ABSTRACT
Neoproterozoic phyllites from the Akuapim range, a prominent part of the Togo Structural
Unit forms part of the Pan-African Dahoeyide orogen exposed at the southeastern part of
Ghana. The area of study exhibit three varieties of phyllites which are carbonaceous, ironstained
and micaceous phyllites. These phyllites have been analyzed for their mineralogical
and geochemical characteristics to infer their source -area weathering, source rock composition
and tectonic setting. The mineralogical content of ten (10) samples were determined using Xray
diffraction method. Twenty-eight (28) samples were analyzed for their major, trace and
rare earth element compositions using ICP-AES and ICP-MS. From the mineralogy, the
phyllites are composed of quartz, feldspar, muscovite, chlorite, illite with some siderite,
graphite and calcium carbonate. Compared to post-Archean Australian average Shale (PAAS),
the phyllites are depleted in major elements with the exception of SiO2 and MnO which are
enriched relative to PAAS. The phyllites show relative depletions in transition metals such as
Sc, V and Cr whereas high field strength elements such as Zr, Hf, Y and Th are at an average
to above-average concentrations as compared to PAAS. The phyllites show a single trend of
LREE enrichment (average LaN/SmN = 3.78), nearly flat HREE and negative Eu anomaly
(average Eu/Eu* = 0.61) similar to the trend of post-Archean Australian average shale. From
geochemistry, the phyllites can be classified mostly as quartz-rich with few quartzintermediate.
Al2O3 shows positive correlations with Sc, V, Cr, Rb, Sr, Cs, Ba and Y
suggesting that these elements are primarily controlled by the dominant clay minerals. High
values of K2O/Na2O (average = 54.31) and SiO2/Al2O3 (average = 8.17) of the phyllites
indicates compositional maturity of the sediments. The phyllites reveal high concentrations of
Zr (average = 408.08 ppm) which suggests sedimentary sorting. This is supported by the plot
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of Th/Sc against Zr/Sc. High Chemical Index of Alteration (average = 74.73%), Plagioclase
Index of Alteration (average = 87.68%), Chemical Index of Weathering (average = 98.36%),
Rb/Sr (average = 4.22), Th/U (average = 4.09) values and low Index of Compositional
Variability (average = 0.64) values of the analyzed samples indicate intense chemical
weathering in the source areas. On the A-CN-K ternary diagram, data for the Neoproterozoic
phyllites from the Akuapim range plot in a trend (along A-K line) indicating intense chemical
weathering. The phyllites show geochemical characteristics typical of sediments derived from
old Upper Continental Crust. Modeling of the average phyllites using the relatively immobile
REEs and Th/Sc shows that the sediments are composed of a mixture of 80% Upper
Continental Crust and 20% granite. The phyllites show mineralogical and geochemical
characteristics indicative of sediments deposited within a passive continental margin and/or
intra-cratonic terrane. The phyllites exhibit provenance characteristics similar to that of the
Kwahu/Bombouaka Group of the Voltaian Basin and the Buem Structural Unit which are
believed to be lateral equivalents and are probably derived from the same source in the
Amazonian Craton.
SAMUEL, B (2021). Geochemistry Of Neoproterozoic Phyllites From The Akuapim Range, Southeastern Ghana. Afribary. Retrieved from https://tracking.afribary.com/works/geochemistry-of-neoproterozoic-phyllites-from-the-akuapim-range-southeastern-ghana
SAMUEL, BONSU "Geochemistry Of Neoproterozoic Phyllites From The Akuapim Range, Southeastern Ghana" Afribary. Afribary, 19 Apr. 2021, https://tracking.afribary.com/works/geochemistry-of-neoproterozoic-phyllites-from-the-akuapim-range-southeastern-ghana. Accessed 09 Nov. 2024.
SAMUEL, BONSU . "Geochemistry Of Neoproterozoic Phyllites From The Akuapim Range, Southeastern Ghana". Afribary, Afribary, 19 Apr. 2021. Web. 09 Nov. 2024. < https://tracking.afribary.com/works/geochemistry-of-neoproterozoic-phyllites-from-the-akuapim-range-southeastern-ghana >.
SAMUEL, BONSU . "Geochemistry Of Neoproterozoic Phyllites From The Akuapim Range, Southeastern Ghana" Afribary (2021). Accessed November 09, 2024. https://tracking.afribary.com/works/geochemistry-of-neoproterozoic-phyllites-from-the-akuapim-range-southeastern-ghana