Christian Coulon

Bio: Christian Coulon is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Mantle plume & Basalt. The author has an hindex of 8, co-authored 8 publications receiving 889 citations.

Temporal evolution of mantle sources during continental rifting: The volcanism of Djibouti (Afar)

Abstract: Magmatism occurred almost continuously over the past 25 m.y. in the Republic of Djibouti. Lavas are mainly basic to intermediate with some rhyolites. Large chemical and isotopic variations among the volcanic series are interpreted in terms of mantle source heterogeneity. Crustal contribution is only evidenced in the oldest rhyolites emplaced during the initial stages of rifting. Excluding these old rhyolites, a clear evolution through time of the mantle sources is observed in relation to rifting. Three sources were involved in the genesis of these lavas: (1) an old subcontinental lithospheric component (87Sr/86Sr ≈ 0.706, 206Pb/204Pb ≈ 17.9), mainly observed in the oldest lavas (25 to 10 Ma), (2) an HIMU (high U/Pb ratio)-type reservoir, and (3) a depleted mantle. As rifting goes on, there is an increasing contribution of an HIMU-type mantle source. It is attributed to the influence of a mantle diapir (Afar plume) thermally eroding the subcontinental lithosphere. The geochemical characteristics of 9 to 1 Ma old lavas, erupted after the strong increase of spreading rate in Afar, reflect this evolution of mantle sources. The influence of the mantle plume is most prominent in the northern youngest lavas (<1 Ma), particularly Manda, characterized by the strongest HIMU signature (87Sr/86Sr ≈ 0.7035, 206Pb/204Pb ≈ l9.2). The contribution of the depleted mantle component originating from the asthenosphere is best recognized in the young (<4 Ma) lavas, particularly Tadjoura and Asal lavas (3 to 1 Ma). The evolution of Djibouti lava sources through time may be accounted for by the recent models developed for plume structure.

Changes of mantle sources in the course of a rift evolution: The Afar Case

Abstract: Afar is a favorable area in which to investigate the interactions between lithosphere and asthenosphere during the opening of a continental rift. The present work focuses on the territory of Djibuti Republic where volcanism has occurred over the past 25 Ma. With the exception of the oldest rhyolites which contain a large crustal-derived component, the Sr, Nd, Pb isotopic compositions of basalts indicate mantle sources without significant crustal contamination. As the rifting process goes on, the sources are evolving from an ancient and isotopically heterogeneous lithospheric subcontinental component (87Sr/86Sr = 0.707 and 206Pb/204Pb = 17.5) to a component having HIMU characteristics (87Sr/86Sr = 0.7035 and 206Pb/204Pb > 19). The influence of the asthenospheric depleted mantle is not established. The present data confirm that a mantle plume is associated with the rifting.

The Ethnic Origins of Nations

Abstract: Preface. Note to Maps. Maps. Introduction. 1. Are Nations Modern?. a Modernistsa and a Primordialistsa . Ethnie, Myths and Symbols. The Durability of Ethnic Communities. Part I: Ethnic Communities in Pre--Modern Eras:. 2. Foundations of Ethnic Community. The Dimensions of Ethnie. Some Bases of Ethnic Formation. Structure and persistence of Ethnie. 3. Ethnie and Ethnicism in History. Uniqueness and Exclusion. Ethnic Resistance and Renewal. External Threat and Ethnic Response. Two Types of Ethnic Mythomoteur. 4. Class and Ethnie in Agrarian Societies. Military Mobilization and Ethnic Consciousness. Two Types of Ethnie. Ethnic Polities. 5. Ethnic Survival and Dissolution. Location and Sovereignty. Demographic and Cultural Continuity. Dissolution of Ethnie. Ethnic Survival. Ethnic Socialization and Religious Renewal. Part II: Ethnie and Nations in the Modern Era. 6. The Formation of Nations. Western Revolutions. Territorial and Ethnic Nations. Nation--Formation. The Ethnic Model. Ethnic Solidarity or Political Citizenship?. 7. From Ethnie to Nation. Politicization of Ethnie. The New Priesthood. Autarchy and Territorialization. Mobilization and Inclusion. The New Imagination. 8. Legends and Landscapes. Nostalgia and Posterity. The Sense of a The Pasta . Romantic Nationalism as an a Historical Dramaa . Poetic Spaces: The Uses of Landscape. Golden Ages: The Uses of History. Myths and Nation--Building. 9. The Genealogy of Nations. Parmenideans and Heraclitans. The a Antiquitya of Nations. Transcending Ethnicity?. A World of Small Nations. Ethnic Mobilization and Global Security. Notes. Bibliography. Index.

Mediterranean extension and the Africa‐Eurasia collision

Abstract: A number of tectonic events occurred contemporaneously in the Mediterranean region and the Middle East 30–25 Myr ago. These events are contemporaneous to or immediately followed a strong reduction of the northward absolute motion of Africa. Geological observations in the Neogene extensional basins of the Mediterranean region reveal that extension started synchronously from west to east 30–25 Myr ago. In the western Mediterranean it started in the Gulf of Lion, Valencia trough, and Alboran Sea as well as between the Maures massif and Corsica between 33 and 27 Ma ago. It then propagated eastward and southward to form to Liguro-Provencal basin and the Tyrrhenian Sea. In the eastern Mediterranean, extension started in the Aegean Sea before the deposition of marine sediments onto the collapsed Hellenides in the Aquitanian and before the cooling of high-temperature metamorphic core complexes between 20 and 25 Ma. Foundering of the inner zones of the Carpathians and extension in the Panonnian basin also started in the late Oligocene-early Miocene. The body of the Afro-Arabian plate first collided with Eurasia in the eastern Mediterranean region progressively from the Eocene to the Oligocene. Extensional tectonics was first recorded in the Gulf of Aden, Afar triple junction, and Red Sea region also in the Oligocene. A general magmatic surge occurred above all African hot spots, especially the Afar one. We explore the possibility that these drastic changes in the stress regime of the Mediterranean region and Middle East and the contemporaneous volcanic event were triggerred by the Africa/Arabia-Eurasia collision, which slowed down the motion of Africa. The present-day Mediterranean Sea was then locked between two collision zones, and the velocity of retreat of the African slab increased and became larger than the velocity of convergence leading to backarc extension. East of the Caucasus and northern Zagros collision zone the Afro-Arabian plate was still pulled by the slab pull force in the Zagros subduction zone, which created extensional stresses in the northeast corner of the Afro-Arabian plate. The Arabian plate was formed by propagation of a crack from the Carlsberg ridge westward toward the weak part of the African lithosphere above the Afar plume.

Timing of the Ethiopian flood basalt event and implications for plume birth and global change

Abstract: Continental flood basalts are often considered as fossil evidence of mantle plume heads impinging on the lithosphere1,2 and have been related to continental breakup3,4,5. Many of these flood basalts erupted within a short time span—of the order of 1 Myr—and were apparently synchronous with crises in global climate and with mass extinctions6. Here we present geochronological (40Ar/39Ar) and magnetostratigraphic results for the Ethiopian traps, one of the last remaining flood basalts for which few such data were available. The bulk of the traps, which have been inferred to mark the appearance of the Ethiopian-Afar plume head at the Earth's surface, erupted approximately 30 Myr ago, over a period of 1 Myr or less. This was about the time of a change to a colder and drier global climate, a major continental ice-sheet advance in Antarctica, the largest Tertiary sea-level drop and significant extinctions.