Les formations precambriennes de l'extremite orientale de l'axe cristallin Yetti-Eglab (Sahara algerien occidental)

1965 ◽  
Vol S7-VII (3) ◽  
pp. 341-352 ◽  
Author(s):  
Renaud Caby
Keyword(s):  
Retrograde Metamorphism ◽  
The South ◽  
Rock Types ◽  
Algerian Sahara ◽  
Acidic Rock ◽  
Lower Series ◽  
Periods Of Stress ◽  
Volcanic Series

Abstract Two volcanic series are evident in Precambrian outcrops at the eastern end of the Yetti-Eglab axis in the Algerian Sahara. The lower series consists of volcanics subjected to two distinct periods of stress: one involving syntectonic metamorphism, accompanied or followed by migmatization and granitization, and a second involving retrograde metamorphism. The upper Precambrian series is represented by varied volcanics and volcanic detritus, folded and strongly granitized. Acidic rock types predominate in the northern part of the area, basic types in the south, and water-laid tuff deposits in the east.

The Petrography and Provenance of the Coniston Grits East of the Lune Valley, Westmorland

1965 ◽  
Vol 102 (3) ◽  
pp. 252-260 ◽  
Author(s):  
R. R. Furness
Keyword(s):  
Sedimentary Rock ◽  
The South ◽  
Border Area ◽  
Rock Fragments ◽  
Land Mass ◽  
Volcanic Series

AbstractThe petrography of the Coniston Grits is described. Volcanic and sedimentary rock fragments suggest that the sediments were derived from the Ballantrae Series of the Southern Uplands, and not the Borrowdale Volcanic Series.There is little palaeocurrent evidence for a border land mass, but it is suggested that coarse sedimentation during the Wenlockian was restricted to the Southern Uplands by a shallowing in the border area, which was finally overcome by Ludlovian times, to allow deposition of coarser material to the south.

scholarly journals Volcanic centres between Frigg Fjord and Midtkap, eastern North Greenland

1981 ◽  
Vol 106 ◽  
pp. 69-75
Author(s):  
I Parsons
Keyword(s):  
Fault Zone ◽  
Fold Belt ◽  
The South ◽  
The North ◽  
Rock Types ◽  
South West ◽  
North Greenland

A series of smal! volcanic centres cut Ordovician turbidites of Formation A in the southem part of Johannes V. Jensen Land between Midtkap and Frigg Fjord (Map 2). Their general location and main rock types were described by Soper et al. (1980) and their nomenclature is adopted here for fig. 22 with the addition of the small pipe B2. A further small intrusion, south-west of Frigg Fjord, was described by Pedersen (1980). The centres lie 5-10 km south of, and parallel to, the important Harder Fjord fault zone (fig. 22) which traverses the southern part of the North Greenland fold belt and shows substantial downthrow to the south (Higgins et al., this report).

scholarly journals XIII. The Old Red Sandstone of the Orkneys

1900 ◽  
Vol 39 (2) ◽  
pp. 383-424 ◽  
Author(s):  
John S. Flett
Keyword(s):  
Point Of View ◽  
The South ◽  
South Side ◽  
Red Sandstone ◽  
Great Thickness ◽  
Subsequent Revision ◽  
The Subject ◽  
Lower Series ◽  
Local Base

As the result of two visits to Orkney, in which he was accompanied by Mr B. N. Peach, he pointed out that the yellow sandstones of Hoy did not pass down conformably into the flagstones which form the basis of that island, but were separated from them by a marked unconformity. At the base, of the upper sandstones lay a series of contemporaneous lavas and ash beds, which were in all probability erupted, from certain ‘necks’ in the low-lying district at the foot of the Hoy Hills. These rocks he regarded as belonging to the upper Old Red Sandstone. The lower Old Red Sandstone consisted principally of a great thickness of flagstones, with which were interstratified beds of yellow and red sandstone, and occasionally of conglomerate. The fossils belonged exclusively to this lower series; and a table is given, compiled by Mr C. W. Peach, showing the distribution 9f fossil fishes in the lower Old Red Sandstone of Lake Orcadie, including those of Orkney so far as known at that time. As Sir Archibald Geikie anticipated, subsequent revision has necessitated “considerable pruning of the fossil lists.” The conglomerates around the granite axis of Stromness formed merely a local base, “due to the uprise of an old ridge of rock from the surface of the sheet of water in which these strata were accumulated,” and were presumably not on the same horizon as the thick conglomerates on which, in Caithness, the lowest flagstones rest. The sandstones interbedded with the flagstones in South Ronaldshay were regarded as in all probability the northward continuation of the similar rocks at Gill's Bay, Huna, and John o'Groats, on the south side of the Pentland Firth. From a geological point of view, the brief notice of the Old Red Sandstone of the Orkneys contained in this paper forms by far the most important contribution to the knowledge of the subject published up to that time.

scholarly journals VII.—On a new Metamorphic Area in Shropshire

1884 ◽  
Vol 1 (8) ◽  
pp. 362-366 ◽  
Author(s):  
C. Callaway
Keyword(s):  
Volcanic Rocks ◽  
The South ◽  
North East ◽  
South West ◽  
Volcanic Ejecta ◽  
Volcanic Series

The occurrence of two Archæan groups in Shropshire is now well known to geologists. The chain of hills which strikes to the south-west from Lilleshall, north-east of Wellington, to the region south of Church-Stretton, is mainly composed of bedded volcanic rocks; but gneissic and granitoid types have been recognized at the Ercal and at Primrose Hill, the elevations forming the opposite extremities of the Wrekin, and a small exposure was detected near Hope Bowdler, east of Church-Stretton. A second axis of the old rocks, ranging parallel to the Wrekin chain, consists of volcanic ejecta and highly indurated grits, which are probably to be referred to the younger of the two Archæan groups hitherto recognized in the county. The relations between the volcanic and the gneissic systems is clearly defined by the Charlton Hill (see map) conglomerate (a band in the volcanic series), which contains numerous well-rounded pebbles of rock precisely similar to the granitoid gneiss of Primrose Hill. This fact implies a considerable break between the two groups.

The Paragenesis of Kyanite-amphibolites (With Plate XX.)

1937 ◽  
Vol 24 (158) ◽  
pp. 555-568 ◽  
Author(s):  
C. E. Tilley ◽  
H. C. G. Vincent
Keyword(s):  
The Other ◽  
Retrograde Metamorphism ◽  
Present Communication ◽  
The South ◽  
South Side ◽  
The Alps ◽  
The One

In an earlier paper the writer has discussed the paragenesis - kyanite-omphacite as observed in certain ec|ogites. The fate of this association under conditions of retrograde metamorphism has led to a consideration of rocks showing the paragenesis amphibole-kyanite, a point which is briefly taken up in the present communication. Rocks containing this latter assemblage include two groups, the one better known, of sedimentary origin, the other essentially igneous in origin.Here are included members of the para-amphibolites, biotite-hornblende- schists, and hornblende-Garbenschiefer derived from sediments of the character of calcareous and dolomitic shales. The best-known examples come from the Alps—particularly the Triassic and pre- Triassic sediments on the south side of the St. Gotthard massif.

scholarly journals Tectonic Fabric, Geochemistry, and Zircon-Monazite Geochronology as Proxies to Date an Orogeny: Example of South Delhi Orogeny, NW India, and Implications for East Gondwana Tectonics

2021 ◽  
Vol 8 ◽  
Author(s):  
Subhash Singh ◽  
Bert De Waele ◽  
Anjali Shukla ◽  
B. H. Umasankar ◽  
Tapas Kumar Biswal
Keyword(s):  
Large Scale ◽  
Greenschist Facies ◽  
Passive Margin ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Mobile Belt ◽  
Brittle Deformation ◽  
The South ◽  
Rock Types ◽  
Greenschist Facies Metamorphism

We have dated the South Delhi orogeny, Aravalli-Delhi Mobile Belt (ADMB), NW India, using the tectonic fabric, geochemistry, and zircon-monazite geochronology as the proxies. The South Delhi Terrane (SDT), a passive margin domain in the ADMB, consists of multiply deformed (D1–D4) greenschist facies rocks and several granite plutons. The D1 deformation is characterized by pervasive isoclinal recumbent F1 fold and axial planar tectonometamorphic fabric, S1, developed in all rock types. The S1 minerals belong to peak greenschist facies metamorphism, M1, suggesting syntectonic nature of M1 with D1. The age of the D1-M1 is constrained by the syncollisional peralkaline S type Sewariya granite which is characterized by magmatic/submagmatic fabric (Sm) coplanar with the S1. The margin of the pluton is turned into quartzofeldspathic gneiss carrying the evidence of high temperature deformation. The age of Sewariya granite is estimated at ca. 878 Ma by zircon geochronology. The D1-M1 is further constrained by monazite geochronology of the mica schist at ca. 865–846 Ma. The other granite plutons and metarhyolite are pre-D1 and emplaced at ca. 992–946 Ma. The D2 deformation produced NE-SW trending open upright F2 folds coaxial with the F1, and northwesterly vergent F2–axial planar thrusts. Monazite geochronology constrains the D2 at ca. 811–680 Ma. The D3 is characterized by small to large scale NW-SE folds, and the D4 by faults and fractures marking the brittle deformation in the rocks. The D4 is constrained by monazite geochronology at ca. 588–564 Ma. There are upper amphibolitic tectonic slivers along the D2-Phulad thrust, belonging to the pre-Delhi rocks, which show ca. 1,638 Ma metamorphism age. From the above study, it is suggested that the South Delhi orogeny belongs to ca. 878–680 Ma marking the final amalgamation of Marwar Craton with the rest of India. This overlaps the early phase of the Pan-African orogeny (900–630 Ma). The brittle deformation, D4, coincides with Kuunga orogeny (650–500 Ma). Our study implies that India, like other continents in the East Gondwana, underwent amalgamation of internal blocks until the late part of the Neoproterozoic.

scholarly journals The South Millevaches Middle Carboniferous crustal melting and its place in the French Variscan belt

2009 ◽  
Vol 180 (6) ◽  
pp. 473-481 ◽  
Author(s):  
Michel Faure ◽  
Eugène Be Mezeme ◽  
Alain Cocherie ◽  
Jérémie Melleton ◽  
Philippe Rossi
Keyword(s):  
Crustal Melting ◽  
Variscan Belt ◽  
French Massif Central ◽  
The South ◽  
Massif Central ◽  
Rock Types ◽  
Fold And Thrust Belt ◽  
Three Samples ◽  
Middle Carboniferous ◽  
Montagne Noire

AbstractSeveral episodes of crustal melting are now well identified in the Variscan French Massif Central. Middle Devonian (ca 385-375 Ma) migmatites are recognized in the Upper and Lower Gneiss Units involved in the stack of nappes. Late Carboniferous migmatites (ca 300 Ma) are exposed in the Velay Massif only and Middle Carboniferous migmatites crop out in the Para-autochthonous Unit and southern Fold-and-Thrust Belt. In the SW part of the Massif Central, the South Millevaches massif exposes migmatites developed at the expense of ortho- and paragneiss. They form kilometer-sized septa within the foliated Goulles leucogranitic pluton, which is in turn intruded by the non-foliated Glény two micas granite pluton. Monazite grains extracted from these three rock-types have been dated by the EPMA chemical method. Three samples of migmatite yield a late Visean age (ca 337-328 Ma), the Goulles and Glény granitic plutons yield ages at 324-323 Ma and 324-318 Ma, respectively. These new results enlarge the evidence of a Middle Carboniferous crustal melting imprint that up to now was only reported in the eastern part of the French Massif Central, in the northern Cévennes and in the Montagne Noire axial zone. At the scale of the French Variscan massifs, the Visean crustal melting event is conspicuously developed since it is recognized from the Massif Armoricain (Vendée and south coast of Brittany) to the Central Vosges. This episode is synchronous with the huge thermal event responsible for the “Tuffs anthracifères” magmatism of the northern Massif Central and Vosges, and took place immediately after the last thickening phase recorded both in Montagne Noire and Ardennes, that is on the southern and northern outer zones of the Variscan Belt, respectively. However, the geodynamic significance of this major event is not fully understood yet.

scholarly journals The Boulders of the Travellers' Rest Gravel Pit, Cambridge

1921 ◽  
Vol 58 (5) ◽  
pp. 200-205
Author(s):  
J. E. A. Whealler
Keyword(s):  
Special Reference ◽  
The South ◽  
Additional Material ◽  
North West ◽  
The North ◽  
Rock Types ◽  
Gravel Pit ◽  
The University ◽  
The Town

ABOUT twelve years ago Dr. R. H. Rastall and Mr. J. Romanes published an account of the Boulders of the Cambridge Drift. In this paper a list was given of the rock-types recognized at that time in the gravels of the Travellers' Rest Pit, situated about a mile north-west of the town of Cambridge on the Huntingdon Road. Since that time Professor Marr has paid much attention to this pit, among others, with special reference to the Palæolithic implements there found. He has embodied his results in two important papers. In the course of this work Professor Marr collected a number of interesting erratics, and the same pit has also been investigated by many geologists connected with the University, both members of the Sedgwick Club and others. During the last ten years, though the North Pit has been abandoned, the South Pit has been very actively worked for gravel, and has been greatly increased in size. In consequence of this a large amount of additional material has been collected, including many new types, while some of the older specimens, whose origin had been left indeterminate by Rastall and Romanes, have been now identified. Hence it is felt that the time has now arrived when these more recent results should be put on record.

Diverse rock types detected in the lunar South Pole–Aitken Basin by the Chang’E-4 lunar mission

Geology ◽  
2020 ◽  
Vol 48 (7) ◽  
pp. 723-727 ◽  
Author(s):  
Jun Huang (黄俊) ◽  
Zhiyong Xiao (肖智勇) ◽  
Long Xiao (肖龙) ◽  
Briony Horgan ◽  
Xiaoyi Hu (胡晓依) ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Near Infrared ◽  
South Pole ◽  
The South ◽  
Crust And Upper Mantle ◽  
Rock Types ◽  
Mineralogical Characteristics ◽  
Lunar Mission ◽  
Infrared Spectrometer ◽  
Near Infrared Spectrometer

Abstract The South Pole–Aitken (SPA) basin, located between the South Pole and Aitken crater on the far side of the Moon, is the largest confirmed lunar impact structure. The pre-Nectarian SPA basin is a 2400 × 2050 km elliptical structure centered at 53°S, 191°E, which should have exposed lower crust and upper mantle due to the enormous excavation depth. Olivine, the dominant mineral in Earth’s mantle, has only been identified in small and localized exposures in the margins of the SPA basin, and the dominant mafic component is, instead, pyroxene. These mineralogical characteristics could be explained by the recent hypothesis that the lunar upper mantle is dominated by low-calcium pyroxene, not olivine. Here, we present observations from imaging and spectral data from China’s Chang’E-4 (CE-4) lunar mission in the first 4 synodic days, especially the first in situ visible/near-infrared spectrometer observations of an exposed boulder. We identified a variety of rock types, but not the recently reported olivine-rich materials in the landing region. The results are consistent with orbital observations. The obtained mineralogical information provides a better understanding of the nature and origin of SPA materials.

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