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Anders Lindh

Anders Lindh

Professor emeritus

Anders Lindh

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

Author

  • Anders Lindh
  • A Kjollerstrom
  • Zoltan Solyom

Summary, in English

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.

Department/s

  • Lithosphere and Biosphere Science

Publishing year

2006

Language

English

Pages

212-228

Publication/Series

Lithos

Volume

86

Issue

3-4

Document type

Journal article

Publisher

Elsevier

Topic

  • Geology

Keywords

  • major elements
  • contamination
  • trace elements
  • mixing
  • mingling
  • ratio correlation
  • hyperbolic modelling
  • Sm-Nd isotopes
  • dolerite

Status

Published

ISBN/ISSN/Other

  • ISSN: 0024-4937