Quick
Search: 		  
advanced search
 GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help 
  Geological Magazine   Don't get GSW? Talk to your librarian.
JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Geological Magazine; July 2009; v. 146; no. 4; p. 485-496; DOI: 10.1017/S0016756808005554
© 2009 Cambridge University Press (CUP)
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Google Scholar
Right arrow Articles by CHISTYAKOVA, S.
Right arrow Articles by LATYPOV, R.
GeoRef
Right arrow GeoRef Citation

Fine-scale chemical zonation in small mafic dykes, Kestiö Island, SW Finland

SOFYA CHISTYAKOVA*,{dagger} and RAIS LATYPOV*,{ddagger}

* Department of Geosciences, University of Oulu, Oulu, Finland
{ddagger} Geological Institute, Kola Science Centre, Apatity, Russia

{dagger} Author for correspondence: sofya.chistyakova{at}oulu.fi

Detailed centimetre-scale sampling across two small dolerite dykes (7 and 21 cm wide) of Kestiö Island, SW Finland, has revealed a well-developed internal zonation, with surprisingly systematic compositional variations. From the margins inwards, the dykes exhibit a steady decrease in whole-rock MgO, Mg number (100Mg/(Mg+Fetotal)) and normative Opx (indicating a normal fractionation trend) with simultaneous increase in normative An (100An/(An+Ab)) and decrease in incompatible Zr, Y, TiO2 and P2O5 (indicating a reverse fractionation trend). In addition, marginal rocks of dykes contain normative corundum that is apparently associated with their significant depletion in whole-rock CaO. The extent of margin-to-centre differentiation of dykes in terms of most components is slight to modest, although in some petrochemical parameters it is quite high (e.g. 15 mol. % of normative An). The dykes are almost glassy and uncontaminated by host rocks, suggesting that their compositional profiles are primary and most likely reflect temporal changes in composition of magma filling the dykes. A mechanism responsible for the systematic changes in composition of inflowing magma remains elusive, however, since no known processes are able to force magma to evolve simultaneously along both normal and reverse fractionation trends. The study thus appears to indicate some not yet specified process of magma differentiation.

Key Words: mafic dykes • internal zonation • reverse and normal differentiation trends • unknown process of magma differentiation






JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2009 by Cambridge University Press (CUP)