Validation of a portable, waterproof blood pH analyser for elasmobranchs

Quantifying changes in blood chemistry in elasmobranchs can provide insights into the physiological insults caused by anthropogenic stress, and can ultimately inform conservation and management strategies. Current methods for analysing elasmobranch blood chemistry in the field are often costly and logistically challenging. We compared blood pH values measured using a portable, waterproof pH meter (Hanna Instruments HI 99161) with blood pH values measured by an i- STAT system (CG4+ cartridges), which was previously validated for teleost and elasmobranch fishes, to gauge the accuracy of the pH meter in determining whole blood pH for the Cuban dogfish (Squalus cubensis) and lemon shark (Negaprion brevirostris). There was a significant linear relationship between values derived via the pH meter and the i- STAT for both species across a wide range of pH values and temperatures (Cuban dogfish: 6.8-7.1 pH 24-30 degrees C; lemon sharks: 7.0-7.45 pH 25-31 degrees C). The relative error in the pH meter's measurements was similar to +/- 2.7%. Using this device with appropriate correction factors and consideration of calibration temperatures can result in both a rapid and accurate assessment of whole blood pH, at least for the two elasmobranch species examined here. Additional species should be examined in the future across a wide range of temperatures to determine whether correction factors are universal

Petrology of high-pressure granulite facies metapelites and metabasites from Tcholliré and Banyo regions: Geodynamic implication for the Central African Fold Belt (CAFB) of north-central Cameroon

International audienceThe Tcholliré and Banyo high-pressure granulites occur mainly as highly strained small lenses, bands or elongated bodies interbedded with gneisses and migmatites in the Central African Fold Belt (CAFB) in north-central Cameroon. They were previously attributed to Palaeoproterozoic but are now shown to be Pan-African. These granulites are made up of two occurrences of metapelites with garnet-kyanite-sillimanite-cordierite-biotite-quartz-plagioclase and metabasites containing garnet-clinopyroxene-orthopyroxene-hornblende-quartz-plagioclase.Eight samples were analysed in detail by electron microprobe for mineral chemistry.Parageneses in both metapelites and metabasites highlight three main stages witnessed by prograde, peak and retrograde mineral assemblages. The prograde stage is preserved as well-defined inclusion trails of kyanite, biotite, plagioclase, quartz, and rutile within porphyroblasts of garnet in metapelites; or with more or less clinopyroxene, hornblende, plagioclase, quartz, ilmenite, rutile and apatite, within porphyroblasts of garnet in metabasites. The peak stage, displaying heterogranular granoblastic texture is characterised by porphyroblastic garnet-kyanite-K-feldspar-biotite in metapelites and garnet-clinopyroxene-plagioclase-quartz in metabasites. This was followed by decompression and cooling during the retrograde stage marked by aggregate of sillimanite prisms presumably after kyanite and cordierite corona around garnet in metapelites and by symplectites or vermicular structures of orthopyroxene-plagioclase and orthopyroxene corona around garnet in metabasites. Geothermobarometric study shows that granulite facies metapelites and metabasites from both Tcholliré and Banyo regions recrystallised under peak pressure-temperature conditions of 13–14 kbar and 800–900 °C. They experienced similar clockwise P-T path with nearly isothermal decompression.Our results provide evidence for a substantial crustal thickening during the Pan-African continent–continent collision but show that there is no significant isothermal decompression as commonly observed in recent collisional orogens. The reconstructed P-T paths are in some ways reminiscent of the ones reported in Precambrian “mixed-hot orogens”

Relics of ophiolite-bearing accretionary wedges in NE Brazil and NW Africa: Connecting threads of western Gondwana´s ocean during Neoproterozoic times

Neoproterozoic breakup of Rodinia resulted in the formation of several oceanic realms between dispersing cratons, which were later consumed during the assembly of Gondwana. In its western portion, the interior orogenic belts of Gondwana formed during the Brasiliano-Pan African Orogeny in the late Neoproterozoic-early Cambrian. Available geophysical, structural and petrological data suggest that the complex network of shear zones that once connected the Borborema province (NE Brazil), Tuareg shield (Hoggar) and Central African domain (NW Africa) likely represent ancient sutures that mark collisional episodes between Archean-Paleoproterozoic paleocontinents such as Amazonian-West African and São Francisco-Congo. Mafic, ultramafic and sedimentary sequences associated with this set of structures respresent dismembered ophiolite slices interpreted as oceanic remnants (sensu lato) that were emplaced during the late stages of the Gondwana assembly. For instance, the composite Transbrasiliano-Khandi-In-Tedeini-Silet shear system crosscuts rock assemblages preserving a complex history of oceanic-crust-transition development (Novo Oriente complex) in association with primitive to evolved magmatic arcs and UHP rocks both in the Borborema province and NW Africa. In the central Borborema province, preserved ophiolitic slices are strongly overprinted by ductile and brittle deformation events, but partially preserved MORB-like amphibolites are akin to subduction-related-types that crystallized in early- and late Neoproterozoic times docked via terrane accretion and dispersed by strike-slip shear zones. In the southern Borborema province, an example of a Neoproterozoic ophiolitic assemblage is the Monte Orebe complex, that encompasses T-MORB mafic rocks, ultramafic lenses, and exhalative sedimentary rocks akin to early to late stages of oceanic basin spreading, emplaced during convergent plate motions between the Pernambuco-Alagoas superterrane and the São Francisco craton. Correlative units are found in Cameroon, including the strongly hydrotermalized ultramafic rocks of the Lomié and Boumnyebel complexes, that are structurally controlled by top-to-the-south verging nappes found in the N-NW margin of the Congo craton. In all scenarios, the ophiolitic complexes are related to intra-oceanic and continental magmatic arcs as well as to geophysical signatures comparable to Phanerozoic suture zones. Although strongly dismembered, scrapped off Neoproterozoic oceanic crust partially preserved within the major belts of western Gondwana demonstrate the role of accretion-collisional orogenesis during its assembly

Geochronology and correlations in the Central African Fold Belt along the northern edge of the Congo Craton: New insights from U-Pb dating of zircons from Cameroon, Central African Republic, and south-western Chad

International audienceThe Central African Fold Belt (CAFB) is the least well-known of all major Pan African belts. Here, we present new geochronologic work carried out in several critical areas of western Central African Republic, the region standing between northern Cameroon and southwestern Chad, and southern Cameroon. Our results allow us to: (1) clarify the regional extension of the Congo Craton in SE Cameroon and in the SW Central African Republic; (2) demonstrate that the units thrust along the northern edge of the Congo Craton from Cameroon to the Central African Republic are comparable in nature and in age; (3) better constrain the limits and described better the role of the Adamawa-Yadé crustal block during the Pan-African pre-collisional and collisional events in relation to the Congo Craton and the Yaoundé-Yangana nappe units to the South, and to the Poli-Leré magmatic arc to the North and; (4) clarify some of the elements of correlation with NE Brazil. Overall, a model involving two subduction zones is proposed to explain the evolution of the Pan-African belt north of the Congo Craton. The main steps include; (1) break-up and basin development from the early Tonian to at least 620 Ma on the northern edge of the Congo Craton, and on both the southern and the northern edges of the Adamawa-Yadé Block, concomitantly with the development of the Poli-Leré arc in northern Cameroon and Chad; (2) pre-tectonic plutonism in all domains since c. 800 Ma with culmination between 650 and 620 Ma; (3) collisional events starting around 620 Ma with metamorphism reaching the granulite facies at c. 600 Ma in all the domains; (4) nappe tectonics with thrusting of the Yaoundé-Yangana units onto the Congo Craton, accretion of the Poli-Leré arc to Adamawa-Yadé Block, and widespread syntectonic magmatism (600–580 Ma) with emplacement partly controlled by transcurrent regional shear zones, and emplacement of post-tectonic granitoids (c. 550 Ma) in both Adamawa-Yadé block and Poli-Leré magmatic arc. Collisional and post-collisional (620–550 Ma) events were synchronous along the entire belt from Central Africa to Brazil