Neoproterozoic serpentinites from the Eastern Desert of Egypt: Insights into Neoproterozoic mantle geodynamics and processes beneath the Arabian-Nubian Shield

Dien, Hamed Gamal El; Hamdy, Mohamed M.; El-Ela, Abdel Salam Abu; Abu-Alam, Tamer; Hassan, Adel; Kil, Yongwoo; Mizukami, Tomoyuki; Soda, Yusuke

doi:10.1016/j.precamres.2016.10.006

Cited by 40 publications

(36 citation statements)

References 72 publications

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“…2). For more details about the geological background of the ANS see Gamal El Dien et al 13 , and for field observations and petrographical and mineralogical descriptions of the studied rocks see Hamdy and Gamal El Dien 14 .…”

Section: Resultsmentioning

confidence: 99%

Cr-spinel records metasomatism not petrogenesis of mantle rocks

et al. 2019

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Mantle melts provide a window on processes related to global plate tectonics. The composition of chromian spinel (Cr-spinel) from mafic-ultramafic rocks has been widely used for tracing the geotectonic environments, the degree of mantle melting and the rate of mid-ocean ridge spreading. The assumption is that Cr-spinel’s core composition (Cr# = Cr/(Cr + Al)) is homogenous, insensitive to post-formation modification and therefore a robust petrogenetic indicator. However, we demonstrate that the composition of Cr-spinel can be modified by fluid/melt-rock interactions in both sub-arc and sub-mid oceanic mantle. Metasomatism can produce Al-Cr heterogeneity in Cr-spinel that lowers the Cr/Al ratio, and therefore modifies the Cr#, making Cr# ineffective as a geotectonic and mantle melting indicator. Our analysis also demonstrates that Cr-spinel is a potential sink for fluid-mobile elements, especially in subduction zone environments. The heterogeneity of Cr# in Cr-spinel can, therefore, be used as an excellent tracer for metasomatic processes.

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Section: Resultsmentioning

confidence: 99%

Cr-spinel records metasomatism not petrogenesis of mantle rocks

et al. 2019

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“…The first stage resulted in the formation of coarse antigorites at 200–250 °C that may have grown directly from the original olivine and orthopyroxene 42 during the initial stage of subduction. During this stage, the slab-derived fluids caused strong hydration of the subducted peridotites protolith forming CA-group, such as the antigorite serpentinites (≥200 °C) 43,44 in the Happo-O’ne area in Japan 45 and some of the other antigorite serpentinites in Eastern Desert, Egypt 21,23 . Although the coarse antigorites could also have crystallized by progressive replacement of lizardite formed during low-temperature oceanic serpentinization 43,46 , we favour the former explanation due to the absences of lizardite relics (i.e., mesh cells) 37 in the studied serpentinites.…”

Section: Discussionmentioning

confidence: 99%

“…Al 2 O 3 , SiO 2 and FeO show negative correlations while MgO shows a positive correlation. The concentrations of these elements were shifted from the original composition of the rock during partial melting and serpentinization process 21 . For the modelling, the x-axes of the pseudosections are assigned to the composition of the system.…”

Section: Methodsmentioning

confidence: 99%

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Origin of arc magmatic signature: A temperature-dependent process for trace element (re)-mobilization in subduction zones

Dien

Kil

et al. 2019

Sci Rep

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Serpentinite is a major carrier of fluid-mobile elements in subduction zones, which influences the geochemical signature of arc magmatism (e.g. high abundances of Li, Ba, Sr, B, As, Mo and Pb). Based on results from Neoproterozoic serpentinites in the Arabian-Nubian Shield, we herein report the role of antigorite in the transportation of fluid-mobile elements (FME) and light rare earth elements (LREE) from the subducted slab to arc-related magma during subduction. The serpentinites contain two generations of antigorites: the older generation is coarse-grained, formed at a temperature range of 165–250 °C and is enriched in Li, Rb, Ba and Cs, whereas the younger generation is finer-grained, formed at higher temperature conditions (425–475 °C) and has high concentrations of B, As, Sb, Mo, Pb, Sr and LREE. Magnesite, on the other hand, remains stable at sub-arc depths beyond the stability field of both antigorites, and represents a potential reservoir of FME and LREE for deeper mantle melts. Magnesite has high FME and LREE absorbing capacity (over 50–60%) higher than serpentine phases. Temperature is the main controlling factor for stability of these minerals and therefore the release of these elements from subducted slabs into arc magmatism. As the liberation of these elements varies along the length of the slab, the resulting cross-arc geochemical variation trend can help to determine the subduction polarity of ancient arcs.

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“…The robust chromian‐spinel is one of the first minerals to crystallize in the mafic–ultramafic suite of magmas; highly stable even in serpentinized peridotites (Arai, Kadoshima, & Morishita, 2006; Dick & Bullen, 1984; Gamal El Dien et al, 2016) and resistant to post‐magmatic alteration processes (Burkhard, 1993; Mellini, Rumori, & Viti, 2005). Hence, the chemistry of the spinel makes them extremely relatable to oxygen fugacity, pressure–temperature condition, degree of partial melting of the source region, and melt–rock interaction process (Arai, 1980; Barnes & Roeder, 2001; González‐Jiménez et al, 2011; Proenza, Gervilla, Melgarejo, & Bodinier, 1999; Sack & Ghiorso, 1991).…”

Section: Introductionmentioning

confidence: 99%

Spinel chemistry and geochemistry of serpentinite of North Delhi fold belt, Rajasthan: Constraining the petrogenesis and geodynamics of northwestern Indian shield

et al. 2020

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The western margin of the north Delhi fold belt, Rajasthan is mostly covered by the thick alluvium-sand cover of the Thar Desert. However, a study on a cluster of scattered and deformed serpentinite bodies exposed in the small opencast quarries are presented here. Though alteration and absence of primary phases possess constraints over petrogenesis, but, the accessory, anhedral spinel chemistry aids in the genetic reconstruction. The unaltered core part of the spinel that is, the Al-chromite (avg. 45.2 wt% Cr 2 O 3 ), followed by ferrit chromite (avg. 32.3 wt% Cr 2 O 3 ) inner rim and magnetite towards the outer rim is the character of spinels present in the host, where the chemistry of the core part is used exclusively. This core part of spinel preserves the primary mantle signature and attests the forearc peridotite character and a similar subduction-related trait is followed by the whole-rock major oxide proxies.Cumulative petrological, whole-rock geochemistry, and mineral chemical signature unequivocally advocate towards a harzburgitic protolith, an arc peridotitic character, and presence of ancient forearc environment. The present communication is the first to describe the detailed characterization of serpentinite bodies with a possible linkage towards the presence of ancient oceanic slices in the north Delhi fold belt, Rajasthan, NW India.

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Neoproterozoic serpentinites from the Eastern Desert of Egypt: Insights into Neoproterozoic mantle geodynamics and processes beneath the Arabian-Nubian Shield

Cited by 40 publications

References 72 publications

Cr-spinel records metasomatism not petrogenesis of mantle rocks

Cr-spinel records metasomatism not petrogenesis of mantle rocks

Origin of arc magmatic signature: A temperature-dependent process for trace element (re)-mobilization in subduction zones

Spinel chemistry and geochemistry of serpentinite of North Delhi fold belt, Rajasthan: Constraining the petrogenesis and geodynamics of northwestern Indian shield

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