The ∼ 550 Ma Kuunga Orogeny extends from the Damara in Namibia, through the Zambesi and Lurio orogenic belts in Zambia and Mozambique, southern Africa, through Dronning Maud Land and Princess Elizabeth Land, Antarctica into western Australia. Sverdrupfjella is located at the western end of Dronning Maud Land where the Kuunga Orogeny is inferred to post-date and overprint the East African Orogeny.

Three complexes are recognized in Sverdrupfjella western Dronning Maud Land, Antarctica. A western basal ∼ 1140 Ma Jutulrora Complex, consisting mostly of arc-related tonalitic trondjhemitic orthogneiss with evolved Sr-Nd isotopic signatures with T_Dm ages >2 Ga. It is structurally overlain by the Fuglefjellet Complex, comprising supracrustal ∼ 800-900 Ma carbonates intercalated with quartzo-feldspathic gneisses with detrital zircons of ∼ 1000-1200 Ma age with ∼ 500 Ma overgrowths. The Fuglefjellet Complex is overlain in the east by the Rootshorga Complex containing paragneisses with minor orthogneisses (∼ 1100-1200 Ma), intruded by granitic orthogneiss of similar age. Strontium-Nd isotopic signatures from the Rootshorga Complex has T_Dm ages <1.8 Ga.

D₁ and D₂ planar fabrics typically dip to SE with vergence top-to-NW in all complexes. D₃ deformation verges top-to-the-SE. In the Jutulrora Complex, D₃ comprises ∼ 100 m scale folds with NW dipping axial planes, cut by SE dipping dilational granite sheets. In the Rootshorga Complex D₃ is characterised by syntectonic granite veins with extensional and compressional displacements with top-to-the SE shear. Discordancies are consistent with low angle thrust planes at Fuglefjellet and Kvikjolen with probable repetition of carbonate layers.

Zircon ages of the granitic sheets are 490-500 Ma. Strontium and Nd isotopic signatures of the granitic sheets intruded into all complexes are consistent with melting of Jutulrora Complex crust with Archaean and Mesoproterozoic xenocrysts in some samples. Top-to-SE shear zones displace pegmatites with an inferred age of 520 Ma and are syntectonic with layer parallel ∼ 490 Ma granite sheets.

P-T-t studies from the Rootshorga Complex yield isothermal decompression paths at ∼ 800-900 °C with decompression from ∼ 1.4 GPa at ∼ 570 Ma to ∼ 700 °C and ∼ 0.7 GPa at ∼ 500 Ma whereas P-T-t estimates from the Jutulrora Complex are ∼ 600-700 °C and <∼ 0.8 GPa at ∼ 500 Ma with a path consistent with crustal loading. The Rootshorga and Fuglefjellet Complex are inferred to comprise a mega-nappe, emplaced during the Kuunga Orogeny ∼ 500 Ma ago, over the footwall Jutulrora Complex. Aerogravity, satellite gravity and seismic tomography data reflecting unusually thick crust are consistent with this interpretation.

In Gondwana reconstructions, Dronning Maud Land (DML), Antarctica is positioned next to southern Africa (Figs. 1a and 1b), against the coastlines of South Africa and Mozambique (Grantham et al., 1988; Groenewald et al., 1991; Grantham et al., 2008, 2019). The position of DML adjacent to N. Mozambique is supported by correlation of the Maud Complex in western Sverdrupfjella with the Barue Complex and Nampula Terrane of N. Mozambique (Grantham et al., 2011, 2019) supported by rocks with similar composition and Mesoproterozoic crystallization and Neoproterozoic to Cambrian metamorphic ages in both areas in Mozambique (Grantham et al., 2008). Whereas the Maud Complex, Barue Complex and Nampula Terrane are correlatable (Grantham et al., 2011, 2019), there are significant differences between the geology underlying Central Dronning Maud Land (CDML) and the Nampula Terrane which are juxtaposed in reconstructed Gondwana (Fig. 1b). The geology of DML is a subject of debate between differing views of the extent of, and relationships between, the East African Orogeny (EAO) (Stern, 1994) and the Kuunga Orogeny (Meert, 2003) (Figs. 1a and 1b).

Figure 1. (a) Map showing relationship between Kuunga and East African Orogens modified after (Meert, 2003) DB, Damara Belt; ZB, Zambesi Belt; MB, Mozambique Belt; M, Madagascar; SL, Sri Lanka. (b) Map of the distribution of continental blocks in Gondwana showing the simplified geology of southern Africa, Dronning Maud Land, Antarctica, Sri Lanka and southern India after (Grantham et al., 2019).

Stern (1994) initially described the EAO as involving the closure of the Mozambique Ocean between ∼ 900-650 Ma during which arc and micro-continental terranes were accreted, the process suturing East and West Gondwana along a N-S oriented orogenic belt. Significant juvenile magmatism within this age range characterized this orogeny and indicated the extent of the EAO as stretching from Arabia to N. Mozambique (Stern, 1994).

Jacobs et al. (2003a, 2003b) and Jacobs and Thomas (2004) proposed a southern continuation of the EAO, from Mozambique to Heimefrontfjella, Antarctica. The southern continuation into Antarctica was questioned by Grantham et al. (2008) and Collins and Pisarevsky (2005) reflecting the termination of the EAO rocks along the ENE-SW oriented Lurio Belt which transects N. Mozambique. Grantham et al. (2008) similarly infer a major crustal boundary along the Lurio Belt of N. Mozambique (Fig. 1b) and suggested it is correlatable with the boundary separating the Highlands and Vijayan Complexes in Sri Lanka, located to the east in a reconstructed Gondwana (Fig. 1b).

Meert (2003) recognized a younger E-W oriented belt cross-cutting the EAO, termed the Kuunga Orogeny, extending westwards through the Zambezi Belt to the Damara Belt of Namibia and eastwards through Dronning Maud Land, Antarctica into Sri Lanka (Fig. 1a). The Kuunga Orogeny is also recognized east of Enderby Land, in the Prince Charles Mountains and at Prydz Bay (Boger, 2011), the Denman Glacier area of Antarctica (Daczko et al., 2018) and in China (Li et al., 2017).

Differences in ages between the KO and EAO are 530-570 Ma and 650-900 Ma respectively (Stern, 1994; Meert, 2003). Bingen et al. (2011) also recognized overprinting of EAO lithologies by the KO progressing southwards toward the Lurio Belt in N. Mozambique. The KO overprinting is recognized in CDML and the intervening ∼ 1100 Ma Nampula Terrane in northern Mozambique (Grantham et al., 2008). No direct contact between the EAO north of the Lurio Belt and CDML in reconstructed Gondwana is seen. Grantham et al. (2008, 2013, 2019) inferred a tectonic-related link between the two areas via erosional klippen in Mozambique (Monapo and Mugeba, Roberts et al., 2005; Grantham et al., 2008, 2013) which overly the Nampula Terrane.

Resolving and understanding these differences are related to current debates around the distribution, nature of, and timing of orogenic events in the area concerning the extents and relationships between the geology of the East African and Kuunga Orogenies which overlap in the broad area between western Dronning Maud Land and southern Africa (Figs. 1a and 1b) in Gondwana.

Sverdrupfjella, western Droning Maud Land, Antarctica is located at the western end of the Neoproterozoic to Mesoproterozoic metamorphic terrain of East Antarctica, separating the Archean-age Enderby Craton in the east and Kalahari Craton in the west (Fig. 1b). The rocks located between these two cratons, west of Enderby Land, comprise the most critical exposures in understanding the Kuunga Orogeny (Meert, 2003; Grantham et al., 2019), albeit with the sparse limited outcrops typical of Antarctica (Fig. 1b). The evolution of the Kuunga Orogeny east of Enderby Land and possible correlations with India is further complicated by younger deformation related to the collision between India and Asia in the Himalayan Orogeny.

This paper describes aspects of the structural geology of the Fuglefjellet and Rootshorga Complexes as well as U-Pb zircon age data from the Fuglefjellet Complex and Rootshorga Complex from laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and sensitive high resolution ion microprobe (SHRIMP) studies. These data are integrated and interpreted with published radiogenic isotope data and P-T-t studies and demonstrate that Sverdrupfjella and Gjelsvikfjella comprise stacked thrust-faulted complexes, each with different lithologies, ages and P-T histories.

The basement geology underlying Sverdrupfjella comprises three gneiss complexes, from west to east and upwards structurally, the Jutulrora, Fuglefjellet and Rootshorga Complexes respectively (Figs. 2 and 3) (Elvevold and Ohta, 2010). The Jutulrora Complex comprises two units namely tonalitic biotite hornblende quartzofeldspathic gneisses, inferred to be of meta-andesitic (Grantham, 1992; Grantham et al., 1995) and a heterogeneous banded gneiss sequence, dominantly quartzofeldspathic with interlayered metabasic gneisses (Grantham, 1992; Elvevold and Ohta, 2010).

Figure 2. Map showing the broad tectonic units of Dronning Maud Land from Ahlmannryggen to Schirmacher Oasis and the location of the study area in central Sverdrupfjella.

Figure 3. Map of the central eastern Sverdrupfjella showing localities referred to in the text as well as the map areas for Fuglefjellet (Fig. 4) and Kvitkjolen and Dyna (Fig. 5).

The chemistry and ∼ 1140 Ma age of the meta-andesitic gneisses are reported in Grantham et al. (2011) and radiogenic isotope data in Wareham et al. (1998). The radiogenic isotope data provide Nd T_Dm ages of >2.0 Ga, reflecting that the Jutulrora Complex is underlain by Archaean crust (Wareham et al., 1998), supported by a 2.8 Ga age for the Brekkerita Granite in western Sverdrupfjella (Grantham et al., 2023), as well as Nd T_Dm ages of >2.0 Ga from ∼ 490 Ma late tectonic granite veins (Grantham et al., 2019).

The Fuglefjellet Complex comprises supracrustal quartzofeldspathic gneisses interlayered with marbles, calc silicates and subordinate metabasic gneisses and meta-conglomerates (Figs. 3-5, and 6a, 6b, and 6d) (Grantham, 1992; Elvevold and Ohta, 2010).

Figure 4. Geological map of Fuglefellet showing sample localities and structural data and interpretation.

Figure 5. Geological Map of Kvitkjolen showing structural data and interpretation.

Figure 6. Photographs of field exposures from the Fuglefjellet and Rootshorga Complexes. (a) Deformed conglomerate at Fuglefjellet. Hammer for scale. (b) Deformed layered marble sequence at Fuglefjellet. Hammer for scale. (c) Ramp structure at the top of Kvitkjolen. Person for scale. (d) Sheath fold at Dyna. Outcrop is ∼ 10 m high (e) Near horizontal top-to-the-S shear zone truncating S1 layering at Kvitkjolen. Person for scale. (f) Truncated pegmatite at Kvitkjolen. Same locality as G. Ice-axe lower right for scale.

The Rootshorga Complex comprises layered quartzofeldspathic, metabasic and metapelitic gneisses interleaved with granitic augen orthogneisses (Figs. 3, 5, 6c, 6e, and 6f) (Groenewald, 1995; Elvevold and Ohta, 2010). Age constraints on the Rootshorga Complex and its extensions into Gjelsvikfjella indicate ages between ∼ 1100-1150 Ma (Moyes, 1993; Moyes et al., 1993; Board et al., 2005) and ∼ 1100 and 1140 Ma (Jacobs et al., 2003a, 2003b, 2003c; Bisnath et al., 2006).

The paragneisses are intruded by ∼ 1100 Ma granitic orthogneiss (Krynauw and Jackson, 1996; Board et al., 2005; Hokada et al., 2019) as well ∼ 480 to 520 Ma granite sheets and pegmatites. Neodymium T_Dm ages >2.0 Ga from the ∼ 490 Ma Brattskarvet pluton and granite veins in Gjelsvikfjella (Moyes, 1993; Paulsson and Austrheim, 2003; Pauly et al., 2016) suggest that the Rootshorga Complex is similarly also underlain at depth by Archaean crust.

Planar structures, defined by upper amphibolite facies mineralogy as well as layer parallel anatectic veins, in west Sverdrupfjella, including the Jutulrora Complex, define a dominantly N-S π girdle showing both N-S dips with SE plunging mineral lineations and fold axes (Grantham et al., 1995, 2006; Bumby et al., 2020). The Fuglefjellet and Rootshorga Complexes structurally overlie the Jutulrora Complex both dipping dominantly southeast with southeast plunging lineations and fold axes (Grantham et al., 1995). The Rootshorga Complex, structurally overlies the Fuglefjellet Complex. D₁ and D₂ deformation in these complexes verge top-to-NW involving isoclinal folds, local sheath folds, low angle thrust faults and ramp structures (Grantham et al., 1995). In contrast, D₃ deformation in the Fuglefjellet and Rootshorga Complexes verges top-to-the-SE, seen in ∼ 490 Ma dilation granite sheets with top-to-SE extensional and compressional displacements of granitic sheets at Salknappen (Grantham et al., 1991, 1995; Bumby et al., 2020). In the Jutulrora Complex, D₃ comprises ∼ 100 m scale folds with NW dipping axial planes cut by SE dipping dilational granite sheets (Bumby et al., 2020).

These two adjacent areas contain the best-exposed relationships between the Fuglefjellet and Rootshorga Complexes. In Figure 3, the boundaries between the Juturora, Fuglefjellet and Rootshorga Complexes are inferred as major thrust faults. The boundary between the former two complexes is nowhere exposed, but its inference is based on the absence of meta-carbonates and calc-silicates in the Jutulrora Complex and the εNd (T) and T_Dm isotopic age differences between the Jutulrora and Rootshorga Complexes described in Grantham et al. (2019). The inference of the boundary is supported by the geological history described in Bumby et al. (2020) who recognized that the structures of the Straumsnutane area and Jutulrora Complex/Maud Belt contrasted with the overlying Fuglefjellet and Rootshorga Complexes in eastern Sverdrupfjella. Extensive meta-carbonates are also exposed at Skarsnuten ∼ 20 km south of Kvitkjolen (see Fig. 3 for locality) with subordinate exposures at Dvergen and Knattebrauta (shown in Fig. 3). The boundary between the Fuglefjellet Complex and Rootshorga Complex is defined lithologically by the absence of metacarbonates in the latter and the absence of granitic augen orthogneisses with ages of 1100-1150 Ma (Moyes, 1993; Board et al., 2005) in the former as well as structural data presented below.

Fuglefjellet. The geology of Fuglefjellet is shown in Figure 4 with field images in Figures 6a and 6b and structural data from the Fuglefjellet Complex in Figures 7a, 7b, 7c, and 7d. Mapping at Fuglefjellet shows dominantly SE steeply dipping layering (Figs. 4, 6b, and 7a). Discordancies in the field facilitate the recognition of a SE dipping thrust fault at the N end of the outcrop (Figs. 4 and 7a). Limited data from the footwall (Fig. 8c) dips toward ESE, in contrast to hanging wall measurements dipping SE to S (Fig. 7c). Measurements adjacent to the thrust fault plane dip S, N and SE (Fig. 7c). Stretching mineral lineations plunge shallowly to the SE and S (Fig. 7b) at both Fuglefjellet and Kvitkjolen. A steeply N dipping discordance ∼ 500 m south of the SE dipping thrust fault is inferred as a back thrust (Fig. 4).

Figure 7. (a) Planar S₀ + S1_-2 data from Fuglefjellet and Kvitkjolen (Figs. 4 and 5). The data show generally steeper dips at Fuglefjellet compared to the Kvitkjolen areas. (b) Mineral stretching lineations L₁ + L₂ measurements from Fuglefjellet and Kvitkjolen. Note the different orientation for lineations from the Rootshorga Complex. (c) Planar S₀ + S_1-2 from Fuglefjellet from different areas of the outcrop. Note the difference in orientation between Footwall and hanging wall rocks. (d) Planar S₀ + S_1-2 from Kvitkjolen.

Figure 8. (a) Early pegmatite dykes cross cutting layering with layer parallel syn-tectonic younger granite sheets showing displacements along the granite planes at Salknappen. Person lower right for scale. Note also the mafic vein within the pegmatite at left shown in (c). (b) Sheared porphyroclastic augen gneiss to blastomylonite at Salknappen. Pencil at left for scale. (c) Pegmatites with later mafic intrusion along the core of the pegmatite vein. White squares are 10 cm wide. (d) Sheared and boudinaged pegmatite of same generation as in (c) showing top-to-the-S sinistral shear cross cut by younger granite vein at Salknappen. (e) Small top-to-the-S reverse shear zone with partial displacement of the margins of a younger granite sheet reflecting syn-tectonic emplacement of the granite. Granite vein is ∼ 20 cm thick. (f) Mesoscale duplex ramp structure in gneiss at Salknappen. Outcrop is ∼ 2 m high.

Kvitkjolen. Mapping at Kvitkjolen shows three separate carbonate exposures separated by intervening quartzofeldspathic gneiss layers (Fig. 5). Within the quartzofeldspathic gneisses discordant structural orientations are observed between layers. For example, the orientation of quartzofeldspathic gneisses along the northern ridge of Kvitkjolen strike NNW and dip toward NE and swing around to NE striking, SE dipping orientations in the overlying carbonates, until truncated by overlying, ∼ E striking, S dipping quartzofeldspathic gneiss (Figs. 5 and 7d). The discordant planar fabrics within the layers facilitates the interpretation of thrust fault planes separating many of the lithological units. The measured layering at Kvitkjolen and Dyna is shallower dipping than those recorded at Fuglefjellet (Fig. 7a). A discontinuous wedge of biotite-hornblende gneiss (Fig. 5) is seen, inferred to represent a blind duplex horse structure. The boundary between the Fuglefjellet and Rootshorga Complexes is inferred as the thrust fault at the top of Kvitkjolen, based on changes in lineation orientations (Fig. 7b). Figure 7b shows lineations from the Fuglefjellet and Kvikjolen areas from Fuglefjellet and lower relief levels of Kvitkjolen, from which it is apparent that lineations from Fuglefjellet and Kvitkjolen, N of the top of Kvitkjolen (Fig. 5), have similar orientations, plunging shallowly to the E and SE. In contrast, those measured S of the thrust inferred at the top of Kvitkjolen, plunge shallowly SE to S, indicating a separate thrust slice (Fig. 7c).

The interpretation of thrust faulting and high-strain deformation is supported by mesoscale structures shown in Figures 6 and 8. These include a frontal ramp structure at the top of Kvitkjolen (Fig. 6b), a sheath fold at the northern end of Dyna (Figs. 5 and 6d), a sheared augen gneiss to blastomylonitic zone from Salknappen (Figs. 4 and 8b) and at central Kvitkjolen, a near horizontal thrust plane and duplex structure (Fig. 6e) truncating a pegmatite (Fig. 6f).

The timing of deformation is poorly constrained but the youngest phase is inferred to be ∼ 490-520 Ma. These younger time constraints are inferred from granitic vein field relationships. Figure 8a shows a N-S oriented face at Salknappen (Fig. 3) in which steeply NW dipping pegmatites are truncated by S dipping granitic sheets, along which top-to-the-S displacement is evident. Figure 8e shows a reverse, steep, top-to-the-S shear which displaces the margins of a thin granite sheet but does not affect/truncate the granite. These two images (Figs. 8a and 8e) indicate syn-tectonic emplacement of the granite. Figure 8c (a close-up image of the base of the cliff in Fig. 8a) shows a pegmatitic vein with a mafic vein in its core suggesting emplacement of the vein and pegmatite under an almost synchronous strain regime. Similar intrusive relationships at Gjelsvikfjella, ∼ 60 km to the N (Fig. 2), are seen where Jacobs et al. (2003a) reported an age of ∼ 525 Ma from the pegmatite-hosted mafic intrusive, interpreted as a lamprophyre. No chemical data supporting a lamprophyric interpretation were available (J. Jacobs, personal communication, 2019). Figure 8d shows a curvilinear pegmatitic vein of the same generation as that in Figure 8c, which is sinistrally sheared and boudinaged with a top-to-the-SE sense of shear along a narrow ductile shear zone, overlying an undeformed granitic vein at Salknappen. Figure 8f shows a small duplex ramp structure with top-to-the-NW in basement gneisses at Salknappen, inferred to be D₂ in age. The younger granite veins are inferred to be ∼ 490-506 Ma in age (see geochronology below and Dalmatian Granite age in Krynauw and Jackson, 1996).

The petrography of six samples selected for zircon separation in support of geochronology are described below. Zircons from five samples were selected for U-Pb analysis from paragneiss units from the Fuglefjellet and Rootshorga Complexes to constrain the ages of zircons in these rocks recognizing that no published age data from the Fuglefjellet Complex are available and that the available data from the Jutulrora and Roootshorga Complexes are from orthogneisses. Zircons from an undeformed granite vein intruding the Fuglefjellet Complex were also analysed to constrain the timing of syn- to post-tectonic granite vein intrusions and to supplement data from similar veins from adjacent areas. Data from metamorphic rims from zircons in the paragneisses facilitate comparison of the timing of metamorphism from adjacent areas as well as from other techniques e.g., ⁴⁰Ar-³⁹Ar in Grantham et al. (2019). Microscope images in plane polarized light and crossed polars from the 6 samples are shown in Figure 9 after which cathodoluminescence images of the extracted zircons are shown and described.

Figure 9. Plane polarized light (left hand column) and crossed polar (right hand column) photomicrographs of samples FG15 (a) and (b), FG31 (c) and (d), 000aX (e) and (f), 0032aB (g) and (h), 0018 (i) and (j), and FG5 (k) and (l). The first four samples are from Fuglefjellet and the latter two samples from Dyna and Vendeholten respectively. Mineral abbreviations are Qtz, quartz; Grt, garnet; Bt, biotite; Tml, tourmaline; Sill, sillimanite; Pl, plagioclase; Crd, cordierite; Mt, magnetite; Ms, muscovite; Kfs, K-feldspar.

Sample FG15 calc-silicate granulite. Photomicrographs of sample FG15 (Figs. 9a and 9b) show mineralogy dominated by quartz (15%) and feldspar (45%) with garnet (15%), magnetite (12%), hornblende (8%), clinopyroxene (3%) and titanite (1%) showing granoblastic textures. Network poikiloblastic pink garnet encloses quartz and feldspar. Magnetite forms subhedral grains, locally containing rims of secondary titanite. Clinopyroxene forms thin xenomorphic grains and is partially replaced by amphibole. Dark green hornblende forms isolated grains in the groundmass.

Sample FG5 granite. Sample FG 5 is equigranular with interlocking quartz (25%) and feldspar (65%) with accessory subhedral garnet (7%) and muscovite (Figs. 9c and 9d). Garnet is relatively homogeneous with few inclusions. Muscovite forms secondary xenomorphic grains as well forming fine alteration sericitic patches in the feldspar. From field appearances, this granite vein is correlated with the Dalmatian Granite (Grantham et al., 1991), which contains biotite, primary muscovite, magnetite and tourmaline, the latter mineral developed where the veins intrude carbonate.

Sample FG 31 Tourmaline-plagioclase-hornblende granulite. The rock comprises pale green amphibole (80%), plagioclase (10%) and tourmaline (10%) with the minerals showing an equigranular granoblastic texture (Figs. 9e and 9f). The granulite is inferred to be of sedimentary origin. Granite veins emplaced into the carbonates typically contain tourmaline, indicting they are the source of boron.

Sample 000aX Quartzofeldspathic gneiss. The rock consists entirely of quartz (40%) and feldspar (60%) forming an equigranular granoblastic texture (Figs. 9g and 9h). Feldspars are typically turbid in plane polarised light suggesting kaolinization and sausseritisation but display twinning in crossed polars as well as very fine sericisation. The rock is interpreted as originating from an impure sandstone or arkose.

Sample 0032aB Biotite-sillimanite-garnet-gneiss. The sample contains quartz (30%), feldspar (40), garnet (10%), sillimanite (5%), muscovite (10%) and biotite (5%) (Figs. 9i and 9j). Quartz and feldspar form xenomorphic granoblastic grains with garnet being both poikiloblastic and porphyroblastic with minor inclusions which are crudely aligned indicating syntectonic growth. Khaki brown biotite forms small grains adjacent to garnet suggesting late-stage hydration. Fibrolitic sillimanite appears to partially replace muscovite. The assemblage is typically metapelitic.

Sample 0018 Biotite-cordierite-garnet gneiss. The sample contains quartz (20%), feldspar (35%), garnet (15%), cordierite (20%) and biotite (10%) (Figs. 9k and 9l). Garnet is porphyroblastic, with smooth grain boundaries and almost inclusion free with inclusions of quartz and biotite. Cordierite has irregular xenopmorphic, porphyroblastic and poikiloblastic grains with inclusions of biotite, quartz, feldspar and zircon, the latter with pleochroic haloes. Biotite defines a weak planar fabric. Quartz, feldspar and biotite form a granoblastic equigranular matrix. The morphology of cordierite and its development peripheral to garnet suggests it has grown post-tectonically, preserving a planar fabric within it and possibly due to a late heat influx and/or decompression.

Summary of petrography. The assemblages described for paragneiss samples (Samples 0018aB, FG31, FG15, and 0032aB) are typical of upper amphibolite facies metamorphism. Sample FG15 containing garnet + clinopyroxene is potentially of granulite facies grade, however the absence of orthopyroxene in any of the samples suggests that granulite facies assemblages have not been preserved or were not developed. The garnet + clinopyroxene assemblage is probably related to its calcsilicate origin in which mixed CO₂ + H₂O fluids, typical of carbonate and calcsilicate metamorphism, may contribute to the development of anhydrous assemblages.

Cathodoluminescence images of the samples analyzed by SHRIMP are shown in Figure 10.

Figure 10. CL Images of zircons analysed by SHRIMP II at NIPR, Tachikawa, Tokyo, Japan. The spot numbers correspond to the data shown in Supplementary Tables S1, S2, and S3. Spot sizes are 25 µm. (a) FG5, (b) FG31, and (c) FG15.

Sample FG5 Garnet-bearing granite. The zircons grains (Fig. 10a) from this sample are typically euhedral with sector zoning and oscilliatory zoning. The grains are stubby with length:breadth ratios of ∼ 1.5:1. Some grains have thin dark rims, too narrow to analyse.

Sample FG31 Calc-silicate paragneiss. The zircon grains (Fig. 10b) from this sample are typically elongate with rounded terminations and with length:width ratios of ∼ 3:1 with grain sizes upto 200 µm. The grains typically have dark cores as well as some having cores showing oscillatory zoning, with dark rims. In addition, almost all grains have well-developed secondary rim overgrowths, light in colour under CL.

Sample FG15 Calc-silicate paragneiss. The zircon grains from this sample are typically elongate with rounded terminations and length:width ratios of ∼ 2:1 with grain sizes upto 300 µm (Fig. 10c). The grains typically have dark cores as well as some having cores showing oscillatory zoning, with dark rims. In addition, almost all grains have well developed secondary rim overgrowths, light in colour under CL.

Cathodoluminescence images of the samples analysed by LA-ICPMS are shown in Figure 11.

Figure 11. CL images of zircons analysed by LA-ICPMS at the University of Johannesburg, South Africa. Spot sizes are 20 µm The ages shown are ²⁰⁷Pb/²⁰⁶Pb and are presented in Supplementary Tables S4, S5, and S6. (a) 00aX, (b) 018bC and (c) 0032B.

Sample 000aX Meta-quartz arenite. CL images for the grains analysed from this sample show that they are small (<50 µm) and mostly elongate with length:breadth ratios of ∼ 4:1 with some grains being near equant (Fig. 11a). Almost all grains have oscillatory zoning. Few grains were analyzed with most grains being extensively metamict.

Sample 018bC Metapelite. These zircons vary in size from ∼ 100 to ∼ 250 µm with length breadth ratios of ∼ 2:1 to 3:1 with rounded grains. Grain cores vary with some showing oscillatory zoning with others having homogenous cores without zoning (Fig. 11b). Many grains have secondary overgrowths. Grains with oscillatory zoned cores preserve older ages >1100 Ma in contrast to those with homogeneous cores which preserve ages of ∼ 530 Ma with overgrowth rims yielding younger ages of ∼ 500-520 Ma, indicating three phases of zircon growth.

Sample 0032aB Metapelite. The zircon grains are typically ∼ 100 µm in size with tabular shapes and length breadth ratios of ∼ 2:1 (Fig. 11c). Most grains have homogeneous cores with some grains showing limited oscillatory zoning. Some grains show dark younger metamorphic rims.

Three samples were analyzed by SHRIMP at the National Institute of Polar Research, Tokyo, Japan and the remaining three were analyzed by LA-ICPMS at the Department of Geology, University of Johannesburg in South Africa. The analytical procedures for the SHRIMP analyses are described in Grantham et al. (2013) and procedures for the LA-ICPMS analyses are reported in Grantham et al. (2021).

The samples selected for analysis are from a post-tectonic granite vein (sample FG5), which intrudes the marbles at Fuglefjellet as well as two samples (FG15 and FG31) from calc-silicate gneisses interlayered with the marble at Fuglefjellet. Sample localities are shown in Figure 4. Data tables for the SHRIMP analyses are presented in Supplementary Tables S1-S3 (Supplementary Tables S1-S7 are available online from https://doi.org/10.2465/jmps.230125). Both rim and core components of the zircons from the calc-silicate gneisses were analysed to constrain the source ages as well as the timing of subsequent metamorphism.

Sample FG15 calc-silicate paragneiss. The data from sample FG15 (Table S1) are summarized in Figures 12a and 12b. Sixty six spots were analyzed from sample FG15 from 48 grains, with most analyses being on grain cores and a lesser number representing metamorphic rims. Fifteen analyses were excluded from the calculation, most of which were excluded based on being more than 10% discordant. The data shows two broad groups (Fig. 12a). The grain core analyses are centered around 1133 Ma with dates varying between 1064 and 1145 Ma (Fig. 12b). The analyses from rim spots define a concordant age of 514.5 ± 4.8 Ma (MSWD = 0.39) (Fig. 12a). The core data are interpreted to represent detrital grains from an erosional source with a limited date range between 1064 and 1145 Ma whereas the rim data are interpreted to represent the timing of metamorphism of the Fuglefjellet Complex.

Figure 12. Terra Wasserberg plots of U-Pb data from zircons from calc-silicate gneisses sample FG15 (a) and (b) and sample FG31 (d) and (e), a granite vein sample FG5 (c), and quartzfeldspar gneiss sample 000aX (i) from Fuglefjellet and samples from Dyna sample 032aC (h) and Vendeholten sample 018 (f) and (g).

Sample FG31 Tourmaline-plagioclase-hornblende granulite. Forty-four spots were analysed from sample FG31 (Table S2) from 40 grains, with most analyses being on grain cores and a subordinate number representing metamorphic rims. The data are summarized in Figures 12d and 12e. Seven analyses were excluded from the calculation on the basis of being more than 10% discordant. The data similarly define two broadly concordant clusters with an array of subordinate discordant grains (Figs. 12d and 12e). The grain core analyses are centered around ∼ 1165, ∼ 1135, ∼ 1109, and ∼ 1071 Ma with dates spread between 1065 and 1185 Ma (Fig. 12e). The analyses from rim spots define a concordant age of 525.6 ± 3.2 Ma (MSWD = 0.17) (Fig. 12d). The core data are interpreted to represent detrital grains from a source with limited date range between 1065 and 1185 Ma whereas the rim data are interpreted to represent the timing of metamorphism of the Fuglefjellet Complex. The range in metamorphic age between the two calc-silicate samples of 515 to 527 Ma suggests relatively long lived metamorphism, consistent with the P-T-t path from Brattskarvet ∼ 40 km to the NE of ∼ 570 to ∼ 520 Ma (Pauly et al., 2016).

Sample FG 5 Garnet-bearing granite. Fifty spots were analyzed with the data (Table S3) with eleven being excluded from the concordant isochron summarized in Figure 12c. Almost all grains (excluding 3) yield dates of between 470 and 580 Ma. Grains excluded from the data calculation are mostly characterized by being more than 10% discordant. Forty nine grains define a concordant age of 506 ± 1.6 Ma (MSWD 1.16). This age is interpreted as the crystallization age of the granite vein and constrains the age of syn-tectonic intrusion of granite veins intruded during deformation.

The samples selected for LA-ICPMS analysis are from a metaquartzite layer from Fuglefjellet, a metapelite from Dyna, within the Fuglefjellet Complex, and a metapelite gneiss from Vendeholten from the Rootshorga Complex. Nunatak localities are shown in Figure 3. Data tables for the LA-ICPMS analyses are presented in Supplementary Tables S4-S6.

Sample 018bC Biotite-cordierite-garnet gneiss. The data from the gneiss (Table S4) are summarized in Figures 12f and 12g. Figure 12f shows all the data (Table S4) from which it can be seen that there is a wide range of dates including an older group with a spread of dates >1200 up to >1800 Ma and a younger cluster around ∼ 500 Ma. These older group are inferred to be detrital being derived from analysis of cores with most grains having dates between ∼ 1100 and ∼ 1400 Ma. All the grains in the younger cluster represent rim analyses with all analyses except 1 plotting near concordantly and defining a concordant age of 517.8 ± 4.7 Ma (MSWD = 2.5) (Fig. 12g). The older and younger data groups are interpreted to represent detrital and metamorphic ages respectively.

Sample 0032aB Biotite-sillimanite-garnet-gneiss. The data from the paragneiss are summarized in Figure 12h (Table S5). The data define a dominantly older group with dates between ∼ 1200 and ∼ 1300 Ma with two strongly discordant grains and a single grain plotting weakly discordant at ∼ 500 Ma. These data are interpreted to dominantly represent detrital zircons and with the remaining grains reflecting isotopic disturbance and a metamorphic rim.

Sample 000aX Quartzite from Fuglefjellet in the Fuglefjellet Complex. The limited data (Table S6) from the metaquartzite are summarized in Figure 12i with only ten grains being analyzed. All analyses plot close to an upper intercept of 1129 ± 46 Ma. Almost all the grains analyzed had excessive common lead, requiring correction contributing to the limited number of samples analyzed.

The whole rock radiogenic isotope and trace element chemistry of carbonates from Sverdrupfjella have been reported in Satish-Kumar et al. (2021) along with data from Sri Lanka, Sør Rondane and Mozambique. The radiogenic isotope data from Sverdrupfjella are shown in Supplementary Table S7 and were collected from Fuglefjellet and Kvasknatten (Fig. 3 for localities). Analytical procedures are described in Satish-Kumar et al. (2021). Application of the radiogenic isotope data from meta-carbonates, specifically ⁸⁷Sr/⁸⁶Sr, is aimed at constraining the approximate depositional age of the carbonates by comparing the data derived from pure carbonates with the sea water evolution curve of ⁸⁷Sr/⁸⁶Sr correlated with age (Halverson et al., 2010) (Fig. 13).

Figure 13. (a) ⁸⁷Sr/⁸⁶Sr data range for the marbles from Sverdrupfjella plotted with the evolution curve complied by (Halverson et al., 2010) and including data ranges from N. Mozambique (Melezhik et al., 2008) and Sri Lanka, Sør Rondane and Lutzoholm Bay (Satish-Kumar et al., 2021). (b) Summary of whole rock Nd-Sr radiogenic isotope data from gneisses and Cambrian granites from Sverdrupfjella and Gjelsvikfjella calculated at 500 Ma. Data sources are from (Moyes, 1993; Moyes et al., 1993; Wareham et al., 1998; Paulsson and Austrheim, 2003; Grosch et al., 2007; Grantham et al., 2019).

The meta-carbonates from eastern Sverdrupfjella have ⁸⁷Sr/⁸⁶Sr which vary between 0.70569 and 0.70648 with one sample with ⁸⁷Sr/⁸⁶Sr of 0.70735 (Table S7). Figure 13a shows that the ⁸⁷Sr/⁸⁶Sr data indicate depositional ages of between ∼ 900 to ∼ 800 Ma for almost all the samples from Sverdrupfjella. Figure 13a also shows that this age range is broadly similar to metacarbonates described by Satish-Kumar et al. (2021) from the Highland Complex, Sri Lanka, Sør Rondane and Lützow-Holmbukta (CDML) and the Montepuez West samples (Melezhik et al., 2008). Carbonates of broadly similar age, broadly define the shape of a Neoproterozoic continent comprising southern Africa, East Antarctica and most of Australia with the inference that carbonate genesis is typically characteristic of shallow marine continental shelf settings (see Fig. 1 in Satish-Kumar et al., 2021).

The data presented above will be discussed in the contexts of geochronology, structural geology, radiogenic isotope chemistry, P-T-t evolution and regional geophysical data of the area.

Five of the samples from paragneisses from the Fuglefjellet and Rootshorga Complexes reported above show zircons dominantly with ages between ∼ 1250 and 1000 Ma with metamorphic rim overgrowths yielding ages of between ∼ 540 and 520 Ma (Fig. 12). The metamorphic rim ages are comparable with ⁴⁰Ar/³⁹Ar ages from hornblende from Sverdrupfjella with ages between 450 and 550 Ma with marginally younger biotite cooling ages varying between 463 to 500 Ma (Grantham et al., 2019). The metamorphic rim ages are also broadly coincident with ages of granitic/pegmatitic veins from Sverdrupfjella and Gjelsvikfjella (Fig. 14a) (Table 1) which range between ∼ 480 and ∼ 525 Ma. The growth of metamorphic rims in the Fuglefjellet and Rootshorga complexes, whose lithologies preserve upper amphibolite facies assemblages, are likely to have been promoted by fluid-assisted Zr diffusion similar to that described from Perlebandet in Sør Rondane (Kawakami et al., 2017). Those authors inferred fluid infiltration during the tectonic emplacement of the NE terrane in Sør Rondane over the SW terrane.

Figure 14. (a) Histogram and relative probability figure for age data for Cambrian Granites in Sverdrupfjella and Gjelsvikfjella. Data sources are shown in Table 1. (b) Histogram and relative probability figure for age data for granitic orthogneissess in Sverdrupfjella and Gjelsvikfjella. Data sources are shown in Table 1.

The ages of the detrital grains in the paragneisses with ages between ∼ 1000 and ∼ 1250 Ma (Fig. 12) partially overlap with orthogneisses and are marginally older than granitic gneisses from Sverdrupfjella and Gjelsvikfjella which vary between ∼ 1000 to 1150 Ma (Fig. 14b) (Table 1). Ages older than ∼ 1140 Ma from orthogneisses in the Rootshorga Complex indicate an inverted age chronostratigraphy, being the age of TTG gneisses (Grantham et al., 2011) in the Jutulrora Complex which structurally underlies the Fuglefjellet and Rootshorga complexes and overlie Archaean basement.

Whereas the carbonate age range derived from the Sr_i analyses in Sverdrupfjella is relatively wide (Fig. 13a), suggesting a depositional age of ∼ 800-900 Ma, the age range is significantly younger than the U-Pb zircon ages of orthogneisses in the Rootshorga Complex (Fig. 14b) and its correlatives in Gjelsvikfjella as well as the detrital U-Pb zircon ages from calc-silicate and pelitic gneisses in the Fuglefjellet Complex and Rootshorga Complex (Fig. 12). It is significant that the data represent an inverted stratigraphy with the Fuglefjellet Complex with depositional age of 800-900 Ma being overlain by the Rootshorga Complex which is intruded by orthogneissic granites with ages between 1000 and 1150 Ma. In addition, zircons with ages in excess of ∼ 1200 Ma are recognized in the Rootshorga Complex but not recognized in the basal Jutulrora Complex, and can therefore not have been derived from the Jutulrora Complex.

A summary of published radiogenic isotope data from Sverdrupfjella and Gjelsvikfjella is shown in Figure 13b, comprising data from paragneisses, orthogneisses and Cambrian granites (excluding pegmatites as described above). The ε_Nd and Sr_i data are calculated at 500 Ma to facilitate comparisons between the basement gneisses and the potential sources of the Cambrian granites at 500 Ma. The data are categorized as sourced from the Rootshorga, and Jutulrora Complexes with no data being available for the Fuglefjellet Complex. Data sources include (Moyes, 1993; Moyes et al., 1993; Wareham et al., 1998; Paulsson and Austrheim, 2003; Grosch et al., 2007; Grantham et al., 2019).

It is apparent that the Rootshorga Complex is isotopically distinct from data from the Jutulrora Complex, being typically more juvenile, in contrast to the Jutulrora Complex which has typically more evolved characteristics (Fig. 13b). Comparison of data from the Cambrian granites with data from the Jutulrora and Rootshorga Complexes shows the Cambrian granites overlap with and are restricted to a more evolved source comparable to the Jutulrora Complex (Fig. 13b). These data suggest that the younger Cambrian granites were sourced in gneisses comparable to the Jutulrora Complex and were emplaced into the overlying Fuglefjellet and Rootshorga Complexes between ∼ 480 and 506 Ma. From Figure 13b, it is also apparent that all the Cambrian granites have similar εNd characteristics whereas Sr_i data show a wide range with granites from the Jutulrora Complex having Sr_i > 0.73 in contrast to those from the Fuglefjellet and Rootshorga Complexes having Sr_i < 0.725.

The recognition of structural discordancies combined with structural measurements of planar and linear fabrics, combined with lithological differences between the complexes has facilitated the identification of different thrust fault slices. Whereas it is difficult to assign ages to the development of the various phases of deformation, particularly D₁ and D₂, it is possible to identify that the age of the youngest top-to-the-south deformation phase (D₃) occurred at <∼ 520 Ma being broadly synchronous with the ∼ 480-500 Ma emplacement of the granite veins, but post-dating the pegmatite vein phase as shown in Figures 6f and 7a. At Fuglefjellet and Kvitkjolen at least 5 separate meta-carbonate layers are seen (Figs. 4 and 5). It is not clear whether these are different layers but the recognition of discordant contacts at some of their margins suggests that it is possible, if not probable, that they are the same layer duplicated and stacked by thrust faulting. The recognition of thrust slices with different ages in Sverdrupfjella is consistent with similar relationships recognized east of Gjelsvikfjella in the Filchnerfjella and Hochlinfjellet in CDML (Fig. 2) in areas where granulites with ∼ 600 Ma metamorphic ages are juxtaposed, along an inferred shear zone, against lower grade gneisses with ∼ 525 Ma metamorphic ages (Baba et al., 2015). Contrasting planar fabric orientations are described from the same area by Jacobs et al. (2003a) with those authors reporting a NW striking thrust fault with top-to-the SW sense of shear. Similarly, in Sør Rondane juxtaposed tectonic blocks with contrasting lithologies and P-T paths have been recognized (Adachi et al., 2013; Baba et al., 2013; Osanai et al., 2013; Kawakami et al., 2017; Adachi et al., 2023).

Further in the west at the boundary between the Grunehogna Craton and the Maud Terrane (Fig. 3), the youngest structures recorded in Straumsnutane and the Jutulrora Complex are recognized as comprising top-to-the SE structures (Bumby et al., 2020). In Straumsnutane, the structures comprise quartz vein arrays, fold vergence directions as well as slickensided shear plane surfaces. In the Juturora Complex D₃ structures comprise top-to-SE mesoscale asymmetric synforms with SE-verging axial planes as well as SE dipping granite veins with poles of dilation toward SE/NW, with ages of ∼ 490 Ma (Dalmatian Granite; Grantham et al., 1991; Krynauw and Jackson, 1996). In Sør Rondane, Tsukada et al. (2017) have identified the youngest deformation as comprising a low angle southward directed brittle shear with an inferred age of ∼ 500 Ma.

Several studies of the P-T evolution of Sverdrupfjella and Gjelsvikfjella have been reported and are summarized in Figure 15. Most of the studies have focused on east Sverdrupfjella i.e., the Rootshorga Complex where the attention has largely been on granulites displaying decompression textures. The P-T-t paths for east Sverdrupfjella (Groenewald and Hunter, 1991; Grantham et al., 1995; Groenewald, 1995; Board et al., 2005; Byrnes, 2015; Pauly et al., 2016) and one study from Gjelsvikfjella (Baba et al., 2008) report isothermal decompression paths (ITD). Peak pressures decreased from ∼ 1.2 to 1.4 GPa down to ∼ 0.6 to 0.7 GPa (Fig. 15) with peak temperatures varying typically between 900 to ∼ 750 °C and down to ∼ 600-700 °C at which the P-T-t path transitioned to a near isobaric cooling path (Fig. 15). Time constraints on the inferred ITD path are ∼ 570 Ma at peak conditions down to ∼ 500 Ma (Pauly et al., 2016) indicating erosional uplift of 15 to 21 km over 80 My. The wide range of temperatures for peak conditions may be attributed to improved thermodynamic models recognizing that the P-T reported estimates range in publication ages over ∼ 30 years. The genesis of the Cambrian granite veins has been interpreted as resulting from melting in the footwall of a mega-nappe structure (Grantham et al., 2008). The evolved εNd data from the Cambrian granites are consistent with such an interpretation.

Figure 15. A summary of P-T-t conditions from east and west Sverdrupfjella and Gjelsvikfjella. Data sources include (Groenewald and Hunter, 1991; Grantham et al., 1995; Groenewald, 1995; Board et al., 2005; Baba et al., 2008; Byrnes, 2015; Grosch et al., 2015; Pauly et al., 2016). Data from Gjelsvikfjella are from (Baba et al., 2008).

P-T studies from west Sverdrupfjella (Jutulrora Complex) report lower peak metamorphic conditions of ∼ 6-10 kb and temperatures of ∼ 600-750 °C, based on samples which do not contain decompression textures and are dominated by hydrated garnet amphibolites (Grantham, 1992; Grantham et al., 1995; Grosch et al., 2015) (Fig. 15). Zoning in garnet showed weakly increased Mg content toward the rim, consistent with heating and increasing pressure suggesting possible increasing burial in the west (Grantham, 1992; Grantham et al., 1995).

It is important to recognize that the Rootshorga Complex, with the highest P-T estimates, structurally overlies the Fuglefjellet and Jutulrora Complexes, indicating an inverted P-T profile, comparable to that reflected by the chronostratigraphy.

Aero-gravity and seismic topography studies over Dronning Maud Land specifically and Antarctica (Riedel, 2008; Riedel et al., 2012; Nogi et al., 2013; Baranov et al., 2021) indicate crustal thicknesses typically in excess of 40 km from Sverdrupfjella in the west up to Lützow-Holmbukta in the east. This data, combined with granulites whose P-T estimates reflect pressures >10 kb from the same areas, indicate that crustal material of similar ∼ 35 km thickness has been eroded, probably related to decompressional tectonic uplift between ∼ 580 and 500 Ma as indicated by P-T-t studies. Thickened crust of this magnitude is consistent with a continent-continent collision tectonic setting. New geochronological data from Sverdrupfjella, combined with radiogenic isotope data from Sverdrupfjella and Gjelsvikfjella indicate that the Jutulrora and Rootshorga Complexes are underlain at depth by Archaean crust (Grantham et al., 2023), and probably the Fuglefjellet Complex, as a consequence of its tectonic position between the Jutulrora and Rootshorga Complexes.

From a broader super-continent correlation and reconstruction perspective, the recognition of tectonic blocks with differing ages, metamorphic evolution paths, lithologies and radiogenic isotope signatures in Sverdrupfjella, CDML (Ravikant et al., 2018; Baba et al., 2023) and Sør Rondane (Adachi et al., 2023; Higashino et al., 2023) is comparable with similar differences being recorded in the Namuno Terrane and Cabo Delgado Accretionary Complex of northern Mozambique (Grantham et al., 2008; Viola et al., 2008; Bingen et al., 2009) but contrasts with the Nampula Terrane which is characterized by Mesoproterozoic granites and gneisses intruded by Cambrian age granites, with the only thrust fault related structures in the Nampula Terrane being klippen described at Mugeba and Monapo (Roberts et al., 2005; Grantham et al., 2008, 2013; Macey et al., 2013).

Grantham et al. (2008, 2013, 2019) proposed a mega-nappe structure emplaced during the Kuunga Orogeny in which part of northern Gondwana, comprising rocks of EAO origin, were thrust ∼ 500-600 km over southern Gondwana during the amalgamation of the Gondwana supercontinent in the Kuunga Orogeny. The timing of the nappe emplacement was inferred to be between 550 and 590 Ma. In this context, it is important to recognize that the current study area is located toward the terminal or southern end of the mega-nappe structure (Grantham et al., 2019) and consequently the younger ages (490-525 Ma) described here are consistent with the mega-nappe model. In this model (Grantham et al., 2008, 2019), initial collision between N. and S Gondwana would have occurred at ∼ 570 Ma along the Lurio Belt in N. Mozambique and Highland Complex-Vijayan Complex interface (Fig. 1) with the nappe progressing southwards until ∼ 480 Ma. The model was postulated to explain geochronological, lithological and metamorphic P-T disparities between the geology of CDML and the Nampula Complex of N. Mozambique and Dronning Maud Land which are juxtaposed in reconstructed Gondwana (Fig. 1). It was inferred that the rocks underlying CDML are lithologically and geochronologically correlatable with those exposed in the Namuno Terrane in Mozambique (north of the Lurio Belt discontinuity) whereas the Maud terrane of western Dronning Maud Land is correlatable with the Nampula Terrane in N. Mozambique (Fig. 1).

The nature and extent of the nappe structure are supported by the presence of klippen in the Mugeba and Monapo areas of N. Mozambique described by Roberts et al. (2005) and Grantham et al. (2013) respectively. The Monapo Complex has granulite assemblages with ages and P-T estimates comparable to those recorded in Sør Rondane, CDML, Antarctica (Grantham et al., 2013). The correlation of rocks from the Cabo Delgado Complex of N. Mozambique is also supported by Ravikant et al. (2018) who have correlated rocks from the Schirmacher Oasis area in CDML, with rocks of the Montepuez Complex of northern Mozambique. Granulites north of the Lurio Belt in the Namuno Terrane and Cabo Delgado Accretionary Complex have isothermal decompression paths comparable to those shown for the Rootshorga Complex in Figure 15 (Engvik and Elvevold, 2004; Engvik and Bingen, 2017).

It is becoming apparent that the Dronning Maud Land extent of the Kuunga Orogeny comprises a diverse collage of complexes of varying age, composition, P-T evolution and structural history. Chemical finger printing of these complexes in some examples have been inferred to suggest that parts, if not almost the whole area, are characterized by thinned or juvenile crust reflected in ∼ 500-550 Ma A-type granites (Jacobs et al., 2008) and ∼ 900-1000 Ma Tonian arc-related lithologies (Ruppel et al., 2018). Whereas the chemistry and ages described from these studies are consistent with the associated interpretations, the location of these study areas over terrains characterized by over-thickened crust (Riedel, 2008; Riedel et al., 2012; Nogi et al., 2013; Baranov et al., 2021) is inconsistent with the extensional and juvenile settings inferred from their A-type and arc-related chemistries respectively. These areas of thickened crust are typically underlain, at surface, by rocks preserving high grade metamorphic assemblages with P constraints of ≥1.0 GPa indicating extensive loss of crust by erosion dominantly between ∼ 570 to ∼ 500 Ma. The emplacement of A-type granites synchronously with the ITD paths indicates a tectonic inversion related process. In contrast, the Tonian arc-related rocks predate the collisional setting inferred for either the East African Orogeny (Jacobs et al., 2008) or the continent-continent collision setting inferred for Kuunga Orogeny (Grantham et al., 2008, 2013, 2019) and consequently are unlikely to be authochtonous.

In Kirwanveggan, in SW Dronning Maud Land, the original extent of the nappe was inferred to be reflected by the decreasing grade of metamorphism southward in mineral assemblages, the increasing ⁴⁰Ar/³⁹Ar ages in hornblende southwards, the absence of Cambrian-age granitic and pegmatite veins in Kirwanveggan and the ∼ 530 Ma Urfjell Group sedimentary rocks exposed in southern Kirwanveggan at Drapane (Grantham et al., 2008, 2019).

The Fuglefjellet and Rootshorga Complexes comprise supracrustal paragneisses and orthogneisses (conglomerates, marbles, volcaniclastic and metapelites + intrusive porphyroclastic granites respectively). Structural field data show mesoscale structures and discordancies typical of thrust fault tectonics and nappe sheets with different geometries and ages and probably duplication of layers. Both the Fuglefjellet and Rootshorga Complexes dip dominantly to the SE and indicate that the former underlies the latter. The Fuglefjellet Complex with depositional ages of ∼ 800-900 Ma and Rootshorga Complex with magmatic intrusion ages of ∼ 1000-1200 Ma structurally overlie the Jutulrora Complex (∼ 1140 Ma), contributing to the recognition of an inverted tectonostratigraphy with the 1000-1200 Ma old Rootshorga Complex overlying the younger ∼ 800-900 Ma old Fuglefjellet Complex.

Late syn-tectonic felsic intrusive veins constrain the youngest deformation to ∼ 480-520 Ma, the youngest with top-to-the-S senses of shear with both compressional and extensional geometries.

The Nd and Sr radiogenic isotope data from basement gneisses from Sverdrupfjella and Gjelsvikfjella, calculated at 500 Ma, show that the gneisses from the Rootshorga Complex in East Sverdrupfjella and Gjelsvikfjella (both in the hanging wall) are relatively juvenile whereas those from the Jutulrora Complex in West Sverdrupfjella (in the footwall) are highly evolved with T_Dm ages >2 Ga.

P-T-t paths from the Rootshorga Complex show typical isothermal decompression clockwise loops (Harley, 1989) from ∼ 1.4 GPa at ∼ >900 °C and ∼ 570 Ma, down to ∼ 0.6-0.7 GPa at ∼ 700 °C at 490 Ma (Pauly et al., 2016), consistent with rapid uplift and erosion, involving an uplift rate ∼ 250 m/my. In contrast, the Jutulrora Complex recorded lower P-T conditions of ∼ 0.7-0.9 GPa at ∼ 700 °C, without the development of decompression reaction textures, with some samples showing zonation in garnet consistent with heating and burial. Comparison of the P-T conditions for the Jutulrora Complex with those from the Rootshorga Complex indicate an inverted P-T profile with rocks of higher grade structurally overlying those of lower grade. The P-T-t paths are comparable to those from granulites exposed in northern Mozambique (Engvik and Elvevold, 2004; Engvik and Bingen, 2017), with which they have been correlated.

HP-HT granulites exposed at the surface, whose assemblages are typical of ∼ 40 km crust erosional removal, combined with gravity and seismic tomography studies are consistent with a continent-continent collision tectonic constrained at ∼ 490-570 Ma for the Kuunga Orogeny which represents a collision between S and N Gondwana blocks along the Damara in Nambia to W. Australia (Meert, 2003), post-dating the earlier amalgamation of E and W Gondwana along the ∼ 600-800 Ma East African Orogen.

The National Research Foundation is thanked for research grants 93079 and 110739 for research under the auspices of the South African National Antarctic Program awarded to GHG. The LA-MC-ICPMS equipment at UJ has been funded by NRF-NEP grant #93208 under DST-NRF CIMERA.

This study was supported by MEXT KAKENHI Grant Numbers JP15H05831, JP20KK0081, and JP21H01182 to M. S-K. Special thanks to Rikako Nohara-Imanaka and Toshiro Takahashi at Niigata University for their help.

The Department of Environmental Affairs, South African Air Force and Starlite Aviation are acknowledged for logistical support in the field and on the SA Aghulhas II. Constructive reviews by an anonymous reviewer as well as K. Das are similarly acknowledged as well as editorial handling by T. Kawakami.

Supplementary Tables S1-S7 are available online from https://doi.org/10.2465/jmps.230125.

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