Proterozoic metamorphism in the Grenville Province: a study in the Double Mer – Lake Melville area, eastern Labrador

1988 ◽  
Vol 25 (11) ◽  
pp. 1895-1905 ◽  
Author(s):  
C. F. Gower ◽  
P. Erdmer
Keyword(s):  
Granulite Facies ◽  
High Grade ◽  
Structural Configuration ◽  
Geochronological Data ◽  
Granitic Gneiss ◽  
Grenville Province ◽  
Accessory Minerals ◽  
Mineral Assemblages ◽  
Host Rocks ◽  
Metamorphic Gradient

A regional metamorphic gradient from upper greenschist to granulite facies is identified south of the Grenville front in the Double Mer – Lake Melville area of eastern Labrador. Mineral assemblages in politic–granitic gneiss, amphibole-bearing quartzo-feldspathic gneiss, and coronitic metagabbro allow three major metamorphic domains to be established. These are collectively divisible into 11 subdomains. Geothermobarometry applied to the higher grade domains suggests that each is characterized by specific P–T conditions, which achieved 1000–1100 MPa and 700–800 °C in the deepest level rocks.The problem of reconciling geochronological data (which record a major orogenic event at 1650 Ma) with the occurrence of high-grade mineral assemblages in 1426 Ma metagabbro (which suggests a pervasive Grenvillian event) is discussed in terms of three models. The preferred model envisages crustal stabilization at 1650–1600 Ma to give high-grade mineral assemblages seen in the host rocks and with which mineral assemblages in coronitic metagabbro equilibrated after their emplacement at 1426 Ma. During Grenvillian orogenesis (1080–920 Ma) the present structural configuration was achieved by thrust stacking. This imparted a sporadic metamorphic and structural overprint and Grenvillian ages in selected accessory minerals.

Progressive metamorphism of pelitic and quartzofeldspathic rocks in the Grenville Province of western Labrador — tectonic implications of bathozone 6 assemblages

1983 ◽  
Vol 20 (12) ◽  
pp. 1791-1804 ◽  
Author(s):  
T. Rivers
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Granulite Facies ◽  
Lithostatic Pressure ◽  
Lower Grade ◽  
High Grade ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Mineral Assemblages ◽  
Grenvillian Orogeny

Aphebian metapelites and quartzofeldspathic rocks from the Grenville Province south of the Labrador Trough display progressive changes in mineral assemblages as a result of Grenvillian metamorphism, consistent with variation in grade from greenschist to upper amphibolite facies. The following metamorphic zones have been delineated: (i) chlorite–muscovite; (ii) chlorite–muscovite–biotite; (iii) chlorite–muscovite–biotite–garnet; (iv) muscovite–staurolite–kyanite; (v) muscovite–garnet–biotite–kyanite; (vi) muscovite–garnet–biotite–kyanite–granitic veins; (vii) K–feldspar–kyanite – granitic veins; (viii) K-feldspar–sillimanite–granitic veins. Reactions linking the lower grade metamorphic zones are interpreted to be dehydration phenomena, whilst anatectic reactions occur at higher grades. At lower metamorphic grades aH2O was high [Formula: see text] but it declined progressively as water entered the melt phase during higher grade anatectic reactions. With the onset of vapour-absent anatexis, the restite assemblage became essentially "dry" [Formula: see text], and biotite breakdown occurred in granulite-facies rocks east of the study area. Consideration of available experimental data suggests that metamorphic temperatures ranged from approximately 450 to 750 °C across the study area. Lithostatic pressure during metamorphism reached about 8 kbar (800 MPa) in the high-grade zones, with estimates at lower grades being poorly constrained; however, a steep pressure gradient across the map area is postulated.This is the first reported occurrence of bathozone 6 assemblages from a progressive metamorphic sequence, and it indicates the presence of an unusually great thickness of supracrustal rocks during the Grenvillian Orogeny. This was achieved by imbricate stacking of thrust slices, perhaps doubling the thickness of the crust in the Grenville Front Tectonic Zone, creating a huge gravity anomaly of which a remnant still persists today.

A model for the origin of the Lac St. Jean anorthosite massif

1976 ◽  
Vol 13 (2) ◽  
pp. 389-399 ◽  
Author(s):  
R. A. Frith ◽  
K. L. Currie
Keyword(s):  
Experimental Data ◽  
Partial Melting ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Calc Alkaline ◽  
Grenville Province ◽  
Thermal Event ◽  
Anorthosite Massif ◽  
Mineral Assemblages ◽  
Potassic Rocks

An ancient tonalitic complex becomes migmatitic around the Lac St. Jean massif, ultimately losing its identity in the high grade metamorphic rocks surrounding the anorthosite. Field relations suggest extreme metamorphism and anatexis of tonalitic rocks. Experimental data show that extensive partial melting of the tonalite leaves an anorthositic residue. The same process operating on more potassic rocks would leave monzonitic or quartz syenitic residues. Synthesis of experimental data suggests that the process could operate at pressures of 5–8 kbar and temperatures of 800–1000 °C, which are compatible with mineral assemblages around the anorthosite massif. Slightly higher temperatures at the end of the process could generate magmatic anorthosite.Application of the model to the Grenville province as a whole predicts generation of anorthosite during a long-lived thermal event of unusual intensity. Residual anorthosite would occur as a substratum in the crust, overlain by high-grade metamorphic rocks intruded by anorthosite and syenitic rocks, while higher levels in the crust would display abundant calc-alkaline plutons and extrusives.

Coeval migmatites and granulites, Muskoka domain, southwestern Grenville Province, Ontario

2002 ◽  
Vol 39 (2) ◽  
pp. 239-258 ◽  
Author(s):  
Hilke Timmermann ◽  
Rebecca A Jamieson ◽  
Randall R Parrish ◽  
Nicholas G Culshaw
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Geochronological Data ◽  
Grenville Province ◽  
Mafic Enclaves ◽  
High Grade Metamorphism ◽  
Granitoid Gneisses ◽  
Central Gneiss Belt ◽  
The Relationship ◽  
Extensional Structures

We present new field observations and petrologic and geochronological data from the Muskoka domain in the southwestern Grenville Province of Ontario in an attempt to constrain the relationship between amphibolite-facies and granulite-facies gneisses in areas of transitional metamorphic grade, and to examine their implication for tectonometamorphic models for the Grenville Province of Ontario. The predominant medium-grained amphibolite-facies migmatitic orthogneisses of the Muskoka domain contain several generations of leucosome, some of which are related to southeast-directed extensional structures. The amphibolite-facies granitoid gneisses contain numerous mafic enclaves with granulite-facies assemblages recrystallized from anhydrous precursors during Grenvillian metamorphism. Other associated granulites are characterized by their patchy occurrence and gradational contacts, similar to the charnockites in southern India. Patchy granulites, leucocratic vein networks in mafic enclaves, and crosscutting leucocratic granulite veins are interpreted to have formed as a result of local differences in reaction sequences and (or) fluid compositions. The U–Pb zircon lower intercept age of the patchy granulites overlaps with the previously determined range of 1080–1060 Ma for high-grade metamorphism in the Muskoka domain, while zircon and titanite from a crosscutting granulite vein crystallized at about 1065–1045 Ma, supporting a Grenvillian age for granulite formation. Peak metamorphic conditions of 750–850°C and 10–11.5 kbar (1 kbar = 100 MPa) were determined from the mafic enclaves, whereas the more felsic migmatites reequilibrated at somewhat lower temperatures. The high temperatures caused extensive migmatization and facilitated rheological weakening of the Muskoka domain 10–25 million years after the start of the Ottawan orogeny in the Central Gneiss Belt.

Metamorphic conditions of late Archean high-grade gneisses, Minnesota River valley, U.S.A.

1986 ◽  
Vol 23 (5) ◽  
pp. 633-645 ◽  
Author(s):  
D. P. Moecher ◽  
D. Perkins III ◽  
P. J. Leier-Englehardt ◽  
L. G. Medaris Jr.
Keyword(s):  
Granulite Facies ◽  
River Valley ◽  
High Grade ◽  
Compositional Zoning ◽  
Minnesota River ◽  
Large Pressure ◽  
Temperature And Pressure ◽  
Minnesota River Valley ◽  
Metamorphic Gradient ◽  
Real Temperature

A detailed, comparative geothermobarometric analysis for the Minnesota River valley (MRV) Archean gneiss and migmatite terrane yields temperature and pressure ranges of 650–750 °C and 4.5–7.5 kbar (450–750 MPa), based on garnet–biotite, two-feldspar, garnet–clinopyroxene, garnet–cordierite, orthopyroxene–clinopyroxene, and magnetite–ilmenite thermometry and garnet–cordierite–sillimanite–quartz and garnet–orthopyroxene–plagioclase–quartz barometry. The temperature variation observed is interpreted to be primarily a result of varying degrees of re-equilibration of assemblages with falling temperature but may include real temperature variations between areas exhibiting granulite facies versus upper amphibolite facies–migmatitic lithologies. The large pressure range is primarily a result of differences among the pressure calibrations applied but may also record variations in pressure within the terrane. Lower pressures are consistent with the occurrence of cordierite-bearing assemblages at Granite Falls and Delhi. Based on the compositional zoning patterns determined in garnet adjacent to clinopyroxene, orthopyroxene, cordierite, and biotite and in orthopyroxene adjacent to garnet, the granulites are interpreted to have experienced nearly isobaric cooling, suggesting a magmatically influenced thermal regime may have been responsible for the high-grade conditions and relatively high transient metamorphic gradient (32 °C/km) attained in the MRV.

Hydrothermally altered volcanic rocks metamorphosed at granulite-facies conditions: an example from the Grenville Province

2017 ◽  
Vol 54 (6) ◽  
pp. 622-638 ◽  
Author(s):  
Marisa Hindemith ◽  
Aphrodite Indares ◽  
Stephen Piercey
Keyword(s):  
Hydrothermal Alteration ◽  
Volcanic Rocks ◽  
Granulite Facies ◽  
Metamorphic Overprint ◽  
Grenville Province ◽  
Rock Types ◽  
Argillic Alteration ◽  
New Findings ◽  
Mineral Assemblages ◽  
Liberation Analysis

A 1.2 Ga association of aluminous gneisses, garnetites, and white felsic gneisses of andesitic composition in the southern Manicouagan area (central Grenville Province) provides evidence consistent with protolith formation and hydrothermal alteration in a submarine volcanic environment. In addition to field relations, potential relics of quartz phenocrysts in the aluminous gneisses, revealed by SEM–MLA (scanning electron microscope with a mineral liberation analysis software) imaging, are consistent with a volcanic precursor. Moreover, in these rocks, aluminous nodules and seams of sillimanite are considered to represent metamorphosed hydrothermal mineral assemblages and to reflect former pathways of hydrothermal fluid. These features are preserved despite the Grenvillian granulite-facies metamorphic overprint and evidence of partial melting. In addition, the garnetites are inferred to represent hydrothermally altered products of the white gneisses, based on the gradational contacts between the two rock types. The compositional ranges of minerals are generally similar to those of granulite-facies metapelites, but moderately elevated contents of Mn in garnet from the garnetites, and Zn in spinel from the aluminous gneisses, are consistent with hydrothermal addition of these elements to the protolith. The most prominent alteration trends are an increase in Fe–Mg–Mn from the white gneisses to the aluminous gneisses and the garnetites, and a trend of increasing alumina index in some white gneisses, suggesting mild argillic alteration. The new findings highlight the preservation of early hydrothermal alteration in high-grade metamorphic belts in the Grenville Province, and these altered rocks are potential targets for exploration.

Polymetamorphism of marbles in the Morin terrane, Grenville Province, Quebec

2005 ◽  
Vol 42 (10) ◽  
pp. 1949-1965 ◽  
Author(s):  
William H Peck ◽  
Michael T DeAngelis ◽  
Michael T Meredith ◽  
Etienne Morin
Keyword(s):  
Shear Zones ◽  
Granulite Facies ◽  
Grenville Province ◽  
Anorthosite Massif ◽  
Mineral Assemblages ◽  
Intrusive Rocks ◽  
Granitic Intrusions ◽  
T Path ◽  
The Village

The Morin terrane (Grenville Province, Quebec) is dominated by the 1.15 Ga Morin Anorthosite Massif and related granitic intrusions, all of which exhibit granulite-facies mineral assemblages. Anorthosite-suite rocks are deformed both in shear zones and in the interior of the terrane and show intrusive contact relations with marble along road cuts near the village of St. Jovite. Intrusive rocks exposed in these road cuts have well-developed skarns, which were deformed with the intrusions after emplacement. Skarn minerals are consumed by garnet-forming reactions (e.g., An + Wo = Gr + Qtz) that preserve granulite-facies temperatures and pressures. Calcite–graphite thermometry of Morin terrane marbles records temperatures of 755 ± 38 °C (n = 21), independent of proximity to anorthosite-suite plutons. Preserved metamorphic conditions and the retrograde pressure–temperature (P–T) path in the Morin terrane are very similar to conditions during the 1.07 Ga Ottawan orogeny in the Adirondack Highlands. Metamorphism and deformation of anorthosite-suite rocks and marbles of the Morin terrane are consistent with anorthosite intrusion followed by a distinct granulite-facies overprint.

Timing and duration of melting in the mid orogenic crust: Constraints from U–Pb (SHRIMP) data, Muskoka and Shawanaga domains, Grenville Province, Ontario

2004 ◽  
Vol 41 (11) ◽  
pp. 1339-1365 ◽  
Author(s):  
Trond Slagstad ◽  
Michael A Hamilton ◽  
Rebecca A Jamieson ◽  
Nicholas G Culshaw
Keyword(s):  
High Grade ◽  
Field Observations ◽  
Ion Microprobe ◽  
Melt Crystallization ◽  
Geochronological Data ◽  
Grenville Province ◽  
Deformational History ◽  
High Grade Metamorphism ◽  
Grenvillian Orogeny ◽  
Central Gneiss Belt

The Central Gneiss Belt in the Grenville Province, Ontario, exposes metaplutonic rocks, orthogneisses, and minor paragneisses that were deformed and metamorphosed at crustal depths of 20–35 km during the Mesoproterozoic Grenvillian orogeny. We present sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon data from eight samples of migmatitic orthogneiss, granite, and pegmatite from the Muskoka and Shawanaga domains that constrain the age and duration of partial melting in the mid orogenic crust. Our results support earlier interpretations that the protoliths to these migmatitic orthogneisses formed at ca. 1450 Ma. Emplacement and crystallization of granite and pegmatite in the Shawanaga domain took place at ca. 1089 Ma, apparently coevally with deformation and high-grade metamorphism. Leucosomes in the Muskoka and Shawanaga domains yield ages of 1067 and 1047 Ma, respectively, interpreted as the ages of melt crystallization. The geochronological data and field observations suggest that melt was present at the mid-crustal level of the Grenville orogen during a significant part of its deformational history, probably at least 20–30 million years. By analogy with modern orogens, the amount and duration of melting observed in the Muskoka and Shawanaga domains may have had an impact on the orogenic evolution of the area.

Quartz microstructures and c-axis preferred orientations in high-grade gneisses and mylonites around the Morin anorthosite (Grenville Province)

1997 ◽  
Vol 34 (6) ◽  
pp. 819-832 ◽  
Author(s):  
Xiao-ou Zhao ◽  
Shaocheng Ji ◽  
Jacques Martignole
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Granulite Facies ◽  
High Grade ◽  
Grenville Province ◽  
The North ◽  
Deformation Features ◽  
Type 3

Quartz in deformed rocks from two large, high-grade shear zones around the Morin anorthosite (Morin terrane, Grenville Province) displays distinctive microstructures, as well as c-axis preferred orientations. In the west-dipping Morin shear zone, east of the Morin anorthosite, four distinct quartz microstructures (types 1–4) are identified, based on deformation features and grain size. The c-axis orientations are characterized by a single maximum near the stretching lineation and two maxima in type 1 microstructure, and by an asymmetrical, single girdle in type 2 microstructure. Quartz c axes show crossed-girdle pattern in type 3 microstructure. Both quartz microstructures and c-axis preferred orientations suggest that crystal–plastic slip and dynamic recrystallization are the dominant deformation mechanisms. The asymmetry of c-axis orientations with respect to the mylonitic foliation, as well as the substructures developed in quartz, indicates a dextral sense of shear in the Morin shear zone. Type 4 microstructure, which developed in some gneisses and granulites, is interpreted to record influence of postdeformation annealing by which quartz c-axis orientations were partially modified. In the north-northeast-trending, subvertical Labelle shear zone that separates the Morin terrane from the Mont-Laurier terrane, metamorphic assemblages and structural elements suggest that an early, sinistral strike-slip deformation occurred under granulite-facies conditions. This was overprinted by a late downdip movement of the Mont-Laurier terrane under retrogressive conditions. Quartz in felsic gneisses from this zone shows two types of microstructures: one is similar to type 4 from the Morin shear zone, the other is named type 5. Quartz c-axis orientations are complex and less systematic, due to overprinting by two episodes of deformation and possible annealing. These complexities limit the utility of quartz microstructures and c-axis data in the structural analysis of the Labelle shear zone.

Amphibolite-granulite facies assemblages in southern Nyasaland

1961 ◽  
Vol 32 (252) ◽  
pp. 725-730 ◽  
Author(s):  
S. W. Morel
Keyword(s):  
Granulite Facies ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Mineral Assemblages ◽  
Metamorphic Facies

SummaryThe mineral assemblages developed in a variety of high-grade metamorphic rocks from southern Nyasaland are compared with standard metamorphic facies mineral assemblages proposed by some authors.

Metamorphic pressure-temperature conditions of the Lützow-Holm Complex of East Antarctica deduced from Zr-in-rutile geothermometer and Al2SiO5 minerals enclosed in garnet

2021 ◽  
Author(s):  
Kota Suzuki ◽  
Tetsuo Kawakami
Keyword(s):  
Granulite Facies ◽  
Transitional Zone ◽  
East Antarctica ◽  
High Grade ◽  
Temperature Conditions ◽  
Mineral Assemblages ◽  
Facies Zone ◽  
Metamorphic Zone ◽  
Reliable Temperature ◽  
Zr In Rutile

<p>The Zr content of rutile coexisting with zircon and quartz is mainly a function of the temperature condition and is calibrated as Zr-in-rutile geothermometers. Because of their robustness under high-temperature conditions, they have been applied to granulite facies rocks instead of the conventional Fe-Mg exchange type geothermometers to estimate more reliable temperature conditions. However, it is recently pointed out that in order for rutile to retain the primary Zr content, rutile must be chemically isolated from zircon and quartz during cooling. In this context, inclusion rutile separately enclosed in garnet can be considered to retain the primary Zr content at the time of entrapment, only if rutile, zircon, and quartz are all enclosed in a contemporaneous domain of the garnet.</p><p>In this study, we re-examined the pressure-temperature (<em>P-T</em>) conditions of high-grade pelitic gneisses from selected regions (Akarui Point, Skarvsnes, Skallen, and Rundvågshetta) of the Lützow-Holm Complex (LHC), East Antarctica. The LHC has been divided into the upper-amphibolite facies zone, the transitional zone, and the granulite facies zone, based on matrix mineral assemblages of mafic- to intermediate gneisses. Akarui Point is located in the transitional zone and others in the granulite facies zone.</p><p>While previous studies commonly applied the conventional Fe-Mg exchange type geothermometers, we applied the Zr-in-rutile geothermometer of Tomkins et al. (2007) to rutile grains enclosed in garnet that also encloses zircon, quartz, and Al<sub>2</sub>SiO<sub>5</sub> minerals. By utilizing the phosphorus zoning in garnet, we defined contemporaneous domains of the garnet and identified coexisting inclusion minerals in each domain. In this way, coexisting Al<sub>2</sub>SiO<sub>5</sub> minerals and rutile grains were utilized to constrain the <em>P-T</em> condition of each domain of the garnet.</p><p>As a result, samples from Akarui Point, Skarvsnes, and Skallen were shown to have experienced almost the same <em>P-T</em> conditions around the kyanite/sillimanite transition boundary (~ 830-850 °C/~ 11 kbar). This is significantly higher than the previously estimated peak condition of 770-790 °C/7.7-9.8 kbar based on the conventional garnet-biotite geothermometer in the case of Akarui Point. From Rundvågshetta, where ultrahigh-<em>T</em> metamorphism is reported by previous studies, higher-<em>T</em> condition (850 ± 15 °C/0.1 kbar to 927 ± 16 °C/12.5 kbar) than those of other three regions was confirmed from inclusion rutile in garnet enclosing sillimanite. Therefore, the traditional metamorphic zone mapping, which classified Akarui Point as belonging to the transitional zone, does not reflect the highest metamorphic grade attained. It should be noted that the regional <em>P-T</em> conditions estimated from inclusion minerals in this study is that of earlier higher-<em>P</em> metamorphic stage than the regional <em>P-T</em> conditions determined by the metamorphic zone mapping utilizing matrix mineral assemblages. This result indicates that the Zr-in-rutile geothermometer is a powerful tool to reveal the <em>P-T</em> evolution of high-grade metamorphic terrains, when combined with detailed microstructural observations focusing on the relationship between rutile, zircon, and quartz.</p>

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