Granulite-Facies Metamorphism and Crustal Magmatism in the Ashuanipi Complex, Quebec--Labrador, Canada

Percival, John A.

doi:10.1093/petrology/32.6.1261

Cited by 75 publications

(67 citation statements)

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“…They appear to have more similarity with the mesocratic diatexites from St. Malo, France (see Milord et al 2001), with the exception of Ca. The Kauhava orthopyroxene-biotite diatexites share chemical similarities with slightly ascended orthopyroxene diatexites in the Ashuanipi Complex, Canada, reported by Percival (1991) but the Kauhava diatexites have lower orthopyroxene/biotite mode. Geochemically, the biotite diatexites and orthopyroxene-biotite diatexites in the Kauhava area are similar to those reported from the southern part of the VMC (see Mäkitie et al 1999, Mäkitie 2000 (Fig.…”

Section: Discussionsupporting

confidence: 67%

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Eastern margin of the Vaasa Migmatite Complex, Kauhava, western Finland: preliminary petrography and geochemistry of the diatexites

Mäkitie¹

2001

Bull Geol Soc Finland

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Extensive biotite diatexites resembling S-type granitoids occur in the eastern part of the Vaasa Migmatite Complex (VMC, 1.89 Ga, 6000 km 2 ) at Kauhava, western Finland. These rocks have undergone a textural homogenization that has destroyed the primary bedding. Pre-migmatization structures are preserved only in inclusions. The diatexites are clearly peraluminous and have relatively high concentrations of TiO 2 (0.7-0.9 wt%), CaO (2.4-3.0 wt%) and total of Fe 2 O 3 tot + MgO (6.6-8.8 wt%). The contact of the diatexites against pelitic metatexites is usually a gradual zone, 1-200 m wide, but locally a boundary limiting places of higher melt fraction. The contacts indicate that the anatectic melt formed, with residual solids, has not ascended greatly; the VMC forms the most voluminous in situ melted rocks with granitoid appearance in Finland.The study area also includes peraluminous orthopyroxene-bearing rocks, granitic in texture, which are hornblende free and have relatively high TiO 2 (1.0-1.2 wt%) and MgO (2.1-2.5 wt%) contents. They gradually change to biotite diatexites and also suggest fusion of metasedimentary rocks at reduced a H2O . The chemical composition of minerals in the orthopyroxene-biotite diatexite indicates crystallization conditions of high-grade metamorphism; X Mg in garnet is 0.23, orthopyroxene has 3 wt% Al 2 O 3 and biotite contains over 5 wt% TiO 2 .

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Section: Discussionsupporting

confidence: 67%

“…Orthopyroxene in the diatexites probably crystallized by reactions (1), (2) and (3) with melt (for references to the reactions, see Percival 1991 andVielzeuf &Montel 1994) and occurred in a solid state.…”

Section: Discussionmentioning

confidence: 99%

Eastern margin of the Vaasa Migmatite Complex, Kauhava, western Finland: preliminary petrography and geochemistry of the diatexites

Mäkitie¹

2001

Bull Geol Soc Finland

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“…Such melts would be capable of assimilating H 2 0 from the lower crust and would also be the source of C O 2. This concept has been recently illustrated by several authors [6][7][8].…”

Section: Introductionmentioning

confidence: 87%

Fluid transfer in anorthosites and related rocks from Rogaland (Southwest Norway): Evidence from stable isotopes

Wilmart

Pineau

Réjou-Michel

et al. 1994

Earth and Planetary Science Letters

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C and H contents and C, H and O isotopic compositions have been measured in sixteen samples of the ,~ma-Sira massif-type anorthosite (Rogaland, Southwest Norway) and in 30 surrounding rocks, including the metamorphic envelope and magmatic intrusions related to the anorthosite emplacement.Oxygen isotopic compositions of the ~tna-Sira anorthositic massif (6a80 = 6.1 ± 0.3%o) and the Tellnes orebody (6180 = 5.2 +_ 0.2%o) are consistent with a pure mantle origin and show no evidence for exchange with hydrothermal fluids. The associated rocks (norites to charnockites) have 6180 values (5.2 + 0.9%0) similar to uncontaminated mantle-derived magmas.The H 2 0 content of the rocks (magmatic or metamorphic) is lower than 0.54%, suggesting the preservation of original granulite facies conditions during cooling and uplift.Due to their cumulate origin, the anorthosites are very poor in carbon (bulk C < 50 ppm), the volatiles having been concentrated in the residual melt. Higher carbon concentrations (up to 1484 ppm) are found in the associated intrusions. Anorthosites and gneisses close to the contacts (less than 500 m) with later intrusions show an increase in their carbon content (up to 700 ppm C), and this carbon is mainly in the form of interstitial carbonate.The carbon distribution observed at the contact between later intrusions and anortbosites as well as gneisses indicates that some CO 2 has fluxed from the later magmas over a distance of a few hundred metres. This suggests only minimal lateral propagation of the fluids by diffusion or infiltration. Tentative carbon budgets suggest that most of the volatiles were transferred upwards into the overlying continental crust.

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“…this study and open squares are the samples of diatexite migmatite from the north Ashuanipi (Percival, 1991b& Lapointe, 1996. The asterix represents the average of the experimental melt compositions, the filled triangle is the average of the possible protolith compositions obtained from the Quetico subprovince 133 projection within quartz-albite-anorthite-orthoclase tetrahedron of Kosinowski (1981).…”

Section: A=alkali Feldspar P=plagioclase Q=quartz 92mentioning

confidence: 99%

“…Structural style changes across the Ashuanipi subprovince; Percival (1991b) and Lapomte (1996) mapped subcircular domains of steeply dipping foliation some 150 to 200 km farther north. Prominent discontinuities in the foliation trajectories in that region (Lapointe 1996) indicate the presence of major east-trending shear zones.…”

Section: The Structurementioning

confidence: 99%

Formation and evolution of granite magmas from migmatites :

Guernina¹

2007

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Many magmas in the continental crust are believed to have formed by partial melting in the lower to middle crust, and the transfer of that melt to the upper crust. However, it is poorly known how the compositions of these magmas evolve. In general, the principal processes involved are redistribution and contamination of the melt fraction with some of the host-rock it passes through and once magma ascends out of the anatectic zone and traverses cooler crust and begins to crystallize. The nature of the protolithrnigmatite-granite transition and the process that creates a granitic magma during anatexis, as well as the processes that control the magma composition outside the source region are of a particular interest as they enable us to constrain the morphological, mineralogical and geochemical variations of anatectic melts produced during anatexis of greywacke metasedimentary rocks.The Ashuanipi subprovince and contiguous metasedimentary subprovinces in the Superior province contains reworked Archaean crust that displays a continuous section from mid-crustal anatectic rocks to shallow level granite plutons. In other words, the superior province represents a crustal section which is continuous from partially melted source to upper crustal magma sink and the Ashaunipi portion of it is an example of a source region for granulitic magma. There, the transition from palaesome to granite was an open system process through intermediate stages of metatexite and diatexite.Field, pétrographie and geochemical methods have been used to estimate how much granitic melt was formed and extracted from granulite facies terrane, and to determine what the grain and outcrop-scale melt-flow paths were during the melt segregation process. More than 85 % of the metasediments in the Ashuanipi subprovince are of metagreywacke composition that was metamorphosed at mid-crustal conditions (820-900 °C and 6-7 kbar). Decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase, together with preserved former melt microstructures indicate that anatexis was by the biotite dehydration reaction: biotite + quartz + plagioclase = melt + orthopyroxene + oxides. Using melt/orthopyroxene ratios for this reaction derived from experimental studies, the modal orthopyroxene contents present in the Ashuanipi rocks indicate that the metagreywacke rocks underwent an average of 31 vol% partial melting.The metagreywackes are enriched in MgO, CaO and FeO and depleted in SÍO2, K2O, Rb, Cs and U, have lower Rb/SR, higher Rb/Cs and Th/U ratios and positive Eu anomalies compared to their likely protolith. These compositions are modelled by the extraction of between 20 and 40 wt % granitic melt from typical Achaean low-grade metagreywackes.The distribution of relict melt at thin section and outcrop scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary (porous) flow from the site of melting, across the layers and into bedding planes between adjacent layers. In other rocks, pervasive g...

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Granulite-Facies Metamorphism and Crustal Magmatism in the Ashuanipi Complex, Quebec--Labrador, Canada

Cited by 75 publications

References 0 publications

Eastern margin of the Vaasa Migmatite Complex, Kauhava, western Finland: preliminary petrography and geochemistry of the diatexites

Eastern margin of the Vaasa Migmatite Complex, Kauhava, western Finland: preliminary petrography and geochemistry of the diatexites

Fluid transfer in anorthosites and related rocks from Rogaland (Southwest Norway): Evidence from stable isotopes

Formation and evolution of granite magmas from migmatites :

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