U-Pb ages of plutonism, wollastonite formation, and deformation in the central part of the Lac-Saint-Jean anorthosite suite

2002 ◽  
Vol 39 (7) ◽  
pp. 1093-1105 ◽  
Author(s):  
Michael D Higgins ◽  
Mohcine Ider ◽  
Otto van Breemen
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Fault System ◽  
Grenville Province ◽  
Zircon Age ◽  
Thermal Event ◽  
Magmatic Event

The Lac-Saint-Jean anorthosite suite (LSJAS) is the largest ensemble of plutons in the Grenville Province. Zircons from a pluton in the central part of the LSJAS yield an age of 1140+10–5 Ma, which accords with existing 1157–1142 Ma ages determined from the southern part of the LSJAS. The Du Bras granite is a linear pluton emplaced into the dominantly dextral Pipmuacan shear zone (PSZ). The U–Pb zircon age of 1148 ± 2 Ma for the Du Bras granite confirms earlier proposals that it is a granophyre, formed at greater depths by partial melting of paragneiss by the heat of the crystallizing anorthosite. Parts of the pluton are strongly deformed by the shear zone, and other parts cut the shear zone. This suggests that the pluton dates one phase of movement of the PSZ. The Canton-St-Onge wollastonite deposit was developed in paragneisses preserved within the PSZ. Titanite from this deposit gives an age of 1163 ± 18 Ma, identical within error to that of the Du Bras granite, indicating that this pluton may have provided the skarn fluids. A second plutonic cycle comprises the post-tectonic Astra granite, which stitches the PSZ, and an amazonite-bearing pegmatite dyke. Zircons gave an age of 1028 ± 2 Ma for the Astra granite. The amazonite-bearing dyke only yielded monazite, one fraction of which gave an age similar to that of the Astra granite. Other fractions record the effects of a thermal event at 1020–1017 Ma that may be related to a widespread magmatic event. The undeformed Venus de Milot syenitic intrusion yields a U–Pb age of 988 ± 2 Ma. It was emplaced along the northwest-trending Lac Rioux fault, indicating that one phase of movement occurred before 988 Ma. Another strand of the same fault system also cuts the intrusion, showing later reactivation that may have been associated with the formation of the Saguenay Graben.

U–Pb zircon age of the southwest lobe of the Havre-Saint-Pierre Anorthosite Complex, Grenville Province, Canada

1993 ◽  
Vol 30 (7) ◽  
pp. 1453-1457 ◽  
Author(s):  
Otto van Breemen ◽  
Michael D. Higgins
Keyword(s):  
Solid State ◽  
Shear Zone ◽  
Late Stage ◽  
Grenville Province ◽  
Zircon Age ◽  
Zircon Dating ◽  
Granitoid Intrusions ◽  
Anorthosite Complex ◽  
Massif Anorthosite ◽  
Magmatic Event

U–Pb zircon dating of the southwest lobe of the Havre-Saint-Pierre anorthosite intrusion indicates that it is 1062 ± 4 Ma old. Parallelism of magmatic and solid-state foliations with the adjacent Abbé–Huard lineament suggest that anorthosite parental magmas rose up this shear zone, which was active at that time. The age of igneous crystallization is much younger than that of a spatially associated mangerite intrusion, but accords with age data from other granitoid intrusions elsewhere in the Grenville Province. Evidence points to a widespread 1.09–1.05 Ga magmatic event that included massif anorthosite intrusions. This magmatic event coincided with late stage convergent tectonics in the southwestern Grenville Province.

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.

U – Pb age constraints for the lithotectonic evolution of the Grenville Province along the Mauricie transect, Quebec

1997 ◽  
Vol 34 (3) ◽  
pp. 299-316 ◽  
Author(s):  
David Corrigan ◽  
Otto van Breemen
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
High Grade ◽  
Isotopic Age ◽  
Grenville Province ◽  
Zircon Age ◽  
South Central ◽  
Continental Arc ◽  
Structural Levels ◽  
Age Constraints

New U–Pb zircon and monazite ages on 12 samples from the Mauricie transect in Quebec provide constraints on the lithologic and tectonic evolution of the south-central Grenville Province. From lowest to highest structural levels, the Mékinac, Shawinigan, and Portneuf – St. Maurice domains are identified on the basis of protolith age, tectonic overprint, and plutonism. The structurally highest Portneuf – St. Maurice domain consists of remnants of an island arc (Montauban Group) that was deformed and metamorphosed before and during the intrusion of continental arc plutons (La Bostonnais complex). A tonalitic orthogneiss yielding a [Formula: see text] zircon age suggests that most of the structurally underlying Mékinac and Shawinigan domains consist of orthogneisses that may be high-grade equivalents of the La Bostonnais complex. A voluminous metasedimentary unit occurring in the Shawinigan domain (St. Boniface unit) was deposited between ca. 1.18 and 1.09 Ga, precluding any correlation with the ca. 1.45 Ga Montauban Group. Two suites of anorthosite–mangerite–charnockite–granite (AMCG) plutonic rocks are identified on the basis of field relationships and isotopic age. A megacrystic granite belonging to the "older" AMCG suite yielded a [Formula: see text] zircon age. Three plutons from the "younger" suite yielded ages of [Formula: see text], 1059 ± 2, and 1056 ± 2 Ma. The Mékinac and Shawinigan domains, excluding the younger AMCG plutons, were penetratively deformed at granulite to uppermost amphibolite facies during west-northwest-directed thrusting between 1.15 and 1.09 Ga. At ca. 1.09 Ga, a transition from contraction to oblique extension resulted in the juxtaposition of the "cold" Portneuf – St. Maurice domain with the "hot" Shawinigan domain, along the Tawachiche shear zone. Oblique extension may have been active from ca. 1.09 to 1.04 Ga and was contemporaneous with emplacement of the younger AMCG suite.

Partial melting of metapelites in the Gagnon terrane below the high-pressure belt in the Manicouagan area (Grenville Province): pressure–temperature (P–T) and U–Pb age constraints and implications

2006 ◽  
Vol 43 (9) ◽  
pp. 1309-1329 ◽  
Author(s):  
Sherri L Jordan ◽  
Aphrodite Indares ◽  
Greg Dunning
Keyword(s):  
High Pressure ◽  
Partial Melting ◽  
Metamorphic Event ◽  
Dehydration Melting ◽  
Melting Reaction ◽  
Grenville Province ◽  
Thermal Event ◽  
Zircon Crystallization ◽  
Age Constraints ◽  
Comparable Intensity

Metapelites of the parautochthonous Gagnon terrane at the footwall of the high-pressure (high-P) belt in the Manicouagan area (central Grenville Province) preserve an impressive textural record of partial melting reactions, mainly in polymineralic inclusions within garnet. The dominant textures were developed within the pressure–temperature (P–T) field of the continuous dehydration melting reaction biotite + kyanite (or sillimanite) + plagioclase + quartz = garnet + K-feldspar + melt, with sillimanite instead of kyanite in the southern part of the footwall. Inferred P–T paths have a hair-pin form in the range of 750–850 °C and 1000–1500 MPa for the kyanite-bearing rocks. Monazite crystallization ages are consistently late Grenvillian, either 995 or 985 Ma, and one sample contains monazite of both ages. Two of these samples also contain inherited monazite with ages of 1738 ± 5 and 1719 ± 30 Ma, indicative of an earlier metamorphic event. Tonalite and diorite from the same area yield Archean zircon crystallization ages and titanite ages of 961 ± 3 and 956 ± 4 Ma, the youngest in the Manicouagan region. The late Grenvillian metamorphism was of comparable intensity but ~50 Ma younger than in the overlying high-P belt in this area and therefore seems to be unrelated to the emplacement of the latter over the Parautochthonous Belt, as previously suggested. Rather, this younger metamorphism suggests a reactivation of the footwall by underthrusting of the Gagnon terrane during the waning stages of convergence, and a link with a major coeval post-tectonic thermal event farther south in the hinterland.

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.

Structure and spatial-temporal relationship of potassic magmatism linked to a continental-scale strike-slip shear zone and post-collisional Cenozoic extension

2021 ◽  
Author(s):  
junyu Li ◽  
shunyun Cao ◽  
Xuemei Cheng ◽  
Haobo Wang ◽  
Wenxuan Li
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Continental Crust ◽  
Red River ◽  
Compositional Variation ◽  
Continental Scale ◽  
Magmatic Rocks ◽  
Western Yunnan ◽  
Potassic Rocks ◽  
Potassic Magmatism

<p>Adakite‐like potassic rocks are widespread in post-collisional settings and provide potential insights into deep crustal or crust-mantle interaction processes including asthenosphere upwelling, partial melting, lower crustal flow, thickening and collapse of the overthickened orogen. However, petrogenesis and compositional variation of these adakite‐like potassic rocks and their implications are still controversial. Potassic magmatic rocks are abundant developed in the Jinshajiang–Ailaoshan tectono-magmatic belt that stretches from eastern Tibet over western Yunnan to Vietnam. Integrated studies of structure, geochronology, mineral compositions and geochemistry indicate adakite-like potassic rocks with different deformation are exposed along the Ailaoshan-Red River shear zone. The potassic felsic rocks formed by mixing and partial melting between enriched mantle-derived ultrapotassic and thickened ancient crust-derived magmas. The mixing of the mafic and felsic melts and their extended fractional crystallization of plagioclase, K-feldspar, hornblende and biotite gave rise to the potassic magmatic rocks. Zircon geochronology provide chronological markers for emplacement at 35–37 Ma of these adakite-like potassic rocks along the shear zone. Temperature and pressure calculated by amphibole-plagioclase thermobarometry range from 3.5 to 5.9 kbar and 650 to 750 ℃, respectively, and average emplacement depths of ca. 18 km for granodiorite within this suite. In combination with the results of the Cenozoic potassic magmatism in the Jinshajiang–Ailaoshan tectono-magmatic belt, we suggest that in addition to partial melting of the thickened ancient continental crust, magma underplating and subsequent crust-mantle mixing beneath the ancient continental crust have also played an important role in crustal reworking and strongly affected the rheological properties and density of rocks. The exhumation underlines the role of lateral motion of the Ailaoshan-Red River shear zone initiation by potassic magma-assisted rheological weakening and exhumation at high ambient temperatures within the shear zone.</p>

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.

Soda-granites from South of Tatanagar, Bihar, India

1966 ◽  
Vol 103 (4) ◽  
pp. 340-351 ◽  
Author(s):  
A. K. Banerji ◽  
A. K. Talapatra
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Confining Pressure ◽  
Residual Liquid ◽  
Copper Sulphide ◽  
Granite Magma ◽  
Singhbhum Shear Zone ◽  
Sudden Release ◽  
Singhbhum Granite

AbstractThe nature and origin of some soda-granites from the western part of the Singhbhum shear zone, Bihar, India, are discussed. These soda-granites are responsible for copper sulphide, apatite-magnetite, and uraniferous mineralization within the shear zone. Earlier workers regarded these rocks as sheared materials representing a portion of the high sodic residual liquid from the neighbouring Singhbhum granite magma. The present work indicates that these rocks are migmatitic in nature and are the products of progressive replacement of pre-existing pelitic and semi-pelitic schists by felspathic materials. Migmatization is essentially post-shearing in age while the Singhbhum granite is pre-shearing in age. The migmatitic materials appear to have been derived by the partial melting of the Singhbhum granite during shearing, particularly in depth, as a result of sudden release of confining pressure consequent upon shearing and generation of heat caused by friction at the base of the shear zone. The resulting liquids, which were albite rich, found easy passage through the shear zone and brought about migmatization and mineralization in its wake.

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