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Contributions to Mineralogy and Petrology

, Volume 143, Issue 3, pp 300–315 | Cite as

Minor- and trace-element zoning in plagioclase: implications for magma chamber processes at Parinacota volcano, northern Chile

  • Catherine Ginibre
  • Gerhard Wörner
  • Andreas Kronz

Abstract.

Textural and compositional zoning in plagioclase phenocrysts in a sample from Parinacota volcano (Chile) was investigated using backscattered electron images and electron microprobe analysis of major and trace elements. Large (2 mm) oscillatory zoned crystals (type I) with resorption surfaces of moderate An discontinuities (⩽10% An) and decreasing trace-element contents (Sr, Mg, Ti) towards the rim reflect melt differentiation and turbulent convection in the main magma body. Early recharge with a low-Sr mafic magma is seen in the core. Small-scale Sr variations in the core indicate limited diffusion and thus residence and differentiation times of the magma shorter than a few thousand years. Smaller crystals (type II) with low trace-element/An ratio reflect the influence of an H2O-rich melt probably from a differentiated boundary layer. Closed-system in-situ crystallisation, mafic magma recharge and the role of a water-rich differentiated boundary layer can be distinguished from the An–trace element relationships. Crystals apparently move relatively freely between different parts and regimes in the magma chamber, evidence for "convective crystal dispersion". High-Sr type II crystals indicate an earlier input of Sr-rich mafic magma. Recharge of two distinct mafic magma types is thus identified (high-Sr and low-Sr), which must have been present – at increasing recharge rates with time – in the plumbing system throughout the volcano's history.

Keywords

Magma Chamber Recharge Rate Mafic Magma Plagioclase Phenocryst Plumbing System 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  • Catherine Ginibre
    • 1
  • Gerhard Wörner
    • 1
  • Andreas Kronz
    • 1
  1. 1.Geowissenschafliches Zentrum Göttingen, Abt. Geochemie, Goldschmidtstr. 1, 37077 Göttingen, Germany

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