PALEOMAGNETIC ROTATIONS IN THE EASTERN BETIC CORDILLERA, SOUTHERN SPAIN

Palaeomagnetic declinations from the External Zones of the eastern Bet ic Cordillera (southern Spain) and an adjacent area of the Internal Zo ne indicate variable and locally very large clockwise rotations. The r otations occurred after latest Oligocene times, and probably before th e tate Miocene. This overlaps a period of dextrally oblique convergenc e during the early to middle Miocene along the Internal/ External Zone Boundary and within the External Zone. Rotations in the External 7-on e are recorded by palaeomagnetic results from 27 sites in Upper Jurass ic (Ammonitico rosso facies) limestones from the Subbetic Zone, and on e site of a similar age from the Prebetic. The sites show either two- or three-component behaviour. The low-temperature component is coincid ent with the present-field direction. The intermediate-temperature com ponent was probably acquired during Miocene folding. The high-temperat ure component passes fold tests (Miocene age) and a conglomerate test (Eocene-early Oligocene age). Palaeomagnetic declinations from individ ual tectonic blocks in the Subbetic are consistent, but indicate large differential rotations between blocks. These blocks are underlain by low-angle thrust faults, which probably accommodated much of the rotat ion. The largest rotations occur on relatively small isolated blocks o f Jurassic carbonates in a highly deformed Triassic evaporite sequence . The single site in the Prebetic has not rotated significantly relati ve to stable Iberia. In Malaguide rocks of the Sierra Espuna, in the a djacent Internal Zone, stable palaeomagnetic components were measured at one site in upper Miocene sedimentary rocks, at three sites in uppe r Oligocene-lower Miocene red marls, at one site in Oligocene marls. a t one site in Jurassic limestones, and at two sites in Permo-Triassic red beds. The palaeomagnetic results suggest that about 60-degrees of clockwise rotation occurred in the latest Oligocene-earliest Miocene, and a further 140-degrees of clockwise rotation subsequently. One site in late Miocene sedimentary rocks yields unrotated declinations which , if not representing an overprinted direction, indicate that the rota tion was complete by the end of the Miocene.