Petrology of peridotite host basaltic lavas of northern  Ngaoundéré (Adamawa plateau,  Cameroon, Central Africa)

Small volcanoes and flows of Cainozoic basaltic lavas, containing numerous mantle peridotite xenoliths, outcrop at northern Ngaoundéré in Adamawa plateau. They are composed of arena of decimeter to meter in size of bowls and blocs of dark matrix, showing crystals of olivine, clinopyroxene and oxides. All lavas present microlitic porphyritic texture with euhedral to subhedral crystals of the same phases drowned in the matrix of the same minerals plus plagioclase microlites.Microprobe analyses show that olivine phenocrysts are relatively Fo-rich (80.9-84.3 %) compared to microphenocrysts and microcrysts (Fo71.1-75.9 %). Olivine xenocrysts are highly magnesian (83.9-89.8 %). Clinopyroxene are diopside and augite. Oxides crystals are Ti-magnetite and plagioclase are labradorite and bytownite.ICP-AES and ICP-MS whole rocks analyses show that the host peridotite basaltic lavas of northern Ngaoundéré are undersaturated basanites of typical alkaline lava series. They seem not contaminated by crustal materials. They are the results of low partial melting rate of the garnet mantle source located at more than 80 km depth. The eruptions of northern Ngaoundéré lavas have been facilitated by Pan African cracks and they have sampled the subcontinental lithospheric mantle as xenoliths at different pressures and depths on their way to the surface.

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Breakdown of orthopyroxene contributing to melt pockets in mantle peridotite xenoliths from the Western Qinling, central China: constraints from in situ LA-ICP-MS mineral analyses

Mineralogy and Petrology ◽

10.1007/s00710-011-0190-6 ◽

2011 ◽

Vol 104 (3-4) ◽

pp. 225-247 ◽

Cited By ~ 10

Author(s):

Ben-Xun Su ◽

Hong-Fu Zhang ◽

Yue-Heng Yang ◽

Patrick Asamoah Sakyi ◽

Ji-Feng Ying ◽

...

Keyword(s):

Mantle Peridotite ◽

Central China ◽

Western Qinling ◽

Peridotite Xenoliths ◽

Icp Ms ◽

Melt Pockets ◽

Mineral Analyses

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New K–AR ages of tchabal mbabo alkaline volcano massif, Cameroon volcanic line and adamawa plateau (central Africa)

International Journal of Advanced Geosciences ◽

10.14419/ijag.v4i2.6516 ◽

2016 ◽

Vol 4 (2) ◽

pp. 62 ◽

Cited By ~ 3

Author(s):

Fagny Mefire Aminatou ◽

Nkouandou Oumarou Faarouk ◽

Temdjim Robert ◽

Bardintzeff Jacques-Marie ◽

Guillou Herve ◽

...

Keyword(s):

Central Africa ◽

Magmatic Activity ◽

Cameroon Volcanic Line ◽

Ti Oxides ◽

Pan African ◽

Three Samples ◽

Icp Ms ◽

Plateau Central ◽

Lithospheric Mantle Source ◽

Ar Geochronology

Tchabal Mbabo in Central Africa is a voluminous volcano massif composed of alkali lava series. K-Ar geochronology data obtained from three samples of basanite - trachyandesite composition defined at least two volcanic activities. The first at end Eocene (38.22 ± 0.80 Ma) and the second during Oligocene (28.88 ± 0.61 and 28.60 ± 0.60Ma). The distribution of different ages along the Cameroon Volcanic Line is difficult to council with any migration of magmatic activity, as previously suggested. The most realistic scenario for the formation of Cameroon Line is that the ascent of lavas has been favored by the crustal discontinuities inherited from the Pan-African orogeny and reactivated during Mesozoic and Cenozoic. ICP MS and ICP AES analyses show that basanite lavas are the result of 2 % melting of sub-lithospheric mantle source containing garnet and phlogopite phases; the trachyandesites are formed by fractional crystallization of K-feldspar, amphibole, clinopyroxene and Fe-Ti oxides.

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Ni-in-garnet geothermometry in mantle rocks: a high pressure experimental recalibration between 1100 and 1325 °C

Contributions to Mineralogy and Petrology ◽

10.1007/s00410-021-01791-8 ◽

2021 ◽

Vol 176 (5) ◽

Author(s):

Z. J. Sudholz ◽

G. M. Yaxley ◽

A. L. Jaques ◽

J. Chen

Keyword(s):

Mole Fraction ◽

Inductively Coupled Plasma ◽

Wave Length ◽

Mantle Peridotite ◽

Garnet Peridotite ◽

Piston Cylinder ◽

Starting Mixture ◽

Peridotite Xenoliths ◽

Icp Ms ◽

New Formulation

AbstractThe temperature-dependent exchange of Ni and Mg between garnet and olivine in mantle peridotite is an important geothermometer for determining temperature variations in the upper mantle and the diamond potential of kimberlites. Existing calibrations of the Ni-in-garnet geothermometer show considerable differences in estimated temperature above and below 1100 °C hindering its confident application. In this study, we present the results from new synthesis experiments conducted on a piston cylinder apparatus at 2.25–4.5 GPa and 1100–1325 °C. Our experimental approach was to equilibrate a Ni-free Cr-pyrope-rich garnet starting mixture made from sintered oxides with natural olivine capsules (Niolv ≅ 3000 ppm) to produce an experimental charge comprised entirely of peridotitic pyrope garnet with trace abundances of Ni (10–100 s of ppm). Experimental runs products were analysed by wave-length dispersive electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We use the partition coefficient for the distribution of Ni between our garnet experimental charge and the olivine capsule $$\left( {{\text{lnD}}_{{{\text{grt}}/{\text{olv}}}}^{{{\text{Ni}}}} ; \frac{{{\text{Ni}}_{{{\text{grt}}}} }}{{{\text{Ni}}_{{{\text{olv}}}} }}} \right)$$ lnD grt / olv Ni ; Ni grt Ni olv , the Ca mole fraction in garnet ($${\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Ca}};$$ X grt Ca ; Ca/(Ca + Fe + Mg)), and the Cr mole fraction in garnet ($${\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Cr}};$$ X grt Cr ; Cr/(Cr + Al)) to develop a new formulation of the Ni-in-garnet geothermometer that performs more reliably on experimental and natural datasets than existing calibrations. Our updated Ni-in-garnet geothermometer is defined here as:$$T \left(^\circ{\rm C} \right)=\frac{-8254.568}{\left(\left( {\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Ca}} \times 3.023 \right)+\left({\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Cr}} \times 2.307 \right)+\left({\mathrm{lnD}}_{\frac{\mathrm{grt}}{\mathrm{olv}}}^{\mathrm{Ni}} - 2.639 \right)\right)}-273\pm 55$$ T ∘ C = - 8254.568 X grt Ca × 3.023 + X grt Cr × 2.307 + lnD grt olv Ni - 2.639 - 273 ± 55 where $${\mathrm{D}}_{\mathrm{grt}/\mathrm{olv}}^{\mathrm{Ni}}= \frac{{\mathrm{Ni}}_{\mathrm{grt}}}{{\mathrm{Ni}}_{\mathrm{olv}}},$$ D grt / olv Ni = Ni grt Ni olv , Ni is in ppm, $${\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Ca}}$$ X grt Ca = Ca/(Ca + Fe + Mg) in garnet, and $${\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Cr}}$$ X grt Cr = Cr/(Cr + Al) in garnet. Our updated Ni-in-garnet geothermometer can be applied to garnet peridotite xenoliths or monomineralic garnet xenocrysts derived from disaggregation of a peridotite source. Our calibration can be used as a single grain geothermometer by assuming an average mantle olivine Ni concentration of 3000 ppm. To maximise the reliability of temperature estimates made from our Ni-in-garnet geothermometer, we provide users with a data quality protocol method which can be applied to all garnet EPMA and LA-ICP-MS analyses prior to Ni-in-garnet geothermometry. The temperature uncertainty of our updated calibration has been rigorously propagated by incorporating all analytical and experimental uncertainties. We have found that our Ni-in-garnet temperature estimates have a maximum associated uncertainty of ± 55 °C. The improved performance of our updated calibration is demonstrated through its application to previously published experimental datasets and on natural, well-characterised garnet peridotite xenoliths from a variety of published datasets, including the diamondiferous Diavik and Ekati kimberlite pipes from the Lac de Gras kimberlite field, Canada. Our new calibration better aligns temperature estimates using the Ni-in-garnet geothermometer with those estimated by the widely used (Nimis and Taylor, Contrib Mineral Petrol 139:541–554, 2000) enstatite-in-clinopyroxene geothermometer, and confirms an improvement in performance of the new calibration relative to existing versions of the Ni-in-garnet geothermometer.

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U/pb dating of precambrian rocks from northern cameroon, orogenic evolution and chronology of the pan-african belt of central africa

Precambrian Research ◽

10.1016/0301-9268(87)90040-4 ◽

1987 ◽

Vol 37 (1) ◽

pp. 71-87 ◽

Cited By ~ 83

Author(s):

S.F. Toteu ◽

A. Michard ◽

J.M. Bertrand ◽

G. Rocci

Keyword(s):

Central Africa ◽

Precambrian Rocks ◽

Pan African ◽

Northern Cameroon

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Microscale effects of melt infiltration into the lithospheric mantle: Peridotite xenoliths from Xilong, South China

Lithos ◽

10.1016/j.lithos.2015.06.013 ◽

2015 ◽

Vol 232 ◽

pp. 111-123 ◽

Cited By ~ 9

Author(s):

Jianggu Lu ◽

Jianping Zheng ◽

William L. Griffin ◽

Suzanne Y. O'Reilly ◽

Norman J. Pearson

Keyword(s):

South China ◽

Lithospheric Mantle ◽

Mantle Peridotite ◽

Peridotite Xenoliths ◽

Melt Infiltration

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Geochemistry evolution of Schists of northwest Obudu area southeastern Nigeria

Global Journal of Geological Sciences ◽

10.4314/gjgs.v19i1.3 ◽

2021 ◽

Vol 19 (1) ◽

pp. 29-39

Author(s):

Young Ezenwa Obioha

Keyword(s):

Modal Analysis ◽

Average Concentration ◽

Metamorphic Grade ◽

Geochemical Evolution ◽

Structural Studies ◽

African Continent ◽

Southeastern Nigeria ◽

Accessory Minerals ◽

Pan African ◽

Icp Ms

Geochemistry of schists of Obudu area was carried out using ICP-MS and ICP-ES techniques in order to determine the geochemical evolution of the area. 40 samples were analyzed for their major, trace and REE composition. Field mapping revealed that gneisses, amphibolites and schists comprising migmatitic schists (MS), quartz-mica schists (QMS), garnet-mica schists (GMS), and hornblende biotite schists (HBS), intruded by granites, granodiorites, quartzofeldspathic rocks and dolerites occur in the area. Structural studies revealed that the schists trend approximately NE–SW (5 – 30o ) indicating the Pan-African event. Modal analysis revealed that the schists have average concentration of quartz (15vol.%), plagioclase (An45-19 vol.%), biotite (15vol.%), garnet (9.0vol.%) and muscovite (6vol.%), the remaining consists of accessory minerals. Geochemistry showed that all the schists have molecular Al2O3 > CaO+K2O+Na2O, indicating they are peraluminous metasedimentary pelites. Trace and REE element results show that all the analyzed schist samples are depleted in Hg, Ag, Be, Bi, and Sb below < 1.0ppm, but relatively enriched in Ba, Sr and Zr with average concentration of 996, 675.73, 243.13 ppm respective. The HREE are depleted with ΣHREE < 10.2, but the LREE are relatively enriched with ΣLREE > 289.54. The ΣLREE/ΣHREE ratio ranges from 9.17 to 33.4, with a large positive delta V at Eu. These findings indicate that the schists of Northwest Obudu area are highly fractionated and had attained at least the uppermost amphibolite metamorphic grade. The schists had contributed to the development of the Pan-African continent.

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