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In the Inner Western Alps, three different types of block-in-matrix structures (BIMs) formed sequentially through time at a convergent plate margin. These show the superposition of progressive deformation from (i) subduction to eclogite-facies depths, (ii) collision, accretion, and exhumation of oceanic crust, represented by the Monviso Meta-ophiolite Complex, to (iii) collision, accretion, and exhumation of the continental Dora Maira units. The Type 1 occurs in the metasedimentary cover of the Dora Maira Unit and consists of a map-scale broken formation with boudinaged ‘native’ blocks of marble (Early Jurassic) in a calcschist matrix. It results from the tectonic overprinting of exhumation-related folding (D2-stage) on an earlier subduction-related dismembered succession (D1-stage). Type 1 also includes ‘non-mappable’ BIMs with ‘exotic’ blocks, resulting from the gravitational collapse of the Triassic carbonate platform of European Continental Margin, triggered by the Early Jurassic rifting. In the Monviso Meta-ophiolite Complex, Types 2 and 3 represent tectonically induced broken and dismembered formations, respectively. They differ from each other in the degree of stratal disruption of primary interbedded horizons of mafic metabreccia (Type 3) and mafic metasandstone (Types 2 and 3) sourced by the Late Jurassic–Early Cretaceous denudation of an oceanic core complex. Dismembered interbeds (Type 2) and isolated blocks were mixed together (Type 3) by the overlap of D2 tectonics and late- to post-exhumation extensional shearing (D3-stage). Development of these types of BIMs may be common in many exhumed convergent plate margins, where severe tectonics and metamorphic recrystallization under high-pressure conditions normally prevent the reconstruction of BIMs or mélange-forming processes. Our findings show that documenting the mode and time of the processes forming BIMs is highly relevant in order to reconstruct the oceanic seafloor morphology and composition of associated stratigraphic successions, and their control in the evolution of those convergent plate margins. [ABSTRACT FROM AUTHOR]

In the peri-Adriatic region, melanges represent a significant component of the Apennine and Dinaride-Albanide-Hellenide orogenic belts as well as ancient and present-day accretionary wedges. Different melange types in this broad region provide an excellent case study to investigate the mode and nature of main processes (tectonic, sedimentary, and diapiric) involved in melange formation in contrasting geodynamic settings. We present a preliminary subdivision and classification of the peri-Adriatic melanges based on several years of field studies on chaotic rock bodies, including detailed structural and stratigraphic analyses. Six main categories of melanges are distinguished on the basis of the processes and geodynamic settings of their formation. These melange types are spatially and temporally associated with extensional tectonics, passive margin evolution, strike-slip tectonics, oceanic crust subduction, continental collision, and deformation. There appears to have been a strong interplay and some overlap between tectonic, sedimentary, and diapiric processes during melange formation; however, in highly deformed regions, it is still possible to distinguish those melanges that formed in different geodynamic environments and their main processes of formation. This study shows that a strong relationship exists between melange-forming processes and the palaeogeographic settings and conditions of melange formation. Given the differences in age, geographic location, and evolutionary patterns, we document the relative importance of melanges and broken formations in the tectonic evolution of the peri-Adriatic mountain belts. [ABSTRACT FROM AUTHOR]