A Gondwana pre-break up related magmatism in Bafoussam area, west Cameroon: source characteristics and 40Ar/39Ar geochronology

Abstract

The Gondwana pre-break up related formations in Bafoussam area are transitional calc-alkaline doleritic dykes exhibiting high Alumina and low Ti-Mg contents. Their REE compositions are similar to those of E-MORB (Nd/Nb≈1, Zr/Nb≤20). A high partial melting of about 20% of Garnet peridotites source having primitive mantle composition, is inferred to the studied rocks. They are slightly evolved 50<Mg#<54, and its clinopyroxenes are augite of high temperature (600°C-1100°C). The studied dykes were emplaced in a within-plate tectonic setting and yield a 40Ar-39Ar plateau ages of 229±7Ma. These ages are slightly different from those of dolerites from the Oban-Obudu massif (Nigeria), from the basaltic dyke of the Cameroon Volcanic Line and from the Karoo-Ferrar mafic magmatism, all interpreted as magmatism that preceded the break-up of Gondwana. The emplacement age of 229±7Ma of dolerites from Bafoussam area relates them to the very early stage of Gondwana pre-break up magmatism in central Africa.

Major, trace elements and Sr–Nd–Pb isotopes systematics of mafic dykes from the Figuil (northern Cameroon) and Léré (southwestern Chad) areas

“…These results clearly indicate at least two magmatic events in the Figuil–Lere area. The literature data also indicate that the DPB dykes swarms in the southern continental part of the CL are much older (192.10–421.3 Ma; Kouankap Nono et al, 2019; Tchouankoue et al, 2012, 2014) compared to the DCSB dated at between 43 and 87 Ma (Wilson & Guiraud, 1998).…”

“…Along the CL, magmatism is characterized by rocks of various ages corresponding to tectonic phases from the Neoproterozoic Pan‐African granites (620–420 Ma) representing the basements to the Cenozoic effusive volcanics and plutonics (73 Ma–Present: Aka et al, 2018; Lasserre, 1966 and references therein). The ages of intrusive dykes on the CL vary from 421.3 to 192.1 Ma (Kouankap Nono et al, 2019; Tchouankoue et al, 2014), which corresponds to a window of approximately 229 Ma for the magmatism of CL dykes. This age gap was concomitant with main magmatic activities in the Baborema province of NE Brazil (310 Ma–Present; Melo et al, 2022; Mizusaki et al, 2002), Central Atlantic Magmatic Province (CAMP; 189–207 Ma; Marzoli et al, 2018 and references therein) and the basaltic dykes of the Amazonian craton (199.3 Ma; Giovanardi et al, 2019).…”

“…The Pan‐African orogeny that affected the CL granitic basement of Neoproterozoic age left behind zones of weaknesses and fractures (Tchaptchet et al, 2017; Toteu et al, 2001) that have facilitated the emplacement of intrusive and extrusive magmatic rocks (Burke, 2001; Njonfang et al, 2011). The first phase of intrusion principally in Pan‐African basement is characterized by dykes from Silurian to Jurassic (Aka et al, 2018; Keutchafo Kouamo et al, 2019; Kouankap Nono et al, 2019; Tchouankoue et al, 2012; Tchouankoue et al, 2014; Vicat et al, 2001). The opening of the Equatorial Atlantic Ocean in the Cretaceous (96–130 Ma) was synchronous with the Benue Trough magmatism (49–147 Ma: Wilson, 1992).…”

“…In fact, alkaline and subalkaline mafic dykes from the Nyos area were dated at 231.1 ± 4.8 Ma and 224.8 ± 4.7 Ma (K–Ar dates, Aka et al, 2018), whereas Ar–Ar ages of 421.3 ± 3.5 Ma, 404.22 ± 3.51 Ma and 192.10 ± 7.45 Ma were reported for basaltic dyke swarms situated at Dschang, Maham and Kendem in the southern continental part of the CL (Tchouankoue et al, 2012, 2014). In addition, Ar–Ar plateau age of 229 ± 7 Ma was obtained from the Bafoussam dolerite dyke (Kouankap Nono et al, 2019). These results indicate that dolerite dykes outcropping in sedimentary basins are younger than those of Precambrian basement.…”