Age and chemical characteristics of some pre-Pan-African rocks in the Egyptian Shield

摘要: Abstract UPb ages on zircons from several types of sialic rocks, together with a variety geochemical data one sample early plutonic activity within the Egyptian Shield are presented. The earliest autochthonous granitic rocks in probably quartz diorites (tonalites) emplaced just prior to main peak Pan-African igneous (550–650 Ma). studied example has an age 711 Ma ± 7 Ma, and is characterized by very low initial Sr ratio (87Sr/86Sr = 0.7026) abundances K2O related large-ion lithophile trace elements. REE contents (less than 20 × chondritic abundances). Abundance patterns show only moderate light rare-earth enrichment (La/Yb 4.5). These characteristics inconsistent any models requiring fractional fusion pre-existing continental crustal material. Granitic arkosic cobbles occur rare conglomerate beds volcanoclastic greywacke sedimentary sequences. wide range (1.1–2.3 Ga) have no obvious source Shield. It suggested that they not indicative plutons which might predate deposition enclosing immature sediments. More probably, were derived adjacent areas such as Uweinat region west, deposited evolving arc-ocean basin complex.