Abstract We present analogue models that illustrate the tectonic evolution of the continental margin of southwestern Mexico and the Early Cenozoic deformation of the Xolapa complex. Together with geological data they suggest that oblique convergence caused distributed deformation and mountain building near the present-day margin of southern Mexico in a general left-lateral transpressional regime. A similar deformation is also observed north of the Xolapa complex in Maastrichtian to Paleocene sedimentary and volcanic rock units. Since post-Oligocene exhumation of middle crust does not significantly affect Late Eocene to Oligocene volcanic rocks, we infer that the evolution of the transform margin led to the formation of discrete boundaries that eventually decoupled exhumed mid-lower crust from the onshore upper-crust sequences since the Late Eocene.

During the Late Miocene to Pleistocene, Western Anatolia and the Aegean area were affected by scattered alkali basaltic activity that was temporally distinct from the older orogenic magmatism related to the subduction of Africa beneath the Anatolian and Aegean plates. On the basis of geochemical and isotopic data, two groups of alkali basalts have been distinguished. The first group (Foça, Urla, Selendi, Samos, Chios, Patmos, and Psathoura) exhibits a wide variability in isotopic composition ( 87 Sr/ 86 Sr 0.7043–0.7079; 143 Nd/ 144 Nd 0.51278–0.51243) and trace-element distribution (Th/Ta 2.4–12.3; Ba/Nb 14–49) probably acquired from a subduction-related component. The second group (Kula, Biga, Kalogeri, and Thrace), on the other hand, retains typical intraplate features with no subduction-related imprinting ( 87 Sr/ 86 Sr 0.7031–0.7035; 143 Nd/ 144 Nd 0.5130–0.51275; Th/Ta 1.2–1.7; Ba/Nb 5–10). The first group of basalts marks the transition between subduction-related and intraplate activity, characterized by the interaction of a mantle source with residual slab fluids, whereas the second group is an expression of a mantle with any subduction signature. Within the second group, the geochemical and isotope variations highlight the involvement of both mid-ocean-ridge basalt (MORB)–like and ocean-island basalt (OIB)–like mantle domains. Overall, the intraplate character of this alkaline association indicates that the mantle wedge, previously metasomatized by slab-derived material, was replaced by the upwelling of subslab mantle. This process is considered to be the consequence of the extension of the hanging-wall Aegean-Anatolian lithosphere, coupled with the subducted African slab, which was stretched and torn. In this interpretation, the track of the alkali basalts would be a useful marker tool of ruptures in the slab.

The northwestern side of the Sicily Channel in the central Mediterranean has been shaped by the occurrence of two independent tectonic processes that overlap each other, the Maghrebides-Apennines accretionary prism and the Sicily Channel rift. Since at least the Pliocene, these two processes have acted simultaneously, being respectively related to the Apennines subduction and to the African rift. Thrust sheets of the accretionary prism crosscut the almost orthogonal rift-related normal faults and vice versa. Analog modeling supports the kinematics inferred from regional structural data. Alkaline magmatism associated with the rift is more pronounced in the foreland of the prism, where the extension is more concentrated. This peculiar setting confirms how independently geodynamic processes can interact in the same area at the same time, suggesting that plate boundaries are passive features responding to far-field velocity fields of the lithosphere.

Abstract Analogue models of polyphase deformation involving crustal differences in strength, thickness and density give insights into lateral and vertical strain propagation during Late Cretaceous shortening and Early Tertiary left-lateral shearing related to the early development of the North America–Caribbean plate boundary in southern Mexico. Analogue models reproduce a two-phase deformation characterized by a first stage of compression orthogonal to the plate boundary, simulating deformation induced by the Laramide orogeny, followed by a later stage of left-lateral transpression associated with the transfer of the Chortis block from the North American to the Caribbean plate during the early stage of development of the new plate boundary in Early Tertiary times. Based on detailed structural observations in the Guerrero–Morelos platform and the western part of the Mixteco terrane of southern Mexico, we document that a transpressive regime affected continental red bed sequences of Early Paleocene to Late Eocene, and rotated and refolded Laramide structures during this second phase. Our model ends before the transtensional regime that affected the region, which is marked by a volcanic episode of Late Eocene–Oligocene. This change in the deformation regime records the passage of the NW tip of the Chortis block (North America-Cocos-Caribbean triple junction), when subduction replaced transform faulting along the southern Mexico margin. The models focus on the structures formed around the flanks of a thicker/more rigid crustal block that simulates the rock assemblages of the Palaeozoic orogens of southern Mexico (Mixteco–Oaxaca–Juarez block, MOJB). The comparison of the mechanism of deformation of three different analogue models with the natural prototype explains most of the structures observed around the MOJB. Counterclockwise vertical-axis rotations of pre-existing structures in the western flank of the MOJB observed in the Guerrero–Morelos platform are consistent with the modelled structures. Vertical movements of the modelled MOJB induced by the transpressive regime can explain the Papalutla thrust and the basement upheaval and gravitational sliding of the cover in the Tentzo Ranges observed at the western and northern margins of the MOJB, respectively. The growth and propagation of thrusting controlled by the geometry of the block along the eastern margin also correlates with the Vista Hermosa fault. The propagation of strain to the north increases with higher contrast in strength of the thick block with respect to the adjacent modelled crust. Analogue modelling failed to reproduce all the structural details of southern Mexico and, specifically, the structures observed inside the MOJB. The latter, however, are controlled by pre-existing discontinuities, which are not simulated in the model. As a whole, the results demonstrate that crustal heterogeneity in a developing left-lateral plate boundary zone produces a stronger vertical coupling between ductile and brittle crust and a widening of the deformation zone along the margin of the North America plate in southern Mexico.