From a Continental Margin to an Alpine Dome: 4D Geodynamic Evolution of the Aar Massif

2025-09-11T14:09:08+00:00

The inversion of crystalline basement units of former passive continental margins is a typical feature of late-stage collisional mountain belts. In this study, a new large-scale 3D geological model of the main lithostratigraphic and structural units of the Aar Massif was built to investigate how the 3D geometry of the passive margin and inherited extensional structures influenced the tectonic evolution during late-stage continent-continent collision. Cross-section restoration of such units and of metamorphic peak temperature data allowed us to reconstruct the 4D geodynamic evolution of the massif during the late-stage Alpine orogeny. Our results show that: (i) The Aar Massif results from the inversion of the unevenly stretched proximal zone of the passive European margin. (ii) 20% of the present-day structural relief of the massif is a legacy of the 3D architecture of the Permian to Mesozoic passive continental margin. Mesozoic rifting structures formed larger-scale basins separated by a central topographic high subdividing the Aar Massif into three SW-NE trending basement blocks. (iii) The inherited spatial variations in graben/basins geometry and associated sediment and crustal thickness variations caused an in-sequence, non-cylindrical exhumation of the Aar Massif, controlled by a dense network of reverse and thrust faults. This interplay between crustal dynamics and crustal inheritance resulted in the uplift and emplacement of the Aar Massif. The results of this study highlight the importance of integrating regional-scale 3D geological modelling in the analysis of complex geological systems, such as orogens. By enabling a comprehensive understanding of their 4D evolution and geodynamic processes, this methodology opens the door to a wide range of applications in tectonics, resource exploration, and hazard assessment.

Unraveling the Kinematics and Morphotectonics of the Petrinja Fault (Croatia), Source of the 2020 M 6.4 Earthquake

2025-03-17T16:44:19+00:00

The 2020 Mw 6.4 Petrinja earthquake in central Croatia is one of the European strongest continental earthquakes in recent decades. This event shed light on the poorly investigated Petrinja-Pokupsko Fault (PPKF) zone, a right-lateral fault system accommodating a fraction of the shortening between the Adria and European plates. Through field observations and high-resolution Lidar-derived digital elevation models of the central section of the PPKF, we precisely mapped the fault trace, revealing a discontinuous geometry with a main fault strand and left-stepping segments in agreement with the position of the 2020 surface ruptures. To the north, the accumulated relief from this transpressive fault system decreases, and the fault trace becomes less distinct, suggesting a northward propagation of the deformation. Cumulative offsets of 4 to 24 meters along the main fault strands in the central and southern sections of the fault attest to its Quaternary activity. Dating results suggest offset markers at the Marine Isotopic Stage 4 (MIS 4), the Late Glacial Maximum (LGM) or the Early Holocene periods, allowing for the first direct estimation of the fault slip rates. Preliminary estimates indicate that, assuming a common MIS 4 or LGM age for the investigated markers, fault slip rates range from 0.2 to 0.7 mm/yr and 0.7 to 1.6 mm/yr, respectively. In contrast, assigning Early Holocene ages would imply much higher - and likely unrealistic - slip rates of 1.6 to 3.9 mm/yr. Although the estimated loading rates vary greatly and depend on strong assumptions regarding the age of the markers abandonment, our results suggest a minimum fault slip-rate of 0.2 mm/yr for local seismic hazard assessments.

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From a Continental Margin to an Alpine Dome: 4D Geodynamic Evolution of the Aar Massif

Unraveling the Kinematics and Morphotectonics of the Petrinja Fault (Croatia), Source of the 2020 M 6.4 Earthquake