102 Nature Vol. 251 September 13 1974 result of fast air travel. Indeed, a num­ Sicily's behaviour, however, it is neces­ ism. Basaltic distensive volcanism was ber of cases have been treated in a sary to look at the eastern part, which absent from eastern Skily from the London hospital. Monath (WHO has been a site of dominantly basaltic Upper Cretaceous to the Upper Mio­ Chronic/e, 28, 212; 1974) wrote that a volcanism since the middle Triassic cene. The occurrence of Upper programme of surveillance must be (although only Cretaceous and younger Oligocene-Lower Miocene andesitic instituted both in West Africa and in rocks are exposed). The most recent volcanism suggests, however, that the the developed countries. To this one episodes of (subaerial) volcanism are compression between Africa and should add the provision of hospital represented by Mt Etna and Mt Iblei; Europe was accompanied by sub­ isolation and laboratory facilities in but all volcanic activity before this was duction of the oceanic crust previously selected centres. submarine, giving rise to pillow lavas formed between Sicily and Europe, a and hyaloclastics emitted through proc-ess whkh gave rise to island arc fissures in a carbonate platform. The type volcanism towards the end of the oldest rocks examined palaeomagnetic­ Oligocene. Crustal consumption lasted Sicily as part ally by Barberi and his colleagues were until the Lower Miocene, when the Upper Cretaceous dykes (with continental ·collision occurred; and of Africa potassium-argon ages in the range since the late Miocene Sicily has been from Peter I. Smith 71-84 million years) cutting hyalo­ joined to Europe, as the Iblei palaeo­ ACCORDING to Barberi et at. (J. geophys. clastics of three different Cretaceous magnetic data indicate. Res., 78, 5221; 1973), the southern -outcrops. From Cretaceous to Upper An obvious problem with this scheme Tyrrhenian Sea contains an island arc Miocene no basaltic volcanism occurred is the post Mi·ocene and current basaltic structure which indudes a sediment in the region, although important distensive volcanism in eastern Sicily, filled trench along the Ionian coast of activity has occurred since, principally which is difficult to explain in terms of Calabria, a metamorphic belt stretching in the vicinity of lblei and Etna. The the general tectonic framework of com­ along Calabria into Sicily, a calc­ second set of rocks studied was there­ pression. The explanation put forward alkaline volcanic arc in an advanced fore of Iblei volcanics within the age by Barberi et al. is that continental state of evolution (Eolian Islands) and range 1.7-5.4 million years. collision has occurred at different points a back-arc marginal basin (Tyrrhenian The palaeomagnetic results are along the Sicilian-Calabrian segment of Abyssal Plain). In short, the Tyrrhenian simply stated. The Upper Cretaceous the plate boundary at different times, Sea area is readily interpreted in the pole is consistent with that for Africa possibly because of the irregular shapes light of the destructive boundary obtained by Shazly and Krs (Geal. of the encroaching continents. For between the African and European Rdsch., 62, 212; 1973) but significantly example, the subduction of ·oceanic plates. But where precisely does the different from the mean Cretaceous crust beneath the Calabrian arc is still plate boundary lie in this region? pole for Europe. The Plio-Pleistocene active (hence the Eolian island arc), McKenzie (Geophys. J., 30, 109; 1972) pole for Sicily is consistent with the although the continental nature of the and several other workers have pro­ mean Upper Tertiary-Quaternary poles crust on both sides of the boundary posed that the boundary line actually for the Central European-Russian plat­ suggests that crustal consumption is crosses northern Sicily, in which case form and for the French Massif Central now nearly complete. In any event, most of Sicily will be a part of the lavas and with the Quaternary poles since the Lower Miocene eastern Sicily African plate. New evidence in favour for Africa and Spain (Gerona volcan­ has been the border zone between of this view has now come from two ics). It thus seems that there has been colliding continental blocks and the quite different sources. no significant motion of eastern Sicily oceanic lithosphere subducting beneath Evidence adduced by Barberi et ai. with respect to Africa since the the Calabrian arc, and has thus (Earth planet. Sci. Lett., 22, 123; 1974) Cretaceous. On the other hand, Sicily probably been affected by local disten­ comes from the distribution, age, has moved with respect to Europe since sion, notwithstanding the general over­ nature and palaeomagnetism of volcanic the Cretaceous, but not since the end all compression. rocks in the east of the island, although of the Miocene. The implication, there­ The second piece of evidence support­ the volcanics are only one of five fore, is that (with the probable excep­ ing the view of Sicily as part of Africa principal provinces in Sicily. In the tion of the extreme northeast of the comes from laser geodimeter measure­ extreme south-east lies the Ragusa­ island) Sicily has been part of the ments between the island and Calabria J.blei carbonate platform which is not African plate since the Cretaccous­ on the Italian mainland. Caputo et ai. affected by Alpine f.olding and seems to and thus in all likelihood since at least (Geophys. J., 38, 1; 1974) report six sets be an extension of the Sahara plat.form. the Triassic. of such measurements made between In other words, the southernmost part Barberi and his colleagues then September 1970 and September 1973. of Sicily is apparently linked geologic­ visualise Sicily's fitting into the evolu­ Needless to say, even with lasers it is a ally with Africa-a view supported by tionary pattern of the region in the difficult task to determine the very small the existence of 20 km-thick continental following way. From the Upper Triassic distance changes likely to be involved type crust to the south of the island. to the Upper Cretaceous the African over such a short period: and the Central and western Sicily comprise a plate moved south-easterly with a variations in the lengths of the sides of Mio-Pliocene resedimentation basin' sinistral shear movement with respect the Sicily-Calabria geometric net are and in the north there is a series of to Europe, resulting ina separation of indeed found to be generally smaner flysch nappes ranging in age from the African and European plates and than the measurement errors and data Cretaceous to Miocene. But the the formation of oceanic crust. The corrections. Nevertheless, Caputo and extreme north-east of the island is a northern edge of the African plate (and his colleagues tentatively conclude that crystalline massif forming the continu­ thus Sicily) then underwent distension­ a statistically significant displacement ation of the Calabrian metamorphic a process consistent with the alkalic between Sicily and Calabria took place belt. In other words, the northernmost products of volcanism observed in between September J 970 and June 1971. part of Sicily is apparen,tly linked geo­ Sicily for the relevant period. From the During this period (but not sub­ logically with Europe. The view that Upper Cretaceous to -the present the sequently) Sicily was displaced roughly the Euro-A~rican plate boundary motion of Africa with respect to northwa.rd with respect to the mainland, crosses Sicily is thus supported in gen­ Europe has been mainly compressional implying that it participates in the eral ,tCm1S by the geology. with minor dextral movement-a movements of Africa rather than For a more quantitative picture of change also reflected in Sicilian volcan- Europe. © 1974 Nature Publishing Group