Cumulative cordieritite formation as a result of anatexis and melt expulsion.An example from the Chavanon sequence, Variscan French Massif Central
DOI:
https://doi.org/10.2451/2011PM0020Keywords:
Anatexis, Variscan French Massif Central, Cordierite, texture, Crystal SizeDistribution.Abstract
Periodico di Mineralogia (2011), 80, 2, 267-285 - DOI:10.2451/2011 PM0020
Cumulative cordieritite formation as a result of anatexis and melt expulsion.
An example from the Chavanon sequence, Variscan French Massif Central
Vincent Thiery
EM Douai, LGCgE-MPE-GCE, 59508 DOUAI, France
vincent.thiery@mines-douai.fr
Abstract
In the upper part of the Chavanon sequence (Variscan French Massif Central), a widespread, high temperature, Devonian regional anatexis led to the genesis of a complex imbrication of cordierite-rich rocks. One striking type is characterised by a high modal (~ 60-70%) amount of euhedral cordierite and its cumulative texture. The cordierite crystals contains inclusions of sillimanite needles that outlines the successive stages of cordierite growth in a melt. The estimated temperature range for the cordierite formation is 725-781 °C. The textural analysis of the rock, coupled with a crystal size distribution (CSD) diagram of cordierite, reveals crystallisation in equilibrium with melt. The complex imbrications between different migmatites types reveal several stages of melt expulsion and crystallisation. The different possibilities for the formation of this peculiar type of rock are also discussed.
Key words: Anatexis; Variscan French Massif Central; Cordierite; texture; Crystal Size, Distribution.
