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- 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.
- Exhumation of an anatectic complex by channel flow and extrusion tectonics: structural and metamorphic evidence from the Porto–Viseu Metamorphic Belt, Central-Iberian ZonePublication . M. Bento dos Santos, Telmo; Rodrigues, José Feliciano; Castro, Paulo; Cotrim, Beatriz; Pereira, Inês; Ferreira, Joana; Pinto De Meireles, Carlos Augusto; Ferreira, Narciso; Ferreira, Priscila; Ribeiro, António; Guimarães, FernandaAbstract: Structural and metamorphic analyses of the Porto–Viseu Metamorphic Belt (PVMB), an anatectic complex located in the Central-Iberian Zone (CIZ), Iberian Variscan Massif, constrain the kinematic features of the polyphase Variscan deformation, as well as the boundary conditions associated with the exhumation and emplacement of the belt onto the CIZ’s lower-grade metasediments. A sharp metamorphic contrast is evident between the lowest grade rocks of the anatectic complex—garnet-staurolite mylonitic schists with a minimum metamorphic peak at P = 5.7 kbar and T = 635 °C—and the host chlorite-biotite metasediments of the CIZ. Additional P–T estimates for metatexites in the PVMB provided P = 7.6–7.9 kbar and T = 770–810 °C, confirming high-grade metamorphic peak conditions. The temperature jump between the anatectic complex and the low-grade host rocks exceeds 400 °C if the anatectic core of the belt (metatexites, diatexites, and S-type granites) is considered, implying a vertical difference of 10–17 km. The PVMB is limited in the NE by a D2 shear zone displaying normal kinematics, which has been explained so far by extensional tectonics. However, the SW boundary is limited by a D2 shear zone showing reverse kinematics. This pair of coeval and antithetical ductile shear zones bordering the PVMB, associated with the increase of the metamorphic grade towards the axial domain of the belt, is consistent with anatectic channel flow, followed by extrusion tectonics of the PVMB within an overall D2 compressive setting.
- Posibles aplicaciones industriales de las arenas del Kalahari de Angola [Resumo]Publication . Lisboa, Jose; Oliveira, Álvaro; Rodrigues, José Feliciano; Fernández, J.; Manuel, JoséRESUMEN: Las arenas de color amarillo ocre con poca o ninguna matriz procedentes de la Formación Arenas Ocres (Mio-Plioceno) y las arenas lavadas de colores claros del Cuaternario (Oliveira y Sousa, 2021), presentes en la cuenca del Kalahari, se extienden sobre una vasta área en el SO de Angola, presentando una gran homogeneidad en todos los niveles a lo largo de esa cuenca. Sin embargo, muestran características morfológicas similares a las de las arenas del desierto y, como tales, no son adecuadas para usos más comunes en la obra civil, como el agregado de cemento. Son arenas de tamaño de grano generalmente < 1 mm, con predominio de fracción fina (125-250 μm), subangulares a subredondeadas, de tendencia bimodal, bien calibradas, con un contenido de matriz generalmente ≤ 7%. Están formados por granos de cuarzo, escasos minerales máficos u otros, dando como resultado una composición química con SiO2 > 98.5% y un reducido contenido en elementos penalizadores. Considerando la granulometría y el análisis químico, estas arenas tienen posibles usos en sectores de la industria cerámica y del vidrio, dependiendo, para aplicaciones menos exigentes, de métodos de beneficio sencillos, en particular para reducir el contenido de alúmina y especialmente de óxidos de hierro concentrados en los recubrimientos que a menudo afectan parcialmente a los granos. Estos pueden reducirse mediante lavados y tratamientos simples de fricción.
- Zircon U-Pb and Lu-Hf isotopes reveal the crustal evolution of the SW Angolan Shield (Congo Craton)Publication . Ferreira, Ezequiel; Lehmann, Jeremie; Rodrigues, José Feliciano; Hayes, Ben; Merino-Martinez, Enrique; Milani, Lorenzo; Bybee, Grant M.; Smith, Trishya M. Owen; García-Lobón, J. L.; Tassinari, Colombo C. G.; Ueckermann, Henriette; Sato, Kei; Silva, Paulo Bravo; Correia, João; Labaredas, José; Duarte, Laurent; Molekwa, Mmasetena Anna; Manuel, José; Victorino, Américo da MataABSTRACT: The crustal evolution of the Angolan Shield (AS) remains poorly constrained. To address this, we analysed U-Pb and Lu-Hf isotopes in detrital and igneous zircons to investigate the age and provenance of extensive sedimentary strata in southwestern Angola and use it as a proxy to gain insight into the Archean to Mesoproterozoic evolution of the region. Mesoproterozoic maximum depositional ages for the Iona (<1323 +/- 13 Ma), Ompupa (<1215 +/- 13 Ma), and Cahama (<1184 +/- 23 Ma) siliciclastics challenge previous correlations with the Paleoproterozoic Chela Group. Provenance analysis reveals that the Mesoproterozoic strata were derived internally from the AS. Our combined dataset indicates that the widespread Eburnean magmatism (-2.05-1.93 Ga) resulted from reworking of Archean crust, possibly in collision orogens. A major increase in the eHf(i) and eNd(i) values at - 1.87-1.73 Ga indicates a change in geodynamics, with magmatism of the Epupa-Namibe Metamorphic Complex (ENMC) generated in an extensional accretionary orogen at the southern margin of the Eburnean-Archean crustal block. Magmatism resumed in the Mesoproterozoic (-1.56-1.50 Ga), with suprachondritic eHf(i) values indicating significant juvenile addition. The Kunene Complex (KC: -1.50-1.36 Ga) anorthosite-mangerite-charnockite-granite magmatism displays variable eHf(i) and eNd(i) values, consistent with mixing between reworked ENMC-crust and juvenile melts in a long-lived accretionary orogen back-arc region. Post-KC (-1.36-1.30 Ga) magmatism shows an increased juvenile contribution, potentially linked to partial melting of ENMC and - 1.56-1.50 Ga juvenile crust during an orogenic event, or alternatively, related to renewed slab retreat and back-arc extension. The Hf isotopic compositions of - 1.29-1.18 Ga zircons are compatible with a renewed input from the depleted mantle and/or reworking of the earlier - 1.56-1.50 Ga juvenile crust. Emplacement of - 1.13-1.10 Ga mafic dikes/sills marks the end of Mesoproterozoic magmatism in the AS. Our new data enhance our understanding of the Archean to Mesoproterozoic crustal evolution of the AS.
- Mapas de potencial mineral en el sur de Angola: el primer enfoque de un mapa de prospectividad basado en datos y conocimiento adquirido en la región de Au-Fe del sur de Angola [Resumo]Publication . Batista, Maria Joao; Martín-Méndez, I.; Merino-Martínez, E.; Prazeres, Cátia; Cuervo, I.; Manuel, José; de Oliveira, Daniel Pipa Soares; Rodrigues, José Feliciano; García-Lobón, J. L.RESUMEN: Los mapas de recursos minerales a escala 1:50.000 fueron realizados en la última fase del Proyecto PLANAGEO con el objetivo de evaluar el potencial mineral de la región sur de Angola. Los objetivos elegidos fueron, entre otros, las zonas que contienen Au-Fe en las áreas de Jamba-Cassinga-Tchamutete, Chipindo y Cuima-Samboto. Los mapas integraron mapas geológicos, datos magnéticos y radiométricos aéreos y resultados de FRXp de campañas de campo de PLANAGEO y yacimientos minerales conocidos. Se obtuvieron análisis univariantes, bivariantes y multivariantes y grupos de pathfinders, tales como: Factor 1 (F1)- Cd, Hg, Fe2O3, As, V, Ni de rocas en Chipindo o Factor 1(F1) - Fe2O3, As, Sn, Sb, Ta en rocas de Jamba. Esos grupos fueron identificados como pathfinders de Au, representados en los Mapas de Potencial por encima del percentil 80. En el caso de Jamba era >0,838 y el área delimitada incluía rocas BIF, rocas metavolcánicas bimodales del terreno Arcaico del Grupo Jamba.
- Contrasting Ordovician high- and low-pressure metamorphism related to a microcontinent-arc collision in the Eastern Cordillera of Perú (Tarma province)Publication . Willner, Arne P.; Tassinari, Colombo C. G.; Rodrigues, José Feliciano; Acosta, Jorge; Castroviejo Bolíbar, Ricardo; Rivera, MiguelHigh-pressure conditions of 11–13 kbar/500–540 °C during maximum burial were derived for garnet amphibolite in the Tapo Ultramafic Massif in the Eastern Cordillera of Peru using a PT pseudosection approach. A Sm–Nd mineral-whole rock isochron at 465 ± 24 Ma dates fluid influx at peak temperatures of ~600 °C and the peak of high pressure metamorphism in a rodingite of this ultramafic complex. The Tapo Ultramafic Complex is interpreted as a relic of oceanic crust which was subducted and exhumed in a collision zone along a suture. It was buried under a metamorphic geotherm of 12–13 °C/km during collision of the Paracas microcontinent with an Ordovician arc in the Peruvian Eastern Cordillera. The Ordovician arc is represented by the western Marañon Complex. Here, low PT conditions at 2.4–2.6 kbar, 300–330 °C were estimated for a phyllite–greenschist assemblage representing a contrasting metamorphic geotherm of 32–40 °C/km characteristic for a magmatic arc environment.
- Evolução e estrutura da zona de cisalhamento dúctil Malpica-Lamego : livro guia da excursão pós-congressoPublication . Castro, Paulo Ferreira; Coke, Carlos; Ferreira, Narciso; Llana-Fúnez, S.; Pamplona, J.; Pereira, Eurico; Pimenta, P.; Rodrigues, B. C.; Rodrigues, José Feliciano
- New data on the deposition age of the volcano-sedimentary Chela Group and its Eburnean basement : implications to post-Eburnean crustal evolution of the SW of AngolaPublication . Pereira, Eurico; Tassinari, Colombo C. G.; Rodrigues, José Feliciano; Van-Dúnem, Maria VitóriaThe Chela Group comprises a volcano-sedimentary sequence deposited in a widespread epicratonic basin that extends to southern of the Lubango region in SW of Angola. The basement rocks of the Chela Group integrate the Eburnean belt, consisting mainly of gneisses and migmatites, syntectonic foliated peraluminous granites, and late-tectonic metaluminous granites of the Chela and Gandarengos Mountains. Rb/Sr radiometric age of 2.1 ± 0.1 Ga was determined for the syntectonic granites whereas the late-tectonic Chela granite yielded a zircon U-Pb age of 1947 ± 5 Ma. This isotopic dating allow us to take it as a maximum age for the Chela Group. Moreover, the porphyritic calc-alkaline granite of the Gandarengos Mountain and a rhyolitic mass, spatially related to this granite, revealed U-Pb zircon ages of 1810 ± 11 Ma and 1814 ± 88 Ma, respectively. The rhyolite is intrusive into Tundavala Formation, base of the Chela Group, and should be the source of the pyroclastites composing the Humpata Formation. The time interval between 1814-1810 Ma obtained for the volcano-plutonism intrusive into the Chela Group restrains its minimum age and permits to define the interval 1947-1810 Ma as the main period of deposition of this sedimentary sequence in a post-orogenic environment. After the deposition of the Chela Group, succeeds a period of crustal accretion marked by the installation of leucocratic peraluminous granites and an extensional Mesoproterozoic (1.4-1.1 Ga) bimodal magmatism, followed during the Neoproterozoic by deposition of the Damara Supergroup and development of the Pan-African belt. At that period, any tectonometamorphic event reportable to Grenville-Kibaran orogeny was not recognized in SW Angola.
- 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.
- Desligamentos interplaca e intraplaca em cadeias deformadas : exemplos no bordo do SW dos Variscides IbéricosPublication . Romão, José; Ribeiro, António; Pereira, Eurico; Fonseca, Paulo E.; Rodrigues, José Feliciano; Mateus, António; Noronha, Fernando; Dias, Rui
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