Origin of volcanism on the flanks of the Pacific-Antarctic ridge between 41°30'S and 52°S

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Briais, Anne, Ondréas, Hélène, Klingelhoefer, Frauke, Dosso, Laure, Hamelin, Cédric, Guillou, Hervé
• Other Authors: Dynamique terrestre et planétaire (DTP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Unité de recherche Géosciences Marines (Ifremer) (GM), Domaines Océaniques (LDO), Centre National de la Recherche Scientifique (CNRS)-Institut d'écologie et environnement-Observatoire des Sciences de l'Univers-Université de Brest (UBO)-Institut national des sciences de l'Univers (INSU - CNRS), Université de Brest (UBO), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Paléocéanographie (PALEOCEAN), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2009
• Subjects: Mid-ocean ridges; Off-axis volcanism; Mantle convection; Plate kinematics; Transform fault; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Antarctic; Pacific; Antarc*
• Online Access: https://hal.archives-ouvertes.fr/hal-00543807; https://hal.archives-ouvertes.fr/hal-00543807/document; https://hal.archives-ouvertes.fr/hal-00543807/file/Briais_G3_09_Pacant2_offaxis_volcanoes.pdf; https://doi.org/10.1029/2008GC002350

20 pages; 12142 words; 6 figures; 3 tables International audience Non-hotspot, intraplate volcanism is a common feature near the East Pacific Rise or Pacific-Antarctic Ridge. Volcanic ridges and seamount chains, tens to hundreds of kilometers long, are asymmetrically distributed about the ridge axis, most volcanic features occurring on the Pacific plate. Their origins remain controversial. We have analyzed off-axis volcanic ridges near the Pacific-Antarctic ridge from bathymetry, backscatter, gravity and geochemistry data of the Pacantarctic2 cruise. K/Ar dating of samples dredged on these structures reveal a contrast of up to 3 Ma between the volcanoes and the underlying crust. The volcanic activity, as suggested by the strong backscatter in sonar images, appears to be limited to areas of seafloor younger than about 3 Ma. All surveyed ridges north of the Menard transform fault (TF) show recent activity close to the ridge axis, and are not affected by faults. The off-axis volcanic ridges south of the Menard TF show recent volcanic flows in their center, and are affected by N-S extension. Two different types of volcanoes can be characterized: conical, flat-topped ones and rough, elongated ones associated with narrow, EW-trending volcanic ridges, some of them showing strong backscattering on the EM12 imagery. From the morphology of the seamount chains and the ages of the lava samples, we infer that the magma source for the volcanic ridges is related to the feeding of the ridge axis through three-dimensional mantle convective circulation. We suggest that a change in the relative plate motion since about 5 Ma might have induced an offset of the mantle upwelling circulation under the ridge axis so that anomalously hot mantle rises under the Pacific ridge flank. The kinematic change is also likely responsible for the tectonic deformation in the young lithosphere south of Menard TF.