A phlogopite-amphibole-plagioclase bearing websterite from Guinadji volcano (Adamawa Plateau, Northern Cameroon): evidence of a cumulate origin and crustal event

Paterne Mulimbi Kagarabi; Theodoros Ntaflos; Jules Tamen; David G. Nkouathio; Kaniki Tumba

doi:10.2478/mipo-2025-0011

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A phlogopite-amphibole-plagioclase bearing websterite from Guinadji volcano (Adamawa Plateau, Northern Cameroon): evidence of a cumulate origin and crustal event

Mineralogia

Volume 56 (2025): Issue 1 (January 2025)

By: Paterne Mulimbi Kagarabi , Theodoros Ntaflos, Jules Tamen, David G. Nkouathio and Kaniki Tumba

Open Access

|Dec 2025

Figures & Tables

(a) Location of Adamawa plateau (red star) and other principal volcanic centers along the CVL (modified according to Nkouathio et al., 2008). Dashed lines are limits between the CVL segments: ocean, COB and continent. (b) Location map of the CVL. The principal geologic features of Africa (Congo Craton, CVL, East African Rift, Hoggar, Kalahari Craton, Tibesti, West African Craton) are indicated. COB, continental ocean boundary; CVL, Cameroon volcanic line.

Photomicrographs of the studied websterite. (a) Cumulative texture. (b) Interstitial phlogopite. (c) Edenite as rim around cpx. (d) Three aspects of opx. Dashed lines represent their triple junctions. hbi, host basalt infiltration, op, opaque minerals; Phl, phlogopite.

BSE images of the studied websterite. (a) Association phlogopite-amphibole-rutile. (b) Amphibolitization of clinopyoxene. (c) Amphibole elongated exsolution lamellae following clinopyroxene cleavage. (d) Plagioclase as intercumulus phase. (e) Image showing that amphibole and phlogopite are of metasomatic origin. (f) Clinopyroxene remants as inclusion in plagioclase. sul, sulfides.

Table 1.

Major (wt.%) and trace elements (ppm) bulk rock compositions of the phlogopite-amphibole-plagioclase-bearing websterite xenolith of Guinadji volcano.

SiO₂ (wt%)	51.54
TiO₂	0.43
Al₂O₃	4.88
Cr₂O₃	0.25
FeO^*	9.5
MnO	0.19
MgO	19.55
CaO	12.98
Na₂O	0.58
K₂O	0.12
P₂O₅	0.07
BaO	0.01
LOI	0.32
Mg#	0.79
Total	100.42
Ba (ppm)	100
Ce	11.1
Cr	1690
Cs	0.05
Dy	1.89
Er	1.15
Eu	0.61
Ga	7.8
Gd	2.07
Hf	0.85
Ho	0.41
La	3.8
Lu	0.12
Nb	1.3
Nd	8.4
Pr	1.68
Rb	3.9
Sc	46.3
Sm	2.36
Sr	76.5
Tb	0.35
Th	0.2
Ti	0.28
Tm	0.12
U	0.08
V	248
Y	9.3
Yb	0.87
Zr	30

* Fe total as FeO.

Chondrite normalized REE (a) and spider diagram (b) of the Guinadji volcano websterite; normalization values are from Sun and McDonough (1989). REE, rare earth elements.

Table 2.

Representative EMPA of pyroxene (wt.%).

cpx
SiO₂	52.53	51.34	51.01	51.73	52.42	51.58	51.44	51.41	51.5	52.16
TiO₂	0.35	0.48	0.50	0.40	0.37	0.47	0.4	0.49	0.56	0.46
Al₂O₃	3.07	4.05	4.21	3.54	3.22	3.95	3.66	4.16	4.5	3.98
Cr₂O₃	0.31	0.38	0.4	0.38	0.32	0.40	0.38	0.40	0.39	0.40
FeO	5.63	5.38	5.37	5.46	5.47	5.53	5.56	5.49	5.53	5.53
MnO	0.16	0.11	0.17	0.16	0.17	0.13	0.16	0.15	0.14	0.12
MgO	15.47	14.97	14.85	15.28	15.42	14.95	15.04	14.85	14.68	14.95
CaO	22.00	22.08	21.96	21.95	21.82	21.91	21.99	21.97	21.8	21.94
Na₂O	0.45	0.49	0.48	0.48	0.45	0.5	0.44	0.51	0.53	0.48
NiO	0.01	0.01	0.02	b.d.l	0.04	0.02	0.01	0.01	0.02	0.01
Total	99.98	99.28	98.98	99.39	99.71	99.44	99.08	99.44	99.64	100.04
Si (a.p.f.u)	1.93	1.9	1.89	1.91	1.93	1.9	1.91	1.9	1.9	1.91
Ti	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.02	0.01
Al	0.13	0.18	0.18	0.15	0.14	0.17	0.16	0.18	0.20	0.17
Cr	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01
Fe³⁺	0.01	0.03	0.03	0.03		0.02	0.03	0.02
Fe²⁺	0.16	0.14	0.14	0.14	0.16	0.15	0.14	0.15	0.17	0.17
Mn			0.01		0.01		0.01
Mg	0.85	0.82	0.82	0.84	0.85	0.82	0.83	0.82	0.81	0.82
Ca	0.87	0.87	0.87	0.87	0.86	0.87	0.87	0.87	0.86	0.86
Na	0.03	0.04	0.03	0.03	0.03	0.04	0.03	0.04	0.04	0.03
Mg#	0.84	0.86	0.86	0.86	0.84	0.84	0.85	0.85	0.83	0.83
Al^VI	0.06	0.07	0.08	0.06	0.07	0.08	0.07	0.08	0.09	0.09
Al^IV	0.07	0.10	0.11	0.09	0.07	0.10	0.09	0.10	0.10	0.09
Al^VI/Al^IV	0.83	0.7	0.69	0.67	0.97	0.79	0.69	0.77	0.91	1.02
Wo	45.91	46.88	46.91	46.24	45.9	46.59	46.53	46.84	46.84	46.63
En	44.92	44.2	44.14	44.79	45.13	44.23	44.28	44.03	43.88	44.2
Fs	9.17	8.92	8.95	8.98	8.98	9.18	9.19	9.14	9.28	9.17
opx
SiO₂	53.89	53.3	54.02	54.26	54.27	54.55	54.16	53.77	53.84	53.72	54.07	54.23	54.12	54.1
TiO₂	0.12	0.12	0.10	0.12	0.11	0.12	0.12	0.11	0.10	0.11	0.12	0.12	0.14	0.11
Al₂O₃	2.23	2.7	2.32	2.24	2.29	2.05	2.32	2.28	2.28	2.54	2.21	2.48	2.78	2.23
Cr₂O₃	0.17	0.23	0.17	0.14	0.17	0.13	0.20	0.20	0.21	0.23	0.20	0.23	0.25	0.15
FeO	14.07	14.23	14.2	14.08	14.23	14.17	14.17	14.19	14.08	14.24	14.14	14.25	14.29	14.43
MnO	0.3	0.28	0.28	0.29	0.28	0.27	0.29	0.29	0.31	0.28	0.29	0.27	0.31	0.29
MgO	27.79	27.64	27.65	27.43	27.39	27.79	27.54	27.36	27.55	27.45	27.61	27.38	27.3	27.4
CaO	0.89	0.61	0.78	0.75	0.75	0.83	0.80	0.85	0.86	0.70	0.81	0.80	0.73	0.78
Na₂O	0.03	0.01	0.03	0.02	0.02	0.01	0.02	0.03	0.02	0.09	0.02	b.d.l	0.03	0.02
NiO	0.02	0.02	0.02	0.01	0.05	b.d.l	0.02	b.d.l	0.04	b.d.l	0.02	0.01	0.04	0.01
Total	99.51	99.14	99.59	99.36	99.6	99.91	99.66	99.07	99.3	99.38	99.48	99.77	100	99.53
Si (a.p.f.u)	1.94	1.92	1.94	1.96	1.96	1.96	1.95	1.95	1.94	1.94	1.95	1.95	1.94	1.95
Al	0.09	0.11	0.10	0.10	0.10	0.09	0.10	0.10	0.10	0.11	0.09	0.10	0.12	0.09
Fe³⁺	0.02	0.02	0.01						0.01	0.01
Fe²⁺	0.40	0.41	0.42	0.42	0.43	0.42	0.43	0.43	0.42	0.42	0.43	0.43	0.43	0.44
Mn	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01
Mg	1.49	1.49	1.48	1.48	1.47	1.49	1.48	1.48	1.48	1.48	1.48	1.47	1.46	1.47
Ca	0.03	0.02	0.03	0.03	0.03	0.03	0.03	0.03	0.03	0.03	0.03	0.03	0.03	0.03
Mg#	0.79	0.79	0.78	0.78	0.77	0.78	0.78	0.78	0.78	0.78	0.78	0.77	0.77	0.77
Al^VI	0.03	0.04	0.04	0.05	0.05	0.04	0.05	0.04	0.04	0.04	0.04	0.06	0.06	0.05
Al^IV	0.06	0.08	0.06	0.04	0.04	0.04	0.05	0.06	0.06	0.06	0.05	0.05	0.06	0.05
Al^VI/Al^IV	0.54	0.52	0.74	1.26	1.2	0.95	0.9	0.76	0.7	0.69	0.79	1.10	1.03	0.9
Wo	1.76	1.21	1.55	1.51	1.51	1.65	1.58	1.69	1.71	1.4	1.62	1.6	1.46	1.56
En	76.51	76.65	76.42	76.47	76.27	76.47	76.37	76.15	76.39	76.38	76.42	76.16	76.17	75.98
Fs	21.74	22.13	22.03	22.03	22.22	21.88	22.05	22.15	21.9	22.22	21.96	22.24	22.37	22.45

[i] EMPA, electron microprobe analyses.

Table 3.

Representative EMPA of phlogopite and amphibole (wt. %).

	Phlogopite								Amphibole
SiO₂	38.93	39.62	39.32	39.48	39.16	38.91	39.53	38.8	44.75	45.58	44.20
TiO₂	3.56	3.61	3.58	3.61	3.67	3.69	3.56	3.56	1.81	1.64	1.65
Al₂O₃	14.03	13.93	13.7	14.01	14.04	14.07	13.73	14.11	11.49	10.52	11.25
FeO	6.05	5.96	6.12	6.02	6.23	5.92	6.11	6.08	6.43	6.19	6.39
MnO	0.02	0.04	b.d.l	0.04	0.02	0.03	0.02	0.06	0.13	0.09	0.1
MgO	20.59	21.27	20.75	20.97	20.6	20.47	20.83	20.46	16.53	17.35	16.96
CaO	b.d.l	b.d.l	0.01	0.01	b.d.l	0.01	0.02	b.d.l	11.78	11.7	11.85
Na₂O	0.57	0.56	0.55	0.57	0.58	0.59	0.57	0.57	1.81	1.75	1.79
K₂O	9.61	9.57	9.67	9.55	9.51	9.42	9.56	9.49	1.71	1.57	1.64
F	2.95	3.04	2.95	3.14	2.79	3.00	2.65	2.87	n.a	1.50	n.a
Cl	n.a	n.a	n.a	n.a	n.a	n.a	n.a	n.a	0.02	0.02	0.02
BaO	0.37	0.39	0.36	0.39	0.38	0.43	0.33	0.36	n.a	n.a	n.a
Total	96.67	98	97.03	97.8	96.99	96.54	96.92	96.36	96.45	97.91	95.85
Si(a.p.f.u)	5.69	5.71	5.73	5.71	5.70	5.69	5.74	5.69	6.51	6.61	6.48
Ti	0.39	0.39	0.39	0.39	0.40	0.41	0.39	0.39	0.20	0.18	0.18
Al	2.42	2.37	2.35	2.39	2.41	2.43	2.35	2.44	1.98	1.80	1.94
Al^VI									0.48	0.41	0.42
Al^IV									1.49	1.39	1.52
Fe²⁺	0.74	0.72	0.75	0.73	0.76	0.72	0.74	0.74	0.78	0.75	0.78
Mn									0.02	0.01	0.01
Mg	4.49	4.57	4.51	4.52	4.47	4.47	4.51	4.47	3.59	3.75	3.71
Ca									1.84	0.82	1.86
Na	0.16	0.16	0.16	0.16	0.16	0.17	0.16	0.16	0.51	0.49	0.51
Na (M4)									0.11	0.08	0.04
Na (A)									0.41	0.41	0.47
K	1.79	1.76	1.80	1.76	1.77	1.76	1.77	1.77	0.32	0.29	0.31
F	1.36	1.39	1.36	1.44	1.29	1.39	1.21	1.33
Mg#	0.86	0.86	0.86	0.86	0.86	0.86	0.86	0.86	0.82	0.83	0.83
Na + K	1.95	1.92	1.96	1.92	1.93	1.93	1.93	1.93	0.83	0.78	0.83

[i] EMPA, electron microprobe analyses.

Table 4.

Representative EMPA of plagioclase (wt.%).

SiO₂	52.92	52.15
TiO₂	b.d.l	0.01
Al₂O₃	29.06	29.77
FeO	0.14	0.15
MnO	0.02	0.01
MgO	0.05	0.06
CaO	12.04	12.60
Na₂O	4.42	4.04
K₂O	0.51	0.49
Total	99.17	99.28
Si (a.p.f.u)	2.42	2.38
Al	1.56	1.60
Fe²⁺	0.01	0.01
Ca	0.59	0.62
Na	0.39	0.36
K	0.03	0.03
An	58.30	61.47
Ab	38.75	35.71
Or	2.94	2.82

[i] EMPA, electron microprobe analyses.

Table 5.

Representative EMPA of rutile and iron oxide (wt.%)

Rutile			Iron oxide
SiO₂	0.09	0.07	0.04
TiO₂	96.73	98.97	b.d.l
Al₂O₃	0.18	0.05	b.d.l
Cr₂O₃	0.94	b.d,l	0.02
Nb₂O₅	0.15	0.28	b.d.l
FeO	0.74	0.65	90.50
MnO	b.d.l.	b.d.l	0.03
CaO	0.58	0.02	0.01
NiO	0.03	b.d.l	0.14
ZnO	0.01	0.02	0.03
V₂O₃	0.21	0.02	b.d.l
Total	99.65	100.09	90.78
Si (a.p.f.u)	0.001	0.001
Ti	0.980	0.993
Al	0.003	0.001
Cr	0.010	b.d.l
Nb	0.001	0.002
Fe²⁺	0.008	0.007
Ca	0.008	b.d.l.

[i] EMPA, electron microprobe analyses.

Pyroxene composition from the studied websterite plotted on the En-Wo-Fs ternary diagram after Morimoto et al. (1988).

Clino- and orthopyroxene mineral chemistry plots. (a) CaO (wt%) versus Mg# content of clinopyroxene, (b) Al₂O₃ versus Mg# for clinopyroxene, (c) CaO (wt%) versus Mg# content of clinopyroxene, (d) Al₂O₃ versus Mg# for clinopyroxene. Plagioclase-bearing olivine websterite from Serri et al. (1988), Layered websterite from Wilson and Chaumba (1997), Abyssal crustal cumulate pyroxenite after Dantas et al. (2007); Mantle websterites from Rogkala et al., 2017; Garnet websterites from Lu et al., 2018, Befang websterite from Tedonkenfack et al. (2021).

(a) Chemical composition of phlogopite on the Mg/(Fe + Mg) versus Al^tot classification diagram of Rieder et al. (1998). Red circles represent chemical compositions of phlogopite. (b) Amphibole classification diagram after Leake et al. (1997). The blue field represents amphiboles described by Pintér et al. (2015) and Njombie Wagsong et al. (2018). TFA, Tetra-Ferri-Annite; TFP, Tetra-Ferri-Phlogopite.

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DOI: https://doi.org/10.2478/mipo-2025-0011 | Journal eISSN: 1899-8526 | Journal ISSN: 1899-8291

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Language: English

Page range: 103 - 119

Submitted on: Aug 10, 2025

Accepted on: Nov 18, 2025

Published on: Dec 31, 2025

Published by: Mineralogical Society of Poland

In partnership with: Paradigm Publishing Services

Publication frequency: Volume open

Keywords:

Phlogopite-amphibole-plagioclase-bearing websterite,

Guinadji volcano,

Adamawa Plateau,

Cumulate origin,

K–F rich crustal-derived fluids

Related subjects:

Geosciences,

Geophysics

© 2025 Paterne Mulimbi Kagarabi, Theodoros Ntaflos, Jules Tamen, David G. Nkouathio, Kaniki Tumba, published by Mineralogical Society of Poland
This work is licensed under the Creative Commons Attribution 4.0 License.

Volume 56 (2025): Issue 1 (January 2025)

A phlogopite-amphibole-plagioclase bearing websterite from Guinadji volcano (Adamawa Plateau, Northern Cameroon): evidence of a cumulate origin and crustal event

Figures & Tables

Figure 1.

Figure 2.

Figure 3.

Table 1.

Figure 4.

Table 2.

Table 3.

Table 4.

Table 5.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

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