EXTENSION OF THE BERIT SUTURE ZONE TO EASTERNMOST TÜRKIYE (EAST OF LAKE VAN): EVIDENCE FROM AN UPPER CRETACEOUS INTRA-OCEANIC ARC, SUPRA-SUBDUCTION ZONE OPHIOLITES, AND PALAEOZOIC-CENOZOIC SEDIMENTARY SUCCESSIONS

Abstract

This paper discusses and interprets an important but little studied part of the regionally important Berit Suture Zone that extends across eastern Türkiye into Iran (>500km). Fragmentary Upper Cretaceous ophiolites, oceanic island arc units and accretionary melange,  east of Lake Van, are keys to understanding the Berit Suture Zone in this area. Field and geochemical evidence suggest that a dismembered ophiolite (Mehmetalan ophiolite) in the study area, mainly composed of depleted mantle harzburgite, dunite and cumulate gabbro, formed in an immature fore-arc setting. Cross-cutting alkaline diabase dykes in one of the ophiolite fragments hint at plume involvement. The volcanic arc, part of the regional Yüksekova Complex, is dominated by variably evolved tholeiitic and calc-alkaline, basaltic-andesitic-rhyolitic volcanics that erupted in an open-ocean, together with minor intrusive rocks. Intercalated pelagic carbonates are dated here as Campanian-Maastrichtian (locally late Maastrichtian) based on planktic foraminifera. The arc-related volcanics display two geochemical trends; one is typical of variably evolved oceanic arc volcanism, whereas the other is alkaline and could represent escape of relatively enriched upper mantle through a slab rupture or plume involvement in SSZ magmatism. Additionally, a dismembered, emplaced Palaeozoic-Mesozoic platform succession in the area is here correlated with the Tauride Malatya-Keban platform, >300 km to the west. The deposition and deformation of Upper Palaeocene-Lower Eocene, and Upper Oligocene-Lower Miocene sedimentary cover units is also taken into account. Three main phases of southward compression, thrusting and subaerial erosion are recognised: latest Cretaceous, Late Eocene and Mid-Late Miocene, followed by plateau uplift,  strike-slip/transpression and westward ‘tectonic escape’. The proposed tectonic model correlates the various units east of Late Van with the Berit suture zone >500 km to the west.