ALPINE BASEMENT OUTCROPS AT NORTHERN PELOPONNESUS: IMPLICATIONS FOR THE EARLY STAGES IN THE EVOLUTION OF THE CORINTH RIFT

We focus on the central and eastern southern onshore parts of the Corinth Rift (CR), where basement outcrops are few and of limited extent, to study three key locations: a basement inlier east of Xylokastro, a new outcrop of the Tripolis Unit at the western edge of the Xylokastro horst, and a re-mapped and re-evaluated outcrop of the Pindos Unit northwest of Nemea. The results of this study show that there are elements which could help overcome the significant difficulties in our understanding of the structure and evolution of the rift, posed by the lack of basement outcrops in the central and eastern onshore parts of the Rift. This, in turn, calls for a reconsideration of the generally accepted idea that the broader onshore eastern sector of the CR lacks significant basement and intrabasinal faults.

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 relationship 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 εHf and εNd 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°C at 4–7.5 kbar, corresponding to a thermal gradient of c. 90–160°C/kbar. From the calculated 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 Tonian 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 Omani basement represents its own tectonic domain separate to the ANS and may be the leading edge of the Neoproterozoic accretionary margin of India.

Age and implications of Early Ordovician (Arenig) plutonism in the type area of the Bay du Nord Group, Dunnage Zone, southern Newfoundland Appalachians

In south Newfoundland, an extensive tract of metamorphosed Ordovician metavolcanic, metasedimentary, and granitoid rocks (Bay du Nord Group) lies north of a late Precambrian basement inlier of peri-Gondwanan affinity, separated from the latter by Silurian rocks. In the Bay du Nord Group type area, the metavolcanic and metasedimentary rocks were ductilely sheared and locally fault imbricated with metagabbro prior to emplacement of the Baggs Hill Granite, herein dated at 477.6 ± 1.8 Ma. Some of the volcano-sedimentary strata within this succession, however, contain foliated clasts of Baggs Hill Granite, and these strata must comprise a younger stratigraphic sequence which, in this area, is thrust northwestward over the older rocks.The pre-477.6 ± 1.8 Ma tectonic interleaving of the Dunnage Zone gabbro and stratified rocks is significantly earlier than the Llandovery (early Salinic) recumbent folding and thrusting of Middle Ordovician Exploits Subzone rocks in the east-central Hermitage Flexure. In both areas, the Dunnage Zone rocks were inhomogeneously thickened and tectonically telescoped north of a rigid block of late Precambrian peri-Gondwanan basement. The emplacement of the Baggs Hill Granite is coeval with intrusion of similar Ordovician granite into ophiolites obducted southeastward onto the Gondwanan margin during Arenigian (Penobscot) orogenesis.