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

2009 ◽  
Vol 122 (5-6) ◽  
pp. 870-883 ◽  
Author(s):  
A. P. Dickin ◽  
R. H. McNutt ◽  
C. Martin ◽  
A. Guo
Keyword(s):  
Grenville Province ◽  
Nd Isotope ◽  
Isotope Evidence ◽  
Juvenile Crust

The Taconian orogeny in southern New England: Nd-isotope evidence against addition of juvenile components

1996 ◽  
Vol 33 (12) ◽  
pp. 1612-1627 ◽  
Author(s):  
B. Bock ◽  
S. M. McLennan ◽  
G. N. Hanson
Keyword(s):  
New England ◽  
Sedimentary Rocks ◽  
Late Ordovician ◽  
Nd Isotope ◽  
Middle Ordovician ◽  
Southern New England ◽  
Isotope Evidence ◽  
Juvenile Crust ◽  
Plutonic Rocks ◽  
Laurentian Margin

Nd-isotope data for pre-Taconian (meta)sedimentary and igneous rocks, syn-Taconian (meta)sedimentary rocks, and Late Ordovician–Silurian plutonic rocks indicate that the Ordovician Taconian orogeny did not add significant amounts of juvenile crust to the Laurentian margin in southern New England. Nd-isotope compositions of Grenvillian crust and Late Proterozoic to Early Cambrian rift sediments range from εNd of −3.1 to −6.6 at 450 Ma. Sedimentary rocks deposited during the Cambrian and the early Middle Ordovician, which represent the drift stage of Laurentia, and earliest Taconian sedimentary rocks show more negative εNd(450 Ma), with a range from −11.7 to −13.3. Sedimentary rocks deposited in response to the Taconian orogeny have uniform εNd(450 Ma) values of about −8. Middle to Late Ordovician and Permian plutonic rocks from southwestern Connecticut have εNd(450 Ma) values of −2 to −5, which indicates that these rocks contain older crustal components. Rocks with juvenile Nd characteristics are the early Paleozoic Maltby Lake Volcanics (εNd(450 Ma) +8) from southwestern Connecticut, and Middle Ordovician igneous samples from the Hawley Formation (εNd(450 Ma) +6 to −0.6) in Massachusetts.

Crustal formation in the Grenville Province: Nd-isotope evidence

2000 ◽  
Vol 37 (2-3) ◽  
pp. 165-181 ◽  
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 When combined with over 250 published Nd analyses and some unpublished analyses, these data can be used to establish a first-order crustal formation age map for most of the Grenville parautochthon and allochthonous polycyclic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.

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

2015 ◽  
Vol 153 (4) ◽  
pp. 681-695 ◽  
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.

Rare earth element, Sr- and Nd-isotope evidence for petrogenesis of Permian basaltic and K-rich volcanic rocks from south-west England

1986 ◽  
Vol 50 (357) ◽  
pp. 481-489 ◽  
Author(s):  
R. S. Thorpe ◽  
M. E. Cosgrove ◽  
P. W. C. van Calsteren
Keyword(s):  
High Field ◽  
Earth Element ◽  
Volcanic Rocks ◽  
Transition Element ◽  
Oceanic Lithosphere ◽  
High Field Strength ◽  
Nd Isotope ◽  
South West ◽  
Isotope Evidence ◽  
South West England

AbstractPermian basic/ultrabasic lavas from south-west England may be divided into a ‘basaltic’ and a K-rich group. Both groups have enrichment of large-ion lithophile (LIL) elements relative to high field strength (HFS) elements, and the K-rich group show large degrees of LIL enrichment (c.50–500 times primordial mantle) in association with varied transition element concentrations. Samples from both groups 87Sr/86Sri = 0.704–0.705 and 143Nd/144Ndi = 0.5123–0.5127 and plot close to the mantle array on an ɛSr−ɛNd diagram. These data are interpreted in terms of derivation of the lavas from magmas resulting from partial melting of mantle which had experienced less (for the basaltic group) or more (for the K-rich group) enrichment in LIL elements as a result of migration of mantle melts. Such enrichment accompanied or followed subduction of oceanic lithosphere below south-west England. The resultant magmas experienced fractional crystallization of olivine and pyroxene prior to eruption.

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