The Geology and Geochronology of the Echo Bay Area, Northwest Territories, Canada

1972 ◽  
Vol 9 (2) ◽  
pp. 158-171 ◽  
Author(s):  
B. W. Robinson ◽  
R. D. Morton
Keyword(s):  
Lava Flow ◽  
Thermal Regime ◽  
Regional Metamorphism ◽  
Contact Metamorphism ◽  
Low Grade ◽  
Ore Genesis ◽  
Bay Area ◽  
Bear Lake ◽  
Granitic Intrusions ◽  
Group Contact

In the Echo Bay region of Great Bear Lake the Echo Bay Group has been intruded by Precambrian granites, granodiorites, aplites, and diabases. This group, which has undergone zeolite-facies regional metamorphism, has a lower dominantly sedimentary-pyroclastic sequence (about 1320 m thick) and an upper volcanic sequence (> 1500 m thick). The Lower Echo Bay sub-Group consists of tuffs and cherts with a 190 m thick intermediate lava flow and occasional thin limestones. A sequence of andesites and pyroclastics comprises the Upper Echo Bay sub-Group. Contact metamorphism of the hornblende hornfels and albite–epidote hornfels facies has been induced by the granitic intrusions. A Rb–Sr isochron for the Upper Echo Bay sub-group volcanics gives an age of 1770 ± 30 m.y. K–Ar apparent ages for the granite, granodiorite, and volcanics average around 1650 m.y., possibly reflecting local argon loss up to this date. Mineralized veins with a pitchblende-Co,Ni arsenide-silver-Fe, Cu, Ag, Bi, Zn. Pb sulfide para genesis are mainly confined to the sedimentary-pyroclastic horizons of the Lower Echo Bay sub-Group. It is possible that the mineralization was effected by fluids generated during the low-grade regional metamorphism and that some contribution was made to ore genesis by the thermal regime developed during the diabase intrusion.

scholarly journals [MnO|SiO2,Al2O3,FeO,MgO] balanced log-ratio in chlorites: a tool for chemo-stratigraphic mapping and proxy for the depositional environment

Clay Minerals ◽  
2018 ◽  
Vol 53 (3) ◽  
pp. 351-375
Author(s):  
Annette Süssenberger ◽  
Solveig Pospiech ◽  
Susanne Theodora Schmidt
Keyword(s):  
Depositional Environment ◽  
Regional Metamorphism ◽  
Upper Jurassic ◽  
Contact Metamorphism ◽  
Low Grade ◽  
Rock Composition ◽  
Magallanes Basin ◽  
Global Sea Level ◽  
Rock Analysis ◽  
Log Ratio

ABSTRACTThe [MnO|SiO2,Al2O3,FeO,MgO] balanced ratio (i.e. the isometric log-ratio of the MnO concentration relative to the concentration of SiO2, Al2O3, FeO and MgO) of chlorite and of whole-rock composition is an effective discriminant between Mesozoic stratigraphic formations in the Magallanes Basin (Chile). The MnO content in chlorite is only controlled by the host rock chemistry and is dependent on the geological environment. The MnO content in chlorite remains unchanged at low-grade metamorphic conditions. Single-grain chlorite analysis (n = 1042, electron microprobe) and whole-rock analysis (n = 40, X-ray fluorescence) were used to discriminate stratigraphic formations and to decipher differences in the depositional environment in the Magallanes Basin. The samples are from one Upper Jurassic and three Cretaceous sedimentary units that were affected either by low-grade regional metamorphism or by Miocene contact metamorphism. The highest [MnO|SiO2,Al2O3,FeO,MgO] values are recorded in the upper Zapata Formation. The Punta Barrosa, Cerro Toro and Tobífera Formations show slightly lower [MnO|SiO2,Al2O3,FeO,MgO] values. Elevated [MnO|SiO2,Al2O3,FeO,MgO] values at the transition between Zapata and Punta Barrosa Formations record an oxygenated shallow marine environment that can be linked to the closure of the Rocas Verdes Basin and the onset of fold-and-thrust belt formation. Decreasing [MnO|SiO2,Al2O3,FeO,MgO] values from the Punta Barrosa towards the Cerro Toro Formation indicate gradually increasing water depths during the Upper Cretaceous that correlate well with the global sea level.

Chemical mineralogy of the aureole of the Nahant Gabbro at East Point, Nahant, Mass., USA

1979 ◽  
Vol 43 (326) ◽  
pp. 201-209 ◽  
Author(s):  
P. K. Verma
Keyword(s):  
Solid Solution ◽  
Experimental Work ◽  
Electron Microprobe ◽  
Lower Cambrian ◽  
Mineral Assemblage ◽  
Regional Metamorphism ◽  
Contact Metamorphism ◽  
Contact Aureole ◽  
Low Grade ◽  
Solid Solution Series

SummaryThe Lower Cambrian Weymouth Formation at Nahant, Massachusetts, consisting of interbedded pelitic and calcareous rocks, was intruded by the Nahant Gabbro. The predominant metapelitic mineral assemblage of the contact aureole is quartz-muscovite-chlorite-magnetite-ilmenite. The calcareous hornfelses exhibit a varied mineral assemblage, and in some cases the variation can be spatially related to the intrusive. A number of cross-cutting thin mineral veins, many containing prehnite, are characteristically associated with these calcsilicate rocks.The minerals have been analysed by electron microprobe and this work indicates the presence of a possible solvus in the Fe3+-Al epidote solid solution series. At the physicochemical conditions of the formation of the Nahant hornfelses, the ferric mole fractions of coexisting epidotes are 0.49 and 0.98.Comparison with experimental work shows that the conditions of the contact metamorphism were T ≃ 500°C, Ptotal ≃ 2 kb, and XCO2 ≃ 0.2. However, the present assemblages are the result of a later low-grade regional metamorphism, the ultimate product of which was prehnite.

scholarly journals Significance of K-Ar dating of very low-grade metamorphism in Triassic-Jurassic pelites from the Coastal Range of central Chile

Clay Minerals ◽  
2004 ◽  
Vol 39 (2) ◽  
pp. 151-162 ◽  
Author(s):  
M. Belmar ◽  
D. Morata ◽  
F. Munizaga ◽  
C. Pérez de Arce ◽  
S. Morales ◽  
...  
Keyword(s):  
Contact Zone ◽  
Regional Metamorphism ◽  
Contact Metamorphism ◽  
Time Interval ◽  
Low Grade ◽  
Central Chile ◽  
Grade Metamorphism ◽  
Jurassic Rocks ◽  
Thermal Influence ◽  
Coastal Range

AbstractK-Ar isotopic dating of very low-grade metamorphism affecting Triassic-Jurassic rocks in the Coastal Range of central Chile was carried out on whole rocks and their <2 mm size fractions. In the study area, a regional-burial low-grade metamorphism at anchizone conditions (T≤190°C) and low-pressure conditions (P≥1.3 kbar) has been described. The highest observed temperatures are related to a contact metamorphism produced by nearby Jurassic intrusions, with aP-Testimate at the immediate contact zone of ~650–690°C and 4 kbar.The whole-rock K-Ar age of 174±5 Ma is interpreted as belonging to the contact metamorphism due to the intrusion of Jurassic plutons (165±5 Ma to 175±5 Ma). A time-interval of ~20 Ma between the diagenesis (206 Ma) and the anchizonal very low-grade metamorphism (181–184 Ma) is obtained, and a rate of subsidence of ~120 m/Ma is proposed for these Triassic-Jurassic basins. A thermal influence on the burial, very low-grade, regional metamorphism is invoked.

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.

Progressive Regional Metamorphism in Southern New Zealand

1938 ◽  
Vol 75 (4) ◽  
pp. 160-174 ◽  
Author(s):  
F. J. Turner
Keyword(s):  
New Zealand ◽  
Regional Metamorphism ◽  
Parent Rock ◽  
Chemical Compositions ◽  
Low Grade ◽  
Scottish Highlands ◽  
The Past ◽  
Structural Peculiarities ◽  
Chemical Conditions ◽  
Pelitic Rocks

During the past ten years a number of papers dealing with progressive regional metamorphism in the southern portion of New Zealand have been published. In the following pages a brief summary of the assemblages of minerals typical of the various metamorphic zones is given, but the writer's main object is to draw attention to certain mineralogical and structural peculiarities that appear to differ in some degree from what are usually regarded as the normal features of regional metamorphism in such classic areas as the Scottish Highlands and the Caledonian chain of Norway. The possibility that such departures from the normal may in some instances be connected with chemical peculiarities in the parent rock is suggested by such phenomena as the well-known general limitation of chloritoid, staurolite, and low-grade garnets to pelitic rocks of special chemical compositions. Other unusual features, especially when found to recur in widely separated regions, may well be governed by some particular combination of physical rather than chemical conditions.

Metamorphism of the Settler Schist, southwest of Yale, British Columbia

1976 ◽  
Vol 13 (3) ◽  
pp. 405-421 ◽  
Author(s):  
Lee C. Pigage
Keyword(s):  
British Columbia ◽  
Linear Regression ◽  
Microprobe Analysis ◽  
Regional Metamorphism ◽  
Fluid Phase ◽  
Contact Metamorphism ◽  
Major Constituent ◽  
Minor Components ◽  
Mineral Assemblages ◽  
Regression Techniques

Pelitic metasediments immediately southwest of Yale, British Columbia contain mineral assemblages characteristic of staurolite through sillimanite zones of the Barrovian facies series. Microprobe analyses of major constituent phases in the pelites are combined with linear regression techniques to formulate probable kyanite- and sillimanite-forming reactions.A zone some 3 km wide contains the assemblage staurolite–kyanite–garnet–biotite–muscovite–quartz–plagioclase-ilmenite-rutile, which is univariant in AFM projection. Within precision limits of microprobe analysis, this assemblage is also univariant using linear regression techniques. Univariant relations are possible if [Formula: see text] with the composition of the fluid phase being buffered by the progressing reaction. This assemblage emphasizes the need for precise analyses when using the regression method, since minor components are often within permissible error limits rather than being balanced.Pelitic and calc-silicate assemblages from the metasediments restrict estimates of pressure–temperature conditions during regional metamorphism to 6–8 kbar and 550–770 °C. Pseudomorphs after andalusite indicate that contact metamorphism preceded regional upgrading of the pelites.

The Flinton Group: a late Precambrian metasedimentary succession in the Grenville Province of eastern Ontario

1980 ◽  
Vol 17 (12) ◽  
pp. 1685-1707 ◽  
Author(s):  
John M. Moore Jr. ◽  
Peter H. Thompson
Keyword(s):  
Regional Metamorphism ◽  
Grenville Province ◽  
Arc Volcanism ◽  
Late Precambrian ◽  
Granitic Intrusions ◽  
Group A ◽  
Eastern Ontario ◽  
Orogenic Cycle ◽  
Uplift And Erosion ◽  
Block Faulting

Clastic and carbonate metasediments, preserved in narrow synclines, have been correlated over an area of 2000 km2. These strata, the Flinton Group, lie unconformably on metamorphosed volcanic, clastic, and carbonate rocks, and on large granitic intrusions. The group, which comprises six formations, has undergone at least two major folding episodes and one main regional metamorphism of varying grade. The only post-Flinton intrusions are pegmatites at high grade and one tectonically emplaced ultramafic slice.Depositional environment ranged from fluvial to moderate-depth marine. Rapid facies changes, coupled with persistence of some units along strike and close relationships between facies and underlying lithology, point to local sources and local tectonic control of deposition basins. At the onset of sedimentation, a deeply weathered source terrain yielded mature basal redbeds, which were succeeded by less mature clastics as block faulting caused increase of relief between sources and basins. These facies passed offshore into finer, more reduced sediments. Deposition took place between 1050 and 1080 (±25) Ma ago, after arc volcanism, plutonism, uplift, and erosion, and before major regional metamorphism. All these events can be grouped within the Grenvillian orogenic cycle, spanning at least the interval 1300–1000 Ma and including, in eastern Ontario, the pre-Flinton Elzevirian Orogeny and post-Flinton Ottawan Orogeny.

Varying Trends in the Metamorphism of Dolerites

1951 ◽  
Vol 88 (1) ◽  
pp. 25-35 ◽  
Author(s):  
John Sutton ◽  
Janet Watson
Keyword(s):  
Regional Metamorphism ◽  
Metamorphic Grade ◽  
Low Grade ◽  
Basic Rocks ◽  
High Metamorphic Grade

AbstractThe metamorphism of Pre-Cambrian dolerites in the Northwest Highlands is described and compared with that of basic rocks in the Southwest Highlands, Banffshire and other regions. The first products of metamorphism are not the same in every area. It is suggested that the trend of regional metamorphism differs according to the environment in which it took place, and that a sequence of changes established in one area cannot be used as a standard by which to judge the changes in other areas. In particular, rocks of high metamorphic grade have not invariably passed through stages characterized by low-grade minerals.

The event geological maps: a new predictive tool to identify potential NOA (Naturally Occurring Asbestos) lithologies, Example from the Pyrenees (France).

2020 ◽  
Author(s):  
Florence Cagnard ◽  
Didier Lahondère ◽  
Benjamin Le Bayon ◽  
Aurore Hertout ◽  
Thierry Baudin ◽  
...  
Keyword(s):  
Hydrothermal Alteration ◽  
Regional Metamorphism ◽  
Contact Metamorphism ◽  
Natural Environments ◽  
Field Observations ◽  
Predictive Tool ◽  
Naturally Occurring ◽  
Geological Maps ◽  
Naturally Occurring Asbestos ◽  
Geological Event

&lt;p&gt;The event geological maps consist in innovative numerical maps that were just designed and produced for the first time, as part of the RGF (&amp;#8220;French Geological Referential&amp;#8221;) mapping program in the Pyrenees. Rocks acquire their mineralogical, structural and textural characteristics through a complex geological history reflecting successive stages of transformation (i.e. metamorphism, deformation, alteration&amp;#8230;), so called &amp;#8220;geological events&amp;#8221;. Classical geological maps can only represent some of these events.&amp;#160; In the Pyrenean orogenic belt, which results from a polyphase tectono-metamorphic history over 600 Ma (from Precambrian to present), 3400 geological events were identified. Such geological events were classified by types (e.g. deposit, volcanism, intrusion, metamorphism, weathering, hydrothermal alteration&amp;#8230;) and time periods. They were referenced into a database and associated to mapped features (120,000 polygons and lines), coming from a compilation of 60 geological maps at 1: 50,000 scale.&lt;/p&gt;&lt;p&gt;In the Pyrenees, Naturally Occurring Asbestos (NOA) mostly occur in specific lithologies such as ultrabasic, basic and intermediate plutonic rocks, and meta-limestones. These rocks may be affected by different metamorphic events (i.e. hydrothermal alteration, greenschist and/or HT-LP regional metamorphism, contact metamorphism). We performed a GIS treatment to produce a predictive map of potential NOA hosting lithologies. This treatment crosses lithological and selected geological event informations (e.g different metamorphic and alteration events).&lt;/p&gt;&lt;p&gt;Subsequent geological field investigations with associated sampling and laboratory analyses (combining optical microscopy, microprobe and SEM analyses) allowed us to identify and characterize fibrous and asbestiform mineralogical species. Results of this work particularly emphasize: (i) the importance of actinolite-asbestos in doleritic rocks, and (ii) the occurrence of fibrous actinolite/tremolite in different marbles and skarns. Finally, we present a 1: 50,000 scale map of potential NOA occurrences in the Pyrenees.&lt;/p&gt;&lt;p&gt;Conversely, field observations allowed us to improve both the lithostratigraphic and the event geological maps, in particular with the identification of geological domains where intense hydrothermal alteration was not previously mapped. All the data (maps of potential NOA occurrences, field observations and results of laboratory analyses) are stored in a geospatial database, partly accessible to the public. This work illustrates a possible use of geological event maps as a powerful innovative and predictivity tool. This approach will be useful in the context of the evolution of French regulations now imposing the search for asbestos before all types of works in natural environments.&lt;/p&gt;

Controls of copper mineralization at Coniston, English Lake District

1977 ◽  
Vol 114 (3) ◽  
pp. 195-202 ◽  
Author(s):  
G. W. Dagger
Keyword(s):  
Regional Metamorphism ◽  
Fracture Pattern ◽  
Main Phase ◽  
Low Grade ◽  
Lake District ◽  
Granite Intrusion ◽  
Copper Mineralization ◽  
English Lake District ◽  
Textural Evidence ◽  
Volcanic Series

SummaryAnalysis of the fracture pattern in the Coniston area of the Lake District indicates that copper mineralization is localized in a series of fractures produced during the main phase of deformation affecting the Borrowdale Volcanic Series. Three events are recognized on the basis of field and textural evidence obtained from polished sections: an early haematite mineralization, correlated with the low grade regional metamorphism affecting the rocks; the main phase of sulphide mineralization, with zoning, which is correlated with a granite intrusion at depth; and a late renewed movement on the veins, with carbonate mineralization, believed to be related to uplift of the granite.

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