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Experimental effects of pressure and fluorine on apatite saturation in mafic magmas, with reference to layered intrusions and massif anorthosites

Tollari N., Baker Don R. et Barnes Sarah-Jane. (2008). Experimental effects of pressure and fluorine on apatite saturation in mafic magmas, with reference to layered intrusions and massif anorthosites. Contributions to Mineralogy and Petrology, 156, (2), p. 161-175.

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URL officielle: http://link.springer.com/article/10.1007/s00410-00...

Résumé

Apatite is a cumulate phase in the upper parts of some mafic layered intrusions and anorthositic complexes. We investigated the effect of pressure and fluorine on apatite saturation in mafic magmas to better understand under which conditions this mineral crystallizes. Apatite saturation gives information about the formation of silicate rocks, and is of interest in explaining the formation of apatite–oxide-rich rocks (e.g. nelsonites comprising approximately, one-third apatite and two-third Fe–Ti oxide). Two models of formation are proposed for this rock type: crystal fractionation followed by accumulation of apatite and Fe–Ti oxides and liquid immiscibility. New experiments carried out with mafic compositions at 500 MPa confirm that the most important variables on phosphate saturation are SiO2 and CaO. Fluorine addition leads to apatite saturation at lower SiO2 and higher CaO concentrations. Comparison of our results with those of previous experimental studies on liquid–liquid immiscibility at upper-to-mid-crustal conditions allows us to investigate the relative importance of apatite saturation versus liquid–liquid immiscibility in the petrogenesis of nelsonites and similar rocks. The liquid line of descent of three natural examples studied (the Sept-Îles intrusive suite, the anorthositic Complex of the Lac-St-Jean and the Skaergaard layered intrusion) do not cross the liquid–liquid immiscibility field before they reach apatite saturation. Thus, the apatite–oxide-rich rock associated with these three intrusive suites are best explained by crystal fractionation followed by accumulation of apatite and Fe–Ti oxides.

Type de document:Article publié dans une revue avec comité d'évaluation
ISSN:0010-7999
Volume:156
Numéro:2
Pages:p. 161-175
Version évaluée par les pairs:Oui
Date:2008
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:Apatite saturation, Silicate magmas, Fluorine, Pressure, Apatite-rich-rocks, Layered intrusions, Massif type anorthosites
Déposé le:17 juin 2016 15:23
Dernière modification:09 déc. 2016 15:41
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