27 Rhyolite/Granite Magmatism II

Tuesday, 26 March 2019
1:30 PM - 5:45 PM
Konza Prairie Room

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

Paper number: 27-3
Program: Theme Sessions
Time: 2:10 PM – 2:30 PM

Authors

Abstract

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.

Geological Society of America Abstracts with Programs. Vol. 51, No. 2

doi: 10.1130/abs/2019SC-325987

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