Evolution of the Pan-African Wadi Haimur metamorphic sole, Eastern Desert, Egypt

• Published in: Journal of metamorphic geology Vol. 18; no. 6; pp. 639 - 651
• Main Authors: Abd El-Naby, H., Frisch, W., Hegner, E.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Inc 01-11-2000
• Subjects: metamorphic sole; ophiolite; Pan-African orogen; subduction; thermobarometry
• ISSN: 0263-4929; 1525-1314
• DOI: 10.1046/j.1525-1314.2000.00286.x

By comparison with the general features of metamorphic soles (e.g. vertical and lateral extension, metamorphic grade and diagnostic mineral parageneses, deformation and dominant rock types), it is inferred that the amphibolites, metagabbros and hornblendites of the Wadi Um Ghalaga–Wadi Haimur area in the southern part of the Eastern Desert of Egypt represent the metamorphic sole of the Wadi Haimur ophiolite belt. The overlying ultramafic rocks represent overthrusted mantle peridotite. Mineral compositions and thermobarometric studies indicate that the rocks of the metamorphic sole record metamorphic conditions typical of such an environment. The highest P–T conditions (c. 700 °C and 6.5–8.5 kbar) are preserved in clinopyroxene amphibolites and garnet amphibolites from the top of the metamorphic sole, which is exposed in the southern part of the study area. The massive amphibolites and metagabbros further north (Wadi Haimur) represent the basal parts of the sole and show the lowest P–T  conditions (450–620 °C and 4.7–7.8 kbar). The sole is the product of dynamothermal metamorphism associated with the tectonic displacement of ultramafic rocks. Heat was derived mainly from the hot overlying mantle peridotites, and an inverted P–T  gradient was caused by dynamic shearing during ophiolite emplacement. Sm/Nd dating of whole‐rock–metamorphic mineral pairs yields similar ages of c. 630 Ma for clinopyroxene and hornblende, which is interpreted as a lower age limit for ophiolite formation and an upper age limit for metamorphism. A younger Sm/Nd age for a garnet‐bearing rock (c. 590 Ma) is interpreted as reflecting a meaningful cooling age close to the metamorphic peak. Hornblende K/Ar ages in the range 570–550 Ma may reflect thermal events during late orogenic granite magmatism.