Revisiting the Arabian-Nubian shield-Saharan meta-craton boundary: Evidence for a ca. 840–655 Ma Keraf intra-oceanic arc terrane

The arc-continent suture zone separating the Neoproterozoic Arabian-Nubian shield from Archean-Paleoproterozoic crust of the Saharan meta-craton has long been thought to coincide with the Keraf structural corridor. This interpretation remains debated, and it is unclear whether crustal blocks on either side of the hypothesised suture have distinct geological histories. In this study, we integrate field observations, whole-rock geochemistry, zircon U-Pb-Hf and whole-rock Sr-Nd isotopic data from plutons sampled along an ∼ 80 km-long transect across the central Keraf domain and propose that it represents a structurally modified, juvenile intra-oceanic arc terrane formed between ca. 840–655 Ma.
Pre- to syn-tectonic intrusions define a two-stage intra-oceanic arc history: (i) juvenile, mantle-derived arc magmatism between ca. 840–810 Ma (εHf(i) ∼ +9.1 to + 10.7, εNd(i) ∼ +3.8 to + 4.7), and (ii) protracted arc thickening by magmatic accretion between ca. 760–655 Ma (εHf$_{(i)}$ ∼ +7.7 to + 9.0, εNd$_{(i)}$ ∼ +3.7 to + 6.2), with contribution from early arc crust material. The apparent absence of zircon crystallisation ages between ca. 810–760 Ma may reflect trenchward arc migration, although alternative processes cannot yet be excluded, and the significance of this pattern remains unclear. ... mehrPost-collisional granites at ca. 620 Ma (εHf$_{(i)}$ ∼ +8.2 to + 8.8; εNd$_{(i)}$ ∼ +3.3 to + 4.6) likely record reworking of the Keraf arc crust, with limited, if any, enriched-mantle input during the late to post-collisional period.
Integration of our results with regional isotopic compilations shows that the isotopically more evolved Bayudian (ca. 970–890 Ma) and syn-Keraf arc magmatic events affected the pre-Neoproterozoic basement in the easternmost Saharan meta-craton. Although this hypothesis remains to be demonstrated, the available data are consistent with a scenario involving subduction transference from the Bayuda continental arc to the Keraf intra-oceanic arc at ca. 890–860 Ma, implying that the Arabian-Nubian shield–Saharan meta-craton suture zone may lie farther west than currently accepted.