New Data on the Genesis and Evolution of the Primitive Magmas of Mount Cameroon: Contribution of Melt Inclusions

Abstract

Mount Cameroon is a Plio-Quaternary volcanic massif, without a central crater, made up ofmore than 140 pyroclastic cones. It is one of the active volcanoes of the Cameroon Line. Mount Cameroon magmatic inclusions are found in microdroplets trapped in the early minerals (olivines) from the pyroclastic products. The analysis of these magmatic inclusions allowed us to find primitive liquids compared to lavas. Major elements study of the magmatic inclusions, trapped in the most magnesian olivines (Mg#84-86) of Mount Cameroon revealed "primitive" liquids of basanite and alkaline basalt type with variable composition compared to the much more uniform basalts of the magmatic series of Mount Cameroon. The study of these trapped liquids shows that: (i)- the original primitive lavas did not undergo the process of evolution by FC, but rather underwent fundamentally (or exclusively) the process of partial melting; (ii) the emitted lavas, evolved essentially by FC; (iii) the variations in the trace element contents of the primitive liquids directly reflect a variation in the rate of partial melting of a homogeneous mantelic source. The very high La/Yb ratios of the Mount Cameroon inclusions (> 20) characterize a garnet lherzolite source. Spectra of the magmatic inclusions show a negative anomaly or depletion in K, Rb and Ba as those of HIMU. The "primitive" liquids and lavas of Mount Cameroon represent a co-genetic sequence formed by varying degrees of partial melting of a source considered as homogeneous.

Magmatism of the Beka Volcanic Massifs (Cameroon Volcanic Line, West-Central Africa): New Petrographical and Mineralogical Data

“…In the Rb/Y vs. Nb/Y digram in Figure 14, part of the Beka rocks as well as the Mount Cameroon, Kapsiki Plateau formations are positioned within the field of uncontaminated alkaline basalt and felsic rocks. These results are in agreement with those of (Ngounouno et al, 2000Tchop et al, 2020). A second part of the Beka and Kapsiki Plateau rocks are located between the field of uncontaminated formations and the field of basement rocks defined by (Kamgang et al, 2010) called "felsic and Precambrian basement of the Bamenda Mountains".…”

“…In the course of the discussion, the lavas of Beka and its surroundings are compared with those of other volcanic formations of the Cameroon Volcanic Line such as the lavas of Mount Cameroon, Mt Bamenda, and the Kapsiki Plateau and Sao Tomé. The latter, studied by several authors, are of mantle origin and result from weak partial melting of a deep asthenospheric mantle (Déruelle et al, 2000;Ngounouno et al, 2000;Marzoli et al, 1999;Ngounouno et al, 2006;Wandji et al, 2009;Kamgang et al, 2010, Tchop et al, 2020.…”

“…Magmas of intermediate or felsic composition have two main formation processes which are fractional crystallisation and assimilation. They can also be formed by the interaction of felsic and contemporary mafic magmas as suggested by Tchop et al (2020); or partial melting of crustal material (Nkouandou et al, 2008;Ngwa et al, 2019), or partial melting of the metasomatised mantle wedge. The absence of mafic enclaves or mafic-felsic mixtures in the study area excludes the hypothesis of interaction of felsic and contemporary mafic magmas.…”

Petrological features of volcanic scoriae from the southern part of the Cameroon Volcanic Line and their supplementary cementations application

“…Figure 4 highlights a positive slope for SiO 2 , CaO, and MgO, and negative one for Al 2 O 3 , Fe 2 O 3 , TiO 2 , MnO and P 2 O 5 . According to several works carried out along the Cameroon Volcanic Line ( Yamgouot et al., 2016 ; Mbowou et al., 2020 ; Tchop et al., 2020 ), the sum of SiO 2 , Al 2 O 3 and Fe 2 O 3 is up to 67.50 wt.% and the alkali contents attain 4.62 wt.% ( Table 2 ). The average contents of major elements are similar along the Cameroon Volcanic Line ( Table 2 ).…”

“…Galim and Djoungo scoriae have already been investigated ( Djobo et al., 2014 ; Tchamdjou et al., 2017 ). Thus, it is known that the alkaline lavas, along the CVL differentiated into basalts and basanites, show similarities with Ocean Island Basalts (e.g., Tchuimegnie et al., 2015 ; Mbowou et al., 2020 ; Tchop et al., 2020 ). In the same vein, the geochemical features of rocks relate them to a mantle source (e.g., Tchamabe et al., 2014 ; Marzoli et al., 2015 ; Asaah et al., 2015 ; Ngwa et al., 2017 ; Dedzo et al., 2019 , 2020 ; Tiabou et al., 2019 ).…”