Search

Highlights: [•] Banded Iron Formation of the Arabian-Nubian Shield (ANS BIF) was deposited ∼750Ma. [•] Deposition was cyclic (alternating Fe-rich and Si-rich bands) and rapid (soft-sediment slumping). [•] ANS-BIF is associated with metavolcanic and volcaniclastic sedimentary rocks. [•] ANS BIF and other ∼750Ma BIF indicate major change in marine redox before Sturtian glaciation. [ABSTRACT FROM AUTHOR]

Presents the results of a study on the deformation history of the Keraf zone in northern Sudan, site of the boundary between the juvenile Neoproterozoic crust of the Arabian-Nubian Shield in the Red Sea Hills and older crust of the Nile craton. Use of Shuttle Imaging Radar; Regional geology of the zone; Significance of structural styles in the zone.

The depositional age of the Wadi Zaghra metasediments (Zaghra Formation) of the Sa’al-Zaghra metamorphic complex (Sinai) in the Arabian–Nubian Shield (ANS) has been constrained by LA-ICP-MS dating of zircons from (1) metaconglomerate granitoid clasts, (2) the metaconglomerate matrix, (3) biotite-schist, and (4) diorites and granites intruding the metasediments. Three granitoid boulders from a metadiamictite of the Zaghra Formation give crystallization ages of 651 ± 3, 647 ± 3, and 640 ± 4 Ma respectively. Detrital zircon age populations from laminated siltsones and conglomerate matrix vary somewhat with stratigraphic position, a variation best explained by changes in depositional environment and source area with time. Three distinct zircon age populations are identified in the matrix; at ca. 1000, 750, and 630 Ma, with less pronounced peaks at ~780 and ~800 Ma. The youngest detrital zircons indicate deposition after 630–625 Ma. The emplacement age of the post-depositional intrusives is enigmatic due to a large population of xenocrystic zircons, but is interpreted to be as old as ca. 615 Ma. This implies deposition and deformation of the Zaghra Formation in the time interval 625–615 Ma, thus older than the inferred depositional age of the Hammamat deposits in the Eastern Desert of Egypt, which is commonly correlated. The inferred depositional age is similar to the deposits in nearby Rutig Basin, where conglomerates were deposited in two pulses; at ca. 620–610 and 600–590 Ma. The appearance of late Mesoproterozoic (ca. 1.1 to –1.0 Ga) detrital zircons in the fine-grained laminated matrix facies of the Zaghra Formation demonstrates that ~1.0 Ga basement rocks (Sa’al terrane?) were exposed when Zaghra basin sediments were being deposited. [ABSTRACT FROM AUTHOR]

Highlights: [•] New Hf-isotopic analyses of zircon from the Eastern Desert of Egypt. [•] Hf-TDM ages for post-collisional granites range between 0.81 and 1.3Ga. [•] Post-collisional granite results indicate evolving juvenile crust. [•] Hf-TDM ages for arc-metavolcanic rocks range between 0.78 and 3.8Ga. [•] Arc-metavolcanicHf results indicate involvement of pre-Neoproterozoic material. [ABSTRACT FROM AUTHOR]

The Arabian-Nubian Shield (ANS) includes Middle Cryogenian-Ediacaran (790-560 Ma) sedimentary and volcanic terrestrial and shallow-marine successions unconformable on juvenile Cryogenian crust. The oldest were deposited after 780-760 Ma shearing and suturing in the central ANS. Middle Cryogenian basins are associated with ~700 Ma suturing in the northern ANS. Late Cryogenian basins overlapped with and followed 680–640 Ma Nabitah orogenesis in the eastern ANS. Ediacaran successions are found in pull-apart and other types of basins formed in a transpressive setting associated with E-W shortening, NW-trending shearing, and northerly extension during final amalgamation of the ANS. Erosion surfaces truncating metamorphosed arc rocks at the base of these successions are evidence of periodic exhumation and erosion of the evolving ANS crust. The basins are evidence of subsequent subsidence to the base level of alluvial systems or below sea level. Mountains were dissected by valley systems, yet relief was locally low enough to allow for seaways connected to the surrounding Mozambique Ocean. The volcanosedimentary basins of the ANS are excellently exposed and preserved, and form a world-class natural laboratory for testing concepts about crustal growth during the Neoproterozoic and for the acquisition of data to calibrate chemical and isotopic changes, at a time in geologic history that included some of the most important, rapid, and enigmatic changes to Earth’s environment and biota. [ABSTRACT FROM AUTHOR]