PALEOMAGNETIC ROTATIONS IN THE EASTERN BETIC CORDILLERA, SOUTHERN SPAIN

Palaeomagnetic declinations from the External Zones of the eastern Betic Cordillera (southern Spain) and an adjacent area of the Internal Zone indicate variable and locally very large clockwise rotations. The rotations occurred after latest Oligocene times, and probably before the tate Miocene. This overlaps a period of dextrally oblique convergence during the early to middle Miocene along the Internal/ External Zone Boundary and within the External Zone. Rotations in the External 7-one are recorded by palaeomagnetic results from 27 sites in Upper Jurassic (Ammonitico rosso facies) limestones from the Subbetic Zone, and one site of a similar age from the Prebetic. The sites show either two- or three-component behaviour. The low-temperature component is coincident with the present-field direction. The intermediate-temperature component was probably acquired during Miocene folding. The high-temperature component passes fold tests (Miocene age) and a conglomerate test (Eocene-early Oligocene age). Palaeomagnetic declinations from individual 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 rotation. The largest rotations occur on relatively small isolated blocks of Jurassic carbonates in a highly deformed Triassic evaporite sequence. The single site in the Prebetic has not rotated significantly relative to stable Iberia. In Malaguide rocks of the Sierra Espuna, in the adjacent Internal Zone, stable palaeomagnetic components were measured at one site in upper Miocene sedimentary rocks, at three sites in upper Oligocene-lower Miocene red marls, at one site in Oligocene marls. at 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 rotation was complete by the end of the Miocene.