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

• DOI: 10.1007/s00710-001-0185-9
• Publication Date: 2003-12-11T00:34:01Z
• Authors: H. M. Helmy; M. M. El Mahallawi
• Keywords: 01 natural sciences; 0105 earth and related environmental sciences

¶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.