New Constraints from Pb-Evaporation Zircon Ages of the M&amp;#233;iganga Amphibole-Biotite Gneiss, Central Cameroon, on Proterozoic Crustal Evolution

Ganwa Alembert Alexandre,Shang Kongnyuy Cosmas,Naimou Seguem,Ekodeck Georges Emmanuel,Siebel Wolfgang

doi:10.4236/ijg.2011.22014

Abstract

The amphibole biotite gneiss (ABGn) in the Meiganga area forms part of a meta volcano-sedimentary sequence of the Adamawa Yade domain (AYD), Central African Fold Belt (CAFB). This sequence shows affinity with immature sediments (greywackes, arkoses) with intercalation of mafic lavas or tuffs. New 207Pb/206Pb zircon evaporation ages for two ABGn samples range from 1887 - 2339 Ma and from 675 - 889 Ma, respectively. These ages and evidence from internal zircon structures indicate that igneous rocks of Archean to Paleoproterozoic and of early Neoproterozoic age contributed to the detritus of the sedimentary sequence. The deposition of detritus took place prior to 614 - 619 Ma which represent the syntectonic emplacement of the Meiganga metadiorite. Leucogranites north to the Meiganga area were generated by melting of crust identical to that which provided the source of the ABGn. The metasedimentary sequence investigated in this study is similar to that of the southern part of the AYD and in the Borborema Province, NE Brazil. The tectonic and geochronologic characteristics of the AYD in the Meiganga area support the idea that during the Proterozoic, Central Africa and NE Brazil were part of the same continental landmass.

Highlights

Introduction and Geological SettingThe Adamawa – Yade Domain (AYD) is one of the three main lithostructural units of the Central African Fold Belt (CAFB), defined by [1] using petrographic, structural, and isotopic data in Cameroon and Central Africa Republic (Figure 1)
The metasedimentary sequence investigated in this study is similar to that of the southern part of the Adamawa Yade domain (AYD) and in the Borborema Province, NE Brazil
In central Cameroon (Adamawa region), the AYD is characterized by Pan-African granitoids intruding Paleo- to Neoproterozoic gneisses which are intensively overprinted by regional-scale transcurrent shear zones [1,2,3]

Summary

Introduction

The Adamawa – Yade Domain (AYD) is one of the three main lithostructural units of the Central African Fold Belt (CAFB), defined by [1] using petrographic, structural, and isotopic data in Cameroon and Central Africa Republic (Figure 1). These authors considered the AYD as a Paleoproterozoic basement unit that was dismembered during the Pan-African orogeny. The Bafia group to the north of Yaoundé, previously considered as a basement tectonic slice overthrusting the Yaoundé Group [4], is regarded as the southern extension of the AYD in Cameroon This interpretation is strengthened by the presence of granulite facies assemblages retrogressed during the Pan-African nappe tectonics [5]. The AYD of the CAFB has several features in common with its equivalent in NE Brazil, the Brasiliano/Pan-African Borborema Province, including 1) a central position in relation to the sur- rounding cratons [11,12,13], 2) a network of transcurrent shear zones, and 3) the presence of metasedimentary sequences

Results

Discussion

Conclusion