Testing a back-arc ‘aulacogen’ model for the Central Metasedimentary Belt of the Grenville Province

AbstractNearly 70 new Nd isotope analyses are presented for plutonic orthogneisses from the Grenvillian Central Metasedimentary Belt (CMB) in order to test a back-arc aulacogen model for its origin. Nd isotope signatures of metaplutonic rocks are used as probes of the formation age of the crust at depth, revealing sharp boundaries between old crustal blocks and juvenile (1.2–1.35 Ga) Elzevirian-age crust. Firstly, a hidden block of old crustal basement is revealed between areas of juvenile crust south of Douglas, Ontario. Secondly, TDM ages refine the boundary between juvenile crust and old basement (1.35–1.55 Ga) within the Weslemkoon batholith, showing this pluton to be a polygenetic stitching pluton that straddles a hidden crustal boundary. Finally, the CMB boundary zone is shown to form a sharp age boundary between juvenile and old crustal domains, and is interpreted as a reactivated rift-bounding normal fault. When the distribution of rift-related alkaline rocks is compared with these crustal boundaries, the Bancroft nepheline syenite suite is centrally located in a juvenile ensimatic zone between blocks of old basement. Such a location, near the axis of a juvenile crustal segment, implies emplacement late in the rifting process. Similarly, the Blue Mountain nepheline syenite appears to post-date an earlier rifting event to the southeast. Hence, a multi-stage model is proposed for the evolution of a back-arc aulacogen, which is consistent with the distribution of marble and volcanic/plutonic units in the CMB. The model places the Bancroft nepheline syenites in a precise plate tectonic context for the first time.

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Neodymium isotope mapping a polygenetic TTG batholith: Failed back-arc rifting in the Central Metasedimentary Belt, SW Grenville Province

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2021-0061 ◽

2021 ◽

Author(s):

Jacob Strong ◽

Alan Dickin

Keyword(s):

Gulf Of California ◽

Source Rocks ◽

Crustal Material ◽

Grenville Province ◽

Nd Isotope ◽

Geochemical Pattern ◽

Modern Analogue ◽

Magma Pulses ◽

Back Arc ◽

Isotope Analyses

Fifty-five new Nd isotope analyses are presented for plutonic orthogneisses from the Grimsthorpe domain in the marble-rich segment of the Grenvillian Central Metasedimentary Belt (CMB) to test the back-arc aulacogen model for its origin. Nd isotope analyses from the Weslemkoon batholith, Elzevir batholith, Lingham Lake complex and Canniff tonalite are used to probe the crustal formation age of their source rocks. Despite its concentric foliation, the Weslemkoon batholith displays a complex geochemical pattern consisting of several NE trending domains with older TDM ages, surrounded by juvenile crustal material. The new Nd isotope results, coupled with geochemistry for the Weslemkoon and Elzevir batholiths depict the fragmentation of a block of old crust that formed a screen between en echelon segments of a mid-Mesoproterozoic back-arc rift zone. The isotope boundaries identified within the Weslemkoon batholith delineate magma pulses sampling two distinct sources, interpreted as Laurentian basement and juvenile basaltic underplate. Underplating could be attributed to slab rollback under the pre-Grenvillian continental margin arc. The intensification of rift-related magmatism in the CMB is demonstrated by its bimodal petrological character. A modern analogue for the tectonic context of the CMB is the Gulf of California, where subduction-related magmatism has transitioned to rift-related magmatism. However, the Gulf of California exhibits more transcurrent motion than is evidenced by the geometry of the CMB rift. A geometrical analogue for the break-up of the Elzevir block between two rift segments is provided by the Danakil block of the Red Sea, which is currently undergoing similar tectonic fragmentation.

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An application of Nd isotope mapping in structural geology: delineating an allochthonous Grenvillian terrane at North Bay, Ontario

Geological Magazine ◽

10.1017/s0016756803008070 ◽

2003 ◽

Vol 140 (5) ◽

pp. 539-548 ◽

Cited By ~ 15

Author(s):

A. P. DICKIN ◽

R. H. MCNUTT

Keyword(s):

Structural Geology ◽

Amphibolite Facies ◽

High Grade ◽

Grenville Province ◽

Nd Isotope ◽

Bay Area ◽

The North ◽

Depleted Mantle ◽

Different Types ◽

Isotope Analyses

Fifty new Nd isotope analyses are presented from the North Bay area of the Grenville Province in Ontario. These data are used to map the extent of an allochthonous Grenvillian terrane which is an outlier of the Allochthonous Polycyclic Belt of the Grenville Province. Amphibolite facies orthogneisses from the allochthonous terrane have depleted mantle Nd model ages (TDM) below 1.8 Ga, whereas the gneisses of the structurally underlying parautochthon almost invariably have model ages above 1.8 Ga. The distribution of model ages is consistent with the distribution of distinct types of metabasic rock, used by other researchers as the criterion for recognizing rocks of the allochthonous and parautochthonous belts of the Grenville Province. The agreement between these different types of evidence demonstrates that Nd isotope mapping is a reliable and powerful tool for mapping terrane boundaries in high-grade metamorphic belts.

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The extent of juvenile crust in the Grenville Province: Nd isotope evidence

Geological Society of America Bulletin ◽

10.1130/b26381.1 ◽

2009 ◽

Vol 122 (5-6) ◽

pp. 870-883 ◽

Cited By ~ 35

Author(s):

A. P. Dickin ◽

R. H. McNutt ◽

C. Martin ◽

A. Guo

Keyword(s):

Grenville Province ◽

Nd Isotope ◽

Isotope Evidence ◽

Juvenile Crust

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Nd isotope mapping of the Frontenac Terrane in the SW Grenville Province

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2020-0063 ◽

2021 ◽

Author(s):

Alan Dickin ◽

Jacob Strong

Keyword(s):

Rift Zone ◽

Geographical Location ◽

Silica Content ◽

Taupo Volcanic Zone ◽

Grenville Province ◽

Nd Isotope ◽

Ottawa River ◽

Crustal Block ◽

Granitoid Rocks ◽

Back Arc

Nd isotope analyses are presented for granitoid rocks from the western part of Frontenac Terrane in the Grenville Province of Ontario. TDM ages show no correlation with the silica content of the rocks, but instead correlate with geographical location, suggesting that the TDM ages are indicative of regional crustal formation age, and do not result from mixing between sources with different provenance ages. Based on these observations, we identify a new crustal age boundary that follows the Desert Lake – Canoe Lake fault and the Rideau Lake fault, and hence a new juvenile crustal block (Westport domain). This domain is identified as part of the ensimatic back-arc rift zone that formed the juvenile segment of the Central Metasedimentary Belt in Ontario. However, additional sampling along the Ottawa River suggests that the juvenile Westport domain does not extend into Quebec. Instead, a narrower ensialic rift zone is represented by the Marble domain in Quebec. Based on comparison with the Taupo volcanic zone and the northern Red Sea as modern analogues, we suggest that the transition from a wide ensimatic rift zone in Ontario to a narrow ensialic rift in Quebec was accommodated by transtensional motion along a zone of diffuse shear east of Ottawa.

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Crustal formation in the Grenville Province: Nd-isotope evidence

Canadian Journal of Earth Sciences ◽

10.1139/e99-039 ◽

2000 ◽

Vol 37 (2-3) ◽

pp. 165-181 ◽

Cited By ~ 82

Author(s):

A P Dickin

Keyword(s):

North America ◽

Grenville Province ◽

Nd Isotope ◽

Precambrian Shield ◽

First Order ◽

Isotope Evidence ◽

Isotope Analyses

Ninety-eight new Nd-isotope analyses are presented for gneissic rocks from the Grenville Province. When combined with over 250 published Nd analyses and some unpublished analyses, these data can be used to establish a first-order crustal formation age map for most of the Grenville parautochthon and allochthonous polycyclic belt. In particular, the geographic extents of a juvenile Labradorian arc (Labradoria) and a juvenile 1.5 Ga arc (Quebecia) are defined, each with an area probably in excess of 100 000 km2. In addition, pre-1.75 Ga arcs are identified in Ontario (Barilia) and Labrador (Makkovikia). This work largely fills the last major gap in the continent-wide crustal formation age map of the Precambrian Shield of North America.

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The Central Metasedimentary Belt (Grenville Province) as a failed back-arc rift zone: Nd isotope evidence

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2007.04.031 ◽

2007 ◽

Vol 259 (1-2) ◽

pp. 97-106 ◽

Cited By ~ 39

Author(s):

A.P. Dickin ◽

R.H. McNutt

Keyword(s):

Rift Zone ◽

Grenville Province ◽

Nd Isotope ◽

Isotope Evidence ◽

Back Arc

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Petrology of the Blue Mountain and Bigwood felsic alkaline complexes of the Grenville province of Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e77-055 ◽

1977 ◽

Vol 14 (4) ◽

pp. 515-538 ◽

Cited By ~ 2

Author(s):

N. A. Duke ◽

A. D. Edgar

Keyword(s):

Partial Melting ◽

Total Pressure ◽

Nepheline Syenite ◽

Regional Metamorphism ◽

High Grade ◽

Grenville Province ◽

Blue Mountain ◽

Melting Curves ◽

Mineral Compositions ◽

Alkaline Complexes

The Blue Mountain, Methuen Township, and Bigwood, District of Sudbury, alkaline gneiss complexes of the southwestern Grenville province occur in areas of medium to high grade regional metamorphism equivalent to temperatures between 550 °C to 700 °C and [Formula: see text] to 7 kb (350 to 700 Mega Pascals (MPa)) total pressure. Textures of the undersaturated alkaline gneisses of both complexes are predominantly characteristic of metamorphic–metasomatic processes. Compositions of the major (feldspar, nepheline) and minor (biotite, muscovite, amphibole, pyroxene, garnet) minerals in these rocks, when compared to known stability relations and minimum melting curves of the Blue Mountain nepheline-bearing gneiss, indicate equilibration at temperatures and pressures below the maximum values for the regional metamorphism.Textures and mineral compositions in the rocks of both complexes also suggest that extensive metasomatism has taken place. Consequently these rocks must now be regarded as metamorphic metasomatic rocks produced during one or more periods of regional metamorphism. Age relationships in both complexes are in agreement with this hypothesis. The ultimate origins of the rocks of both complexes are unknown but, in the case of the Blue Mountain complex, partial melting of alkali olivine basalts, or of an unknown and possibly mantle derived source in the Bigwood complex, may have produced liquids of nepheline syenite compositions from which the present rocks were derived by metamorphic and metasomatic processes.

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Axial Compressor Mean-Line Analysis: Choking Modelling and Fully-Coupled Integration in Engine Performance Simulations

International Journal of Turbomachinery Propulsion and Power ◽

10.3390/ijtpp6010004 ◽

2021 ◽

Vol 6 (1) ◽

pp. 4

Author(s):

Ioannis Kolias ◽

Alexios Alexiou ◽

Nikolaos Aretakis ◽

Konstantinos Mathioudakis

Keyword(s):

Axial Compressor ◽

Engine Performance ◽

Engine Model ◽

Multi Stage ◽

Transient Simulations ◽

Full Knowledge ◽

Compressor Performance ◽

First Time ◽

Performance Calculation ◽

Fully Coupled

A mean-line compressor performance calculation method is presented that covers the entire operating range, including the choked region of the map. It can be directly integrated into overall engine performance models, as it is developed in the same simulation environment. The code materializing the model can inherit the same interfaces, fluid models, and solvers, as the engine cycle model, allowing consistent, transparent, and robust simulations. In order to deal with convergence problems when the compressor operates close to or within the choked operation region, an approach to model choking conditions at blade row and overall compressor level is proposed. The choked portion of the compressor characteristics map is thus numerically established, allowing full knowledge and handling of inter-stage flow conditions. Such choking modelling capabilities are illustrated, for the first time in the open literature, for the case of multi-stage compressors. Integration capabilities of the 1D code within an overall engine model are demonstrated through steady state and transient simulations of a contemporary turbofan layout. Advantages offered by this approach are discussed, while comparison of using alternative approaches for representing compressor performance in overall engine models is discussed.

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