Geochemistry of low-grade metavolcanic rocks from the Pan-African of the Axum area, northern Ethiopia

1999 ◽  
Vol 96 (1-2) ◽  
pp. 101-124 ◽  
Author(s):  
T. Tadesse ◽  
M. Hoshino ◽  
Y. Sawada
Keyword(s):  
Low Grade ◽  
Northern Ethiopia ◽  
Pan African ◽  
Metavolcanic Rocks

scholarly journals PHYSICAL-MECHANICAL PROPERTIES OF METAVOLCANIC ROCKS OF THE MOUNTAIN CRIMEA

2018 ◽  
Vol 13 (4-5) ◽  
pp. 36-51
Author(s):  
J. V. Frolova ◽  
V. V. Ladygin ◽  
E. M. Spiridonov ◽  
G. N. Ovsyannikov
Keyword(s):  
Mechanical Properties ◽  
Magnetic Susceptibility ◽  
Volcanic Rocks ◽  
Low Grade ◽  
Secondary Mineral ◽  
Grade Metamorphism ◽  
Clastic Rocks ◽  
Metavolcanic Rocks ◽  
Physical Density ◽  
Characteristic Values

The article considers the petrogenetic features of the volcanogenic rocks of the Middle Jurassic age of the Mountain Crimea and analyzes their influence on physical (density, porosity, water absorption, and magnetic susceptibility) and physical-mechanical properties (strength, modulus of elasticity, and Poisson's ratio). Among volcanogenic strata there are subvolcanic, effusive and volcanogenic-clastic rocks. All volcanic rocks were altered under the influence of the regional low-grade metamorphism of the zeolite and prehnite-pumpellyite facies, which resulted in a greenstone appearance. Among the secondary mineral the most common are albite, chlorite, quartz, adularia, sericite, calcite, pumpellyite, prenite, zeolites, epidote, sphene, and clay minerals. It is shown that low-grade metamorphism is characterized by heterogenious transformations: there are both slightly modified, practically fresh differences, and fully altered rocks. Tuffs are usually altered to a greater extent than effusive and subvolcanic rocks. In general, effusive and volcanogenic-clastic rocks differ markedly in their physicalmechanical properties, which is due to the peculiarities of their formation: the former are substantially more dense and stronger, less porous and compressible. However, these differences are leveled as a result of intensive changes in mineral composition and porosity in the process of low-grade metamorphism. The most characteristic values of metavolcanite properties were revealed. It is shown that among all studied parameters, the magnetic susceptibility most clearly correlates with the degree of rocks alteration.

scholarly journals Geochemistry of Umm Rus gold - quartz veins, Central Eastern Desert Egypt. A new contribution

2001 ◽  
Vol 34 (3) ◽  
pp. 1139
Author(s):  
O. A. KAMEL ◽  
M. M. EL MAHALLAWI ◽  
H. M. HELMY
Keyword(s):  
Hybrid Zone ◽  
Eastern Desert ◽  
Quartz Diorite ◽  
Low Grade ◽  
Gold Content ◽  
Strongly Correlated ◽  
Quartz Veins ◽  
Central Eastern Desert ◽  
Pan African ◽  
Gold Bearing

Gold-bearing quartz veins of the Umm Rus area occur at the south-eastern contact of a Precambrian granodiorite cupola within younger gabbros of 573-615 Ma belonging to the Pan African orogenic belt. The rocks are intruded within low-grade metasediments. At such contact, a hybrid zone is developed characterized by the occurrence of quartz diorite which grades into diorite and meta-ferrogabro. A limited number of mineralized quartz veins cut the granodiorite-gabbro complex. Different alteration zones are developed in the vicinity of the quartz veins. The quartz veins have two main trends; NS and N30 E, the latter one is usaually gold-bearing. The mineralized parts of the veins commonly consist of highly sheared and banded smoky quartz, and the gold content depends on the relation with the dykes. The element is strongly correlated with As and Ag, but moderately with Cu. Near to intermediate and basic dykes, the contents of Au, Ag and As are noticably increased

Zircon ages of the metavolcanic rocks and metagranites of the Ollo de Sapo Domain in central Spain: implications for the Neoproterozoic to Early Palaeozoic evolution of Iberia

2007 ◽  
Vol 144 (6) ◽  
pp. 963-976 ◽  
Author(s):  
P. Montero ◽  
F. Bea ◽  
F. González-Lodeiro ◽  
C. Talavera ◽  
M. J. Whitehouse
Keyword(s):  
Passive Margin ◽  
Variscan Orogeny ◽  
Compositional Variation ◽  
The West ◽  
Middle Ordovician ◽  
Pan African ◽  
Metavolcanic Rocks ◽  
High Fraction ◽  
Early Palaeozoic ◽  
High Level

AbstractDating the pre-Middle Ordovician metavolcanic rocks and metagranites of the Ollo de Sapo Domain has, historically, been difficult because of the small compositional variation, the effects of the Variscan orogeny and, as revealed in this paper, the unusually high fraction of inherited zircon components. The first reliable zircon data (U–Pb ion microprobe and Pb–Pb stepwise evaporation) indicate that the Ollo de Sapo volcanism spanned 495±5 Ma to 483±3 Ma, and was followed by the intrusion of high-level granites from 483±3 Ma to 474±4 Ma. In both metavolcanic rocks and metagranites, no less than 70–80% of zircon grains are either totally Precambrian or contain a Precambrian core overgrown by a Cambro-Ordovician rim. About 80–90% of inherited zircons are Early Ediacaran (602–614 Ma) and derived from calc-alkaline intermediate to felsic igneous rocks generated at the end of the Pan-African arc–continent collision. In the Villadepera region, located to the west, both the metagranites and metavolcanic rocks also contain Meso-Archaean zircons (3.0–3.2 Ga) which ultimately originated from the West African Craton. In the Hiendelaencina region, located to the east, both the metagranites and metavolcanic rocks lack Meso-Archaean zircons, but they have two different inherited zircon populations, one Cryogenian (650–700 Ma) and the other Tonian (850–900 Ma), which suggest older-than-Ediacaran additional island-arc components. The different proportion of source components and the marked variation of the 87Sr/86Srinit. suggest, at least tentatively, that the across-arc polarity of the remnants of the Pan-African arc of Iberia trended east–west (with respect to the current coordinates) during Cambro-Ordovician times, and that the passive margin was situated to the west.

Accretion tectonics in northern Eritrea revealed by remotely sensed imagery

1993 ◽  
Vol 130 (2) ◽  
pp. 177-190 ◽  
Author(s):  
S. A. Drury ◽  
S. M. Berhe
Keyword(s):  
Remotely Sensed ◽  
Ductile Deformation ◽  
Low Grade ◽  
Arc Volcanism ◽  
Remotely Sensed Imagery ◽  
Pan African ◽  
Major Fault ◽  
High Level ◽  
Back Arc ◽  
Layered Sequence

AbstractNew details from remotely sensed images of the structure and disposition of broad lithological variations in the Pan-African of northern Eritrea are discussed in the context of accretionary tectonics. The recognition of major north-south structural discontinuities allows the area to be divided into three discrete terranes with apparently different histories of deformation and metamorphism, magmagenesis and sedimentation. The central Hagar Terrane is dominated by large ultramafic masses with a volcano-sedimentary layered sequence, and shows the effects of major sinistral transpression and lateral expulsion. It is bounded to the west by a major fault, the Barka suture, and abuts the older Barka Terrane that comprises metasediments with evidence for polyphase ductile deformation and pre-kinematic dyke emplacement. The Hagar Terrane is thrust against the eastern Nacfa Terrane, which is dominated by low-grade calc-alkaline metavolcanics and immature volcanoclastic sediments intruded by syn-kinematic plutons. These units are pre-dated by an earlier high-grade basement and post-dated by high-level unmetamorphosed silicic volcanics and redbed sediments. The complex is suggested to have been assembled by oblique accretion from the southeast after arc volcanism in the Nacfa Terrane and back-arc extension in the Hagar Terrane ended with the cease of subduction.

Central Superior Province geology: evidence for an allochthonous, ensimatic, southern Abitibi greenstone belt

1990 ◽  
Vol 27 (4) ◽  
pp. 582-589 ◽  
Author(s):  
S. L. Jackson ◽  
R. H. Sutcliffe
Keyword(s):  
Crustal Structure ◽  
Greenstone Belt ◽  
Superior Province ◽  
Low Grade ◽  
Simple Correlation ◽  
Abitibi Greenstone Belt ◽  
Structural Style ◽  
Metavolcanic Rocks ◽  
Crustal Model ◽  
Greenstone Belts

Published U–Pb geochronological, geological, and petrochemical data suggest that there are late Archean ensialic greenstone belts (GB) (Michipicoten GB and possibly the northern Abitibi GB), ensimatic greenstone belts (southern Abitibi GB and Batchawana GB), and possibly a transitional ensimatic–ensialic greenstone belt (Swayze GB) in the central Superior Province. This lateral crustal variability may preclude simple correlation of the Michipicoten GB and its substrata, as exposed in the Kapuskasing Uplift, with that of the southern Abitibi GB. Furthermore, this lateral variability may have determined the locus of the Kapuskasing Uplift. Therefore, although the Kapuskasing Uplift provides a useful general crustal model, alternative models of crustal structure and tectonics for the southern Abitibi GB warrant examination.Thrusting of a juvenile, ensimatic southern Abitibi GB over a terrane containing evolved crust is consistent with (i) the structural style of the southern Abitibi GB; (ii) juvenile southern Abitibi GB metavolcanic rocks intruded by rocks having an isotopically evolved, older component; and (iii) Proterozoic extension that preserved low-grade metavolcanic rocks within the down-dropped Cobalt Embayment, which is bounded by higher grade terranes to the east and west.

Structural cross sections based on a gravity survey of parts of the Quetico and Wawa subprovinces near Thunder Bay, Ontario

1990 ◽  
Vol 27 (2) ◽  
pp. 187-199 ◽  
Author(s):  
M. M. Kehlenbeck ◽  
S. P. Cheadle
Keyword(s):  
Cross Sections ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Gravity Models ◽  
Low Grade ◽  
Thunder Bay ◽  
Metavolcanic Rocks ◽  
Dimensional Gravity ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

In this study, gravity data from 350 new gravity stations are combined with those from 50 previously surveyed stations in a detailed Bouguer anomaly map of a portion of the Quetico and Wawa subprovinces north and west of Thunder Bay, Ontario.In general, high gravity values characterize the southern and southwestern part of the area where metavolcanic rocks of the Wawa subprovince dominate. Much of the Quetico subprovince forms a broad gravitational low, reflecting extensive exposures of gneisses, schists, and migmatites. Well-defined gravity lows are associated with several granitic intrusive bodies.Three- and [Formula: see text]-dimensional gravity models of subsurface configuration of the density contrasts, representative of major rock units, indicate a trough-like structure for the metavolcanic rocks of the Wawa subprovince. This trough-like structure is flanked by a domical feature in the granitoid rocks to the south. North of the metavolcanic rocks, a succession of low-grade greywackes and slates occupies a basinal structure. These structures form the principal subsurface elements of the Wawa subprovince in this area.The gneisses, schists, and migmatites of the Quetico subprovince form a thick, southward-dipping, wedge-shaped structure that may extend under the structures of the Wawa subprovince. This wedge-shaped structure is underlain by a model unit of greater density representative of mafic gneisses and amphibolites. The denser substratum is modelled with local abrupt changes in dip corresponding in position with the Quetico and Hawkeye Lake faults.

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