Metallogenetic evolution of the East Alpine Paleozoic basement
TL;DR: Paleo-metallogenetic sketch maps of the East Alpine area are presented in this article for the Ordovician/Silurian, the Devonian/Lower Carboniferous, and the Upper Carboniferic/Permian.
Abstract: Paleo-metallogenetic sketch maps of the East Alpine area are presented for the Ordovician/Silurian, the Devonian/Lower Carboniferous, and the Upper Carboniferous/Permian. Mineralization and tectonic evolution are then discussed in the frame of a plate tectonic model compatible with recent results in Western Europe. A group of microcontinents originally dispersed in an ocean north of Gondwana, comprising in the investigated area a Bohemian, Penninic and a South/Austro-Alpine microcontinent was sutured after earlier localized orogenies to a Central European continent during the Devonian resulting from a general northward drift from the Cambrian onwards. This was followed by the development of a new destructive plate margin in the South with a northerly dipping subduction zone, enabling the consumption of the Proto-Tethys ocean. Mainland Gondwana then collided with the newly formed continent during the Carboniferous. Contrary to the generally convergent tectonic pattern most mineralizations in the South/Austro-Alpine area appear associated with crustal extension and related volcanism continuing into the Lower Carboniferous. Especially in the Upper Ordovician this conforms well with the concept of a back arc extensional cratonic basin setting. Metal zoning similar to the Andean/Cordilleran situation cannot be observed. Notably different, however, is the orogenic setting of the Penninic area during the Lower Paleozoic, with an economic scheelite-mineralization and associated trace elements reflecting mainly crustal affinities. The Upper Carboniferous calc-alcaline magmatism of the South/Austro-Alpine-Penninic area with its Cu-Pb-Zn-Ag-F mineralisation in the South and anomalous Be-Bi-F-Li-Mo-W-U contents further North displays many features of a back arc magmatic belt. The orogenetic stage is followed in the Upper Carboniferous-Permian by molasse with sandstone type U, graphite (coal) and acidic volcanism giving rise to (Ba-F-) Cu-Pb-Zn-U ores. A renewed tensional regime accompanied by marine transgression during the higher Permian produced evaporite deposits and minor epigenetic mineralization dominated by Fe in the Austro-Alpine area.
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TL;DR: In this article, the authors investigated metasomatic magnesite, siderite and ankerite mineralizations within Paleozoic sediments of the Northern Greywacke zone and its metamorphic counterpart in the crystalline "basement" (Upper Austroalpine unit) with respect to their strontium isotopic composition.
Abstract: Metasomatic magnesite, siderite and ankerite mineralizations within Paleozoic sediments of the Northern Greywacke zone and its metamorphic counterpart in the crystalline “basement” (Upper Austroalpine unit) were investigated with respect to their strontium isotopic composition. The results support a sedimentary (s.l.) model for the magnesites within Visean platform carbonates of the Veitsch nappe and an epigenetic hydrothermal model for the siderites and ankerites in Devonian platform carbonates of the Noric nappe and from Huttenberg. The Fe transporting fluids can be characterized either as magmatogene or, more probably, as metamorphogene. By increasing the stage of recrystallization and/or remobilization due to at least two later metamorphic overprints, Sr in the various ore minerals beame ± enriched in radiogenic 87Sr.
24 citations
TL;DR: The Zentralgneise in the Hohe Tauern (Penninic Zone, Eastern Alps, Austria) can be interpreted essentially as metamorphosed Late Paleozoic orogenic plutonites with original compositions mainly of granites, granodiorites and tonalites.
18 citations
TL;DR: The role of metamorphism in East Alpine metallogeny was tentatively explored for more than 60 y, although for a long time without tangible results as discussed by the authors, and the role of water falling into the metamorphic field was only recently confirmed by micro-thermometric, geochemical and isotopic investigations of fluid inclusions from selected Alpine mineral deposits.
Abstract: The two Alpine orogenic phases of the Eastern Alps, in the Cretaceous and in the Tertiary, were both accompanied by the formation of mineral deposits. However, subduction-related magmatic belts as well as the typical “Andean” ore deposits are missing. Therefore, the role of metamorphism in East Alpine metallogeny was tentatively explored for more than 60 y, although for a long time without tangible results. Microthermometric, geochemical and isotopic investigations of fluid inclusions from selected Alpine mineral deposits presented allow a preliminary confirmation of the involvement of metamorphic fluids in their origin. Deposits which were formed immediately after the first, Cretaceous orogeny, were produced at high pressures by fluids of very high salinity and high density, and with an isotopic composition of the water falling into the metamorphic field. These fluids are best understood as products of metamorphic de-volatilization of rocks of the subducted South Pennine domain. In contrast to this, the deposits formed after the second, Tertiary orogeny, originated at relatively low pressures from fluids with an appreciable content of CO2 and of low to moderate salinities. Isotopic compositions of this carbon indicate a deep crustal or even mantle source for CO2, while the water is isotopically more heterogeneous and may have mixed sources, both surficial and metamorphic. Tectonic control of these mineralizations is late-orogenic trans-tensional faulting, which exposed hot metamorphic rocks to fluid convection along brittle structures. These deposits conform best to the model of metamorphogenic metallogenesis by retrograde leaching, although ponded metamorphic fluids and mantle volatiles may also have been involved.
17 citations
Cites background from "Metallogenetic evolution of the Eas..."
...Mineral deposits formed in the area of the later Eastern Alps during the Pan-African (Cadomian), Caledonian and Hercynian cycles ( Pohl 1984 ), and the deposits related to the geosynclinal stage of the Eastern Alps (e.g....
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TL;DR: In this paper, three types of previously undated metagranitoids (central gneisses) are distinguished and preserve intrusive contacts with pre-Alpine metamorphosed supracrustal rocks.
Abstract: Vein-type Mo mineralization at Alpeiner Scharte occurs in the Penninic units of the western Tauern Window in the Eastern Alps. Three types of previously undated metagranitoids (central gneisses) are distinguished and preserve intrusive contacts with pre-Alpine metamorphosed supracrustal rocks. The granitic protoliths represent fractionated late to post-orogenic, calc-alkaline, I-type magmas with minor S-type components. The Mo veins are restricted to a biotite and alkali feldspar-rich gneiss variety and occur in E–W trending normally sub-vertical quartz veins with adjacent thin discontinuous garnet- and biotite-rich zones; the latter are interpreted as metamorphosed vein selvages. Prior to this work the age of the intrusive host rocks as well as the age of Mo mineralization were unknown.
9 citations
Cites background from "Metallogenetic evolution of the Eas..."
...A second group (Schulz, 1977; Pohl, 1984; Lammerer, 1986) favoured a magmatic-hydrothermal origin and argued for a Variscan age of mineralization....
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...A second group (Schulz, 1977; Pohl, 1984; Lammerer, 1986) favoured a magmatic-hydrothermal origin and argued for a Variscan age of mineralization....
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TL;DR: The molybdenite deposit of the Alpeinerscharte (Austria) is situated in Variscan greenschist-to amphibolite-facies metamorphosed granodiorites and granites of the western Tauern Window.
Abstract: The molybdenite deposit of the Alpeinerscharte (Austria) is situated in Variscan greenschist- to amphibolite-facies metamorphosed granodiorites and granites of the western Tauern Window. These granitoids represent strongly fractionated calc-alkaline I-type magmas with minor S-type components and reveal post-orogenic affinities. Molybdenum contents (average 4.3 ppm) are slightly above the general background of average granites. Molybdenite mineralization is restricted to narrow quartz veins and quartz vein selvages which are presently composed of biotite and (almandine-grossular) garnet. These selvages show geochemical features typical of intermediate argillic alteration in a hydrothermal system postdating granite intrusion: instability of plagioclase causes removal of Na, Ba, Sr, Pb and Eu, while K and Ca remain nearly constant. Rare earth elements (apart from Eu) and metals are extremely enriched. Application of Fe-Mg exchange (garnet-biotite) and oxygen isotope (quartz-garnet, quartz-plagioclase) geothermometers to vein selvage mineral assemblages reveals temperatures of the late-Alpine (35–55 Ma) metamorphic overprint (∼540°C, 7–10 kbar). Leucocratic rocks composed of mainly orthoclase and plagioclase are occasionally spatially related to molybdenite-bearing veins; they are interpreted as episyenites formed by hydrothermal alteration of the host granite. This episyenitic alteration is characterized by a mass loss of ca. 30%, relative enrichment of plagioclase components, extreme depletion of Si, and minor depletion of Fe, Zn, Cu and Mo.
7 citations
References
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Book•
01 Jan 1969
TL;DR: In this article, the authors discuss the permo trassic devlopment of pangea and the pangean disintegration: opening of the central atlantic the north and the neo-tethys.
Abstract: This book contents about :
- Suturing of pangea
- Permo trassic devlopment of pangea
- pangean disintegration : opening of the central atlantic the north atlantic and neo tethys
atc
2,237 citations
TL;DR: In this article, the authors consider that continental collision is followed by crustal thickening, to accommodate further plate convergence, with ensuing partial melting of the lower crust, resulting in a dry refractory lower crust consisting of pyroxene granulites and anor-thosites.
Abstract: Extensive terranes of basement reactivation are interpreted as resulting from crustal thickening following continental collision. It is suggested that terranes, such as the Grenville Province and much of the Variscan orogenic belt in Europe, have their modern analog in the Tibetan Plateau. The Tibetan Plateau is underlain by a continental crust between 60 and 80 km thick and is characterized by extensive high-potash Neogene vulcanism. Following T. H. Green's arguments that partial melting of a dioritic lower crust may yield potassic granitic liquids and refractory anorthositic residues, we consider that continental collision is followed by crustal thickening, to accommodate further plate convergence, with ensuing partial melting of the lower crust. At high structural levels, silicic-potassic ignimbrites are extruded in intermontane basin-horst terranes, with subjacent granite plutons. At deeper levels, a dry refractory lower crust consisting of pyroxene granulites and anor-thosites is generated.
848 citations
TL;DR: In this paper, the authors interpreted the late Paleozoic wrench faulting in southern Europe and northern Africa as a right-lateral shear zone induced by the relative motion of two plates, a northern one that includes the Canadian Shield, Greenland, and stable Europe and a southern one that including the African Shield plus an unknown eastern extension.
Abstract: Late Paleozoic wrench faulting in southern Europe and northern Africa is interpreted as a right-lateral shear zone induced by the relative motion of two plates – a northern one that includes the Canadian Shield, Greenland, and stable Europe and a southern one that includes the African Shield plus an unknown eastern extension. The relative movement of these two plates was transformed into shortening at both ends of the shear zone and led to the formation of late Paleozoic mountain belts: the Urals to the east and the southern Appalachians to the west. Theoretical and experimental models of the dynamics of faulting may account for the arrangement of the fractures in the shear zone and for the observed displacements.
751 citations
Book•
01 Jan 1981
TL;DR: A review on mineralization at plate boundaries as discussed by the authors was published in 1976 and was used as a basis for courses on plate tectonics mineralization courses at many American universities, and many Heads of earth science departments requested at that time that we should amplify the review into a textbook for use by senior undergraduate and postgraduate geology students, economic and exploration geologists and other earth scientists with an interest in recent advances in understanding of global patterns of tectonic and mineralization.
Abstract: The revolution in the earth sciences consequent on the formulation of the plate or global tectonics hypothesis some 14 years ago is familiar to all concerned with the earth sciences. The effects of this revolution on our understanding of the relationship of ore body genesis and distribution to major tectonic settings can be seen from the voluminous literature on the subject which has appeared in the last decade, compared to the few papers, other than in the USSR, which were published previously. Extensive though the literature is, it is virtually confined to individual papers in journals, to proceedings of meetings, seminars and workshops, and to books consisting of chapters by individual contributors. Since the terminology applied to tectonic settings is as yet ill-defined, and since individual authors differ in their interpretations of the relationship of many smaller-scale settings to major plate boundaries, these publications do not always present material in a form which can be readily assimilated either by geologists concerned largely with mineral deposits. The preparation of this book was stimulated to a large extent by the encouraging response to our review on Mineralization at plate Boundaries published in 1976. This review was adopted as a basis for courses on plate tectonics mineralization at many American universities, and many Heads of earth science departments requested at that time that we should amplify the review into a textbook for use by senior undergraduate and postgraduate geology students, economic and exploration geologists and other earth scientists with an interest in recent advances in understanding of global patterns of tectonics and mineralization.
186 citations