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- 저자 : Tessontsap Teutsong (검색결과 1 건)
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Gaelle Assomo,Tessontsap Teutsong,Gentry Fuh,Sylvestre Ganno,Alembert Ganwa,Paul-Désiré Ndjigui 한국지질과학협의회 2022 Geosciences Journal Vol.26 No.1
Ngaye area belongs to the Adamawa-Yadé domain (AYD) of the Central African Fold Belt (CAFB) in Cameroon. It is underlain by gneisses and amphibolites intruded by a variety of granitoids including granites and granodiorites. Petrographic, mineralogical and bulk-rock geochemical analyses were applied to assess the characteristics, petrogenesis and tectonic settings of these formations. Gneisses and amphibolites are characterized by a heterogranular granoblastic texture and a weakly to well-developed foliation. The granodiorites are characterized by high SiO2 (65.32 to 69.04 wt%) and K2O/Na2O < 1, with Mg-number (Mg#) of 23.44 to 43.67. They display affinities to calc-alkaline, peraluminous to metaluminous, magnesian I-type granites. Granite samples display higher SiO2 contents (69.62–81.04 wt%) with wide ranges of K2O/Na2O (0.44–4.72) and Mg# (5.85–41.16). These granites are classified mostly as ferroan, calc-alkaline, peraluminous, I-type granites. Comparable features were observed in the Hawal Massif granitoids in the eastern Nigeria and in the Ngoura-Moyto granitoids of south-central Chad. The chondrite-normalized REE patterns of the studied granitoids are weakly to strongly fractionated, with negative to weak positive Eu anomalies (Eu/Eu* = 0.28–1.36) for granodiorites and mostly positive Eu anomalies (Eu/Eu* = 1.54–5.78) for granites. In primitive mantle-normalized multi-element diagrams, all granitoids show enrichment in LILE relative to HFSE and display positive Ba, K and Pb, and negative Nb, Ta, Ti and P anomalies. The gneisses show high and variable contents in SiO2 (48.78–68.17 wt%), Al2O3 (13.06–18.03 wt%), and moderate Mg# (35.41 to 59.99). Their REE patterns are weakly to strongly fractionated ((La/Yb)N ≈ 3–168) and exhibit negative and positive Eu anomalies (Eu/Eu* = 0.59–2.05). Amphibolites display lower SiO2 (48.13–50.84 wt%) and Al2O3 (13.53–15.37 wt%), with Mg# ranging from 34.38 to 58.18. Their REE patterns are weakly fractionated ((La/Yb)N ≈ 3–5) with no Eu anomalies. Both gneiss and amphibolite samples are marked by troughs of Ta and P, and peaks of K, Pb and Nd on the primitive-mantle normalized spidergrams, suggesting that they were derived from the same source. Petrological and geochemical characteristics show that the Ngaye granitoids emplaced in a volcanic arc subductionrelated environment, from partial melting of metabasaltic, metatonalitic and metagreywacke source rocks, under hydrous conditions. The Ngaye amphibolites display geochemical features of island arc basalt with MORB-like signature, continental forearc setting with calc-alkaline signature and syn-orogenic environment, implying an overall arc environment for the Ngaye formations.
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