scholarly journals PETROGRAPHY AND GEOCHEMISTRY OF SOME PALEOPROTEROZOIC GRANITOIDS AT THE NORTH-EASTERN MARGIN OF THE KUMASI BASIN IN GHANA

2020 ◽  
Vol 4 (2) ◽  
pp. 118-126
Author(s):  
Blestmond A. Brako ◽  
Gordon Foli ◽  
Kofi Adomako- Ansah ◽  
Derrick Aikins ◽  
Solomon Dery ◽  
...  
Keyword(s):  
Continental Crust ◽  
Fractional Crystallization ◽  
Distribution Patterns ◽  
Quartz Diorite ◽  
Geodynamic Setting ◽  
Petrographic Analysis ◽  
Eastern Margin ◽  
The North ◽  
North Eastern ◽  
Water Saturated

This study investigates basin-type granitoid samples from the north-eastern margin of the Kumasi Basin in Ghana to establish their source and geodynamic setting. Petrographic analysis, TAS and A/NK-A/CNK plots classify the granitoids as metaluminous quartz diorite, metaluminous granodiorite, and peraluminous monzogranite; and exhibiting I-type signatures. These rocks are formed by magma differentiation and/or partial melting at various stages. Distribution patterns of incompatible elements and the positive Eu/Eu* anomalies of 1.15 and 1.47 exhibited by quartz diorite and granodiorite, respectively, the values suggest the rocks crystallized from melts formed in a water-saturated environment. The negative Eu/Eu* anomaly exhibited by monzogranite indicate fractionation of plagioclase in the final stages of the magma evolution. The water-rich environment is probably due to dewatering of the basin’s foreland volcaniclastic sediments during regional subsidence, burial and metamorphism. K2O enrichments and wide variations suggest that the granodiorite and monzogranite are formed from fractional crystallization and/or crustal assimilation of the continental crust by under-plating dioritic magma. The higher Al2O3/TiO2 enrichment and the shift from metaluminous to peraluminous in the monzogranite suggest a longer residence time within the continental crust, during which fractional crystallization and the assimilation of pre-existing crustal components into the dioritic magma that resulted in the formation of the monzogranite. The study requires replication at other areas within the basin to generate enough data to enhance metallogenic studies in the terrain.

Nouvelles observations sur la serie de la Gara Sayada (bordure nord-est de l'Eglab, Sahara occidental)

1961 ◽  
Vol S7-III (2) ◽  
pp. 127-132
Author(s):  
Pierre Dourthe ◽  
O. Serra
Keyword(s):  
Western Sahara ◽  
Eastern Margin ◽  
The North ◽  
North Eastern

Abstract A subhorizontal sandy series, the Gara Sayada series, some hundreds of meters thick, overlies a folded sandstone-shale series, more than 1,000 meters thick, on the north-eastern margin of the Eglab massif (Algeria) in the western Sahara. The intra-Caradocian (Ordovician) unconformity already known at several other localities in the Sahara is thus also represented in this region.

Petroleum system of the North-Eastern margin of the Pechora Platform

1996 ◽  
Author(s):  
V. Martirosyan ◽  
A. Simonov ◽  
L. Popova ◽  
F. Kevorkov ◽  
L. Tichomirova
Keyword(s):  
Petroleum System ◽  
Eastern Margin ◽  
The North ◽  
North Eastern

scholarly journals Notes on the Permian to Recent Geology of the Kruger National Park

Koedoe ◽  
1986 ◽  
Vol 29 (1) ◽  
Author(s):  
J.W. Bristow ◽  
F.J. Venter
Keyword(s):  
National Park ◽  
Kruger National Park ◽  
Eastern Margin ◽  
The North ◽  
North Eastern ◽  
Extreme North

Permian to Recent rocks form narrow, roughly north- south and east-south-east trending belts in the north-eastern Transvaal. The rocks consist of a thin succession of Karoo sediments, a thick overlying succession of mafic and felsic volcanics referred to as the Lebombo Group, isolated outcrops of Cretaceous sediments and fairly extensive Tertiary-Recent Gravels and sediments. These rocks are in general well exposed along the eastern margin of the Kruger National Park and also crop out in the extreme north. Emplacement of the Lebombo volcanics and subsequent deposition of the Cretaceous rocks was intimately associated with the fragmentation of Gondwanaland.

Bathymetric distribution patterns and biodiversity of benthic Medusozoa (Cnidaria) in the Bay of Biscay (north-eastern Atlantic)

2007 ◽  
Vol 87 (3) ◽  
pp. 681-694 ◽  
Author(s):  
Alvaro Altuna
Keyword(s):  
Distribution Patterns ◽  
The Arctic ◽  
Distribution Data ◽  
Depth Range ◽  
Bay Of Biscay ◽  
Bathymetric Distribution ◽  
Western Atlantic ◽  
The North ◽  
North Eastern ◽  
Substantial Drop

Bathymetric distribution data were compiled on benthic Medusozoa (Cnidaria) of the Bay of Biscay and nearby seas. The area of study extended from 42°N to 48°30′N, and westwards to 10°W. The depth range of each species was traced in a review of the literature. The number of species in each of several depth zones is summarized here: intertidal, intertidal–30 m, 30–100 m, and thereafter at 100 m depth intervals throughout the entire column (0–5000 m). Some 200 species were included (six Scyphozoa, four Staurozoa, 190 Hydrozoa). Of these, 196 could be ascribed to the Coastal Realm (0–200 m) (118 exclusives; 60% of the fauna) and Deep Benthic Realm (200+m) (31 exclusives;16%), with 47 species inhabiting both (24%). Eighty-eight species (45%) were present intertidally. Biodiversity was highest above the summer thermocline (30 m) (133 species, 67%), and no species have been recorded from depths greater than 4706 m. Beyond the thermocline, biodiversity dropped with increasing depth. A significant change occurred in the 30–100 m interval (123 to 78 species; Distinctiveness=51%), although all intervals down to the 300 m isobath exhibited substantial changes. Most species in the Deep Benthic Realm thrive on the upper part of the slope (200–800 m; 50 species). Biodiversity appeared homogeneous across wide bathymetric ranges in deep bathyal and abyssal regions, perhaps due to unique vertical biocenological units. Thus, 15 species are known between 1400 and 2000 m, and four between 3100 and 4300 m. Fifty-four species were considered eurybathic (34%), with some showing impressive bathymetric ranges of over 4000 m, but most species were stenobathic (106, 66%).As with data on benthic medusozoans from South Africa, the north-western Atlantic, the Arctic, and the warm western Atlantic (Bermuda), bathymetric biodiversity was highest in the first 100 m, with a substantial drop below that in species numbers on the shelf and at the beginning of the bathyal. While numbers of species may vary widely from one geographical region to another, such variations are due to differences in biodiversity in the upper 100 m. Hydroid species richness in the deep bathyal and abyssal is similar and always low. Worldwide, benthic medusozoan biodiversity is highest at shallow depths, and these organisms normally seem to be minor components of deep benthos. Very likely, the graph of biodiversity at increasing depth is similar worldwide for the Hydrozoa.

Petrogenesis of Ordovician granitoids in Western Kunlun, NW Tibetan Plateau: Insights into the evolution of the Proto-Tethys Ocean

2020 ◽  
Author(s):  
Peng Wang ◽  
Guochun Zhao ◽  
Yigui Han ◽  
Qian Liu ◽  
Jinlong Yao ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Partial Melting ◽  
Fractional Crystallization ◽  
Mantle Wedge ◽  
Saturation Index ◽  
Oceanic Lithosphere ◽  
Quartz Diorite ◽  
The North ◽  
Western Kunlun ◽  
Granitoid Intrusions

Granitoid rocks are universal in continental crust and are of special significance in understanding tectonic settings. This paper presents detailed zircon U-Pb dating, Hf isotope, whole-rock geochemistry, and Sr-Nd-Pb isotope analyses, and mineralogy of two Ordovician granitoid intrusions and one quartz diorite intrusion in Western Kunlun, NW Tibetan Plateau. The Yutian Complex is composed of diverse rock suites, including monzogabbros, quartz monzodiorites, monzogranites, and monzodioritic enclaves. These suites have similar rock formation ages (447−440 Ma) and minerals, e.g., amphibole grains from different suites belonging to pargasite. Moreover, they exhibit geochemical similarities, such as broadly parallel trace-element patterns characterized by enrichments in light rare earth elements and large ion lithophile elements, and depletions in high field strength elements, which are typical features of arc rocks. Furthermore, the studied samples display homogeneous zircon Hf values, e.g., εHf(t) = −1 to −3, and whole-rock isotopic compositions, e.g., εNd(t) = −4 to −6. Thus, they were most likely derived from a mantle wedge enriched by subducted sediments and fluids, which then evolved into different suites through fractional crystallization of hornblende and plagioclase. The ca. 440 Ma North Yutian quartz diorite intrusion, with an average of εHf(t) value of −6, was a product of the partial melting of mafic lower crust through slightly fractional crystallization of hornblende. In contrast, the ca. 470 Ma Aqiang granodiorite intrusion has εHf(t) values varying from −5 and −2, but it has heterogeneous petrological and geochemical features. It is considered to be a product of the partial melting of the overriding mantle wedge modified by fluids derived from the subducted Proto-Tethys slab and some mixed crustal materials. The Aqiang samples belong to the slightly fractionated I-type series, but they have variable alumina saturation index (ASI = molar Al2O3/[CaO − 3.33 × P2O5 + Na2O + K2O]) values (0.74−1.03) due to variable peraluminous biotite contents. The different suites in the Yutian Complex display low ASI values (<1) controlled by sources and fractional crystallization. The Yutian Complex and the North Yutian intrusion were emplaced during the southward subduction of the Proto-Tethys oceanic lithosphere, and the Aqiang intrusion was emplaced in response to the northward subduction.

scholarly journals GEODYNAMICS

GEODYNAMICS ◽  
2011 ◽  
pp. 28-36
Author(s):  
G.P. Yarotskiy ◽  
Keyword(s):  
Seismic Events ◽  
The South ◽  
Strong Earthquakes ◽  
Eastern Margin ◽  
The North ◽  
South West ◽  
North Eastern

Earthquakes on the south-west of Koryak highlands are connected with a block-key tectonics of lithosphere of marine transital of north-eastern margin of Eurasia and the block-key structure of its strata. The cloud of shocks of three strong earthquakes: Koryak`s (13.10.1988), Khailin`s (8.03.1991) and Olutor`s (20.04.2006) is located over the downfold of lithosphere bottom with drop of depths equal to 15-20 km. Preparation for the seismic events evolution to the north-eastward is possible.

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