Research Article| February 01, 2017 Evidence of an axial magma chamber beneath the ultraslow-spreading Southwest Indian Ridge Hanchao Jian; Hanchao Jian 1Institute of Theoretical and Applied Geophysics, School of Earth and Space Science, Peking University, Beijing 100871, China2Laboratoire de Géosciences Marines, Institut de Physique du Globe de Paris, 1 rue Jussieu, 75238 Paris Cedex 05, France Search for other works by this author on: GSW Google Scholar Satish C. Singh; Satish C. Singh * 2Laboratoire de Géosciences Marines, Institut de Physique du Globe de Paris, 1 rue Jussieu, 75238 Paris Cedex 05, France *E-mails: singh@ipgp.fr; johnyc@pku.edu.cn. Search for other works by this author on: GSW Google Scholar Yongshun John Chen; Yongshun John Chen * 1Institute of Theoretical and Applied Geophysics, School of Earth and Space Science, Peking University, Beijing 100871, China3School of Oceanography, South University of Science and Technology of China, Shenzhen 518055, China *E-mails: singh@ipgp.fr; johnyc@pku.edu.cn. Search for other works by this author on: GSW Google Scholar Jiabiao Li Jiabiao Li 4Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China Search for other works by this author on: GSW Google Scholar Author and Article Information Hanchao Jian 1Institute of Theoretical and Applied Geophysics, School of Earth and Space Science, Peking University, Beijing 100871, China2Laboratoire de Géosciences Marines, Institut de Physique du Globe de Paris, 1 rue Jussieu, 75238 Paris Cedex 05, France Satish C. Singh * 2Laboratoire de Géosciences Marines, Institut de Physique du Globe de Paris, 1 rue Jussieu, 75238 Paris Cedex 05, France Yongshun John Chen * 1Institute of Theoretical and Applied Geophysics, School of Earth and Space Science, Peking University, Beijing 100871, China3School of Oceanography, South University of Science and Technology of China, Shenzhen 518055, China Jiabiao Li 4Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China *E-mails: singh@ipgp.fr; johnyc@pku.edu.cn. Publisher: Geological Society of America Received: 14 Jul 2016 Revision Received: 02 Nov 2016 Accepted: 03 Nov 2016 First Online: 02 Jun 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2016 Geological Society of America Geology (2017) 45 (2): 143–146. https://doi.org/10.1130/G38356.1 Article history Received: 14 Jul 2016 Revision Received: 02 Nov 2016 Accepted: 03 Nov 2016 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hanchao Jian, Satish C. Singh, Yongshun John Chen, Jiabiao Li; Evidence of an axial magma chamber beneath the ultraslow-spreading Southwest Indian Ridge. Geology 2017;; 45 (2): 143–146. doi: https://doi.org/10.1130/G38356.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Ultraslow-spreading ridges are a novel class of spreading centers symbolized by amagmatic crustal accretion, exposing vast amounts of mantle-derived peridotites on the seafloor. However, distinct magmatic centers with high topographies and thick crusts are also observed within the deep axial valleys. This suggests that despite the low overall melt supply, the magmatic process interacting with the tectonic process should play an important role in crustal accretion; however, this has been obscured due to the lack of seismic images of magma chambers. Using a combination of seismic tomography and full waveform inversion of ocean bottom seismometer data from the Southwest Indian Ridge at 50°28′E, we report the presence of a large low-velocity anomaly (LVA) ∼4–9 km below the seafloor, representing an axial magma chamber (AMC) in the lower crust. This suggests that the 9.5-km-thick crust here is mainly formed by a magmatic process. The LVA is overlain by a high-velocity layer, possibly forming the roof of the AMC and defining the base of hydrothermal circulation. The steep velocity gradient just below the high-velocity layer is explained by the ponding of magma at the top of the AMC; this could provide the overpressure for lateral dike propagation along the ridge axis, leading to a complex interaction between magma emplacement, tectonic, and hydrothermal processes, and creating a diversity of seafloor morphology and extremely heterogeneous crust. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.