Rb–Sr Isotopic Studies of the Lac Croche Complex Grenville Province, Quebec

1972 ◽  
Vol 9 (9) ◽  
pp. 1180-1186 ◽  
Author(s):  
Jackson M. Barton Jr. ◽  
Ronald Doig
Keyword(s):  
Common Source ◽  
Grenville Province ◽  
Shaped Body ◽  
Rock Types ◽  
Igneous Origin ◽  
Isotopic Studies ◽  
Augen Gneiss

The Lac Croche complex is a deformed basin-shaped body of igneous origin, situated northeast of the Morin anorthosite pluton. Rb–Sr isotopic studies of the rock-types comprising the complex yield the following results: (a) The mangeritic augen gneiss, leuconoritic gneiss, monzonite, and monzonorite crystallized approximately 1124 m.y. ago with an initial 87Sr/86Sr ratio of 0.7042, compatible with these rocks being derivatives from a common source; (b) The K-feldspar – quartz gneiss crystallized approximately 1143 m.y. ago with an 87Sr/86Sr ratio of 0.7025; and (c) the granite crystallized approximately 961 m.y. ago with an 87Sr/86Sr ratio of 0.7084. Because the mangeritic augen gneiss and leuconoritic gneiss were deformed with the complex and the monzonite and monzonorite crystallized after this deformation, and because these rock types define an isochron, we conclude that the deformation of the Lac Croche complex took place approximately 1124 m.y. ago. If this deformation was a result of the emplacement of the Morin pluton, then this latter body also had to be emplaced at this time. These events constitute the main penetrative deformation in the area and represent the Grenville orogenic event.

The nature of the upper mantle

1981 ◽  
Vol 44 (333) ◽  
pp. 1-18 ◽  
Author(s):  
J. B. Dawson
Keyword(s):  
Plastic Deformation ◽  
Brittle Fracture ◽  
Isotopic Composition ◽  
Upper Mantle ◽  
Rare Gases ◽  
Rock Types ◽  
Igneous Origin ◽  
Isotopic Studies ◽  
Original Rock

AbstractThe nature of the upper mantle below the ancient cratonic areas can be deduced by study of the xenolith suites in kimberlites. Studies on the proportions of xenoliths, together with their mineralogy and chemistry, suggest an upper mantle containing an upper harzburgite zone and a lower lherzolite zone, with both of these zones containing chemical and mineralogical variants, together with minor rock types such as glimmerites, MARID-suite rocks, pyroxenites, and eclogites. Isotopic studies of the phases in xenoliths have yielded restricted ranges of values for the isotopic composition of hydrogen, carbon, oxygen, and sulphur which are tentatively identified as the true isotopic values for these elements in the upper mantle. In addition, recent discoveries suggest that diamond may be a primary uppermantle phase.The textures and fabrics of the xenoliths indicate that plastic deformation has taken place in connection with the intrusive kimberlite event, and also in earlier events unconnected with the kimberlite event. In addition, brittle fracture has been observed, this fracturing often being accompanied by the filling of the ensuing veins and joints by fluids that have crystallized potassium-, titanium-, and water-rich phases; limited metasomatism of peridotite wall rocks accompanies this vein filling and more widespread pervasive metasomatism may also be present.Although most upper-mantle rocks are now metamorphic, in some rare instances there are relics of earlier rock types that have not been completely obliterated by subsequent metamorphic events; most of these could be attributed to an igneous origin and in most cases during subsequent metamorphism the original rock types have been subjected to increasing pressures and/or lower temperatures.Although the source of most materials now present at the earth's surface can be directly attributed to some identifiable source within upper-mantle rocks, no source has yet been identified for CO2, N, P, and the rare gases.

The oxygen isotope composition of the surface crystalline rocks of the Canadian Shield

1978 ◽  
Vol 15 (11) ◽  
pp. 1773-1782 ◽  
Author(s):  
Yuch-Ning Shieh ◽  
Henry P. Schwarcz
Keyword(s):  
Isotope Composition ◽  
Crystalline Rocks ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Baffin Island ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Northern District ◽  
Basic Rocks

The average 18O/16O ratios of the major rock types of the surface crystalline rocks in different parts of the Canadian Precambrian Shield have been determined, using 47 composite samples prepared from 2221 individual rock specimens. The sampling areas include Baffin Island, northern and southwestern Quebec, Battle Harbour – Cartwright, northern District of Keewatin, Fort Enterprise, Snowbird Lake, Kasmere Lake, and Saskatchewan, covering approximately 1 400 000 km2. The granitic rocks from the Superior, Slave, and Churchill Provinces vary only slightly from region to region (δ18O = 6.9–8.4‰) and are significantly lower in 18O than similar rock types from the younger Grenville Province (δ = 9.2–10.0‰). The sedimentary and metasedimentary rocks have δ18O = 9.0–11.7‰ and hence are considerably lower than their Phanerozoic equivalents, possibly reflecting the presence of a high percentage of little-altered igneous rock detritus in the original sediments. The basic rocks in most regions fall within a δ18O range of 6.8–7.6‰, except in northern and southwestern Quebec where the δ-values are abnormally high (8.5–8.9‰). The overall average 18O/16O ratio of the surface crystalline rocks of the Canadian Shield is estimated to be 8.0‰, which represents an enrichment with respect to probable mantle derived starting materials by about 2‰.

Computerized geological mapping in the Grenville Province, Quebec

1970 ◽  
Vol 7 (6) ◽  
pp. 1357-1373 ◽  
Author(s):  
H. R. Wynne-Edwards ◽  
A. Nandi ◽  
M. M. Kehlenbeck ◽  
A. F. Laurin ◽  
K. N. M. Sharma ◽  
...  
Keyword(s):  
Processing System ◽  
Structural Data ◽  
Data Bank ◽  
Geological Mapping ◽  
Grenville Province ◽  
Geological Interpretation ◽  
Rock Types ◽  
Potential Map ◽  
Computer Based ◽  
Project Data

Since 1965, the Quebec Department of Natural Resources has conducted reconnaissance mapping in the Grenville Province, completing to date over 70 000 square miles (181 000 km2). In 1968 a computer-based data processing system was designed at Queen's University, and applied to this Grenville Project. Data are recorded in the field on input documents designed to recover a complete description of the structure and lithology of an outcrop in a standard and reproducible form. From these records a data bank, now with descriptions of over 5000 outcrops, has been constructed for the field seasons of 1968 and 1969. Lthological sorting programs based on the textural and mineralogical qualities used to define rock types have been written to provide listings of some 40 potential map-units. Outcrop maps identifying lithologies have been drawn on a computer-driven drum plotter to provide the geologist with a basic document from which to make geological interpretation. Structural data have been extracted and plotted in equal-area projections, and also plotted on maps directly by machine, using standard structural symbols for layering, foliation, and lineation. The system has upgraded the standard of data collection in the field, and provides a rapid and versatile means of handling data and of interpreting the geology. The data bank, when made publicly available, will enable users of government geological maps and reports to reinterpret the area in their own manner, or freely to add any proprietary data in the preparation of revisions.

Crustal architecture and tectonic assembly of the Central Gneiss Belt, southwestern Grenville Province, Canada: a new interpretation

2000 ◽  
Vol 37 (2-3) ◽  
pp. 217-234 ◽  
Author(s):  
J WF Ketchum ◽  
A Davidson
Keyword(s):  
Structural Model ◽  
Hanging Wall ◽  
Mafic Rock ◽  
Grenville Province ◽  
The North ◽  
Rock Types ◽  
Structural Barrier ◽  
New Interpretation ◽  
Central Gneiss Belt ◽  
Tectonic Boundary

The Central Gneiss Belt, southwestern Grenville Province, is characterized by parautochthonous crust in the north and allochthonous lithotectonic domains in the south. Despite nearly two decades of study, the basal décollement to allochthonous domains transported from the southeast, known as the allochthon boundary thrust, has not been precisely located throughout much of the belt. Between Lake Nipissing and Georgian Bay where its surface trace is known, it separates 1.24 Ga Sudbury metadiabase in the footwall from eclogite remnants and 1.17-1.15 Ga coronitic olivine metagabbro confined to its hanging wall. On the premise that this relationship can be used to trace the allochthon boundary thrust elsewhere in the Central Gneiss Belt, we have sought to extend the known distribution of these mafic rock types, making use of field, petrographic, and geochemical criteria to identify them. New occurrences of all three mafic types are identified in a region extending from south of Lake Nipissing to western Quebec, and the mutually exclusive pattern of occurrence is maintained within this region. Structural trends and reconnaissance mapping of high-strain zones that appear to represent a structural barrier to the mafic suites suggest that the allochthon boundary thrust lies well to the north of its previously suggested location. Our preferred surface trace for it passes around the southern end of the Powassan batholith and through the town of North Bay before turning east to join up with the Lac Watson shear zone in western Quebec. This suggests that a large segment of "parautochthonous" crust lying north of, and including, the Algonquin domain is in fact allochthonous. The mutually exclusive distribution of the mafic suites points to significant separation of allochthonous and parautochthonous components prior to the Grenvillian orogeny, in accord with models of pre-Grenvillian continental rifting proposed by others. Despite a relative abundance of geological and geochronological data for the Central Gneiss Belt and a mafic rock distribution that appears to successfully locate a major tectonic boundary, we emphasize the need for additional field and laboratory work aimed at testing our structural model.

Pre-Grenvillian and Grenvillian lithotectonic regions in eastern Labrador—correlations with the Sveconorwegian Orogenic Belt in Sweden

1984 ◽  
Vol 21 (6) ◽  
pp. 678-693 ◽  
Author(s):  
Charles F. Gower ◽  
Victor Owen
Keyword(s):  
Orogenic Belt ◽  
Grenville Province ◽  
Pluton Emplacement ◽  
Mafic Intrusions ◽  
The North ◽  
Rock Types ◽  
Structural Style ◽  
Opening And Closing ◽  
Layered Mafic Intrusions ◽  
Middle Proterozoic

The Trans-Labrador batholith, Groswater Bay Terrane, and Lake Melville Terrane are three major crustal segments located adjacent to or within the Grenville Province in eastern Labrador. Each crustal segment is a distinct lithotectonic entity displaying contrasts with each other in proportions of rock types, structural style, and metamorphic imprint. Together they indicate a unilateral polarity to the region, partly reflecting Grenvillian tectonism, which sliced the region into thrust-bound blocks.In all three crustal segments, an Archean or Aphebian gneissic basement is inferred onto or adjacent to which ca. 1900–1700 Ma supracrustal rocks were deposited. Deformation, metamorphism, and granitoid pluton emplacement were partly coeval with and partly postdated the supracrustal assemblages. In the north, tectonothermal effects can be assigned to Hudsonian–Ketilidian orogenesis but their peak was 50–100 Ma later farther south. Post-tectonic granitoid plutons and layered mafic intrusions were emplaced at about 1650–1600 Ma, and further pulses of mafic intrusion occurred prior to the Grenvillian Orogeny.Comparison with the Sveconorwegian Orogenic Belt in southern Sweden shows remarkable similarities in lithologies, geological histories, and structural style. The Småland–Värmland granitoid belt, Eastern Pregothian mega-unit, and Western Pregothian mega-unit are interpreted here to be the Scandinavian counterparts of the Trans-Labrador batholith, Groswater Bay Terrane, and Lake Melville Terrane, respectively. This correlation is taken to indicate that both regions were part of the same tectonic margin during Middle Proterozoic times.The implication of this correlation is that the opening and closing of the lapetus Ocean resulted in a 2000 km sinistral "offset" of the Grenvillian–Sveconorwegian Front and other Precambrian features on either side of the Caledonides suture.

scholarly journals A preliminary engineering geological study in the northern part of the Taplejung Window, far eastern Lesser Nepal Himalaya

2004 ◽  
Vol 29 ◽  
Author(s):  
T. P. Gautam ◽  
D. R. Sonyok ◽  
B. N. Upreti ◽  
S. M. Rai ◽  
H. Sakai
Keyword(s):  
Hanging Wall ◽  
Agricultural Practices ◽  
Main Central Thrust ◽  
Rock Types ◽  
Valley Slope ◽  
Detailed Surface ◽  
Subsurface Investigation ◽  
Augen Gneiss ◽  
Bottom To Top ◽  
Far Eastern

In the northern part of the Taplejung area, two tectonic units are recognised. These are the Higher Himalayan and Lesser Himalayan Sequences separated by the Main Central Thrust (MCT). The Lesser Himalayan Sequence is exposed in the Taplejung Window represented by Taplejung Formation, Mitlung Augen Gneiss, and Lingkhim Schist from the bottom to top. The main rock types in the Lesser Himalayan Sequence are phyllite, schist, metasandstone, quartzite and augen gneiss. Three Proterozoic granitic bodies are intruded into Taplejung Formation: Tamor River Granite, Amarpur Granite and Kabeli Khola Granite. The rocks of the Higher Himalaya on the hanging wall of the MCT are composed of kyanite-sillimanite bearing banded gneiss, orthogneiss, migmatite, quartzite. Three major landslides in the area, viz., Hangdewa, Hireba, and Paire lie along the valley slope sides of the Tamor River. Stream erosion and incision, presence of highly weathered rocks, surface and subsurface drainage are responsible in activating the landslides. Due to the presence of mainly weathered phyllites, favourable structural orientations and wet cultivation practice in the area have contributed to the development of these landslides.  The Hangdewa and Hireba landslides have endangered the villages in between them and ultimately the Suketar airport. The landslides are gradually destroying more and more areas of cultivated land and property and increased loss of human lives. Excessive anthropogenic interference in the form of development activities like unplanned urbanization, deforestation and unfavorable agricultural practices have greatly aggravated the situation. The intensity of damages amplifies during the late part of monsoon each year. The study suggests that further detailed surface and subsurface investigation of the landslides are needed to prevent further loss of lives and property.

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