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.

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.

scholarly journals Field mapping of Bjørneøen and the adjacent coast of Nordlandet, Godthåbsfjord, southern West Greenland

1975 ◽  
Vol 75 ◽  
pp. 58-62
Author(s):  
P.R James
Keyword(s):  
East Coast ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Field Mapping ◽  
West Greenland ◽  
Structural Relationships ◽  
Field Season ◽  
The Relationship

Mapping at a scale of 1:50 000 was carried out on the gneisses and supracrustals of Bjørneøen and the granulites of the adjacent east coast of Nordlandet; the area has previously been described by Noe-Nygaard & Ramberg (1961) and Bridgwater & McGregor (1974). During the present study special emphasis was placed on the structural relationships of the various rock units and also on the relationship and contact between the amphibolite facies and granulite facies areas. A short excursion was made at the beginning of the field season around Godthåbsfjord and Arneralik with the helpful guidance of V. R. McGregor whose kind assistance is especially acknowledged.

Late Labradorian metamorphism and anorthosite–granitoid intrusion, Cape Caribou River allochthon, Grenville Province, Labrador: evidence from U–Pb geochronology

1995 ◽  
Vol 32 (9) ◽  
pp. 1411-1425 ◽  
Author(s):  
François Bussy ◽  
Thomas E. Krogh ◽  
Richard J. Wardle
Keyword(s):  
Hanging Wall ◽  
Granulite Facies ◽  
Grenville Province ◽  
Mafic Dykes ◽  
North West ◽  
The North ◽  
Form Part ◽  
Thrust System ◽  
Granitoid Gneisses ◽  
New Generation

In the Cape Caribou River allochthon (CCRA), metaigneous and gneissic units occur as a shallowly plunging synform in the hanging wall of the Grand Lake thrust system (GLTS), a Grenvillian structure that forms the boundary between the Mealy Mountains and Groswater Bay terranes. The layered rocks of the CCRA are cut by a stockwork of monzonite dykes related to the Dome Mountain suite and by metadiabase–amphibolite dykes that probably form part of the ca. 1380 Ma Mealy swarm. The mafic dykes appear to postdate much of the development of subhorizontal metamorphic layering within the lower parts of the CCRA. The uppermost (least metamorphosed) units of the CCRA, the North West River anorthosite–metagabbro and the Dome Mountain monzonite suite, have been dated at 1625 ± 6 and 1626 ± 2 Ma, respectively. An amphibolite unit that concordantly underlies the anorthosite–metagabbro and is intruded discordantly by monzonite dykes has given metamorphic ages of 1660 ± 3 and 1631 ± 2 Ma. Granitoid gneisses that form the lowest level of the CCRA have given a migmatization age of 1622 ± 6 Ma. The effects of Grenvillian metamorphism become apparent in the lower levels of the allochthon where gneisses, amphibolite, and mafic dykes have given new generation zircon ages of 1008 ± 2, 1012 ± 3, and 1011 ± 3 Ma, respectively. A posttectonic pegmatite has also given zircon and monazite ages of [Formula: see text] and 1013 ± 3 Ma, respectively. Although these results indicate new growth of Grenvillian zircon, this process was generally not accompanied by penetrative deformation or melting. Thus, the formation of gneissic fabrics and the overall layered nature of the lower CCRA are a result primarily of Labradorian (1660–1620 Ma) tectonism and intrusion, and probably reflect early movement on an ancestral GLTS. Grenvillian heating and metamorphism (up to granulite facies) was strongly concentrated towards the base of the CCRA and probably occurred during northwestward thrusting of the allochthon over the Groswater Bay terrane.

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.

Post-convergent structures in lower parts of the 1090–1050 Ma (early-Ottawan) thrust-sheet stack, Grenville Province of Ontario, southern Canadian Shield

2014 ◽  
Vol 51 (3) ◽  
pp. 243-265 ◽  
Author(s):  
W.M. Schwerdtner ◽  
Toby Rivers ◽  
Brant Zeeman ◽  
C.C. Wang ◽  
Jason Tsolas ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Lateral Extension ◽  
Significant Component ◽  
Thrust Sheet ◽  
Grenville Province ◽  
Granite Pegmatite ◽  
Horizontal Length ◽  
History Of ◽  
Central Gneiss Belt ◽  
Highly Strained

Remnants of the early-Ottawan thrust-sheet stack are exposed in the Central Gneiss Belt (CGB, lower portion of stack) and the Composite Arc Belt (upper portion of stack). Post-collisional vertical thinning and associated horizontal extension of the stack produced structures ranging over eight orders of magnitude in horizontal length, and both orogen-parallel and orogen-perpendicular in orientation. At the 100 km scale, the fold-induced constriction in the northern Parry Sound domain appears to have been enhanced, and lineation trend lines in its footwall locally deflected, by a component of NW–SE (i.e., orogen-perpendicular) flattening and a component of NE–SW (i.e., orogen-parallel) ductile extension. At the 10 km scale, four non-cylindrical lenticular bodies of gabbro–anorthosite gneiss within the domain, inferred to be triaxial mega-boudins or heterogeneously strained plutons, are separated by large extensional bending folds, the complementary structures attesting to a component of NW–SE flattening and a component of NE–SW extension. Non-cylindrical lenticular structures in other domains of the CGB, interpreted as triaxial foliation mega-boudins, exceed 30 km in length. Their moderately strained granulite-facies interiors give way to highly strained amphibolite-facies margins, thus documenting subvertical ductile flattening and multi-lateral extension during retrogression. Well-layered, highly strained gneiss is commonly deformed by steep NE–SW-trending extensional faults and associated monoclinal fault-propagation folds (FPFs). The short limbs of the FPFs bend the regional elongation lineation and host a set of fault-parallel, unstrained to slightly deformed, granite–pegmatite dikes. Dilation vectors of most dikes are oblique to the granite–pegmatite contacts, and the sense of their tangential components attests to orogen-perpendicular extension. The fault-parallel dikes and associated FPFs are cut by a set of unstrained dikes. Collectively these observations document a prolonged history of post-collisional extension of the mid crust, from ductile structures indicative of a significant component of orogen-parallel extension shortly after the metamorphic peak at mid-crustal depths, to brittle–ductile structures indicative of a component of orogen-perpendicular extension and associated magmatic dilation following its exhumation and cooling in the upper crust.

Ductile thrusting at mid-crustal level, southwestern Grenville Province

1988 ◽  
Vol 25 (7) ◽  
pp. 1049-1059 ◽  
Author(s):  
Simon Hanmer
Keyword(s):  
Shear Zones ◽  
Wall Rock ◽  
Grenville Province ◽  
Low Viscosity ◽  
Ductile Shear Zones ◽  
Thrust Sheets ◽  
Grenvillian Orogeny ◽  
Central Gneiss Belt ◽  
Viscosity Fluid ◽  
Extensional Structures

The northwestern boundary zone of the Central Metasedimentary Belt (Grenville Province) in the Haliburton area (Ontario) is a stack of alternating tonalitic and syenitic crystalline thrust sheets, transported toward the northwest on out-of-sequence, upper amphibolite facies, ductile thrust zones during the Grenvillian Orogeny, at 1060 Ma, approximately 100 Ma after the initiation of thrusting in the underlying Central Gneiss Belt. Kinematics of the deformation are complex. Predominant northwestward thrusting was, at least partly, coeval with subordinate northeastward thrusting. Late synmetamorphic extensional shears cut both thrusts and thrust sheets. Minor late thrusting on discrete ductile shear zones postdates the extensional structures. Belts of mechanically weak pelite(?) appear to have localised the thrust sheets. Highly mobile marble behaved as a relatively low viscosity fluid during transport, able to intrude and erode more competent wall rock.

scholarly journals The geology and petrology of the Precambrian rocks to the north-east of the fjord Qagssit, Frederikshåb district, South-West Greenland

1972 ◽  
Vol 103 ◽  
pp. 1-98
Author(s):  
G Rivalenti ◽  
A Rossi
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Brittle Deformation ◽  
Metamorphic History ◽  
North East ◽  
The North ◽  
South West ◽  
Five Phases ◽  
The Relationship

The area consists of migmatitic gneisses (with related pegmatites) containing small inclusions and larger concordant layers of unmigmatised rocks (mainly represented by amphibolites, metasediments and ultramafics), and a few discordant amphibolite dykes. The petrography of the various lithotypes is described and their petrogenesis discussed. The following metamorphic history is proposed: 1) an increase in metamorphic grade to the biotite-almandine-cordierite subfacies of the low hornblende-granuIite facies, shown only by a few relic assemblages, followed by 2) retrogression to within the almandine-amphibolite facies. Migmatisation (quartz dioritisation or granodioritisation) started in the low hornblende-granulite facies and reached its maximum in the upper almandine-amphiboIite facies. A general microcline blastesis and formation of microcline-rich mobilisates is ascribed to the medium to low almandine-amphibolite facies. Further retrogression to epidoteamphiboIite or greenschist facies is only local and weak. Several generations of post-orogenic basic dykes intersect the gneisses. Structurally, five phases of ductile deformation and three phases of brittle deformation are distinguished, and the relationship between deformation and metamorphism tentatively established. The metamorphic and structural events are mostly pre-Ketilidian.

Time of metamorphism beneath the Central Metasedimentary Belt boundary thrust zone, Grenville Orogen, Ontario: accretion at 1080 Ma?

1997 ◽  
Vol 34 (7) ◽  
pp. 1023-1029 ◽  
Author(s):  
H. Timmermann ◽  
R. A. Jamieson ◽  
N. G. Culshaw ◽  
R. R. Parrish
Keyword(s):  
Linear Array ◽  
High Grade ◽  
Granitoid Rock ◽  
Metamorphic Zircon ◽  
Grenville Province ◽  
Grade Metamorphism ◽  
Regional Tectonic ◽  
Thrust Zone ◽  
High Grade Metamorphism ◽  
Central Gneiss Belt

New U–Pb zircon and titanite data from the Muskoka domain, Grenville Province, Ontario, provide protolith and metamorphic ages for the southwestern Central Gneiss Belt. Discordant analyses from a migmatitic orthogneiss and its leucosome form a linear array with an upper intercept age of 1457 ± 6 Ma and a lower intercept age of 1064 ±18 Ma. U–Pb analyses on metamorphic zircon from an amphibolite yield a set of concordant analyses with an average 207Pb/206Pb age of 1079 ± 3 Ma. A weakly migmatitic granitoid rock and a transecting charnockitic vein in the immediate footwall of the Central Metasedimentary Belt boundary thrust zone yielded a discordant array of analyses wth an upper intercept age of 1394 ± 13 Ma and a lower intercept age of 1066 ± 8 Ma. The charnockitic vein yielded concordant zircon ages of 1077 ± 2 Ma. The upper intercept ages are interpreted in terms of protolith crystallization, and the concordant and lower intercept ages as Grenviilian high-grade metamorphism and associated anatexis. We have found no evidence for a ca. 1190–1160 Ma metamorphic event in these rocks, as required by some regional tectonic interpretations. We conclude that emplacement of the Central Metasedimentary Belt over the Central Gneiss Belt, which caused high-grade metamorphism in the Muskoka domain, occurred at or shortly before ca. 1080 Ma, and that this marks the time of accretion of the Central Metasedimentary Belt to the southeast margin of Laurentia.

scholarly journals Precambrian and Tertiary geology between Kangerdlugssuaq and Angmagssalik, East Greenland

1978 ◽  
Vol 83 ◽  
pp. 1-17
Author(s):  
D Bridgewater ◽  
F.B Davis ◽  
R.C.O Gill ◽  
B.E Gorman ◽  
J.S Myers ◽  
...  
Keyword(s):  
Large Scale ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Mobile Belt ◽  
East Greenland ◽  
Reconnaissance Survey ◽  
Gneiss Complex ◽  
Igneous Intrusions ◽  
Igneous Complexes ◽  
Granitoid Gneisses

The preliminary results of a reconnaissance survey of the coast between Kangerdlugssuaq and Angmagssalik are summarized. The Archaean gneiss complex between Kangerdlugssuaq and Kap Japetus Steenstrup is fairly uniform and comprises granitoid gneisses with inclusions of supracrustal rocks, layered basic igneous complexes and older gneisses. Inland areas generally show low deformation states, large scale recumbent folds, and rocks are in granulite facies, whereas a belt of stronger deformation, steep foliation and amphibolite facies matamorphism extends alng the outer coast. To the south of Kap Japetus Steenstrup, Archaean rocks are strongly deformed in the Nagssugtoqidian mobile belt and granulite facies rocks are retrograded to amphibolite facies, except in pods of low deformation, between 2800--2600 m.y. ago. Large bodies of diorite and granodiorite (the Blokken gneisses) were emplaced and metamorphosed in amphibolite facies 2400 m.y. ago, and around Angmagssalik a complex of Ieuco-norite and charnockite was emplaced in granulite facies and caused coarse recrystallization of the adjacent gneisses. Post-tectonic igneous intrusions ranging from ultramafic to granite were intruded 1600 m.y. ago. Numerous Tertiary dykes and plutonic complexes ranging from gabbro to granite were emplaced along the coast between Tasilaq and Kangerdlugssuaq 60-35 m.y. ago.

Sign in / Sign up

Export Citation Format

Share Document