Geotectonic and metallogenetic evolution of Gemericum (Inner Western Carpathians) from Ordovician to Jurassic

摘要

The Early Paleozoic evolution of Gemericum is connected with opening a riftogeneous basin. The evolution of the pre-rift stage was bound to an active (Gondwana) continental margin in Cambrian to Ordovician times. The first phases of continental rifting represent the megacycles of the sedimentary basin fill with bimodal volcanism of inferred Devonian age. During the last phases of rifting in the middle part of the rift a mid-oceanic ridge has developed, being accompanied with the first metamorphic recrystallization MO (LP/HT amphibolite facies), producing new oceanic-type crust, recently representing a part of Rakovec (Zlatnik) and Klatov ophiolitic complexes (LP/HT amphibolite facies). The massive effusions and extrusions have provided ages ca 410-380 Ma. The Early Paleozoic complexes were deformed in the Early Carboniferous, when also subduction-accretionary wedge metamorphism Mia (pumpellyite-actinolite facies) has occurred. Part of the mid-oceanic ridge complexes and their associated sediments were subducted northward, but the rest underwent obduction, forming an accretio-nary wedge. This process transported most of the Early Paleozoic basin fill over the northern continental plate in the form of nappes. Subduction ceased in the Late Carboniferous, being accompanied by further plate convergence and formation of melange-related conglomerates. In Permian period, the Iate-Variscan post-collision collapse and uplift of the asthenosphere have increased the thermal gradient beneath the overlying plate. The Permian high thermal gradient brought about regional metamorphism associated with anatectic melting, causing formation and emplacement of granite during the late Variscan metamorphic phase Mlb (amphibolite facies), coinciding with the beginning of origin of Fe-carbonate mineralization. During Permian, previous subduction processes culminated in the formation of an island arc associated with rhyolitic volcanism and granite intrusions. Late compressional and extensional Variscan tectonic processes completed the Variscan nappe structure of the Gemericum and marked the transition to the extensional phase, associated with the origin of Alpine sedimentary basins. In Jurassic, Gemericum was exposed to a compressional deformation. The structural pattern was a result of the rebound of the lithospheric mantle and asthenosphere after their loading by subducted material in the Permian. At the beginning, reverse movement of the asthenosphere exhumed blocks of metamorphic rocks of the high-pressure, low-temperature blueschist facies (M2), followed towards the end by the uplift of high-pressure metaperidotites from the great depths of minimum 50 km and embedded into unmetamorphosed sediments of Permian-Mesozoic units. Paper provides summary of metallogenetic processes related to each evolutionary phase.