Magmato‐tectonic cyclicity at the ultra‐slow spreading Southwest Indian Ridge: Evidence from variations of axial volcanic ridge morphology and abyssal hills pattern

Abstract

[1] On-axis deep tow side scan sonar data are used together with off-axis bathymetric data to investigate the temporal variations of the accretion processes at the ultra-slow spreading Southwest Indian Ridge. Differences in the length and height of the axial volcanic ridges and various degrees of deformation of these volcanic constructions are observed in side scan sonar images of the ridge segments. We interpret these differences as stages in an evolutionary life cycle of axial volcanic ridge development, including periods of volcanic construction and periods of tectonic dismemberment. Using off-axis bathymetric data, we identify numerous abyssal hills with a homogeneous size for each segment. These abyssal hills all display an asymmetric shape, with a steep faulted scarp facing toward the axis and a gentle dipping volcanic slope facing away. We suggest that these hills are remnants of old split axial volcanic ridges that have been transported onto the flanks and that they result from successive periods of magmatic construction and tectonic dismemberment, i.e., a magmato-tectonic cycle. We observe that large abyssal hills are in ridge sections of thicker crust, whereas smaller abyssal hills are in ridge sections of thinner crust. This suggests that the magma supply controls the size of abyssal hills. The abyssal hills in ridge sections of thinner crust are regularly spaced, indicating that the magmato-tectonic cycle is a pseudoperiodic process that lasts $0.4 m.y., about 4 to 6 times shorter than in ridge sections of thicker crust. We suggest that the regularity of the abyssal hills pattern is related to the persistence of a nearly constant magma supply beneath long-lived segments. By contrast, when magma supply strongly decreases and becomes highly discontinuous, regular abyssal hills patterns are no longer observed.

Interactions between hotspots and the Southwest Indian Ridge during the last 90 Ma: Implications on the formation of oceanic plateaus and intra-plate seamounts

“…It has been shown that intensive magmatism has caused a thickened crust or higher mantle temperature. This area may be affected by the Marion hotspot [23][24][25]. From the east of DII transform fault to 49°30′E, the ridge axis deepens and the RMBA becomes more positive.…”

“…Previous geophysical and geochemical studies have shown that there is a decreasing trend of the magmatic flux from west to east between the AB transform fault and RTJ [20][21][22]. According to the geophysics (bathymetry, side scan, gravity, and magnetic), geometry (the length of ridge segments, oblique spreading angle, incidence of transform fault), geochemical and petrologic characteristics of the SWIR, the eastern part of the SWIR is separated into four super segments by the DII (42°E), GA (52°20′E) and MEL (60°45′E) FZs [23,24]. The shallowest part from the AB to DII FZs corresponds to a negative residual mantle Bouguer gravity anomaly (RMBA).…”

230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

“…Duanqiao field is located near the central volcano and there is a hot mantle and/or fertile melt beneath Duanqiao field (Tao et al 2012;Niu et al 2015). The crust thickness is 9.5 km, suggesting the existence of AMC (Axial Magma Chamber) which provides magma source to the field Mendel et al 2003). The periodic hydrothermal activity at Duanqiao may be related to the heat source provided by the local interaction of magmatism and tectonism.…”

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

“…Dashed lines run along axis, in white for oblique domains and in black for orthogonal domains. Grey shaded areas extending off-axis along flow lines from orthogonal domains have thicker than average gravity-derived crust (Mendel et al 2003). (b) Along-axis depth profile (detail of Fig.…”