http://www.jacques-bourgois.org 

Charles Jacob award, Académie des Sciences

Co-Editor in Chief of the “International Journal of Geosciences” IJG 

AIM OF ACADEMIC WORK 

Basically, I am geologist and geophysicist. I have worked extensively in Latin America from Baja California (Mexico) to Patagonia (Chile) exploring processes related to Middle America and Andean subductions. I have worked both onland and at sea conducting field works from the foreland to the Pacific coastline and off shore campaigns, respectively. I was Chief Scientist of seven cruises off Mexico, Peru and Chile including three deep-sea diving cruises using the submersible NAUTILE. We explored and sampled seafloor at the Peru-Chile and the Middle America trenches down to 6000-m. It allowed us to better understand the tectonic regime and processes associated with the underthrust of the Pacific oceanic lithosphere beneath the Middle and South America continental basements.

L’essentiel de mes travaux ont été conduits en Amérique Latine, de la Basse Californie (Mexique) jusqu’en Patagonie (Chili, Argentine). L’objectif scientifique est l’étude des processus associés aux subductions de l’Amérique Centrale et des Andes (sous-charriage de la lithosphère océanique pacifique sous le socle continental de l’Amérique Centrale et de l’Amérique du Sud à l’origine des séismes et du volcanisme). J’ai travaillé à terre et en mer. Les travaux de terrain couvrent la totalité du zonage orogénique, de l’avant-pays jusqu’à la côte pacifique. J’ai été chef de mission de sept campagnes océanographiques (Mexique, Pérou, Chili) dont trois ont utilisé les moyens du submersible NAUTILE. Nous avons exploré et échantillonné les fosses du Pérou-Chili et d’Amérique Centrale jusqu’à 6000 m de profondeur. Cela a permis en particulier de mesurer la déformation et de comprendre les processus à l’origine de l’évolution du régime tectonique de l’avant-arc.

BRIEF DESCRIPTION OF ONGOING ACADEMIC RESEARCH 

Since about ten years, part of my studies focused at the interface of tectonics, oceanography, and climatology. The main objective is to understand the feedback processes between climate and tectonic deformation at the time scale of the glacial-interglacial cycle. Abrupt changes in the climate system induce tectonic responses including at the millennium time scale. To document these changes, to date them precisely and to understand the mechanisms require to use technique of analytical chemistry including ¹⁰Be cosmogenic isotopes. 

My main contributions are related to the following topics: (1) At the Chile triple junction area; the climate-induced variation of the sediment supply to the trench axis is the main factor controlling the continental margin tectonic regime. During the warm period of the interglacial episode at 117-130,000 years, rapid increase of the trench sediment accumulation caused the margin to switch from subduction-erosion or nonaccretion to subduction-accretion. (2) Along the northwestern Peru forearc area, we infer that eustacy exerts important feedback coupling to seismic behavior of the Northern Peru subduction zone. We speculate that during sea level fall, pore-fluid pressure diminishes along the subduction channel inducing a possible seaward migration of the locked zone reaching a maximum by the end of the eustatic low stand at 19-23,000 years. (3) At the Chile triple junction area (Bourgois et al., in progress), the major retreat of the northern Patagonia ice cap at 11-14,000 years controls the tectonic rebound of this segment of the Andes, and the funneling of the Andean runoff to the Pacific.

Selected references 

Bourgois, J., D. Bourles, and R. Braucher, 2011, Reply to comment by K. Pedoja et al. on “Tectonic record of strain buildup and abrupt coseismic stress release across the northwestern Peru coastal plain, shelf, and continental slope during the past 200 kyr”, Journal of Geophysical Research, 116, B09402, doi:10.1029/2011JB008582.

Bourgois, J., 2010, A comment on “Non-steady long-term uplift rates and Pleistocene marine terrace development along the Andean margin of Chile (31 °S) inferred from 10Be dating”, Earth and Planetary Science Letters, doi:10.1016/j.epsl.2010.05.018

Bourgois, J., Bigot-Cormier, F., Bourles, D., Braucher, R., Dauteuil, O., Witt, C., Michaud, F., 2007, Tectonic record of strain buildup and abrupt coseismic stress release across the northwestern Peru coastal plain, shelf, and continental slope during the past 200 kyr”, Journal of Geophysical  Research, 116, B09402, doi:10.1029/2011JB008582.

Bourgois, J., Guivel, C., Lagabrielle, Y., Calmus, T., Boulègue, J., Daux, V., 2000, Glacial-interglacial trench supply variation, spreading-ridge subduction, and feedback controls on the Andean margin development at the Chile triple junction area (45-48° S), Journal of Geophysical Research, 105, 8355-8386.

WASTE ELIMINATION FROM NUCLEAR FUEL

Along the ~60,000 km of deep oceanic trenches the subduction process participates in oceanic lithosphere recycling. In other words the basalt and associated sediment cover of the seafloor are moving downward together with trench sediment. They underthrust the continental margin of the upper plate towards the asthenosphere. Therefore the subduction process appears as a well for sub-surface material to be removed at depth greater than ~100-150 km. This natural well is potentially appropriate for nuclear fuel waste to be permanently eliminated.

However, slab rock melting is occurring beneath the volcanic arc at distances ranging from 100 to 250 km from the subduction front. Along fast subductions –i.e. such as the SW Pacific- it takes about 800,000 years for the subducted material to erupt at volcanic edifices of the volcanic arc. At slower subduction, the transit time for the subducted material is longer than one Million years. Subductions such as the Peru and northern Chile exhibit no active volcanic arc. At those sites no subducted material is removed to the atmosphere. This situation is stable along the 1500 km long Peru subduction zone since ~20 Million years. For these reasons, I proposed (Bourgois, 1996) the Peru subduction zone (see also Bourgois et al., 1988; von Huene et al., 1988; Dia et al., 1993, Bourgois et al., 1993; Aquilina et al., 1997; Bourgois et al., 2007) to be extensively surveyed in the perspective of having an accurate field understanding of its potentials for nuclear waste elimination.

Selected References

Bourgois, J., Bigot-Cormier, F., Bourles, D., Braucher, R., Dauteuil, O., Witt, C., Michaud, F., 2007, Tectonic records of strain buildup and abrupt co-seismic stress release across the northwestern Peru coastal plain, and continental slope during the past 200 kyr. Journal of Geophysical Research, 112, B04104, doi:10.1029/2006JB004491.

Aquilina, L., Dia, A.N., Boulègue, J., Bourgois, J., and Fouillac, A.M., 1997, Massive barite deposits along the convergent margin of Peru: implications for fluid circulation within subduction zones. Geochimica.Cosmochimica.Acta, 61, 1233-1245.

Bourgois, J., 1996, Un processus naturel pour éliminer définitivement les déchets nucléaires, Réalités Industrielles, Annales des Mines, janvier 1996, p. 5-12.

Dia, A.N., Aquilina, L., Boulègue, J., Bourgois, J., E. Suess, and Torres, M., 1993, Origin of fluids and related-barite deposits at vent sites along the Peru convergent margin, Geology, 21, 1099-1102.

Bourgois, J., Lagabrielle, Y., De Wever, P., Suess, E., and NAUTIPERC team, 1993, Tectonic History of the northern Peru convergent margin during the past 400 Ka, Geology, 21, 531-534.

von Huene, R., Bourgois, J., Miller, J., and Pautot, G., 1989, A large Tsunamogenic landslide and debris along the Peru Trench, Journal of Geophysical Research,  94, 1703-1714.

Bourgois, J., Pautot, G., Bandy, W., Boinet, T., Chotin, P., Huchon, P., Mercier de Lepinay, B., Monge, F., Monlaü, J., Pelletier, B., Sosson, M., and von Huene, R., 1988, Seabeam and seismic reflexion imaging of the tectonic regime of the Andean continental margin off Peru (4°S to 10°S), Earth and Planetary Science Letters, 87, 111-126.

 OIL AND GAS

From 1980 to 1995, I had the opportunity to be funded by Petroleum and Mining companies including Elf Ecuador, Elf Colombia, Ecuatomin, and the BRGM. During my subsequent five-years stay (2001-2006) in Ecuador as Professor at the Escuela Politecnica Nacional (EPN-Quito), a close collaboration with Petroecuador and Perupetro allowed us to constrain the evolution of the Gulf of Guayaquil-Tumbes basin for the past 1.8-1.6 Million years. At less few ten of kilometers south of the Ecuador Peru border, major gas and oil reservoirs exist along the northern Peru forearc. Instead geologic and geophysical evidences suggest that these gas and oil reservoirs should extend along the Ecuadorian side, they are not identified yet. Our published works suggest that a new strategy should be designed in order to find what is the exact location of sites to be surveyed for successful discovery of major reservoirs along the Ecuadorian forearc.

Selected References

Bourgois, J. 2013, A review on tectonic record of strain buildup and stress release across the Andean forearc along the Gulf of           Guayaquil-Tumbes basin (GGTB) near Ecuador-Peru border. International Journal of Geosciences, accepted.

Witt, C., Bourgois, J. 2010, Forearc basin formation in the tectonic wake of a collision-driven, coastwise migrating crustal block : the example of the North Andean block and the extensional Gulf of Guayaquil-Tumbes basin (Ecuador-Peru Border area). Geological Society of America Bulletin, 122, p. 89-108, doi: 10.1130/B26386.1.

Bourgois, J., Bigot-Cormier, F., Bourles, D., Braucher, R., Dauteuil, O., Witt, C., Michaud, F., 2007, Tectonic records of strain buildup and abrupt co-seismic stress release across the northwestern Peru coastal plain, and continental slope during the past 200 kyr. Journal of Geophysical Research, 112, B04104, doi:10.1029/2006JB 004491.

Witt, C., Bourgois, J., Michaud, F., Ordoñez, M., Jimenez, N., Sosson, M., 2006, Development of the Gulf of Guayaquil (Ecuador)        during the Quaternary as an effect of the North Andean Block tectonic escape. Tectonics, 25, TC3017, doi:                                 10.1029/2004TC001723.

More details at: http://www.jacques-bourgois.org

165 publications in Refereed Journals Including: Journal of Geophysical Research, Geology, Tectonics, Geophysical Research Letters, Journal of Geology, Geological Society of America Bulletin, Nature, Earth and Planetary Science Letters, Geochimica Cosmochimica Acta, Tectonophysics, Journal of Volcanology, Lithos, Marine Geology, Marine Geophysical Research, Marine Micropaleontology, Geo-Marine Letters, Pure and Applied Geophysics, Bulletin de la Société Géologique de France, Comptes rendus de l’Académie des Sciences, and 34 other journals. 2 geological maps: 1/100 000 and 1/50 000, southern Spain and Ecuador, respectively. 150 presentations at scientific meetings, including invited papers. Convener of two special sessions at AGU Fall meetings.