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Continental indentation is associated with deformation transfer from shortening to strike-slip faulting and is often affected by subduction related processes such as slab roll-back driven back-arc extension. We use crustal-scale analogue modelling to investigate the effects of extension direction on the strain partitioning and deformation transfer during indentation. The modelling results show that extension parallel to the strike-slip margin of the indenter creates subsidence distributed in several areas which may connect to form a large sedimentary basin behind the indenter. This transtensional basin with v-shape geometry narrows gradually towards the strike-slip margin of the indenter. In contrast, models with extension perpendicular to the strike-slip margin distributes transtensional deformation away from the indenter. Our results are in good correlation with the evolution of the Carpatho-Balkanides orocline of South-Eastern Europe, where the Circum-Moesian Fault System accommodates oroclinal bending during indentation against the Moesian Platform. In this area, the modelling explains the coeval and contrasting extensional features observed along the strike-slip margin and behind the indenter (i.e. the Getic Depression and the Morava Valley Corridor), driven by the roll-back of the Carpathian embayment and Adriatic slabs. • Extension parallel to the strike-slip margin of the indenter opens a connected sedimentary basin. • Extension perpendicular to the strike-slip margin of the indenter distributes transtensional deformation away from the indenter. • Different slab roll-backs create a complex strain partitioning in the Carpatho-Balkanides during the indentation of Moesia. [ABSTRACT FROM AUTHOR]

Two-dimensional numerical modeling methods were used to study the thermomechanical consequences of closure of the Meliata-Hallstatt ocean and Cretaceous continent-continent collision in the eastern Alps of Austria. It is deduced that the temperature evolution during eclogite exhumation is mainly reliant on rates of tectonic movements, but independent of the mode of exhumation.

Unlike for subaerial settings, the impact of subaqueous relay ramps on sediment dispersal is still poorly understood. A combination of analogue laboratory experiments in a sandbox with numerical flow calculations is used to simulate relay ramp topographies on rifting continental margins and to analyse the resulting turbidity current pathways and their deposits. Various scenarios are investigated, including inflow perpendicular and oblique to the relay ramp axis as well as flow constrained by an incised channel on the ramp and by a landward-directed tilt of the ramp. Without channelling, most sedimentation takes place on the basin floor because the bulk of the flow follows the steepest gradient down the fault and into the rift basin. With a channel along the relay ramp, significant flow occurs initially down the ramp axis, but channel spillover and basinward ramp tilting combine to redirect much of the sediment down the fault slope into the basin. When the relay ramp has a landward-oriented tilt, most of the current flows down the ramp and deposits its sediment load there and at the foot of the ramp. However, also here a considerable amount of the flow is shed over the hanging wall fault and into the basin, forming a secondary depocentre, while ponding redistributes thin deposits over a wider area of the basin. The quantitative dependence of these results on the specific ramp geometries remains to be investigated further but may bear great importance for refined sedimentary models in subaqueous rifted settings as well as for hydrocarbon exploration therein. [ABSTRACT FROM AUTHOR]

Large-scale strike-slip faults are associated with significant strain partitioning in releasing/restraining bends and often display map-view curvatures ending in horse-tail geometries. Such faults are commonly associated with indentation tectonics, where shortening in front of indenters is transferred laterally to transpression, strike-slip and the formation of transtensional/extensional basins. We investigate how these structurally distinct domains are kinematically linked by the means of a crustal-scale analogue modelling approach where a deformable crust is moved against a stable and rigid indenter. The modelling demonstrates that the geometry of the indenter is the major controlling parameter driving strain partitioning and deformation transfer from thrusting and transpression to strike-slip and transtension, whereas the rotation of the mobile plate controls the opening of triangular shaped transtensional basins. Flow of the ductile crust leads to the distribution of deformation over a wider area, facilitating strike-slip splaying into transtension/extension behind the indenter. Our results show a very good correlation with the Moesian indentation in the Carpatho-Balkanides system of South-Eastern Europe, where strain is partitioned around the dextral Cerna and Timok strike-slip faults and transferred to thrusting in the Balkanides part of the Moesian indenter and to transtension/extension in the neighbouring South Carpathians. • Indenter geometry controls the strain partitioning around its margins during oroclinal bending. • Crustal ductile flow creates splaying strike-slip faults and extension behind the indenter. • A large dextral offset is transferred to coeval extension and shortening during the rotation of the Carpatho-Balkanides. [ABSTRACT FROM AUTHOR]

Extension is a key process controlling the post-orogenic exhumation of metamorphic rocks in subduction and collision zones. Previous studies have largely focused on the mechanics of localized core-complex style post-orogenic extension and the large-scale effects of various internal (e.g. rheology) and external (e.g. plate motions) parameters on the mode of extension. However, many regions on earth underwent rock exhumation during post-orogenic extension, which is characterized by distributed rather than localized deformation. We explore conditions of distributed deformation as illustrated by the Pelagonian unit in the Aegean subduction system. In particular, we explore the influence of structural inheritance related to the pre-extension shortening and mechanical stratigraphy on the localization of extension on the scale of the upper crust through detailed structural analysis on the islands of Skiathos and Skopelos. Additionally, the time frame of deformation has been established by 40Ar/39Ar dating of key shear zones. Shortening on the islands predominantly took place by ductile top-SW thrusting under low-grade metamorphic conditions, localized in weak calcite marble layers within the Upper Cretaceous and Upper Triassic carbonates at ~55 Ma. We show that the presence of shallow decoupling levels in the upper crust resulted in the formation of thin (several 100 m thick) thrust sheets that are defined for the first time on Skiathos. The Early Paleogene accretion of the Pelagonian upper crust to the upper plate (Eurasia/Rhodopia) was followed by the extensional inversion of the nappe stack. Extension was accommodated by opposite-sense, generally top-NE, ductile to brittle shearing, which localized at inherited heterogeneities such as reverse-sense shear zones and stratigraphic contacts at around 35 Ma, as suggested by our 40Ar/39Ar age spectra. The dense network of such northerly-dipping, inherited weakness zones resulted in a highly distributed pattern of extensional deformation dominated by layer-parallel shearing. We argue that the distribution of crustal heterogeneities substantially influences the style of post-orogenic extension. • Mechanical stratigraphy controls shortening geometries during tectonic burial • Crustal heterogeneities control extensional strain localization • Multiple small extensional shear zones promote layer-parallel shearing • Detachment formation is hindered by the lack of linkages between shear zones [ABSTRACT FROM AUTHOR]

Strength contrasts and spatial variations in rheology are likely to produce significant stress differences in the Εarth's crust. The buildup and the relaxation of stresses have important consequences for the state of stress of the brittle crust, its deformational behaviour and seismicity. We performed scaled analogue experiments of a classic wedge-type geometry wherein we introduced a weak, fluid-filled body representing a low-stress heterogeneity. The experiments were coupled to direct pressure measurements that revealed significant pressure differences from their surrounding stressed matrix. The magnitude of the pressure variations is similar to the magnitude of the differential stress of the strongest lithology in the system. When rocks with negligible differential stresses are considered, their pressure can be more than twice larger than the surrounding lithostatic stress. The values of the pressure variations are consistent with the stresses that are estimated in analytical studies. This behaviour is not restricted to a particular scale or rheology, but it requires materials that are able to support different levels of stress upon deformation. For non-creeping rheological behaviours, the stress and pressure variations are maintained even after deformation ceases, implying that these stress variations can be preserved in nature over geological timescales. [ABSTRACT FROM AUTHOR]

Tearing of the lithosphere at the lateral end of a subduction zone is a consequence of ongoing subduction. The location of active lithospheric tearing is known as a Subduction-Transform-Edge-Propagator (STEP), and the tearing decouples the down going plate and the part of the plate that stays at the surface. STEPs can be found alongside many subduction zones, such as at the south Caribbean or the northern end of the Tonga trench. For the Caribbean, the San Sebastián/El Pilar fault zone represents the surface expression of the wide STEP fault between the Caribbean and South America, and the active STEP is located near Trinidad. However, what parts of the deeper lithosphere participate in the tearing process is largely unknown. Some constraints on the deformation of the deep part of the lithosphere are available from gravity, which suggests significant lateral variability in densities of the lithospheric mantle to the south of the STEP fault zone. A sub-crustal low-density zone beneath northern South America may result from higher sub-crustal temperatures, such as would arise from an asthenospheric window resulting from a wide STEP fault at depth. Here we investigate what controls the evolution and geometry of the lithospheric STEP.We study the ductile tearing in the process of STEP evolution by physical analogue models, which are dynamically driven by the buoyancy of the subducting slab. In our experiments, the lithosphere as well as asthenosphere are viscoelastic media in a free subduction setup. A stress-dependent rheology plays a major role in localization of strain in tearing processes of lithosphere such as slab break-off. Therefore we developed and tested new analogue materials that can serve as mechanical analogues for the stress-dependent lithosphere rheology, such as has been inferred by rock laboratory test for dislocation creep of olivine. We show the influence of age and integrated strength of the lithosphere and its contrasts across the passive margin, on the timing, depth, and the degree of localization of the tearing process. When tearing of the lithosphere is dominated by ductile deformation, we find that gradual necking of the passive margin precedes tearing. Furthermore, we relate the tearing at depth to deformation at the surface during the evolution of the STEP. [ABSTRACT FROM AUTHOR]

Thrusting and extensional exhumation in an Accretionary Wedge: The Paleogene evolution of the Northern Sporades (Greece)Kristóf Porkoláb1, Ernst Willingshofer1 Dimitrios Sokoutis1, Iverna Creton1, Jan Wijbrans21 Faculty of Geosciences, Utrecht University, Utrecht, Netherlands,2 Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, NetherlandsAbstractWe present a study on the latest Cretaceous - Paleogene tectonic evolution of the Northern Sporades islands (Greece) using multi-scale structural analysis and white mica Ar/Ar dating. We show new geological maps, cross sections, and kinematic datasets from the islands of Skiathos, Skopelos, and Alonnissos. Structural observations are supplemented by the Ar/Ar dating of mylonitic sericite foliations. The Northern Sporades are part of the Pelagonian zone that experienced burial and exhumation related to the Aegean subduction system in Late Cretaceous-Paleogene times. The islands largely consists of metasediments that belong to 1) a Paleozoic to Jurassic passive margin succession (Pelagonian and Eohellenic units), and 2) an Albian to Paleocene succession that transgresses the older formations (Mesoautochtonous and Palouki units).Tectonic burial by top-SW thrusting initiated in the latest Cretaceous – Early Paleocene, and resulted in the stacking of the outcropping geological units of the islands. All the formations were buried to greenschist facies conditions, where shortening was largely accommodated by the formation of reverse-sense shear zones. These shear zones localized along pre-existing weak zones such as marble layers in the Cretaceous strata and resulted in the formation of thin thrust slices. Between the shear zones, distributed top-SW to top-S shearing is observed which is especially pronounced on Skiathos. Mylonitic sericite foliations of Skopelos which are most likely related to top-SW burial yield Ar/Ar ages between 75 and 54 Ma. Top-SW thrusting was followed by top-NE shearing related to the extensional exhumation of the formations. Top-NE shear zones localized at pre-existing stratigraphical and tectonic contacts, and are subparallel with the main foliation. These shear zones may have a minor to medium (few 100 or 1000 m) displacement and consequently do not cut out major parts of the stratigraphy. However, they triggered distributed top-NE shearing between the shear zones that is especially characteristic on Skopelos. Ductile top-NE shearing was gradually replaced by normal faulting which was driven by both NE-SW and NW-SE extensional directions. Normal faults are characteristic features of the whole Northern Sporades and are linked to the formation and evolution of the North Aegean Trough. Our kinematic dataset (stretching lineations and shear sense indicators) shows that Skiathos and Skopelos shares the characteristic directions of top-SW burial and top-NE exhumation which is in good agreement with regional constraints. However, the same dataset on Alonnissos deviates from that by ~ 90°, possibly implying extreme post-Eocene vertical axis rotation of the island. [ABSTRACT FROM AUTHOR]

Basin inversion involves the reversal of subsidence in a basin due to compressional tectonic forces, leading to uplift of the basin's sedimentary infill. Detailed knowledge of basin inversion is of great importance for scientific, societal, and economic reasons, spurring continued research efforts to better understand the processes involved. Analogue tectonic modelling forms a key part of these efforts, and analogue modellers have conducted numerous studies of basin inversion. In this review paper we recap the advances in our knowledge of basin inversion processes acquired through analogue modelling studies, providing an up-to-date summary of the state of analogue modelling of basin inversion. We describe the different definitions of basin inversion that are being applied by researchers, why basin inversion has been historically an important research topic and what the general mechanics involved in basin inversion are. We subsequently treat the wide range of different experimental approaches used for basin inversion modelling, with attention to the various materials, set-ups, and techniques used for model monitoring and analysing the model results. Our new systematic overviews of generalized model results reveal the diversity of these results, which depend greatly on the chosen set-up, model layering and (oblique) kinematics of inversion, and 3D along-strike structural and kinematic variations in the system. We show how analogue modelling results are in good agreement with numerical models, and how these results help researchers to better understand natural examples of basin inversion. In addition to reviewing the past efforts in the field of analogue modelling, we also shed light on future modelling challenges and identify a number of opportunities for follow-up research. These include the testing of force boundary conditions, adding geological processes such as sedimentation, transport, and erosion; applying state-of-the-art modelling and quantification techniques; and establishing best modelling practices. We also suggest expanding the scope of basin inversion modelling beyond the traditional upper crustal "North Sea style" of inversion, which may contribute to the ongoing search for clean energy resources. It follows that basin inversion modelling can bring valuable new insights, providing a great incentive to continue our efforts in this field. We therefore hope that this review paper will form an inspiration for future analogue modelling studies of basin inversion. [ABSTRACT FROM AUTHOR]

• Spatially heterogeneous fault gouges exhibit transient changes of friction and rate dependence related to the amount of displacement. • Clay smearing and shear localization on continuous foliation planes are responsible for strong weakening and a shift from velocity-weakening to velocity-strengthening behaviour. • Incorporation of quartzofeldspathic grains and disruption of the continuity of foliation planes in the principal slip zone cause strengthening. • The velocity dependence of Slochteren sandstone gouge obtained in this study, better explain the depth range of observed induced seismicity in the Groningen reservoir. Along-fault lithological heterogeneity is observed in all fault zones that cross-cut compositional layering. Numerical modelling studies on fault rupture nucleation, propagation and arrest often assume that the fault mechanical behaviour is governed by either the rheologically weak phase or by a homogeneous gouge mixture of juxtaposing lithologies. However, the effects of spatial heterogeneity on fault gouge composition and hence its frictional behaviour are less known. In this study, we simulate a mixture of mechanically contrasting rheologies of claystones and sandstones in fault gouges by using lithologies available in the well-known Groningen gas field stratigraphy (Ten Boer and Slochteren members, respectively). Friction experiments were performed in a rotary shear configuration to accommodate the large displacements required to study mixing and clay smearing in faults with large offsets. A velocity stepping procedure was conducted to quantify the rate-dependence of friction and its evolution with displacement. A spatial heterogeneity was introduced by segmentation of the simulated gouge in claystone and sandstone patches. In contrast to previous studies, we show that Slochteren sandstone gouges can exhibit velocity-weakening behaviour related to strain-localization in a principal slip zone with reduced grain size. Our experiments on segmented gouges show displacement-dependent changes in the sliding friction and its rate-dependence. Clay smearing and shear localization on foliation planes cause weakening of the gouge and a shift from velocity-weakening to velocity-strengthening behaviour. Progressive shearing leads to juxtaposition of sandstone segments that are separated only by a thin clay smear. We propose that the associated increase in friction is caused by lithology mixing at the interfaces between the clay smear and the bulk Slochteren sandstone gouge, and by the disruption of continuous Y-shears. Progressive shearing does not lead to a decrease in the rate-sensitivity parameter (a-b). This observation suggests that shearing remains localized on phyllosilicate foliations, possibly accommodated by the increased width of the principal slip zone (PSZ) with displacement. Our results show that fault friction and its rate-dependence are not simply governed by the weakest lithology along a fault plane, nor that they can be simply represented by a homogeneous mixture of the juxtaposing lithologies. Detailed knowledge of the stratigraphic layering in combination with the fault offset is required to predict the macroscopic frictional behaviour of heterogeneous fault gouges. [ABSTRACT FROM AUTHOR]

Abstract Stress-dependent nonlinear upper mantle rheology has a firm base in rock mechanical tests, where this nonlinearity results from dislocation creep of minerals. In the last few decades there has been some attention to nonlinear, power-law, materials for application in scaled analogue experiments for tectonic processes. However, studies describing the rheology of analogue materials with the same nonlinear dependency on stress as observed for lithospheric mantle materials at relevant stress levels, are still lacking. In this study we have developed and rheologically tested materials based on combinations of silicone polymers and plasticine, with the aim of obtaining a material that can serve as a laboratory analogue to the power-law rheology of olivine aggregates at lithospheric mantle conditions. From our steady-state creep tests we find that it is possible to obtain such a power-law material, with effective viscosities over relevant model stress ranges [5–4000 Pa] that allow for nonlinear deformation at laboratory time scales. We apply the developed material to a process where localized deformation of the lithosphere can be expected: slab break-off. We study this process using analogue models, where we apply the new nonlinear material to the lithospheric mantle domains, while we use Newtonian glucose to represent the low viscous asthenosphere. Now that we properly manage power-law behavior in our analogue lithosphere materials, we are able to model localized lithospheric tearing. Highlights • New materials to represent the lithospheric mantle in analogue models. • find power-law behavior comparable to olivine rheology. • We observe localized deformation in an analogue slab break-off model. [ABSTRACT FROM AUTHOR]

Abstract The evolution of relict fore-arc basins and their kinematic relationships with sedimentation is often less well understood due their fragmentation or amalgamation of individual basins and continental units by the subsequent collision or other post-orogenic deformation. One example is the Cretaceous–Paleogene closure and associated sedimentation of the Neotethys Ocean that was located between the European and Adriatic continental units. Our combined structural, lithostratigraphic and sedimentological study in the NE Dinarides of Serbia demonstrates a variable Cretaceous fore-arc deposition on the European plate that correlates with the shallow- to deep-water sedimentation over the subducting Adriatic margin. The fore-arc was affected by an initial Early Cretaceous–Cenomanian period of contraction, followed by Turonian–Santonian extension, the basin being exhumed by contraction during the latest Cretaceous–Early Paleogene collision. The collisional geometry was subsequently fragmented by structures associated with the Neogene evolution of the Pannonian Basin. The correlation with the preserved amount and depositional character of Cretaceous trench sediments documents an interplay between subduction accretion and subduction erosion associated with external tectonic forcing, slab retreat and back arc extension. Highlights • Cretaceous - Early Paleogene evolution of the subduction – fore-arc – back-arc system in the NE Dinarides • A dynamic forearc – trench – foreland system integrates complex deformation histories and associated deposition • Sedimentation controlled by interplay between subduction accretion and subduction erosion associated with slab retreat • Regional Turonian - Senonian extension in the European fore-arc and back-arc domain controlled subduction-related magmatism • Entire subduction/collision system subsequently affected by Miocene extension of the Pannonian Basin [ABSTRACT FROM AUTHOR]

The Main Ethiopian Rift, East Africa, is characterized by the presence of major, enigmatic structures which strike approximately orthogonal to the trend of the rift valley. These structures are marked by important deformation and magmatic activity in an off-axis position in the plateaus surrounding the rift. In this study, we present new structural data based on a remote and field analysis, complemented with analogue modelling experiments, and new geochemical analysis of volcanic rocks sampled in different portions of one of these transversal structures: the Goba-Bonga volcano-tectonic lineament (GBVL). This integrated analysis shows that the GBVL is associated with roughly E–W-trending prominent volcano-tectonic activity affecting the western plateau. Within the rift floor, the approximately E–W alignment of Awasa and Corbetti calderas likely represent expressions of the GBVL. Conversely, no tectonic or volcanic features of similar (E–W) orientation have been recognized on the eastern plateau. Analogue modelling suggests that the volcano-tectonic features of the GBVL have probably been controlled by the presence of a roughly E–W striking pre-existing discontinuity beneath the western plateau, which did not extend beneath the eastern plateau. Geochemical analysis supports this interpretation and indicates that, although magmas have the same sub-lithospheric mantle source, limited differences in magma evolution displayed by products found along the GBVL may be ascribed to the different tectonic framework to the west, to the east, and in the axial zone of the rift. These results support the importance of the heterogeneous nature of the lithosphere and the spatial variations of its structure in controlling the architecture of continental rifts and the distribution of the related volcano-tectonic activity. [ABSTRACT FROM AUTHOR]

The evolution of oroclines is often driven by the interplay of subduction and indentation associated with complex patterns of deformation transfer from shortening to strike-slip and extension. We study the kinematics and mechanics of indentation in an orocline with a backarc-convex geometry, the European Carpatho-Balkanides Mountains. Within this orocline, the kinematic evolution of the Serbian Carpathians segment is less understood. The results demonstrate that the overall deformation was accommodated by the Circum-Moesian Fault System surrounding the Moesian indenter, where strain was partitioned in a complex network of coeval strike-slip, thrust and normal faults. This system represents one of the largest European intracontinental strike-slip deformation zones, with a northward-increasing accumulated 140 km dextral offset along previously known and newly found faults. These strike-slip faults transfer a significant part of their offset eastwards to thrusting in the Balkanides and westwards to orogen-parallel extension and the formation of intramontane basins. The correlation with paleogeographic and geodynamic reconstructions demonstrates that the overall formation of the fault system is driven by subduction of the Carpathian embayment, resulting in laterally variable amounts of translation and rotation associated with indentation of the Moesian Platform. The onset of Carpathian slab retreat and backarc extension at 20 Ma has dramatically increased the rates of dextral deformation from ~3.5 mm/yr to ~2 cm/yr, facilitated by the pull exerted by the retreating slab. Our study demonstrates that indentation requires a strain partitioning analysis that is adapted to the specificity of deformation mechanics and is, therefore, able to quantify the observed kinematic patterns. • Moesian indentation is associated with significant strain partitioning during backarc-convex oroclinal bending. • Strike-slip is partitioned to frontal shortening and orogen parallel extension. • The Circum-Moesian Fault System accommodates one of the largest European intracontinental strike-slip deformations. [ABSTRACT FROM AUTHOR]

Highly curved orogens often demonstrate a complex poly-phase tectonic evolution and significant strain partitioning. While the oroclinal bending towards the outer arc is understood to be often driven by rapid slab roll-back, processes driving such bending towards the back-arc domain are less understood. The Serbian segment of the larger, highly bended Carpathians–Balkanides Mountains is one key example where we studied the kinematics of nappe stacking and the mechanics of oroclinal bending by the means of a field kinematic study correlated with available information in adjacent orogenic segments. Although not apparent in the large-scale structure of the Serbian Carpathians, our results demonstrate a poly-phase evolution, where the late Early Cretaceous nappe stacking was followed by Oligocene–middle Miocene ~40° of clockwise rotations. The superposition of Dinarides extension with the oroclinal bending in the Carpathians created overlapping stages of orogen-perpendicular extension and dextral strike-slip coupled with orogen-parallel extension, driven by the 100 km cumulated offset of the Cerna and Timok Faults. Extension was associated with the formation of Oligocene–Miocene basins, providing critical timing constraints for our kinematic study. These deformations were followed by the late Miocene E -ward thrusting of the Upper Getic sub-unit, which was driven by a transfer of deformation in the orocline and around the Moesian Platform during the last stages of Carpathians collision. These results show that the mechanics of oroclinal bending is associated with the activation of strike-slip faults and strain partitioning by bi-modal extension, enhanced by the overlap between different geodynamic processes. • Orocline formed during coeval bi-directional extensions and strike-slip; • Strain partitioning took place during oroclinal bending; • Late stage E-ward thrusting occurred during Carpathians docking to Moesia. [ABSTRACT FROM AUTHOR]

Continental subduction below oceanic plates and associated emplacement of ophiolite sheets remain enigmatic chapters in global plate tectonics. Numerous ophiolite belts on Earth exhibit a far-travelled ophiolite sheet that is separated from its oceanic root by tectonic windows exposing continental crust, which experienced subduction-related high pressure-low temperature metamorphism during obduction. However, the link between continental subduction-exhumation dynamics and far-travelled ophiolite emplacement remains poorly understood. Here we combine data collected from ophiolite belts worldwide with thermo-mechanical simulations of continental subduction dynamics to show the causal link between the extrusion of subducted continental crust and the emplacement of far-travelled ophiolites. Our results reveal that buoyancy-driven extrusion of subducted crust triggers necking and breaking of the overriding oceanic upper plate. The broken-off piece of oceanic lithosphere is then transported on top of the continent along a flat thrust segment and becomes a far-travelled ophiolite sheet separated from its root by the extruded continental crust. Our results indicate that the extrusion of the subducted continental crust and the emplacement of far-travelled ophiolite sheets are inseparable processes.