Geochronology and nature of the Palaeoproterozoic basement in the Central African Copperbelt (Zambia and the Democratic Republic of Congo), with regional implications

U-Pb SHRIMP zircon age data, together with geochemical analyses, from the basement to the Katanga Supergroup in the Central African Copperbelt reveal the existence of a widespread Palaeoproterozoic magmatic arc terrane. The Lufubu schists represent a long-lived calc-alkaline volcanic arc sequence and, where dated in both Zambia and the Democratic Republic of Congo (DRC), yield ages of 1980 ± 7, 1968 ± 9, 964 ± 12 and 1874 ± 8 Ma. The oldest dated unit from the region, the Mkushi granitic gneiss from south-east of the Zambian Copperbelt, has an age of 2049 ± 6 Ma. The copper-mineralized Mtuga aplites, which crosscut the foliation in the Mkushi gneisses, have mainly xenocrystic, zoned zircons with cores dated at ca. 2.07-2.00 Ga. Overgrowths on these cores are dated at 1059 ± 26 Ma, which is interpreted as the intrusive age of the aplites. An augen gneiss from the Mulungushi Bridge locality yielded an emplacement age of 1976 ± 5 Ma. The Mufulira Pink Granite has an age of 1994 ± 7 Ma, while the Chambishi granite has been dated at 1983 ± 5 Ma, an age within error of Lufubu schist metavolcanics from elsewhere in the Chambishi basin. The gneisses, granitoids and acid-intermediate calc-alkaline metavolcanics are considered to represent stages in the evolution of one or more magmatic arcs that formed episodically over a 200 million year period between 2050 and 1850 Ma. We suggest naming this assemblage of rocks the "Lufubu Metamorphic Complex". The rocks of the Lufubu Metamorphic Complex are interpreted to be part of a regionally extensive Palaeoproterozoic magmatic arc terrane stretching from northern Namibia to northern Zambia and the DRC. This terrane is termed the Kamanjab-Bangweulu arc and is inferred to have collided with the Archaean Tanzanian craton during the ca. 2.0-1.9 Ga Ubendian orogeny, to produce a new composite minicontinental entity that we term the "Kambantan" terrane. The Kambantan terrane was accreted onto the southern margin of the Congo craton during the ca. 1.4-1.0 Kibaran orogeny

Provenance ages of the Neoproterozoic Katanga Supergroup (Central African Copperbelt), with implications for basin evolution

New age data on detrital zircons and micas are presented from key units within the Neoproterozoic Katanga Supergroup, which hosts the major stratiform Cu-Co deposits of the Central African Copperbelt. Detrital zircon ages indicate a mainly Palaeoproterozoic (between 2081 ± 28 and 1836 ± 26 Ma) provenance for the Katanga basin, derived from the Lufubu Metamorphic Complex of the Kafue Anticline and the Bangweulu Block to the north of the outcrop belt. Detrital zircons and clasts from the Grand Conglomerat glacial diamictite indicate a source from the Palaeoproterozoic metavolcanic porphyries and granitoids of Luina Dome region, which was a basement high during Nguba Group deposition. Minor zircons of Mesoproterozoic age may have been derived from the Kibaran belt. Finally, 40Ar/39Ar age data from detrital muscovites from Biano Group siltstones give a maximum age of sedimentation of 573 Ma, strongly supporting previous models that the Biano Group was deposited in a foreland basin of the Lufilian Orogen

A cryptic Mesoarchaean terrane in the basement to the Central African Copperbelt

In a study of the geochronology of the Katangan Sequence and its basement in the Central African Copperbelt, detrital and xenocrystic zircons from Muva quartzites and Katangan lapilli tuffs, were dated using the Sensitive High-Resolution Ion Microprobe (SHRIMP). A detrital population (dated between 3007 and 3031 Ma) and a group of xenocrystic zircons aged between 3169 and 3225 Ma provide the first evidence for the existence of a Mesoarchaean basement beneath the Central African Copperbelt

Monazite U-Pb dating and 40 Ar- 39 Ar thermochronology of metamorphic events in the Central African Copperbelt during the Pan-African Lufilian Orogeny

New SHRIMP U-Pb age data on metamorphic monazite, as well as step-heating 40Ar-39Ar ages on metamorphic biotite, muscovite and microcline, from Katangan metasedimentary rocks of the Central African Copperbelt are presented. These rocks were deformed and metamorphosed during the Pan-African Lufilian Orogeny. Three samples of metamorphic monazite from the Chambishi structural basin give ages of 592 ± 22 Ma, 531 ± 12 Ma and 512 ± 17 Ma, which correspond respectively to the ages of eclogite facies metamorphism, high-pressure talc-kyanite whiteschist metamorphism, and of a regional metamorphism/mineralisation pulse elsewhere within the Lufilian Orogen. A biotite population from Luanshya gives a 40Ar/39Ar plateau age of 586.1 ± 1.7 Ma, coinciding with the oldest monazite age. Several samples from the Chambishi basin and the Konkola area give 40 Ar/39Ar biotite plateau ages in the range of 496.6 ± 0.6-485.2 ± 0.9 Ma, and a muscovite plateau age of 483.6 ± 1.1 Ma, which are a manifestation of regional uplift and cooling that affected the whole Katangan basin. The youngest apparent 40Ar/39Ar ages obtained are from microcline at Musoshi and range from 467.0 ± 2.7 Ma to 405.8 ± 3.8 Ma, reflecting continued slow cooling of the Lufilian Orogen

Characterization of air-sea exchanges over the Western Mediterranean Sea during HyMeX SOP1 using the AROME-WMED model

International audienceAir-sea exchanges play an important role during intense weather events over the Mediterranean Sea, especially in supplying heat and moisture for heavy precipitation events, which often affect the area. Observations collected during the first Hydrological cycle in the Mediterranean Experiment (HyMeX) Special Observation Period (SOP1) over the Western Mediterranean area in autumn 2012 provide an unprecedented dataset for assessing the capabilities of numerical weather prediction systems to represent the air-sea interface and marine boundary layer during the heavy precipitation season. A HyMeX-dedicated version of Application de la Recherche a l'Operationnel a Meso-Echelle, in French (AROME) covering the whole western Mediterranean basin, named AROME-WMED, was evaluated through comparisons against moored buoys, drifting buoys and ship measurements deployed during the HyMeX campaign. A general, good agreement is found for near-surface meteorological parameters, whereas significant discrepancies are observed during strong air-sea exchange periods. The two main reasons are that (1) sea-surface temperature (SST) is kept constant during the model runs and (2) sensible heat flux is overestimated in strong wind regimes by the AROME turbulent flux parametrization. Air-sea exchanges during SOP1 were characterized thanks to AROME-WMED short-range (1-24h) forecasts. This shows some areas of strong air-sea fluxes in the Gulf of Lion and the Balearic, Ligurian and Tyrrhenian Seas. The Gulf of Lion is the area showing the highest variability of air-sea fluxes, due to dominant strong regional winds (Mistral/Tramontane). Whereas some heavy precipitation events occur without significant air-sea fluxes, all strong air-sea exchange events include, or occur only 1 or 2 days before, heavy precipitation events. A detailed analysis of an Intense Observation Period (IOP) dedicated to a heavy precipitation event (IOP13, from 12-15 October) illustrates how both dynamic (wind) and thermodynamic (temperature and humidity gradient effect) contributions influence air-sea flux evolution

Out of Africa: detrital zircon provenance of central Madagascar and Neoproterozoic terrane transfer across the Mozambique ocean

The Neoproterozoic East African Orogen reflects closure of the Mozambique Ocean and collision of the Congo and Dharwar cratons. This palaeogeographic change and its environmental consequences are poorly understood, but new detrital zircon ages from Madagascar and published data from elsewhere provide evidence for multiple ocean basins and two-stage collision. We propose that central Madagascar rifted from the Congo Craton and crossed a Palaeomozambique Ocean to collide with the Dharwar Craton at c. 700 Ma, opening a Neomozambique Ocean in its wake. Closure of the Neomozambique Ocean at c. 600 Ma juxtaposed the Congo and Dharwar cratons and resulted in prolonged collisional orogenesis concluding at c. 500 Ma

High-resolution air-sea coupling impact on two heavy precipitation events in the Western Mediterranean

International audienceThe Mediterranean Sea is an important source of heat and moisture for heavy precipitation events (HPEs). Moreover, the ocean mixed layer (OML) evolves rapidly under such intense events. Whereas short‐term numerical weather prediction systems generally use low‐resolution non‐evolving sea surface temperature (SST), the development of high‐resolution high‐frequency coupled system allows us to fully take into account the fine‐scale interactions between the low‐level atmosphere and the OML which occur during HPEs.The aim of this study is to investigate the impact of fine‐scale air–sea interactions and coupled processes involved during the HPEs which occurred during 12–15 October 2012 (IOP13) and 26–28 October 2012 (IOP16a/b) of the HyMeX first field campaign. For that purpose, the high‐resolution coupled system AROME‐NEMO WMED was developed. This system is based on the 2.5 km‐resolution non‐hydrostatic convection‐permitting atmospheric model AROME‐WMED and the 1/36°‐resolution NEMO‐WMED36 ocean model. The coupling frequency is 1 h. To distinguish the effects due to the change in the initial SST field from that due to the interactive 3D ocean, the coupled run is compared to two AROME‐WMED atmosphere‐only experiments with no SST evolution during the 48 h forecast cycles—one using the AROME‐WMED SST analysis, the second using the SST field of the coupled experiment each day at 0000 UTC. The results of the three experiments re‐assert that the SST initial condition strongly influences the HPE forecast, in terms of intensity and location. With water budget analyses, the significant impact of the ocean interactive evolution on the surface evaporation water supply for HPEs is also highlighted. In cases of strong and intense air–sea exchanges, as in the mistral event of IOP16b, the coupling reproduces the intense and rapid surface cooling and demonstrates the importance of representing the ocean turbulent mixing with entrainment at the OML base