Large-Scale Crustal-Block-Extrusion During Late Alpine Collision.

Area of Science:

• Geosciences
• Tectonics
• Structural Geology

Background:

• Classical subduction models explain Alpine tectonics via compressional wedge tectonics and isostatic rebound.
• External Crystalline Massifs, like the Aar massif, disrupt the upper crust, exhibiting significant vertical uplift (>12 km) and steep metamorphic gradients.
• These features suggest mid-crustal exhumation along steep shear zones, challenging traditional models.

Purpose of the Study:

• To investigate the role of lower crustal delamination and buoyancy-driven extrusion in shaping the European Alps' crustal geometry.
• To explain the vertical disruption and exhumation of the Aar massif within the broader Alpine context.
• To identify key indicators of continent-continent collision final stages.

Main Methods:

• Modeling of lithosphere mantle rollback and its temporal migration.
• Analysis of buoyancy forces driving upper crustal block extrusion.
• Identification of fault networks (reverse and normal faults) dissecting the crust.
• Correlation of tectonic processes with topographic and metamorphic gradients.

Main Results:

• Delamination of European lower crust migrates northward with lithosphere mantle rollback.
• The Aar massif extrudes buoyantly, accumulating lower crustal material beneath.
• Buoyancy-driven deformation creates extensive steep reverse fault networks, with secondary normal faults.
• Reduced vertical motion and late compression lead to north-directed thrusting.

Conclusions:

• Buoyancy-driven vertical tectonics, coupled with late compression and erosion, explains Alpine topography and metamorphic patterns.
• These processes offer insights into the final stages of continent-continent collisions.
• The Aar massif's structure is a product of delamination, extrusion, and subsequent compressional events.