NDLI: Gabbro Akarem mafic-ultramafic complex, Eastern Desert, Egypt: a Late Precambrian analogue of Alaskan-type complexes

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Gabbro Akarem mafic-ultramafic complex, Eastern Desert, Egypt: a Late Precambrian analogue of Alaskan-type complexes

Content Provider	Springer Nature Link
Author	Helmy, H. M. El Mahallawi, M. M.
Copyright Year	2003
Abstract	¶Gabbro Akarem is a Late-Precambrian concentrically-zoned mafic-ultramafic intrusion located along a major fracture zone trending NE-SW in the Eastern Desert of Egypt. It intruded low-grade metasedimentary rocks, and has a contact metamorphic aureole a few meters wide. This intrusion comprises a dunite core enveloped by clinopyroxene hornblende-bearing lherzolite, olivine-hornblende clinopyroxenite and plagioclase hornblendite. The contacts between the rock types are gradational. They have cumulate textures and the observed crystallization sequence is: olivine ( + cotectic spinel)-orthopyroxene (Opx)-clinopyroxene (Cpx)-hornblende. Mafic minerals from the core of the intrusion are highly magnesian, a consistent increase in the Mg# of olivine (from 69 to 87), Opx (from 62 to 89), Cpx (from 85 to 96) and hornblends (from 62 to 88) is observed from the mafic to the ultramafic units. Spinel has a wide range of Cr# and Mg# ratios. The various rock units define a fractionation trend. The mafic rocks are slightly LREE-enriched relative to the ultramafic units and chondrites.In many aspects, the Gabbro Akarem intrusion is similar to Alaskan-type complexes. Mineralogical and geochemical data suggest that the different rock units were fractionated from a hydrous picritic magma with no apparent crustal contamination. A petrogenetic model involving a rapid rise of hydrous mantle magma along a major fracture zone is proposed. Extensive fractional crystallization led to magma chamber stratification; internal circulation and strong vertical stretching up the center of the rapidly rising diapir increased the rate of magma ascent towards the core. Due to cooling and high viscosity the marginal mafic magma was partly crystallized while the unsolidified core ultramafic magma continued its ascent. As a result, different mineral phases crystallized at different pressure-temperature paths. Field relations, geophysical, petrological and experimental studies support this model which explains many of the characteristics of the Gabbro Akarem and some other concentrically zoned mafic-ultramafic intrusions.
Starting Page	85
Ending Page	108
Page Count	24
File Format	PDF
ISSN	09300708
Journal	Mineralogy and Petrology
Volume Number	77
Issue Number	1-2
e-ISSN	14381168
Language	English
Publisher	Springer-Verlag
Publisher Date	2003-01-01
Publisher Place	Wien
Access Restriction	One Nation One Subscription (ONOS)
Content Type	Text
Resource Type	Article
Subject	Geophysics Geochemistry and Petrology

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