Julien Berger

Reasearch disciplines:

Regional studies

Variscan eclogites and ophiolites: Numerous basic-ultrabasic rocks from the French Massif Central and the Vosges are witnesses for the early oceanic evolution predating the polycyclic Variscan orogeny. My research activities on this subject include deciphering the dynamic and geochronology of oceanic subductions and the geotectonic setting of Lower Paleozoic European oceans.

West African Precambrian geodynamics: The Pan-African belt bordering the eastern edge of the West African craton contains numerous basic-ultrabasic markers that can help constrains its evolution. Amongst other is the Amalaoulaou island arc root, which is an unusual object at the scale of the World. It can help to understanding the processes active in the deep root of an island arc and it gives some constraints on the link between island arc and continental crust composition as well as on recycling of ultramafic-mafic lithologies into the mantle in response to gravitational instabilities at the base of arcs. My current research activities are focused on the Archean block of the West African Craton and aims to modelise the geodynamic evolution of some basic-ultrabasic associations and to decipher their role in the Archean crustal growth.

Process-oriented themes

Crustal growth and Precambrian geodynamics: Archean cratons have preserved their characteristics since 2.7 Ga. They are outdoor laboratories to study and understand the mechanism of continental crust growth, the Early Earth structure and evolution, and to compare modern plate tectonics to Archean geodynamics. The best challenge in this subject is to search for oceanic relics that will bring information on the Early Earth oceans and their spreading modes.

Chemical geodynamics of HP-UHP rocks: Eclogites and related rocks are crucial object to understand subduction dynamics and chemical exchanges between the slabs and the overlying mantle wedge. Geochemical studies of eclogites revealed that they are subject to dehydration and fluid-rock interaction at depth which will lead to significant element transfert under arcs. HP-UHP rocks can act as a trap for elements or, at the opposite, can release elements that will be transported by deep fluid into the source of island arc magmas. The nature and mass balance of the chemical exchanges are strongly controlled by the nature of the fluids at depth, the P-T conditions and the bulk composition of the eclogite precursors.

Source, differentiation and geotectonic setting of alkaline volcanic rocks:: Alkaline volcanism is most of the time found in intraplate setting. These peculiar volcanic-subvolcanic rocks are strongly enriched in trace-elements such as REE, Zr, Nb and can even be a potential resource for these latter’s. However, their origin is most of the time associated with mantle plumes and thus implies the involvement of deep reservoirs from the lower mantle. In continental setting however and by integrating geological, geochemical, geophysical and tectonic studies it can be demonstrated that the plume hypothesis is no more viable. Alkaline undersaturated volcanic rocks are most of time the product of partial melting in refertilised mantle (by metasomatism or crustal recycling) at shallow levels (uppermost mantle). The peculiar geochemical fingerprint of these rocks can be explained by very low degree partial melting of carbonated peridotites that were mixed with recycled sediments or mafic-ultramafic crustal rocks during previous orogenies.

Structure and maturation of thick island arcs: The geochemistry of island arc lavas is currently well understood and best explained by a mantle source being a mix between depleted mantle and recycled pelagic sediments. The deep structure of intra-oceanic arcs is however less known but many observations show that arc are subject to internal differentiation (mostly by partial melting of preexisting basic rocks) and this can lead to the production of dehydrated or restitic mafic-ultramafic garnet granulites and pyroxenites together with silicic melts resembling those in TTG suites. Understanding arc roots is of crucial importance to test if accreted island arcs have significantly contributed to the growth of the continental crust.

Structure and evolution of lost oceans: Ophiolites are the only relics of fossil oceanic lithosphere older than 200 Ma. These objects can help us to compare old oceans to present day ones and to understand the processes of ocean spreading from Archean to Paleozoic. However, Precambrian ophiolites are rare and difficult to discern of basic intrusions. Recognition of ocean relics therefore involves multidisciplinary approaches to test the different genetic hypothesis.

Tools

The tools used in these studies are field observation, mapping and microstructural studies, anisotropy of magnetic suceptibility; qualitative and quantitative petrography; electronic microprobe and scanning electron microscope for mineralogical interests and a large range of geochemical instrument for major-, trace-elements and isotopic analyses (XRF, ICP-AES, ICP-MS, LA-ICP-MS, TIMS).

Teaching:

Lectures: magmatic geochemistry; isotopic geochemistry and geochronology.

Exercices: geological mapping, geochronology, fractional crystallisation modeling.

Field exercices: magmatic and metamorphic terrains, field mapping and structural geology, introduction to the geology of Belgium.

Publications :

Thesis

Berger, J. 2008 Les associations de roches basiques - ultrabasiques néoprotérozoïques d'Amalaoulaou (Gourma, Mali) et du Tassendjanet (Hoggar occidental, Algérie) et cénozoïques du Saghro (Anti-Atlas, Maroc), témoins de l'évolution géodynamique de la ceinture péri-cratonique ouest-africaine. PhD thesis. Université Libre de Bruxelles, Université de La Rochelle. pdf

Berger J. 2003 Pétrologie et thermobarométrie des associations symplectitiques et coronitiques observées dans les xénolites mafiques du Puy Beaunit (chaîne des Puys, France). Master 2 Thesis.

Berger J. 2002 Etude pétrologique et géochimique des xénolithes mafiques de Beaunit (chaîne des Puys, France). Master 1 Thesis.

In preparation

Berger, J., Ennih, N., Liégeois, J-P., Demaiffe, D. Geochemistry of Cenozoic nephelinite-phonolite associations from the Moroccan Anti-Atlas (Saghro) and related fractionation of Nb-Ta and Zr-Hf pairs during fractional crystallisation.

Berger, J., Bendaoud, A., Ouzegane, K., Liégeois, J-P, Kiénast, J-R., Caby, R. Continental subduction and High-pressure metasomatism evidenced by Neoproterozoic from Western Hoggar (Algeria). To be submitted to Journal of Metamorphic Geology.

Submitted

Berger, J., Diot, H., Lo, K., Ohnenstetter, D., Féménias, O., Pivin, M., Demaiffe, D., Bernard, A., Charlier, B. Petrogenesis of Archean PGM-bearing chromitites and associated ultramafic-mafic-anorthositic rocks from the Guelb el Azib complex (West African craton, Mauritania). Submitted to Precambrian Research.

Published/ In press

(16) Plissart, G., Diot, H., Monnier, C., Marintiu, M., Berger, J. Relationship between a syntectonic granitic intrusion and a shear zone in the Southern Carpathian-Balkan area (Almaj Mountains, Romania): implications for Late Variscan kinematics and Cherbelezu granitoid emplacement. Journal of Structural Geology, in press.

(15) Berger, J., Caby, R., Liégeois, J-P., Mercier, J-C. C., Demaiffe, D. Deep inside a Neoproterozoic intra-oceanic arc: Growth, differentiation and exhumation of the Amalaoulaou complex (Gourma, Mali). Contributions to Mineralogy and Petrology, . pdf

(14) Pivin, M., Berger, J., Demaiffe, D. Nature and origin of an exceptional Cr-rich kyanite-bearing clinopyroxenite xenolith from Mbuji-Mayi kimberlite (DRC). European Journal of Mineralogy. 23, 257-268. pdf

(13) Berger, J., Féménias, O., Ohnenstetter, D., Bruguier, O., Plissart, G., Mercier, J-C. C., Demaiffe, D. New occurrence of UHP eclogites in Limousin (French Massif Central): age, tectonic setting and fluid-rock interactions. Lithos, 118, 365-382. pdf

(12) Berger, J., Féménias, O., Ohnenstetter, D., Plissart, G., Mercier, J-C. C. Origin and tectonic significance of corundum-kyanite-sapphirine amphibolites from the Variscan French Massif Central. Journal of Metamorphic Geology, 28, 341-360. pdf

(11) Berger, J., Liégeois, J-P., Ennih, N., Bonin, B., 2010. Flow of Canary mantle plume material through a subcontinental lithospheric corridor beneath Africa to the Mediterranean: COMMENT. Geology, 38, 262-262. pdf

(10) Berger, J., Ennih, N., Mercier, J-C. C., Liégeois, J-P., Demaiffe, D., 2009. The role of fractional crystallisation and late-stage peralkaline melts segregation in the mineralogical evolution of Cenozoic nephelinites/phonolites from Saghro (SE Morocco). Mineralogical Magazine, 73, 59-82. pdf

(9) Berger, J., Caby, R., Liégeois, J-P., Mercier, J-C. C., Demaiffe, D., 2009. Dehydration, melting and related garnet growth in the deep root of a Neoproterozoic magmatic arc (Gourma, NE Mali). Geological Magazine, 146, 173-186. pdf

(8) Berger, J., Ennih, N., Liégeois, J-P., Nkono, C., Mercier, J-C. C., Demaiffe, D., 2008. A complex multi-chamber magmatic system beneath a late Cenozoic volcanic field: evidence from CSDs and thermobarometry of clinopyroxene from a single nephelinite flow (Djbel Saghro, Morocco). Geological Society of London, Special Publications, 297, 509-524. pdf

(7) Berger, J., Féménias, O., Coussaert, N., Mercier, J-C. C., Demaiffe, D., 2007. Cumulating processes at the crust-mantle transition zone inferred from Permian mafic-ultramafic xenoliths (Puy Beaunit, France). Contributions to Mineralogy and Petrology, 153, 557-575. pdf

(6) Féménias, O., Berger, J., Mercier, J.C.C., Demaiffe, D., 2006. Upper mantle evolution during the variscan orogeny: A xenolith perspective from Puy Beaunit (French Massif Central). Mineralogical Society of Poland - Special Papers, 29, 22-27.

(5) Berger, J., Féménias, O., Mercier, J.-C.C., Demaiffe, D., 2006. A Variscan slow-spreading ridge (LHOT-MOR) in the French Massif Central: its magmatic evolution and tectonic setting trough mineral chemistry. Mineralogical Magazine, 70, 175-185. pdf

(4) Berger, J., Féménias, O., Mercier, J.-C.C., Demaiffe, D., 2005. Ocean-floor hydrothermal metamorphism in the Limousin ophiolites (western French Massif Central): evidence of a rare preserved Variscan oceanic marker. Journal of Metamorphic Geology, 23, 795-812. pdf

(3) Berger, J., Féménias, O., Coussaert, N., Demaiffe, D., 2005. Magmatic garnet-bearing mafic xenoliths (Puy Beaunit, French Massif Central): P-T path from crystallisation to exhumation. European Journal of Mineralogy, 17, 687-701. pdf

(2) Féménias, O., Ohnenstetter, D., Coussaert, N., Berger, J., Demaiffe, D., 2005. Origin of micro-layering in a deep magma chamber: evidence from two ultramafic-mafic layered xenoliths from Puy Beaunit (French Massif Central). Lithos, 83, 347-370. pdf

(1) Féménias, O., Coussaert, N., Berger, J., Mercier, J.-C.C., Demaiffe, D., 2004. Metasomatism and melting history of a Variscan lithospheric mantle domain: Evidence from the Puy Beaunit xenoliths (French Massif Central). Contributions to Mineralogy and Petrology, 148, 13-28. pdf

Congrès et colloques:

(23) Berger, J., Ennih, N., Mercier, J-C. C., Liégeois, J-P. (2010). Mineralogical control on the behaviour of Nb-Ta and Zr-Hf pairs in Cenozoic nephelinites and peralkaline phonolites from Saghro (Moroccan Anti-Atlas). IMA meeting 2010. Budapest, Hungary.

(22) Berger, J., Diot, H., Féménias, O., Lo, K. (2010). Archean chromitites and PGM from the Northern West African Craton (Amsaga, Mauritania). IMA meeting 2010. Budapest, Hungary.

(21) Kiénast, J-R., Ouzegane, K., Berger, J., Caby, R., Derridj, A., Godard, G., Adjerid, Z., Boubazine, S., Fettous, H., Zetoutou, S. (2008) Les éclogites du Hoggar: traceurs des enfouissements et des exhumations des "terranes". Colloquim of African Geology, Tunis, Tunisia.

(20) Berger, J., Ennih, N., Liégeois, J-P., Mercier, J-C. C., Demaiffe, D (2008) A poorly known occurrence of strongly alkaline Cenozoic lavas in NW Africa: the nephelinite-phonolite-carbonatite association from Saghro (Anti-Atlas, Morocco). Colloquim of African Geology, Tunis, Tunisia.

(19) Berger, J., Caby, R., Liégeois, J-P., Mercier, J-C. C., Demaiffe, D (2008) Deep inside a Neoproterozoic intra-oceanic arc root: the Amalaoulaou massif in Gourma, Mali. Colloquim of African Geology, Tunis, Tunisia.

(18) Berger J., Féménias, O., Ohnenstetter, D., Mercier, J-C. C., Demaiffe, D. (2008) Paragenèses à corindon-sapphirine-disthène dans les métatroctolites de l'ophiolite varisque du Limousin (Massif central français): témoins de la subduction d'une paléo-ride océanique? Réunion du groupe de contact FNRS "Géochimie et géodynamique de la lithosphère", MRAC, Tervuren.

(17) Berger, J., Caby, R., Liégeois, J-P., Mercier, J-C. C., Demaiffe, D. (2007) Deep inside a Neoproterozoic island arc: structure, P-T path and petrogenesis of the Amalaoulaou massif (Gourma, Mali). IGCP 485 meeting, El Jadida, Morocco.

(16) Berger, J., Ennih, N., Mercier, J-C. C., Liégeois, J-P., Demaiffe, D. (2007) Source and differentiation of the nephelinite-phonolite association from the Saghro Cenozoic volcanic field. IGCP 485 meeting, El Jadida, Morocco.

(15) Berger J., Caby R., Buscail F., Liégeois J-P., Mercier J-C. C., Demaiffe D. (2007) Structure et pétrogenèse d'une racine d'arc insulaire protérozoïque: le complexe d'Amalaoulaou (Gourma, Mali). Réunion du groupe de contact FNRS "Géochimie et géodynamique de la lithosphère", ULB, Bruxelles.

(14) Berger J., Ennih N., Liégeois J-P., Mercier J-C. C., Demaiffe D. (2007) CSD and thermobarometry as a tool to evaluate depth and numbers of magma chambers beneath a volcanic field: an example from the Cenozoic hyperalkaline lavas of Saghro. 3M, Fès, Maroc.

(13) Berger J., Bendaoud A., Ouzegane K., Kiénast J-R., Caby R., Liégeois J-P., Mercier J-C., C., Demaiffe D. (2006) Ultrabasic and basic rocks from the Tileouine Area (Western Hoggar): from subduction-related metamorphism to post-collisional magmatism. Réunion du PICG 485, Alger.

(12) Berger J., Ennih N., Liégeois J-P., Mercier J-C. C., Demaiffe D. (2006) The Saghro Cainozoic volcanic field (Anti Atlas, Morocco): peralkaline lavas along a cratonic boundary. Réunion du PICG 485 , Alger.

(11) Berger J., Ennih N., Demaiffe D., Liégeois J-P. (2006) Reactivation of a cratonic boundary in an intraplate setting: The Cenozoïc alkaline lavas from Djbel Sarhro (Anti-Atlas, Morocco). Geologica Belgica Meeting.

(10) Berger J., Féménias O., Mercier J-C. C., Demaiffe D. (2006) Fossil oceanic lithosphere in Limousin (French Massif Central): geodynamic evolution of pre-Variscan events in W. Europe. Geologica Belgica Meeting.

(9) Berger J., Féménias O., Mercier J-C. C., Demaiffe D. (2005) Co-existence of ophiolite and eclogite in an orogenic suture zone: an example from Limousin in the Variscan French Massif Central. IGCP 485, Gao-Mali.

(8) Berger J., Féménias O., Demaiffe D. (2005) Les enclaves ultramafiques et mafiques du Puy Beaunit (Massif Central français) : témoin de l’activité magmatique tardi-hercynienne en Europe de l’ouest. 3M, Agadir, Maroc.

(7) Berger J., Féménias O., Demaiffe D. (2005) Nature et composition de la transition croûte manteau sous le Massif central français échantillonnée par les xénolites du Puy Beaunit. Géologie et métallogénie des massifs du Hoggar et des Eglabs, Tamanrasset.

(6) Demaiffe D., Féménias O., Berger J. (2005) Variscan Moho beneath the French Massif central: a xenolith perspective from Puy Beaunit. Goldschmidt Conference, Moscow, USA.

(5) Berger J., Féménias O., Mercier J-C.C., Demaiffe D. (2004) Ocean-floor hydrothermal metamorphism in the ophiolite from Limousin (French Massif Central). RST, Strasbourg.

(4) Berger J., Féménias O., Coussaert N., Demaiffe D. (2003). Pétrologie et géochimie des xénolites mafiques du Puy Beaunit (France). Origine de la série et effets du pyrométamorphisme. Réunion du groupe géochimie du FNRS.

(3) Berger, J.; Féménias, O.; Demaiffe, D. (2003). Coronitic textures in mafic xenoliths from Puy Beaunit (French Massif Central): Evidence for pyrometamorphism on cumulate rocks from a deep layered complex. Geophysical Research Abstracts, vol. 5, EAE03-02097.

(2) Demaiffe, D.; Berger, J.; Féménias, O.; Coussaert, N. (2003). Trace element distribution in silicate phases from the cumulate mafic xenoliths of Puy Beaunit (French Massif Central): A LA-ICP-MS study. Geophysical Research Abstracts, vol. 5, EAE03-02105.

(1) Demaiffe D., Berger J., Féménias O., Coussaert N., Mercier J.-C. C. (2002). A differentiated ultramafic-mafic deep magma chamber beneath the French Massif Central. Evidence from the xenoliths of Puy Beaunit. Colloque en l’honneur de J.-C. Duschene, Modelling of magma chambers and implications for the evolution of the continental crust.