Outstanding contribution to african geology a tribute to professor maarten de wit (1947 - 2022)

On the 15th April, 2022 Geology lost one of its finest brains and one of the most amiable geologists to my knowledge, Professor Maarten De Wit of South Africa. I first met amiable Maarten on July 3, 1990 while attending the 23rd Geocongress in Cape Town, South Africa. We became instant friends

Preliminary review of the geology of the hornblende biotite gneisses of Obudu Plateau Southeastern Nigeria

The Obudu Plateau, southeastern Nigeria is dominantly underlain by gneissose rocks with migmatitic characteristics, one of which is the hornblende-biotite gneiss. The gneisses are banded with quartz and plagioclase as the major minerals in the leucosome while hornblende and biotite occur in the palaeosome. Geochemically, the rocks are enriched in silica and alumina with an average of 71.6wt% and 14wt% respectively. Geochemical plots indicate that they are calc-alkaline to tholeiitic in character and derived from protholiths of igneous origin with minor sedimentary input.KEYWORDS: Obudu Plateau, migmatitic gneiss, calc-alkalin

P-T conditions of Pan-African orogeny in southeastern Nigeria

Abstract Different rock types from the area northeast of Obudu, southeastern Nigeria were investigated in order to place constraints on their metamorphic conditions. Detailed petrographic studies indicate four main rock groups in the studied area, namely migmatitic gneiss, migmatitic schist, granite gneiss and a minor amount of amphibolite, metagabbro and dolerite. The chemistry of minerals in these rocks is used to estimate metamorphic pressure and temperature (P-T) using appropriate geothermometers and geobarometers. The estimated temperature for migmatitic gneiss of the area is ∼600–625 °C and 600–650 °C for migmatitic schist; the pressure is ∼ 8 kbar. For amphibolite the temperature is ∼600–700 °C and pressure is 8–12 kbar. The estimated pressures and temperatures for the northeast Obudu rocks correspond to upper amphibolite to lower granulite facies metamorphism. The metamorphism occurred due to continent-continent collision during the Pan-African orogeny, most likely during the D1 deformational phase of the area. The recorded high pressures possibly resulted from crustal thickening in the area. P-T conditions for Pan-African orogeny in northeast Obudu area are in good agreement with P-T estimations for the Pan-African event in adjacent areas

Geochemistry of crystalline basement rocks SW Ugep, Nigeria

Geochemical data on low-grade metasedimentary phyllites and schists of SW Ugep show that they were derived from predominantly pelitic parent rocks. They form a supracrustal cover on an orthogneiss of granitic composition. The metasediments are enriched in Si02, Al203 and Zr but improverished in Ni. Intrusion of pegmatite was accompanied by boron metasomatism and tourmalinization. This, as well as, the unconformable contact of the basement rocks with calcareous sandstone of Cretaceous age, may have raised the Na20, Si02, Ca0 and Mg0 contents of some outcrops. The Ti02, Al203 values (0.033 to 0.144) confirm that the metasediments were derived from a parent rock rich in quartz and clay. A dark- coloured garnet-mica schist has a composition of metagreywacke. The first episode of calc-alkaline magmatism in the area shows the emplacement of the peraluminous orthogneiss whilst the last episode indicates the intrusion of the granodiorite. Rocks in SW Ugep area correlate well in both petrography and geochemistry with those of Uwet area in the south. This confirms earlier studies, which indicated that metasedimentary schists occur in the Oban massif of southeast Nigeria and that metamorphism in the area increased in grade from upper greenschist facies in the west to upper amphibolite and locally granulite facies in the east. Key Words: Ugep, metasediments, orthogneiss, metasomatism. [Global Jnl Geol. Sci. Vol.1(2) 2003: 143-158

PETROGENESIS OF SCHISTS IN SOUTHEAST LOKOJA, CENTRAL NIGERIA

Schists in southeast Lokoja, central Nigeria are enriched in Si02 and AI203. Cr, Ni and Tio2 are also relatively high in these rocks. The chemical compositions of the schists indicate that they were derived from a shale-greywacke sequence of sedimentary rocks. As a result, they have high Ti02/Al203 and variable K20/ Na20 ratios. The grey wackes had a granodioritic provenance. The high Ti02 and Ni content of these metasediments suggest that mafic debris were possibly mixed in their source- rocks. The schists are products of metamorphism of immature sediments which were deposited in an intracratonic extensional basin. Available geochronological data indicate that most intensive reworking of these sedimentary rocks occurred ca. 687±13 Ma ago during the Pan African orogency. Earlier metamorphism of the sediments could have occurred ca. 1315 Ma ago during the Kibaran orogeny. Keywords: Lokoja, shale-greywacke, immature-sediments, Pan-African, Kibaran [Global Jnl Geol. Sci. Vol.1(1) 2003: 29-42

Rare Earth Element Geochemistry And Protoliths Of Schists In Southeast Lokoja, Central Nigeria

The Nigerian schist belts constitute the most important lithologic units necessary for the unravelling of the geochemical and geodynamic evolution of the basement complex. The schists have however undergone extensive alterations owing to weathering and metamorphism. REE abundance and distribution patterns of Lokoja schists indicate that the schist belts are metamorphosed shale-greywacke sequence. Their provenance possibly contained volcanogenic debris and the passive margin of the West African craton provided most of the materials. The reworking and metamorphism of the sediments took place during the Pan-African Orogeny ca. 687 Ma ago. KEY WORDS: Schists, Provenance, Reworking, Rare Earth Element, Evolution Global Journal of Geological Sciences Vol.3(1) 2005: 9-1

Preliminary investigation of pegmatites in Obudu Area, Southeastern Nigeria, using stream sediments geochemistry

Stream sediments of Obudu Plateau were investigated with a view to elucidating their geochemical features, mineralization potentials and element concentrations. Stream sediment samples were collected from Southern Obudu Plateau area and analyzed for 22 elements, comprising major and trace elements, using Inductively Coupled Plasma – Mass Spectrometry (ICP-MS). The data obtained were statistically treated. Ba, Sr, Nb, Co, Pb, Ta and Na show moderate to high concentrations, when compared with threshold values of these elements. The concentrations of these elements in sediments of Southern Obudu show low mineralization potentials of pegmatites of the Obudu Plateau. The elements in Obudu stream sediments show perfect, strong, moderate and weak correlations among themselves, indicative of variations in their mobility.Keywords: Correlation matrix, Major and Trace Elements, Stream sediments, Threshol