Chemical and isotopic composition of the lower crust beneath the Meguma Lithotectonic Zone, Nova Scotia: evidence from granulite facies xenoliths

1991 ◽  
Vol 109 (1) ◽  
pp. 69-88 ◽  
Author(s):  
G. W. Eberz ◽  
D. B. Clarke ◽  
A. K. Chatterjee ◽  
P. S. Giles
Keyword(s):  
Nova Scotia ◽  
Isotopic Composition ◽  
Lower Crust ◽  
Granulite Facies ◽  
Lithotectonic Zone

Interaction among upper crustal, lower crustal, and mantle materials in the Port Mouton pluton, Meguma Lithotectonic Zone, southwest Nova Scotia

2000 ◽  
Vol 37 (4) ◽  
pp. 579-600 ◽  
Author(s):  
D Barrie Clarke ◽  
Raymond Fallon ◽  
Larry M Heaman
Keyword(s):  
Nova Scotia ◽  
Lower Crust ◽  
Early Stage ◽  
Late Devonian ◽  
Upper Crust ◽  
Middle Stage ◽  
Two Component ◽  
Granitoid Rocks ◽  
Mafic Magmas ◽  
Lithotectonic Zone

The Port Mouton pluton is unique among the Late Devonian peraluminous granitoid bodies in the Meguma Lithotectonic Zone of southwestern Nova Scotia in its lithological heterogeneity, extensive physical and chemical interaction with the country rocks, clear evidence for mingling and mixing with mafic magmas, and highly abundant pegmatites. New U–Pb age determinations on monazite establish an intrusion age of 373 ± 1 Ma, similar to the ages of other Meguma Lithotectonic Zone granitoid plutons and mafic intrusions. Field relations, petrology, and geochemistry define three stages of intrusion of the Port Mouton pluton: (i) early stage, discontinuously exposed around the outer margin of the pluton, dominated by coarse-grained tonalite-granodiorite, and with Rb/Sr < 0.55, Eu/Eu* > 0.40, and GdN/LuN < 2; (ii) middle stage, occupying the interior of the pluton, dominated by medium-grained granodiorite-monzogranite, and with Rb/Sr > 0.55, Eu/Eu* < 0.40, and GdN/LuN > 2; and (iii) late stage, consisting of abundant minor sheets throughout the pluton, dominated by fine-grained tonalite, granodiorite, and leucogranite that are similar to rocks of the early and middle stages. The Port Mouton pluton shows a wider range of 87Sr/86Sri (0.7036-0.7154), and a wider range and generally higher εNdi (–3.72 to +2.12), than other granitoid rocks in the Meguma Lithotectonic Zone, potentially reflecting a complex, partially equilibrated, interaction among mantle, lower crust, and upper crust. Field, petrological, and chemical evidence for the involvement of mantle-derived magmas and melting of upper crust permit modelling of the Port Mouton pluton granitoid compositions by three simultaneous mixing equations. These mixing model results suggest that the early stage granitoid rocks can form from simple three-component mixing relationships when the bulk distribution coefficients between residuum and melt for Sr and Nd range from 1.05 to 1.18, or two-component mixing combined with fractionation of material like the known felsic lower crust. The middle stage granitoid rocks only yield solutions involving two-component mixing and fractionation of material unlike the known felsic lower crust. We conclude that the Late Devonian mafic magmas played a major role in the formation of granitoid magmas in the Meguma Lithotectonic Zone by supplying heat and material to cause partial fusion of the Avalon lower crust.

Mylonitic mafic granulite in fault megabreccia at Clarke Head, Nova Scotia: a sample of Avalonian lower crust?

1995 ◽  
Vol 132 (1) ◽  
pp. 81-90 ◽  
Author(s):  
Wes Gibbons ◽  
J. Brendan Murphy
Keyword(s):  
Nova Scotia ◽  
Lower Crust ◽  
Mafic Magma ◽  
Granulite Facies ◽  
Fault System ◽  
High Grade ◽  
Deep Crust ◽  
Clay Matrix ◽  
Meguma Terrane ◽  
North And South

AbstractThe Clarke Head fault megabreccia was produced within a major Late Palaeozoic transcurrent structure (the Minas fault system) which separates the displaced Meguma terrane of southern Nova Scotia from rocks more typical of the Avalon Superterrane. A large clast of anomalously high grade metabasite embedded in the clay matrix of the fault megabreccia displays a fresh granulite facies mineralogy (2-pyroxene + garnet + plagioclase) and mylonitic to ultramylonitic textures induced by anhydrous shearing deep in the roots of the fault zone. Whole rock geochemistry reveals the granulite protolith to have been a continental, within-plate mafic magma transitional between theoleiitic and alkaline. The original geochemical signature has survived strong dynamic recrystallization at granulite grade. Well-preserved REE abundances testify to a lack of metasomatic fractionation during high grade shearing under water-absent conditions. Sm—Nd data indicate that the basic granulite has a TDM age of c. 1 Ga. Isotopic comparisons with adjacent areas reveal similar TDM ages both north and south of the Minas fault system. The high grade clast may be typical of the lower crust in Nova Scotia and is thought to offer a rare window into the deep crust of the Avalon Superterrane in North America.

scholarly journals Granulite-Facies Xenoliths in Rift Basalts of Northern Tanzania: Age, Composition and Origin of Archean Lower Crust

2014 ◽  
Vol 55 (7) ◽  
pp. 1243-1286 ◽  
Author(s):  
A. T. Mansur ◽  
S. Manya ◽  
S. Timpa ◽  
R. L. Rudnick
Keyword(s):  
Lower Crust ◽  
Granulite Facies ◽  
Age Composition ◽  
Northern Tanzania

Granulite facies xenoliths from the Yuhuashan complex, central Jiangxi, South China: constraints on Late Palaeozoic orogeny and middle-lower crust components

2016 ◽  
Vol 34 (1) ◽  
pp. 45-61 ◽  
Author(s):  
C. Zhang ◽  
J. Yu ◽  
S. Y. O'Reilly ◽  
W. L. Griffin ◽  
J. Qian ◽  
...  
Keyword(s):  
South China ◽  
Lower Crust ◽  
Granulite Facies ◽  
Late Palaeozoic

scholarly journals O, H and C isotopic systematics of Icelandic groundwater

2019 ◽  
Vol 98 ◽  
pp. 07031
Author(s):  
Arny E. Sveinbjörnsdóttir ◽  
Andri Stefánsson ◽  
Jan Heinemeier
Keyword(s):  
Isotopic Composition ◽  
Carbon Isotopes ◽  
Upper Mantle ◽  
Lower Crust ◽  
Natural Waters ◽  
Large Range ◽  
Carbon Sources ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Range Of Values

Stable water isotopes of oxygen and hydrogen have been studied in Icelandic natural waters since 1960 for hydrological and geothermal research. All the waters are of meteoric and seawater origin. The measured range in δD and δ18O is large -131 to +3.3‰ and -20.8 to +2.3‰ respectively. Some of the waters are more depleted than any present-day precipitation suggesting a pre-Holocene component in the groundwater. Carbon isotopes of streams, rivers, soil and groundwater have been studied since 1990 in order to evaluate the carbon sources and reactions that possibly influence the carbon systematics of the water. Results show large range of values, for δ13CDIC -27.4 to +4.5‰ and for 14CDIC +0.6 to +118 pMC. Apart from atmospheric, organic and rock leaching, input of gas at depth with similar isotopic composition as the pre-erupted melt of the upper mantle and lower crust beneath Iceland have been identified as sources for carbon in the deeper groundwater.

Oxygen Isotope Studies on Sea Scallops, Placopecten magellanicus, from Browns Bank, Nova Scotia

1988 ◽  
Vol 45 (8) ◽  
pp. 1378-1386 ◽  
Author(s):  
F. C. Tan ◽  
D. Cai ◽  
D. L. Roddick
Keyword(s):  
Nova Scotia ◽  
Isotopic Composition ◽  
Oxygen Isotope ◽  
Placopecten Magellanicus ◽  
Ambient Seawater ◽  
Annual Cycles ◽  
Isotope Studies ◽  
Biological Evidence ◽  
Sea Scallops ◽  
External Growth

Oxygen isotope records from two sea scallops, Placopecten magellanicus, collected alive from Browns Bank, Nova Scotia, show annual cycles that closely approximate the isotopic composition predicted as a function of observed temperatures and the isotopic composition of the ambient seawater. The external growth lines coincided with the most positive δ18O values of the cycles, suggesting their formation during the period of coldest water temperatures (spring). The δ18O results indicate that the growth lines are annual events, consistent with the biological evidence.

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