Geology of the Asinara Island (Sardinia, Italy)

Sardinia (Italy) represents one of the most comprehensive cross-sections of the Variscan orogen. The metamorphic and structural complexity characterizing its axial zone still presents many unresolved issues in the current state of knowledge. The data presented from the structural study of the entire axial zone of this area have allowed the authors to propose a subdivision into two new structural complexes. In particular, a younger complex is identified as the New Gneiss Complex, containing remnants of an older and higher-grade metamorphic complex defined as the Old Gneiss Complex. The structural and geometric relationships between the two complexes suggest the redefinition of the axial zone of Sardinia as part of the intracontinental East Variscan Shear Zone/medium-temperature Regional Mylonitic Complex. Comparable relationships are also highlighted in many other areas of the Variscan chain (e.g., Morocco, Corsica, Maures Massif, and Argentera Massif). Extending this new structural interpretation to other axial zones of the South European Variscan orogen could provide new hints for reconstructing the collision boundaries between Gondwana and Laurussia in the late Carboniferous to the early Permian periods.

The East Variscan Shear Zone (EVSZ) and Its Regional Mylonitic Complex: A New Geodynamic Interpretation of the Variscan Axial Zone in Sardinia (Italy)?

Mantovani,

Elter

2024

The Relationships between the Internal Nappe Zone and the Regional Mylonitic Complex in the NE Variscan Sardinia (Italy): Insight from a New Possible Regional Interpretation?

Elter,

Mantovani

2024

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 geological data has highlighted a more intricate structural framework than what is currently documented in the 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 Inner Nappe Zone and the Regional Mylonitic Complex or High-Grade Metamorphic Complex (HGMC) as traditionally thought. Instead, the authors’ findings indicate that the transition boundary is confined to a shear band with a variable thickness ranging from 10 to 70 m at its widest points. The development of the Posada Valley Shear Zone is characterized by a series of transitions from mylonite I S-C to mylonite II S-C, extending over approximately 5 km. The formation of the Posada Valley Shear Zone is chronologically confined between the development of the East Variscan Shear Zone (EVSZ) and the emplacement of the Late Variscan granites. The differing orientations of Sm and S3 observed in the mylonitic events of the Posada Valley Shear Zone and the Regional Mylonitic Complex, respectively, 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 mechanism, should be recognized as the true transition zone between the Inner Nappe Zone and the Regional Mylonitic Complex or High-Grade Metamorphic Complex. This new interpretation challenges the previously accepted notion of increasing Variscan metamorphic zonation toward 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 (OGC in the Regional Mylonitic Complex) and the lithologies of the Inner Nappe Zone and the Condensed Isogrades Zone. 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.

Geology of the Mulkhura River Valley, Georgian Caucasus

Kumladze,

Tielidze,

Gamkrelidze

et al. 2024

Geological mapping provides vital information about the structure, evolution, natural resource potential, and geohazards of a specific area. The role of geological mapping is especially valuable for mountainous countries like Georgia. In this context, we present a geological map of the Mulkhura River Valley in the Georgian Caucasus (43°3′ N, 42°52′ E) with accompanying cross-sections at a scale of 1:30,000, covering approximately 220 km2. The geological information in the map is based on a comprehensive review of previously published geological maps and literature, combined with original analysis of satellite imagery and hitherto unpublished field data. The extensive spatial coverage and accompanying cross-sections provide detailed insights into the structure of the region. This new map will serve as a foundation for future geological research, hazard management, and resource exploration in the area, as well as for geoconservation to develop the national geotourism industry in this region.