Geochemistry and Petrogenetic Relationships Between Pegmatites and Host Rocks in the Keffi Area, North Central, Nigeria

Keffi pegmatites area which contains numerous mineralised and non-mineralised pegmatites lie between the Wamba pegmatite field to the NE and Nasarawa pegmatite field to the SW on the North Central Pegmatite belt of Nigeria. In Keffi area exploitation of deposits is currently being done by small scale miners, whose activities are haphazard and uncoordinated, because of that information on the geology and petrology that will enable a systematic study of the pegmatites in the area is scanty. Systematic geochemical investigations of the pegmatites and surrounding host rocks aimed at establishing petrogenetic relationships amongst the various rock types in the area were conducted. Major, trace and REE investigations of the pegmatites and associated granitoids have indicated petrogenetic relationships amongst the pegmatites and between the pegmatites and surrounding granitoids of Keffi area. Also, the variation diagram of major, trace and REE in whole rocks and K-feldspar samples show patterns which categorised the pegmatites of Keffi area into; (1) Non-mineralised, (2) intermediate and (3) mineralised pegmatites. It was also deduced from the geochemical characteristics (variation diagrams in major and trace element, REE geochemistry and tectonic environment classification) that a genetic model based on the evolution of melt by partial melting of metasedimentary protolith during ultrametamorphic and deformational activities (anatexis) is proposed for the granite-pegmatite system of Keffi area. This information will be useful as guide for fruitful exploration of the pegmatites and serves as model for the exploitation of pegmatite veins in similar geologic settings.

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The petrology and age of alkaline mafic lavas from the nunatak zone of central East Greenland

Bulletin Grønlands Geologiske Undersøgelse ◽

10.34194/bullggu.v133.6675 ◽

1979 ◽

Vol 133 ◽

pp. 1-28

Author(s):

C.K Brooks ◽

A.K Pedersen ◽

D.C Rex

Keyword(s):

Partial Melting ◽

Fracture Zone ◽

Small Scale ◽

Limited Extent ◽

East Greenland ◽

Rock Types ◽

Basaltic Magmas ◽

Mafic Lavas ◽

Late Stages ◽

Primary Magmas

Alkaline basic lavas occurring as outcrops of limited extent in the nunatak zone of East Greenland beyond the head of Kejser Franz Josephs Fjord have been examined in detail on the basis of new collections. These rocks show considerable diversity and include highly magnesian, perovskite-bearing nephelinites, slightly less magnesian nephelinites, basanitoids and nepheline hawaiites. Phonolite, reported earlier, is absent from the new collection. Apart from the perovskite-bearing nephelinites, probably primary magmas derived by small degrees of partial melting of normal mantle, these rock types have evolved in a complicated way and do not appear to be related by low pressure processes. While it is possible that alkaline basaltic magmas have been a widespread feature in the late stages of volcanism in this part of East Greenland, the nephelinites appear to be restricted to intracontinental areas. They represent small-scale flank activity possibly related to the prolongation of the Jan Mayen fracture zone.

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The importance of in situ crystallisation and loss of interstitial melt during formation of the Kærven Syenite Complex, Kangerlussuaq, East Greenland

Bulletin of the Geological Society of Denmark ◽

10.37570/bgsd-2019-67-07 ◽

2020 ◽

Vol 67 ◽

pp. 107-146

Author(s):

Paul Martin Holm ◽

Niels-Ole Prægel

Keyword(s):

Alkali Feldspar ◽

Fractional Crystallisation ◽

Geochemical Data ◽

Magma Chambers ◽

Quartz Syenite ◽

East Greenland ◽

The North ◽

Rock Types ◽

Host Rocks ◽

Residual Melt

The Kærven Syenite Complex (KSC) is one of the oldest felsic intrusions in the Tertiary East Greenland province. Here we update our previous description of the KSC and supply a greatly expanded and comprehensive geochemical dataset. New data allow us to present a more detailed petrogenetic model for the evolution of the KSC and to investigate the geochemical characteristics of igneous cumulates subjected to loss and, occasionally, replacement of residual liquid. The KSC comprises eleven mappable units that generally young westwards. Rock types range from quartz syenite to quartz alkali feldspar syenite and alkali feldspar granite. Individual intrusive units are relatively narrow and steep-sided and are collectively suggested to represent a ring dyke complex. Basement gneiss and gabbro host rocks have locally contaminated the oldest quartz syenite KSC unit, but most of the main part of the complex escaped significant influence from host rocks. A late suite of E–W to NE–SW striking peralkaline dykes of trachytic to phonolitic compositions intrude the KSC. Compositions of the KSC rocks span a considerable range in SiO2, 59–73 wt%. Concentrations of several elements vary widely for a given SiO2 (especially at SiO2 < 66 wt%), and variation diagrams do not suggest a single model for the evolution of the units of the complex. A cumulative origin is envisaged for several KSC units. Geochemical modelling suggests that KSC magmas were derived from more than one primary magma, and that the complex evolved through a four-stage process: fractional crystallisation in precursory magma chambers was followed by final emplacement of each unit, establishment of a crystal/melt mush, expulsion of part of the residual melt and, finally, crystallisation of the remaining melt. Trace element disequilibria between alkali feldspar and host rocks in two closely associated quartz alkali feldspar syenite units indicate that highly evolved residual melt was replaced by a less evolved melt phase. Modelling of potential parent melt compositions to the Kærven magmas suggests an origin not in the Iceland plume asthenosphere, but rather in a moderately enriched source, possibly in the continental lithosphere. The course of melt evolution by fractional crystallisation is indicated to have taken place in magma chambers at depth, and repeated rise of magma into the upper crustal magma chambers and crystallisation there formed the KSC. Based on our survey of published geochemical data, the inferred parental magmas seem to have few equivalents in the North Atlantic Igneous Province and may have been generated mainly from melting of enriched dry lithospheric mantle of possibly Archaean age.

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Partial melting of zoisite eclogite from the Sanddal area, North-East Greenland Caledonides

European Journal of Mineralogy ◽

10.5194/ejm-32-405-2020 ◽

2020 ◽

Vol 32 (4) ◽

pp. 405-425 ◽

Cited By ~ 2

Author(s):

Wentao Cao ◽

Jane A. Gilotti ◽

Hans-Joachim Massonne

Keyword(s):

Partial Melting ◽

Mineral Assemblage ◽

Peak Pressure ◽

Bulk Rock ◽

East Greenland ◽

Equilibrium Modeling ◽

North East ◽

The North ◽

Area North ◽

T Path

Abstract. Metamorphic textures and a pressure–temperature (P–T) path of zoisite eclogite are presented to better understand the metamorphic evolution of the North-East Greenland eclogite province and this particular type of eclogite. The eclogite contained the mineral assemblage garnet, omphacite, kyanite, phengite, quartz and rutile at peak pressure. Partial melting occurred via breakdown of hydrous phases, paragonite, phengite and zoisite, based on (1) polymineralic inclusions of albite and K-feldspar with cusps into host garnet, (2) small euhedral garnet with straight boundaries against plagioclase, (3) cusps of plagioclase into surrounding phases (such as garnet), and (4) graphic intergrowth of plagioclase and amphibole next to anhedral zoisite grains. Isochemical phase equilibrium modeling of a melt-reintegrated composition, along with XNa-in-omphacite and Si-in-phengite isopleths, yields a peak pressure of 2.4±0.1 GPa at 830±30 ∘C. A peak temperature of 900±50 ∘C at 1.9±0.2 GPa is determined using the rim composition of small euhedral garnet, as predicted by modeling a crystallized melt pocket. Zoisite growth at the expense of kyanite suggests that the P–T path crossed the fields of zoisite growth at ∼1.9 GPa, 800–900 ∘C on the modeled phase diagram of the bulk rock. A point on the exhumation path at ∼1.3 GPa and 750 ∘C is derived from hornblende-plagioclase thermometry and Al-in-hornblende barometry. The study demonstrates that paragonite, phengite and zoisite could contribute to partial melting of eclogite at near-peak P and during exhumation.

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The Upper Critical Zone in the Swartklip Sector, north-western Bushveld Complex, on the farm Wilgerspruit 2JQ: II. Origin by intrusion of ultramafic sills with concomitant partial melting of host norite-anorthosite cumulates

South African Journal of Geology ◽

10.25131/sajg.122.0011 ◽

2019 ◽

Vol 122 (2) ◽

pp. 143-162 ◽

Cited By ~ 6

Author(s):

A.A. Mitchell ◽

R.N. Scoon ◽

M.R. Sharpe

Keyword(s):

Partial Melting ◽

Bushveld Complex ◽

Critical Zone ◽

Merensky Reef ◽

The North ◽

Host Rocks ◽

North Western ◽

Different Levels

Abstract In the Bushveld Complex, the ultramafic (orthopyroxenite/harzburgite with chromitite) layers that host most of the PGE and chromite mineralization in the Upper Critical Zone display well-documented discordant basal contacts with their anorthositic and noritic host rocks. Whilst not so well documented, there is evidence that the upper contacts of these units are also discordant. We review the nature of the contacts between the ultramafic units and adjacent plagioclase-rich lithologies. These include contact phenomena like pegmatoidal lithologies and thin magmatic reaction chromite stringers. We conclude that most, if not all, ultramafic layers were intruded as sills into pre-existing norite/anorthosite cumulates. The sequence of norites and anorthosites that hosts the ultramafic layers was built up by a prior series of multiple tholeiitic (A-type) magma intrusions. The spectrum of lithologies from melanorite through to (mottled) anorthosite represents differing degrees of partial melting in response to these successive magma influxes. Density and competence contrasts between layers of plagioclase-rich rocks in turn provided pathways for sill propagation of subsequent ultramafic (U-type) magmas. The ultramafic magmas further modified the host norites and anorthosites by processes of partial melting and metasomatism. The ultramafic units themselves accumulated as composite sills in response to multiple magma injections. In the western Bushveld Complex, particularly including the Swartklip Sector in the north-western part of the complex, the Merensky Reef is represented by various facies that occur at different levels in the host stratigraphy. This phenomenon has been referred to by the term “regional potholing”, and has been attributed to the erosion of footwall cumulates by new influxes of magma. We suggest that a series of step-and-stair-type transitions of intruding sills to successive stratigraphic levels might more appropriately explain the various facies of the Merensky Reef.

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INTERPRETATION OF AEROMAGNETIC DATA AND LANDSAT IMAGERY OVER THE NIGERIAN YOUNGER GRANITES IN AND AROUND KAFANCHAN AREA, NORTH-CENTRAL NIGERIA

FUDMA Journal of Sciences ◽

10.33003/fjs-2020-0404-489 ◽

2021 ◽

Vol 4 (4) ◽

pp. 323-333

Author(s):

S. Mustapha ◽

S. Suleman ◽

S. R. Iliyasu ◽

E. E. Udensi ◽

Y. A. Sanusi ◽

...

Keyword(s):

Landsat Imagery ◽

Magnetic Anomalies ◽

Biotite Granite ◽

Aeromagnetic Data ◽

North Central ◽

The North ◽

Area North ◽

First Vertical Derivative ◽

Basic Igneous Rock ◽

Western Half

In this research the lineaments of the Kafanchan area in North-central Nigeria were investigated in order to explore the mineralization zones of the area. Aeromagnetic data over Kafanchan and environs within the Younger Granite Province, in the North-Central Nigeria were collated and analyzed. The aeromagnetic map of the area was interpreted both qualitatively and quantitatively so as to identify the nature of the magnetic sources and the trends direction in the study area. The trend of the Total Magnetic Intensity (TMI) map is predominantly in NE-SW. The First Vertical Derivative (FVD) Lineaments Map was also correlated with LADSAT lineaments map and both maps agreed in most areas. The study area is characterized by predominant magnetic lineament trend in NE-SW direction and subordinate E-W direction. The result also shows that the most significant structural trends affecting the distribution of these magnetic anomalies in the study area is in NE-SW direction. The TMI map indicates that there are three major mineralization zones in the study area. The high magnetization contrast in the NE and SE parts of the study area correlates with the migmatite-gneiss, biotite-granites, granites and basalts which are associated with high magnetic contrasts. Also, the high magnetization contrast in the NW part of the area correlates with basalt and the biotite-granite. However, the predominant low magnetization contrast observed in the western half does not correlate with the basic igneous rock

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Hopscotch Modernism: On Everyday Life and the Blurring of Art and Social Science

Modernist Cultures ◽

10.3366/e2041102209000197 ◽

2006 ◽

Vol 2 (1) ◽

pp. 70-79 ◽

Cited By ~ 7

Author(s):

Ben Highmore

Keyword(s):

Twentieth Century ◽

Social Science ◽

Everyday Life ◽

Systematic Study ◽

Cultural Practices ◽

Health Centre ◽

Small Scale ◽

Modernist Literature ◽

The Everyday ◽

Point Of Departure

From a remarkably innovative point of departure, Ben Highmore (University of Sussex) suggests that modernist literature and art were not the only cultural practices concerned with reclaiming the everyday and imbuing it with significance. At the same time, Roger Caillois was studying the spontaneous interactions involved in games such as hopscotch, while other small scale institutions such as the Pioneer Health Centre in Peckham, London attempted to reconcile systematic study and knowledge with the non-systematic exchanges in games and play. Highmore suggests that such experiments comprise a less-often recognised ‘modernist heritage’, and argues powerfully for their importance within early-twentieth century anthropology and the newly-emerged field of cultural studies.

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