The Paleozoic evolution of the northeastern margin of the supercontinent Gondwana remains relatively obscured. Assembled during the Neoproterozoic Pan-African orogeny (800-550 Ma), its subsequent evolution is often masked by extensive unconformity extending over 200 Ma beneath the Permian sequence. This study examines the thermal history of the northern margin of Gondwana along the Arabian-Nubian shield including the potential imprint of the remote Hercynian (Variscan) orogeny during the assembly of Pangea and the Tethys rifting events. We utilize samples from 6 deep boreholes and 6 transects extending along ~350 km: from the southern tip of the Sinai Peninsula to the Dead Sea focusing on late Neoproterozoic rocks (igneous and arkose).
More than 250 zircon grains from ~30 samples were (U-Th)/He dated so far, yielding distinct inverse correlation between age and effective uranium (eU). The distribution of these ages highlights prominent age clusters with plateaus in the age-eU space at ~550, 500, 450, 380, 300, 200 and 90 Ma. These clusters are examined in light of the Cadomian orogeny, Rheic rifting, late Ordovician glaciation, paleo-Tethys rifting, Variscan orogeny, Neo-Tethys rifting, late Triassic volcanism and the Neo-Tethys closure.
The oldest ZHe ages (low eU) are significantly older than previously published zircon fission track ages (327-360 Ma). Surprisingly, even the deepest Precambrian samples exposed along the Dead Sea transform and the Suez rift margins have not experienced temperatures > ~200 c throughout the phanerozoic period.
Inverse thermal modeling indicates that our current understanding of radiation damage effect on zircon retentivity may be still incomplete and the alpha-damage threshold for rapid decrease in helium retentivity may be lower than expected. On-going modeling with an improved radiation damage model will enable us to better constrain the magnitude, timing and distribution of Paleozoic thermal events in northern Gondwana and improve our understanding of their driving mechanism.