Cordierite–gedrite rocks and associated gneisses of Fishtail Lake, Harcourt Township, Ontario

1969 ◽  
Vol 6 (1) ◽  
pp. 145-165 ◽  
Author(s):  
R. K. Lal ◽  
W. W. Moorhouse
Keyword(s):  
Compositional Data ◽  
High Grade ◽  
Geologic Mapping ◽  
The North ◽  
Gneiss Complex ◽  
Argillaceous Rocks ◽  
Two Samples ◽  
Anatectic Granite ◽  
High Grade Metamorphism ◽  
Petrographic Study

The cordierite–gedrite rocks and associated gneisses on the north side of Fishtail Lake, Harcourt Township, Ontario, occur within the Grenville gneiss complex of the Haliburton Highlands. The investigation comprises a petrographic study, based on geologic mapping, and supplemented by new chemical analyses of gedrites, cordierites, garnets, biotites, and typical rocks. Comparison with compositional data from other metamorphic environments shows that the compositions of associated cordierite, garnet, and anthophyllite (gedrite) and garnet–cordierite–biotite have lower FeO/(MgO + FeO) ratios in high-grade regional metamorphic environments such as exemplified at Fishtail Lake than in contact metamorphic associations. The chemical composition of the rocks is characterized by high MgO and FeO and low lime and alkalies, compared with argillaceous rocks and metamorphic rocks derived from them. It is suggested that this unusual composition results from the removal of an anatectic granite fluid from the parent rock during partial melting associated with high-grade metamorphism. Pegmatites and aplites associated with the gneisses may represent a part of this granite fluid. This hypothesis is shown to be consistent with published experimental data, field observations, and the composition of the cordierite–gedrite rocks compared with hypothetical argillaceous parents.The rocks of the area were metamorphosed initially to the staurolite–almandine subfacies, as indicated by the occurrence of inclusions of staurolite in garnet. With increasing intensity of metamorphism, in the sillimanite–almandine–orthoclase subfacies, the staurolite became unstable, and apart from relicts, is now represented by garnet and sillimanite. Partial anatexis and removal of a melted fraction of granite composition took place, leading to the crystallization of cordierite–gedrite assemblages. Subsequent retrograde metamorphism altered some of the cordierite to kyanite–andalusite–chlorite and pinite. This secondary generation of kyanite and andalusite has resulted, in two samples studied, in the association of kyanite, andalusite, and sillimanite.

U-Pb ages of plutonism, sedimentation, and metamorphism of the Paleoproterozoic Kisseynew metasedimentary belt, Trans-Hudson Orogen (Manitoba, Canada)

1999 ◽  
Vol 36 (11) ◽  
pp. 1829-1842 ◽  
Author(s):  
N Machado ◽  
H Zwanzig ◽  
M Parent
Keyword(s):  
Ocean Floor ◽  
Arc Magmatism ◽  
High Grade ◽  
Plate Convergence ◽  
Grade Metamorphism ◽  
The North ◽  
Continental Arc ◽  
High Grade Metamorphism ◽  
Flin Flon ◽  
Uplift And Erosion

The Kisseynew Domain is a metasedimentary belt in the central Reindeer Zone of the Trans-Hudson Orogen. It is bounded by 1.92-1.86 Ga volcanic-plutonic belts to the north and south, by an Archean terrane to the east (Superior Province), and by a volcanic-plutonic terrane underlain by an Archean terrane to the southwest (Glennie Domain). The Kisseynew Domain developed in an arc-related setting in the final stages of plate convergence involving the northward migration of arc-ocean floor complexes toward the Archean Hearne Craton. Terminal collision, involving also the Superior Craton, originated multiple fold-thrust systems and high-grade metamorphism. U-Pb ages of 1874-1860 Ma for pretectonic plutonic units in southern Kisseynew Domain are identical to ages of plutonism intruding the arc-ocean floor accretionary complex in the Flin Flon domain (Amisk collage) and indicate its northern extension. Deposition of the Burntwood Group turbidites started at ca. 1860 Ma, indicating uplift and erosion of the volcanic complexes and was coeval with arc magmatism that succeeded the Amisk collage. From 1848 Ma, Burntwood sedimentation was coeval with deposition of Missi Group continental sediments, with continental arc magmatism and early deformation. New and published ages for detrital zircon indicate that sediments were derived both from local 1.89-1.84 Ga units and also from 2.55-2.36 Ga sources. The latter suggest that a Neoarchean-Paleoproterozoic cratonic block was undergoing erosion, remnants of which occur in the Flin Flon Belt. Basin closure started after 1823 Ma and is marked by regional high-grade metamorphism lasting for ca. 30 million years from 1818 Ma to 1785 Ma; late- to posttectonic metamorphic activity lasted until ca. 1775 Ma.

Basic magmatism in relation to metamorphism and orogeny in Guiana: a speculation

1973 ◽  
Vol 110 (4) ◽  
pp. 365-371 ◽  
Author(s):  
A. Choudhuri
Keyword(s):  
Volcanic Rocks ◽  
High Grade ◽  
Crustal Rocks ◽  
Gneiss Complex ◽  
Mantle Peridotites ◽  
Gravity Measurements ◽  
Basic Magmatism ◽  
High Grade Metamorphism ◽  
Basic Rocks ◽  
Block Faulting

SummaryThe northern part of the Guiana Shield consists of large tracts of basic and intermediate volcanic rocks and sediments which are thought to have formed under geosynclinal conditions. During the 2000 m.y. Trans-Amazonian Orogeny these rocks were subjected to tectonism and metamorphism resulting in a broad belt of green schist facies with local and isolated patches of high grade metamorphic rocks and gneiss complexes. In the early stages of orogeny during which folding and probable block faulting of the sediments and volcanics took place, these rocks were intruded by basic and ultra-basic rocks giving rise to metagabbro-amphibolite-peridotite associations, commonly in the areas of subsequent high-grade metamorphism. In an attempt to account for the frequent supply of basic magma during and after the orogeny it is postulated that mantle peridotites rose diapir-like below the sinking geosyncline, and by partial melting not only provided basic magmas but also thermal energy which spread upwards to metamorphose the already tectonized crustal rocks; recent gravity measurements indicate an upwarped ‘sima’ under the Bartica Assemblage gneiss complex.

Comparative petrology of gneissic rocks in southwestern Newfoundland

1992 ◽  
Vol 29 (12) ◽  
pp. 2663-2676 ◽  
Author(s):  
J. Victor Owen
Keyword(s):  
Confining Pressure ◽  
Metamorphic Grade ◽  
High Grade ◽  
Grade Metamorphism ◽  
Metasedimentary Rocks ◽  
Gneiss Complex ◽  
High Grade Metamorphism ◽  
Tonalitic Gneiss ◽  
Silicate Layers ◽  
Bulk Chemistry

In southwestern Newfoundland, pelitic migmatites of the Meelpaeg Subzone of the Gander Zone are separated by faults and plutons from metasedimentary rocks of the Port-aux-Basques gneiss complex (PBGC). The PBGC is a polymetamorphic sequence of amphibolite-facies, pelitic, semipelitic, and psammitic rocks (and associated metabasic dykes). Maximum metamorphic grade surpassed the first sillimanite (i.e., staurolite-consuming) isograd. Metamorphic conditions approached 650–700 °C at Pmax approximately 6.5–8.5 kbar (1 kbar = 100 MPa).The Meelpaeg gneisses also include sillimanite-grade, two-mica rocks, but they lack the Barrovian mineralogy (e.g., kyanite, staurolite, rutile) characterizing parts of the PBGC. The Meelpaeg rocks attained temperatures similar to those of the PBGC, but confining pressure was substantially lower (approx. 4 kbar), indicating uplift from relatively shallow structural levels.Both groups of paragneisses also differ in some aspects of their bulk chemistry (notably CaO/K2O ratios) and their lithologic associations. The Meelpaeg metapelites are less calcic and relatively potassic (mean CaO/K2O = 0.32) compared with their counterparts in the PBGC (mean CaO/K2O = 1.12), but both groups of rocks have similar bulk Fet/(Fet + Mg) ratios (mean XFe ≈ 0.75). In contrast with the PBGC, which contains abundant metabasites and thin coticule-like (garnet + quartz) seams, the Meelpaeg metapelites are associated with biotite + garnet "tonalitic" gneiss and, despite their relatively lime-poor composition, calc-silicate layers and pods.In terms of contrasting lithologic associations and bulk chemistry, paragneiss of the PBGC is distinct from gneissic rocks in the Meelpaeg Subzone. This underscores difficulties in relating rocks in the Port-aux-Basques area to well-established lithotectonic entities elsewhere in Newfoundland. Despite apparent differences in their protoliths and contrasts in metamorphic pressure, available U–Pb data suggest that high-grade metamorphism in both areas occurred during the middle Silurian.

scholarly journals Rb/Sr whole rock isochron age determinations on metamorphosed acid volcanic rocks and granitic gneisses from the Ketilidian mobile belt, South-East Greenland

1974 ◽  
Vol 66 ◽  
pp. 12-20
Author(s):  
S Pedersen ◽  
O Larsen ◽  
D Bridgwater ◽  
J Watterson
Keyword(s):  
Volcanic Rocks ◽  
Mobile Belt ◽  
High Grade ◽  
East Greenland ◽  
Volcanic Material ◽  
Grade Metamorphism ◽  
The North ◽  
Acid Volcanic ◽  
High Grade Metamorphism ◽  
Age Determinations

The metamorphosed supracrustal rocks and paragneisses studied were collected during a reconnaissance traverse across the trend of the Ketilidian mobile belt in South-Bast Greenland (Andrews et al., 1971, 1973). All the samples are taken from gneisses regarded as derived from supracrustal material which was originally composed of acid volcanic material deposited as lavas, ignimbrites or sediments with a large volcanic component. Sample localities are shown in fig. 2. All the rocks have been affected by at least one metamorphic episode during the formation of the Ketilidian mobile belt. All are regarded as deposited after the end of regional high grade metamorphism in the Archaean block to the north (which has yielded a U/Pb zircon diffusion age of 2808 m.y.) and are intruded by a variety of synto late tectonic granites within the Ketilidian mobile belt which have yielded U/Pb diffusion and concordia ages between 1850 and 1770 m.y. in this area (Gulson & Krogh, 1972).

scholarly journals Persistence of melt-bearing Archean lower crust for >200 m.y.—An example from the Lewisian Complex, northwest Scotland

Geology ◽  
2019 ◽  
Vol 48 (3) ◽  
pp. 221-225 ◽  
Author(s):  
Richard J.M. Taylor ◽  
Tim E. Johnson ◽  
Chris Clark ◽  
Richard J. Harrison
Keyword(s):  
Trace Element ◽  
Lower Crust ◽  
Mafic Magma ◽  
High Grade ◽  
Trace Element Data ◽  
Metamorphic Zircon ◽  
Geochronological Data ◽  
Zircon Age ◽  
Gneiss Complex ◽  
High Grade Metamorphism

Abstract Geochronological data from zircon in Archean tonalite–trondhjemite–granodiorite (TTG) gneisses are commonly difficult to interpret. A notable example is the TTG gneisses from the Lewisian Gneiss Complex, northwest Scotland, which have metamorphic zircon ages that define a more-or-less continuous spread through the Neoarchean, with no clear relationship to zircon textures. These data are generally interpreted to record discrete high-grade events at ca. 2.7 Ga and ca. 2.5 Ga, with intermediate ages reflecting variable Pb loss. Although ancient diffusion of Pb is commonly invoked to explain such protracted age spreads, trace-element data in zircon may permit identification of otherwise cryptic magmatic and metamorphic episodes. Although zircons from the TTG gneiss analyzed here show a characteristic spread of Neoarchean ages, they exhibit subtle but key step changes in trace-element compositions that are difficult to ascribe to diffusive resetting, but that are consistent with emplacement of regionally extensive bodies of mafic magma. These data suggest suprasolidus metamorphic temperatures persisted for 200 m.y. or more during the Neoarchean. Such long-lived high-grade metamorphism is supported by data from zircon grains from a nearby monzogranite sheet. These preserve distinctive trace-element compositions consistent with derivation from a mafic source, and they define a well-constrained U-Pb zircon age of ca. 2.6 Ga that is intermediate between the two previously proposed discrete metamorphic episodes. The persistence of melt-bearing lower crust for hundreds of millions of years was probably the norm during the Archean.

Persistence of melt-bearing Archean lower crust for >200 m.y.— An example from the Lewisian Complex, northwest Scotland

2020 ◽  
Author(s):  
Tim Johnson ◽  
Rich Taylor ◽  
Chris Clark
Keyword(s):  
Trace Element ◽  
Lower Crust ◽  
Mafic Magma ◽  
High Grade ◽  
Trace Element Data ◽  
Metamorphic Zircon ◽  
Geochronological Data ◽  
Zircon Age ◽  
Gneiss Complex ◽  
High Grade Metamorphism

<p><strong>Geochronological data in zircon from Archaean tonalite–trondhjemite–tonalite (TTG) gneisses is commonly difficult to interpret. A notable example are TTG gneisses from the Lewisian Gneiss Complex (LGC), northwest Scotland, which have metamorphic zircon ages that define a more-or-less continuous spread through the Neoarchaean, with no clear relationship to zircon textures. These data are generally interpreted to record discrete high-grade events at c. 2.7 Ga and c. 2.5 Ga, with intermediate ages reflecting variable Pb-loss. Although ancient diffusion of Pb is commonly invoked to explain such protracted age spreads, trace element data in zircon may permit identification of otherwise cryptic magmatic and metamorphic episodes. Although zircons from the TTG gneiss analyzed here show a characteristic spread of Neoarchaean ages, they exhibit subtle but key step changes in trace element compositions that are difficult to ascribe to diffusive resetting, but which are consistent with emplacement of regionally-extensive bodies of mafic magma. These data suggest suprasolidus metamorphic temperatures persisted for 200 Myr or more during the Neoarchaean. Such long-lived high-grade metamorphism is supported by data from zircon grains from a nearby monzogranite sheet. These preserve distinctive trace element compositions suggesting derivation from a mafic source, and define a well-constrained U–Pb zircon age of c. 2.6 Ga that is intermediate between the two previously proposed discrete metamorphic episodes. The persistence for hundreds of millions of years of melt-bearing lower crust was probably the norm during the Archaean.</strong></p>

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