Garnet evolution in pre-Variscan pelitic rocks from the Lake Emosson area, Aiguilles Rouges Massif, Western Alps期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

按检索

Garnet evolution in pre-Variscan pelitic rocks from the Lake Emosson area, Aiguilles Rouges Massif, Western Alps

Authors:	JÜRGEN F VON RAUMER HANS W SCHWANDER

Institution:	Institut de Minéralogie et de Pétrographie, Université-Pérolles, CH-1700 Fribourg, Switzerland; Mineralogisch-Petrographisches Institut der Universität, Bernoullistrasse 30, CH-4056 Basel, Switzerland

Abstract:	Abstract The chemical evolution of garnets from pelitic rocks of probable Palaeozoic age corresponds to a complex metamorphic evolution of the host rocks. Among the almandine-rich garnets (Alm_60–80), two main types of evolution can be distinguished. Early Mn-rich garnets coexisting with kyanite may be replaced by plagioclase and then, during a late stage, by biotite and/or sillimanite. The second type of evolution corresponds to an overgrowth of Mn-poor late-stage garnet on older Mn-rich garnets which corresponds to a thermal peak with sillimanite-type of metamorphism. This new garnet may appear either as an overgrowth with a strong discontinuity, or as small, new euhedral garnet or as skeletal garnet. This chemical evolution of garnet corresponds to an early collisional stage of metamorphism (of high pressure type with high Mn values) of probable Ordovician age followed by uplift and a thermal peak (low Mn values) in Devonian times.

Keywords:	Key-words: chemistry garnet Hercynian P–T–t path pelite Swiss Alps