Origin and tectonic evolution of the NE basement of Oman: a window into the Neoproterozoic accretionary growth of India?

The Omani basement is located spatially distant from the dominantly juvenile Arabian-Nubian Shield (ANS) to its west, and its relationship to the amalgamation of those arc terranes has yet to be properly constrained. The Jebel Ja'alan (NE Oman) basement inlier provides an excellent opportunity to better understand the Neoproterozoic tectonic geography of Oman and its relation-ship to the ANS. To understand the origin of this basement inlier, we present new radiogenic isotopic data from igneous bodies in Jebel Ja'alan. U-Pb and 40Ar/39Ar geochronological data are used to constrain the timing of magmatism and metamorphism in the jebel. Positive epsilon Hf and epsilon Nd values indicate a juvenile origin for the igneous lithologies. Phase equilibria modelling is used to constrain the metamorphic conditions recorded by basement. Pressure-temperature (P-T) pseudosections show that basement schists followed a clockwise P-T path, reaching peak metamorphic conditions of c. 650-700 degrees C at 4-7.5 kbar, corresponding to a thermal gradient of c. 90-160 degrees C/kbar. From the cal culated thermal gradient, in conjunction with collected trace-element data, we interpret that the Jebel Ja'alan basement formed in an arc environment. Geochronological data indicate that this juvenile arc formed during Tongan time and is older than basement further west in Oman. We argue that the difference in timing is related to westwards arc accretion and migration, which implies that the Oman basement represents its own tectonic domain separate to the ANS and may be the leading edge of the Neoproterozoic accretionary margin of India.