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Paleomagnetism of a late Neoproterozoic mafic-ultramafic layered intrusion of Gebel Dahanib, South Eastern Desert (Egypt): Implications for magma evolution and timing of magnetization acquisition

Research Authors
Fawzy FarahatAbu El-ElaaAhmed NasserMahgoubabHamza AhmedIbrahimaIbrahim AliEl-HemalycLuis ManuelAlva-ValdiviabHaraldBöhneld
Research Abstract

We present detailed rock magnetic and paleomagnetic results for a late Neoproterozoic mafic-ultramafic layered intrusion of Gebel Dahanib, South Eastern Desert, Egypt. Gebel Dahanib intrusion (GDI) is an elliptical body with saucer or funnel shape, and was intruded into deformed country rocks at ~710 Ma. It consists of two main undeformed and unmetamorphosed sequences: I) a lower ultramafic sequence composed mainly of peridotite (dunite and lherzolite cumulate) and pyroxenite (olivine websterite and websterite cumulates). Dunite cumulate occupies the basal part, which grades upward to lherzolite and pyroxenite cumulates at the top of the ultramafic sequence; and II) an upper mafic sequence that comprises olivine gabbronorite, gabbronorite, norite, and a chilled margin of fine-grained gabbronorite. An intrusive contact was observed between ultramafic and mafic sequences, which suggests an asynchronous emplacement history. To understand the magmatic evolution of GDI and to make a new contribution to the small African Neoproterozoic paleomagnetic database, 260 oriented samples were collected from four rock units (peridotite, pyroxenite, gabbro, and fine-grained gabbro). Rock magnetic experiments combined with Fe–Ti microscopic observations and demagnetization procedures indicate that both sequences have different magnetic mineral contents and paleomagnetic components. A stable component with northwesterly declination and shallow negative inclination carried by magnetite and pyrrhotite was isolated from the ultramafic sequence (Dec = 326.6°, Inc = −28.2°, α95 = 5.5°, and k = 58.72), and the corresponding paleomagnetic pole lies at lat = 39.0°N, long = 261.5°E, A95 = 4.6°, and K = 83.13. Paleomagnetic analyses on the mafic sequence yielded northeast-directed declinations, with intermediate positive inclinations (Dec = 11.3°, Inc = 47.6°, α95 = 3.9°, and k = 103.19), and a paleomagnetic pole lat = 78.7°N, long = 96.2°E, A95 = 4.4°, and K = 81.49. We postulate that the Dahanib intrusion was emplaced in two pulses: the first includes the ultramafic assemblages at the base of the intrusion; the second magma pulse makes up the upper mafic sequence. Assessment of Egyptian paleomagnetic poles from a similar time period (~710-540 Ma) indicates that only one pole (out of 21) can be considered reliable, and also from the African dataset only five of 43 poles are of high quality. These indicate that new high-quality paleomagnetic poles are needed to refine the late Neoproterozoic paleomagnetic database for Egypt and the African continent.

Research Department
Research Journal
Journal of African Earth Sciences
Research Member
Research Publisher
Pergamon
Research Rank
1
Research Vol
172-104016
Research Website
NULL
Research Year
2020
Research Pages
NULL