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

doi:10.13745/j.esf.sf.2020.12.7

Abstract

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

CLC Number:

P736
P542

ZHANG Huatian, LI Jianghai, TAO Chunhui. Discussions on the bathymetric segmentation and tectonogenesis of the oblique spreading Southwest Indian Ridge[J]. Earth Science Frontiers, 2021, 28(2): 271-283.

Figures/Tables 10

Fig.1 Tectonic sketch map of the Southwest Indian Ocean

Fig.2 Segmentation pattern (a) and bathymetric profile (b) of SWIR Indomed-Gallieni

Fig.3 Segmentation pattern (a) and bathymetric profile (b) of SWIR Shaka-DuToit

Table 1 Parameters used for numerical modeling of gabbro from lower crust (adapted from [42])

物理量		数量	物理量		数量
密度(ρ)	标准密度(ρ₀)	3 000 kg/m³	比热容(C_p)		1 000 J/kg
	热膨胀系数(α)	3×10^-5 K^-1	黏滞系数η	物质常数(A_D)	3.3×10^-4 MPa^-ⁿ•s^-1
	压缩系数(β)	1×10^-11 Pa^-1		应力指数(n)	3.2
热导率(κ)	标准热导率(κ₀)	1.18 W•m^-1•K^-1		活化能(E_a)	238 kJ/mol
热导率(κ)	热导率系数(α)	474 W/m		活化体积(V_a)	0 J/Pa
剪切模量(μ)		2.5×10¹⁰ Pa	放射产热率(H_r)		2.5×10^-7 W/m³

Fig.4 Initial setup of oblique spreading model

Fig.5 Results of oblique spreading model

Fig.6 Volume strain rate of mid-ocean ridge with various spreading obliquityies

Fig.7 Volume strain rate of mid-ocean ridge with various spreading obliquities (no initial temperaure disturbance)

Fig.8 Bathymetry (upper panel) and structural interpretation (lower panel) of SWIR segments 28 and 29

Fig.9 Schematic diagram showing the influence of oblique spreading on mid-ocean ridge segmentation pattern

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