Banatite Belt

The Alpine-Balkan-Carpathian-Dinarides (ABCD) orogen is characterized over large sectors by the superposition of Tertiary collisional structures on Early to Late Cretaceous ones. The Cretaceous orogen formed during an independent orogenic cycle due to consumption of oceanic tracts and subsequent early Late Cretaceous collision of continental blocks. The assembled Cretaceous terrane collage was heavily modified by Tertiary collisional, extrusional and oroclinal processes during invasion of these units into the Carpathian arc and the indentation of the Moesian block as the present-day arcuate mountain belt formed. The Cretaceous orogenic belt displays significant variations along strike, namely strong subduction-collision metamorphism and missing Cretaceous magmatism in western sectors of the belt, and apparent weak metamorphism/deformation in southeastern sectors (Apuseni Mts./Southern Carpathians, Bulgarian Srednogorie zone). There, the belt is superposed by extensive Late Cretaceous plutonism/volcanism ("banatites") associated with widespread mineralizations. Magmatism is contemporaneous with the formation of collisional-type successor sedimentary basins. The reconstruction of Cretaceous collisional structures, magmatic features, and mineralizations reveals significant variations along strike, which are not well understood at present and which are the focus of current investigations as part of the GEODE ABCD project of the European Science Foundation (coordinated by the project propoeser). The proposed research (FWF) includes: (1) 40Ar/ 39Ar dating of minerals including biotite, amphibole and muscocite from magmatic rocks to reveal the timing and duration of magmatism, specifically of volcanism and plutonism, of ca. 10-12 selected sites distributed along the whole strike of the ca. 1,500 km long banatite belt. (2) 40Ar/ 39Ar dating of alteration minerals like adularia, sercite and alunite to reveal the timing of mineralization of these sites. (3) Structural investigations on ore deposits to reveal kinematic and dynamic conditions of the emplacemnent of plutons and the mineralizations. (4) Studies of selected collisional structures within the underlying basement to reveal the kinematic and dynamic relations to banatite intrusion. Together, the new data should allow to distinguish between different geodynamic models which were proposed for that region: post-collisional slab break-off vs. subduction related origin.

The project found significant geodynamic and structural controls on formation of major ore provinces and underlying plutonic and volcanic rocks of superposed Cretaceous and Tertiary orogens in southeastern Europe, which comprises some of the largest gold and copper ore deposits of Europe. The most important of these controls include: (1) late syn- to post-collisional setting; (2) inherited cross-cutting lineaments in the underlying crust; (3) melt generation by erosion of the subducted lithosphere; (4) favorable structures like fault oversteps, cross-cutting block boundaries; and (5) shallow level intrusions for fluid channelling. Together, the systems show that mineralization was probably controlled by the superposition of favourable mantle lithospheric conditions and partly independent, evolving upper crustal deformation conditions during late stages of mountain building. These principles apply both for the Upper Cretaceous Banatite belt and the Neogene ore provinces of souheastern Europe and can be applied and tested in other mountain belts. Particularly, western sectors of the ca. 1,500 km long Banatite magmatic belt were formed within a ca. east-west- trending (Late Cretaceous coordinates) double-vergent mountain belt by slab break-off after plate collision. Collsion formed a double-veregnt mountain range, which was overthrusted on their continental forelands. A wide range of melts were formed, which range from mantle-derived alkaline massifs and intermediate calcalkaline rocks to acidic crustal melts like granite and rhyolite. Melt erosion of the lithosphere may explain much of the features and melt evolution. In Late Cretaceous coordinates, the Banatite magmatism formed an E-W belt and shows two trends during development, westward and southward younging. Youngest Banatites were found at the western (now northern) termination of the belt, in Romanian Apuseni Mts. where volcanic rocks intercalated in Maastrichtian collapse basins. Structural data from Banatites belt show evidence for cross-cutting inherited basement structures, like the Panagyurishte corridor in Bulgaria. These resulted in fault oversteps during subsequent collapse basin formation. Several palaeostress orientations have been recognized all over the Banatite belt: (1) ca. N-S extension between 94 and 86 Ma, which also resulted in sedimentary basin formation possibly triggered by slab break-off model by post-collisional extension. The later model is preferred because it explains all existing tectonic data and the prior double-vergent orogen. (2) The subsequent change to N-S compression (during the 86-70 Ma period) may have been driven by large-scale plate motion. (3) Particularly the South Carpathian and Balkan segment is also affected by final N-S shortening during Eocene.