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Petrogenesis and geodynamic setting of the Bingo alkaline-carbonatite complex, DRC: Constraints from petrography, geochemistry, C-O isotopes and U-Pb geochronology
No full textThis study presents petrographic, whole-rock geochemical, stable isotope (C-O) and U-Pb geochronological data for a suite of carbonatite, nepheline syenite and ijolite from the Bingo complex. The Bingo alkaline-carbonatite complex is located within the western branch of the East African Rift System (EARS) in the Democratic Republic of Congo (DRC). The carbonatites are petrographically classified into calcite and magnetite-calcite carbonatite but have similar geochemical compositions. The ∑REE vary from 960 to 2400 ppm and the LaN/YbN ratios fall within the spectrum of 20 to 145. Calcite stable isotope compositions, δ13C(V-PDB) (− 3.51 to − 3.87 ) and δ18O(V-SMOW) (+12.12 to + 13.70 ), plot within the primary igneous carbonatite field and therefore reflect carbonated mantle melts. Based on similarity of geochemical trends between the carbonatite and the alkaline silicate suite, such as negative anomalies in Th, Ta, Pb, Zr, Ti and positive anomalies in Ba, Sr, La and Nb, we suggest that carbonatite and alkaline rocks could have been generated from a carbonated mantle source through extensive fractional crystallization and liquid immiscibility processes. U-Pb titanite dating of the ijolite suggests an emplacement age of 861.5 ± 7.0 Ma during the Neoproterozoic era, consistent with carbonatite magmatism elsewhere along the western branch of the EARS (i.e., Lueshe and Upper Ruvubu Alkaline Complex). This timing is associated with the initial break-up stages of the Rodinia supercontinent, a significant geological event recorded in central Africa during the Neoproterozoic. Additionally, in-situ U-Pb pyrochlore dating of the carbonatite indicates an age of 48.13 ± 0.80 Ma, coupled with a low (radiogenic) 207Pb/206Pb ratio of 0.1554. We discuss three potential interpretations of this anomalous U-Pb age. Firstly, it could represent a primary magmatic crystallization age, implying carbonatite magmatism during the Eocene. A second interpretation is that the age indicates resetting of the U-Pb system due to hydrothermal alteration of the pyrochlore. Thirdly, the pyrochlore could have recrystallized during intense tropical weathering (lateritization). The first and second interpretation are deemed unlikely given the apparent petrogenetic and geochemical relationship between the silicate and carbonatite suites, as well as the fact that this age would predate any recorded rift activity within the western branch of the EARS. Furthermore, the low 207Pb/206Pb ratio points to a highly radiogenic reservoir that is incompatible with a magmatic-hydrothermal source. We thus consider the third option of supergene recrystallization of pyrochlore most likely, possibly from Nb, U and Pb rich fluids released from the overlying weathering profile. As such, supergene pyrochlore might offer a novel approach to determine the absolute age of tropical weathering affecting carbonatites
Technical Expertise Report n° exp-392, 22/10/2021 - Applicant: Bureau voor Expertise & Architectuur, Abdijmolenstraat 14, 9031 Drongen, 18/10/2021
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Synthesis of national carbon fluxes of African rainforest countries
Get PDFAfrican tropical ecosystems possess great potential for nature-based solutions in mitigating anthropogenic green house gas emissions and biodiversity loss. However, past studies mostly focused on pan-continental carbon bal ance quantification, often ignoring regional differences. Remarkably, few science-informed attempts have been made to refine national-level carbon flux estimates within African rainforest countries. Yet, such refined estimates are essential to improving the quantification of Nationally Determined Contributions for the United Nations Frame work Convention on Climate Change. Here, we present preliminary results on quantifying national carbon budgets for African rainforest countries, dis entangling four major carbon fluxes for 2003-2019: (1) the net carbon uptake in intact tropical terrestrial eco systems, (2) land-use change fluxes, 3) CO2 outgassing in inland waters, and (4) fossil fuel emissions. The net carbon uptake in intact terrestrial ecosystems is based on Dynamic Global Vegetation Models TRENDY v111,2 (DG VMs), ground-based data (AfriTRON3 ), CARDAMOM4 , and remote sensing data products of Net Primary Productivity5 and soil heterotrophic respiration6-7. Land-use change emissions are calculated using bookkeeping models (BLUE8 , H&N20179 , OSCAR10), DVGMs1,2, and CARDAMOM4 . Additionally, we estimate carbon emissions from land-use change by analyzing various satellite images and related products providing data on land-use change11 12, soil and tree carbon stocks13 18, fire emissions19 20, and carbon recovery in regrowing forests21 22 in tropical Africa. We also quantify carbon emissions from CO2 outgassing in estuaries23 and inland waters24-25. National carbon balances are complet ed by using data on fossil fuel emissions from the Global Carbon Project2 . Besides calculating national-level net carbon fluxes using a bottom-up approach by summing individual carbon fluxes, we quantify the net carbon flux using a top-down approach based on atmospheric inversion models (GCP-GridFED26, CAMS27, Jena CarboScope28 , MIROC4-ACTM29, NISMON-CO2 30). We reveal that carbon balances of African rainforest countries remain highly uncertain. Our bottom-up estimates show that Congo Basin countries are net carbon sinks, while most West-African countries are net carbon sources. In contrast, our top-down estimates of net carbon fluxes indicate that African rainforest countries are net carbon sources. Overall, tropical terrestrial ecosystems have played an important role in mitigating anthropogenic carbon emissions in African rainforest countries. Our insights into nation-level carbon fluxes will be crucial for informing African rainforest countries, guiding climate policies to help stay on track to keep global warming well below 2°C
Studies on African Crambidae II On the identity of <i>Asopia onychinalis</i> Guénée,1854, its synonyms, generic placement and related species (Pyraloidea: Crambidae: Spilomelinae)
No full textTechnical Expertise Report ref. exp-63 - Applicant: Mr. Armand Stockmans, Somex S.A., Malachietstraat 2, 2030 Antwerpen, 13/10/2014
No full textPrimate Phenotypes: A Multi-Institution Collection of 3D Morphological Data Housed in MorphoSource
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