Along-axis variation in crustal thickness at the ultraslow spreading Southwest Indian Ridge (50 degrees E) from a wide-angle seismic experiment

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Niu, Xiongwei, Ruan, Aiguo, Li, Jiabiao, Minshull, T. A., Sauter, Daniel, Wu, Zhenli, Qiu, Xuelin, Zhao, Minghui, Chen, Y. John, Singh, Satish
• Other Authors: Ruan, AG (reprint author), State Ocean Adm, Inst Oceanog 2, Hangzhou, Zhejiang, Peoples R China., State Ocean Adm, Inst Oceanog 2, Hangzhou, Zhejiang, Peoples R China., Univ Southampton, Natl Oceanog Ctr Southampton, Ocean & Earth Sci, Southampton, Hants, England., Univ Strasbourg, EOST, CNRS, Inst Phys Globe Strasbourg,IPGS,UMR 7516, Strasbourg, France., Chinese Acad Sci, South China Sea Inst Oceanol, Guangzhou, Guangdong, Peoples R China., Peking Univ, Dept Geophys, Sch Earth & Space Sci, Beijing 100871, Peoples R China., Inst Phys Globe Paris, Lab Geosci Marines, Paris, France.
• Format: Journal/Newspaper
• Language: English
• Published: geochemistry geophysics geosystems 2015
• Subjects: Southwest Indian Ridge; oceanic crust; thick crust; wide-angle seismic experiment; mantle; MID-ATLANTIC RIDGE; SEA-FLOOR GENERATION; GRAVITY-ANOMALIES; OCEANIC-CRUST; CROZET HOTSPOT; PLATE MOTIONS; FRACTURE-ZONE; GAKKEL RIDGE; ARCTIC-OCEAN; THIN CRUST; Arctic; Arctic Ocean; Gakkel Ridge; Indian; Mid-Atlantic Ridge
• Online Access: https://hdl.handle.net/20.500.11897/206389; https://doi.org/10.1002/2014GC005645

The Southwest Indian Ridge (SWIR) is characterized by an ultraslow spreading rate, thin crust, and extensive outcrops of serpentinized peridotite. Previous studies have used geochemical and geophysical data to suggest the presence of a thicker crust at the central and shallowest portions of the SWIR, from the Prince Edward (35 degrees 30E) to the Gallieni (52 degrees 20E) fracture zones. Here we present a new analysis of wide-angle seismic data along the ridge 49 degrees 17E-50 degrees 49E. Our main conclusions are as follows: (1) we find an oceanic layer 2 of roughly constant thickness and steep velocity gradient, underlain by a layer 3 with variable thickness and low velocity gradient; (2) the crustal thickness varies from approximate to 5 km beneath nontransform discontinuities (NTDs) up to approximate to 10 km beneath a segment center; (3) the melt supply is focused in segment centers despite a small NTD between adjacent segments; (4) the presence of a normal upper mantle velocity indicates that no serpentinization occurs beneath this thick crust. Our observation of thick crust at an ultraslow spreading ridge adds further complexity to relationships between crustal thickness and spreading rate, and supports previous suggestions that the extent of mantle melting is not a simple function of spreading rate, and that mantle temperature or chemistry (or both) must vary significantly along axis. Geochemistry & Geophysics SCI(E) EI 0 ARTICLE [e-mail] 2 468-485 16