Earth Science Frontiers ›› 2021, Vol. 28 ›› Issue (2): 271-283.DOI: 10.13745/j.esf.sf.2020.12.7

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Discussions on the bathymetric segmentation and tectonogenesis of the oblique spreading Southwest Indian Ridge

ZHANG Huatian1(), LI Jianghai1,*(), TAO Chunhui2   

  1. 1. Ministry of Education Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China
    2. Ministry of Natual Resources Key Laboratory of Submarine Geosciences, Second Institute of Oceanography, Ministry of Natual Resources, Hangzhou 310012, China
  • Received:2019-01-02 Revised:2020-06-30 Online:2021-03-25 Published:2021-04-03
  • Contact: LI Jianghai

Abstract:

Oblique spreading is a characteristic feature of ultra-slow spreading ridges. As its bathymetric segmentation pattern is distinct from classical fast-slow spreading ridge models, it can provide insight into the geological process of ultra-slow spreading ridges. Based on multibeam bathymetric data, the segmentation patterns (with variable spreading obliquity (α)) of the Southwest Indian Ridge (SWIR) Indomed-Gallieni and Shaka-DuToit zones are analyzed. Results show that the SWIR segments, between 46.5°E and 47.5°E (α=5°), 16°E and 25°E (α=10°), and 48.5°E and 52°E (α=15°), respectively, are quasi-orthogonal spreading segments, which have developed en échelon axial volcanic ridges. Along the axis of the oblique spreading SWIR, between 47.5°E and 48.5°E (α=50°) and between 16°E and 25°E (α=60°), only one axial volcanic ridge has formed at the center of the axis. The distribution of the strain rates along the mid-ocean ridges with variable obliquity (α) is calculated by a ‘finite difference+markers in cells’ (FD+MIC) technique. Combined with bathymetry analysis, two factors influencing the segmentation pattern of oblique spreading results, namely, the spreading obliquity and distribution of temperature disturbance, are proposed. Along the quasi-orthogonal spreading segments (α<20°), temperature disturbance led to localization of extensional strain and development of en echelon axial volcanic ridges. In the oblique spreading segments (α>20°), strain localization was controlled by oblique geometry so the axial volcanic ridges only developed in the middle of the segment. These volcanic ridges were insensitive to temperature disturbance, therefore, they could form lasting fixed local magmatic centers.

Key words: oblique spreading, ultra-slow spreading ridges, bathymetric segmentation, multibeam bathymetry, numerical modeling

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