Water-assisted migmatization of metagraywackes in a Variscan shear zone, Aiguilles-Rouges massif, western Alps

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• 作者：Florian Genier ; Franç ; ois Bussy ; Jean-Luc Epard ; Lukas Baumgartner
• 关键词：Migmatite ; Leucosome ; LA-ICP-MS ; Variscan belt ; Aiguilles-Rouges massif ; Alps
• 刊名：Lithos
• 出版年：2008
• 期刊代码：54_00244937
• 类别：ear
• 出版时间：May 2008
• 卷：102
• 期：3-4
• 页码：575-597
• 文件大小：1610 K

摘要

Migmatitic rocks developed in metagraywackes during the Variscan orogeny in the Aiguilles-Rouges Massif (western Alps). Partial melting took place 320 Ma ago in a 500 m-wide vertical shear zone. Three leucosome types have been recognised on the basis of size and morphology: (1) large leucosomes > 2 cm wide and > 40 cm long lacking mafic selvage, but containing cm-scale mafic enclaves; (2) same as 1 but with thick mafic selvage (melanosome); (3) small leucosomes < 2 cm and < 40 cm) with thin dark selvages (stromatic migmatites). Types 1 + 2 have mineralogical and chemical compositions in keeping with partial melting experiments. But Type 3 leucosomes have identical plagioclase composition (An_19–28) to neighbouring mesosome, both in terms of major- and trace-elements. Moreover, whole-rock REE concentrations in Type 3 leucosomes are only slightly lower than those in the mesosomes, unlike predicted by partial melting experiments. The main chemical differences between all leucosome types can be related to the coupled effect of melt segregation and late chemical reequilibration.