Metamorphism and Tectonic Evolution of Metamorphic Belts

Dear Colleagues,

The study of metamorphism and the tectonic evolution of metamorphic belts provides critical insights into the dynamic processes shaping the Earth's crust (compression vs. extension). By analyzing metamorphic rocks and their formation conditions, geologists can reconstruct the history of plate movements, the nature of past environments at great depths and the mechanisms driving the Earth's tectonic activities. This knowledge is fundamental to our understanding of the planet's geological past, present and future. We call for research contributions studying these closely related processes of metamorphism and structural evolution of metamorphic belts produced either during plate convergence, nappe stacking and crustal thickening or plate divergence, crustal thinning and the exhumation of deep crustal rocks.  As an example, we referred to the Himalayan Metamorphic Belt, The Alps, Dinnarides and Hellenides orogenic belts or the Franciscan complex in California.

Dr. Adamantios A. Kilias
Dr. Ilias Lazos
Prof. Dr. Hans-Jürgen Gawlick
Guest Editors

Dr. Emmanouil Katrivanos
Guest Editor Assistant

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• compression
• extension
• nappe stacking
• crustal exhumation
• orogeny
• subduction
• obduction
• metamorphism
• migmatites

Title: Thick-skinned triangle zones: An example from pro- and retro-wedges of the western and central Greater Caucasus orogen
Authors: Victor Alania
Affiliation: Institute of Geophysics, I. Javakhishvili Tbilisi State University, Tbilisi, Georgia
Abstract: The Greater Caucasus is one of the best field laboratories to investigate mechanisms of collision-driven far-field double wedge orogen formed by the ongoing collision between the Arabian and Eurasian plates. Within pro-and retro-wedges of the western and central GC orogen, we identify thick-skinned triangle zones where the external side of the triangle involves the foreland basement in the deformation. Our new 2D seismic data from the frontal part of the pro-wedge of Greater Caucasus (Dzirula-Imereti Uplift Zone) have revealed the presence of a crustal-scale triangle zone. The formation of the Dzirula-Imereti Uplift Zone is complicated by the interaction between several detachments from the mid-crustal detachment to the uppermost detachments along the lower and upper Jurassic shales. The structure of the retro-wedge of the Greater Caucasus is very complex as evidenced by 2D seismic sections presented in previous studies (e.g. Sobornov, 2021). The structural styles presented along the Kuban and Terek foreland basins, evidence an evolution of complex geometries like passive-roof duplexes, passive-roof thrust, active-roof duplexes, and growth fault-related folds. Triangle zones in the pro- and retro-wedge of the Greater Caucasus are interpreted as multiple fault-bend fold wedges models and are a good example of the wedge-dominated thick-skinned triangle zone.

Title: Polymetamorphic evolution of Parvenets complex, Bulgaria - U-Th-Pb monazite and zircon geochronology
Authors: Milena Georgieva1*, Valerie Bosse2, Zlatka Cherneva1, Tzvetomila Vladinova3
Affiliation: 1 Sofia University “St. Kliment Ohridski”, Tsar Osvoboditel Blv, 1504 Sofia, Bulgaria; 2 Université Clermont Auvergne (UCA) - Clermont Ferrand – France, Campus universitaire des Cézeaux - 6 av. Blaise Pascal; 3 Geological Institute, Bulgarian Academy of Sciences, Acad.G. Bonchev str., 1113, Sofia Bulgaria

Title: The relationships between the Internal Nappe Zone and the Regional Mylonitic Complex in the NE Variscan Sardinia (Italy): a new regional interpretation?
Authors: Franco Marco Elter; Federico Mantovani
Affiliation: University of Genoa
Abstract: This study presents an updated interpretation of geological data collected between 1984 and 2022. The area under consideration holds significant regional importance as it is located between the Internal Nappe Zone (INZ) and the Regional Mylonitic Complex (RMC). Re-evaluation of the ge-ological data has highlighted a more intricate structural framework than what is currently docu-mented in existing literature. This paper aims to illustrate, through structural analysis, that the Posada Valley Shear Zone (PVSZ) does not serve as the transitional boundary between the INZ and RMC as traditionally thought. Instead, authors findings indicate that the transition boundary is confined to a shear band with a variable thickness ranging from 10 to 70 meters at its widest points. The development of the PVSZ is characterized by a series of transitions from mylonite I S-C to mylonite II S-C, extending over approximately 5 kilometers. The formation of the PVSZ is chronologically confined between the development of the East Variscan Shear Zone and the em-placement of the Late Variscan granites. The differing orientations of Sm (PVSZ) and S3 (RMC) observed in the mylonitic events of the RMC and PVSZ are likely attributable to an anticlockwise rotation of the shortening directions during the upper Carboniferous period. Furthermore, this study proposes that the Condensed Isogrades Zone (CIZ), despite its unclear formation mecha-nism, should be recognized as the true transition zone between the INZ and the RMC. This new interpretation challenges the previously accepted notion of increasing Variscan metamorphic zo-nation towards the northeast. This conclusion is supported by the identification of the same NE-SW orientation of the D2 tectonic event in both the Old Gneiss Complex (RMC) and the li-thologies of the INZ and CIZ. The comprehensive analysis and new insights provided in this paper contribute to a refined understanding of the geological relationships and processes within this region, offering significant implications for future geological studies and interpretations.