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Bouyo M.H.,Center for Geological and Mining Research | Penaye J.,Center for Geological and Mining Research | Barbey P.,University of Lorraine | Toteu S.F.,UNESCO Nairobi office | Wandji P.,University of Yaounde I
Precambrian Research

The 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" © 2012 Elsevier B.V. Source

Bouyo M.H.,Chinese Academy of Geological Sciences | Bouyo M.H.,Center for Geological and Mining Research | Zhao Y.,Chinese Academy of Geological Sciences | Penaye J.,Center for Geological and Mining Research | And 2 more authors.
Precambrian Research

This paper presents new geochemical and geochronological data for the low to medium grade Rey Bouba Greenstone Belt (RBGB), located in northern Cameroon at the northern margin of the Central African Fold Belt (CAFB), and discusses the maximum age of volcanic activity, the maximum depositional age of metasedimentary rocks and geotectonic implications. Geochemical data on volcanic rocks highlight the predominance of transitional to calc-alkaline magma compositions (Zr/Y. = 3.62-26.38) with mostly andesite to basaltic andesite with an unusually high Mg concentration (>5. wt.%, high-Mg andesite), but also basalt and trachy-andesite protoliths. Moreover, chondrite-normalized REE patterns and primitive mantle-normalized spidergrams show enrichment of LREE relative to HREE with flat to depleted elements, and moderate to slight negative Nb-Ta, Ti and Eu anomalies respectively; which are consistent with a continental arc setting related to a subduction zone. U-Pb zircon LA-ICP-MS geochronology on felsic metavolcanic or metatuff fix the maximum age for the volcanic activity in the RBGB at ca 670. Ma. Detrital zircon grains indicate that Neoproterozoic zircon (Ediacaran to Cryogenian) are the main source for the detritus that fed the basin, combined with minor Paleoproterozoic and Mesoproterozoic inputs. The maximum depositional age, corresponding to the youngest graphical age peak controlled by multiple grain ages is consistently constrained between 645 and 630. Ma, whereas the age of low grade metamorphism weakly recorded by overgrowths on detrital zircon in the RBGB basin is around 600. Ma. These results provide new insights into the geodynamic processes during the Neoproterozoic along the northern margin of the CAFB of northern Cameroon, suggesting that the RBGB, where high-Mg andesite magmatism has taken place is consistent with a continental arc-related basin. © 2015 Elsevier B.V. Source

Houketchang Bouyo M.,Center for Geological and Mining Research | Penaye J.,Center for Geological and Mining Research | Njel U.O.,Center for Geological and Mining Research | Moussango A.P.I.,Center for Geological and Mining Research | And 8 more authors.
Journal of African Earth Sciences

The Sinassi Batholith in the Central African Fold Belt (CAFB) of northern Cameroon represents the largest volume of plutonic rocks or granitoids massif of the Western Cameroonian Domain. It is made up dominantly of tonalite-trondhjemite-granodiorite (TTG) suite and lesser granite which are locally more or less deformed, and composed of varying proportions of quartz, plagioclase, K-feldspar, biotite, hornblende, sphene, magnetite, apatite and zircon. Major and trace element compositions of fifteen rock samples of granitoids (Djourdé granodiorite, Sinassi quartz diorite and orthogneisses groups) indicate that investigated rocks from the Sinassi Batholith are characterized by medium- to high-K calc-alkaline affinity and metaluminous I-type signature. In addition, their chondrite- and primitive mantle-normalized trace element patterns are strongly fractionated ((La/Yb)N = 2.96-61.40) and show respectively enrichment in LREE relative to HREE and enrichment in LILE compared to HFSE with moderate to slight negative Nb-Ta, Ti and Eu anomalies consistent with a continental magmatic arc setting related to a subduction zone.Geothermobarometric calculations using hornblende-plagioclase thermometry and aluminum-in-hornblende barometry on eleven rock samples indicate that plutons from Sinassi Batholith were emplaced at average temperatures and pressures ranging between 698 and 720 °C and 4.06-5.82 kbar (Djourdé granitoids), 698-728 °C and 4.04-5.34 kbar (Sinassi granitoids) and 667-670 and 4.23-4.76 kbar (orthogneisses group) respectively. The average emplacement depths estimates for the investigated granitoids is constrained at ca 16-18 km, indicating that at least 16 km of crustal rocks of the Sinassi Batholith must have been eroded or uplifted at approximately exhumation rates of 0.08-0.10 mm/year.Regardless of their Th/U ratios, geochronological results highlight three main events characterizing the Neoproterozoic tectonomagmatic evolution within the Sinassi Batholith at the northern margin of CAFB of northern Cameroon: (1) inherited magmatic sources ranging from one group to another at ca 692, 713, 722, 746 and 772 Ma; (2) successive emplacement ages at ca 670-686 Ma (orthogneisses group), ca 661-666 Ma (synchronous emplacement of the Djourdé and Sinassi groups) and ca 644 Ma (emplacement age of eyespots quartz diorite in the Sinassi group); and (3) post-magmatic alteration or metamorphism at ca 600 Ma.Correlations with the neighboring Mayo Kebbi Batholith in southwestern Chad show geochemical and geochronological similarities, demonstrating that the Sinassi and Mayo Kebbi granitoids beyond political boundaries are parts of a unique Sinassi-Mayo Kebbi Batholith witnessing a Neoproterozoic subduction-related continental magmatic arc setting of Andean-type. © 2015 Elsevier Ltd. Source

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