Palaeozoic strike-slip rift pulses and palaeogeography in the circum-Mediterranean Tethyan realm

Abstract

Five main rifting cycles, supported by different types of field evidence (including magmatism, sedimentation and tectonics), have been recognized in the circum-Mediterranean area (western Tethys realm) before the opening of the Jurassic Tethys proper. They occurred roughly in the late Cambrian-early Ordovician, early Silurian, late Devonian-Dinantian, early-mid Permian and mid-Triassic times. Each of these rifting cycles began with intracontinental, mainly shallow-marine conditions, evolving usually to basinal environments of quite different bathymetry (the Palaeozoic CCD has been proved to be much less deep than the post Liassic one). Minor suboceanic seaways cut across and fragmented the Gondwana-South European plate following the early Palaeozoic rifting cycles. The long mid Palaeozoic (Devono-Dinantian) rifting cycle migh possibly have resulted in a wider system of suboceanic sea-ways connecting a Palaeo-Tethys ocean to the east of Gondwana with the Rheic ocean to the west of it. The birth of Palaeo-Tethys, or of its westward extension, would have been directly linked with the gradual death of the Devono-Mississippian Rheic Ocean. A complex, large-scale, dextral transform system is inferred to have connected the two respectively expanding and contracting oceans. Fragmentation and mutual displacement of microblocks in the connection area (the circum-Mediterranea area and Southern Europe) resulted from strike-slip, oblique rift pulses with coeval, local contractional and extensional processes. A major change of the Gondwana rotational vector is believed to have produced the mid-late Carboniferous transpressional strike-slip Hercynian orogen. This is a good explanation of the peculiar thermal regime of the Hercynian diastrophism all over Europe. There is no support for the hypothesis of a very wide (more than 3000 km) Palaeozoic ocean separating Northern Europe from Southern Europe or Gondwanaland. This idea was mainly based on poor palaeomagnetic data and is heavily contradicted by palaeobiogeographical and geological data. Furthermore, it ignores the dramatic shortening of the Hercynian orogen all over Europe. The early Palaeozoic to early Mesozoic history of the circum-Mediterranean area involves the cyclic recurrence of oblique rifts, culminating in the early Jurassic strike-slip rift and subsequent limited opening of the Tethys proper. To avoid confusion in terminology, one should use prefixes referring to age, bathymetry-physiography and geotectonic setting to qualifying the general term “Tethys” (e.g., shallow Cretaceous Tethys, basinal intracontinental Devonian Tethys, oceanic Jurassic Tethys, etc.).