scholarly journals Petrology and Geochemistry of Hama Koussou Dolerite Dyke Swarms (North Cameroon, Central Africa)

2019 ◽  
pp. 1-19
Author(s):  
Fagny Mefire Aminatou ◽  
Bardintzeff Jacques-Marie ◽  
Nkouandou Oumarou Faarouk ◽  
Lika Gbeleng Thomas D’Aquin ◽  
Ngougoure Mouansie Samira
Keyword(s):  
Central Africa ◽  
Alkali Feldspar ◽  
Rift System ◽  
Spinel Lherzolite ◽  
Dolerite Dyke ◽  
Pan African ◽  
Tholeiite Basalt ◽  
Petrology And Geochemistry ◽  
African Rift ◽  
Geochemical Analyses

The Pan African granitoid basement of Hama Koussou Cretaceous half basin in North Cameroun (Central Africa) is transected by near N-S, NE-SW and ENE-WSW giant doleritic dykes trending along the same Pan African directions. Hama Koussou dolerites are compliant with the regional distension that occurred after the Pan African basement consolidation prior to the development of West and Central African Rift System at Late Jurassic-Early Cretaceous times. Studied lavas are composed of large clinopyroxene oïkocrysts, plagioclase and alkali feldspar laths and oxides phenocrysts exhibiting ophitic, sub-ophitic and intercertal textures. Microprobe chemical analyses carry out on the main mineral phases show that clinopyroxenes are diopside and augite, plagioclases are labradorite, andesine, oligoclase and albite and alkali feldspars are mainly sanidine with a few percent of orthoclase. ICP-MS and ICP-AES geochemical analyses of Hama Koussou lavas exhibit basalt, basaltic trachyandesite and trachyandesite compositions of continental tholeiite features. Tholeiite basalts of Hama Koussou are the results of high partial melting of E-MORB mantle source of spinel lherzolite composition, located at 65-55 km depth. More evolved tholeiite lavas of Hama Koussou basin are the products of tholeiite basalt differentiation trough assimilation and fractional crystallization coupled with fluids circulation.

scholarly journals The dolerite dyke swarm of Mongo, Guéra Massif (Chad, Central Africa): Geological setting, petrography and geochemistry

2017 ◽  
Vol 9 (1) ◽  
Author(s):  
Oumarou Faarouk Nkouandou ◽  
Jacques-Marie Bardintzeff ◽  
Oumar Mahamat ◽  
Aminatou Fagny Mefire ◽  
Alembert Alexandre Ganwa
Keyword(s):  
Central Africa ◽  
Dyke Swarm ◽  
Dolerite Dyke ◽  
Geological Setting ◽  
Pan African ◽  
Basement Rocks

AbstractDolerite dykes are widespread in the Mongo area within the granitic Guéra Massif (Chad, Central Africa). Dykes are several hundred metres to several kilometres long, a metre to decametre thick, and vertical, crosscutting the Pan-African granitic basement rocks. They are controlled by major Pan-African NNE-SSW, NE-SW and ENE-WSW faults. Rocks constituting the dykes exhibit typical doleritic textures (

Geochronology of the Nabwal Hills: a record of earliest magmatism in the northern Kenyan Rift Valley

2005 ◽  
Vol 143 (1) ◽  
pp. 25-39 ◽  
Author(s):  
IAN McDOUGALL ◽  
RONALD T. WATKINS
Keyword(s):  
Late Miocene ◽  
Alkali Feldspar ◽  
East African Rift ◽  
Late Eocene ◽  
Rift System ◽  
Crustal Extension ◽  
East African Rift System ◽  
East African ◽  
Metamorphic Basement ◽  
African Rift

The Nabwal Hills, northeast of Lake Turkana, contain a record of magmatism associated with the initiation and early development of the East African Rift System in northernmost Kenya. The predominantly volcanic Asille Group, 1400 m thick, directly overlies metamorphic basement and comprises a sequence of basaltic lava flows with significant intervals of rhyolitic pyroclastic units, and minor intercalations of fluviatile sediments. The basement gneisses yield K–Ar cooling ages on biotite of 510 and 522 Ma, typically Pan-African. The 40Ar–39Ar ages on alkali feldspar crystals from the rhyolitic units are concordant and show that the Asille Group spans an interval from at least 34.3 to 15.8 Ma, continuing to at least as young as 13 Ma based on previous measurements. Vertebrate fossil sites, containing primate remains, at Irile and Nabwal are shown to be 17 ± 2 Ma old, Early Miocene, based upon K–Ar age measurements on immediately overlying basalts. Variably reliable whole rock K–Ar ages, determined on basalt samples from low in the sequence, indicate that volcanism commenced as early as 34.8 Ma ago. The overall geochronological results show that magmatism in the Nabwal Hills began about 35 Ma ago in Late Eocene times, interpreted as the time of initiation of crustal extension that led to the development of this segment of the East African Rift System. The Asille Group is tilted about 6° to the SSW. This tilting occurred later than 13 Ma ago, and prior to the eruption of the flat-lying Gombe Group basalts. These basalts may have begun erupting about 6 Ma ago in Late Miocene times, although much of this volcanism occurred between about 3.9 and 4.2 Ma ago in Pliocene times. It is suggested that the main rifting, which continues today, commenced in Late Miocene times, less than 13 Ma ago, and is partly reflected in the tilting of the Asille Group.

A new mantle xenolith locality from Simien shield volcano, NW Ethiopia

2008 ◽  
Vol 146 (1) ◽  
pp. 144-149 ◽  
Author(s):  
DEREJE AYALEW ◽  
NICK ARNDT ◽  
FLORENCE BASTIEN ◽  
GEZAHEGN YIRGU ◽  
BRUNO KIEFFER
Keyword(s):  
Trace Element ◽  
Electron Probe ◽  
Mantle Xenolith ◽  
Rift System ◽  
Spinel Lherzolite ◽  
Shield Volcano ◽  
East African Rift System ◽  
East African ◽  
Trace Element Contents ◽  
African Rift

AbstractThin-section observations and electron probe analyses, and trace element data are reported from a new mantle xenolith hosted in Miocene alkali basalt from the western flank of Simien shield volcano, Ethiopia. The spinel lherzolite enclaves contain variable proportions of olivine, orthopyroxene, green clinopyroxene and brown spinel, and have undergone deformation and partial recrystallization. They represent unmetasomatized, fertile xenoliths which were subjected to a late-stage melt–rock reaction. Trace element contents of clinopyroxene crystals are extremely low and quite different from those of the other xenoliths within the East African Rift System.

TECTONOMAGMATIC EVOLUTION OF THE EAST AFRICAN RIFT SYSTEM AS DOCUMENTED IN WEST TURKANA, KENYA

2017 ◽  
Author(s):  
Sara Mana ◽  
◽  
Merry Yue Cai ◽  
Catherine C. Beck ◽  
Steven L. Goldstein
Keyword(s):  
East African Rift ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
African Rift

PLIO-PLEISTOCENE PALEOENVIRONMENTS IN WEST TURKANA (EAST AFRICAN RIFT SYSTEM, KENYA)

2020 ◽  
Author(s):  
Alexis Nutz ◽  
◽  
Mathieu Schuster ◽  
Doris Barboni ◽  
Ghislain Gassier ◽  
...  
Keyword(s):  
East African Rift ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
African Rift

scholarly journals Statherian (ca. 1714–1680 Ma) Extension-Related Magmatism and Deformation in the Southwestern Korean Peninsula and Its Geological Significance: Constraints from the Petrological, Structural, Geochemical and Geochronological Studies of Newly Identified Granitoids

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 557
Author(s):  
Byung-Choon Lee ◽  
Weon-Seo Kee ◽  
Uk-Hwan Byun ◽  
Sung-Won Kim
Keyword(s):  
Korean Peninsula ◽  
Tectonic Setting ◽  
Alkali Feldspar ◽  
Ductile Deformation ◽  
Southwestern Part ◽  
The North ◽  
Deformation Event ◽  
Geochemical Analyses ◽  
A Minor ◽  
T Values

In this study, petrological, structural, geochemical, and geochronological analyses of the Statherian alkali feldspar granite and porphyritic alkali feldspar granite in the southwestern part of the Korean Peninsula were conducted to examine petrogenesis of the granitoids and their tectonic setting. Zircon U-Pb dating revealed that the two granites formed around 1.71 Ga and 1.70–1.68 Ga, respectively. The results of the geochemical analyses showed that both of the granites have a high content of K2O, Nb, Ta, and Y, as well as high FeOt/MgO and Ga/Al ratios. Both granites have alkali-calcic characteristics with a ferroan composition, indicating an A-type affinity. Zircon Lu-Hf isotopic compositions yielded negative εHf(t) values (−3.5 to −10.6), indicating a derivation from ancient crustal materials. Both granite types underwent ductile deformation and exhibited a dextral sense of shear with a minor extension component. Based on field relationships and zircon U-Pb dating, it was considered that the deformation event postdated the emplacement of the alkali feldspar granite and terminated soon after the emplacement of the porphyritic alkali feldspar granite in an extensional setting. These data indicated that there were extension-related magmatic activities accompanying ductile deformation in the southwestern part of the Korean Peninsula during 1.71–1.68 Ga. The Statherian extension-related events are well correlated with those in the midwestern part of the Korean and eastern parts of the North China Craton.

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