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Magmatic and tectonic segmentation of the intermediate-spreading Costa Rica Rift - a fine balance between magma supply rate, faulting, and hydrothermal circulation

Robinson, A.H.; Zhang, L.; Hobbs, R.W.; Peirce, C.; Tong, V.C.H.

Magmatic and tectonic segmentation of the intermediate-spreading Costa Rica Rift - a fine balance between magma supply rate, faulting, and hydrothermal circulation Thumbnail


Authors

A.H. Robinson

L. Zhang

R.W. Hobbs

V.C.H. Tong



Abstract

3-D tomographic modelling of wide-angle seismic data, recorded at the intermediate-spreading Costa Rica Rift, has revealed a P-wave seismic velocity anomaly low located beneath a small overlapping spreading centre that forms a non-transform discontinuity at the ridge axis. This low velocity zone displays a maximum velocity anomaly relative to the ‘background’ ridge axis crustal structure of ∼0.5 km s−1, has lateral dimensions of ∼10 × 5 km, and extends to depths ≥2.5 km below the seabed, placing it within layer 2 of the oceanic crust. We interpret these observations as representing increased fracturing under enhanced tectonic stress associated with the opening of the overlapping spreading centre, that results in higher upper crustal bulk porosity and permeability. Evidence for ongoing magmatic accretion at the Costa Rica Rift ridge axis takes the form of an axial magma lens beneath the western ridge segment, and observations of hydrothermal plume activity and microearthquakes support the presence of an active fluid circulation system. We propose that fracture pathways associated with the low velocity zone may provide the system through which hydrothermal fluids circulate. These fluids cause rapid cooling of the adjacent ridge axis and any magma accumulations which may be present. The Costa Rica Rift exists at a tipping point between episodic phases of magmatic and tectonically enhanced spreading. The characteristics inherited from each spreading mode have been preserved in the crustal morphology off-axis for the past 7 Myr. Using potential field data, we contextualize our seismic observations of the axial ridge structure at the whole segment scale, and find that the proposed balance between magmatic and tectonically dominated spreading processes observed off-axis may also be apparent along-axis, and that the current larger-scale magma supply system at the Costa Rica Rift may be relatively weak. Based on all available geophysical observations, we suggest a model for the inter-relationships between magmatism, faulting and fluid circulation at the Costa Rica Rift across a range of scales, which may also be influenced by large lithosphere scale structural and/or thermal heterogeneity.

Citation

Robinson, A., Zhang, L., Hobbs, R., Peirce, C., & Tong, V. (2020). Magmatic and tectonic segmentation of the intermediate-spreading Costa Rica Rift - a fine balance between magma supply rate, faulting, and hydrothermal circulation. Geophysical Journal International, 222(1), 132-152. https://doi.org/10.1093/gji/ggaa152

Journal Article Type Article
Acceptance Date Mar 20, 2020
Online Publication Date Mar 28, 2020
Publication Date Jul 31, 2020
Deposit Date Jun 10, 2019
Publicly Available Date Mar 29, 2024
Journal Geophysical Journal International
Print ISSN 0956-540X
Electronic ISSN 1365-246X
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 222
Issue 1
Pages 132-152
DOI https://doi.org/10.1093/gji/ggaa152

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Accepted Journal Article (7.6 Mb)
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Copyright Statement
This article has been accepted for publication in Geophysical journal international ©: 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





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