Deep Origin of the Dome-Shaped Hyblean Plateau, Southeastern Sicily: A New Tectono-Magmatic Model

摘要

Southeastern Sicily is characterized by a prominent topography known as the Hyblean Plateau. It is commonly considered as a flexural bulge formed by the northwest plunging of the Hyblean-Malta platform beneath the Sicilian Fold and Thrust Belt. However its noncylindrical shape and multiphase uplift history correlated to the Late Miocene and Plio-Pleistocene volcanism outline a possible magmatic control on the Hyblean Plateau topographic expression. We argue, using 2-D flexural models, that the flexural bending alone is unlikely to explain the high anomalous elevation of the Hyblean Plateau. Moreover, topographic analysis show that the Hyblean Plateau has a dome shape composed of radially tilted preserved surfaces defining individual blocks. The block edges seem to be related to deep-seated inherited faults. Using an analogue modeling approach, we show that magmatic intrusions beneath the thick Meso-Cenozoic sedimentary cover can reproduce the first-order morphology of the Hyblean Plateau when a structural inheritance is imposed. Accordingly, we propose a tectono-magmatic model that favors mafic sill intrusions as the major uplift source for the topographic anomaly. However, to explain the strong positive Bouguer anomaly, a deeper high-density intracrustal body is needed. Moho uprising related to Mesozoic rifting or mafic lower crust underplating/intraplating since the Late Cretaceous can be evoked. The small wavelength of the topography and the deep intracrustal mass anomaly makes the lithospheric elastic stresses sufficiently high to maintain a nonisostatic state over the geological time scales.