525 Ma riebeckite in a quartz vein into the Noqui granite: evidence for a late Pan African extensional event in the West Congo Belt (Matadi area, Bas-Congo region, DR Congo)
| dc.contributor.author | Tack, L. | |
| dc.contributor.author | De Grave, J. | |
| dc.contributor.author | Burgess, J. | |
| dc.contributor.author | Baudet, D. | |
| dc.contributor.author | Fernandez-Alonso, M. | |
| dc.contributor.author | Kongota-Isasi, E. | |
| dc.contributor.author | Nseka-Mbemba, P. | |
| dc.contributor.author | Delvaux, D. | |
| dc.date | 2018 | |
| dc.date.accessioned | 2024-03-14T13:16:31Z | |
| dc.date.available | 2024-03-14T13:16:31Z | |
| dc.identifier.uri | https://orfeo.belnet.be/handle/internal/12142 | |
| dc.description | The Pan African West Congo Belt (WCB) is part of the Araçuaí West Congo Orogen (AWCO) formed during Gondwana amalgamation (550 Ma). In the WCB, the AWCO is underlain by a 2.1 Ga Eburnean-aged orogenic system. The WCB extends from SW Gabon to NW Angola parallel to the Atlantic ocean. Its central part displays an ENE-verging fold-and-thrust belt with eastward decreasing deformation and regional metamorphism dated in the Bas-Congo region (DR Congo) at 566 Ma. This age is in line with the 585-560 Ma ages for the paroxysm of AWCO as obtained from the Araçuaí Belt of Brazil. The Neoproterozoic West Congo Supergroup comprises from old to young - the Nzadi, Seke-Banza / Tshela and Cataractes Groups (Baudet et al, this meeting). In the Matadi area (Bas-Congo region), the 1.0 Ga Noqui peralkaline granite intrudes the metaquartzites of the Matadi Formation (Nzadi Group; De Grave et al, Baudet et al., this meeting). Whereas overlying Formations are not affected by the intrusion. The Noqui granite is composed of mesoperthite, quartz, aegyrine ± lepidomelane ± opaques ± riebeckite and has an A1-type geochemical composition. Pegmatites have never been observed. In the Fretin quarry (northern part of the granite body, Kinzao locality) a quartz vein is exposed. It consists of colourless coarse-crystalline quartz, centimetric monomineralic dark prismatic riebeckite (locally fibrous and/or with bluish luster) and platy ilmenite (both minerals confirmed by X-ray diffractometry). The vein has a zig-zag pattern trending almost N 10 20°E over about 5 meter long. It is composed of en-echelon right- stepping tension gashes linked with shear fractures. The gashes are filled dominantly with the quartz and occasionally with the riebeckite and ilmenite. The pattern of the fractures and mineral filling suggests that they formed in brittleductile transitional conditions. A brittle fracture analysis and tectonic stress inversion was performed, using the orientation of both the tension gashes and the shear fractures, and processed with the Win-Tensor program. Results show that they formed in a transtensional stress regime, with ENE-WSW horizontal extension. This vein thus suggests segregation, remobilization and migration of fluids in cracks and fissures opened by extensional tectonic activity giving rise to neocrystallization of minerals in the vein. 40Ar-39Ar dating of the monomineralic riebeckite, devoid of any deformation, has given one single plateau age for the crystallization of the riebeckite of 524.6 ± 4.6 Ma. This age thus dates the tectonic event (tension gashes and shear fractures under transtentional regime) corresponding to late-orogenic extension after the main 566 Ma ENE-WSW Pan-African compression that structured the WCB. Whether the 525 Ma event also relates to extensional collapse, exhumation and/or lateral escape post-dating the AWCO compressional history is debatable. Finally, in the Matadi area and adjacent NW Angola (Noqui-Tomboco map sheet) abundant sub N-S trending lineaments truncate and off-set Pan African regional fold structures. Field data suggest that they formed under brittle regime. The study of their significance is still in progress (Delvaux et al, this meeting). | |
| dc.language | eng | |
| dc.title | 525 Ma riebeckite in a quartz vein into the Noqui granite: evidence for a late Pan African extensional event in the West Congo Belt (Matadi area, Bas-Congo region, DR Congo) | |
| dc.type | Article | |
| dc.subject.frascati | Earth and related Environmental sciences | |
| dc.audience | Scientific | |
| dc.subject.free | Geodynamics and mineral resources | |
| dc.source.title | CAG 27 Portugal, Aveiro | |
| dc.source.volume | abstracts | |
| dc.source.page | 24 | |
| Orfeo.peerreviewed | No | |
| dc.identifier.rmca | 5296 |
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