Abstract
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.
Highlights
The Arabian-Nubian Shield (ANS) is in the northern part of the East African Orogen (EAO) [1], an accretionary orogen that extends from Arabia to East Africa and into Antarctica
The bulk of the ANS consists of Tonian to Ediacaran arcs that originated in the Mozambique Ocean, the ocean basin that opened during the middle Neoproterozoic break-up of Rodinia
The terminal stages of orogeny included the onset of posttectonic A-type granitoid magmatism (~610 Ma onward); orogenic collapse, tectonic escape, and orogen-parallel extension (605–595 Ma); local extension and rifting (620–545 Ma); gneiss core complex formation, exhumation, and cooling (620–580 Ma); NNW-ward thrusting (605–600 Ma); SW-ward and NE-ward thrusting (600–590 Ma); E-W shortening and transpression (620–580 Ma); Najd strike-slip faulting 625–565 Ma); subhorizontal low-angle shearing (605–600 Ma); amalgamation of terranes in the eastern Arabian Shield (
Summary
The Arabian-Nubian Shield (ANS) is in the northern part (present-day coordinates) of the East African Orogen (EAO) [1], an accretionary orogen that extends from Arabia to East Africa and into Antarctica. In the eastern and southern ANS, arc assemblages are structurally intercalated with or overlie gneiss that has model ages as old as 3.0 Ga, moderately to strongly negative εNd values, and crystallization ages as old as 1.8 Ga [5,6]. These old units possibly represent fragments of Rodinia that were preserved as microplates in the Mozambique Ocean and were subsequently incorporated in the otherwise juvenile Neoproterozoic rocks of the shield. Shield assembly terminated at about 560 Ma, by which time the ANS had been accreted to the Saharan Metacraton [8] and had evolved as part of the southern margin of Paleotethys
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
