Browsing by Author "Cordeiro, Domingos"
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- Depth estimation of pre-Kalahari basement in Southern Angola using seismic noise measurements and drill-hole dataPublication . Carvalho, João; Alves, Daniela; Borges, José Fernando; Caldeira, Bento; Cordeiro, Domingos; Machadinho, Ana; Oliveira, Álvaro; Ramalho, Elsa; Rodrigues, José Feliciano; Llorente, J.; Ditutala, M.; Lobón, Jose Luis Garcia; Máximo, J.; Carvalho, Cristina Isabel Paulo; Labaredas, José; Ibarra, P.; Manuel, JoséABSTRACT: The remote Southern region of Angola is covered by siliciclastic Kalahari Cenozoic formations that host underground aquifers of great importance to local populations affected by water scarcity problems. These aquifers are well developed where Kalahari sands reach appropriate thicknesses. On the other hand, at the eastern end of this area, regional aeromagnetic data recently acquired suggested the possibility of the continuity of the geological structures of the Lufilian Arc, sited in the nearby Zambia and Congo, southwestwards into Angola under the Kalahari formations. Once the Lufilian Arc is associated with the presence of the so-called Central African Copperbelt, this possibility increased the interest in determining the depth to Pan-African rocks under the Kalahari basin. To estimate the thickness of Kalahari formations in this area of difficult access and poor logistics, an expedited and non-invasive geophysical method was needed. Seismic noise and the single-station Nakamura technique were chosen, but due to the large distance of the study area from the ocean, one of the major sources of seismic noise, a test survey was acquired in the Cuvelai region to assess the signal quality, where the data was calibrated using available drill-holes. >170 points of seismic ambient noise were later acquired and the horizontal/vertical (HVSR) amplitude versus frequency curves were 1D inverted for the best velocity/density model for each station. The results were compared with 1D inverted legacy vertical electrical soundings reprocessed and validated in this work, showing similar depth-to-basement, while interpreted velocities/densities of geological formations were sampled and confirmed with measurements. A depth-to-basement map was produced using seismic information, mechanical soundings, and geological information. Despite the relatively reduced geographical area covered, the map presents valuable information for hydrogeology and mineral exploration purposes and agrees with a previously available coarser map of Kalahari thickness and with observations from geological surveys simultaneously conducted at the time of the seismic surveys.
- El Complejo Calco-Alcalino de la Serra da Neve (SW Angola): trabajos en curso [Resumo]Publication . Prazeres, Cátia; Batista, Maria Joao; Lopes, R.; Barros, B.; Ferreira da Costa, P.; Labaredas, José; Guimarães, Fernanda; Rodrigues, José Feliciano; Cordeiro, DomingosRESUMEN: El Complejo Calco-Alcalino de la Serra da Neve (CACSN) constituye un conjunto de estructuras alcalinas volcánicas, subvolcánicas y plutónicas emplazadas en una tendencia general ONO-ESE a NOSE (Pereira y Moreira, 1978; Lopes y Caessa, 2021). Fue remapeado a escala 1:100.000 para la cartografía geológica del proyecto PLANAGEO y posteriormente fue una de las áreas seleccionadas para realizar exploración mineral para ETR-Nb-Ta a escala regional. Las campañas de campo incluyeron levantamientos con FRX portátil y SRG portátil, cuyos resultados mostraron patrones preliminares de distribución de ETR en las litologías del CACSN (Prazeres et al., en revisión). Los muestreos realizados durante el trabajo de campo permitieron estudios petrográficos y análisis con microsonda electrónica, que son la base para comprender la mineralogía de los ETR. Hasta ahora se ha demostrado que algunos carbonatos (bastnasita), fosfatos (apatito y xenotima), minerales de Zr (eudialita) y esfena incorporan cantidades apreciables de ETR, especialmente ETR ligeros.
- Metallogenetic potencial of the Paleoproterozoic mafic-ultramafic Hamutenha intrusion (SW Angola). New data from PLANAGEO project [Abstract]Publication . Morais, Igor; Batista, Maria Joao; Represas, Patricia; Albardeiro, Luís; Prazeres, Cátia; Plastov, José Manuel; Sousa, João Carlo; Bravo, Paulo; Sousa, Pedro; Carvalho, João; Rodrigues, José Feliciano; de Oliveira, Daniel Pipa Soares; Cordeiro, DomingosABSTRACT: In the SW sector of the Angolan shield occur the Kunene Anorthositic Complex (KAC), one of the most remarkable magmatic anorthositic suites worldwide. The KAC is considered a long-lived magmatic system that operated in the area intermittently during the Mesoproterozoic (1450 ± 2 Ma to 1371 ± 2.5 Ma). Smaller mafic-ultramafic intrusive bodies ranging in composition from dunite to harzbugite, pyroxenite, troctolite and gabbro are located in the KAC periphery (e.g. Epupa, Ombuku, Hamutenha, Oncócua). The Hamutenha body is a 3 km long oriented NW-SE, banded intrusion with internal zonation hosted in the Paleoproterozoic granitic rocks (1970 ± 2 Ma). The internal zone is composed by rocks with ultramafic nature, mostly harzburgites and dunites with diorites in the external zone.
- Modelización magnética del Complejo de Cunene (SW Angola) [Resumo]Publication . Mochales, Tania; Merino-Martínez, E.; Rey-Moral, Carmen; Machadinho, Ana; Carvalho, João; Represas, Patricia; García-Lobón, J. L.; Feria, María Carmen; Martín-Banda, Raquel; López-Bahut, T.; Alves, Daniela; Ramalho, Elsa; Manuel, José; Cordeiro, DomingosRESUMEN: El Complejo de Cunene (CC) representa un extenso macizo ígneo mesoproterozoico compuesto por rocas anortosíticas, gabroicas y ácidas contemporáneas, que aflora 18.000 km2 en dirección NNE-SSW desde el SW de Angola al NW de Namibia. Se han interpretado y modelizado en 2,5/3D los datos aerogeofísicos obtenidos en el proyecto PLANAGEO para investigar los límites no expuestos del CC, reconstruyendo la estructura de la corteza superficial bajo la cobertera del Kalahari. Gracias a la modelización se descifra una geometría lobular cuya extensión es casi tres veces la superficie aflorante y superior a la estimada mediante gravimetría (45.000 km2; Rey-Moral et al., 2022). Las anomalías magnéticas identificadas definen cuerpos individuales que conforman diversos pulsos magmáticos coalescentes durante el Mesoproterozoico. Las lineaciones magnéticas indican grandes sistemas de cizallamiento desarrollados en varias fases intrusivas en un contexto colisional de arco. Los lineamientos magnéticos al E sugieren un emplazamiento asociado a etapas transtensivas. Al W, con los pulsos más jóvenes, se detectan lineamientos en un régimen contraccional complejo. Estructuras tardías NNW-SSE extensionales, involucran magmas mantélicos y cuencas mesoproterozoicas tardías (<1,33 Ga).
- New insights on the ultramafic intrusions surrounding the Kunene Anorthosite Complex (SW Angola) from gravity, magnetic and radiometric data [Abstract]Publication . Represas, Patricia; Sousa, Pedro; Morais, Igor; Cordeiro, Domingos; Carvalho, João; Batista, Maria Joao; Dito, Manuel; Llorente, J.; Marques, Fábio; Mateus, T.; Rodrigues, José Feliciano; Lobón, Jose Luis Garcia; de Oliveira, Daniel Pipa SoaresABSTRACT: The Kunene Anorthosite Complex (KAC), located in SW Angola, is one of the largest anorthosite structures in the world. Dating from the Mesoproterozoic, its installation process is still not clear. Several mafic and ultramafic outcrops can be found surrounding the KAC. Once considered related with its emplacement, the study of these bodies may help us understand the history of this unique geological feature. While geochronological data show that they are synchronous, or possibly a bit younger, than the embedding granites and migmatites of Paleoproterozoic age, the question arises of whether they are intrusions installed in the host rock or if they are instead recycled remains of older Arch crust. The development of these outcrops in depth provides relevant clues regarding the origin of these bodies and their relationship with the Eburnean (~1.93-2.04 Ga) and Epupa-Namibe (~1.83-1.74 Ga) events. One of these mafic outcrops, designated the Hamutenha outcrop (Huíla Province) exhibits an elongated shape and a NW-SE orientation and is characterized by an internal zonation. Generally, the innermost part is composed of ultramafic rocks of (mostly harzburgites and dunites), with diorites outcropping in its NW and SE borders. The Hamutenha outcrop was previously identified for potentially bearing Cr, Ni and PGE mineralization.