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Strong, localised country-rock contamination and partial homogenisation of a mafic magma: An example from west central Sweden

Lindh, Anders LU ; Kjollerstrom, A and Solyom, Zoltan LU (2006) In Lithos 86(3-4). p.212-228
Abstract
A dolerite sill cutting slightly older basalt in west-central Sweden shows a strong chemical variation (54%<SiO2<73%) within a restricted area (<100x100 m(2)). The linear correlation among almost all elements is extremely high; in addition, epsilon(NdT) is strongly correlated with the SiO2 content. Least-square hyperbolic-ratio and three-element ratio modelling (common denominator) suggests that most of the chemical variation is explained by mixing and/or micro-mingling. In all, we test 407 hyperbolas, of which 402 are fitted. The five ratio pairs, which could not be fitted to a hyperbola using a least-square fitting procedure, have the ratio Th/Eu in common. Testing the goodness of fit is problematic for hyperbolic distributions;... (More)
A dolerite sill cutting slightly older basalt in west-central Sweden shows a strong chemical variation (54%<SiO2<73%) within a restricted area (<100x100 m(2)). The linear correlation among almost all elements is extremely high; in addition, epsilon(NdT) is strongly correlated with the SiO2 content. Least-square hyperbolic-ratio and three-element ratio modelling (common denominator) suggests that most of the chemical variation is explained by mixing and/or micro-mingling. In all, we test 407 hyperbolas, of which 402 are fitted. The five ratio pairs, which could not be fitted to a hyperbola using a least-square fitting procedure, have the ratio Th/Eu in common. Testing the goodness of fit is problematic for hyperbolic distributions; for comparing purposes we 4 sum the distances to chords approximating the hyperbola. Mobile and immobile elements behave similarly, suggesting that no A elements are lost or added from outside the system. The data suggests that already the most mafic of the analysed rocks is a mixture of the 'normal' dolerite and a siliceous crustal rock. A mafic magma intruded into the base of the crust, where it fractionated resulting in a decreased Mg number. The magma was then contaminated with country rocks in an intermediate magma chamber due to country rock melting; during mixing/mingling almost no fractionation took place. The contaminated rock suggests the presence of a fluid phase. This was probably a prerequisite for country-rock melting. Enrichment in some incompatible elements suggests that besides major mixing/mingling a thermochemical separation process has affected the most felsic rock enriching it in light rare earths and Zr. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
major elements, contamination, trace elements, mixing, mingling, ratio correlation, hyperbolic modelling, Sm-Nd isotopes, dolerite
in
Lithos
volume
86
issue
3-4
pages
212 - 228
publisher
Elsevier
external identifiers
  • wos:000235408700002
  • scopus:30944451950
ISSN
0024-4937
DOI
10.1016/j.lithos.2005.06.005
language
English
LU publication?
yes
id
2eb7bb5f-de89-41fb-95bc-4d1b1d645b66 (old id 417377)
date added to LUP
2016-04-01 11:42:19
date last changed
2019-11-26 03:01:15
@article{2eb7bb5f-de89-41fb-95bc-4d1b1d645b66,
  abstract     = {A dolerite sill cutting slightly older basalt in west-central Sweden shows a strong chemical variation (54%&lt;SiO2&lt;73%) within a restricted area (&lt;100x100 m(2)). The linear correlation among almost all elements is extremely high; in addition, epsilon(NdT) is strongly correlated with the SiO2 content. Least-square hyperbolic-ratio and three-element ratio modelling (common denominator) suggests that most of the chemical variation is explained by mixing and/or micro-mingling. In all, we test 407 hyperbolas, of which 402 are fitted. The five ratio pairs, which could not be fitted to a hyperbola using a least-square fitting procedure, have the ratio Th/Eu in common. Testing the goodness of fit is problematic for hyperbolic distributions; for comparing purposes we 4 sum the distances to chords approximating the hyperbola. Mobile and immobile elements behave similarly, suggesting that no A elements are lost or added from outside the system. The data suggests that already the most mafic of the analysed rocks is a mixture of the 'normal' dolerite and a siliceous crustal rock. A mafic magma intruded into the base of the crust, where it fractionated resulting in a decreased Mg number. The magma was then contaminated with country rocks in an intermediate magma chamber due to country rock melting; during mixing/mingling almost no fractionation took place. The contaminated rock suggests the presence of a fluid phase. This was probably a prerequisite for country-rock melting. Enrichment in some incompatible elements suggests that besides major mixing/mingling a thermochemical separation process has affected the most felsic rock enriching it in light rare earths and Zr.},
  author       = {Lindh, Anders and Kjollerstrom, A and Solyom, Zoltan},
  issn         = {0024-4937},
  language     = {eng},
  number       = {3-4},
  pages        = {212--228},
  publisher    = {Elsevier},
  series       = {Lithos},
  title        = {Strong, localised country-rock contamination and partial homogenisation of a mafic magma: An example from west central Sweden},
  url          = {http://dx.doi.org/10.1016/j.lithos.2005.06.005},
  doi          = {10.1016/j.lithos.2005.06.005},
  volume       = {86},
  year         = {2006},
}