Fractional Crystallization and Partial Melting of the Paleoproterozoic Gneisses and Pegmatite in the Giant Husab Uranium Deposit, Namibia

: The giant Husab uranium deposit is located in the Paleoproterozoic Abbabis Metamorphic Complex, which was highly partially melted and metamorphosed during the Damara Orogenic Event. The timing of Magma emplacement has been investigated; however, the petrogenesis is unclear. Here we reported petrology, geochemistry, and monazite U-Pb age data from biotite granitic gneisses, syeno-granite, syeno-granitic pegmatites, syeno-granitic gneiss, granitic syenite and biotite quartz monzonites of this complex. Geochemical data suggest that these Paleoproterozoic rocks show high SiO 2 , Al 2 O 3 , and K 2 O, moderate Na 2 O, low CaO and Fe 2 O 3 , and MgO abundance. The alkali-calcic to alkalic, peraluminous, low Fe-number, depletion in HFSE (Nb-Ta, Ti) and enrichment in LILE (e.g., Rb, Pb) characteristic correspond with I- and S-type granite. Major and trace elements are strongly fractionated with the increase of SiO 2 , which, together with strongly fractionated LREE patterns and high (La/Yb) N ratios of the biotite granitic gneiss and syeno-granitic gneiss, suggest that the Magma was highly evolved and fractionated. Monazite U-Pb data show three metamorphic age groups of 581–535 Ma, 531–522 Ma and 518–484 Ma. The increasing trend of La/Sm and La/Yb with the increase of La, suggest these rocks most likely experienced a partial melting process during the late Palaeozoic metamorphism. We, thus, propose a fractional crystallization model for the generation of the Paleoproterozoic Abbabis Metamorphic Complex basement rock, which was metamorphosed and melted during the late Palaeozoic Damara Orogenic Event and provided the Magma sources for primary uranium mineralization.

Previous studies reported zircon U-Pb ages and show the Abbabis Metamorphic Complex formed at ca. 2093-2014 Ma [21], and partial melting of these gneisses generated the early Paleozoic (ca. 547-497 Ma) magmatic intrusions and the primary uranium mineralization [8,14,15], whereas their petrogenesis remains ambiguous. In this study, we present the results from coupled petrology, whole-rock geochemistry, and monazite U-Pb geochronology to constrain the petrogenesis of the Abbabis Complex, and the correlation of metamorphism with the intrusive granite formation during the Damara Orogeny.
The Abbabis Metamorphic Complex in the sCZ of the Damara Orogenic Belt is considered as the pre-Damara basement, which comprise of Paleo-Mesoproterozoic (ca. 1925 Ma, ca. 1300-1100 Ma) quartzofeldspathic gneiss, augen gneiss, banded gneiss, amphibolite dykes, and supracrustal rocks, and experienced the Pan-African orogenic metamorphism and partial melting [21,33] ( Figure 1B). The AMC is covered by the Neoproterozoic metasedimentary rocks of the Nosib and Swakop Groups. The sedimentary rocks of the Nosib and Swakop Groups comprise of quartzite, arkoses and conglomerate, calc-silicate rocks, Marble, metapelitic schist, and glaciogenic diamictites [2]. The Nosib Group comprises of the Etusis and the Khan formations. From bottom to top, the Swakop Group consists of the Rössing, Chuos, Karibib, and Kuiseb Formations. The basement and sedimentary sequence are intruded by extensive early Paleozoic granite comprising 96% of the succession with minor diorite, granodiorite and Mafic rock comprising 4%. The giant Husab uranium deposit is formed within the Rössing and Khan Formations during the late Paleozoic Magmatic event [17,18].
The studied samples are collected from a large quarry of the Abbabis Metamorphic Complex, which is located in the southwest of the Husab uranium deposit (15 • 00 27" E, 22 • 37 18" S) ( Figure 1A). The quarry exposes well-foliated granitic gneisses, Massive pegmatite and red-colored syenite (Figure 2A,B). The granitic gneisses experienced variable degrees of migmatization and are intruded by the pink pegmatite ( Figure 2A). The syenite is profusely traversed by decimeter-to meter-sized veins of pegmatite, which is strongly deformed and fragmented ( Figure 2B). Ten samples, including three biotite granitic gneisses, one syeno-granite, two syeno-granitic pegmatites, one syeno-granitic gneiss, one granitic syenite, and two biotite quartz monzonites, were collected for petrology and geochemistry, and, among them, three samples were sent for monazite U-Pb dating. A summary of petrology, geochemistry, and monazite results are given in the following sections.

Whole-Rock Geochemistry
The major-element analysis of ten samples was carried out in the Yanduzhongshi Geological Analysis Laboratories Ltd., Beijing, China. Fresh samples were first crushed to centimeter sizes; only the fresh pieces were selected, washed with deionized water, dried, and then ground to less than 200 mesh (0.5200 ± 0.0001 g) for geochemical analyses. Sample powders were mixed with flux Li2B4O7 (1:8) to make homogeneous glass disks at 1250 °C using a V8C automatic fusion machine produced by the Analymate Company in China. The bulk rock major elements were analyzed using X-ray fluorescence spectrometry techniques (Zetium, PANalytical, XRF-1800, Shimadzu Corporation, Kyoto, Japan). The analytical errors for major elements were better than 1%. Trace (including rare earth elements) element analyses of the sample were conducted in the National Research Center for Geoanalysis, Beijing. Trace element concentrations were determined as solute by Thermo fisher X-Series inductively coupled plasma mass spec-

Whole-Rock Geochemistry
The Major-element analysis of ten samples was carried out in the Yanduzhongshi Geological Analysis Laboratories Ltd., Beijing, China. Fresh samples were first crushed to centimeter sizes; only the fresh pieces were selected, washed with deionized water, dried, and then ground to less than 200 mesh (0.5200 ± 0.0001 g) for geochemical analyses. Sample powders were mixed with flux Li 2 B 4 O 7 (1:8) to Make homogeneous glass disks at 1250 • C using a V8C automatic fusion Machine produced by the Analymate Company in China. The bulk rock Major elements were analyzed using X-ray fluorescence spectrometry techniques (Zetium, PANalytical, XRF-1800, Shimadzu Corporation, Kyoto, Japan). The analytical errors for Major elements were better than 1%. Trace (including rare earth elements) element analyses of the sample were conducted in the National Research Center for Geoanalysis, Beijing. Trace element concentrations were determined as solute by Thermo fisher X-Series inductively coupled plasma Mass spectrometry (ICP-MS). About 25 mg of powder was dissolved for about 48 h at 120 • C using 1 mL HF and 0.5 mL HNO 3 mixtures in screwtop Teflon beakers, followed by evaporation to dryness. The Material was re-dissolved in 2 mL 1:1 HNO 3 for 8 h at 120 • C [36]. The analytical errors are less than 10% depending on the concentration of any given element.

Monazite U-Pb Dating
U-Pb dating of monazite from three samples was conducted by LA-ICP-MS at the Wuhan Sample Solution Analytical Technology Co., Ltd., Wuhan, China. Laser sampling was performed using a GeolasPro laser ablation system that consists of a COMPexPro 102 ArF excimer laser (wavelength of 193 nm and Maximum energy of 200 mJ) and a MicroLas optical system. An Agilent 7700 e ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas. Argon was used as the Make-up gas and mixed with the carrier gas via a T-connector before entering the plasma ICP. A "wire" signal smoothing device is included in this laser ablation system, by which smooth signals are produced even at very low laser repetition rates down to 1 Hz [37]. It is very useful for in-situ U-Pb dating of high-U mineral [38]. The spot size and frequency of the laser were set to 16 µm and 2 Hz, respectively. Monazite standard 44,069 and glass NIST610 were used as external standards for U-Pb dating and trace element calibration, respectively. Each analysis incorporated a background acquisition of approximately 20-30 s followed by 50 s of data acquisition from the sample. An Excel-based software ICPMSDataCal 10.9 (China University of Geosciences, Wuhan, China) was used to perform off-line selection and integration of background and analyzed signals, time-drift correction, and quantitative calibration for trace element analysis and U-Pb dating [39,40]. Concordia diagrams and weighted mean calculations were Made using Isoplot/Ex_ver3 [41].

Monazite U-Pb Geochronology
Three samples were dated for monazite U-Pb geochronology, including biotite granitic gneiss, syeno-granite, and syeno-granitic pegmatite, with all monazite data given in Table 2 and morphology shown in Figure 6 and data plotted in Figure 7.

Monazite U-Pb Geochronology
Three samples were dated for monazite U-Pb geochronology, in nitic gneiss, syeno-granite, and syeno-granitic pegmatite, with all mo Table 2 and morphology shown in Figure 6 and data plotted in Figur       Monazite grains in sample 21HS01 are angular or round, and up to 150 µm in length. The grains are either homogenous in CL, or show core-rim internal structures and some grains contain abundant inclusions in the core ( Figure 6). Twenty-nine spots were analyzed on twenty-six grains and show 206

Petrogenesis Fractional Crystallization and Partial Melting
The biotite granitic gneisses, syeno-granite, syeno-granitic pegmatites, syeno-granitic gneiss, and granitic syenite are characterized by high SiO 2 , Al 2 O 3 , and K 2 O, moderate Na 2 O, low CaO, Fe 2 O 3 , MgO, and MnO, and TiO 2 abundance. The alkali-calcic to alkalic and low Fe number characteristic suggest an igneous source resembling an I-type granite formed in an active continental Margin setting [48]. However, their K-rich nature and high K 2 O/Na 2 O (1.7-4.0) ratios, and peraluminous (A/CNK: 1.03-1.12) characters similar to an Al-rich sedimentary source and correspond to S-type granite rather than the peralkaline A-type granite [6]. In contrast, the biotite quartz monzonites are alkalic and peraluminous, and characterized by relatively lower SiO 2 and Na 2 O, elevated Fe 2 O 3 and TiO 2 abundance, higher K 2 O/Na 2 O (6.1-10.1) ratios than the rocks described above, which together with the abundance of muscovite, indicate a sedimentary source and resemble S-type granites ( Figure 8A-H). On the CaO/(FeO T + MgO + TiO 2 ) versus CaO + FeO T + MgO + TiO 2 diagram, the granitic and syeno-granitic rocks plot in the greywacke and pelite fields, which suggests that the parent Magma has a sedimentary source contribution [49] (Figure 8I). In terms of high-field strength elements (HFSE), all these samples are characterized by pronounced negative anomalies at Nb-Ta, and Ti further support a calc-alkaline Magma source ( Figure 5). Thus, the parent Magma for the granitic gneiss and syeno-granitic rocks, granitic syenite and biotite quartz monazites, was derived from a mixed igneous and metasedimentary source.
Fe2O3 and TiO2 abundance, higher K2O/Na2O (6.1-10.1) ratios than the rocks described above, which together with the abundance of muscovite, indicate a sedimentary source and resemble S-type granites ( Figure 8A-H). On the CaO/(FeO T + MgO + TiO2) versus CaO + FeO T + MgO + TiO2 diagram, the granitic and syeno-granitic rocks plot in the greywacke and pelite fields, which suggests that the parent magma has a sedimentary source contribution [49] (Figure 8I). In terms of high-field strength elements (HFSE), all these samples are characterized by pronounced negative anomalies at Nb-Ta, and Ti further support a calc-alkaline magma source ( Figure 5). Thus, the parent magma for the granitic gneiss and syeno-granitic rocks, granitic syenite and biotite quartz monazites, was derived from a mixed igneous and metasedimentary source. The granitic gneiss and syeno-granitic rocks, granitic syenite and biotite quartz monazite, are characterized by negative Eu, Sr, and Ba anomalies, which indicate plagio- The granitic gneiss and syeno-granitic rocks, granitic syenite and biotite quartz monazite, are characterized by negative Eu, Sr, and Ba anomalies, which indicate plagioclase and K-feldspar fractionation [50,51]. Depletion in the HREE and high (La/Yb) N ratios suggest a high degree of fractionation of the parent Magma with residual garnet ( Figure 5). One biotite granitic gneiss and two syeno-granitic pegmatites exhibit positive Eu anomalies and HREE enrichment features, indicating the absence of plagioclase fractional crystallization. Plagioclase fractional crystallization is also supported by the negative correlation of Sr and Eu versus SiO 2 and positive correlation of Na 2 O versus SiO 2 ( Figure 9A-H). Low abundance in P 2 O 5 and Zr, and negative correlation of P 2 O 5 and TiO 2 versus SiO 2 are explained by the moderate to abundant titanite, apatite and zircon. Negative correlation of CaO, MgO, Fe 2 O 3 , Co, and Ni versus SiO 2 indicates pyroxene and amphibole residue in the early crystallization stage. High K 2 O and low MgO, Ni, and Co, and Cr abundance, and negative correlation of Rb, Sr, La, and V versus SiO 2 suggest that the Magma is highly evolved. The granitic gneiss and syeno-granitic rocks, granitic syenite and biotite quartz monazite, are characterized by variable (La/Yb) N ratios, indicating that the Magma has a high degree of fractionation.
SiO2 are explained by the moderate to abundant titanite, apatite and zircon. Negative correlation of CaO, MgO, Fe2O3, Co, and Ni versus SiO2 indicates pyroxene and amphibole residue in the early crystallization stage. High K2O and low MgO, Ni, and Co, and Cr abundance, and negative correlation of Rb, Sr, La, and V versus SiO2 suggest that the magma is highly evolved. The granitic gneiss and syeno-granitic rocks, granitic syenite and biotite quartz monazite, are characterized by variable (La/Yb)N ratios, indicating that the magma has a high degree of fractionation. The fractionation crystallization model is further supported by the compatible (e.g., V, Ni) versus incompatible (e.g., Rb) element classification diagrams. These samples dominantly plot along the decreasing trend of compatible elements versus incompatible elements ( Figure 10A,B). However, the studied samples exhibit a variable increasing trend of La/Sm and La/Yb ratios versus La abundance, suggesting these samples experienced variable degrees of partial melting, which is also consistent with the petrographic observation ( Figure 10C,D). Kröner et al. [21] and Hawkeworth et al. [52] proposed that the late Paleoproterozoic pre-Damara basement experienced high degrees of partial melting during the late Neoproterozoic Damara Orogenic event. Therefore, we suggest that partial melting of the granitic gneiss and syeno-granitic rocks, granitic syenite and biotite quartz monazite occurred after crystallization of the rock. The fractionation crystallization model is further supported by the compatible (e.g., V, Ni) versus incompatible (e.g., Rb) element classification diagrams. These samples dominantly plot along the decreasing trend of compatible elements versus incompatible elements ( Figure 10A,B). However, the studied samples exhibit a variable increasing trend of La/Sm and La/Yb ratios versus La abundance, suggesting these samples experienced variable degrees of partial melting, which is also consistent with the petrographic observation ( Figure 10C,D). Kröner et al. [21] and Hawkeworth et al. [52] proposed that the late Paleoproterozoic pre-Damara basement experienced high degrees of partial melting during the late Neoproterozoic Damara Orogenic event. Therefore, we suggest that partial melting of the granitic gneiss and syeno-granitic rocks, granitic syenite and biotite quartz monazite occurred after crystallization of the rock.
In the (Na 2 O + K 2 O)/CaO versus 10,000Ga/Al diagram, the granitic gneiss and pegmatite plot in the A-type and S-and I-type granite field [55] (Figure 11A). Since the samples are characterized by low Fe-number, peraluminous rather than peralkaline, which together with the absence of sodic Mafic minerals, suggest that the A-type granite can be excluded [48]. Therefore, a convergent Margin setting is required for the parent Magma to receive both igneous and sedimentary sources. In the Nb-Y and Rb-Y + Nb diagrams, the granitic gneiss and pegmatite plot in the syn-collision granite and within plate granite fields, which, together with their peraluminous and alkali-calcic and alkalic signature, suggest a continental arc setting and the Magma was emplaced during the syn-collisional event [44] ( Figure 11B,C). Low Sr/Y ratios and increasing Y contents also corroborate an arc affinity, indicating that the parent Magma was generated from an arc setting or partial melting of a rock that was formed within an arc [56] (Figure 11D). In the R1-R2 diagram, the rocks plot in the late orogenic to syn-collisional fields [57] ( Figure 11E). Thus, the parent Magma of the AMC is generated in an arc setting near the collisional belt and the rocks formed via fractional crystallization and partial melting process during a syn-collision event. In the (Na2O + K2O)/CaO versus 10,000Ga/Al diagram, the granitic gneiss and pegmatite plot in the A-type and S-and I-type granite field [55] (Figure 11A). Since the samples are characterized by low Fe-number, peraluminous rather than peralkaline, which together with the absence of sodic mafic minerals, suggest that the A-type granite can be excluded [48]. Therefore, a convergent margin setting is required for the parent magma to receive both igneous and sedimentary sources. In the Nb-Y and Rb-Y + Nb diagrams, the granitic gneiss and pegmatite plot in the syn-collision granite and within plate granite fields, which, together with their peraluminous and alkali-calcic and alkalic signature, suggest a continental arc setting and the magma was emplaced during the syncollisional event [44] (Figure 11B,C). Low Sr/Y ratios and increasing Y contents also corroborate an arc affinity, indicating that the parent magma was generated from an arc setting or partial melting of a rock that was formed within an arc [56] (Figure 11D). In the R1-R2 diagram, the rocks plot in the late orogenic to syn-collisional fields [57] ( Figure  11E). Thus, the parent magma of the AMC is generated in an arc setting near the collisional belt and the rocks formed via fractional crystallization and partial melting process during a syn-collision event.

Arc Building and Crust Evolution
The Proterozoic pre-Damara basement is broadly exposed in the Damara Orogenic Belt, surrounding cratonic Margins and orogenic belts of southern Africa, and these complexes were formed during the Paleoproterozoic Eburnian orogenic event [6,19].

Arc Building and Crust Evolution
The Proterozoic pre-Damara basement is broadly exposed in the Damara Orogenic Belt, surrounding cratonic margins and orogenic belts of southern Africa, and these complexes were formed during the Paleoproterozoic Eburnian orogenic event [6,19]. The quartzo-feldspathic orthogneiss of the pre-Damara basement from the south-western extension of the Abbabis Inlier near Rössing Uranium Mine of the Central Damara Belt show strong migmatization and are associated with magma crystallization at 1196-1040 Ma, and minor xenocrytic zircons (2093-2014 Ma) are sourced from the Abbabis basement [21]. Longridge et al. [4] reported zircon U-Pb ages of 2026 Ma from the amphibolite of the Abbabis basement and the correlate the complex with the Congo Craton. However, the basement gneiss and granitoids of the Epupa and Huab Complex of the pre-Damara basement from northern Namibia and Angola show Paleoproterozoic ages To the northeast, SHRIMP zircon U-Pb ages from the granitoid gneisses of the Tsodilo Hills Group of the Damara Belt in western Botswana also record Paleoproterozoic Magmatic ages of 2036-1978 Ma, which formed during the Eburnian orogenic event [58]. Further northeast, the migmatitic granite from the Magondi Orogenic Belt of northeast Botswana show Magmatic zircon U-Pb age of 2039 Ma and is correlated with the Paleoproterozoic orogeny between Kubu Island in the west of Sua Pan and the northwest of the Zimbabwe Craton [59]. Northeast to the Central African Copperbelt, the Katanga Supergroup comprises of 2.07-1.87 Ga Lufubu schist, granitoids and granitiod gneiss, and 1.06 Ga aplite and are considered as part of the extensive Paleoproterozic arc equivalent to northern Namibia [60]. To the east of the Damara Orogenic Belt, the felsic gneiss from the Hohewarte Metamorphic Complex record Magmatic ages of 1758 Ma, 1290 Ma, and 1168 Ma, and are well correlated with the Abbabis Complex and considered as part of the pre-Damara basement accreted onto the Kalahari Craton [3]. The positive εHf(t) values of +1.7 to +3.0 for the Paleoproterozoic (1758 Ma) quartzo-feldspathic gneiss, and +0.7 to +3.2 for the Mesoproterozoic gneiss (1290 Ma and 1168 Ma), suggest that the Magma sources for the Hohewarte Metamorphic Complex are derived from depleted Mantle [3].
To the northwest, in the Angolan Shield of SW Angola, the granite and ignimbrite also record Paleoproterozoic ages of 2.04-1.80 Ga, which formed in a Magmatic arc stretching from NW Zambia to NE Angola and Namibia [61]. In the nearby large exposure of the Epupa Metamorphic Complex of the southwestern Congo Craton, the amphibolite and orthogneiss show zircon U-Pb ages of 2027 Ma and 1862-1758 Ma and are correlated with the arc Magmatism of the Eburnian Orogenic event [4,6,19]. The gabbros sporadically exposed with the amphibolite and orthogneiss suggest that the Epupa Metamorphic Complex was generated in an arc setting [19]. The anatexis and migmatitic gneiss from the Epupa Metamorphic Complex show zircon U-Pb ages of 1762-1757 Ma and suggest prograde metamorphism and partial melting [6]. The augen gneiss, monzogranite and microgranite from the Okwa Basement Complex on the northwestern edge of the Kaapvaal craton show Paleoproterozoic ages of 2.10-2.06 Ga and might represent the eastern continuous Magmatic branch of the Paleoproterozoic basement [62]. Further south in the Namaqua-Natal Metamorphic Province, the granitoid orthogneisses also show crystallization ages of 1825-1810 Ma and variable εHf(t) values of −24.34 to +3.03 with T DM model ages of 2.41-1.67 Ga, suggesting the Magmas are dominantly derived from the Paleoproterozoic crust Material [60]. Geochemically, these granitoids are peraluminous to metaluminous and high-K alkaline and are equivalent to I-type granites formed in a Magmatic arc setting [63]. Thus, the extensive Paleoproterozoic Magmatic rocks and complexes in the Damara Orogenic belt and surrounding areas suggest multiple arc construction and May represent microcontinent fragments formed during the Eburnian orogenic event.

Metamorphism during the Damara Orogeny
In a recent study, Goscombe et al. [31] evaluated the metamorphic evolution history of the Damara Orogenic Belt and proposed that the Khomas Oceanic crust subduction initiates before 555 Ma, ocean closure and collision of the Congo and Kalahari cratons occurred at 555-550 Ma, peak metamorphism at 530-515 Ma, shortening associated with local extension at 515-505 Ma, and extension and exhumation at 505-470 Ma. Clemens and Kisters [64] reported gabbros, diorites, and granites from the Goas Intrusive Suite of the Southern Central Zone show bimodal composition and proposed that these rocks are formed through partial melting of the ancient crust at different depth levels during the subduction of the Khomas Oceanic Crust at ca. 580-575 Ma. Milani et al. [65] proposed that the 575 Ma Mafic to felsic rocks of the Goas Complex recorded the earliest Magmatism, and the variable εHf(t) of −3.8 to −34.4 indicate that the Magma was dominantly sourced from the central-western African Paleoproterozoic Eburnean Orogen. Jung et al. [66,67] reported diorites, granodiorites and granites from the Oamikaub diorite (Goas Intrusive Suite) and Otjimbingwe alkaline complex of the northern Margin of the Southern Zone, which show variable initial εNd values of −2.1 to −18.8 and suggest that ancient crust was involved in the Magma through a flat subduction process of the Kalahari Oceanic Crust and emplaced during the syn-collisional event of the Damara Orogeny at 545-563 Ma. However, Pontow et al. [68] reported a ca. 560 Ma from the Okamutambo alkaline Complex and variable initial εNd values of −3.5 to −7.1, suggesting that the Magma May have been sourced from the Proterozoic crust within an extensional setting. The late Neoproterozoic (556-547 Ma) granodiorites, leucogranite and granites in the central Damara Orogenic Belt display variable εNd (init.) values of −7.2 to −20.6 and T DM ages of 2.5-1.9 Ga, indicating they were formed by partial melting of the ca. 1.95 Ga Paleoproterozoic felsic basement [9,69,70]. The lithological sequence of the lower unit of diatexites, and granite plutons, middle unit of metatexites, metasedimentary-sourced granitic rocks, and upper unit of metamorphic rocks with intrusive leucogranitic rocks from the Central Zone of the Damara orogenic belt represent an increasing degree of fractional crystallization and partial melting [33].
Longridge et al. [71] reported zircon and monazite ages of 520-510 Ma in the anatectic leucogranite from the southern Central Zone and correlate it with the extension and crust thinning process, and the 550-530 Ma Salem-type granite and Goes Suite are corresponding to the convergent shorting and crust thickening. Goscombe et al. [72] further divided the ca. 530-505 Ma Damara Orogenic event into peak metamorphism and NW-SE to NNW-SSE shortening at ca. 530-525 Ma, E-W shorting at ca. 508 Ma, and N-S extension and thinning of the orogenic core at ca. 505 Ma. In terms of the peak metamorphic P-T condition, the Central Zone experienced lower metamorphic conditions than the North and South Zone, being 637 • C and 10.4 kbar for the east Northern Zone, 760-800 • C and 4.4-6.2 kbar for the Central Zone, 550-640 • C and 8.6-11.2 kbar for the Southern Zone [31]. High temperatures and low pressures in the Central Zone indicate crustal melting during uplift and thickening corresponding to an extensional process during the collision of the Congo and Kalahari Cratons at 505-407 Ma [31,48,73].
Therefore, the metamorphic data from the biotite granitic gneisses, syeno-granite, and syeno-granitic pegmatites of this study suggest the Abbabis basement rocks May have undergone low pressure and high temperature partial melting and metamorphism during the Damara Orogenic event. The 581-535 Ma ages are consistent with the Khomas oceanic crust subduction and early collision of the Kalahari and Congo Cratons, 531-522 Ma corresponds to the syn-collisional peak metamorphism, and 518-484 Ma corresponds to the post-collision [31,[60][61][62][63][64][65][66][67][68]. In addition to metamorphism, extensive intermediate to felsic Magmatic rocks within the Damara Orogenic Belt were generated during syncollisional and post-collisional metamorphism [66,67,73]. Simon et al. [9] reported an age of 547 Ma from the calcic to calc-alkalic diorite and leucogranite of the Achas intrusion and suggested the intermediate igneous rocks were formed by partial melting of the Proterozoic basement during the synorogenic process of the Damara Orogeny. Jung et al. [50] reported negative ε Nd t values of −4.1 to −10 and T DM age of 2.5-1.9 Ga from the peraluminous and alkalic and calc-alkalic 530 Ma pegmatite and aplite of the Donkerhoek batholith and suggest the Magma was sourced from the meta-igneous basement and emplaced during the syn-tectonic Damara Orogeny. Fan et al., [8] reported negative ε Nd t values of −14.8 to −16.5 and T DM 2 of 2.56-2.43 Ga from the 506-497 Ma uraniferous leucogranite from the uranium deposit area in the Gaudeanmus and suggest the Main source for uranium primary mineralization was derived from the Paleoproterozoic basement. Cross et al. [74] reported U-Th-Pb age of 496 Ma from the uraninite of a leocogranite in the Husab uranium deposit and suggested that the age represents uranium mineralization. Briqueu et al. [75] and Cuney and Kuser [76] interpreted the monazite and uraninite ages of 508-509 Ma from the leucogranite of the Goanikonte as the uranium mineralization age, and the Magma was emplaced during metamorphism and partial melting of Damara Orogenic Event. Therefore, the metamorphic ages from the Abbabis Metamorphic Complex are consistent with the mineralization ages from uranium deposit, which, together with the negative ε Nd t values and the Paleoproterozoic model ages of the Cambrian leucogranite, indicating that the Magma provenance for the intrusive rocks and uranium might source from the Paleoproterozoic basement.

Conclusions
The following general conclusions can be drawn from the present study: 1.
The biotite granitic gneiss, syeno-granite, syeno-granitic pegmatite, syeno-granitic gneiss, granitic syenite, and biotite quartz monzonite are highly evolved and formed by a fractional crystallization process during the Paleoproterozoic, and experienced variable degrees of partial melting during the late Proterozoic Damara Orogenic event.

2.
A review of the Paleoproterozoic basement rocks show that the Paleoproterozoic AMC basement rock was correlated well with the extensive Paleoproterozoic Magmatic complexes in southern Africa, which were formed during the Paleoproterozoic Eburnian orogenic event.