Azrou N’Fad (Central Hoggar, Algeria) one of the deepest terranes of LATEA: arguments based on P–T evolution in eclogite

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• 作者：Souad Zetoutou ; Khadidja Ouzegane ; Saliha Boubazine ; Jean-Robert Kienast
• 关键词：Eclogite ; Azrou N’ ; Fad terrane ; Central hoggar
• 刊名：Journal of African Earth Sciences
• 出版年：2004
• 出版时间：June-August 2004
• 年：2004
• 卷：39
• 期：3-5
• 页码：193-200
• 全文大小：482 K

文摘

The Azrou N’Fad terrane is remarkable by the presence of eclogites that are particularly rich in magnesium, as reflected in the compositions of the primary phases such as garnet (44.33 % pyrope). These eclogites are only preserved in the cores of large lenses that mark out shear zones, and their margins are indeed completely transformed into amphibolite. Variations in pressure are indicated by the breakdown of primary omphacitic clinopyroxene, leading to a progressive depletion in jadeite component. This is linked to the successive formation of different types of plagioclase, with the most sodic appearing first. At the same time, the garnet becomes more and more enriched in iron, eventually breaking down into symplectites with hornblende + plagioclase or clinopyroxene + plagioclase + hornblende in contact with primary clinopyroxene and quartz. This last stage corresponds to the exhumation of the eclogite, with pressures falling from 15 ± 0.5 kbar to 11.1 ± 1.6 kbar at a temperature between 700 and 800 °C.