Neoproterozoic Tectonics of the Arabian-Nubian Shield: Insights from U-Pb Zircon Geochronology, Sr-Nd-Hf Isotopes, and Geochemistry of the Deki Amhare Complex Granitoids, Central Eritrea

The Deki Amhare complex is located in central Eritrea, within the Arabian-Nubian Shield (ANS). It consists of an inner core of monzogranite porphyry and diorite enclaves (MMEs), surrounded outwardly by granodiorite and quartz diorite. The zircon U-Pb ages, whole-rock geochemistry, and Sr-Nd-Hf isotopic compositions of the Deki Amhare complex granitoids were used to discuss the Neoproterozoic tectonics of the ANS. The Late Tonian granodiorite and quartz diorite are metaluminous and calc-alkaline to slightly high-K calc-alkaline I-type plutons, with ages of 811.2 +/- 4.8 Ma and 811.6 +/- 5.7 Ma, respectively. They exhibit positive epsilon(Hf)(t) (7.6-9.5) and epsilon(Nd)(t) (3.9-4.7) values and relatively low (Sr-87/Sr-86)(i) ratios (0.70374-0.70463), indicating that they derived from the partial melting of a metasomatized mantle wedge during intra-oceanic subduction. The Ediacaran monzogranite porphyry and MMEs are subalkaline to alkaline A(2)-type granitoids with ages of 620.0 +/- 4.3 Ma and 614.8 +/- 3.9 Ma. These display positive epsilon(Hf)(t) (5.3-8.7) and epsilon(Nd)(t) (4.2-4.7) values, as well as low (Sr-87/Sr-86)(i) ratios (0.70310-0.70480), implying that they formed through crust-mantle magma mixing related to post-collisional slab break-off. Based on these data, three stages of regional tectonic evolution can be described: (1) from similar to 1200 Ma to similar to 875 Ma, the mafic oceanic crust was derived from depleted mantle during the opening of the Mozambique Ocean; (2) from similar to 875 Ma to similar to 630 Ma, intra-oceanic subduction and arc formation occurred with the development of I-type batholiths; and (3) from similar to 630 Ma to similar to 600 Ma, crustal and lithospheric reworking took place post-collision, leading to the formation of A(2)-type granitoids.