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| Titel |
Thermodynamic constraints on metamorphism of ultramafic rocks from different tectonic settings at Gebel Arais and Gebel Malo Grim, Eastern Desert, Egypt |
| VerfasserIn |
Mohamed Hamdy, El-Metwaly Lebda, Tamer Abu-Alam |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054785
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| Zusammenfassung |
| Here we apply to solve a set of independent reactions between minerals end-members to
through light on the pressure-temperature conditions of serpentinization and regional
metamorphism of the Neoproterozoic ultramafic rocks of Gebel Arais and Gebel Malo Grim,
Eastern Desert, Egypt, estimating the relative timing of the rock serpentinization to the
exhumation. The studied rocks include ophiolitic peridotites (spinel harzburgite and
spinel lherzolite from the Gebel Arais and Gebel Malo Grim) and non-ophiolitic
(intrusive-affiliated) olivine websterite (from the Gebel Arais) occurring within the ophiolitic
peridotite rocks. The preliminary thermodynamic study reveals that the serpentinization
process occurred in a temperature range of 250 - 450 ºC. Source of fluids, PT conditions and
the environment of serpentinization of the two types of the ultramafic rocks are different
(Hamdy and Lebda, 2007). The ophiolitic peridotites were mostly serpentinized after their
obduction in intraoceanic setting to the West Gondwana rocks. The non-ophiolitic olivine
websterites, on the other hand, were probably serpentinized before their incorporation
into the obducted ophiolitic peridotites and during their cooling. This might took
place in the continental mantle wedge over the subducted oceanic lithosphere. The
serpentinized ultramafic rocks suffered prograde regional metamorphism during the closing
of Mozambican Ocean. The peak conditions of this regional metamorphic cycle
are around 500–550 ºC and 3-4.5 kbar (greenschist-amphibolite facies transition).
During the exhumation process, the serpentinized rock was subjected to retrograde
metamorphism with temperature around 176 to 245 ºC. The pressure of the retrograde
metamorphism is difficult to be estimated due to slow kinetics at these temperatures as well
as the PT slope of most reactions between mineral end-members is close to be
vertical.
M. M. HAMDY and E. M. LEBDA (2007): Metamorphism of ultramafic rocks at
Gebel Arais and Gebel Malo Grim, Eastern Desert, Egypt: mineralogical and O-H
stable isotopic constraints. Egyptian Journal of Geology, v. 51, 2007, p. 105- 124 |
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