Abstract Critical gravity and magnetic data suggest the presence of a continuous zigzag exhumed mantle body inside the attenuated crust of the north Iberia continental margin. We propose that this body greatly conditioned the structural domains of the Cantabrian–Pyrenean fold-and-thrust belt during their evolution from hyperextension in Early Cretaceous times to shortening and inversion during the Cenozoic. This may be seen as a new line for cross-section construction and balancing, because previous cross-sections do not incorporate comparable volumes of exhumed mantle. Five structural cross-sections, constrained by the results of 3D gravity inversion, feed our discussion of the complexities of the doubly vergent Pyrenean orogen in view of the inversion of a precursor hyperextended rifted margin. In all sections, crustal rocks underthrust the lithospheric mantle in the hyperextended region, supporting that the near-surface exhumed mantle lithosphere acts as a more rigid buttress, allowing weaker continental material to be expelled outwards and upwards by thrusting during the Alpine collision; thus giving rise to two uplifted crustal triangular zones at the boundaries with the exhumed mantle. Contractional slip is localized in lithospheric-scale thrusts, which in turn reactivate parts of the extensional system. The NE–SW transfer zones that offset the rift therefore behave as compartmental faults during the orogenic phase. The amount of shortening increases from 34 km in the Cantabrian Cordillera, where the Basque–Cantabrian Basin partially preserves its original extensional geometry, to 135 km in the nappe stack of the central Pyrenees.

Abstract Regional strike-slip faults are widely distributed in continental interiors and play a major role in the distribution of far-field deformation due to continental collisions. Constraining the deformation history of the Talas–Fergana Fault (TFF), one of the largest of such faults in the Himalayan deformed interior, is vital to comprehend the hinterland kinematics of the India–Asia collision. New apatite fission track results from the NW Tien Shan define a rapid exhumation event at c . 25 Ma. This event is correlated with a synchronous pulse in the South Tien Shan, implying that both ranges experienced a simultaneous onset of rapid exhumation. We suggest that strike-slip motion along the TFF commenced at c . 25 Ma, facilitating counter-clockwise rotation of the Fergana Basin and enabling exhumation of the linked horsetail splays. Pamir indentation, located south of the Western Tien Shan, is postulated to be underway by c . 20 Ma. Recently published results suggest synchronous strike-slip deformation in the western Tarim Basin and eastern flank of the Pamir. Based on our results and published data, we are able to connect Tarim and Pamir deformation to the onset of TFF slip. We suggest that this pre-existing regional structure was responsible for transferring Pamir-induced shortening to the NW Tien Shan. Supplementary material: Supplementary material is available at http://www.geolsoc.org.uk/SUP18845

The indentation of Arabia has influenced the post-Oligocene evolution of the eastern Mediterranean–European region, from Anatolia to the Carpathians and even the central Mediterranean area, since the late Miocene. The efficient transmission of compressional stress from the Arabia-Eurasia collision zone into such a broad area was facilitated by the Tethyan orogenic belt, developed during the Late Cretaceous–Paleogene closure of the northern Neotethyan Ocean, and in particular by its strong inner metamorphic core. The lateral displacement of this orogenic belt, due to the push of Arabia, was progressively accommodated by bowing and extrusion of those sectors that faced low-buoyancy lithospheric domains. This extrusion process first involved the outward expulsion of the Carpathian arc at the expense of the low-buoyancy Magura oceanic domain, and then the lateral escape of the Cycladic arc at the expense of the low-buoyancy Ionian-Levantine oceanic domain. The lateral migration of the Tethyan orogenic belt began to influence the deformation pattern of the central Mediterranean region around the late Miocene, when its Cycladic-Pelagonian sector welded into the southern Adriatic continental domain. Under the westward push of the Tethyan belt, the Adria plate decoupled from Africa and from its Padanian protuberance and rotated clockwise at the expense of the western Apulian low-buoyancy zone. The available geological evidence in the study area suggests that volcanic activity was spatially associated with extension in the upper crust. We discuss the possible implications of this inferred geodynamic connection between the Arabian indentation and regional deformation patterns for the temporal evolution of deep tectonic processes in the central–eastern Mediterranean.

Abstract The mechanism for structural damage during incipient slip on joints within the Melechov Granite, Czech Republic, changes with the misalignment of the joint's mesotopography, largely a plumose surface morphology. Prior to slip, the joint surfaces are well mated so that contact area is organized on a microscopic scale. During the first phase of slip, diffusion-mass transfer is the active deformation mechanism between the sliding surfaces of the joints, as indicated by the extensive growth of crystal-fibre lineations characteristic of slickenside surfaces. After slip of the order of 1 cm or more, the mesotopography becomes mismatched and the contact area is reorganized to form indentation pits aligned on the ridges of hackle plumes. Indentation pits, that are testimony to a brittle process, are generated by the excavation of Hertzian ring cracks that propagate under contact loading of a brittle substrate. The depth of the indentation pits increases with contact width, suggesting that indentation creep is active. Following indentation along Hertzian ring cracks the slip mechanism transforms to a frictional abrasion. The distribution of indentation track lengths is consistent with laboratory wear grooves generated during earthquake-like stick-slip sliding. The elliptical shape of the indentation pits indicates a gradual decrease in contact area, a process that is consistent with a slip-weakening mechanism during a stick-slip cycle.

Abstract The process by which magma ascends into and deforms a volcanic edifice is studied by analogue modelling. A control experiment is conducted with a wooden piston moving vertically into a sand cone. This reveals a well-defined fault pattern that makes it possible to draw the main compressive stress trajectory within the cone during the ascent of the piston. This makes it possible to show that the deformational process is that of indentation of the cone by the rigid piston. Experiments with an indenter that is viscous, as in nature, show that the motion of the viscous body is controlled by the first fault created in the cone. This fault serves as a structural guide, making the viscous body deviate from the vertical and resulting in deformation of the flank of the cone, which bulges out. Other major shear faults that were observed in the control experiment are then inhibited and do not form. This result emphasizes that the structural evolution of an indentation process within a brittle cone and at low rate depends on the rheology of the indenter.