NEOPROTEROZOIC TERRANES IN THE MOESIAN BASEMENT AND IN THE ALPINE DANUBIAN NAPPES OF THE SOUTH CARPATHIANS

Abstract

Geological, geochronological and geochemical evidence suggest that several distinct parts of the Neoproterozoic orogen developed at the active margin of Gondwana are preserved in Moesia and South Carpathians. Parts of a Neoproterozoic volcanic arc and foreland basin are preserved in East Moesia while the Alpine Danubian Nappes preserve remnants of a Pan- African (Cadomian) volcanic arc and its marginal backarc basin. The East Moesian basement exposed in Central Dobrogea includes Pre-Cambrian tholeiitic metabasites from Altin Tepe showing arc/back arc affi nities, subjected to a deformation together with the Neoproterozoic-Early Cambrian turbidites of Histria Formation. In subsurface of South Dobrogea, a Neoproterozoic volcano-sedimentary suite with alkali basalts, related to rifting of the Precambrian Moesian crust, was deformed during latest Neoproterozoic thusting. The Precambrian basement of the Danubian Nappes includes Pan-African island arc metavolcanics (Dragsan type terranes) with an amphibolite facies metamorphism connected to subduction of the arc complex. Emplacement of late-kinematic, high-K calc-alkaline granitoids records late accretion of oceanic rocks to a continent (Gondwana). Metasedimentary successions (Lainici-Paius type terranes) show HT-LP regional metamorphism and pervasive migmatization, prior to the intrusion of Neoproterozoic calc-alkaline and alkali-calcic plutons. Well documented Late Proterozoic ages of the magmatic protoliths in the Lower Danubian basement range between 780 to 570 Ma suggesting Cadomian affi nities. The Pan-African tectono-metamorphic evolution can be dated by U/Pb, K/Ar and Ar/Ar isotopic data at 580-560 Ma. Mineralogical and chemical characters of the Tisoviţa-Iuţi mafi c-ultramafi c complex from the Upper Danubian resemble ophiolite complexes generated in ocean basins associated with arc systems formed at fast- to intermediate-spreading centres.