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Part 2: Margin Overviews |
Department of Tectonics, Faculty of Earth Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands bert{at}geo.vu.nl
The geological record of the currently exposed South Alpine transect of the Mesozoic passive continental margin provides information on the evolution of Atlantic-type margins. Before the onset of rifting, in Mid-Triassic to Carnian time, strong subsidence affected the central parts of the Southern Alps, in the Lombardian basin. No major fault is documented for this time span. Thermal conditions were strongly perturbed. Continental rifting began in Norian times, and until the beginning of the Liassic period was characterized by overall subsidence of the Lombardian basin with rates up to 200 mm ka–1. The strong subsidence is a result of continuing extension and of generalized crustal cooling. Subsidence rates were still important in Liassic times, although lower than in Late Triassic time. At the end of the Liassic period, the site of extension shifted towards the west, where crustal break-up eventually took place in Mid-Jurassic times. Previously poorly documented features such as the very strong subsidence in the initial rifting stages, the changing geometry and mechanics of normal faults are here associated with the thermal interactions between pre-existing thermal anomalies and rifting.
