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.

Advances in the Geochronology of the Rice Lake – Beresford Lake Area, Southeastern Manitoba

1971 ◽  
Vol 8 (5) ◽  
pp. 572-579 ◽  
Author(s):  
Andrew Turek ◽  
Zell E. Peterman
Keyword(s):  
Greenstone Belt ◽  
Regional Metamorphism ◽  
Granitic Rocks ◽  
Metamorphic Rocks ◽  
Lake Area ◽  
The South ◽  
Quartz Veins ◽  
The North ◽  
Granite Emplacement ◽  
Second Period

The Rice Lake – Beresford Lake area consists of an easterly trending Precambrian greenstone belt which is flanked on the north by granitic rocks and on the south by granitic and metamorphic rocks. Analyses of an intrusive, late tectonic quartz monzonite at Black Lake, yield an isochron age of 2735 ± 55 m.y. with an initial 87Sr/80Sr composition 0.7019 ± 0.0008. This age is a minimum for the granitic rocks to the south of the greenstone belt and is the oldest age obtained in this area. On the other hand, analyses of a quartz diorite pluton intrusive into the greenstones give a metamorphic age of 2555 ± 70 m.y. with an initial 87Sr/86Sr of 0.7016 ± 0.0012. Mylonite zones are developed along the northern and southern boundaries of the greenstone belt. Analyses of whole-rock samples from these zones yield an age of 2345 ± 100 m.y. with initial 87Sr/88Sr 0.7044 ± 0.0024, and is the youngest age obtained in the area.These new data, combined with our previous work, indicate three major events. The first and oldest event is 2730 ± 50 m.y. and is interpreted as a period of regional metamorphism, granite emplacement, and the emplacement of gold–quartz veins which postdate the greenstones. A second period of metamorphism and granite emplacement occurred at 2530 ± 40 m.y. and it affected the area as a whole, as evidenced by updated mineral ages. The third and youngest event, 2345 ± 100 m.y., is recorded by the mylonites and may represent epeirogenic movement in the area.

Rapid fluid-driven transformation of lower continental crust associated with thrust-induced shear heating

2020 ◽  
Author(s):  
Bjørn Jamtveit ◽  
Kristina G. Dunkel ◽  
Arianne Petley-Ragan ◽  
Fernando Corfu ◽  
Dani W. Schmid
Keyword(s):  
Regional Metamorphism ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Source Rocks ◽  
Granitic Rocks ◽  
Time Interval ◽  
Fluid Infiltration ◽  
Facies Metamorphism ◽  
Shear Heating ◽  
Host Rocks

<p>Caledonian eclogite- and amphibolite-facies metamorphism of initially dry Proterozoic granulites in the Lindås Nappe of the Bergen Arcs, Western Norway, is driven by fluid infiltration along faults and shear zones. The granulites are also cut by numerous dykes and pegmatites that are spatially associated with metamorphosed host rocks. U-Pb geochronology was performed to constrain the age of fluid infiltration and metamorphism. The ages obtained demonstrate that eclogite- and amphibolite-facies metamorphism were synchronous within the uncertainties of our results and occurred within a maximum time interval of 5 Myr, with a mean age of ca. 426 Ma.  Caledonian dykes and pegmatites are granitic rocks characterised by a high Na/K-ration, low REE-abundance and positive anomalies of Eu, Ba, Pb, and Sr. The most REE-poor compositions show HREE-enrichment. Melt compositions are consistent with wet melting of plagioclase- and garnet-bearing source rocks. The most likely fluid source is dehydration of Paleozoic metapelites, located immediately below the Lindås part of the Jotun-Lindås microcontinent, during eastward thrusting over the extended margin of Baltica. Melt compositions and thermal modelling suggest that short-lived fluid-driven metamorphism of the Lindås Nappe granulites was related to shear heating at lithostatic pressures in the range 1.0-1.5 GPa. High-P (≈2 GPa) metamorphism within the Nappe was related to weakening-induced pressure perturbations, not to deep burial. Our results emphasize that both prograde and retrograde metamorphism may proceed rapidly during regional metamorphism and that their time-scales may be coupled through local production and consumption of fluids.</p>

Petrogenesis of spilite and keratophyre from a Permian and Triassic volcanic arc terrane, eastern Oregon and western Idaho, U.S.A.

1978 ◽  
Vol 15 (8) ◽  
pp. 1356-1369 ◽  
Author(s):  
T. L. Vallier ◽  
Rodey Batiza
Keyword(s):  
Mass Balance ◽  
Ion Mobility ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Internal Mass ◽  
Volcanic Arc ◽  
Sea Floor ◽  
General Internal ◽  
Low Potassium

Spilite, keratophyre, and quartz keratophyre from a Permian and Triassic volcanic arc assemblage in eastern Oregon and western Idaho originally were low-potassium basalt, andesite, dacite, and possibly rhyolite. Amphibolite from an abyssal sea floor or marginal basin environment of either Permian or Triassic age originally was low-potassium basalt. Present mineralogies are characteristic of the greenschist and amphibolite facies of regional metamorphism. Greenschist facies minerals are mostly albite, epidote, chlorite, calcite, and quartz, whereas amphibolite facies minerals are predominantly hornblende, plagioclase (andesine), and epidote. In the volcanic arc assemblage, mineralogies of the Permian rocks are nearer equilibrium in the greenschist facies than those of the overlying Triassic rocks, probably reflecting deeper burial. Bulk compositions indicate extensive ion mobility, but there has been a general internal mass balance of most components. Na2O, CO2, and H2O were probably added to most rocks, but the source of those components has not been established.

The greenschist facies of an Archean assemblage near Wawa, Ontario

1983 ◽  
Vol 20 (9) ◽  
pp. 1409-1420 ◽  
Author(s):  
Paul A. Studemeister
Keyword(s):  
Native Gold ◽  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
White Mica ◽  
Greenschist Facies ◽  
Contact Metamorphism ◽  
Contact Aureole ◽  
Metamorphic Fluid ◽  
Vein Quartz ◽  
Low Salinity

A stock of trondhjemite intrudes an Archean succession metamorphosed to the greenschist facies at Gutcher Lake, 30 km north of Wawa in Ontario. The stock is 4 km2 in plan and is partly enveloped by an aureole of epidote–amphibole hornfels up to 1 km wide. Within this aureole chlorite partly replaces biotite; chlorite, calcite, and quartz mantle hornblende and epidote; zoned amphibole has a rim of actinolite; and albite varies from 0 to 8% An. The stock has chlorite pseudomorphous after biotite, and feldspar is mottled by white mica and has a clear rim of albite. Fractures filled with quartz, calcite, ankerite, white mica, chlorite, pyrite, and native gold cross-cut the stock and its aureole. Wall rocks to these veins were modified by hydrothermal alteration with addition of Si, Fe, K, H2O + CO2, S, and Rb, leaching of Na, and a shift in Fe2+/Fet from ~0.66 to ~0.90. Primary inclusions in the vein quartz have a solution with a CO2 gas bubble that homogenizes into the liquid at around 300 °C.Initial contact metamorphism of volcanic rocks at T = 450–550 °C and P < 200 MPa (2 kbar) formed an aureole of epidote–hornblende hornfels near the stock. Subsequent regional metamorphism during the Archean at T = 325–450 °C and P = 200–300 MPa (2–3 kbar) retrograded the stock and its contact aureole to a lower greenschist assemblage. The retrogression involved hydration and CO2 fixation in hornfels and trondhjemite by a hot reducing fluid of low salinity. This metamorphic fluid precipitated native gold with quartz and pyrite along fractures in response to cooling and chemical reaction with wall rocks.

scholarly journals Employing contact metamorphism to assess the conditions of pluton emplacement and timing of recrystallization in southwestern Kellys Mountain, Cape Breton Island, Nova Scotia

2017 ◽  
Vol 54 (11) ◽  
pp. 1165-1178 ◽  
Author(s):  
Nabil A. Shawwa ◽  
Robert P. Raeside ◽  
David W.A. McMullin ◽  
Christopher R.M. McFarlane
Keyword(s):  
Nova Scotia ◽  
Regional Metamorphism ◽  
Low Pressure ◽  
Contact Metamorphism ◽  
Contact Aureole ◽  
Low Grade ◽  
Cape Breton Island ◽  
Metasedimentary Rocks ◽  
Cape Breton ◽  
George River

At Kellys Mountain, Cape Breton Island, Nova Scotia, the late Neoproterozoic Glen Tosh formation (a low-grade metapsammite–metapelite unit of the George River Metamorphic Suite) has been intruded by diorite, granodiorite, and granite plutons, and the diorite hosts a narrow contact metamorphic aureole. New mapping and sampling in the contact aureole reveals that the metasedimentary rocks have reached amphibolite-facies metamorphism resulting in the development of neoformed biotite, muscovite, cordierite, ilmenite, garnet, andalusite, sillimanite, monazite, and spinel within the meta-pelite, a mineral assemblage also found in the Kellys Mountain Gneiss as a result of low-pressure regional metamorphism. Neoformed minerals and the disappearance of foliation defines a contact metamorphic aureole within 300 m of the pluton contacts. Petrographic and microprobe analyses of equilibrium assemblages in metapelitic units of the contact aureole yielded metamorphic pressures of 250 MPa, implying an intrusion depth of ∼9 km, with temperatures ranging from 365 to 590 °C. The presence of earlier-formed andalusite and garnet indicates the rocks may have initially undergone a low-pressure regional metamorphic event prior to contact metamorphism. Monazite in the contact aureole was dated using in-situ U–Pb methods and yielded an age of 480.9 ± 3.7 Ma, interpreted as the time of formation of the contact metamorphic aureole.

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.

On the possible analogy between the Dizi Series of the Southern slope zone of the Greater Caucasus and the folded basement of the plain Crimea: composition, metamorphism, magmatism and age

2021 ◽  
Author(s):  
Irakli Javakhishvili ◽  
David Shengelia ◽  
Tamara Tsutsunava ◽  
Giorgi Chichinadze ◽  
Giorgi Beridze ◽  
...  
Keyword(s):  
Middle Jurassic ◽  
Regional Metamorphism ◽  
Geological Structure ◽  
Greenschist Facies ◽  
Igneous Rocks ◽  
Contact Metamorphism ◽  
Southern Slope ◽  
Quartz Syenite ◽  
Greater Caucasus ◽  
Geological Conditions

&lt;p&gt;The Dizi Series is exposed within the Southern slope zone of the Greater Caucasus that occurs as a complex geological structure, which constitutes an integral part of the Mediterranean (Alpine-Himalayan) collisional orogenic belt. It is built up of terrigenous and volcanogenic-sedimentary rocks faunistically dated from the Devonian to Triassic inclusive (Somin, 1971; Somin, Belov, 1976; Kutelia 1983). Most of them are metamorphosed under conditions of chlorite-sericite subfacies of the greenschist facies of regional metamorphism (chlorite-phengite-albite&amp;#177;quartz, graphite-sericite-quartz phyllites and marbleized limestones), and only a minor part represented by clay-carbonaceous, phengite-chlorite-carbonaceous and prehnite-chlorite-carbonate schists underwent anchimetamorphism (Shengelia et al., 2015). The Dizi Series is intruded by numerous magmatic bodies of gabbro-diabases, diabases, diorites, diorite-porphyries, syenites, monzo-syenites and granitoids. The age of the intrusions was defined by K-Ar method at 176-165 Ma (Dudauri, Togonidze, 1998) and by U-Pb LA-ICP-MS zircon dating at 166.5 &amp;#177; 4.6 Ma (authors` unpublished data) and corresponds to the Bathonian orogeny. The Middle Jurassic intrusions caused intense contact metamorphism of the rocks of the Dizi Series resulted in the formation of various hornfelses containing andalusite, cordierite, corundum, biotite, plagioclase, potassium feldspar, clinozoisite, hornblende, cummingtonite, clinopyroxene, wollastonite and scapolite. These rocks correspond to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels subfacies of the contact metamorphism (Javakhishvili et al., 2020). The analogues of the Dizi Series rocks have not previously been established either in the Greater Caucasus or in the neighboring regions. In our view, Paleozoic rocks similar to the Dizi Series occur under the Cretaceous and Jurassic deposits within the folded basement of the plain Crimea where they were recovered by wells. Most of these rocks, as in the Dizi Series, underwent metamorphism of chlorite subfacies of the greenschist facies and, to a lesser extent, deep epigenesis (clayey-carbonaceous, sericite-carbonaceous, actinolite-chlorite-prehnite, muscovite-albite-chlorite, epidote-actinolite-chlorite and graphite-talc-quartz schists) (Chernyak, 1969). These rocks are also intruded by Middle Jurassic igneous rocks, including gabbro-diabases, diabases, diorites, syenites, monzo-syenites, granite-porphyries, etc. (Shniukova, 2016; Shumlyanskyy, 2019). As a result of the contact metamorphism of the basement rocks, muscovite-quartz-cordierite and cordierite-quartz-feldspar micaceous hornfelses were formed. Quartz syenite yielded a K-Ar age of 158 Ma (Scherbak, 1981), while monzo-syenite was dated at 170 &amp;#177; 5 Ma applying 40Ar/39Ar method (Meijers, 2010). Thus, based on the rock associations, the nature of metamorphism, the age of the metamorphic and igneous rocks, and on the spatial position of the Dizi Series and folded basement of the plain Crimea we assume that these units developed coevally in similar environment and geological conditions.&lt;br&gt;&lt;br&gt;Acknowledgements.This work was supported by Shota Rustaveli National Science Foundation (SRNSF) [PHDF-19-159, Regional and Contact Metamorphism of the Dizi Series].&lt;/p&gt;

The Cold Spring Melange and a possible model for Dunnage–Gander zone interaction in central Newfoundland

1990 ◽  
Vol 27 (8) ◽  
pp. 1126-1134 ◽  
Author(s):  
Harold Williams ◽  
M. A. J. Piasecki
Keyword(s):  
Full Range ◽  
Regional Metamorphism ◽  
Black Shales ◽  
Contact Metamorphism ◽  
Early Ordovician ◽  
Clastic Rocks ◽  
Ophiolitic Mélange ◽  
Structural Relationships ◽  
Ductile Shearing ◽  
Cold Spring

Structural relationships at Cold Spring Pond and the recognition of ophiolitic melange bear on the important questions of timing and style of structural superpositioning of Dunnage Zone rocks above Gander Zone rocks in central Newfoundland. The latest models emphasize ductile shear boundaries and orogen-parallel movements. Previous models proposed west-to-east or head-on obduction of Dunnage ophiolitic rocks across the Gander Zone.At the Dunnage (Exploits Subzone) – Gander (Meelpaeg Subzone) boundary at Cold Spring Pond, discrete, outcrop-size ultramafic blocks and smaller quartzite blocks are randomly distributed, and they are surrounded by, or are embedded in, homogeneous black graphitic shale or phyllite. The ultramafic blocks are typical of nearby Early Ordovician Dunnage ophiolite suites, the quartzite blocks are typical of adjacent Early Ordovician or earlier Gander clastic rocks, and the matrix black shales are similar to those of Middle or Early Ordovician age that occur throughout central Newfoundland. This chaotic mixture of almost coeval lithologies at Cold Spring Pond is interpreted as an olistostromal melange; the Cold Spring Melange. It resembles melanges that are dated as Ordovician elsewhere in Newfoundland.The Cold Spring Melange is overprinted by the full range of structures and metamorphic effects evident in adjacent rocks of the Exploits (Dunnage) and Meelpaeg (Gander) subzones. These include the development of lineations, cleavages, schistosities, zones of ductile shearing, regional metamorphism, and contact metamorphism. The oldest of these effects are interpreted as Silurian, based on isotopic dating in southern Newfoundland.The formation of olistostromal, ophiolitic melange implies disruption of the oceanic tract (Exploits Subzone of the Dunnage Zone), and in the case of the Cold Spring example, juxtapositioning or transport of Exploits Subzone ophiolite suites against or across the supracrustal rocks of the Meelpaeg Subzone (Gander Zone). The age and provenance of Cold Spring components, lack of post-Ordovician components, overprinting structural relationships, and comparison with other Newfoundland melanges all support an Ordovician age of formation. Overprinting relationships indicate that major ductile shears at other Dunnage–Gander zone boundaries postdate initial Dunnage–Gander superpositioning.

On an anatectic granite from Bygland, south Norway

1973 ◽  
Vol 39 (302) ◽  
pp. 216-223
Author(s):  
R. Sen ◽  
Ananda Deb Mukherjee
Keyword(s):  
Trace Element ◽  
Crystalline State ◽  
Regional Metamorphism ◽  
Element Distribution ◽  
Amphibolite Facies ◽  
Granitic Rocks ◽  
Trace Element Distribution ◽  
Rock Types ◽  
Anatectic Granite

SummaryThe Pre-Cambrian granitic rocks of Bygland are structurally and texturally concordant with the metamorphosed country rocks. Both these rock types plot close together in Q-Or-Ab and Ab-An-Or normative diagrams; trace element distribution is also similar. The granite has been reconstituted from the country rocks under epidote-amphibolite facies conditions. Plagioclase feldspars show that the granite is not a ‘mature’ rock; they are, however, ‘mature’ in the country rocks and are products of typical regional metamorphism (Ohta et al, 1968). Plagioclases in the granite are relicts of country rocks showing traces of a premetamorphic crystalline state. They have been rejuvenated with the introduction of alkali material during the reconstitution.

Radiometric Ages of Granitic Rocks, Southwestern Nova Scotia

1973 ◽  
Vol 10 (8) ◽  
pp. 1201-1210 ◽  
Author(s):  
R. F. Cormier ◽  
T. E. Smith
Keyword(s):  
Nova Scotia ◽  
Field Work ◽  
Granitic Rocks ◽  
Lower Paleozoic ◽  
Granite Emplacement ◽  
Radiometric Ages ◽  
Eastern Half

Granitic rocks comprising the eastern half of the main batholith of southwestern Nova Scotia have been studied. The granitic rocks intrude Lower Paleozoic metasediments of the Meguma Group. Field work, the chemistry and petrology of the granitic rocks, and Rb–Sr whole-rock isochron dates indicate that there were at least two episodes of granite emplacement, the earlier about 415 m.y. ago and the later about 350 m.y. ago. Samples from a much smaller pluton some 65 mi (104 km) away from the study area were also dated and are correlated with rocks in the main batholith.

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