Crustal formation in the Grenville Province: Nd-isotope evidence

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 When combined with over 250 published Nd analyses and some unpublished analyses, these data can be used to establish a first-order crustal formation age map for most of the Grenville parautochthon and allochthonous polycyclic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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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 location of the Allochthon Boundary Thrust and the Archean–Proterozoic suture in the Mattawa area of the Grenville Province: Nd isotope evidence

Precambrian Research ◽

10.1016/s0301-9268(00)00153-4 ◽

2001 ◽

Vol 107 (1-2) ◽

pp. 31-43 ◽

Cited By ~ 15

Author(s):

A.P. Dickin ◽

A. Guo

Keyword(s):

Grenville Province ◽

Nd Isotope ◽

Isotope Evidence

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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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Mesoproterozoic and Paleoproterozoic crustal growth in the eastern Grenville Province: Nd isotope evidence from the Long Range inlier of the Appalachian orogen

Memoir 197: Proterozoic Tectonic Evolution of the Grenville Orogen in North America ◽

10.1130/0-8137-1197-5.495 ◽

2004 ◽

pp. 495-503 ◽

Cited By ~ 1

Author(s):

Alan P. Dickin

Keyword(s):

Long Range ◽

Crustal Growth ◽

Grenville Province ◽

Nd Isotope ◽

Appalachian Orogen ◽

Isotope Evidence

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

Geological Magazine ◽

10.1017/s0016756815000874 ◽

2015 ◽

Vol 153 (4) ◽

pp. 681-695 ◽

Cited By ~ 6

Author(s):

ALAN DICKIN ◽

EDEN HYNES ◽

JACOB STRONG ◽

MARK WISBORG

Keyword(s):

Nepheline Syenite ◽

Normal Fault ◽

Grenville Province ◽

Nd Isotope ◽

Blue Mountain ◽

Multi Stage ◽

Juvenile Crust ◽

Back Arc ◽

First Time ◽

Isotope Analyses

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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