Three‐dimensional seismic structure of the Dragon Flag oceanic core complex at the ultraslow spreading Southwest Indian Ridge (49°39′E)
Minghui ZhaoXuelin QiuJiabiao LiDaniel SauterAiguo RuanJohn ChenMathilde CannatS. C. SinghJiazheng ZhangZhenli WuXiongwei Niu
77
Citation
58
Reference
10
Related Paper
Citation Trend
Abstract:
The Southwest Indian Ridge (SWIR) is an ultraslow spreading end‐member of mid‐ocean ridge system. We use air gun shooting data recorded by ocean bottom seismometers (OBS) and multibeam bathymetry to obtain a detailed three‐dimensional (3‐D) P wave tomographic model centered at 49°39′E near the active hydrothermal “Dragon Flag” vent. Results are presented in the form of a 3‐D seismic traveltime inversion over the center and both ends of a ridge segment. We show that the crustal thickness, defined as the depth to the 7 km/s isovelocity contour, decreases systematically from the center (∼7.0–8.0 km) toward the segment ends (∼3.0–4.0 km). This variation is dominantly controlled by thickness changes in the lower crustal layer. We interpret this variation as due to focusing of the magmatic activity at the segment center. The across‐axis velocity model documents a strong asymmetrical structure involving oceanic detachment faulting. A locally corrugated oceanic core complex (Dragon Flag OCC) on the southern ridge flank is characterized by high shallow crustal velocities and a strong vertical velocity gradient. We infer that this OCC may be predominantly made of gabbros. We suggest that detachment faulting is a prominent process of slow spreading oceanic crust accretion even in magmatically robust ridge sections. Hydrothermal activity at the Dragon Flag vents is located next to the detachment fault termination. We infer that the detachment fault system provides a pathway for hydrothermal convection.Keywords:
Seafloor Spreading
Detachment fault
Seismometer
Abstract Oceanic detachment faults play a central role in accommodating the plate divergence at slow-ultraslow spreading mid-ocean ridges. Successive flip-flop detachment faults in a nearly-amagmatic region of the ultraslow spreading Southwest Indian Ridge (SWIR) at 64°30’E accommodate ~100% of plate divergence, with mostly ultramafic smooth seafloor. Here we present microseismicity data, recorded by ocean bottom seismometers, showing that the axial brittle lithosphere is on the order of 15 km thick under the nearly-amagmatic smooth seafloor, which is no thicker than under nearby volcanic seafloor or at more magmatic SWIR detachment systems. Our data reveal that microearthquakes with normal focal mechanisms are colocated with seismically-imaged damage zones of the active detachment fault and of antithetic hanging-wall faults. The level of the hanging-wall seismicity is significantly higher than that documented at more magmatic detachments of slow-ultraslow ridges, which may be a unique feature of nearly-amagmatic flip-flop detachment systems.
Seafloor Spreading
Seismometer
Detachment fault
Mid-Atlantic Ridge
Ridge push
Cite
Citations (17)
Researchers devised a simple way to deliver ocean bottom seismometers accurately to the seafloor to study ongoing seismic and volcanic activity near the islands of Mayotte.
Seafloor Spreading
Seismometer
Ocean bottom
Cite
Citations (0)
Seafloor spreading and the cooling of oceanic lithosphere is a fundamental feature of plate tectonics in the Earth, the details of which are unveiled by modeling with constraints from mineral physics and geophysical observations. To work toward a more complete model of the thermal evolution of oceanic lithosphere, we investigate the contributions of axial hydrothermal circulation, oceanic crust, and temperature‐pressure‐dependent thermal properties. We find that models with only temperature‐dependent properties disagree with geophysical observations unless properties are artificially modified. On the other hand, more comprehensive models are in better agreement with geophysical observations. Our preferred model requires a thermal expansivity reduction of 15% from a mineral physics estimate, and predicts a plate thickness of about 110–130 km. A principal result of our analysis is that the oceanic crust is a major contributor to the cooling of oceanic lithosphere. The oceanic crust acts as an insulating lid on the mantle, causing the rate of lithospheric cooling to increase from “crustal” values near the ridge to higher mantle values at old‐age. Major consequences of this insulation effect are: (a) low seafloor subsidence rate in proximity to ridge axes (<5 Ma), (b) the thermal structure of oceanic lithosphere is significantly warmer than previous models, (c) seafloor heat flow is significantly lower over young (<35 Ma) seafloor compared to simple models, (d) a low net seafloor heat flux (∼27 TW), and (e) temperature at the base of the seismogenic zone extends to 700–800°C mantle.
Seafloor Spreading
Hotspot (geology)
Cite
Citations (81)
In seafloor seismic observation, the seismometer is usually installed in the seafloor. The data obtained from the seismometer installed in the seafloor is influenced by background noise. In seafloor observation, it is necessary to install seismometer with consideration of influence from installation environment for observation with high accuracy. This paper introduces the past results from seafloor seismic observation in several installation environments and a new approach to conduct high quality seismic observation in the seafloor.
Seafloor Spreading
Seismometer
Seismic Noise
Cite
Citations (15)
Large-offset oceanic detachment faults are a characteristic of slow- and ultraslow-spreading ridges, leading to the formation of oceanic core complexes (OCCs) that expose upper mantle and lower crustal rocks on the seafloor. The lithospheric extension accommodated by these structures is now recognized as a fundamentally distinct "detachment-mode" of seafloor spreading compared to classical magmatic accretion. Here we demonstrate a paleomagnetic methodology that allows unequivocal recognition of detachment-mode seafloor spreading in ancient ophiolites and apply this to a potential Jurassic detachment fault system in the Mirdita ophiolite (Albania). We show that footwall and hanging wall blocks either side of an inferred detachment have significantly different magnetizations that can only be explained by relative rotation during seafloor spreading. The style of rotation is shown to be identical to rolling hinge footwall rotation documented recently in OCCs in the Atlantic, confirming that detachment-mode spreading operated at least as far back as the Jurassic.
Seafloor Spreading
Detachment fault
Cite
Citations (37)
Seafloor Spreading
Earth crust
Cite
Citations (6)
Seafloor Spreading
Cite
Citations (65)
Seafloor Spreading
Continental Margin
Rift valley
Cite
Citations (313)