Geofísica - GF
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- Detailed in-depth mapping of the world largest anorthositic complex: Magnetic anomalies, 2.5-3D modelling and emplacement constraints of the Kunene Complex (KC), SW AngolaPublication . 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, DomingosABSTRACT: The Kunene Complex (KC) represents a very large Mesoproterozoic igneous body, mainly composed of anorthosites and gabbroic rocks that extends from SW Angola to NW Namibia (outcropping 18,000 km2 , NE-SW trend, and ca. 350 km long and up to 50 km wide). Little is known about its structure at depth. Here, we use recently acquired aerogeophysical data to accurately determine its hidden extent and to unravel its morphology at depth. These data have been interpreted and modelled to investigate the unexposed KC boundaries, reconstructing the upper crustal structure (between 0 and 15 km depth) overlain by the thin sedimentary cover of the Kalahari Basin. The modelling reveals that the KC was emplaced in the upper crust and extends in depth up to ca. 5 km, showing a lobular geometry and following a large NE-SW to NNE-SSW linear trend, presumably inherited from older Paleoproterozoic structures. The lateral continuation of the KC to the east (between 50 and 125 km) beneath the Kalahari Cenozoic sediments suggests an overall size three times the outcropping dimension (about 53,500 km2 ). This affirmation clearly reinforces the economic potential of this massif, related to the prospecting of raw materials and certain types of economic mineralization (Fe-Ti oxides, metallic sulphides or platinum group minerals). Up to 11 lobes have been isolated with dimensions ranging from 135.5 to 37.3 km in length and 81.9 to 20.7 km in width according to remanent bodies revealed by TMI mapping. A total volume of 65,184 km3 was calculated only for the magnetically remanent bodies of the KC. A long-lasting complex contractional regime, where large strike-slip fault systems were involved, occurred in three kinematic pulses potentially related to a change of velocity or convergence angle acting on previous Paleoproterozoic inherited sutures. The coalescent magmatic pulses can be recognized by means of magnetic anomalies, age of the bodies as well as the lineations inferred in this work: (i) Emplacement of the eastern mafic bodies and granites in a stage of significant lateral extension in a transtensional context between 1500 Ma and 1420 Ma; (ii) Migration of the mantle derived magmas westwards with deformation in a complex contractional setting with shearing structures involving western KC bodies and basement from 1415 Ma to 1340 Ma; (iii) NNW-SSE extensional structures are relocated westwards, involving mantle magmas, negative flower structures and depression that led to the formation of late Mesoproterozoic basins from 1325 Ma to 1170 Ma. Additionally, we detect several first and second order structures to place the structuring of the KC in a craton-scale context in relation to the crustal structures detected in NW Namibia. (c) 2025 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing).
- Heat Flow Density Estimations in the Portuguese Northern Hercynian Massif using Silica GeothermometryPublication . Correia, Antonio; Ramalho, ElsaABSTRACT: Surface heat flow density (HFD) estimates in the Portuguese northern Hercynian Massif are difficult to obtain using the usual Fourier method. As a matter of fact, this zone is mostly composed by granitoid and metamorphic rocks, and most wells drilled there are too shallow for reliable HFD calculations; furthermore, HFD estimates are scarce and their geographical distribution is still very irregular. All these conditions imply that a HFD map for this region must be obtained using alternative methods, such as the silica geothermometry method. Under certain conditions, the use of silica geothermometers to estimate HFD in mineral waters has proved to be an effective way to understand and establish the thermal regime in areas with scarce conventional HFD determinations. Because temperatures obtained with silica geothermometry are related to deep thermal conditions in the crust and to water-rock equilibrium, a regional HFD analysis may be carried out using those temperatures. The silica geothermometer, developed by Truesdell in 1976 (Truesdell, 1976), give good results for low SiO2 concentrations, which is the case for the Portuguese northern Hercynian Massif, and is applied to more than 30 samples of mineral water occurrences reported for the zone. This number of samples, even though small, is considerably higher and more evenly distributed than conventional HFD estimates for the same area. Application of silica geothermometry to northern Hercynian Massif waters shows a discrete reservoir temperature zoning, ranging from about 45 ºC, in its southwest limit, to more than 120 ºC, towards its northeast limit. Using temperatures obtained by silica geothermometry and heat flow density values calculated through the conventional method in an area of 1º x 1º in the study zone, an empirical linear relationship between HFD and temperatures obtained by silica geothermometry is obtained and used to construct a HFD map for the Portuguese northern Hercynian Massif. The resulting HFD map is compared with the general geological and structural framework, and an attempt to a geothermal characterisation of the Portuguese northern Hercynian Massif is made.
- SedDARE-IB: an open-access repository of sediment data for the Iberian Peninsula and its continental marginsPublication . Torne, Montserrat; Alves, Tiago M.; Jimenez-Munt, Ivone; Carvalho, João; Ayala, Conxi; Ramalho, Elsa; Gomez-Garcia, Angela Maria; Matias, Hugo; Heida, Hanneke; Balaguera, Abraham; Garcia-Lobon, Jose Luis; Verges, JaumeABSTRACT: Sediments provide valuable information for geologists and geophysicists whenever they strive to understand, and reproduce, the geological evolution, lithology, rock properties, seismic response, and geohazards of a region. The analysis of sedimentary sequences is thus useful for the interpretation of depositional environments, sea-level change, climate change, and recognition of the sediments' source areas. By integrating sedimentary data into geophysical modeling, such interpretations are improved in terms of their accuracy and reliability. To further help our understanding of the Iberian Peninsula's geological evolution, geological resources, and geohazards, this work presents to the scientific community the SedDARE-IB data repository. This repository includes available data on the depth to the Base of the Cenozoic and Top of the Paleozoic stratigraphic markers for the Iberian Peninsula, the surrounding West Iberian Atlantic Margin and Western Mediterranean Neogene basins, or the acoustic basement as interpreted for the Valencia Trough and Alboran Mediterranean basins. As an example of the broad applicability of the data included in SedDARE-IB, we investigate how sediment thickness affects the depth to the 150 degrees C isotherm in specific basins, as commonly used in geothermal exploration. The calculated trend suggests that, given constant measured surface heat flow and thermal conductivity, the 150 degrees C isotherm becomes shallower as the sediment thickness increases, until a critical threshold value is reached for the latter. The SedDARE-IB database has been compiled thanks to a Portuguese-Spanish collaboration promoting open data exchange among institutions and research groups. SedDARE-IB is freely available at 10.20350/digitalCSIC/16277 (Torne et al., 2024), bringing opportunities to the scientific, industrial, and educational communities for diverse applications.
- Unconventional Three-Dimensional Active Seismic Tomography Applied in the Lousal Mine (Iberian Pyrite Belt, Portugal)Publication . Hamak, Ines; Teixeira, Pedro; Borges, José Fernando; Koulakov, Ivan; Oliveira, Rui Jorge; Caldeira, Bento; Bezzeghoud, Mourad; Xavier Matos, João Manuel; Andringa, SofiaABSTRACT: The Lousal Mine (Iberian Pyrite Belt, Portugal) was operated from 1900 to 1988 for the extraction of massive sulphides and was later rehabilitated as a science museum. It was selected as a test site for underground muon tomography applied to geophysical surveys, as part of the LouMu project. This study focuses on seismic tomography to analyse the subsurface above the mine gallery, primarily surveyed by a muography telescope, which was developed specifically for this site by the Laboratory of Instrumentation and Experimental Particle Physics. To validate the muon tomography results, an initial approach using conventional 2D seismic refraction failed to reach the Waldemar gallery depth, due to limited seismic ray coverage. Therefore, an innovative setup using surface shots and in-gallery geophones was implemented, providing full ray coverage. A 3D velocity model was then produced using the ATOM3D code, which enabled the integration of this configuration and performed travel-time inversion for velocity calculation. A regional dextral strike-slip fault, the Corona Fault (CF), crosses the surveyed area, and served as the main focus of this investigation. The 3D velocity model successfully detected this structure, that corresponded to the boundary between positive anomalies of the Volcano-Sedimentary Complex (VSC) and negative anomalies of the Phyllite-Quartzite Group (PQG). The absolute velocity distribution showed a distinct offset around the Corona Fault (CF), indicating a dextral strike-slip mechanism. A subvertical extension of secondary faults was observed, reflecting deformation similar to that of the main tectonic context. Previous data from the gallery confirmed that these results are consistent with the known geology and can serve as a reference for the muon tomography interpretations.