Subduction-related metamorphism in the Alps: Review of isotopic ages based on petrology and their geodynamic consequences
Alfons Berger, Romain Bousquet, 2008. "Subduction-related metamorphism in the Alps: Review of isotopic ages based on petrology and their geodynamic consequences", Tectonic Aspects of the Alpine-Dinaride-Carpathian System, S. Siegesmund, B. Fügenschuh, N. Froitzheim
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We summarize ages of the high-pressure/low-temperature (HP/LT) metamorphic evolution of the central and the western Alps. The individual isotopic mineral ages are interpreted to represent either: (1) early growth of metamorphic minerals on the prograde path; (2) timing close to peak metamorphism; or (3) retrograde resetting of the chronometers at still-elevated pressures. Therefore, each individual age cannot easily be transferred to a geodynamic setting at a certain time. These different data indicate a subduction-related metamorphism between 62 and 35 Ma in different units (e.g. Voltri Massif, Schistes Lustrés of the western Alps, Tauern Window). Oceanic and continental basement units show isotope ages related to eclogitic or blueschist facies metamorphism between 75 and 40 Ma. Most of these ages may record equilibration along the retrograde path, except of some Lu/Hf garnet ages and some zircon SHRIMP ages, which provide information on the prograde path. These different isotope ages are interpreted as different steps along pressure–time paths and so may provide some information on the geodynamic evolution. The data record a continuous subduction, which is ongoing for several tens of millions years. In a large-scale picture, we have to assume fragmentation of the downgoing plate in order to explain the available P–T and t data. This interpretation questions the ongoing driving force for subduction during the disappearance of the Alpine Tethys.
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Tectonic Aspects of the Alpine-Dinaride-Carpathian System
The Alps, Carpathians and Dinarides form a complex, highly curved and strongly coupled orogenic system. Motions of the European and Adriatic plates gave birth to a number of ‘oceans’ and microplates that led to several distinct stages of collision. Although the Alps serve as a classical example of collisional orogens, it becomes clearer that substantial questions on their evolution can only be answered in the Carpathians and Dinarides. Our understanding of the geodynamic evolution of the Alpine-Dinaride-Carpathian System has substantially improved and will continue to develop; this is thanks to collaboration between eastern and western Europe, but also due to the application of new methods and the launch of research initiatives. The largely field-based contributions investigate the following subjects: pre-Alpine heritage and Alpine reactivation; Mesozoic palaeogeography and Alpine subduction and collision processes; extrusion tectonics from the Eastern Alps to the Carpathians and the Pannonian Basin; orogen-parallel and orogen-perpendicular extension; record of orogeny in foreland basins; tectonometamorphic evolution; and relations between the Alps, Apennines and Corsica.