ICGP is a joint endeavour of UNESCO (United Nations Educational, Scientific and Cultural Organisation) and IUGS (International Union of Geological Sciences).

The International Geoscience Programme (IGCP) 
of the UNESCO and the IUGS

The Rheic Ocean:
Its Origin, Evolution and Correlatives

IGCP Project 497

IGCP 497 Board:
Ulf Linnemann (Germany) (address)
Richard Damian Nance (U.S.A.) (address)
Maarten de Wit (South Africa) (address)
Erdin Bozkurt (Turkey) (address)
Petr Kraft (Czech Republic) (address)
Francisco Pereira (Portugal) (address)
Robin A. Strachan (UK) (address)
Kerstin Drost & Mandy Hofmann (Germany) (address)

The evolution of the Appalachian-Caledonide Orogen is commonly described in terms of the Iapetus Ocean whose opening produced the rifted margin of eastern Laurentia and whose closure resulted in the collision of this margin with Baltica and a variety of peri-Gondwanan terranes. However, the climactic collision in the Appalachian Orogen and much of Eastern and Central Europe was not that of Iapetus closure but that of its immediate successor, the Rheic Ocean. Closure of the Rheic Ocean produced the vast Ouachita-Alleghanian-Variscan Orogen and was one of the principal events in the Late Palaeozoic assembly of the supercontinent Pangaea.

The Rheic Ocean is generally held to have opened between Gondwana and a number of terranes that rifted from the Amazonian-West African margin of Gondwana. Its growth occurred at the expense of the Iapetus Ocean and its closure brought Gondwana into collision with Laurussia during the assembly of Pangaea. Despite its importance during the Palaeozoic, however, the history of the Rheic Ocean has not received the same attention as that of its better-known forerunner, and much controversy surrounds its origin, palaeogeography and evolution. These controversies result from uncertainties in the identification of its rifted margins, in the timing of its initial rifting and rift-drift transition, in its size and geography, and in the geodynamics of its final closure. Lying behind these uncertainties is the broad geographic area to which regions of Rheic geology were scattered following the breakup of Pangaea, including North and Central America, Western, Central and Eastern Europe (including former "Eastern-Block" countries), and Northwest Africa, and the widely varying disciplines involved in its study. As a result, communication between interested geoscientists is impeded by language and cross-disciplinary barriers. To remedy this, we believe it is timely to bring together geoscientists of varying disciplines from each of these areas in order that a more comprehensive understanding of the evolution of this important ocean can be developed. In particular, scientists from less developed nations and former "Eastern-Block" countries will be invited in order to promote information and technology transfer that will both promote the goals of the project and enhance the development of the geosciences in their own countries. The fields of expertise involved (stratigraphy, sedimentology, palaeontology, igneous and metamorphic petrology, geochronology, geochemistry, structural geology, tectonics, palaeogeography, palaeoceanography, geophysics, etc.) span the entire discipline and, because of the vagaries of Pangaea breakup, are developed to differing degrees amongst the countries in which the story of the Rheic Ocean is recorded. Thus, the Czech Republic, for example, possesses vital expertise on the stratigraphy, sedimentology and palaeontology of the Rheic Ocean because of the superb sedimentary record preserved in the Prague Basin, the palaeoecology of which has been used to trace the radiation and extinction events that chart the ocean's evolution. Poland, Germany and Slovakia, on the other hand, possess well-exposed records of the collisional processes that accompanied ocean closure, while Spain and Portugal possess records of its initial rifting, and the United Kingdom preserves vestiges of the ocean itself. The transfer and exchange of this expertise with that from other areas of Rheic geology, for example, the sedimentary records preserved in Morocco and South Africa, the rifting and ophiolitic records preserved in Mexico, and the collisional histories preserved in Turkey, eastern North America and northern South America are central to resolving the ocean's origin and evolution, and its relationship to correlative oceanic tracts, such as proto-Tethys, Tornquist, Aegir and other unnamed seaways in Europe, the Middle East, Kazakhstan, Ukraine, Russia and China, with which it played a collective geodynamic role in the assembly of Pangaea.

Our special topics for investigations on the remnants of the Rheic Ocean will be focused on:

• sutures and related metamorphic units
• subduction complexes and related metamorphic units
• shelf and remnant basins
• continental margins
• magmatic suites
• volcano-sedimentary complexes
• arc remnants and related basins
• character, timing and nature of major unconformities
• character, timing and nature of major shear zones
• reconstruction of rift, drift and collision processes focused on the history of the Rheic Ocean

The main disciplines of geosciences will be:

• Stratigraphy
• Sedimentology
• Palaeontology
• Palaeogeography
• Palaeooceanography
• Igneous and Metamorphic Petrology
• Tectonics
• Structural Geology
• Geochemistry
• Geochronology
• Geophysics (especially Palaeomagnetism)

Duration: 2004-2008

The expected result is a much better understanding of the geodynamic framework of the evolution of the Rheic Ocean and its associated peri-Gondwanan terranes and their evolution with respect to the orogenic processes of the Ouachita-Alleghanian-Variscan Orogen from the Americas to Central Europe and beyond. Related events from other parts of Gondwana and Laurussia will clearify linkages to correlative oceanic tracts and their relationship to Pangaea assembly. Each meeting will produce a published field guide and the papers submitted to the conference are expected to result several theme volumes. A palaeogeographic map of the Rheic Ocean that combines geologic evidence with the palaeomagnetic data base is also planned. In addition, a data base of geochemical and geochronological data for the correlation of tectono-magmatic events will be produced.

Benefit to society: Each meeting will give young scientists (especially those from developing and former eastern-block countries) a chance to present the results of their research to an international audience and make vital contacts with interested scientists from around the world.

Countries agreeing to cooperate: Austria, Brazil, Canada, China, Columbia, Czech Republic, France, Georgia, Germany, Ireland, Italy, Kazakhstan, Mexico, Morocco, Mauritania, Poland, Portugal, Romania, Russia, South Africa, Spain, Slovakia, Switzerland, Turkey, U.K., Ukraine, U.S.A., Venezuela.

2007 (i) Conference (Joint meeting of IGCP 485 and IGCP 497) and field trip in El Jadida, Morocco (Antiatlas) (IGCP 485-board: Jean-Paul Liégeois & Nasser Ennih, responsibility for IGCP 497: Francisco Pereira, Scott Samson, Richard D`Lemos, Ulf Linnemann)
(ii) field trip "The rootless Variscan suture of NW Iberia (Galicia)" in NW-Spain (responsibility: Ricardo Arenas, José Ramon Martinez Catalan, Jacobo Abati, Sonia Sánchez Martinez).

2008 (i) Conference and field trip in Cape Town, South Africa (responsibility: Maarten de Wit) and
(ii) final meeting in Mexico (responsibility: Duncan Keppie & Damian Nance)