Petrology and Geochemical Characteristic of Granitoids From Guéra Massif in the Central Part of Chad: An Example of Mixing Magmas

The granitoids of Guéra Massif are composed of biotite-granite, amphibole-biotite granite and gabbro-diorite and commonly contain micro granular mafic enclaves which vary from monzogabbro to syenite composition. They are metaluminous, high-K calc-alkaline to shoshonitic series. Gabbro-diorite rocks are magnesian while amphibole-biotite granites are magnesian to ferroan, and biotite granites are ferroan. They are enriched in LREEs relative to HREE and display negative anomalies in Nb, Ta and Ti. Fields relationships, petrology and geochemistry indicate that mixing and mingling processes could be more relevant for the genesis of granitoids associated to fractional crystallization. Thus, the presence of mafic enclaves of gabbro-diorite composition in the granites, the resumption of alkaline feldspar xenocrystals in the gabbro-diorites, as well as the linear correlation between the granites and the gabbro-diorites and the intermediate position of the mafic enclaves between the two formations, enable us to propose magmatic mixing as the major process that presided over the evolution of the Guéra granitoids. The delamination of the continental lithosphere during the post-collisional phase of the Pan-African orogeny would have caused the partial melting of the subduction-modofied mantle and lower continental crust and thus produced the magmas of the Guéra granitoids.

Download Full-text

Petrology and geochemistry of the Pan-African high-K calc-alkaline to shoshonitic–adakitic Bapé plutonic suites (Adamawa-Yade block, Cameroon): evidence of a hot oceanic crust subduction

International Journal of Earth Sciences ◽

10.1007/s00531-021-02060-6 ◽

2021 ◽

Author(s):

Jacqueline Numbem Tchakounté ◽

Fuh Calistus Gentry ◽

Aurélie Ngamy Kamwa ◽

Metang Victor ◽

Joseph Mvondo Ondoa ◽

...

Keyword(s):

Oceanic Crust ◽

Calc Alkaline ◽

Pan African ◽

High K ◽

Petrology And Geochemistry

Download Full-text

Syn-collisional pan-African granite in the northern part Birnin Gwari schist belt in NW Nigeria

International Journal of Advanced Geosciences ◽

10.14419/ijag.v8i2.31095 ◽

2020 ◽

Vol 8 (2) ◽

pp. 197

Author(s):

Kehinde Oluyede ◽

Urs Klötzli

Keyword(s):

Mafic Magma ◽

Biotite Granite ◽

Trace Element Data ◽

Schist Belt ◽

Calc Alkaline ◽

Fractionation Factor ◽

Volcanic Arc ◽

Pan African ◽

High K ◽

Ree Patterns

Syn-collisional granite in the northern part of the Birnin Gwari schist belt consists dominantly of granite and lesser granodiorite and quartzolite. Petrographic and ge¬ochemical data revealed three granite groups: the biotite-hornblende granite (quartzolite - BHG); the biotite granite (BG) and the biotite-muscovite granite (BMG). The rocks generally have calc-alkaline and high-K calc-alkaline affinities, and calc-alkalic to alkali-calcic, peraluminous and ferroan and magnesian geochemistry. They are characterized by LILE enrichment, high LREE fractionation factor [(La/Yb) (6.74 to 45.14] with weak to moderate negative Eu (Eu/Eu* = 0.38 to 0.62) and strong negative Nb, P and Ti anomalies. Variation in the behavior of lithophile elements (Ba, Sr and Rb) revealed diverse granite trend such as “high and low Ba-Sr”; “normal”, “anomalous” “strongly differentiated” and “granodiorite and quartz diorite” granite. Their display of similar trace elements and REE patterns suggest they are cogenetic. Major and trace element data indicate differentiation of a mafic magma and partial melting of crustal components inherited from shale-greywacke and quartzose sedimentary protoliths in volcanic arc and post collisional settings. The field and geochemical characteristics of this granite suggest that they are similar to other granites in schist belts in other parts of Nigeria, forming the lateral continuation of the same Pan-African magmatic belt.

Download Full-text

The Pan-African high-K calc-alkaline peraluminous Elat granite from southern Israel: geology, geochemistry and petrogenesis

Journal of African Earth Sciences ◽

10.1016/j.jafrearsci.2004.11.005 ◽

2004 ◽

Vol 40 (3-4) ◽

pp. 115-136 ◽

Cited By ~ 36

Author(s):

M. Eyal ◽

B.A. Litvinovsky ◽

Y. Katzir ◽

A.N. Zanvilevich

Keyword(s):

Calc Alkaline ◽

Pan African ◽

High K

Download Full-text

Neoproterozoic magmatic evolution of the southern Ouaddaï Massif (Chad)

BSGF - Earth Sciences Bulletin ◽

10.1051/bsgf/2020032 ◽

2020 ◽

Vol 191 ◽

pp. 34 ◽

Cited By ~ 1

Author(s):

Félix Djerossem ◽

Julien Berger ◽

Olivier Vanderhaeghe ◽

Moussa Isseini ◽

Jérôme Ganne ◽

...

Keyword(s):

Geothermal Gradient ◽

Isotopic Signature ◽

Biotite Granite ◽

Granite Sample ◽

Metasedimentary Rocks ◽

Rock Types ◽

Pan African ◽

High K ◽

Back Arc ◽

Lower Crustal

This paper presents new petrological, geochemical, isotopic (Nd) and geochronological data on magmatic rocks from the poorly known southern Ouaddaï massif, located at the southern edge of the so-called Saharan metacraton. This area is made of greenschist to amphibolite facies metasediments intruded by large pre- to syn-tectonic batholiths of leucogranites and an association of monzonite, granodiorite and biotite granite forming a late tectonic high-K calc-alkaline suite. U-Pb zircon dating yields ages of 635 ± 3 Ma and 613 ± 8 Ma on a peraluminous biotite-leucogranite (containing numerous inherited Archean and Paleoproterozoic zircon cores) and a muscovite-leucogranite, respectively. Geochemical fingerprints are very similar to some evolved Himalayan leucogranites suggesting their parental magmas were formed after muscovite and biotite dehydration melting of metasedimentary rocks. A biotite-granite sample belonging to the late tectonic high-K to shoshonitic suite contains zircon rims that yield an age of 540 ± 5 Ma with concordant inherited cores crystallized around 1050 Ma. Given the high-Mg# (59) andesitic composition of the intermediate pyroxene-monzonite, the very similar trace-element signature between the different rock types and the unradiogenic isotopic signature for Nd, the late-kinematic high-K to shoshonitic rocks formed after melting of the enriched mantle and further differentiation in the crust. These data indicate that the southern Ouaddaï was part of the Pan-African belt. It is proposed that it represents a continental back-arc basin characterized by a high-geothermal gradient during Early Ediacaran leading to anatexis of middle to lower crustal levels. After tectonic inversion during the main Pan-African phase, late kinematic high-K to shoshonitic plutons emplaced during the final post-collisional stage.

Download Full-text

Petrography and Geochemical Characterization of a Granite Batholith in Idanre, Southwestern Nigeria

Sains Malaysiana ◽

10.17576/jsm-2021-5002-04 ◽

2021 ◽

Vol 50 (2) ◽

pp. 315-326

Author(s):

Oluwatoyin O. Akinola ◽

Azman A. Ghani ◽

Elvaene James

Keyword(s):

Calc Alkaline ◽

Southwestern Nigeria ◽

Geochemical Characterization ◽

Fine Grained ◽

Rock Types ◽

Pan African ◽

High K ◽

Granite Batholith ◽

Type Granite

Idanre granite batholith in southwestern Nigeria contain three rock types, namely, Older granite undifferentiated (OGu), Older granite porphyritic (OGp) and Older granite fine-grained (OGf). The granitoids intruded into a basement rock of primarily migmatite gneiss. Petrography indicates that quartz, orthoclase, hornblende, and biotite are common to all members while microcline is more prominent in OGp and plagioclase is poorly represented in OGf. Despite minor differences in petrographic features, the granite units generally have similar geochemical relationships. The average SiO2 contents in OGp (70.49%), OGu (68.7%) and OGf (65.8%) are comparable to similar Pan-African suites located in eastern and northern Nigeria. Na2O+K2O-CaO versus SiO2 diagram shows all the granite members are calcic, K2O vs SiO2 plot classify the granites as high-K calcic alkali to shoshonitic. ANK vs ACNK plot indicatesthey are peraluminous. Plot of A/CNK vs SiO2 and K2O vs Na2O diagrams classified the rock as S-type granite. The granitoids are calc-alkaline with elevated Na2O (>2.6%) and Al/(Na2O+CaO) contents (OGu, 2.1-3.4; OGp, 2.4-3.1 and OGf, 2.2-2.9). The tectonic diagram (Rb vs (Y+Nb) indicatesthatthe batholith is Within Plate Granite (WPG.

Download Full-text

The Genesis of the Askartor Be-Mo Deposit in the North Xinjiang, Northwest China: Evidence From Geology, Geochemistry, U-Pb, and Re-Os Geochronology

Frontiers in Earth Science ◽

10.3389/feart.2021.646772 ◽

2021 ◽

Vol 9 ◽

Author(s):

Tang Yong ◽

Zhang Hui ◽

Lv Zheng-Hang

Keyword(s):

Northwest China ◽

Biotite Granite ◽

Tetrad Effect ◽

Calc Alkaline ◽

Magma Evolution ◽

The North ◽

Altay Orogenic Belt ◽

High K ◽

North Xinjiang ◽

Ore District

The Askartor Be-Mo deposit is located in the southeastern area of the Chinese Altay orogenic belt in Xinjiang, NW China. Zircon U-Pb data show that there are two periods of magmatic activities in the Askartor Be-Mo ore district, namely, the Devonian granodiorite (386.8 ± 2.6 Ma) and biotite granite (385.4 ± 4.4 Ma), and the Triassic two-mica granite (247.5 ± 2.2 Ma) and muscovite granite (231.4 ± 2.0 Ma). The zircon U-Pb age of pegmatoid orebody is 220.6 ± 1.6 Ma which coincides with the molybdenite Re-Os isochron age of 228.7 ± 7.1 Ma. The two-mica and muscovite granites belong to the high-K Calc-alkaline series with peraluminous features, and are characterized by high SiO2 (71.92–75.41 wt%), and Al2O3 (13.43–15.98 wt%), and low TiO2 (0.01–0.25 wt%), Fe2O3 (0.11–1.14 wt%) and CaO (0.07–0.76 wt%). The highly fractionated element ratios of Y/Ho, Zr/Hf and Nb/Ta, and the rare earth element tetrad effect occur in the muscovite granite, indicating the fluid exsolution occurs at the late stage of magma evolution, and the muscovite granite experienced the strong self-metasomatism. Rayleigh fractional calculations show that the Askartor Be-Mo deposit is the product of multistage fractional crystallization of initial Be-enriched magma.

Download Full-text

The Anvil plutonic suite, Faro, Yukon Territory

Canadian Journal of Earth Sciences ◽

10.1139/e85-122 ◽

1985 ◽

Vol 22 (8) ◽

pp. 1204-1216 ◽

Cited By ~ 8

Author(s):

Lee C. Pigage ◽

Robert G. Anderson

Keyword(s):

Alkali Feldspar ◽

Biotite Granite ◽

Yukon Territory ◽

South Fork ◽

Calc Alkaline ◽

Rapid Cooling ◽

High K ◽

Intrusive Activity ◽

High Level ◽

Main Deformation

The Anvil plutonic suite consists of three phases: a peraluminous muscovite–biotite granite (Mount Mye phase) and two metaluminous to peraluminous hornblende–biotite granodiorite and minor granite intrusions (Orchay and Marjorie phases). The suite is massive or foliated, equigranular or seriate, and contains alkali-feldspar megacrysts. The Marjorie phase is characteristically porphyritic.Geochemical trends are irregular for the suite and for individual phases. High-K2O, low-CaO, and low-MgO compositions typify the silicic, calc-alkaline suite. Hornblende-bearing phases contain less SiO2, K2O, and Rb and more cafemic oxides, TiO2, Sr, Ba, and Y than the Mount Mye phase and are compositionally similar to coeval South Fork volcanics.Isochrons from some of the Orchay phase whole-rock samples (t = 99 ± 2.5 Ma; 87Sr/86Sri = 0.7161 ± 0.0001) and from whole rocks and minerals of the Mount Mye phase (t = 100 ± 2 Ma; 87Sr/86Sri = 0.7405 ± 0.0001) indicate they are coeval but not comagmatic, accounting for the lithologic, petrographic, and geochemical distinctions. Similar K–Ar isotopic ages (81–102 Ma) suggest rapid cooling and therefore high-level emplacement. Together, the isotopic ages provide a minimum (youngest) age for the main deformation of the surrounding metasediments and a maximum (oldest) age for movement along the Tintina Fault.A petrographically and geochemically distinct sample from the Orchay phase yielded a Rb–Sr isochron age of 61 ± 1.5 Ma and an initial 87Sr/86Sr ratio of 0.7090 ± 0.0001, implying intrusive activity in the Paleocene.Field relations, lithology, petrography, geochronometry, and geochemistry suggest that the Orchay and Marjorie phases are plutonic equivalents of the South Fork volcanics. Similarities in plutonic style characterize the extensive mid-Cretaceous igneous event in southeast Yukon.

Download Full-text