rowspan="2">Area</th><th colspan="8">Lineations</th><th colspan="8">Foliations</th></tr><tr><th>n</th><th>ρ</th><th>Max1</th><th>Max2</th><th>Max3</th><th>R1</th><th>R2</th><th>n</th><th>ρ</th><th>Max1</th><th>Max2</th><th>Max3</th><th>R1</th><th>R2</th><th>Δ AC 1-2</th></tr></thead><tbody><tr><td>NY3</td><td>84</td><td>3.5</td><td>351/33</td><td>3.4</td><td>090/62</td><td></td><td></td><td>383</td><td>2.8</td><td>065/72</td><td>2.4</td><td>297/75</td><td>2.1</td><td>137/76</td><td>086/70</td><td>324/71</td><td>204/10</td></tr><tr><td>NY4</td><td>124</td><td>5.8</td><td>345/78</td><td></td><td></td><td></td><td></td><td>640</td><td>4.5</td><td>005/72</td><td></td><td></td><td></td><td></td><td>355/71</td><td></td><td></td></tr><tr><td>MZ2</td><td>48</td><td>10.7</td><td>018/12</td><td></td><td></td><td>124/53</td><td></td><td>286</td><td>4.3</td><td>099/42</td><td></td><td>2.4</td><td>299/75</td><td></td><td>033/27</td><td>318/73</td><td>129/17</td></tr><tr><td>MZ1</td><td>60</td><td>6.8</td><td>358/09</td><td>5.2</td><td>028/10</td><td></td><td></td><td>321</td><td>4.9</td><td>104/45</td><td></td><td>1.9</td><td>298/44</td><td></td><td>021/09</td><td></td><td></td></tr><tr><td>MW2</td><td>20</td><td>20.0</td><td>074/27</td><td></td><td></td><td></td><td></td><td>225</td><td>4.0</td><td>348/30</td><td></td><td></td><td></td><td></td><td>062/09</td><td>004/29</td><td></td></tr><tr><td>MW1</td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td>87</td><td>4.6</td><td>042/69</td><td></td><td>3.5</td><td>336/62</td><td></td><td>001/60</td><td></td><td></td></tr><tr><td>KA1</td><td>44</td><td>9.1</td><td>212/06</td><td></td><td></td><td>207/30</td><td></td><td>327</td><td>5.1</td><td>136/33</td><td></td><td>2.5</td><td>318/36</td><td></td><td>220/03</td><td></td><td></td></tr><tr><td>KA2</td><td>103</td><td>4.9</td><td>183/18</td><td>3.5</td><td>080/21</td><td></td><td></td><td>656</td><td>3.4</td><td>131/33</td><td></td><td>1.9</td><td>317/64</td><td></td><td>210/16</td><td></td><td></td></tr><tr><td>KA3</td><td>158</td><td>6.1</td><td>185/15</td><td></td><td></td><td>306/62</td><td></td><td>585</td><td>5.2</td><td>270/21</td><td></td><td>3.3</td><td>126/43</td><td></td><td>207/12</td><td></td><td></td></tr><tr><td>KA4</td><td>22</td><td>9.3</td><td>175/15</td><td></td><td></td><td>033/70</td><td></td><td>147</td><td>4.4</td><td>134/39</td><td></td><td></td><td></td><td></td><td>163/32</td><td>244/30</td><td>022/52</td></tr><tr><td>KA5</td><td>227</td><td>8.1</td><td>178/15</td><td></td><td></td><td>054/61</td><td></td><td>1098</td><td>8.7</td><td>170/18</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>KA6</td><td>84</td><td>11.3</td><td>340/36</td><td></td><td></td><td>038/68</td><td></td><td>490</td><td>7.1</td><td>296/51</td><td></td><td>1.5</td><td>124/65</td><td></td><td>343/39</td><td>211/05</td><td>117/40</td></tr><tr><td>LI1</td><td>201</td><td>4.2</td><td>329/27</td><td>4.1</td><td>006/20</td><td></td><td>161/64</td><td>1108</td><td>2.9</td><td>069/39</td><td></td><td>2.9</td><td>015/07</td><td></td><td>356/10</td><td></td><td></td></tr><tr><td>NC1</td><td>212</td><td>10.3</td><td>325/39</td><td></td><td></td><td>130/52</td><td></td><td>1036</td><td>6.6</td><td>304/42</td><td></td><td>4.3</td><td>040/49</td><td></td><td>345/34</td><td></td><td></td></tr><tr><td>MC1</td><td>15</td><td>14.2</td><td>090/78</td><td></td><td></td><td></td><td>161/64</td><td>85</td><td>6.2</td><td>091/75</td><td></td><td></td><td></td><td></td><td>069/72</td><td>282/58</td><td>181/07</td></tr><tr><td>MC2</td><td>18</td><td>12.7</td><td>082/33</td><td></td><td></td><td>250/60</td><td></td><td>238</td><td>7.5</td><td>052/45</td><td></td><td></td><td></td><td></td><td>100/32</td><td>060/44</td><td></td></tr></tbody></table>

the Pan-African Ntcheu SZ. NE-dipping foliations and several drag folds in vicinity of the contact (near Namitete) suggest transpressive west-directed movements with a sinistral component and the overlying position of the Lilongwe SD (Fig. 3).

Numerous rafts of Mchinji migmatitic paragneiss in the Dzalanyama granite (Thatcher and Wilderspin, 1968) dated at 1054 ± 17 Ma constrain the minimum age of Irumide deformation and high-grade metamorphism. The regional fold style is characterized by tight to isoclinal folds with upright to steeply east and NE dipping curvilinear axial planes that change from a NW trend in the west to a southerly trend in the east. They are intruded by the Mesoproterozoic granite.

Two stereograms illustrate the orientation of gneissic foliation and lineation in the NW (MC1) and SE (MC2). MC-1 shows mainly steeply east dipping planes and a smaller group of moderately west dipping planes. Lineations show predominantly steep east-plunges (Table 2). Most have been measured in the mylonitic rocks north of Mchinji, where they constrain east directed down-dip movements. A small group of stretching lineations plunge moderately to the south, which is the characteristic Irumide direction. In MC2, gneissic foliations dip mostly NE and a smaller group SW. Lineations have low to moderate east-plunges coinciding with the axes of drag folds in the Lilongwe SD.

## 3.2. U-Pb zircon geochronology

Thirty-nine samples of paragneisses and quartzites (detrital studies), orthogneisses, granites and anatectic leucosomes from the IRD provide a wealth of new data on the timing of sedimentation, magmatism and metamorphism. The detailed description of the samples, the analytical methods and results are presented in Appendices 2–4. The results are summarized in Table 3 (supracrustal rocks) and Table 4 (plutonic rocks), and in Figs. 6 and 7. In addition, monazite ages from studies by Karmakar and Schenck (2016), Hieber (2021) and Sakuwaha and Tsunogae (2024) are shown in Fig. 7b.

### 3.2.1. Detrital zircon geochronology

Six samples of paragneiss and quartzite from the IRD were analysed for detrital zircon ages, four of which gave broadly similar results (Fig. 6b).

(1) NK1543 is a Mzimba SD migmatitic paragneiss. The extracted homogeneous translucent, light pink zircons vary in habit from short-to long prismatic and euhedral to subhedral grains, often with well-preserved terminations. The edges of the crystals are, however, commonly rounded, attesting to limited sedimentary transport. CL imagery shows magmatic oscillatory zoning, and sometimes rounded and angular xenocryst cores indicating an inherited component. The data display Late Archaean to Paleoproterozoic ages (Fig. 15 of Appendix 3). The low number of data is insufficient to support robust statistical analysis. However, the results suggest a predominant source with an age of approximately 1886 Ma, which provides a maximum depositional age ca. 80 Ma after Ubendian high-grade metamorphism (Le Bayon et al., 2024). This, in turn, constrains the Irumide age of high-grade metamorphism recorded in these rocks.

(2) NK1670 is quartzite from the Mzimba SD. Small, rounded zircons form a single population of long, prismatic euhedral translucent crystals of orange colour. CL imagery reveals oscillatory magmatic zoning and rare xenocryst cores. The ages display a continuous spectrum between 1854 and 2089 Ma (Fig. 16 of Appendix 3), although statistical unmixing suggests there are two populations with ages of ~2030 and 1950 Ma. Sixteen analyses define the youngest coherent near-concordant group, from which a weighted mean Pb$^{207}/206$ age of 1952 ± 11 Ma (MSWD = 0.59) is obtained, providing a conservative estimate for the maximum depositional age of the quartzite. Two younger single analyses yielded ages of 1892 ± 21 Ma and 1854 ± 26 Ma and might argue the quartzite was deposited after ~1850 Ma.

(3) NT4531 is a cordierite gneiss from the Champira dome. The rocks exposed at this location are comprised of migmatitic cordieritesillimanite magnetite-bearing metapelitic gneiss. 32 analyses were undertaken and these gave a complex distribution of concordant and discordant data. A grouping of the three youngest analyses fall on concordia a yield a weighted mean Pb$^{207}/206$ age of 1051 ± 27 Ma, which is interpreted to date the timing of (Irumide) metamorphism. The remaining analyses lie along discordia lines that project to a ~1050 Ma lower intercept and upper intercepts at 2697 ± 30 Ma (6 grains), 2360 ± 42 Ma (5 grains)
<figure><img src="image_7.png" /><figcaption>Fig. 5. Stereogram presentations of linear structures (1421 data points).</figcaption></figure>

and 2137 ± 27 Ma (11 grains). The youngest of these intercept ages is interpreted to provide a maximum depositional age for this rock, while the older intercept ages point to Palaeoproterozoic and Archaean inherited components. The youngest grains with discordance <10 % yield Pb²⁰⁷/²⁰⁶ ages from 1965 ± 21 Ma to 1817 ± 21 Ma, which together with the absence of Palaeoproterozoic intrusions argues for the Irumide age of deposition.

(4) NT4800 is a migmatitic paragneiss from the northern Kasungu SD. Anhedral zircons up to 120 µ in size are well rounded indicating extensive sedimentary transport. 55 data points were concordant within <15 % and show a range of ages between 950 and 2750 Ma. The youngest 9 grains (Th/U = 0.01–0.57) yielded

Pb²⁰⁷/²⁰⁶ ages between 950 and 1120 Ma, from which 7 group to yield a weighted mean ²⁰⁷/²⁰⁶Pb age of 1038 ± 36 Ma, taken to date the timing of regional metamorphism (Fig. 30 of Appendix 3). The remaining data are variably discordant and define a number of discordia lines that project away from ~1050 Ma. The largest such group (43 analyses) defines an upper intercept at 1994 ± 29 Ma. However, the concordant data within the group yield ages between 1810 and 2030 Ma, indicating that more than one age population is present. A second discordia (9 analyses) yields an upper intercept age of 2645 ± 59 Ma, while a third, poorly-defined discordia (4 grains) yield an upper intercept age of 2883 ± 70 Ma. The youngest 11 Palaeoproterozoic zircons yield a weighted mean Pb²⁰⁷/²⁰⁶ age of 1865 ± 26 Ma, which
<caption>**Table 3**</caption>

Summary of U-Pb detrital zircon geochronology, supracrustal rocks from the IRD. PP_Met = Palaeoproterozoic metamorphism, MP_Met = Mesoproterozoic metamorphism, PanAf_Met = Pan-African metamorphism, Detrital = detrital age, Xenocryst = xenocryst age. For abbreviation of minerals, see Table 1.

<table><caption>**Table 4**</caption><thead><tr><th>Group</th><th>Sample</th><th>Rock</th><th>PP_Met</th><th>MP_Met</th><th>PanAf_Met</th><th>Detrital</th><th>Xenocryst</th></tr></thead><tbody><tr><td rowspan="4">Mzimba</td><td>NK1615</td><td>leucosome</td><td>1989 ± 11</td><td></td><td></td><td></td><td>2026 ± 23</td></tr><tr><td>NK4355-2</td><td>leucosome</td><td>2006 ± 13</td><td></td><td>509 ± 10</td><td></td><td></td></tr><tr><td>NK1543</td><td>mig gt-bt gneiss</td><td></td><td></td><td>c. 550</td><td>1886 2560</td><td></td></tr><tr><td>NT4531</td><td>mig cd-mt gneiss</td><td></td><td>1051 ± 27</td><td></td><td></td><td>2700 ± 31 2366 ± 38 2133 ± 27</td></tr><tr><td rowspan="4">Kasungu</td><td>NK1670</td><td>quartzite</td><td></td><td></td><td></td><td>1852 ± 26 1950 ± 11 2030 ± 15</td><td></td></tr><tr><td>SA0704-1</td><td>leucosome</td><td></td><td>1058 ± 17</td><td>601 ± 7</td><td></td><td>1990 ± 17</td></tr><tr><td>LL0414</td><td>mig gt-bt paragneiss</td><td></td><td>1083 ± 5</td><td></td><td>1095 ± 14 1253 ± 47 1808 ± 57 2015 ± 33 3025 ± 50</td><td></td></tr><tr><td>NT1823</td><td>mig paragneiss</td><td></td><td>1042 ± 20</td><td>518 ± 29</td><td></td><td></td></tr><tr><td rowspan="2">Mchinji</td><td>NT4800</td><td>mig gt bt sl gneiss</td><td></td><td>1038 ± 36</td><td></td><td>1865 ± 26 1994 ± 29 2618 ± 40 2645 ± 59 2883 ± 70</td><td></td></tr><tr><td>LL0369</td><td>mylonitic quartzite</td><td></td><td></td><td></td><td>1773 ± 5 1887 ± 4 2034 ± 7 2188 ± 7 2626 ± 6</td><td></td></tr></tbody></table>

Summary of U-Pb zircon geochronology, plutonic rocks. MP_Met = Mesoproterozoic metamorphism, PanAf_Met = Pan-African metamorphism, Detrital = detrital age, Xenocryst = xenocryst age. For abbreviation of minerals, see Table 1.

<table><thead><tr><th>Suite</th><th>Sample</th><th>Rock</th><th>Emplacement</th><th>MP_Met</th><th>PanAf_Met</th><th>Xenocryst</th></tr></thead><tbody><tr><td>Bua</td><td>LL1869</td><td>gt-px-hb-pl metaggabro</td><td>1040 ± 9</td><td></td><td>529 ± 8</td><td></td></tr><tr><td rowspan="21">Mkanda</td><td rowspan="16">non-migmatitic</td><td>NT0006</td><td>bt-orthogneiss</td><td>1030 ± 11</td><td></td><td>517 ± 14</td><td></td></tr><tr><td>NT4498</td><td>ms-bt orthogneiss</td><td>1037 ± 15</td><td></td><td></td><td></td></tr><tr><td>NT1370</td><td>bt granite</td><td>1040 ± 10</td><td></td><td></td><td>1153 ± 20</td></tr><tr><td>LL0118</td><td>bt-ks augengneiss</td><td>1042 ± 13</td><td></td><td></td><td>1147 ± 19</td></tr><tr><td>LL0127</td><td>bt orthogneiss</td><td>1045 ± 2</td><td></td><td></td><td>1153-1075</td></tr><tr><td>LL1846</td><td>bt orthogneiss</td><td>1047 ± 9</td><td></td><td>512 ± 13</td><td>2072 ± 49</td></tr><tr><td>NK1506</td><td>bt-orthogneiss</td><td>1048 ± 22</td><td></td><td></td><td>1152 ± 51</td></tr><tr><td>LL0186</td><td>non-mig px-bt charnockite</td><td>1053 ± 4</td><td></td><td></td><td>1285</td></tr><tr><td>NK1329</td><td>gt leucogneiss</td><td>1053 ± 93</td><td>1019 ± 13?</td><td></td><td></td></tr><tr><td>NK4346</td><td>ks granite (post-kinematic)</td><td>1056 ± 11</td><td></td><td></td><td>1907 ± 26, 1522 ± 26, 1149 ± 30</td></tr><tr><td>NT1448</td><td>bt granite</td><td>1057 ± 8</td><td></td><td></td><td>1168 ± 23</td></tr><tr><td>NK1259</td><td>bt augengneiss</td><td>1058 ± 15</td><td></td><td>c. 550</td><td>1115 ± 36</td></tr><tr><td rowspan="10">migmatitic (Euthini)</td><td>NK1265</td><td>mig orthogneiss</td><td>1024 ± 12</td><td></td><td></td><td></td></tr><tr><td>NK1282-2</td><td>mig bt orthogneiss</td><td>1031 ± 10</td><td></td><td></td><td></td></tr><tr><td>NT4583</td><td>mig hb-bt-cpx gneiss</td><td>1032 ± 8</td><td></td><td>518 ± 10</td><td></td></tr><tr><td>NK1697</td><td>mig hb-bt gneiss</td><td>1035 ± 10</td><td></td><td>c. 550</td><td>1205 ± 42</td></tr><tr><td>NT1400</td><td>bt orthogneiss</td><td>1040 ± 14</td><td></td><td>c. 550</td><td></td></tr><tr><td>NT1445</td><td>mig bt orthogneiss</td><td>1041 ± 13</td><td></td><td>533 ± 60</td><td></td></tr><tr><td>NK1581</td><td>mig hb-bt gneiss</td><td>1042 ± 11</td><td></td><td></td><td></td></tr><tr><td>NT4634</td><td>mig hb-bt-gt gneiss</td><td>1043 ± 43</td><td></td><td>525 ± 5</td><td>2365 ± 38 2011 ± 41</td></tr><tr><td>NT4575</td><td>mig hb-bt gneiss</td><td>1051 ± 11</td><td>1049 ± 12</td><td></td><td>c. 1850 1152 ± 22</td></tr><tr><td>NT4715</td><td>syenogranite gneiss</td><td>1051 ± 7</td><td>1051 ± 7</td><td></td><td>1127 ± 10</td></tr><tr><td rowspan="3">Older granites</td><td>NK4436</td><td>ms-bt granite</td><td>1067 ± 14</td><td></td><td></td><td>1993 ± 35</td></tr><tr><td>NT4563</td><td>ks granite gneiss</td><td>1083 ± 11</td><td></td><td></td><td></td></tr><tr><td>NK1609</td><td>bt granite</td><td>1086 ± 12</td><td>1020 ± 13</td><td></td><td></td></tr><tr><td>Nyika</td><td>NK1611</td><td>qz-fs orthogneiss</td><td>1993 ± 11</td><td></td><td></td><td>2552 ± 20 2410 ± 27 2112 ± 19 2092 ± 19</td></tr></tbody></table>

corresponds to similar ages in the Mafingi Group (Thomas et al., 2022) and constrains the post-Ubendian age of deposition and high-grade metamorphism.

(5) LL0369 is a sample of massive quartzite from the Mchinji SD. Zircons are of small size, translucent, light beige to pink, mostly long-prismatic, and rounded to subhedral. All 100 analyses are within ~15 % concordant with ages ranging from 2741 to 1597 Ma and the majority of the dates between 2200 and 1700 Ma (Fig. 35 of Appendix 3). The weighted mean age of the youngest group of three grains gives a Pb²⁰⁷/²⁰⁶ age of 1757 ± 24 Ma, although the youngest grain in the rock has an age of 1597 ± 23 Ma. The age of 1757 ± 24 Ma is taken as a conservative estimate for the maximum depositional age of this rock, which is consistent with its correlation with the nearby Mafingi Group of the Muva Supergroup.

(6) LL0414 is a paragneissic diatexite from the SW Kasungu SD. The zircon crystals form one population which is of small size, colourless, long prismatic, and euhedral to subhedral. CL reveals

small xenocryst cores in most of the grains. 32 analyses yield data that are within ~15 % concordant (Fig. 31 of Appendix 3). The dataset is dominated by late Mesoproterozoic ages, although it includes 1 grain that yielded a Mesoarchaean Pb²⁰⁷/²⁰⁶ age of 3025 ± 50 Ma. 3 grains give a weighted mean Pb²⁰⁷/²⁰⁶ age of 2015 ± 32 Ma, 1 grain gave an age of 1808 ± 57 Ma and a group of 2 grains yields a weighted mean Pb207/206 age of 1253 ± 47 Ma. The remaining 25 analyses yield a continuous spectrum of ages between 1190 and 1022 Ma, with the youngest 21 analyses grouping to yield a weighted mean Pb²⁰⁷/²⁰⁶ age of 1095 ± 14 Ma. This age is taken to provide a maximum depositional age for this rock i.e. it gives evidence for a second, Mesoproterozoic igneous and depositional event, contrasting with the previous samples. The three youngest analyses yield a weighted mean Pb²⁰⁷/²⁰⁶ age of 1046 ± 38 Ma coinciding with the peak of Irmide metamorphism.
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** Left: Sample positions for U-Pb zircon studies. Right: Xenocryst and detrital zircon ages.</figcaption></figure>

### 3.2.2. Magmatic rocks

3.2.2.1. *Palaeoproterozoic.* An age of 1993 ± 11 Ma was determined on orthogneiss sample NK1611 from the NE part of the Mzimba subdomain. This is coeval with the late-to post-tectonic Nyika Suite of the Ubendian Domain (Le Bayon et al., 2024) and confirms the transitional nature of the boundary between the Irumide and Ubendian domains (Fig. 7a)

#### 3.2.2.2. Mesoproterozoic.

(1) Intrusion ages of granitoids from the Mkanda Suite fall within three age groups.

a) The oldest group of 3 samples is from the northern Kasungu and Mzimba SD, which were dated at 1067 ± 14 Ma (NK4436), 1083 ± 11 Ma (NT4563) and 1086 ± 12 Ma (NT1609) respectively.

b) 21 samples gave ages ranging from 1030 ± 11 Ma to 1058 ± 15 Ma. They occur throughout the Irumide subdomains, with no discernible age trend and complete overlap between migmatitic (Euthini facies) and non-migmatitic orthogneiss. The weighted mean age was calculated at 1045.6 ± 1.5 Ma (two sigma), indicating a short pulse of voluminous magmatism.

c) One sample from the Mzimba SD (NK1265) gave an age of 1024 ± 12 Ma. It may be significant that this is coeval with the "Group IV porphyritic granites" which form a >500 × 70 km, NE trending-magmatic belt in NE Zambia (De Waele et al., 2006a; DeWaele, 2009).

(2) Sample LL1869 is a metagabbro of the Bua Suite forming a small intrusive body about 25 km SW of Kasungu in the SID. 26 analyses yield 20 Pb<sup>207</sup>/<sub>206</sub> ages between 1065 and 515 Ma. The dataset shows clusters of analyses at both ends of this range, together with a well-defined discordia line defined by the more discordant analyses. The youngest 3 analyses have Th/U < 0.05 and group to yield a weighted mean Pb <sup>206</sup>/<sub>238</sub> age of 529 ± 8 Ma. This age is taken to date the timing of metamorphism. 18 analyses with Th/U between 0.4 and 3.0 group to yield a weighted mean Pb<sup>207</sup>/<sub>206</sub> age of 1046 ± 15 Ma. A discordia fitted to the dataset yielded in the Wetherill plot upper and lower intercepts of 1074 ± 24 Ma and 501 ± 25 Ma, respectively (Fig. 8a). The seven most concordant grains yielded an age of 1040 ± 7 Ma, which is interpreted as the age of magmatic emplacement of the rock (Fig. 8b).

3.2.2.3. *Xenocryst ages.* Xenocryst ages were determined in 16 orthogneiss samples from the IRD and provide information on the age of the source and/or country rocks of the protolith granitoids. The ages have been classified into intercept and weighted mean Pb<sup>207</sup>/<sub>206</sub> age concordia ages. The youngest age in the sample is shown in black in Fig. 6b with the number of grains given in brackets; additional ages are shown in blue italics. In the Mzimba SD, only sample NK1611, probably associated with the Nyika Suite, contains Paleoproterozoic xenocrysts ranging in age from 2552 to 2092 Ma. The oldest stage of Mesoproterozoic magmatism is recorded in sample NK1697 in the northern Mzimba SD. The discordia age of 1205 ± 42 Ma is defined by 8 grains. Five samples from the Mkanda suite in the central and southern Mzimba SD contain xenocrysts from 1168 ± 23 to 1152 ± 22 Ma documenting a major magmatic pulse not present in the surface geology, except in the
<figure><img src="image_9.png" /><figcaption>**Fig. 7.** Left: Magmatic emplacement ages. Right: Metamorphic U-Pb zircon and monazite ages * Karmakar and Schenk (2016); ** Hieber (2021); *** Sakuwaha and Tsunogae (2024), ****Wakabayashi et al., 2024.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Fig. 8.** a) Sample photo of the gabbro; b) Tera-Wasserburg plot of all data; c) Wetherill plot of all analyses; d) Wetherill plot of analyses close to the upper intercept.</figcaption></figure>

Ubendian Domain to the north (Mwenga Suite; Thomas et al., 2023b).

In the Kasungu SD five samples contain Palaeoproterozoic xenocrysts ranging from 1967 ± 20 Ma to 2365 Ma. Mesoproterozoic xenocryst ages range from 1153 ± 33 Ma (NT1370) to 1099 ± 12 Ma (LL0095).

In the Mchinji SD, xenocryst ages in three samples range from 1285

to 1073 Ma, two of which record magmatism at 1147 ± 15 and 1153 Ma.

In summary, the geochronology of detrital and xenocryst zircons confirms the predominantly post-Ubendian deposition of the precursor sediments for the paragneisses and quartzites in the IRD. The youngest age of 1095 ± 14 Ma documents late Mesoproterozoic igneous activity
that is not recorded by the intrusive rocks of the Euthini and Mkanda Suites. Xenocrysts in orthogneiss record Mesoproterozoic magmatism from c. 1250 to 1075 Ma throughout the domain with a well-defined event at 1153 ± 9.4 Ma (weighted mean of six samples) that has not been identified by in outcrop.

### 3.2.3. Metamorphism

Metamorphic zircon ages were grouped into anatectic leucosome ages, newly formed zircons/rim ages (grain) ages, and discordia intercept ages (Fig. 7b).

Two Palaeoproterozoic leucosome ages of 1989 ± 11 Ma (NK1615) and 2006 ± 13 Ma (NK4355-2) were obtained in migmatitic paragneiss of the NE Mzimba SD, confirming the presence of Ubendian crust in this area. They record the main metamorphic event of the Ubendian orogeny, which was dated in the Nyika SD by monazite U-Pb geochronology at ca. 1980 Ma (Le Bayon et al., 2024).

Three Mesoproterozoic leucosome ages of 1067 ± 9 Ma (SA0789), 1058 ± 17 Ma (SA704) and 1020 ± 5 Ma (SA0897) have been dated in the southern Kasungu SD that we interpret to date local and/or regional anatexis. SA0789 is a local leucosome at the Kasungu/Lilongwe boundary (i.e. the Irumide/South Irumide suture) and its age is considered to date a first phase of island arc accretion (Fullgraf et al., 2026). SA0704 is a sample of a massive leucogranite layer formed by coalescing anatectic melts of a highly migmatitic host rock. Xenocrysts date in this sample date the Palaeoproterozoic age of the host rock at 1990 ± 17 Ma. SA0897 dates local anatectic granite at the Kasungu/Lilongwe boundary (Fullgraf et al., 2026). The well-defined age of 1020 ± 5 Ma represents the youngest Mesoproterozoic crystallisation age in the study area and probably dates the reactivation of the contact during the late phase of the Irumide orogeny.

The second group of Mesoproterozoic metamorphic ages was determined on zircon rims or newly crystallised zircons and suggests two discrete metamorphic events. The older event is poorly constrained by two samples in the southern Nyika (NK4253) and SW Kasungu (LL0414) subdomains. Nk4253 is a garnet-bearing augen gneiss in the southern Nyika SD whose emplacement was dated of 2010 ± 17 Ma. A zircon rim date of 1082 ± 44 Ma corresponds to the age of Mesoproterozoic metamorphism. Sample LL0414 in the SW Kasungu SD is a diatectic paragneiss with a maximum deposition age of 1095 ± 14 Ma (see below). Eighteen analyses yield a concordia age of 1083 ± 5 Ma that could represent the migmatitic event that the sedimentary protolith underwent. The three youngest dates in this sample yield an age of 1046 ± 43 Ma, coinciding with the peak of magmatism and probably also the main metamorphic event. The Mesoproterozoic metamorphic ages of three other samples from the southern Mzimba SD (NT4531) and the northern Kasungu SD (NT4575, NT4800) are in the same range. NT4531 is a cordierite gneiss of the Champira Dome (Fig. 3). The three youngest analyses fall on a concordia, yielding a weighted mean Pb²⁰⁷/²⁰⁶ date of 1051 ± 27 Ma, which is interpreted as the age of the Irumide metamorphism. Sample NT4575 is a strongly migmatitic orthogneiss (Euthini facies) with two age populations of 1139 ± 18 Ma and 1051 ± 11 Ma representing either a combination of emplacement/metamorphism, or xenocryst/emplacement, or xenocryst/emplacement/metamorphism. Sample NT4800 is another migmatitic paragneiss. The youngest, most concordant 7 grains date the time of metamorphism at 1038 ± 36 Ma coinciding with the peak of Irumide magmatism.

Mesoproterozoic discordia intercept ages were calculated in four samples of the southern Nyika (NK0932, 1034 ± 28 Ma; NK4461, 1048 ± 62 Ma) and northern Mzimba (NK1329, 1019 ± 13 Ma; NK1609, 1020 ± 20 Ma) subdomains. They coincide with the main and late phase of Irumide magmatism and metamorphism and, despite considerable errors argue for two discrete rather than one protracted continuous event. It shows that Irumide metamorphism affected the southern part of the Ubendian Nyika SD quite extensively.

In summary, the U-Pb zircon data suggest three Mesoproterozoic metamorphic events at c. 1080 Ma, 1050 ± 5 Ma and 1020 ± 13 Ma. The

weighted mean age of the main event at 1050 ± 5 Ma has been calculated on a group of six samples.

Pan-African metamorphic ages document the increasing influence of this orogeny from the north to the south of Malawi: None of the samples north of the MwSZ show signs of new zircon growth, but 8/34 samples are affected by partial reset of the U-Pb isotope system resulting in imprecise lower intercept ages between 500 and 550 Ma (Fig. 7a–Table 4). Samples that record new zircon growth (rims and grains) begin immediately south of the MwSZ where it was identified in 14/32 samples. They record three age ranges in the [600-580 Ma], the [560-565 Ma] and the [530-520 Ma] intervals. The weighted mean age of the third, most abundant group has been calculated to be 521 ± 3.3 Ma (nine samples).

### 3.3. Sm-Nd whole rock isotopes

Methods, data and results of this study are presented in Fullgraf et al., 2026, the relevant points of which are summarized and expanded below.

* $T_{DM2}$ model ages between 2.0 and 2.7 Ga were obtained in the samples (8) from the Mzimba SD, demonstrating a strong influence of Palaeoproterozoic (Ubendian) crust to the north

* $T_{DM2}$ model ages between 1.7 and 2.0 Ga were determined in 5/14 samples from the Kasungu SD, suggesting mixing of Ubendian crust with those from Mesoproterozoic magmatic rocks in an active (Irumide) continental margin setting. The remaining nine samples vary from 2.1 to 2.8 Ga.

* $T_{DM2}$ model ages of the mafic rocks vary mainly from 1.09 to 1.47 Ga (7/8 samples) demonstrating the input of Mesoproterozoic magmas into the IRD. One sample of the Mzimba SD yielded a model age of 2.0 Ga.

* $T_{DM2}$ model ages of migmatitic and non-migmatitic orthogneiss of the Mkanda Suite overlap entirely and vary from 1.7 to 2.7 Ga.

* $T_{DM2}$ model ages of paragneiss (5 samples) vary from 2.0 to 2.8 Ga recording the erosion and sedimentation of Ubendian-type crust

The evolution of the Mkanda and Bua suites and the Irumide paragneisses is illustrated in Fig. 9. Where available, the U-Pb zircon emplacement age determines the abscissa and the ¹⁴³Nd/¹⁴⁴Nd initial ratio the ordinate. Where U-Pb data are not available, the ¹⁴³Nd/¹⁴⁴Nd ratio of the metaigenous and sedimentary rocks is calculated at 1045 Ma. The Mkanda Suite is further distinguished into non-migmatitic and migmatitic facies. The diagram shows in addition the evolution lines of depleted mantle (DM), the Chondritic Uniform Reservoir (CHUR), the Ubendian bulk lithosphere (UBL) and the fields for Ubendian granitoids (UGF) and juvenile crust of the SID (modified from Fullgraf et al., 2026).

<figure><img src="image_11.png" /><figcaption>**Fig. 9.** Isotopic evolution of neodymium in Meso- and Palaeoproterozoic magmatic rocks of Malawi. The emplacement age of most granitoids has been determined by U-Pb zircon geochronology (modified from Fullgraf et al., 2026).</figcaption></figure>
Non-migmatitic Mkanda Suite granitoids extend from the CHUR trajectory into the UGF, suggesting recycling of Ubendian crust and mixing with variable amounts of lithospheric mantle. Samples of migmatitic orthogneiss (Euthini facies) cluster predominantly around the UBL trajectory (7/11 samples) indicating their origin by anataxis of the hosting country rocks. Paragneisses extend mostly from the UBL to the UGF, suggesting their origin from an Ubendian source area.

Bua Suite mafic rocks cluster in the field of SID crust between the DM and CHUR trajectories indicating their origin from mantle magmas of similar isotopic composition. The age of 1040 Ma coincides with the climax of Irumide tectono-metamorphism suggesting the origin of the magmatism by lithospheric delamination and subsequent rise of hot asthenosphere at the base of the lithosphere. This mechanism may be also explain the short peak of voluminous Irumide granite magmatism at $1045.6 \pm 1.5$ Ma.

## 3.4. Whole rock geochemistry

The geochemistry of the main igneous rocks suites is discussed below. Analytical methods and data are presented in Appendix 1 and 5.

### 3.4.1. Mkanda Suite

The whole rock geochemical data form a tight compositional cluster consisting of predominantly silicic rocks containing between 61 and 76 wt% $SiO_2$ and normative compositions of monzogranite-granodiorite and alkali-feldspar granite-syenogranite (Fig. 10a-c). A single more mafic sample classifies as quartz diorite. The rocks are metaluminous to peraluminous, with ASI values varying between 0.91 and 1.16 and show a general trend towards more peraluminous compositions with increasing $SiO_2$. Total alkalis and Fe* have mean values of 0.82 and 7.2, classifying them as subalkaline and ferroan (Fig. 10a and b), with $K_2O >

$Na_2O CaO$ Normalised to primitive mantle the rocks show high concentrations (~500) for the large ion lithophile elements $Cs-Rb-Ba$ and moderate negative anomalies for Nb-Ta, Sr-P and Ti (Fig. 11). Chondrite normalised HREE concentrations are somewhat depleted at <10. A total REE plot for these rocks (Fig. 11) shows a fairly consistent negative slope characterised by a mean $(La/Lu)_N$ of 19 and a moderate negative Eu anomaly (mean Eu/Eu* = 0.7).

In contrast to the monzogranites and granodiorites, the alkali-feldspar granites and syenogranites of the Mkanda Suite show a number of distinct trace element trends. Two compositional groupings are HREE-depleted, but differ in that one grouping has significantly higher concentrations in most trace elements and shows a strongly fractionated chondrite normalised pattern (Fig. 11). These rocks we call HREE-depleted Group 1, which is the most common composition observed (N = 10), and which is characterised by a primitive mantle normalised trend that shows negative anomalies for Ba, Ta-Nb, Sr-P and Ti (Fig. 11). When normalised to chondrites, the rocks of this grouping show strong fractionation between LREE and HREE and a distinct negative Eu anomaly. For this grouping the mean $(La/Lu)_N$ equals 41 and the mean Eu/Eu* equals 0.4. The second HREE-depleted grouping (HREE-depleted Group 2), is defined by 3 analyses and when normalised to primitive mantle, is characterised by a deep negative anomalies for Ba-Th, Ta-Nb, Ti and a shallow negative anomaly for Sr. The shallower Sr anomaly observed for these rocks is not a function of higher Sr concentrations, but rather much lower concentrations of light and intermediate REE. This is most clearly illustrated in the chondrite-normalised plot, where these rocks have lower abundances of REE compared to the other two compositional groups, together with a shallower negative slope. $(La/Lu)_N$ is consequently low for this group and has a mean value of 6. The depth of the Eu anomaly for this group is similar to the other compositional groups and Eu/Eu* has a mean value of 0.4. The final

<figure><img src="image_12.png" /><figcaption>**Fig. 10.** Major element geochemical data for the Mkanda Suite (c. 1050-1035 Ma). (a) Plot of total alkalis verse silica with rock type boundaries taken from Le Bas et al. (1986). (b) Plot of Fe* (FeT/(FeT + MgO)) verse silica with ferroan/magnesian boundary from Frost and Frost (2008). (c) Plot of normative Q' verse ANOR (Streckeisen and Le Maitre, 1979) for silica oversaturated (normative quartz >0) rocks. A: NS = nepheline syenite, S = syenite, M = monzogranite, GA = gabbro, D = diorite, GD = granodiorite, G = granite. C: AFG = alkali feldspar granite, SG = syeno granite, MG = monzogranite, GD = granodiorite, QD = quartz diorite.</figcaption></figure>
<figure><img src="image_13.png" /><figcaption>**Fig. 11.** Primitive mantle and chondrite normalised plots of trace element data for Mkanda Suite (c. 1050-1035 Ma) intrusions. Coloured areas show the 0.25–0.75 percentile ranges of normalised element concentrations, solid lines show mean compositions for sub-groups. N values give the total number of analyses plotted. Normalisation values after Sun and McDonough (1989).</figcaption></figure>

compositional grouping is defined by a single intrusion (NK1697 = 1035 ± 10 Ma) and shows a HREE-undepleted pattern. When normalised to primitive mantle, this rock also shows a negative Ba anomaly, but the Nb-Ta anomaly is shallower than those observed for the other groupings (Fig. 11), while the negative Sr-P and Ti anomalies are deeper. If normalised to chondrite, this rock shows the highest REE concentrations, moderate LREE to HREE fractionation and a Eu anomaly of similar depth to the other groupings. For this rock (La/Lu)N and Eu/Eu* are equal to 13 and 0.3 respectively.

When plotted on the Y + Nb vs. Rb discrimination plot (not shown), the majority of the Mkanda Suite monzogranites and granodiorites plot in the within-plate field, with a subset scattering into the volcanic arc field. The alkali-feldspar granites and syenogranites show some scatter depending on their trace element compositional grouping. The HREE-depleted Group 1 rocks plot in the syn-collisional and within-plate fields, the HREE-depleted Group 2 rocks in the syn-collisional field and the single HREE-undepleted rock within the within-plate field.

The most common within-plate signatures recorded by the bulk of the monzogranites and granodiorites and some of the HREE-depleted Group 1 alkali-feldspar granites and syenogranites may reflect melting of refractory Ubendian crust, which is inferred to define the basement of the IRD. The syn-collisional signatures more common to the some of the HREE-depleted Group 1 and HREE-depleted Group 2 alkali-feldspar granites and syenogranites may instead reflect the partial melts of previously unmelted metasediments. In the IRD this source could be defined by the equivalents of the Mafingi Group, which in the Ubendian Domain unconformably overlie the Palaeoproterozoic crystalline rocks that define the basement of this domain.

Taken together, the within-plate and syn-collisional signatures observed for the Euthini-Mkanda Suite are interpreted to reflect the effects of Irumide orogenesis, which was driven by the late

Mesoproterozic (1070-1020 Ma) accretion of the SID and possibly - Proto-Kalahari Craton onto the southern margin of the Congo- Craton (i. e. the BaNy Block).

### 3.4.2. Bua Suite

The mafic Bua Suite is comprised mainly of sub-alkaline rocks gabro, quartz gabbro and quartz diorite with a normative composition of quartz tholeiite to olivine tholeiite (Fig. 12). The rocks contain 44–51 wt % SiO₂ with total alkalis ranging from 0.7 to 3.5 wt%. The observed compositional ranges for the major oxides are: FeO = 6–15 wt%, MgO = 0.7–15.5 wt%, and TiO = 0.4–3.6 wt%. Fe* (FeT/(FeT + MgO)) for these rocks varies between 0.42 and 0.90, although the majority of the rocks are classified as magnesian.

The trace element data show a slightly fractionated primitive mantle normalised trend with some enrichment in the large ion lithophile elements Cs, Rb and Ba, and subtle negative anomalies for Nb-Ta and P. The chondrite normalised REE pattern shows a smooth, almost flat trend with no Eu anomaly. For these rocks the mean values for (La/Lu)N and Eu/Eu* are 3.5 and 1.0 respectively. Both the primitive mantle and chondrite-normalised trends observed for mafic rocks of the Bua Suite closely match the global mean for ocean island arc basalts (Fig. 13), suggesting they were derived from a subduction metasomatised, depleted mantle source.

A small group of Bua Suite rocks (N = 4) consists of slightly more siliceous rocks of tonalitic composition (Fig. 12a). These rocks contain approximately 55 wt% SiO₂ and, like the Bua gabbros, are characterised by low total alkali concentrations of between 3.1 and 4.6. These rocks are therefore also sub-alkaline, although they generally have high Fe* values (mean = 0.75) and are ferroan rather than magnesian (Fig. 12b). The mean concentrations of FeO, MgO and TiO₂ for these rocks are 12.9 wt%, 4.2 wt% and 1.7 wt%, values that are within the range observed for
<figure><img src="image_14.png" /><figcaption>**Fig. 12.** Major element geochemical data for Bua Suite (c. 1045-1030 Ma) (a) Plot of total alkalis versus silica. (b) Plot of Fe* (Fe/T/(Fe_T + MgO)) versus silica. (c) Plot of normative Q' versus ANOR for silica oversaturated (normative quartz >0) rocks. (d) Ne-Ol-Ab + Or-Hy-Q normative plot. Sources of plots and abbreviated field names are given in the caption to Fig. 10.</figcaption></figure>

the Bua Suite gabbros. Trace element abundances are higher than those observed for the gabbros, although the trends are similar (Fig. 13). When normalised to primitive mantle the Bua Suite tonalites show subtle negative anomalies for Nb-Ta-Sr-P and Ti. When normalised to chondrite, there is a higher degree of LREE fractionation relative to HREE and a slight negative anomaly for Eu. For these rocks the mean values for (La/Lu)N and Eu/Eu* equal 8.4 and 0.8 respectively.

# 4. Discussion

## 4.1. Boundaries of the IRD in Malawi

The IB is a NE trending orogen occupying most of central-eastern Zambia and running eastwards into Malawi. Our work has clearly shown that the old accepted boundaries (the Mugesse and Mwembeshi SZs are not fundamental sutures and do not define the boundaries of the IB. In the north, the Mzimba Subdomain of the IRD is tectonically juxtaposed with the Nyika SD of the Ubendian Domain along an arcuate, NE-dipping transitional contact zone which in the east, is truncated by the Pan-African MwSZ. (Fig. 3). The Mzimba SD is typified by extensive Mesoproterozoic plutonism and Mesoproterozoic high-grade

metamorphism, both dated at c. 1040 Ma (Hieber, 2021; Sakuwaha and Tsunogae, 2024; this study, Fig. 7b). Palaeoproterozoic migmatitic paragneisses and plutonic rocks were identified in the transition zone as a result of tectonic stacking.

The Pan-African MwSZ is not a major suture in Malawi – it merely separates the Irumide Mzimba and Kasungu Sds from the Ubendian -Nyika subdomain, all of which record similar gneissic fabrics and trends, magmatism and metamorphism. This also explains the results of detrital and isotopic studies by Alessio et al. (2019a,b), which demonstrates the influence of Palaeoproterozoic crust in the area south of the MwSZ, formerly classified as SID.

The southern margin of the IRD and its contact with the SID lies approximately 50 km south of the MwSZ. The sharp, folded contact is marked by the sudden appearance of kyanite-bearing graphitic schist and minor carbonate rocks of the Lilongwe Subdomain (SID). It also sees an abrupt change to Mesoproterozoic Nd model ages, island arc-related granitoids and mafic rocks.

## 4.2. IRD supracrustal rocks

The histogram of all detrital ages from this study (Fig. 14) suggests
<figure><img src="image_15.png" /><figcaption>**Fig. 13.** Primitive mantle and chondrite normalised plots of trace element data for Bua Suite (c. 1045-1030 Ma). Coloured areas show the 0.25–0.75 percentile ranges of normalised element concentrations, solid lines show mean values for rock-types with a low number of analyses. N values give the total number of analyses plotted. Normalisation values after Sun and McDonough (1989); Global mean IAB composition after Kelemen et al. (2014).</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>**Fig. 14.** Histogram of detrital ages from the IRD.</figcaption></figure>

three main periods of supracrustal rock genesis. The first age group ranges from 1750 to 3000 Ma and displays the main maximum at 2030 Ma, the timing of Ubendian active arc magmatism (Thomas et al., in prep). The second largest peak at 1860 Ma may be associated with the Luapula volcanic sequence and associated calc-alkaline granites in NE

Zambia (De Waele et al., 2006a), recording an active arc at the southern margin of the Congo Craton (Rainaud et al., 2005; Kleinhanns et al., 2013; Becker et al., 2023).

Smaller peaks from 2290 to 2990 Ma indicate distal cratonic sources or erosion of the BaNy Block. Altogether, this age spectrum is characteristic for Muva SG sediments (De Waele et al., 2006a; Thomas et al., 2022). The third age interval from 1040 to 1140 Ma suggests another period of arc magmatism at the southern margin of the Congo Craton and late Mesoproterozoic supracrustal rocks that so far have not been identified in Zambia. The origin of the zircons from Kibaran sources is unlikely because older parts of the Kibaran age spectrum are missing. Two ages of about 1550 Ma can be associated in the BaNy Block with a period of anorogenic granitoid emplacement between 1650 and 1550 Ma (De Waele et al., 2006a). Ubendian source areas of the sediments are suggested by T<sub>DM2</sub> model ages of the paragneisses from 2.0 to 2.8 Ga characterizing the Ubendian rocks (Thomas et al., in prep). The absence of Palaeoproterozoic plutonic rocks in the IRD is another indicator for the post-Ubendian age of the paragneisses implying the Mesoproterozoic or Pan-African age of high-grade metamorphism.

### 4.3. IRD magmatism

Most of the magmatic rocks in the IRD were emplaced after > c. 1050 Ma, despite their older heritage, as defined by the Nd isotopic compositions. Interestingly, though, older Irumide granitoids are found in the Ubendian Domain, such as the A-type granite orthogneisses of the Mwenga Suite dated at 1142 ± 4.9 Ma (Thomas et al., 2023b). The authors proposed emplacement in a NW-SE trending rift along reactivated Ubendian structures, which is considered as SE continuation of the Late Kibara Rift in Tanzania and eastern DRC. Evidence for early Irumide magmatism from within the IRD is restricted to a small group of
<figure><img src="image_17.png" /><figcaption>**Fig. 15.** NNW-SSE cross-section of the IB in NE Zambia in an active continental margin setting followed by accretion and continent collision (modified from Daly, 1986).</figcaption></figure>

three samples dated between 1067 ± 14 Ma to 1086 ± 12 Ma and zircon cores dated at 1095 ± 14 Ma, which may represent vestiges of limited continental arc magmatism (this study).

The short but intense pulse of voluminous felsic plutonism of the Mkanda Suite in the IRD of Malawi is dated at 1045.6 ± 1.5 Ma. The geochemical and isotopic signatures of the suite probably reflect analysis of Ubendian crust forming the basement of the IRD. Syncollision signatures, more common in the alkali feldspar granites and syenogranites, may document melting of immature Muva SG sediments. This is also supported by Nd-whole model ages between 2.0 and 2.7 Ga, which indicate recycling of the Ubendian crust and mixing with varying amounts of lithospheric mantle. Geochemistry and Nd-isotope ratios of metamorphic mafic rocks combined into the Bua Suite indicates their origin from a subduction metasomatised, depleted mantle source. The emplacement age of c. 1040 Ma coincides within error with peak regional metamorphism and the climax of felsic magmatism. Crustal thickening through continental collision followed by lithospheric delamination and subsequent upwelling of hot asthenosphere at the base of the lithosphere represents a plausible scenario to explain the simultaneity of bimodal magmatism, tectonics and metamorphic overprint in the period from 1045 to 1040 Ma.

The Malawi data complement geochronological data from the voluminous magmatism in northern Zambia (De Waele, 2009), but with some differences. For example, recalculation of the weighted mean emplacement ages from Zambian granitoids (De Waele, 2009) indicates a wider range of ages in three episodes at 1051 ± 12 Ma (2 samples), 1033 ± 3.4 Ma (11 samples), and 1021 ± 7 Ma (5 samples) documenting additional younger pulses. Geochemically, the Zambian granitoids are peraluminous and characterised by high SiO₂ and K₂O contents, strong enrichment in LILE and HFSE and low TiO₂ content, suggesting a strong influence of crustal melts with calc-alkaline affinity on the magma composition. The data suggest that they were formed by partial melting of metamorphosed igneous and sedimentary rocks.

### 4.4. IRD metamorphism

The polyphase nature of metamorphism in the IRD is demonstrated by the geochronology of local leucosomes, zircon rims, metamorphic zircon and monazite grains and discordia intercepts.

(1) The oldest event is dated at 1067 ± 9 Ma by local leucosomes at the IRD/SID contact (=suture) and interpreted as the timing of accretion of the SID arc at the Congo margin;

(2) The main metamorphic event at 1050 ± 5 Ma is based on six samples from the IRD and is slightly before the peak of Irumide magmatism at 1045.4 ± 1.4 Ma and possibly related to the docking of the Proto-Kalahari craton. Th-U-Pb monazite geochronology yielded similar ages in the Mzimba SD (1048 ± 10 Ma; Hieber, 2021; Sakuwaha and Tsunogae, 2024; Wakabayashi et al., 2024), and slightly younger ages in the Mchinji SD (1031 ± 4 Ma; Karmakar and Schenk, 2016)

(3) Late-stage metamorphism and reactivation of the IRD/SID suture is dated by local anatectic gneisses at 1020 ± 13 Ma, which coincides with the last phase of Mesoproterozoic magmatism in Zambia. This age is again confirmed by U-Pb monazite geochronology in the Mzimba and Mchinji subdomains (Karmakar and Schenk, 2016; Wakabayashi et al., 2024).

Granulite peak metamorphic conditions vary little from 950 to 1000 °C/7–8.5 kbar in the Mzimba SD (Hieber, 2021; Wakabayashi et al., 2024) to 900–1000 °C/5–6 kbar in the Mchinji SD (Karmakar and Schenk (2016). The main and late metamorphic events have also been identified in southern Tanzania (Thomas et al., 2016), and all three events in the Tete-Chipata SD of NW Mozambique (Cox et al., 2002; Westerhof et al., 2008; Petry et al., 2023).

### 4.5. IRD tectonics

Remote sensing, field observations and statistical treatment of structural data reveal the complex deformation that the IRD underwent. Where unaffected by the later Pan-African orogeny, deformation in the IRD is characterised by flat-lying foliations typical of nappe tectonics, with general structural younging to the north. This resulted in a tectonic stack of crustal slices with rocks of the SID at the base, overlain by the IRD, in turn overlain by the older Ubendian Domains. This sequence confirms the findings of Daly (1986) who interpreted the IB in NW Zambia as a 150 km wide thrust belt with NW-verging structures in the northwest, upright structures in the central zone and SE-verging structures in the southeast; in other words a bi-directional orogeny (Fig. 15). Malawi represents the SE part of this model, with a tectonic style characterised by recumbent SE-verging isoclinal folds.

Most of the Kasungu and Mzimba subdomains are characterised by shallow north-plunging lineations, implying east-west shortening. This suggests oblique movement along the SE-striking active margin with a dextral strike-slip component. The foliation distribution pattern documents complex interference folding confirming the interpretation of the
geophysical data indicating three phases of folding in both the Kasungu and Mzimba subdomains. The influence of the Pan-African MwSZ is evident from the clockwise rotation of foliations and lineations into the NW trending structure, indicating dextral movements. Extensive mylonitic schists north of the MwSZ indicate reactivation of the Irumide-Ubendian boundary in a transpressive setting.

The Mchinji SD appears to form the eastern part of a gneissic dome, the bulk of which is in Zambia. While intercalated Neoproterozoic rocks in Zambia constrain the Pan-African age of the structure, the regional granulite metamorphism is clearly Mesoproterozoic in age (Karmakar and Schenk, 2016). Structural observations at the eastern margin in Malawi show Pan-African westward transport of the Lilongwe SD over the Mchinji SD (Fullgraf et al., 2026). Subsequent E-W extension is documented by steep, east-dipping mylonites with down-dip stretching lineations, probably associated with late orogenic uplift and collapse observed elsewhere in Malawi and northern Mozambique (Miller et al., 2013; Fullgraf et al., 2026).

At a more regional scale, the Irumides were a unidirectional orogeny with transport to the SE, over the Proto-Kalahari Craton. This in turn suggests that the nappe tectonics is associated with an active Mesoproterozoic continental margin and subsequent continental collision (Fig. 15). The cross-section in Fig. 15 is similar to those constructed by Goscombe et al. (2020) for the Damara and Zambezi belts but differs significantly from that constructed for Malawi in that article, where a positive flower structure was postulated to have uplifted the Unango SD. Tectonic stacking and metamorphism are linked with the Pan-African Kuunga orogeny by Goscombe et al. (2020), while we believe the major juxtaposition event took place during the Irumide orogeny. Structural observations along the Irumide - South Irumide contacts rule out a positive flower structure and instead show that the Malawian part of the collision zone is characterized by a similar tectonic stacking style as described in the Damara and Zambezi belts by Goscombe et al. (2020). The Mesoproterozoic age of the collision is constrained by the line of weakly deformed Neoproterozoic alkaline intrusions (Nyassa Suite) that run throughout the length of Malawi that were emplaced in Mesoproterozoic migmatitic gneisses (Fullgraf et al., 2026.). This further implies the collision of the Congo and Proto-Kalahari cratons during the Irumide Orogeny and the reactivation of the structures during the Kuunga Orogeny.

## 5. Conclusions

This study revises understanding of the Irumide Domain in Malawi by redefining its boundaries, tectonic history, and relationship to surrounding crustal blocks. The MwSZ, long considered a fundamental suture is, in Malawi at least, considered to be a Pan-African structure separating Irumide subdomains rather than marking the margin of the IRD. The true southern boundary lies further south at the Kasungu-Lilongwe Subdomain boundary, where a sharp lithological and isotope transition reflects the juxtaposition of the IRD with the SID.

Detrital zircon age spectra from supracrustal rocks record three main age sources, most importantly from ~1140 to 1040 Ma, which coincides with the main phase of arc magmatism and crustal growth along the southern margin of the Congo Craton. This time span is manifested in limited sedimentation in (presumably) small sedimentary basins, peneccontemporaneous voluminous felsic magmatism, synchronous high-grade metamorphism and subsequent mafic magmatism, all pointing to a tectonic scenario of crustal thickening, collision, and lithospheric delamination causing voluminous synorogenic mafic magmatism. Nd model ages and geochemical signatures demonstrate recycling of Ubendian crust, combined with inputs from a subduction-metasomatised mantle source.

Metamorphic and structural evidence shows the IRD to be a poly-phase event with at least three Mesoproterozoic episodes between 1067 and 1020 Ma, linked to successive accretion, collision, and late-orogenic reactivation. Deformation patterns in Malawi continue the bidirectional

thrust architecture first described in Zambia, with tectonic stacking of Ubendian, Irumide, and South Irumide units in a superposed, nappe-style geometry. Convergence was oblique with a marked strike-slip component and extensive Pan-African reactivation during the East African Orogeny further complicate the structural record.

Within the larger region, the Malawian segment of the Irumide Belt shows a unidirectional, SE-directed transport over the Proto-Kalahari Craton. The Pan-African Damara-Zambezi (Kuunga) orogeny reactivated this ancient structure. We propose that the Irumide Orogeny in essence represents the closure of a Mesoproterozoic ocean basin ("Irumide Ocean"), with an early arc-forming phase and culmination in continental collision between the Congo and Proto-Kalahari cratons. The full story of the Irumides naturally must integrate data from both the Irumide and South Irumide Domains. To that end, the latter is described in a second paper on the South Irumide Domain as Part 2 in the Special Issue, which concludes with a synthesis of the entire Irumide Belt, along with an integrated evolutionary model.

## CRediT authorship contribution statement

**Thomas Fullgraf:** Writing – original draft, Investigation, Conceptualization. **Steven D. Boger:** Writing – original draft, Investigation.

**Robert J. Thomas:** Writing – original draft, Investigation.

**Alexis Plunder:** Investigation. **Kondwani Dombola:** Project administration.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgements

The Geological Mapping and Mineral Assessment Project (GEMMAP) was funded by the French Government through a Debt Reduction and Development Contract (C2D). Fieldwork was carried out with GSD geologists B. Manda, J. Chirwa, E. Kabuwe, C. Ngwata, S. Mhango, J. Mtegha, H. Mtumbuka, V. Nyalugwe, G. Tsokonombwe, and N. Zungu, assisted by local field guides. Work in the Kasungu National park was made possible by M. Mumba and N. Kumanga of the Park Authority who provided access to the park, shelter and protection through Chief Ranger Grant, who accompanied the mapping team for three weeks field work. T. Fullgraf thanks the anonymous reviewers for their constructive feedback.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jafrearsci.2025.105982.

## Data availability

Data will be made available on request.

## References

Ackermann, E.H., 1936. Das Problem der Mkushi-Gneise am NW-rand der Rhodesischen Masse. Geol. Rundsch. 27, 81–87. https://doi.org/10.1007/bf01800150.

Ackermann, E.H., 1950. Ein neuer Faltengürtel in Nordrhodesien und seine tektonische Stellung im Afrikanischen Grundgebirge. Geol. Rundsch. 38, 24–39. https://doi.org/10.1007/bf01766570.

Ackermann, E.H., 1960. Strukturen im Untergrund eines interkratonischen Doppel-Orogens (Irumiden Nordrhodesien). Geol. Rundsch. 50, 538–553. https://doi.org/10.1007/bf01786869.

Alessio, B.L., Collins, A.S., Siegfried, P., Gloriea, S., DeWaele, B., Paynee, J., Archibald, D.B., 2019a. Neoproterozoic tectonic geography of the south-east Congo craton in Zambia as deduced from the age and composition of detrital zircons. Geosci. Front. 10 (6), 2045–2061. https://doi.org/10.1016/j.gsf.2018.07.005.
Alessio, B.L., Collins, A.S., Clark, C., Glorie, S., Siegfried, P.R., Taylor, R., 2019b. Age, origin and palaeogeography of the southern irumide belt, Zambia. J. Geol. Soc. 176 (3), 505–516. https://doi.org/10.1144/jgs2018-174.

Becker, T., Nolte, N., Wilsky, F., Depiné, M., Kleinhanns, I., Klemd, R., Mhopjeni, K., Muvangua, E., Wiegand, B., Wemmer, K., Sergeev, S., Sudo, M., 2023. The geology of the Kamanjab Inlier, Northern Namibia, vol. 23. Geological Survey of Namibia, p. 144. Memoir.

Bellingham, K.S., Bromley, J., 1973. The geology of the ntchisi-middle Bua area. Geological Survey Department Bulletin 27, 50.

Bingen, B., Jacobs, J., Viola, G., Henderson, I.H.C., Skår, Ø., Boyd, R., Thomas, R.J., Solli, A., Key, R.M., Daudi, E.X.F., 2009. Geochronology of the Precambrian crust in the Mozambique belt in NE Mozambique, and implications for gondwana assembly. Precambr. Res. 170 (3-4), 231–255. https://doi.org/10.1016/j.precamres.2020.01.001.

Bloomfield, K., 1966. Geological Map of Malawi, Scale 1:1 000,000. Geological Survey Department, Zomba.

Boger, S.D., Callec, Y., Chêne, F., Garcin, M., Liwata-Kenttälä, P., Ngalonde, S., Nyalugwe, V., Staudt, M., Tsokonombwe, G., Zammit, C., 2021a. 1:100,000 Geological Map Series, Sheet South Viphya-East 36E; Sheet Explanation.

Boger, S.D., Adam, E., Callec, Y., Chêne, F., Chirwa, J., Fullgraf, T., Garcin, M., Kabuwé, E., Liwata-Kenttälä, P., Ngalonde, S., Nyalugwe, V., Staudt, M., Tsokonombwe, G., Zammit, C., 2021b. 1:100,000 Geological Map Series, Sheet Nkhata Bay South 38S; Sheet Explanation.

Böhme, A., 2021. New Insights into the Age and Metamorphic Evolution of the Irumide Orogeny in Malawi. M.Sc. Thesis University of Mainz, Germany, p. 49.

Boyd, R., Nordgulien, O., Thomas, R.J., Bingen, B., Bjerkgard, T., Grenne, T., Henderson, I., Melezhik, V.A., Often, M., Sandstad, J.S., Solli, A., Tveten, E., Viola, G., Key, R.M., Smith, R.A., Gonzalez, E., Hollick, L.J., Jacobs, J., Jamal, D., Rose, D., 2010. The geology and geochemistry of the East African orogen in northeastern Mozambique. S. Afr. J. Geol. 113 (1), 87–129. https://doi.org/10.2113/gssajg.113.1.87.

Cox, R.A., Rivers, T., Mapani, B., Tembo, D., De Waele, B., 2002. New U-Pb data for the irumide belt: LAM-ICP-MS results for luangwa terrane. Abstracts, 11th IAGOD Quadrennial Symposium and Geocongress Windhoek, pp. 414–415.

Daly, M.C., 1986. Crustal shear zones and thrust belts: their geometry end continuity in Central Africa. Royal Society of London. Philosophical Transactions, Series A 317 (1539), 111–128. https://doi.org/10.1098/rsta.1986.0028.

Daly, M.C., Unrug, R., 1982. The muva supergroup, northern Zambia: transactions of the geological society of South Africa, 85, 155–165.

De Waele, 2009. The geochronological framework of the Irumide belt: a prolonged crustal history along the margin of the Bangweulu craton. Am. J. Sci. 309, 132–187. https://doi.org/10.2475/02.2009.03.

De Waele, B., Fitzsimons, I.C.W., 2007. The nature and timing of palaeoproterozoic sedimentation at the southeastern margin of the Congo craton; zircon U-Pb geochronology of plutonic, volcanic and clastic units in northern Zambia. Precambr. Res. 159, 95–116. https://doi.org/10.1016/j.precamres.2007.06.004.

De Waele, B., Mapani, B., 2002. Geology and correlation of the central irumide belt. J. Afr. Earth Sci. 35, 385–397. https://doi.org/10.1016/s0899-5362(02)00149-5.

De Waele, B., Wingate, M.T.D., Fitzsimons, I.C.W., Mapani, B.S.E., 2003. Untying the kibaric knot: a reassessment of Mesoproterozoic correlations in Southern Africa based on SHRIMP U-Pb data from the irumide belt. Geology 31 (6), 509–512. https://doi.org/10.1130/0091-7613(2003)031<0509:utkkar>2.0.co;2.

De Waele, B., Johnson, S.P., Nkemba, S., Tembo, F., 2005. High-temperature, low-pressure tectono-thermal evolution of the irumide belt, central Southern Africa: lithosphere delamination during arc-accretion. Frontier Research on Earth Evolution Report V2 (9), 2002–2004.

De Waele, B., Kampunzu, A.B., Mapani, B.S.E., Tembo, F., 2006a. The Mesoproterozoic irumide belt of Nigeria. J. Afr. Earth Sci. 46, 36–70. https://doi.org/10.1016/j.jafrearsci.2006.01.018.

De Waele, B., Liegeois, J.P., Nemchin, A.A., Tembo, F., 2006b. Isotopic and geochemical evidence of Proterozoic episodic crustal reworking within the irumide belt of south central Africa, the southern metatectonic boundary of an Archaean bangweulu craton. Precambr. Res. 148, 225–256. https://doi.org/10.1016/j.precamres.2006.05.006.

De Waele, B., Johnson, S.P., Pisarevsky, S.A., 2008. Palaeoproterozoic to Neoproterozoic growth and evolution of the eastern Congo craton: its role in the rodinia puzzle. Precambr. Res. 160, 127–141. https://doi.org/10.1016/j.precamres.2007.04.020.

Fritz, H., Abdelsalam, M., Ali, K.A., Bingen, B., Collins, A.S., Fowler, A.R., Ghebreab, W., Hauzenberger, C.A., Johnson, P.R., Kusky, T.M., Macey, P., Muhongo, S., Stern, R.J., Viola, G., 2013. Orogen styles in the east African orogen: a review of the Neoproterozoic to Cambrian tectonic evolution. J. Afr. Earth Sci. 86, 65–106. https://doi.org/10.1016/j.jafrearsci.2013.06.004.

Frost, B.R., Frost, C.D., 2008. A geochemical classification for feldspathic igneous rocks. J. Petrol. 49 (11), 1955–1969. https://doi.org/10.1093/petrology/egn054.

Fullgraf, T., Boger, S.D., Callec, Y., Chêne, F., Garcin, M., Liwata-Kenttälä, P., Mtegha, J., Ngalonde, S., Ngwata, C., Nyalugwe, V., Staudt, M., Tsokonombwe, G., Zammit, C., 2021a. 1:100,000 Geological Map Series, Sheet Kasungu North West 25N; Sheet Explanation.

Fullgraf, T., Callec, Y., Chêne, F., Garcin, M., Liwata-Kenttälä, P., Mäkitie, H., Mhango, S., Mtegha, J., Ngalonde, S., Ngwata, C., Staudt, M., Zammit, C., 2021b. 1: 100,000 Geological Map Series, Sheet Kasungu South West 25S; Sheet Explanation.

Fullgraf, T., Boger, S.D., Callec, Y., Chêne, F., Chirwa, J., Garcin, M., Liwata-Kenttälä, P., Ngalonde, S., Nyalugwe, V., Tsokonombwe, G., Staudt, M., Zammit, C., Zungu, N., 2021c. 1:100,000 Geological Map Series, Sheet South Viphya-West 36W; Sheet Explanation.

Fullgraf, T., Boger, S.D., Callec, Y., Chêne, F., Chirwa, J., Garcin, M., Kabuwé, E., Liwata-Kenttälä, P., Ngalonde, S., Staudt, M., Zammit, C., 2021d. n. 1:100,000 Geological Map Series, Sheet Mbima 37; Sheet Explanation.

Fullgraf, T., Thomas, R.J., Boger, S.D., Plunder, A., Blein, O., Charles, N., Nombola, K., Hyvönen, E., Le Bayon, B., Le Roux, P., 2026. Precambrian crustal architecture of Malawi: a keystone in SE Africa. J. Afr. Earth Sci. 233, 105857. https://doi.org/10.1016/j.jafrearsci.2025.105857.

Fullgraf, T., Thomas, R.J., Le Bayon, B., Boger, S.D., Charles, N., 2022. Tectonics. GEMMAP Memoir Series. Geological Survey Department, Zomba, Malawi, p. 132.

Gaskell, R.J., 1973. The geology of the Mbima area, GSD Bulletin 37, 41.

Goscombe, B., Foster, D.A., Gray, D., Wade, B., 2020. Assembly of central gondwana along the Zambezi belt: metamorphic response and basement reactivation during the kuunga orogeny. Gondwana Res. 80, 410–465. https://doi.org/10.1016/j.gr.2019.11.004.

Hieber, R., 2021. The two-stage Metamorphic Evolution of the Southern Ubenidian Belt. M.Sc. Thesis University of Mainz, Germany, p. 57.

Jacobs, J., Pizarevsky, S., Thomas, R.J., Becker, T., 2008. The kalahari craton during the assembly and dispersal of rodinia. Precambr. Res. 160, 142–158. https://doi.org/10.1016/j.precamres.2007.04.022.

Johnson, S.P., Oliver, G.J.H., 2004. Tectonothermal history of the kaourae arc, northern Zimbabwe: implications for the tectonic evolution of the irumide and Zambezi belts of south central Africa. Precambr. Res. 130 (1-4), 71–97. https://doi.org/10.1016/j.precamres.2003.10.016.

Johnson, S.P., Oliver, G.J.H., Tembo, F., De Waele, B., Rivers, T., 2004. Mesoproterozoic supra-subduction magmatic and accretionary tectonics in the southern irumide belt, central southern Africa. Abstracts, Geoscience Africa 2004, pp. 311–312. Johannesburg.

Johnson, S.P., Rivers, T., De Waele, B., 2005. A review of the Mesoproterozoic to early Palaeozoic magmatic and tectonothermal history of south-central Africa: implications for rodinia and gondwana. J. Geol. Soc. 162 (3), 433–450. https://doi.org/10.1144/0016-764904-028.

Johnson, S.P., De Waele, B., Evans, D., Banda, W., Tembo, F., Milton, J.A., Tani, K., 2007a. Geochronology of the Zambezi supracrustal sequence, southern Zambia: a record of Neoproterozoic divergent processes along the southern margin of the Congo craton. J. Geol. 115 (3), 355–374. https://doi.org/10.1086/512757.

Johnson, S.P., De Waele, B., Tembo, F., Katongo, C., Tani, K., Chang, Q., Ilzuka, T., Dunkley, D., 2007b. Geochemistry, geochronology and isotopic evolution of the chewore-rufunsa terrane, southern irumide belt: a Mesoproterozoic continental margin arc. J. Petrol. 48 (7), 1411–1441. https://doi.org/10.1093/petrology/egm025.

Karmakar, S., Schenk, V., 2016. Mesoproterozoic UHT metamorphism in the southern irumide belt, Chipata, Zambia: petrology and in situ monazite dating. Precambr. Res. 275, 332–356. https://doi.org/10.1016/j.precamres.2016.01.018.

Kelemen, P.B., Hanghøj, K., Greene, A.R., 2014. One view of the geochemistry of subduction-related magmatic arcs, with an emphasis on primitive andesite and lower crust. Treatise on Geochemistry 749–806. https://doi.org/10.1016/b978-0-08-095975-7.00323-5.

Kleinhanns, I.C., Fullgraf, T., Wilsky, F., Nolte, N., Fliegel, D., Klemd, R., Hansen, B.T., 2013. U-Pb Zircon Ages and (Isotope) Geochemical Signatures of the Kamanjab Inlier (NW Namibia): Constraints on Palaeoproterozoic Crustal Evolution Along the Southern Congo Craton. Geological Society, London, pp. 165–195. https://doi.org/10.1144/sp389.1. Special Publications, 389(1).

Le Bas, M.J., Le Maître, R.W., Streckeisen, A., Zanettin, B., 1986. A chemical classification of volcanic rocks based on the total alkali-silica diagram. J. Petrol. 27 (3), 745–750. https://doi.org/10.1093/petrology/27.3.745.

Le Bayon, B., Plunder, A., Thomas, R.J., Fullgraf, T., Charles, N., Nyalugwe, V., Boger, S. D., Lach, P., Frei, D., Lahaye, Y., 2024. Crustal evolution of the northern nyika subdomain of the palaeoproterozoic ubendian belt in Malawi. J. Afr. Earth Sci. 213, 10561, https://doi.org/10.1016/j.jafrearsci.2024.105216.

Macey, P.H., Thomas, R.J., Grantham, G.H., Ingram, B.A., Jacobs, J., Armstrong, R.A., Roberts, M.P., Bingen, B., Hollick, L., de Kock, G.S., Viola, G., Bauer, W., Gonzales, E., Bjerkgård, T., Henderson, I.H.C., Sandstad, J.S., Cronwright, M.S., Harley, S., Solli, A., Nordguleng, Ø., Motuza, G., Daudi, E., Manhiça, V., 2010. Mesoproterozoic geology of the Nampula block, northern Mozambique: tracing fragments of Mesoproterozoic crust in the heart of gondwana. Precambr. Res. 182 (1-2), 124–148. https://doi.org/10.1016/j.precamres.2010.07.005.

Miller, J.A., Faber, C., Rowe, C.D., Macey, P.H., du Plessis, A., 2013. Eastward transport of the monapo klippe, Mozambique determined from field kinematics and computed tomography and implications for late tectonics in central gondwana. Precambr. Res. 237, 101–115. https://doi.org/10.1016/j.precamres.2013.09.007.

Peters, E.R., 1969. The geology of the of the Kasungu area: In: Geological Survey of Malawi, Bulletin, vol. 25, p. 68.

Peters, E.R., 1975. The geology of the of the south viphaya area. In: Geological Survey of Malawi, Bulletin, vol. 36, p. 56.

Petry, T.S., Philipp, R.P., Cabrita, D.I.G., Jamal, D.L., Machado, R., Lana, C., 2023. Subduction to accretion in the southern irumide belt: perspective from geochronology and petrology of granulites and charnockites in NW Mozambique. Precambr. Res. 397, 107190. https://doi.org/10.1016/j.precamres.2023.107190.

Rainaud, C., Master, S., Armstrong, R.A., Robb, L.J., 2005. Geochronology and nature of the palaeoproterozoic basement in the Central African Copperbelt (Zambia and the Democratic Republic of Congo), with regional implications. J. Afr. Earth Sci. 42 (1–5), 1–31. https://doi.org/10.1016/j.jafrearsci.2005.08.006.

Ramsay, C., Ridgway, J., 1977. Metamorphic patterns in Zambia and their bearing on problems of Zambian tectonic history*. Precambr. Res. 4 (4), 321–337. https://doi.org/10.1016/0301-9268(77)90002-x.
Ring, U., 1993. Aspects of the kinematic history and mechanisms of superposition of the Proterozoic mobile belts of eastern central Africa (northern Malawi and southern Tanzania). Precambr. Res. 62 (3), 207–226. https://doi.org/10.1016/0301-9268 (93)90022-t.

Sakuwaha, K., Tsunogae, T., 2024. Metamorphic P-T-t evolution of ultrahigh-
temperature granulite facies metapelites from the lundazi terrane, irumide belt,
eastern Zambia. Precambr. Res. 401, 107271. https://doi.org/10.1016/j.
precamres.2023.107271.

Streckeisen, A.L., Le Maitre, R.W., 1979. A chemical approximation to the modal QAPF classification of the igneous rocks. Neues Jahrbuch fur Mineralogie – Abhandlungen 136, 169–206.

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of ocean basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in Ocean Basins. Geological Society, London, pp. 313–345. https://doi.org/10.1144/gsl.sp.1989.042.01.19. Special Publications, 42.

Thatcher, E.C., Wilderspin, K.E., 1968. The geology of the of the mchinji-upper Bua area. Geological survey of Malawi., Bulletin 24, 72.

Thomas, R.J., Boger, S.D., Plunder, A., Fullgraf, T., Le Bayon, B., Charles, N., Frei, D., Lahaye, Y., Dombola, K. (in prep). Geology and geochronology of the Ubendian belt in Malawi; whither the bangweulu block. J. Afr. Earth Sci., 202.

Thomas, R.J., Spencer, C., Bushi, A.M., Baglow, N., Boniface, N., de Kock, G.S., Horstwood, M.S.A., Hollick, L., Jacobs, J., Kajara, S., Kamihanda, G., Key, R.M., Maganga, Z., Mbawala, F., McCourt, W.J., Momburi, P., Moses, F., Mruma, A., Myambilwa, Y., Roberts, N.M.W., Saidi, H., Nyanda, P., Nyoka, K., Millar, I., 2016. Geochronology of the central Tanzania craton and its southern and eastern orogenic margins. Precambr. Res. 277, 47–67. https://doi.org/10.1016/j.precamres.2016.02.008.

Thomas, R.J., Fullgraf, T., Charles, N., Le Bayon, B., Boger, S.D., Frei, D., Lach, P.,
Dombola, K., 2022. Age and correlation of the Proterozoic mafingi group in Malawi.
J. Afr. Earth Sci. 196. https://doi.org/10.1016/j.jafrearsci.2022.104723.

Thomas, R.J., Fullgraf, T., Plunder, A., Boger, S.D., Le Bayon, B., Charles, N., 2023a.
Geological evolution of northern Malawi: the final piece of the Ubendian jigsaw. 29th
Colloquium of African Geology. Book of Abstracts, Windhoek, p. 58, 26-29
September 2023.

Thomas, R.J., Boger, S.D., Fullgraf, T., Charles, N., Le Bayon, B., Frei, D., Plunder, A., Lahaye, Y., Le Roux, P., Mumba, R., 2023b. Two pulses of Mesoproterozoic intra-plate magmatism in the heart of the palaeoproterozoic ubendian domain of northern Malawi. J. Afr. Earth Sci. 202. https://doi.org/10.1016/j.jafrearsci.2023.104897.

Vrána, S., Kachlík, V., Kröner, A., Marheine, D., Seifert, A.V., Žáček, V., Babúrek, J., 2004. Ubendian basement and its late Mesoproterozoic and early Neoproterozoic structural and metamorphic overprint in northeastern Zambia. J. Afr. Earth Sci. 38 (1), 1–21. https://doi.org/10.1016/j.jafrearsci.2003.09.001.

Waele, De, 2009. The geochronological framework of the irumide belt: a prolonged crustal history along the margin of the bangweulu craton. Am. J. Sci. 309, 132–187. https://doi.org/10.2475/02.2009.03.

Wakabayashi, S., Grace Sakuwaha, K., Tsunogae, T., Santosh, M., Wandembo
Nyirongo, M., 2024. Sapphire + quartz assemblage from the irumide belt,
northern Malawi: implications for Mesoproterozoic ultrahigh-temperature
metamorphism related to rodinia assembly. Precambr. Res. 414, 107607. https://
doi.org/10.1016/j.precamres.2024.107607.

Walter, M.J., 1972. The geology of the Lilongwe-Dowa area. In: Geological Survey Department, Bulletin, vol. 26, p. 52.

Westerhof, A. B. Phil, Lehtonen, M.I., Mäkitie, H., Manninen, T., Pekkala, Y., Gustafsson, B., Tahon, A., 2008. The tete-chipata belt: a new multiple terrane element from Western Mozambique and southern Zambia. Geological Survey of Finland, Special Paper 48, 145–166.