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BSE-CL images, U-Th abundance, and U-Pb ages were obtained for zircons from the Nkogho granitic basement rocks cropping out in the Mamfe Basin (SW Cameroon). These data are used to characterize and classify each zircon, eluciding their geochemical traits. They were also used to formulate a model of their host composition to acertaine the source, an...
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Context 1
... areas (C: core) and (R: rim or zone) in selected zircon crystals ( Tables 1, 2, and 3). ...Context 2
... crystals from NK1 (Table 1), the U, Th, and Pb contents (in C spots) range from 111 ppm to 679 ppm, 75.0 ppm to 566 ppm, and 32.0 ppm to 253 ppm, respectively. The lowest Pb contents is quantified in spots with lowest U-Th contents (due to low U and Th concentration and limited radioactive nuclei decaying of these two elements to give daughter Pb). ...Context 3
... Th/U ratios generally ranging from 0.2-1.3 are within the range limit of crustal igneous zircons published in Ka- nouo et al. (2017a), Kirkland et al. (2015), Hoskin and Schaltegger (2003), Belousova et al. (2002), and Konzett et al. (1998), this shows that the studied zircons were mainly crystallized within crustal magmas. The U-Th-Pb abundances for samples NK1 and NK3 with some core and rim difference distinguish two groups of zircons (Tables 1 and 3): (1) those with rim U-Th-Pb abundance higher than that of the core, and (2) those with core U-Th-Pb abundance higher than that of the rim. The variability of U and Th contents in the analyzed spots can be caused by the availability these two elements in their cooling magmas, with some of these magmas being considerably U-Th enriched than others. ...Context 4
... similarity shows that part of zircons from NK1 and NK2 were crystallized during the same period, probably, in relatively U-Th depleted and U-Th fairly enriched melts, respectively. The main U-Th enrichments of their source magma(s) was obtained in Early Cretaceous time (Fig. 7), although other enrichments were noted in the Late Devonian and Middle Ordovician (Tables 1-3). The recorded Aptian core age for NK2-5C show that its host rock was probably affected by a post-Late Neoproterozoic magmatic event during Aptian times. ...Context 5
... age difference shows that the Nkogho granite is older than the Otu granitic pegmatite. The Late Neoproterozoic to Early Cambrian ages recorded in the core zones and rims of some zircons from the Nkogho granite (Tables 1 and 3) are close to those of zircons from Otu granitic pegmatite and Babi mica schist. This shows that the magmatic event source of the Otu granitic pegmatite was also recorded in part of the Nkogho granite, which probably underwent partial fusion (with crystallization zircons during the Late Neoproterozoic); the formation of granitic overgrowth zones on some early formed-zircon crystals occurred during Early Cambrian. ...Similar publications
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Citations
... Orthogneisses, granitoids and plutonic massifs are common within the CAFB included within the Adamawa-Yade domain and parts of the Cameroon territory to the west of the Tchollire-Banyo Fault (TBF) (Fig. 1b). These rocks are I-and S-types showing high-K calc-alkaline to shoshonitic affinities (e.g., Djouka-Fonkwé et al., 2008;Kamguia Kamani et al., 2021;Kwékam et al., 2020aKwékam et al., , 2020bNgamy Kamwa et al., 2019;Ngo Belnoun et al., 2013;Tchakounté et al., 2021;Tchameni et al., 2006;Tchouankoue et al., 2016) and were emplaced during the initial to paroxysmal phase of the Pan-African orogeny at ca. 660-580 Ma (e.g., Azeuda Ndonfack et al., 2022;Ganwa et al., 2018;Kamguia Kamani et al., 2021;Kanouo et al., 2021;Kwékam et al., 2020b;Li et al., 2017;Tchakounté et al., 2021;Tchouankoue et al., 2016). However, researchers suggested that the emplacement in western Cameroon would have ended at ca. 565-545 Ma (e.g., Kwékam et al., 2020aKwékam et al., , 2020bNgo Belnoun et al., 2013). ...
The Central African Fold Belt (CAFB) holds a key position in understanding the process and implications of the Pan-African orogeny in central Africa. However, it has not been fully understood as geological information on some vital domains is not yet available. The Linte massif in the Adamawa-Yade, one of the unrepresented terranes, was investigated and its whole rock geochemical, zircon U-Pb geochronology and Hf-O isotope characteristics and whole rock Sr-Nd data are presented and discussed here. The Linte massif is largely constituted of syenite and subordinate monzonite. The zircon U - Pb dating reveals three major ages at 660, 630 and 600 Ma, indicating a protracted magmatism which lasted at least 60 Ma, during the Neoproterozoic. The rocks are shoshonites, I-type and metaluminous. They have high LILEs (Cs, Rb, Ba and Sr), HFSEs (Th and U) and LREE contents. Their Nb/U, Ta/U, Ce/Pb, Th/La and Th/U ratios, δ¹⁸Ozrn (5.3–7.6‰) and zircon εHf(t) (−14.7 to +3.2), point toward predominantly crustal with or without a mantle component in the sources. The negative εNd(t) values (−8.1 to −10.0), Paleoproterozoic Nd-TDM model ages (ca. 1700–1900 Ma), Hf-TDM2 ages of ca. 1300–2400 Ma of zircon grains in Neoproterozoic rocks underline their derivation from Mesoproterozoic to Paleoproterozoic basement rocks.
The lithospheric mantle-generated heat facilitated partial melting in the sources region, as inferred from the shoshonitic affinity and the subduction-related geochemical features (Nb, Ta and Ti depletion). A mainly crustal source with a minor mantle component is inferred for the 660 Ma magmatism and for the 630 Ma rocks emplaced during crustal thickening. On the other hand, the 600 Ma (youngest) magmatic rocks were derived from a crustal source. We infer a subduction-collision setting for the Linte massif during the 660–600 Ma interval. The 630–600 Ma interval of the culmination of collision is consistent with the timing of the main convergence of the Brasiliano Orogeny recorded in South America (∼630–600 Ma), suggesting continuation of tectonic features into the western Gondwana.
... Orthogneisses, granitoids and plutonic massifs are common within the CAFB included within the Adamawa-Yade domain and parts of the Cameroon territory to the west of the Tchollire-Banyo Fault (TBF) (Fig. 1b). These rocks are I-and S-types showing high-K calc-alkaline to shoshonitic affinities (e.g., Djouka-Fonkwé et al., 2008;Kamguia Kamani et al., 2021;Kwékam et al., 2020aKwékam et al., , 2020bNgamy Kamwa et al., 2019;Ngo Belnoun et al., 2013;Tchakounté et al., 2021;Tchameni et al., 2006;Tchouankoue et al., 2016) and were emplaced during the initial to paroxysmal phase of the Pan-African orogeny at ca. 660-580 Ma (e.g., Azeuda Ndonfack et al., 2022;Ganwa et al., 2018;Kamguia Kamani et al., 2021;Kanouo et al., 2021;Kwékam et al., 2020b;Li et al., 2017;Tchakounté et al., 2021;Tchouankoue et al., 2016). However, researchers suggested that the emplacement in western Cameroon would have ended at ca. 565-545 Ma (e.g., Kwékam et al., 2020aKwékam et al., , 2020bNgo Belnoun et al., 2013). ...
The geological evolution of the Central African Fold Belt (CAFB) remains debated. The granitoids, orthogneisses and granitic veins from the Goa-Mandja area (Adamawa-Yade domain) are considered to constrain this belt. These rocks are consistent with late-D2 regional emplacement and synchronous with the magmatism at ~600 Ma within the CAFB in Cameroon and its extension into northeastern Brazil, as the zircon UPb points to 603–598 Ma crystallization ages. Analytical data reveal slightly elevated δ¹⁸Ozrn (6.45–7.17‰) and δ¹⁸OWR (8.20–8.61‰), moderate to high SiO2 (59.70–77.23 wt%), low MgO (0.07–2.77 wt%), Cr (0.29–55.12 ppm), Ni (0.45–33.6 ppm), V (1.52–116.62 ppm) and Mg# (0.02–0.36) contents, indicating crustal origin. The low to medium ⁸⁷Sr/⁸⁶Sri (0.703328–0.722670) and positive to negative εNd(t) (+5.7 to −9.9), coupled with the diversity of Nd model ages (TDM2) support the heterogeneity of crustal protoliths. The high positive εNd(t) (+5.7) of the granitic vein indicates derivation from juvenile Neoproterozoic (Nd-TDM2 at 854 Ma) crustal protolith. TDM2(Nd) and TDM2(Hf) ages of 1188–2120 Ma and 2173–2480 Ma also suggest the involvement of Mesoproterozoic to Paleoproterozoic crustal protoliths.
Samples show metaluminous to weakly peraluminous, high-K calc-alkaline to shoshonitic and I-type granitoids features and are similar with crustal rocks in regard to LILE (Rb, K) and LREE enrichments and HFSE (Nb, Ta, Ti) depletions. These combined features indicate slab subduction related setting for the magma generation. Slab subduction may have generated the heat necessary to provoke partial melting at the lower crustal level. Considering their position close to the Tchollire-Banyo Fault corridor, at the transition between the Adamawa-Yade and northern domains, the subduction derived features shown by the Goa-Mandja I-type granitoids could be related to the subduction of an old plate boundary during amalgamation of Gondwana. Therefore, the Goa-Mandja area records dominant magmatic accretion along the northern margin of the Congo craton (active margin) associated with a possible northwestern subduction.
https://authors.elsevier.com/c/1ipqk,XIvbtMx3
Lacustrine mudstones developed in the synrift Wenchang and Enping formations are the major source rocks of the Pearl River Mouth Basin (PRMB) and vary in both richness and quality of hydrocarbons generated. While organic productivity is known to have played a role in the development of these rocks, it has been mostly neglected in prior research. In this study, new zircon geochronological data from igneous intrusive and volcanic rocks in boreholes of the PRMB are used alongside compiled detrital zircon data from Paleogene sandstones to decipher the roles of sediment provenance and volcanic activity in the development of source rocks. The result suggests that in the Wenchang Formation (49-39 Ma), sediments were mainly derived from intrabasinal structural highs dominated by Yanshanian igneous rocks (180-90 Ma). Similarities in young ages (42–45 Ma) in volcanic and clastic units of the Wenchang formation suggest volcanic activity concurrent with its deposition. Chemical weathering of the proximal source area together with volcanic materials provided abundant nutrients for the basin and enhanced the primary organic productivity, resulting in the development of high-quality lacustrine source rocks, derived mainly from plankton. In contrast, the detrital zircon provenance of the Enping Formation (39-33 Ma) suggests sediments were derived from the South China Block (SCB), far to the north, with complicated lithologies and more older zircon grains. The long-distance transport of SCB sediments diluted the productive nutrition conditions of the larger and shallower lakes, and introduced organic matter derived from higher terrestrial plants. This study provides a new approach to evaluating the lacustrine source rocks especially for the deep-water areas with limited mudstone samples.
The pre- to post-Late Neoproterozoic geological histories in the south to southwestern part of Mamfe Basin (SW Cameroon) were reported following analysis of the zircon crystals from their host rocks. A genetic model was developed for the zircon host rocks’ formation conditions, and the registered post-emplacement events were presented. The obtained ages were correlated with the data available for rocks in the Cameroon Mobile Belt, SE Nigeria, and the Borborema Prov-ince of NE Brazil. Separated zircons from Araru black to whitish gneiss, Araru whitish-grey gneiss, and Mboifong migmatite were analyzed for their morphology and texture U-Th-Pb com-position, and U-Pb ages. Published U-Pb zircon ages for Otu granitic pegmatite, Babi mica schist, and Nkogho I-type anatectic granite were updated. Zircon ages in Araru black to whitish gneiss; Araru whitish-grey, Mboifong migmatite, Babi mica schist, Nkogho I-type anatectic granite, and Otu granitic pegmatite date the Eburnean tectono-magmatic/metamorphic event in Cameroon and SE Nigeria. The Late Paleoproterozoic to Early Mesoproterozoic ages record extensional (continental rift) settings and anorogenic magmatism in the Borborema Province in the NE of Brazil. These ages date collisional phases between the São Francisco–Congo and West African cratons and the Saharan metacraton with metamorphism and magmatism in Cameroon. They al-so date the Kibarian tectono-magmatic/metamorphism and PanAfrican tectono-magmatic/metamorphism in SE Nigeria. The Late Paleoproterozoic to Early Mesoproterozoic ages date the Cariris Velhos orogeny in the Borborema Province in NE Brazil, with Early Tonian crustal rifting, magmatism, and metamorphism and the collisional phase of the Brasiliano orog-eny with syn-collisional plutons and extensive shear zoning and post-collisional granite intru-sions
