The TRANSMED Atlas. The Mediterranean Region from Crust to Mantle Geological and Geophysical Framework of the Mediterranean and the Surrounding Areas Bearbeitet von William Cavazza, François M. Roure, Wim Spakman, Gerard M. Stampfli, Peter A. Ziegler 1. Auflage 2004. Buch. xxiii, 141 S. ISBN 978 3 540 22181 4 Format (B x L): 19,3 x 27 cm Gewicht: 660 g Weitere Fachgebiete > Physik, Astronomie > Angewandte Physik > Geophysik Zu Inhaltsverzeichnis schnell und portofrei erhältlich bei Die Online-Fachbuchhandlung beck-shop.de ist spezialisiert auf Fachbücher, insbesondere Recht, Steuern und Wirtschaft. Im Sortiment finden Sie alle Medien (Bücher, Zeitschriften, CDs, eBooks, etc.) aller Verlage. Ergänzt wird das Programm durch Services wie Neuerscheinungsdienst oder Zusammenstellungen von Büchern zu Sonderpreisen. Der Shop führt mehr als 8 Millionen Produkte. Chapter 1 The Mediterranean Area and the Surrounding Regions: Active Processes, Remnants of Former Tethyan Oceans and Related Thrust Belts William Cavazza · François Roure · Peter A. Ziegler Abstract 1.1 Introduction The Mediterranean domain provides a present-day geo- From the pioneering studies of Marsili – who singlehand- dynamic analog for the final stages of a continent-conti- edly founded the field of oceanography with the publi- nent collisional orogeny. Over this area, oceanic lithos- cation in 1725 of the Histoire physique de la mer, a scien- pheric domains originally present between the Eurasian tific best-seller of the time (Sartori 2003) – to the tech- and African-Arabian plates have been subducted and par- nologically most advanced cruises of the R/V JOIDES tially obducted, except for the Ionian basin and the south- Resolution, the Mediterranean Sea has represented a cru- eastern Mediterranean. A number of interconnected, yet cible of scientific discoveries. Similarly, the peri-Medi- discrete, Mediterranean orogens have been traditionally terranean terranes on land have been accurately surveyed considered collectively as the result of an “Alpine” orog- over the centuries by amateur, academic and industrial eny, when instead they are the result of diverse tectonic geologists alike, and some locations have represented events spanning some 250 Myr, from the late Triassic to geological training grounds for several generations of the Quaternary. To further complicate the picture, through- Earth scientists. out the prolonged history of convergence between the Although relatively small on a global scale – its area two plates, new oceanic domains have been formed as being roughly equivalent to half of that of the People’s back-arc basins either (i) behind active subduction zones Republic of China – the Mediterranean region has an during Permian-Mesozoic time, or (ii) associated with exceedingly complex geological structure. For example, slab roll-back during Neogene time, when during advanced tectonic activity here spans from the Panafrican orog- stages of lithospheric coupling the rate of active subduc- eny (Precambrian) of the Gondwanan, northern Africa tion was reduced. The closure of these heterogenous oce- craton to the destructive present-day seismicity along anic domains produced a system of discrete orogenic belts the North Anatolian Fault. Many important ideas and which vary in terms of timing of deformation, tectonic set- influential geological models were developed based on ting and internal architecture, and cannot be interpreted research undertaken in the Mediterranean region. For as the end product of a single Alpine orogenic cycle. example, the Alps are the most studied orogen in the Similarly, the traditional paleogeographic notion of a world, their structure has been elucidated in great de- single – albeit complex – Tethyan ocean extending from tail for the most part and has served as an orogenic the Caribbean to the Far East and whose closure pro- model applied to other collisional orogens. Ophiolites duced the Alpine-Himalayan orogenic belt must be dis- and olistostromes were defined and studied for the first carded altogether. Instead, the present-day geological time in this region. The Mediterranean Sea has possibly configuration of the Mediterranean region is the result the highest density of DSDP/ODP sites in the world, and of the opening and subsequent consumption of two ma- extensive research on its Messinian deposits and on their jor oceanic basins – the Paleotethys (mostly Paleozoic) on-land counterparts provided a spectacular example and the Neotethys (late Paleozoic-Mesozoic) – and of for the generation of widespread basinal evaporites. additional smaller oceanic basins, such as the Atlantic Other portions of this region are less well understood Alpine Tethys, within an overall regime of prolonged in- and are now receiving much international attention. teraction between the Eurasian and the African-Arabian Apart from its historical and cultural importance as plates. Paradoxically, the Alps, that have long been con- a crossroad among various religions, trade routes and sidered as the classic example of Tethys-derived orogen, civilizations, the Mediterranean constitues also a geo- are instead the product of the consumption of an east- logical transition between the Middle East and the At- ward extension of the central Atlantic ocean, the middle lantic, as well as between Europe and Africa. For exam- Jurassic Alpine Tethys, and of the North Atlantic ocean, ple, the Mediterranean represents a proxy of the long- the middle Cretaceous Valais ocean. lasting interactions between Eurasia and Gondwana, 2 CHAPTER 1 · The Mediterranean Area and the Surrounding Regions with successive episodes of continental break-up and complex tectonic events which closed different oceanic oceanic development, subduction, continental collision basins of variable size and age (see Stampfli and Borel, and orogeny. The Neotethyan oceanic domain initiated this volume). In addition, some Mediterranean foldbelts during the Permian in the eastern part of the Mediter- developed by inversion of intracontinental rift zones (e.g. ranean, separating progressively the Gondwanan conti- Atlas, Iberian Chain, Provence-Languedoc, Crimea). The nental margin to the south from the Eurasian margin to Pyrenees – somehow transitional between these two end the north. Opening in a scissor-like fashion, the Neo- members – evolved out of a continental transform rift tethys widened toward the east where it was connected zone. with the world ocean, whereas it remained closed to the A large wealth of data – including deep seismic sound- west until the onset of spreading in the central Atlantic ings, seismic tomographies, paleomagnetic and gravity during the Jurassic. As a result, oceanic crust in the for- data, and palinspastic reconstructions – constrains the mer Tethyan domains and in currently allochthonous lithospheric structure of the various elements of the ophiolitic units still preserved in Alpine thrust belts dis- Mediterranean Alpine orogenic system and indicates that play a wide range of ages, depending on whether they the late Mesozoic and Paleogene convergence between are derived from the Neotethys (in areas already oce- Africa-Arabia and Europe has totalled hundreds of kil- anic before the Jurassic) or from younger Piedmont- ometers. Such convergence was accomodated by the sub- Ligurian-Carpathian oceanic domains once connected duction of oceanic and partly continental lithosphere (de with the Atlantic (see Stampfli and Borel, this volume). Jong et al. 1993), as indicated also by the existence of The present-day Mediterranean Sea is a composite ar- lithospheric slabs beneath the major fossil and modern ray of oceanic and continental domains of various af- subduction zones (e.g. Spakman et al. 1993; Wortel and finities, including remnants of the Neotethys in the east- Spakman 2000; Spakman and Wortel, this publ.). The ernmost Mediterranean and the Ionian Sea, neoformed Mediterranean orogenic system features several belts of oceanic basins in the western Mediterranean, and shal- tectonized and obducted ophiolitic rocks which are lo- low epicontinental seas like the Adriatic. cated along often narrow suture zones within the alloch- This contribution is by no means intended as a thor- thon and represent remnants of former extensional ba- ough description of the geological structure of the Medi- sins. Some elements of the Mediterranean orogenic sys- terranean region. This and the following two chapters tem, such as the Pyrenees and the Greater Caucasus, may by Spakman and Wortel and by Stampfli and Borel aim comprise local ultramafic rock bodies but are devoid of at (i) providing the reader unfamiliar with the Mediter- true ophiolitic sutures. Following is a very concise de- ranean domain with an updated, yet opinionated, over- scription – largely abstracted from the text accompany- view of such complex area, particularly in terms of de- ing the TRANSMED transects – of the main fold-and- scription of those geological-geophysical features which thrust belts of the Mediterranean orogenic system. the authors deem representative, and (ii) setting the stage The Pyrenees run between the Bay of Biscay and the for the TRANSMED CD-ROM which contains detailed Gulf of Lion for a length of about 450 km and a width of information on the majority of the most significant ar- 50–100 km. In spite of some differences in terms of chro- eas of the Mediterranean. Fulfilling these tasks clearly nology and structural style, the Pyrenees are physically involved (over)simplification of a complex matter and