The Feiran–Solaf metamorphic complex, Sinai, Egypt: Geochronological and geochemical constraints on its evolution

Abstract

Ion-microprobe U–Th–Pb geochronological data are presented for fourteen samples from the Feiran–Solaf metamorphic complex in the Sinai Peninsula, Egypt. These data reveal a succession of magmatic and metamorphic events from ca. 1000Ma to <600Ma. The oldest age of ∼1.0Ga is obtained from zircon in Solaf zone metapsammites, representing the age of a locally restricted acidic igneous source which eroded and was deposited as arkose sometime after ∼975±10Ma. A similar ∼1.0Ga age from granodioritic biotite gneisses is interpreted as dating its crystallization. A biotite gneiss sample bordering the Solaf granodioritic gneiss yields an age of 792±7Ma, suggesting at least two phases of arc development over ca. 200Ma. While detrital zircon from migmatitic metapelites indicates input of material as old as ∼1.0Ga, the probable maximum sedimentation age for their immature pelitic protolith, which was likely deposited in an active continental marginal basin within a continental arc, is 656±6Ma. These metapelites were metamorphosed at 603±6Ma.Leucosome and mesosome samples from migmatitic biotite-hornblende gneisses of the Feiran zone yield polyphase zircon with ca. 700Ma cores interpreted as dating igneous crystallization, while overgrowths of 627±7Ma and 592±10Ma define the time of high-grade metamorphism. A biotite-hornblende gneiss sample from the Feiran-zone contains zircon that defines a protolith crystallization age at 623±6Ma, with rim overgrowths defining a metamorphic age of 587±7Ma. Zircon from the diorite body separating the Feiran and Solaf zones yields crystallization ages of 617±4Ma and 602±4Ma for samples collected from the periphery and core, respectively, while zircon from a late-tectonic granodiorite sample intruding the metapsammitic gneisses yields a crystallization age of 589±6Ma.High spatial resolution age dating from the Feiran–Solaf metamorphic complex and intruding magmatic rocks thus reveals four episodes of arc magmatism at 799–785Ma, 713–692Ma, 629–613Ma, and 606–583Ma. The timing of regional high-grade metamorphism is constrained by the zircon rims in the migmatitic metapelites and migmatized biotite-hornblende gneisses which record two distinct events at 627±7Ma and 592±10Ma, interpreted to represent peak and isothermal decompressional metamorphic events, synchronous with heat flow from concurrent young magmatism.