Geochronological, geochemical and mineralogical constraints of emplacement depth of TTG suite from the Sinassi Batholith in the Central African Fold Belt (CAFB) of northern Cameroon: Implications for tectonomagmatic evolution
Abstract 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 (Djourde 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 degC and 4.06 5.82 kbar (Djourde granitoids) 698 728 degC 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 Djourde 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.