origin of the Canary Islands, from the Ancient World to the present, is carried out.
This ... This is the case of the hot spot, propagating fracture, uplifting blocks, and ...
The Origin of the Canary Islands A chronology of ideas and related concepts, from the Antiquity to the end of 20th century*. Cándido Manuel García Cruz Member of INHIGEO I.E.S Mencey Acaymo, Güímar, Tenerife, Canary Islands, Spain e-mail: [email protected]
Abstract A chronological statement of both major ideas and other related concepts concerning the origin of the Canary Islands, from the Ancient World to the present, is carried out. This origin has had some bearing on some catastrophe myths such as Atlantis or Noah’s Flood. The first geological hypotheses were suggested early in the 19th century, namely the elevation craters and the “continentalisation" of this archipelago. Plate Tectonics, which are the framework for the more modern hypotheses (hot spot, uplifting blocks, synthetic model, and so on), have not been able to solve this problem. On the contrary, the genetic models have multiplied to become ad hoc situations in some cases (e.g. blob model). Maybe a more reliable theory of the origin of the Canary Islands could be found in an eclectic model related to African plate dynamics, as suggested by the unifying model. A bibliographical revue concerning this subject is included.
“Mind the volcano!” “What volcano?” said the King, looking up anxiously into the fire, as if he thought that was the most likely place to find one. LEWIS CARROL Through the looking-glass (1872)
Presentation The Canary Islands form a volcanic archipelago placed on the Northwest continental margin of the African plate, and have been a matter of great interest for earth scientists. The suggestions explaining the origin of Canarian archipelago have really been diverse throughout its history, and even in the present day its origin continues to be controversial. In this paper I shall present the evolution of all these ideas in a simple chronological way (year, author, suggestion), including any major geological concepts that have had repercussions on the origin of the Canaries. From the Ancient World and for many centuries, the Canary Islands have been related to myths and catastrophe stories, such as Atlantis and the Noah’s Flood. The islands' origin starts to be included in the geological phenomenology only from the 19th century, e.g. with the theory of elevation craters and the African “continentalisation” of the islands. With the development from the 1960s of the new basic ideas belonging to Plate Tectonics, *
Originally published by INHIGEO (International Commission on the History of Geological Sciences). Sidney (Australia), October/2001.
several hypotheses were also promoted which either directly or indirectly had a bearing on the origin of the Canary Islands. This is the case of the hot spot, propagating fracture, uplifting blocks, and the synthetic models. Although the new paradigm has opened new prospects of researches in Earth Sciences, it is, however, necessary to place on record that within this framework the problem of the origin of the Canarian archipelago has not been solved. Mobilist geology has allowed us to distinguish with enough reliability the ideas that we should discard, such as Atlantis, the elevation craters, or the “continentalisation” of the islands. The genetic hypotheses, however, have multiplied with the new geology, and occasionally theses are nothing but ad hoc suggestions adding to the multiplicity and the confusion. Over and over again in the history of the scientific knowledge especially in geology, the following has been repeated: different scientists, analysing the same phenomenon, with the same facts, samples, data, and evidence, produce explanations which are totally different, and generally suggest that in some cases those explanations would be totally incompatible, with no possibility of any agreement between them. Let's take an obvious example, a recent paper on stratigraphic inversion (Cross and Lessenger, 2000)1, which starts as follows: “Ten geologists observe an outcrop of strata and produce eleven interpretations (one geologist had a change of mind), and all interpretations are considered equally valid” In other words, we are, maybe unconsciously, immersed in an Alice in Wonderland situation, and we are disconsolately “stripping the leaves off the daisy” of the Canaries origin: some researchers claim some suggestions with a vehemence that is equally denied by others. Thus, the petals have been stripped off, and they are nothing but the Humpty Dumpty’s “glories”: African plate: it moves-it does not move; thermal anomaly: it exists, it doesn't exist; fracture; it propagates-it does not propagate; uplifting blocks: they are noticed-they are not noticed; Canarian volcanism and Atlas tectonics: they are related-they are not related; rift: it exists-it doesn't exist; seismic profiles: they support-they contradict; magma blobs: what blobs?... In this sense, far from trying to present a synthesis of those rather likely hypotheses, are we not truly, such as in other geological cases, facing a problem whose future solution should be irredeemably looked for in eclectic terms? Maybe any of the above phenomena are either occurring simultaneously, or occurred in any time during the history of the Atlantic Ocean, around the Canarian zone. Mantel anomalies, failed triple-junctions, crustal weakness, unsuccessful rifts, transcurrent and propagating fractures, (incipient subduction?), magma blobs, uplifting blocks, in relation to (either as a whole or to any extent) the Moroccan Atlas dynamic, and so on... Maybe any of those phenomenon triggered off the other ones, but which one? With which one must we begin? Could it be, in fact, that what we were watching in the present-day is nothing but the consequences of a process of chain reaction which has, either overlapping or not, expanding throughout the last 25-30 Ma, or more? If the causal explanation about the origin of the Canary Islands has any bearing on this former reflection, I would finish this paper using the title of an interesting article of Officer and Drake 1
CROSS, T.A. & LESSENGER, M. (2000). The scientific basis for stratigraphic inversion. Geol. Soc. America Bull. (in press).
(1989)2 about the great extinction of the end of Cretaceous period: “We know the answers, but what is the question?” Then, I show the major ideas concerning this interesting subject. But when you finished reading this chronology, maybe you will think like me that the Chilean poet Pablo Neruda was perhaps right when he wrote: “Todas las islas del mar las hizo el viento” (All the islands of the sea were done by the wind). All the while, I am beginning to believe it! Acknowledgements. I am in debt to the following people for their assistance and suggestions: Francisco Anguita, Telesforo Bravo, Michel Duran-Delga, Francisco Hernán, David Oldroyd, and Maria Wong
CHRONOLOGY Ancient World -The Canarian Archipelago has a bearing on Atlantis, among other myths. 1665 -KIRCHER is a supporter of the Atlantis theory. 1669 -STENO, regarding uniformitarianist ideas, sheds doubt on the Platonian myth. 1695 -WOODWARD asserts that Noah’s Flood shaped the islands. 1776 -VIERA Y CLAVIJO supports the idea that Canaries are the remains of Atlantis. 1778 -BUFFON also supports Atlantis as the origin of the islands and other lands. 1803 -BORY DE SAINT-VINCENT draws an Atlantis chart in the Canarian zone. 1820-25 -BUCH suggests the elevation craters hypothesis. 1825 -CUVIER supports the Atlantis cataclysm. 1830 -LYELL is opposed to BUCH’s ideas, and supports an origin due to volcanic accumulation. 1845 -HUMBOLDT is a supporter of the elevation craters hypothesis. 1855 -MAURY, with the first undersea chart of the Atlantic Ocean, provides evidence about the existence of the mid-Atlantic ridge. 1867-68 -FRITSCH also supports the theory of origin by volcanic accumulation. 2
OFFICER, C.B. & DRAKE, C.L. (1989). Cretaceous/Tertiary extinctions. We know the answers, but what is the question? EOS, Am. Geophys. Un., Trans., 70(25), 659-661.
1872-76 -H.M.S. Challenger confirms the existence of mid-Atlantic ridge: some scientific circles see it as the remains of Atlantis. 1876 -CALDERÓN Y ARANA suggests that the Atlantic islands are continental stakes beginning to be formed, rather than remains of a sunken continent. 1910-24 -Several authors (GAGEL, GENTIL, GERMAIN, JEANNEL, LEMOINE, SHARPF) plan the “continentalisation” of the islands associated with the African sial block. 1913 -GENTIL posits that the Canaries are like a prolongation of the Atlas range, penetrating and standing out from the ocean. 1915-29 -WEGENER frames the origin of Canaries within the continental drift, similar to African island festoons after the opening of the Atlantic Ocean. 1938 -LE DANOIS places Atlantis in the Canarian zone, regarding it as a land-bridge. 1939 -CLOOS suggests the model of crust doming by three-armed rift in intra-continental rifting. 1942 -BETZ & HESS propound the propagating fracture model for the Pacific Ocean. 1945 -BENÍTEZ PADILLA rejects the connection of the origin of the Canary Islands with the continental drift. 1951 -MARTEL SAN GIL explains the Canarian volcanism as a result of rifts and folds in the sial because of simatic currents promoted by the tendency towards isostatic equilibrium. 1954 -BRAVO regards the origin of the Canary Islands in the frame of an alternating mixed volcanism (both continental and oceanic). 1958 -HAUSEN, with regard to the existence of old blood basalts of a great thickness, suggests that the Canarian Archipelago was a portion of an African peninsula which underwent tectonic rifting, giving rise to the different islands. 1960-62 -HESS suggests the sea-floor spreading hypothesis 1963 -MACAU VILAR rejects also the origin of the Canaries as island festoons after the continental drift. -WILSON draws similarities between the origin of the Atlantic (Canaries among them) and Indian island chains on the sea-floor spreading from the ridges. -WILSON suggests the hot-spot hypothesis for the origin of the Hawaiian Islands. 1965-68 -MCKENZIE, MORGAN, PARKER & WILSON define a dynamic earth: Plate Tectonics is born. 1966 -WILSON propounds the opening-closing cycle of the Atlantic Ocean (Wilson’s Cycle). 1968 -DASH & BOSSHARD consider that in the Canarian zone there is a transitional crust. 4
-ROTHE & SCHMINCKE suppose a mixed origin for the Canaries: continental origin for the eastern islands and oceanic origin for the central and western islands. 1969 -CENDRERO points out compressive structures (folds) in the basal complex of La Gomera Island. 1970 -BOSSHARD & MACFARLANE determine the independence of the islands as blocks isolated from the African continent. The volcanism should probably be due to fracture zones in relation to the tectonics of the Atlas. 1971 -ABDEL-MONEM et al. establish, by radiometric dating, a progression of the ages of the islands, decreasing with the distance to the African continent: thus Lanzarote should be the oldest isle and El Hierro the youngest. -MCDOUGALL develops the model of propagating fracture as the origin of the volcanic island chains with relation to the sea-floor spreading. -MORGAN introduces the concept of the mantle plume in the hot-spot model. 1972 -BURKE & WILSON support the theory that Africa stoped its development more than 25 Ma ago. -BURKE et al. Propound the theory of the motion of the hot-spots of the Atlantic Ocean; however, the Canary Archipelago is not one of that group. -FÚSTER associates the Canary Islands with an old rift near eastern margin of the Atlantic Ocean. -MORGAN supports the existence of a hot-spot under the Canaries. -PITMAN & TALWANI relate the origin of Canaries to transcurrent faults and fractures. 1973 -HERNÁNDEZ PACHECO & IBARROLA define the major tectonic trends of the Canarian archipelago with regard to petrologic and geochemical studies. -RICHTER propounds, as an alternative to the hot-spot hypothesis, the existence of magmatic lobules in convective cells due to the different motion between lithosphere and asthenosphere. -SCHMINCKE supports the hot-spot model for the Canaries. -TURCOTTE & OXBURGH relate the Canarian volcanism to zones of crustal weakness. -WILSON considers the Canarian hot-spot as stationary. 1974 -ANGUITA & HERNÁN apply the propagating fracture model to the genesis of the Canary Islands in relation to the Atlas fracture. -BECK & LEHNER consider the volcanics of the eastern Canaries are held up by a Hercinian folded and uplifted basement. At the same time, they propound prolonging the southern Atlas fault to coincide with a fracture line of the archipelago (trend ENE). -DILLON & SOUGY relate the origin of Canaries to fault zones off the African continental margin, deducing that the Anti-Atlas does not continue to the ocean. -ROTHE continues to defend the theory of a mixed origin to the Islands. -SCHILLING & NOE-NYGAARD propound the blob-model for the Färoe-Iceland plume. 1975 -ARAÑA et al. propound the uplifted blocks hypothesis, relating it to the existence of reverse faults. -FÚSTER continues to associate the origin of the Canaries to fractures and an old rift. -HAYES & RABINOWITZ deduce by mean of magnetic analyses an oceanic crust under the Canaries. 5
1976 -BURKE & WILSON place (graphically) two hot-spots in Canaries. 1977 -HERMAN et al. relate the origin of Canaries to the uplifting of convective magmatic lobules caused by the stopping of the African plate over the asthenosphere in motion. 1979 -CARRACEDO finds major constraints in applying the hot-spot model in the Canaries. -ROBERTSON & STILLMAN are supporters of the propagating fracture, finding recumbent folds in the basal complex of Fuerteventura. 1981 -BANDA et al. confirm the oceanic nature of the crust under Canaries. -DUNCAN establishes the motion of the African plate for the last 60 Ma as 1 cm/year. 1982 -ANDERSON posits the supercontinent cycle, whose driving force is both conduction and loss of heat through the earth crust. -HINZ et al., by mean of seismic profile, consider that there is no relation between the Canary Islands and African continental tectonics. -SCHMINCKE insists on the relation of the Canarian volcanism to asthenospheric rather than lithospheric characteristics. 1985 -DAÑOBEITIA, by mean of undersea geophysical studies, supports the theory that there is no connection between the Canarian volcanism and Atlas tectonics. -PHILLPS & BROWN determine the motion of the African plate as a slow displacement (0.75 cm/year). 1986 -JUNG & RABINOWITZ observe neither bathymetrical doming nor high anomalies of geoid on the Canarian zone. -NANCE et al. & WORSLEY et al. develop the supercontinent cycle. -SURIÑAC studies by means of deep seismic profiles the crustal structure of the Canaries, deducing to some extent support for both propagating fracture model and the uplifted blocks hypothesis. 1988 -FILMER & MCNUTT consider that the hot-spot model is not in line with both the geoid increase and the lithosphere thickness (about 48 km) in this area. 1990 -SLEEP relates some kinds of intraplate volcanism to both incipient continental rifting and intraplate stresses, rather than to hot-spots. 1991 -HOLIK et al. support the hot-spot and its influence on the Moroccan coast. -ROEST et al. confirm the oceanic nature of the crust under the Canaries. -ARAÑA & ORTIZ maintain the existence of uplifted blocks as the origin of the archipelago. 1992 -COELLO et al. through new radiometric dating, establish that Fuerteventura (20.6 Ma) is older than Lanzarote (15.5 Ma). 1993 -HOERNLE & SCHMINCKE apply the blob model to Canaries. 1994 -CARRACEDO supports the Canarian hot-spot. -WATTS relates the crustal weakness in the Canarian zone to thermal perturbations caused by an underlying mantle plume. 6
1995 -HOERNLE et al. detect by means of seismic tomography a high thermal anomaly in the Canarian area, though not directly under the archipelago. 1996 -BEAUCHAMP et al. interpret the Atlas fault as an aborted rift system, and the tectonic intersection between the Middle Atlas and High Atlas as a failed triple junction. -GUILLOU et al. confirm that there is not a total age progression in the islands, where, for example, La Gomera (12.0 Ma) is older than Tenerife (7.5 Ma). -SOCÍAS & MEZCUA, by mean of an aeromagnetic study, determine the existence of great tilted blocks in the insular basement. 1997 -CARRACEDO et al. do not find a total age progression in the islands. -FERNÁNDEZ et al. study the basal complex of Fuerteventura, and relate it to both extensional tectonics (transtensive system) and mantle anomalies in the oceanic crust. -HOFMANN relates a certain intraplate volcanism to local fusion anomalies on the oceanic floor rather than to hot-spots. -NEUMANN et al. compare the thickness of lithosphere in the archipelago: concluding that it is thinner in its eastern end than in the western one, and that the thermal anomaly must be placed in the Lanzarote zone. -OYARZUN et al. take up again the idea of a local rift. 1998 -CARRACEDO et al. claim the Canarian hot-spot is at present found under the La Palma and El Hierro islands. 1999 -GREVEMEYER asserts the Canarian basin has the typical aspect of a radial swelling of thermal origin. -ANGUITA and HERNÁN analyse several pieces of evidence about the “African connection” to the origin of the Canary Islands and put forward the synthetic hypothesis (unifying model). 2000 -ANGUITA & HERNÁN suggest the synthetic hypothesis (unifying model) as the origin of the Canaries. -DAÑOBEITIA & CANALES support the idea of a Canarian hot-spot with new geological and geophysical evidence.