Neoproterozoic dextral faulting on the Najd Fault System, Saudi Arabia, preceded sinistral faulting and escape tectonics related to closure of the Mozambique Ocean

Abstract

The Neoproterozoic Najd Fault System extends for 2000km across the East African Orogen, yet its history of motion and tectonic significance are widely debated. The Halaban-Zarghat Fault is the northeastern-most of the major NW-strildng Najd faults in the Arabian Shield. Several sedimentary basins of the Neoproterozoic Jibalah Group are bounded by strands of the Halaban-Zarghat Fault and other Najd faults, particularly along right steps in the fault trace. Among the largest of the basins is the Jifn. The geometry of the Jifn Basin and the sedimentary facies of Jibalah Group indicate that it is a dextral pull-apart basin between strands of the Halaban-Zarghat Fault. A zone of high-grade mylonitic gneiss is located along a left step in the fault zone and may be a deeply eroded pop-up structure related to dextral transpression. Analysis of structural data from around and within the Jifn Basin, the position of other pull-apart basins and high-grade mylonite zones along the Halaban-Zarghat Fault are all consistent with early dextral movement along the Halaban-Zarghat Fault. Offsets of distinctive older rock units and transection of the Jifn Basin by sinistral faults, however, show that the latest and most significant sense of offset on the Halaban-Zarghat Fault and other Najd faults was sinistral.A U-Pb zircon date of 624.9 _-+4.2Ma from rhyolitic basement of the Jifn Basin gives a lower limit for the formation of the basin and initiation of dextral movement along the Halaban-Zarghat Fault. This age is interpreted as the earliest age for the collision of East and West Gondwana. A 621 _-_7Ma pluton is offset 10km dextrally along the Halaban-Zarghat Fault, showing that dextral motions continued for some time past 621Ma, before switching to sinistral motions, and accreted terranes caught between the two continents were forced toward an oceanic-free face to the north. A 576.6 __. 5.3 Ma U-Pb zircon date from an undeformed felsite dyke that intrudes the Jibalah Group gives an upper time limit for movement along the Halaban-Zarghat Fault. This may mark the time that collision and escape tectonics ended, or it may reflect the time that displacements were transferred to other Najd faults in more interior parts of the East African Orogen.

Sr–Nd isotopes and geochemistry of granite-gneiss complexes from the Meatiq and Hafafit domes, Eastern Desert, Egypt: No evidence for pre-Neoproterozoic crust

“…One Meatiq metasediment lies on the isochron (EB10) while the other, with very high Rb/Sr, lies above. The existence of this composite isochron suggests that the Rb-Sr geochronometer has been reset during the late Neoproterozoic c. 600 Ma Pan-African thermal event, perhaps related to Najd strike-slip deformation (Fritz et al, 1996;Kusky and Matsah, 2003). The low initial 87 Sr/ 86 Sr for all Meatiq and Hafafit samples, even those with high 87 Rb/ 86 Sr, is a strong indication that this resetting occurred shortly after the intrusion of various juvenile protoliths.…”

Evidence for the Snowball Earth hypothesis in the Arabian-Nubian Shield and the East African Orogen

“…The Jibalah Group was deposited in isolated, pull-apart basins caused by strike-and dip-slip movements of the Najd fault system. A study of $3 km thick section of conglomerate, limestone, sandstone, and shale in the Jifn Basin (NE Arabian Shield) was reported by Kusky and Matsah (2003). They constrained its age (by U-Pb zircon techniques) to lie between 625 ± 4 Ma and 577 ± 5 Ma, so the Jibalah Group in the Jin Basin could have been deposited during Gaskiers glaciation.…”

A detrital record of the Nile River and its catchment

“…The Arabian-Nubian Shield is a collage of Neoproterozoic (c. 870 -670 Ma) continental margin and juvenile island arcs, cut by voluminous granitoid intrusions as young as latest Neoproterozoic, and overlain by younger sedimentary and volcanic basins (Stern & Hedge 1985;Stern 1994;Johnson & Woldehaimanot 2003;Kusky & Matsah 2003). Only minor outcrops of pre-Neoproterozoic crust are found.…”