TY - JOUR
T1 - Assimilation and high-pressure fractional crystallization (AFC) recorded by Paleo-proterozoic mafic dykes, Southeast Greenland
AU - Lassen, Birgitte
AU - Bridgwater, David
AU - Bernstein, Stefan
AU - Rosing, Minik
N1 - Funding Information:
We wish to thank the Danish Lithosphere Centre for fully supporting fieldwork in East Greenland and for financing part of the geochemical analyses. D.B. further acknowledges the Carlsberg Foundation. K. Mayborn is thanked for assistance during laboratory work and with the ICP-MS. This article was written, while B.L. was supported by Forskningsstyrelsen (Danish Research Agency). Tom Andersen and George Jenner are thanked for constructive reviews which significantly improved the manuscript.
PY - 2004/1
Y1 - 2004/1
N2 - The northern margin of the Nagssugtoqidian mobile belt in Southeast Greenland exposes a suite of moderately fractionated Fe-rich tholeiitic dykes of Paleo-proterozoic age. The dykes were intruded during extension of the crust prior to the development of the Nagssugtoqidian mobile belt. Although the dykes recrystallized under amphibolite facies conditions during Proterozoic orogenesis, they suffered little deformation. Excluding two very evolved samples, the compositions range between: 7.8-4.6 wt.% MgO, 44.5-52.9 wt.% SiO2 and 1.8-6.9 wt.% total alkalis. One group of mafic dykes shows distinct mantle-normalized trace element patterns with high abundance of low field strength elements and light rare earth elements and low abundances of high field strength elements. These characteristics are consistent with a process of fractional crystallization coupled with assimilation of the regional granulitic crust. Relatively high rates of assimilation to fractional crystallization (0.7) are required to generate the level of incompatible trace elements. This points to lower crustal conditions, and the assimilation is believed to have taken place at the base of the continental crust. Trace element variations indicate fractionation at high pressure involving clinopyroxene as the main extracted phase. We evaluate two fractionation models corresponding to a pressure of 0.9 and 1.5 GPa, respectively, and show that the trace element variations require polybaric fractionation at pressures from a maximum of 1.5 GPa to a minimum of 0.9 GPa.
AB - The northern margin of the Nagssugtoqidian mobile belt in Southeast Greenland exposes a suite of moderately fractionated Fe-rich tholeiitic dykes of Paleo-proterozoic age. The dykes were intruded during extension of the crust prior to the development of the Nagssugtoqidian mobile belt. Although the dykes recrystallized under amphibolite facies conditions during Proterozoic orogenesis, they suffered little deformation. Excluding two very evolved samples, the compositions range between: 7.8-4.6 wt.% MgO, 44.5-52.9 wt.% SiO2 and 1.8-6.9 wt.% total alkalis. One group of mafic dykes shows distinct mantle-normalized trace element patterns with high abundance of low field strength elements and light rare earth elements and low abundances of high field strength elements. These characteristics are consistent with a process of fractional crystallization coupled with assimilation of the regional granulitic crust. Relatively high rates of assimilation to fractional crystallization (0.7) are required to generate the level of incompatible trace elements. This points to lower crustal conditions, and the assimilation is believed to have taken place at the base of the continental crust. Trace element variations indicate fractionation at high pressure involving clinopyroxene as the main extracted phase. We evaluate two fractionation models corresponding to a pressure of 0.9 and 1.5 GPa, respectively, and show that the trace element variations require polybaric fractionation at pressures from a maximum of 1.5 GPa to a minimum of 0.9 GPa.
KW - AFC processes
KW - High-pressure fractionation
KW - Mafic dykes
KW - Southeast Greenland
UR - http://www.scopus.com/inward/record.url?scp=1542350754&partnerID=8YFLogxK
U2 - 10.1016/S0024-4937(03)00088-4
DO - 10.1016/S0024-4937(03)00088-4
M3 - Article
AN - SCOPUS:1542350754
SN - 0024-4937
VL - 72
SP - 1
EP - 18
JO - Lithos
JF - Lithos
IS - 1-2
ER -