scholarly journals Some border relations between supracrustal and infracrustal rocks in South-West Greenland

1966 ◽  
Vol 9 ◽  
pp. 1-43
Author(s):  
B.F Windley ◽  
N Henriksen ◽  
A.K Higgins ◽  
E Bondesen ◽  
S.B Jensen
Keyword(s):  
Transition Zone ◽  
Metamorphic Grade ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Granitic Rocks ◽  
Second Phase ◽  
Concomitant Increase ◽  
West Greenland ◽  
South West ◽  
Volcanic Series

Three types of border relation between supracrustal and intracrustal rocks are described from South-West Greenland. In the Ravns Storø area a largely volcanic series, possibly equivalent in age to the Tartoq Group, passes downwards into the underlying gneisses via a transitional migmatite front. The supracrustal bedding passes conformably downwards into the gneissic foliation and there is a progressive downward increase in metamorphic grade and degree of mineral orientation. In the northern part of the Ivigtut region Ketilidian supracrustals lie with a major unconformity on pre-Ketilidian gneisses (and Tartoq Group) supracrustals; between which there is a migmatite front relation. Passing southwards the autochthonous unconformity between the Ketilidian supra­crustals and the underlying rocks is affected by a series of progressive tectonic modifications. Faulting parallel to the axial planes of Ketilidian second phase folds in the supracrustals is followed by thrusting along the unconformity, giving rise to a parautochthonous border, which further south passes into an allochthonous border modified by gneissification and associated with the formation of granitic rocks. Earlier basic dykes together with the gneissic foliation are dragged along the transitional border which simulates a transition zone between a superstructure and an infrastructure. In association with this increase in tectonisation there is a concomitant increase in grade of metamorphism of the supracrustal rocks from an almost unmetamorphosed state through greenschist facies and epidotemphibolite facies to amphibolite facies.

scholarly journals Stratigraphy and structural development of the Precambrian rocks in the area north-east of Disko Bugt, West Greenland

1967 ◽  
Vol 13 ◽  
pp. 1-28
Author(s):  
A Escher ◽  
M Burri
Keyword(s):  
Transition Zone ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Structural Development ◽  
West Greenland ◽  
Precambrian Rocks ◽  
The Third ◽  
North East ◽  
Area North

The Precambrian rocks in the area north-east of Disko Bugt can be divided into a lower gneiss group and an upper supracrustal group. The lower part of the supracrustal group consists of quartzites, amphibolites and garnet-staurolite schists, while the upper part is mainly semipelitic schist. The gneisses were affected by three successive phases of deformation, while in the supracrustals only the two latest phases of folding can be recognized. Evidence is given in support of the idea that the supracrustals were deposited on a gneiss basement after the first phase of folding, the basement being later reactivated mainly during the third and last deformation. Two main tectonic compLexes can be distinguished in the area mapped: a southern complex characterized by a predominarit ENE direction of the fold axes and a northern complex in which the main fold axes are strongly curved around a central gneiss dorne. The transition zone between the southern and northern complex is marked by the presence of severaL important faults and mylonites. The gneiss dorne is flanked in its northern part by a thick granite sheet. The dorne structure appears to have been forrned by a combination of diapiric movements and the interference between two successive deformations. The gneisses and lower supracrustals recrystallized under amphibolite facies conditions, while greenschist facies conditions prevaiLed during the recrystallisation of the upper supracrustals.

METAMORPHISM OF THE MEGUMA GROUP OF NOVA SCOTIA

1966 ◽  
Vol 3 (7) ◽  
pp. 959-974 ◽  
Author(s):  
F. C. Taylor ◽  
E. A. Schiller
Keyword(s):  
Nova Scotia ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Contact Metamorphism ◽  
Granitic Rocks ◽  
Structural Elements ◽  
Early Ordovician ◽  
Quartz Veins ◽  
Granite Emplacement

The Meguma group of lithic greywacke, feldspathic quartzite, slate siltstone, and argillite is Early Ordovician or older in age and has undergone both regional and contact metamorphism. Both types of metamorphism have resulted in recrystallization and locally in orientation of newly formed minerals. Metasomatism and retrogressive metamorphism are subordinate and only locally important. Regionally metamorphosed rocks are divided into greenschist and almandine–amphibolite facies, although some assemblages cannot be assigned with certainty. Locally, biotite and garnet isograds are mappable within the greenschist zone.Relationships between regional metamorphism and structural elements (folding) show that deformation preceded regional metamorphism. Intrusion of granitic rocks has produced a zone of contact metamorphism (hornblende–hornfels facies) that is superimposed upon regional greenschist facies rocks, which shows that granite emplacement occurred after the regional grade was reached. Gold–quartz veins are confined to areas lying in the greenschist zone of regional metamorphism, which suggests that the almandine–amphibolite zone is not favorable.

scholarly journals Thermodynamic modelling of carbonate-silicate rocks from the Sakar unit, Sakar-Strandzha zone, SE Bulgaria

2021 ◽  
Vol 82 (3) ◽  
pp. 76-78
Author(s):  
Tzvetomila Vladinova ◽  
Milena Georgieva
Keyword(s):  
Metamorphic Grade ◽  
Thermodynamic Modelling ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
General Increase ◽  
Metasedimentary Rocks ◽  
Town Area ◽  
East West ◽  
Silicate Rocks

The P-T evolution of carbonate-bearing metasedimentary rocks from the Sakar unit (Sakar-Strandzha Zone, SE Bulgaria) has been obtained using Perple_X modelling and conventional geothermometry. The metamorphic conditions vary from greenschist facies (250–350 °C/2–4 kbar) in the Klokotnitsa village area to amphibolite facies (550–650 °C/4.5–6.5 kbar) in the Topolovgrad town area, confirming a general increase of the metamorphic grade at east-west direction.

Craton-Mobile Belt relations with particular reference to the Mosetse-Matsitama area, north-eastern Botswana

1970 ◽  
Vol 107 (2) ◽  
pp. 113-123 ◽  
Author(s):  
John D. Bennett
Keyword(s):  
Metamorphic Grade ◽  
Granitic Rocks ◽  
Mobile Belt ◽  
Schist Belt ◽  
The South ◽  
The West ◽  
South West ◽  
Metavolcanic Rocks ◽  
North Eastern ◽  
Area North

SummaryThe Pre-Cambrian rocks of north-eastern Botswana comprise two major geotectonic domains: the south-western extremity of the Rhodesian craton, and the surrounding mobile belts– namely the Limpopo Mobile Belt to the south and the Shashi Mobile Belt to the west-southwest. The Mosetse-Matsitama area bears affinity to both these environments and this contribution attempts to assess the relationships of the area within the context of the regional geological framework. The area is underlain by a supracrustal schist belt which is interfolded with an infracrustal basement of gneisses and granitic rocks. The schist belt includes metasedimentary and probably metavolcanic rocks of low metamorphic grade and, therefore, contrasts sharply with the rocks of higher metamorphic grade which comprise the basement. Only in the south-west of the belt does a transitional relationship between the two major units occur. Geographical and geological criteria characteristic of both the major geotectonic environments are described, and it is concluded that the area shows a transition from a cratonic to a mobile belt environment. Involvement in a developing mobile belt would initially affect the infracrustal basement, allowing the supracrustal rocks to retain their cratonic characteristics to a more advanced stage.

scholarly journals Late Archaean metamorphic Rb-Sr isochron ages from basic and ultrabasic rocks in the Bjørnesund – Ravns Storø region, southern West Greenland

1978 ◽  
Vol 90 ◽  
pp. 135-141
Author(s):  
A.D.M Burwell ◽  
C.R.L Friend ◽  
D.J Hughes
Keyword(s):  
Amphibolite Facies ◽  
Ultramafic Rocks ◽  
Late Archaean ◽  
West Greenland ◽  
South West

The Archaean complex of South-West Greenland (Bridgwater et al., 1976) consists largely of polyphase quartzo-feldspathic gneisses which intrude horizons of amphibolite and anorthosite with genetically and spatially associated ultramafic rocks and minor occurrences of meta-sedimentary material. In the Bjørnesund - Ravns Storø region (fig. 46) 150 km south of Godthåb the amphibolite units are structurally linked together and are considered to represent the same unit (Friend, 1975). The complex was variably metamorphosed to hornblende-granulite or amphibolite-facies conditions. This metamorphism accompanied three main phases of deformation within the region (Kalsbeek & Myers, 1973) and post-dated the formation of the precursors of the amphibolites.

scholarly journals The Tartoq Group on Nuna qaqertoq and in the Iterdlak area, South-West Greenland

1968 ◽  
Vol 17 ◽  
pp. 1-17
Author(s):  
A.K Higgins
Keyword(s):  
Sedimentary Rocks ◽  
Greenschist Facies ◽  
West Greenland ◽  
Pillow Lavas ◽  
South West

The Tartoq Group schists of Nuna qaqertoq appear to have comprised pillow lavas, sills and sediments. Those of the Iterdlak area appear to have been composed of sills and a variety of sedimentary rocks, including a conglomerate. Both areas of schists have suffered deformation and metamorphism under high greenschist facies conditions, and have in part been extensively veined by pegmatite or aplite. Comparisons of the structures in these schists with those in the gneisses of adjacent areas supports the view that these gneisses represent the gneissified, deformed basement on which the Tartoq Group was deposited.

scholarly journals Magnetic anomalies and metamorphic boundaries in the southern Nagssugtoqidian orogen, West Greenland

2006 ◽  
Vol 11 ◽  
pp. 179-184 ◽  
Author(s):  
John A. Korstgård ◽  
Bo Møller Stensgaard ◽  
Thorkild M. Rasmussen
Keyword(s):  
Shear Zone ◽  
Magnetic Field Intensity ◽  
Granulite Facies ◽  
Metamorphic Grade ◽  
Amphibolite Facies ◽  
Dyke Swarm ◽  
Magnetic Minerals ◽  
West Greenland ◽  
Thrust Zone

Within the southern Nagssugtoqidian orogen in West Greenland metamorphic terrains of both Archaean and Palaeoproterozoic ages occur with metamorphic grade varying from low amphibolite facies to granulite facies. The determination of the relative ages of the different metamorphic terrains is greatly aided by the intrusion of the 2 Ga Kangâmiut dyke swarm along a NNE trend. In Archaean areas dykes cross-cut gneiss structures, and the host gneisses are in amphibolite to granulite facies. Along Itilleq strong shearing in an E–W-oriented zone caused retrogression of surrounding gneisses to low amphibolite facies. Within this Itivdleq shear zone Kangâmiut dykes follow the E–W shear fabrics giving the impression that dykes were reoriented by the shearing. However, the dykes remain largely undeformed and unmetamorphosed, indicating that the shear zone was established prior to dyke emplacement and that the orientation of the dykes here was governed by the shear fabric. Metamorphism and deformation north of Itilleq involve both dykes and host gneisses, and the metamorphic grade is amphibolite facies increasing to granulite facies at the northern boundary of the southern Nagssugtoqidian orogen. Here a zone of strong deformation, the Ikertôq thrust zone, coincides roughly with the amphibolite–granulite facies transition. Total magnetic field intensity anomalies from aeromagnetic data coincide spectacularly with metamorphic boundaries and reflect changes in content of the magnetic minerals at facies transitions. Even the nature of facies transitions is apparent. Static metamorphic boundaries are gradual whereas dynamic boundaries along deformation zones are abrupt.

scholarly journals The Precambrian rocks of the Egedesminde–Christianshåb area, West Greenland

1969 ◽  
Vol 23 ◽  
pp. 1-37
Author(s):  
G Henderson
Keyword(s):  
Granulite Facies ◽  
Quartz Diorite ◽  
Amphibolite Facies ◽  
Granitic Rocks ◽  
Minor Importance ◽  
Mica Schist ◽  
Prominent Feature ◽  
West Greenland ◽  
Precambrian Rocks ◽  
Metamorphic Complexes

Most of the area described consists of quartzo-feldspathic gneisses with zones and bands of mica schist and pelitic gneiss, amphibolite, and a few thin marble and calc-silicate bands. Granitic rocks are also present, but are of minor importance. A large quartz diorite body is thought to represent a folded and metamorphosed intrusive sheet. Two metamorphic complexes are present, a predominantly amphibolite facies complex and a granulite facies complex. Migmatites are a prominent feature in some areas of mica schist and pelitic gneiss. At least two, and probably three, deformation phases are represented. A good correlation has been established with adjoining areas.

Barian mica and distribution of barium in metacherts and quartzofeldspathic schists, Southern Alps, New Zealand

1993 ◽  
Vol 57 (387) ◽  
pp. 265-272 ◽  
Author(s):  
Rodney H. Grapes
Keyword(s):  
New Zealand ◽  
Southern Alps ◽  
Metamorphic Grade ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Compositional Variation ◽  
Low Grade ◽  
Reducing Conditions ◽  
Facies Metamorphism ◽  
Low K

AbstractZoned barian muscovite (2.52-5.66% BaO) and unzoned biotite (0.99-1.77% BaO) occur in two amphibolite grade metacherts of the Alpine schists, Southern Alps, New Zealand. The Ba-micas are associated with quartz-chlorite-Mn-garnet-tourmaline-apatite-sulphide ± oligoclase ± rutile ± magnetite ± ankerite. Increasing Ba (core to rim) in the muscovite is accompanied by a decrease in Si, Ti, Fe + Mg, and K and an increase in [4]Al, [6]Al, and Na. The main substitution that accounts for entry of Ba into both micas is [A]Ba2+ + [4]Al3+ ⇋ [A]K+ + [4]Si4+ and possibly [A]Ba2+ ⇋ [A]K+ + □. Compositional variation of the muscovite is also governed by the substitutions, [6]Al3+ + [4]Al3+ ⇋ [6](Mg,Fe)2+ + [4]si4+, and [A]Na+ ⇋ [A]K+. The presence or absence of oligoclase, rutile, magnetite and Mg/(Mg + Fe) ratio of coexisting biotite control the Na, Ti, Fe and Mg contents of muscovite in the respective metacherts. Important variables controlling the occurrence of Ba-mica is the Ba-rich composition of the metacherts (1387 and 2741 ppm Ba) and metamorphic grade. In metacherts, siliceous and quartzofeldspathic schists with <1000 ppm Ba barium increases with increasing K2O content indicating that in K-feldspar-absent rocks barium is mainly contained in micas (<0.70% BaO). In greenschist facies metacherts and siliceous schists with high Ba (>1000 ppm) and low K2O, barian micas are not present and most of the Ba occurs in baryte ± barian carbonate with implication of a significant original hydrothermal-hydrogenous input. Although low grade illite/sericite/smectites containing Ba are the most likely precursor of the barian micas in the metacherts, strong marginal Ba enrichment in the muscovite indicates a later Ba-metasomatism resulting from the breakdown of baryte under reducing conditions during amphibolite facies metamorphism.

scholarly journals Preliminary report on K/Ar datings in the south-eastern part of the Ivigtut region

1971 ◽  
Vol 35 ◽  
pp. 49-52
Author(s):  
O Larsen
Keyword(s):  
Preliminary Report ◽  
Metamorphic Grade ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
The South ◽  
South Eastern ◽  
The North ◽  
North Side ◽  
Narrow Belt

In the lvigtut region the Ketilidian supracrustal rocks are exposed mainly on Arsuk ø and in a narrow belt stretching along the margin of the Inland lee (Berthelsen & Noe-Nygaard, 1965; Windley et al., 1966). This belt narrows to less than 1 km along the north side of Qôrnoq fjord. The metamorphic grade of the supracrustal rocks increases southwards from lower greenschist facies in northern Grænseland and on Midternæs to epidote amphibolite facies around Qôrnoq fjord and Kiniilik.

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