THE NORTHERN ARABO-NUBIAN FELSIC LIP (NAN-FLIP) PROVINCE: AN EDIACARAN ANALOGUE FOR THE MID-CONTINENT GRANITE-RHYOLITE PROVINCE?

The tectonic setting in which Mesoproterozoic igneous rocks of the US mid-continent granite rhyolite province occurred continues to defy confident interpretation. Some insights may be obtained by comparing these rocks to ~630 to ~580 Ma igneous rocks exposed in Cenozoic uplifts around the Red Sea in Egypt, Israel, Jordan, and Saudi Arabia. These rocks are dominated by granites that evolved from early mesozonal I-type to late epizonal A-type. Remnants of volcanic cover (~600 Ma Dokhan Volcanics) and terrigeneous sediments (~590-610 Ma Hammamat Group) are preserved, as is evidence of associated extensional core complexes (in Sinai). Swarms of mostly NE-SW trending bimodal and sometimes composite dikes were emplaced ~600 Ma and further testify to strong extension accompanying igneous emplacement. The ~ 50 m.y. of magmatic evolution began before fragments of E and W Gondwana collided to form the East African Orogen ~610 Ma to form especially I-types above a subduction zone and continued for some time after collision; cessation of igneous activity resulted in cutting the “Great Unconformity”. The felsic LIP was emplaced about the same time as left-lateral movements on the NW-trending Najd strike-slip system. Formation of Cadomian ~550 Ma crust on the N. flank of Gondwana testifies to formation of a new, S-dipping subduction zone; peri-Gondwanan Cadomian crust now makes up the crust of Iran, Turkey, and S and W Europe. NAN-FLIP rocks are especially abundant in northern exposures but isolated intrusions are found as far south as Ethiopia and Yemen. Granitic rocks show strong mantle affinities (positive e-Nd and zircon d¹⁸O) control by feldspar (deep Eu anomalies, flat HREE patterns). Fractionation of mafic magmas, perhaps in the lower crust, is suspected for generating NAN-FLIP a-type magmas. We need geophysical imaging of the lower crust and study of lower crust xenoliths brought up in Cenozoic alkali basalts in Arabia to test this hypothesis.