High field strength element/rare earth element fractionation during partial melting in the presence of garnet: Implications for identification of mantle heterogeneities

2001 ◽  
Vol 2 (7) ◽  
pp. n/a-n/a ◽  
Author(s):  
Wim van Westrenen ◽  
Jonathan D. Blundy ◽  
Bernard J. Wood
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
Partial Melting ◽  
Rare Earth Element ◽  
High Field ◽  
Earth Element ◽  
High Field Strength Element ◽  
High Field Strength ◽  
Mantle Heterogeneities ◽  
Element Fractionation

Origin of the Late Devonian Weekend lamprophyre dykes, Meguma Zone, Nova Scotia

1993 ◽  
Vol 30 (12) ◽  
pp. 2295-2304 ◽  
Author(s):  
M. C. Tate ◽  
D. B. Clarke
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
Rare Earth Element ◽  
High Field ◽  
Earth Element ◽  
High Field Strength Element ◽  
Late Devonian ◽  
High Field Strength ◽  
Element Abundances ◽  
Depleted Mantle

The Weekend dykes consist of 10 Late Devonian spessartite lamprophyres cropping out within the allochthonous Meguma lithotectonic terrane of the northern Appalachians. The dykes have characteristic panidiomorphic textures, with seriate phenocrysts of amphibole, clinopyroxene, and rare biotite set in a groundmass of intergrown plagioclase, K-feldspar, and quartz, with deuteric calcite and epidote. All dykes intruded during one magmatic episode (ca. 370 Ma) following terrane accretion of the Acadian Orogeny. The unaltered Weekend dykes show restricted major element variation (SiO2 54–58 wt.%, Al2O3 14–16 wt.%, MgO 7–11 wt.%, and total alkalies 2.4–5.5 wt.%) and have high Mg# (71–80) and moderate to high concentrations of Ni (69–278 ppm) and Cr (390–992 ppm). Large ion lithophile element (e.g., Sr, Ba 294–1194 ppm) and light rare earth element (13–67CN) abundances are high relative to high field strength element (e.g., Nb, Ta, Y 0.45–26 ppm) and heavy rare earth element (6–30CN) abundances. Geochemical variation largely corresponds to minor phenocryst fractionation, but high Mg# indicate the primitive nature of most dykes and preclude significant evolution of lamprophyric magmas in the crust. Incompatible element enrichments coupled with depleted mantle high field strength element abundances probably require a melt derived from reenriched lithospheric mantle sources, whereas Nb depletion and the volatile-rich mineralogy suggest metasomatic contributions from subducted ocean lithosphere. Geochemical comparisons with continental margin arc basalts and immobile element tectono-magmatic discrimination reinforce a subduction model for the Weekend dykes and strongly suggest active subduction prior to the emplacement of the Meguma terrane.

scholarly journals Quantifying metasomatic high-field-strength and rare-earth element transport from alkaline magmas

Geology ◽  
2021 ◽  
Author(s):  
Krzysztof Sokół ◽  
Adrian A. Finch ◽  
William Hutchison ◽  
Jonathan Cloutier ◽  
Anouk M. Borst ◽  
...  
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
Rare Earth Element ◽  
High Field ◽  
Earth Element ◽  
Chemical Interaction ◽  
Hydrothermal Systems ◽  
Initial Reaction ◽  
High Field Strength ◽  
Alkaline Magmas

Alkaline igneous rocks host many global high-field-strength element (HFSE) and rare-earth element (REE) deposits. While HFSEs are commonly assumed to be immobile in hydrothermal systems, transport by late-stage hydrothermal fluids associated with alkaline magmas is reported. However, the magnitude of the flux and the conditions are poorly constrained and yet essential to understanding the formation of REE-HFSE ores. We examined the alteration of country rocks (“fenitization”) accompanying the emplacement of a syenite magma at Illerfissalik in Greenland, through analysis of changes in rock chemistry, mineralogy, and texture. Our novel geochemical maps show a 400-m-wide intrusion aureole, within which we observed typically tenfold increases in the concentrations of many elements, including HFSEs. Textures suggest both pervasive and structurally hosted fluid flow, with initial reaction occurring with the protolith’s quartz cement, leading to increased permeability and enhancing chemical interaction with a mixed Ca-K-Na fenitizing fluid. We estimated the HFSE masses transferred from the syenite to the fenite by this fluid and found ~43 Mt of REEs were mobilized (~12% of the syenite-fenite system total rare-earth-oxide [TREO] budget), a mass comparable to the tonnages of some of the world’s largest HFSE resources. We argue that fenite can yield crucial information about the tipping points in magma evolution because retention and/or loss of volatile-bonded alkali and HFSEs are key factors in the development of magmatic zirconosilicate-hosted HFSE ores (e.g., Kringlerne, at Ilímaussaq), or the formation of the syenite-hosted Nb-Ta-REE (Motzfeldt-type) roof-zone deposits.

scholarly journals Supplemental Material: Quantifying metasomatic high-field-strength and rare-earth element transport from alkaline magmas

2021 ◽  
Author(s):  
Krzysztof Sokół ◽  
et al.
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
High Field ◽  
Earth Element ◽  
Estimation Method ◽  
Model Description ◽  
High Field Strength ◽  
Data Standardization ◽  
Element Transport ◽  
Alkaline Magmas

Petrographic information, parameterization of the Grant model, description of the HFSE tonnage estimation method, and supplemental tables of whole-rock data, standardization, and HFSE volume-tonnage calculations.<br>

scholarly journals Supplemental Material: Quantifying metasomatic high-field-strength and rare-earth element transport from alkaline magmas

2021 ◽  
Author(s):  
Krzysztof Sokół ◽  
et al.
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
High Field ◽  
Earth Element ◽  
Estimation Method ◽  
Model Description ◽  
High Field Strength ◽  
Data Standardization ◽  
Element Transport ◽  
Alkaline Magmas

Petrographic information, parameterization of the Grant model, description of the HFSE tonnage estimation method, and supplemental tables of whole-rock data, standardization, and HFSE volume-tonnage calculations.<br>

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