Rift-enhanced foredeep and contractional tectonics interplay in the outer Albanides

Abstract

The Albanides thrust belt is associated with the ENE-ward subduction of the Adriatic lithosphere facing the Peri-Adriatic Basin, a foredeep filled with a Neogene-Quaternary sedimentary sequence more than 6 km thick. This basin segment is anomalously deep, compared to the adjacent foredeeps, and dominated by Neogene strata deposited at a rate of circa 0.3–0.4 mm/yr. Moreover, the Upper Miocene deposits of the Peri-Adriatic Basin lie on deeply eroded anticlines composed of Meso-Cenozoic carbonate units. This observation is in contrast with the expected constant steady-state fold uplift trend generally observed in orogens related to E-NE directed subductions. These observations suggest that following a Late Oligocene to Early-Middle Miocene contractional tectonic phase associated with subaerial erosion, the northern portion of the frontal zone of the outer Albanides accretionary prism was affected by strong subsidence during the Late Miocene. Evidence from field mapping combined with the integration of exploration wells and seismic reflection profiles indicate that this unexpected subsidence may be related to a Miocene extensional/transtensional tectonic phase. The actual anomalously high heat flow (>80 mW/m2) in the offshore depocenter of the Peri-Adriatic Basin also supports this interpretation.This extensional tectonic phase was unrelated to the subduction process, suggested by the obliquely orientation of the new basin with respect to the strike of the Albanides thrust belt, also partially superimposed on it. This Miocene event and the associated thermal pulse could have played a crucial role for the generation of hydrocarbons in the Outer Albanides. The tectonic interplay between this rifting episode and the usual foredeep flexural evolution may explain the peculiar evolution of the Outer Albanides and the associated anomalous foredeep. This basin can be defined as a rift-enhanced foredeep generated by two spatially co-existing, but independent tectonic processes, i.e., by the flexural loading exerted by the orogenic fold-and-thrust system and the rifting in the foreland itself.