Along-strike variations of fold and thrust belt architecture and tectonic evolution revealed by 3D structural modelling of the outer Albanides

Seismic interpretation, cross-section balancing and sequential restoration unravel how inherited (rifted continental margin-related) and syn-kinematic stratigraphy, structural features and rheology played different roles at various times and locations along the fold and thrust belt to produce major changes in structural style in the outer Albanides. Different processes appear to have concurred to slowdown and/or arrest detachment-dominated thrusting of the sedimentary cover during a late-stage (<5 Ma) switch from thin-skinned to thick-skinned thrusting. In the northern outer Albanides, the limited thickness of Triassic evaporites inhibited thrust belt propagation within the Ionian basin succession, favoring further advancement of the detached carbonate platform (Kruja) units in its hanging wall. The rapid accumulation of an up to 10 km thick succession of syn-tectonic strata in the Peri-Adriatic Depression likely had a twofold effect of: (i) stopping detachment-dominated thrust belt propagation into the foredeep strata; and (ii) providing a burial that substantially contributed to thermal weakening of the crust. On the other hand, in the southern outer Albanides the Ionian basin carbonate succession, here overlying thick Triassic evaporites, was intensely shortened. Folding and detachment-dominated thrusting proceeded efficiently up to the western margin of the basin. There, normal faults controlling the platform-to-basin transition and the reduced thickness of the Triassic evaporites at the base of the Sazani (Apulia) carbonate platform succession hindered thrust belt propagation into the thick shallow-water carbonate succession. The latter was later broadly folded and significantly uplifted above regional by deformation associated with the crustal thrust ramp controlling the present-day blind thrust front in this southern sector of the belt. In this region, tectonic burial – produced by the imbricated and thickened sedimentary cover – rather than sedimentary burial likely contributed to thermal weakening of the crust. 3D structural modelling effectively shows the role of major, inherited transverse structures in compartmentalizing fold and thrust belt architecture and tectonic evolution.