Lithospheric Structure and Tectonic Processes Constrained by Microearthquake Activity at the Central Ultraslow-Spreading Southwest Indian Ridge (49.2° to 50.8°E)
Authors
Wang, W
Hu, H
Zhang, J
Liang, Y
Publication Date
2018Journal Title
Journal of Geophysical Research: Solid Earth
ISSN
2169-9313
Publisher
American Geophysical Union (AGU)
Volume
123
Issue
8
Pages
6247-6262
Type
Article
Metadata
Show full item recordCitation
Yu, Z., Li, J., Niu, X., Rawlinson, N., Ruan, A., Wang, W., Hu, H., et al. (2018). Lithospheric Structure and Tectonic Processes Constrained by Microearthquake Activity at the Central Ultraslow-Spreading Southwest Indian Ridge (49.2° to 50.8°E). Journal of Geophysical Research: Solid Earth, 123 (8), 6247-6262. https://doi.org/10.1029/2017JB015367
Abstract
Beneath ultra‐slow spreading ridges, the oceanic lithosphere remains poorly understood. Using recordings from a temporary array of ocean bottom seismometers, we here report a ~17‐days‐long microearthquake study on two segments (27 and 28) of the ultra‐slow spreading Southwest Indian Ridge (49.2° to 50.8° E). A total of 214 locatable microearthquakes are recorded; seismic activity appears to be concentrated within the west median valley at segment 28 and adjacent nontransform discontinuities (NTDs). Earthquakes reach a maximum depth of ~20 km beneath the seafloor, and they mainly occur in the mantle, implying a cold and thick brittle lithosphere. The relatively uniform brittle/ductile boundary beneath segment 28 suggests that there is no focused melting in this region. The majority of earthquakes are located below the Moho interface, and a 5‐km‐thick aseismic zone is present beneath segment 28 and adjacent NTDs. At the Dragon Flag hydrothermal vent field along segment 28, the presence of a detachment fault has been inferred from geomorphic features and seismic tomography. Our seismicity data show that this detachment fault deeply penetrates into the mantle with a steeply dipping (~65°) interface, and it appears to rotate to a lower angle in the upper crust, with ~55° of rollover. There is a virtual seismic gap beneath magmatic segment 27, which may be connected to the presence of an axial magma chamber beneath the spreading centre as well as focused melting; in this scenario, the increased magma supply produces a broad, elevated temperature environment which suppresses earthquake generation.
Identifiers
External DOI: https://doi.org/10.1029/2017JB015367
This record's URL: https://www.repository.cam.ac.uk/handle/1810/279901
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