Evolution of P–T conditions during a high-grade metamorphic event in the Maniwaki area (Grenville Province)

1984 ◽  
Vol 21 (7) ◽  
pp. 853-863 ◽  
Author(s):  
A. Indares ◽  
J. Martignole
Keyword(s):  
Granulite Facies ◽  
Grenville Province ◽  
Mineral Equilibria ◽  
Metamorphic History ◽  
Average Slope ◽  
History Of ◽  
Mineral Compositions ◽  
Uplift And Erosion ◽  
Peak Pressures ◽  
Basic Rocks

Pelitic and basic rocks of the Grenville Supergroup in the Maniwaki area (100 km north of Ottawa) were selected for a detailed investigation of the metamorphic history of the Central Metasedimentary Belt of the Grenville Province.Mineral assemblages suggest metamorphic conditions of the granulite facies with local and irregular persistence of the amphibolite facies. Chemical analysis of minerals reveals a lack of equilibrium on the thin section scale. Systematic variation of mineral compositions is explained as the net result of several mineral equilibria established at different stages during the metamorphic evolution of the area. Peak temperatures obtained by biotite–garnet thermometry (cores of isolated grains) are between 760 and 860 °C, whereas clinopyroxene–garnet thermometry gives 740–820 °C. Retrograde temperatures as estimated by various thermometers range between 550 and 750 °C (biotite–garnet), 498 and 670 °C (cordierite–garnet), and 690 and 720 °C (clinopyroxene–garnet). Peak pressures were 6.5–8.5 kbar (650–850 MPa) based upon the ga–pl–sil–qtz barometer and the cpx–ga–pl–qtz barometer. Retrograde pressures of 3.5–5.5 kbar (350–550 MPa) (ga–pl–sil–qtz), 4.1–5.2 kbar (410–520 MPa) (cd–ga), and 5.7–7 kbar (570–700 MPa) (cpx–ga–pl–qtz) were determined.A compilation of results in a P–T diagram allows us to construct a retrograde gradient convex towards the T axis, with an average slope of 12 bar/°C (1.2 MPa/°C). This curve suggests fast uplift and erosion just after the peak of metamorphism followed by a long cooling stage accompanied by minor uplift.

Mineralogy and metamorphic history of norite dykes within granulite facies gneisses from Sand Mata, Rajasthan, NW India

1987 ◽  
Vol 51 (360) ◽  
pp. 207-215 ◽  
Author(s):  
Ram S. Sharma ◽  
Jane D. Sills ◽  
M. Joshi
Keyword(s):  
Country Rock ◽  
Granulite Facies ◽  
Slow Cooling ◽  
Granulite Facies Metamorphism ◽  
Tholeiitic Magma ◽  
Metamorphic History ◽  
Gneiss Complex ◽  
Corona Formation ◽  
History Of ◽  
Mineral Compositions

AbstractMetanorite dykes intrude the Banded Gneiss Complex at various places in Rajasthan, N.W. India. They show neither chilled margins nor gradational contacts with the country rock amphibolite or granulite facies gneisses. They have ophitic to subophitic texture with strongly zoned subcalcic clinopyroxene and orthopyroxene, olivine and plagioclase, with subsidiary biotite. During slow cooling a series of reaction coronas developed with garnet forming round biotite, ilmenite and orthopyroxene; hornblende round pyroxenes and orthopyroxene, hornblende ± spinel round olivine, which may be totally replaced. It is inferred that the dykes crystallised from a tholeiitic magma at about 1100-1150 °C and were intruded during the waning stages of granulite facies metamorphism. The corona minerals grew at about 650–700 °C. A series of reactions to account for the development of the coronas is proposed using measured mineral compositions. Although these reactions do not balance for individual corona formation, metamorphism was probably isochemical with Ca, Na, K, Ti, Si and H2O only mobile on the scale of a thin section. Si and H2O were possibly mobile on a larger scale.

Regional geothermobarometry in the granulite facies terrane of South India

1983 ◽  
Vol 73 (4) ◽  
pp. 221-244 ◽  
Author(s):  
M. Raith ◽  
P. Raase ◽  
D. Ackermand ◽  
R. K. Lal
Keyword(s):  
South India ◽  
Analytical Data ◽  
Granulite Facies ◽  
Critical Discussion ◽  
Granulite Facies Metamorphism ◽  
Northern Margin ◽  
Mineral Equilibria ◽  
Metamorphic History ◽  
Facies Metamorphism ◽  
History Of

ABSTRACTIn the southern part of the Archaean craton of South India, an approximately 3.4–2.9 b.y. old migmatite–gneiss terrane (Peninsular gneiss complex) has been subjected to granulite facies metamorphism about 2.6 b.y. ago. During this event, the extensive charnockite-khondalite zone of southern India developed. A younger metamorphism (Proterozoic?) led to retrogression of the charnockites and khondalites, mainly under the conditions of the amphibolite facies.The physical conditions of metamorphism have been evaluated by applying methods of geothermobarometry to the widespread charnockitic assemblages with garnet, orthopyroxene, clinopyroxene, plagioclase, and quartz. The interpretation of the P–T estimates includes a critical discussion of potential error sources, e.g. errors of the analytical data and the calibrations of the models, and takes into account the complex metamorphic history of the rocks and the kinetics of the mineral equilibria.P-T estimates were obtained for seven subareas from the rim compositions of the coexisting minerals: Shevaroy Hills 680±55°C—7·4±1 kb; Kollaimalai area 680±40°C—8·6± 1 kb; Nilgiri Hills 680±90°C—6·6±0.8kb (upland massif) and 705±60°C—9·3±0.8 kb (northern margin); Bhavani Sagar area 650±50°C—7·2± 1 kb; Sargur-Mysore area 690±60°C—7·6 kb; Bangalore-Kunigal-Satnur area 760±50°C—6 kb. Except for the last subarea, the P-T model data reflect the conditions of a late annealing stage probably related to the retrogressive metamorphism. Conditions near the peak of granulite facies metamorphism (730–800°C—6·5–9·5 kb) are recorded by the core compositions of the minerals. Although a rather uniform cooling history of the main part of the charnockite-khondalite terrane is suggested from the temperature data, differential uplift of smaller blocks is indicated by the regional variation of the pressure data.

Metamorphic constraints on the evolution of the gneisses from the parautochthonous and allochthonous polycyclic belts, Grenville Province, western Quebec

1990 ◽  
Vol 27 (3) ◽  
pp. 357-370 ◽  
Author(s):  
A. Indares ◽  
J. Martignole
Keyword(s):  
Granulite Facies ◽  
Ultramafic Rocks ◽  
Significant Discrepancy ◽  
Grenville Province ◽  
Narrow Strip ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
Tectonic Transport ◽  
History Of ◽  
Grenvillian Orogeny

The tectono-metamorphic history of polycyclic "grey gneisses" located in the central Grenville Province of western Quebec has been constrained along a transect perpendicular to the length of the Grenville Orogen. Two terranes, the Réservoir Dozois terrane (RDT) and the Réservoir Baskatong terrane (RBT), were recognized from their structural, lithological, and geochronological characteristics. This subdivision has been confirmed by application of geothermobarometric techniques to appropriate mineral assemblages.The RDT is the southern extension of the parautochthonous belt of the Grenville Province, which in this area is composed of Archean rocks of upper-amphibolite grade. During the Grenvillian Orogeny, northwest-directed thrusting resulted in the tectonic burial of this terrane as a single tectonic unit, in contrast with the northern part of the parautochthonous belt, where several slices were imbricated against the Grenville Front. Maximum P–T conditions in the RDT (850 MPa, 720 °C) were likely Grenvillian and were followed by pervasive retrogression down to the hornblende–epidote subfacies. Locally, the RDT is overlain by remnants of thrust slices composed of monocyclic metasedimentary rocks that were deformed and metamorphosed in the granulite facies during the Grenvillian Orogeny.To the southeast, the RBT is an allochthonous or exotic terrane probably of Proterozoic age. It also experienced tectonic burial by thrusting (1030 MPa, 710 °C) during the Grenvillian Orogeny, whose thermal climax (790 °C) coincided with charnockite emplacement during decompression to 850 MPa.These two terranes are separated by a narrow strip of sheared rocks, the Renzy shear belt (RSB), which comprises mafic and ultramafic rocks subjected to high P and T (975 MPa, 745 °C). In view of the significant discrepancy between the metamorphic histories of the two terranes separated by the RSB, major tectonic transport has to be envisaged along this zone.

scholarly journals Monazite U–Th–Pb geochronology of the Central Metasedimentary Belt Boundary Zone (CMBbz), Grenville Province, Ontario Canada

2018 ◽  
Vol 55 (9) ◽  
pp. 1063-1078 ◽  
Author(s):  
Michelle J. Markley ◽  
Steven R. Dunn ◽  
Michael J. Jercinovic ◽  
William H. Peck ◽  
Michael L. Williams
Keyword(s):  
Shear Zone ◽  
Crustal Thickening ◽  
Boundary Zone ◽  
Grenville Province ◽  
Metamorphic History ◽  
Crustal Thinning ◽  
Tectonic Significance ◽  
History Of ◽  
Central Gneiss Belt ◽  
Scale Shear

The Central Metasedimentary Belt boundary zone (CMBbz) is a crustal-scale shear zone that juxtaposes the Central Gneiss Belt and the Central Metasedimentary Belt of the Grenville Province. Geochronological work on the timing of deformation and metamorphism in the CMBbz is ambiguous, and the questions that motivate our study are: how many episodes of shear zone activity did the CMBbz experience, and what is the tectonic significance of each episode? We present electron microprobe data from monazite (the U–Th–Pb chemical method) to directly date deformation and metamorphism recorded in five garnet–biotite gneiss samples collected from three localities of the CMBbz of Ontario (West Guilford, Fishtail Lake, and Killaloe). All three localities yield youngest monazite dates ca. 1045 Ma; most of the monazite domains that yield these dates are high-Y rims. In comparison with this common late Ottawan history, the earlier history of the three CMBbz localities is less clearly shared. The West Guilford samples have monazite grain cores that show older high-Y domains and younger low-Y domains; these cores yield a prograde early Ottawan (1100–1075 Ma) history. The Killaloe samples yield a well-defined prograde, pre- to early Shawinigan history (i.e., 1220–1160 Ma) in addition to some evidence for a second early Ottawan event. In other words, the answers to our research questions are: three events; a Shawinigan event possibly associated with crustal thickening, an Ottawan event possibly associated with another round of crustal thickening, and a late Ottawan event that resists simple interpretation in terms of metamorphic history but that coincides chronologically with crustal thinning at the base of an orogenic lid.

The Pikwitonei Granulite Domain, Manitoba: a giant Neoarchean high-grade terrane in the northwest Superior ProvinceThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.N. Machado, T.E. Krogh, and W. Weber are deceased.

2011 ◽  
Vol 48 (2) ◽  
pp. 205-245 ◽  
Author(s):  
L. M. Heaman ◽  
Ch. O. Böhm ◽  
N. Machado ◽  
T. E. Krogh ◽  
W. Weber ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Superior Province ◽  
High Grade ◽  
Metamorphic Zircon ◽  
Special Issue ◽  
Metamorphic History ◽  
Zircon Growth ◽  
The World ◽  
Northwestern Margin ◽  
History Of

The Pikwitonei Granulite Domain located at the northwestern margin of the Superior Province is one of the largest Neoarchean high-grade terranes in the world, with well-preserved granulite metamorphic assemblages preserved in a variety of lithologies, including enderbite, opdalite, charnockite, and mafic granulite. U–Pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities; Natawahunan Lake, Sipiwesk Lake, and Cauchon Lake. The U–Pb age results indicate that some of the layered enderbite gneisses are Mesoarchean (3.4–3.0 Ga) and the more massive enderbites are Neoarchean. The high-grade metamorphic history of the Pikwitonei Granulite Domain is complex and multistage with at least four episodes of metamorphic zircon growth identified: (1) 2716.1 ± 3.8 Ma, (2) 2694.6 ± 0.6 Ma, (3) 2679.6 ± 0.9 Ma, and (4) 2642.5 ± 0.9 Ma. Metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent, corresponding to M1 amphibolite- and M2 granulite-facies events, respectively, consistent with previous field observations. The youngest metamorphic episode at 2642.5 Ma is only recognized at southern Cauchon Lake, where it coincides with granite melt production and possible development of a major northeast-trending deformation zone. The timing and multistage metamorphic history recorded in the Pikwitonei Granulite Domain is similar to most Superior Province high-grade terranes and marks a fundamental break in Archean crustal evolution worldwide at the termination of prolific global Neoarchean greenstone belt formation.

New age constraints on magmatism and metamorphism in the Morin terrane (Grenville Province, Quebec)

2022 ◽  
Author(s):  
William H Peck ◽  
Matthew P Quinan
Keyword(s):  
Shear Zone ◽  
Granulite Facies ◽  
Western Boundary ◽  
Grenville Province ◽  
Granulite Facies Metamorphism ◽  
Metamorphic History ◽  
Crustal Block ◽  
Two Samples ◽  
Western Side ◽  
Age Constraints

The Morin terrane is an allochthonous crustal block in the southwestern Grenville Province with a relatively poorly-constrained metamorphic history. In this part of the Grenville Province, some terranes were part of the ductile middle crust during the 1.09–1.02 Ga collision of Laurentia with the Amazon craton (the Ottawan phase of the Grenvillian orogeny), while other terranes were part of the orogen’s superstructure. New U-Pb geochronology suggests that the Morin terrane experienced granulite-facies metamorphism during the accretionary Shawinigan orogeny (1.19–1.14 Ga) and again during the Ottawan. Seven zircon samples from the 1.15 Ga Morin anorthosite suite were dated to confirm earlier age determinations, and Ottawan metamorphic rims (1.08–1.07 Ga) were observed in two samples. U-Pb dating of titanite in nine marble samples surrounding the Morin anorthosite suite yielded mixed ages spanning between the Shawinigan and Ottawan metamorphisms (n=7), and predominantly Ottawan ages (n=2). Our results show that Ottawan zircon growth and resetting of titanite ages is spatially heterogeneous in the Morin terrane. Ages with a predominantly Ottawan signature are recognized in the Morin shear zone, which deforms the eastern lobe of the anorthosite, in an overprinted skarn zone on the western side of the massif, and in the Labelle shear zone that marks its western boundary. In the rest of the Morin terrane titanite with Shawinigan ages appear to have been only partially reset during the Ottawan. Further work is needed to better understand the relationship between the character of Ottawan metamorphism and resetting in different parts of the Morin terrane.

scholarly journals The Archaean gneiss complex of northern Labrador A review of current results, ideas and problems

1991 ◽  
Vol 39 ◽  
pp. 153-166
Author(s):  
D. Bridgwater ◽  
L. Schiøtte
Keyword(s):  
Major Part ◽  
Granulite Facies ◽  
High Grade ◽  
Late Archaean ◽  
West Greenland ◽  
Metamorphic History ◽  
Gneiss Complex ◽  
History Of ◽  
Augen Gneiss ◽  
Dominant Phase

1. The early Archaean rocks in northern Labrador can be subdivided into the ea. 3.78 Ga Nulliak supracrus­tal association, the migmatitic Uivak I gneisses, the dominant phase of which was emplaced at ea. 3.73 Ga, and the Uivak II augen gneiss. Inherited low-U rounded inclusions within igneous zircons in the Uivak I gneisses have ages between 3.73 and 3.86 Ga and are more likely to have been derived from a pre-existing high-grade metamorphic gneiss complex than from the Nulliak association. In the early Archaean there were probably several rapid cycles of sedimentary deposition and volcanism followed by emplacement of major plutons. Mid Archaean gneisses are more abundant in northern Labrador than previously realised. The late Archaean metamorphic history of these gneisses is different from the history of the early Archaean gneisses. Whereas an important part of the mid Archaean suite was emplaced in granulite facies and retrogressed at the time of granitoid veining at ea. 2.99 Ga, the major part of the early Archaean rocks were reworked under granulite facies conditions in a sequence of closely spaced events between 2. 7 and 2.8 Ga. The two groups of gneisses had different metamorphic histories until ea. 2.7 Ga, but late and post-tectonic granites of 2.5- 2. 7 Ga age cut across both. It is suggested that the terrane model in southern West Greenland can be extended to Labrador and that tectonic intercalation of early and mid Archaean gneisses took place around 2.7 Ga. Correlation between the Maggo gneisses around Hopedale, mid Archaean gneisses in northernmost Labrador and gneisses from the Akia terrane in West Greenland is suggested. Like the Malene supracrustals in West Greenland the Upernavik supracrustals in Labrador are composite associations, the youngest of which are thought to have been deposited around 2. 7 Ga.

Evolution of the granulites and sub-division of the granulite facies in Ceylon

1972 ◽  
Vol 109 (5) ◽  
pp. 435-443 ◽  
Author(s):  
D. J. A. C. Hapuarachchi
Keyword(s):  
Granulite Facies ◽  
Metamorphic History ◽  
History Of ◽  
Division Ii ◽  
Geochronological Evidence

SummaryThree subfacies of the granulite facies are recognized: garnet–diopside–quartz subfacies; pyroxene–granulite subfacies; and hornblende–granulite subfacies The erection of a garnet–diopside–quartz subfacies follows De Waard's suggestion (1965) of a garnet–clinopyroxene subfacies. Two major divisions of the hornblende–granulite subfacies are now recognized, (i) garnet–biotite division, (ii) cordierite division. Three sub-divisions of the former are suggested on the basis of critical basic assemblages. Since wollastonite has been found to have a limited areal occurrence within the latter, a two-fold sub-division of the cordierite division is suggested on the basis of the assemblages, (a) calcite–quartz, (b) wollastonite. A seven-fold sub-division of the granulite facies is thus proposed for Ceylon rocks. An attempt is made to trace briefly the major events in the metamorphic history of the rocks supported by available geochronological evidence.

Old K–Ar Mineral Ages from the Grenville Province, Ontario

1971 ◽  
Vol 8 (11) ◽  
pp. 1495-1498 ◽  
Author(s):  
M. R. Dence ◽  
J. B. Hartung ◽  
J. F. Sutter
Keyword(s):  
Grenville Province ◽  
Thermal Event ◽  
Metamorphic History ◽  
Minimum Age ◽  
History Of

Hornblende-rich concentrates from quartz–feldspar gneisses of the Grenville Province near Brent Ontario, have yielded K–Ar apparent ages of 1570 to 1480 ± 80 m.y., while coexisting biotite- and feldspar-rich separates give 'normal' Grenville K–Ar ages near 900 ± 40 m.y. Comparison with the nearest Rb–Sr isochron dates suggests that the indicated hornblende K–Ar age represents a minimum age for time of crystallization of the gneisses in the Brent area and that the younger ages for minerals with lower blocking temperatures indicate a later thermal event in the metamorphic history of the Grenville Province.

scholarly journals Alpine peak pressure and tectono-metamorphic history of the Monte Rosa nappe: evidence from the cirque du Véraz, upper Ayas valley, Italy

2021 ◽  
Vol 114 (1) ◽  
Author(s):  
Joshua D. Vaughan-Hammon ◽  
Cindy Luisier ◽  
Lukas P. Baumgartner ◽  
Stefan M. Schmalholz
Keyword(s):  
Structural Analysis ◽  
Peak Pressure ◽  
Geological Mapping ◽  
Temperature History ◽  
Metamorphic History ◽  
Wide Range ◽  
History Of ◽  
Nappe Emplacement ◽  
Monte Rosa ◽  
Peak Pressures

AbstractThe Monte Rosa nappe consists of a wide range of lithologies that record conditions associated with peak Alpine metamorphism. While peak temperature conditions inferred from previous studies largely agree, variable peak pressures have been estimated for the Alpine high-pressure metamorphic event. Small volumes of whiteschist lithologies with the assemblage chloritoid + phengite + talc + quartz record peak pressures up to 0.6 GPa higher compared to associated metapelitic and metagranitic lithologies, which yield a peak pressure of ca. 1.6 GPa. The reason for this pressure difference is disputed, and proposed explanations include tectonic mixing of rocks from different burial depths (mélange) or local deviations of the pressure from the lithostatic value caused by heterogeneous stress conditions between rocks of contrasting mechanical properties. We present results of detailed field mapping, structural analysis and a new geological map for a part of the Monte Rosa nappe exposed at the cirque du Véraz field area (head of the Ayas valley, Italy). Results of the geological mapping and structural analysis shows the structural coherency within the western portions of the Monte Rosa nappe. This structural coherency falsifies the hypothesis of a tectonic mélange as reason for peak pressure variations. Structural analysis indicates two major Alpine deformation events, in agreement with earlier studies: (1) north-directed nappe emplacement, and (2) south-directed backfolding. We also analyze a newly discovered whiteschist body, which is located at the intrusive contact between Monte Rosa metagranite and surrounding metapelites. This location is different to previous whiteschist occurrences, which were entirely embedded within metagranite. Thermodynamic calculations using metamorphic assemblage diagrams resulted in 2.1 ± 0.2 GPa and 560 ± 20 °C for peak Alpine metamorphic conditions. These results agree with metamorphic conditions inferred for previously investigated nearby whiteschist outcrops embedded in metagranite. The new results, hence, confirm the peak pressure differences between whiteschists and the metagranite and metapelite. To better constrain the prograde pressure–temperature history of the whiteschist, we compare measured Mg zoning in chloritoid with Mg zoning predicted by fractional crystallization pseudo-section modelling for several hypothetical pressure–temperature paths. In order to reach a ca. 0.6 GPa higher peak pressure compared to the metapelite and metagranite, our results suggest that the whiteschist likely deviated from the prograde burial path recorded in metapelite and metagranite lithologies. However, the exact conditions at which the whiteschist pressure deviated are still contentious due to the strong temperature dependency of Mg partitioning in whiteschist assemblages. Our pseudo-section results suggest at least that there was no dramatic isothermal pressure increase recorded in the whiteschist.

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