Abstract
Deep-sea hydrothermal systems at slow/ultraslow-spreading mid-ocean ridges are often located within ultramafic rocks that are part of oceanic core complexes. These complexes contain lower-crustal and mantle sections exhumed due to detachment faulting. Hydrothermal circulation in these environments leads to massive sulfide deposits, hydration of oceanic lithosphere and conditions resembling early Earth’s life origin. However, the relationship between hydrothermal pathways in these environments and crustal and mantle lithologies, faulting, magmatism, serpentinization and alteration is poorly understood. Here we present seismic models of a Mid-Atlantic Ridge core complex and its ultramafic-hosted hydrothermal system derived from full waveform inversion of controlled-source seismic data and from local earthquake tomography. The models and derived rock properties reveal high-permeability channels within serpentinized peridotite along the flanks of the core complex. These channels converge beneath active and fossil hydrothermal fields and are diverted around mechanically strong, impermeable shallow mafic intrusions (2–3 km wide, ~1 km thick), causing hydrothermal outflow and the formation of massive sulfide deposits around the intrusions’ edges. These mafic intrusions also act as lids that limit fluid downflow—and thus serpentinization—in the centre of the core complex. Our results demonstrate that hydrothermal flow in ultramafic settings is controlled by lithology contacts, with mafic intrusions modulating hydrothermal pathways and extent of mantle serpentinization at depth.
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Data availability
The MCS raw data are archived with the IEDA Marine Geoscience Data System (https://doi.org/10.1594/IEDA/320244). The OBS data are archived at the IRIS Data Management Center under code X3 (https://www.fdsn.org/networks/detail/X3_2013). The local earthquake catalogue and travel-time data used in this study are available at figshare (https://doi.org/10.6084/m9.figshare.25484716)89. Source data are provided with this paper. Seismic models and derived rock properties are provided in the source data files associated with Fig. 2 and Extended Data Figs. 4 and 5.
Code availability
The LOTOS code for local earthquake tomography is publicly accessible (http://www.ivan-art.com/science/LOTOS/). Other codes are available upon request from the corresponding authors.
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Acknowledgements
We are grateful to the captain, crew, technical staff and science party of the R/V M. G. Langseth leg MGL1305 and the R/V Pelagia leg 64PE382, and the NSF-funded Ocean Bottom Seismic Instrument Center (formerly OBSIP, https://obsic.whoi.edu) team. We thank R. Sohn for providing the microseismicity catalogue. This work was supported by the NSF grant OCE-2001012 to J.P.C. and H.J. Data acquisition was supported by NSF grants OCE-0961680 and OCE-0961151 to J.P.C. and R.D. H.J. was partially supported by the Ocean Frontier Institute International Postdoctoral Fellowship Program of Dalhousie University in partnership with Woods Hole Oceanographic Institution.
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H.J. performed the multichannel seismic data processing and modelling, interpreted the results, wrote the manuscript and acquired funding. J.P.C. co-led the data acquisition, conducted the local earthquake tomography and effective medium modelling, interpreted the results, wrote the manuscript and acquired funding. R.D. co-led the data acquisition, provided the controlled-source ocean-bottom seismometer tomography model and revised the manuscript. M.R.N. revised the manuscript and acquired funding.
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Extended data
Extended Data Fig. 1 VP model evolution through the streamer tomography and full waveform inversion (FWI) of profile 112.
a and b, VP model and spatial gradients after the streamer traveltime tomography; c and d, after FWI of 3-6 Hz data; e and f, after FWI of 3-9 Hz data; g and h, after FWI of 3-14 Hz data, same as shown in Fig. 2. Models in a, c and e are used as starting models in following stages that result in models in c, e and g, respectively. Inverted triangles are projected locations of hydrothermal fields as shown in Fig. 1b.
Extended Data Fig. 2 Waveform data fitting along profile 112 around the Rainbow massif.
a, Bathymetry along profile 112. b, Sum of squared amplitude within each windowed shot gather, for the observed data, initial residual (modeled with the tomography-derived starting model and inverted 3-14 Hz source signature) and final residual, respectively. c, The initial and final residual normalized by the observed data size. d, The cross-correlation coefficients between the observed and the initial model data and between the observed and final model data.
Extended Data Fig. 3 Chequerboard tests for the full waveform inversion (FWI) of profile 112.
a, c and e, Input chequerboard patterns with different anomaly size or half wavelength that are described in the plot. b, d and f, Recovered anomalies from the FWI of the noisy synthetic data generated using input patterns of a, c and e, respectively. Labeled contours are VP from the final FWI model of field data (Fig. 2a).
Extended Data Fig. 4 Geophysical cross-sections along profile 114.
a. VP; b. VP anomalies; and c. VP gradients (amplitude of total spatial gradient combined with the sign of vertical gradient) derived from the full waveform inversion of multichannel seismic data. Labeled black contours in a-c all correspond to the VP model in a. d. VP/VS ratios derived from the local earthquake tomography. Preferred estimates of, e. degree of serpentinization and, f. porosity from effective medium theory consistent with the [VP, VP/VS] results in a and d (Methods). Inverted triangles are projected locations of hydrothermal fields as shown in Fig. 1b. The insets in a and b show zoomed-in plots of the shallow low-VP zones associated with the hydrothermal fields. Black-white dashed lines in a, b and e delineate low-VP channels as interpreted in b. Red-white dashed lines in c and f delineate high-VP gradients as interpreted in c. The dark gray patches on e and f mark interpreted gabbro-dominant regions.
Extended Data Fig. 5 Geophysical cross-sections along profile 113.
a. VP; b. VP anomalies; and c. VP gradients (amplitude of total spatial gradient combined with the sign of vertical gradient) derived from the full waveform inversion of multichannel seismic data. Labeled black contours in a-c all correspond to the VP model in a. d. VP/VS ratios derived from the local earthquake tomography. Preferred estimates of, e. degree of serpentinization, and, f. porosity from effective medium theory consistent with the [VP, VP/VS] results in a and d (Methods). Inverted triangles are projected locations of hydrothermal fields as shown in Fig. 1b. The insets in a and b show zoomed-in plots of the shallow low-VP zones associated with the hydrothermal fields. Black-white dashed lines in a, b and e delineate low-VP channels as interpreted in b. Red-white dashed lines in c and f delineate high-VP gradients as interpreted in c. The dark gray patches on e and f mark interpreted gabbro-dominant regions.
Extended Data Fig. 7 Relationship of VP/VS ratio and lithology.
The dataset is a compilation of results derived from laboratory measurements (see Methods for data source details). a, VP versus VS diagram with dashed lines denoting constant VP/VS values. b-d, Histograms of VP/VS values for different lithology groups. Solid curves represent cumulative distribution functions, with black curves for groups represented by gray histograms, and dark green curves for groups represented by green histograms. Vertical lines indicate the 95% confidence level (dashed lines) and the 5% confidence level (dotted lines), respectively.
Extended Data Fig. 8 VP vs. VP/VS diagrams and effective medium theory predictions.
Scatter plot of the full waveform inversion (FWI) VP and local earthquake tomography (LET) VP/VS model values. Multi-colored curves represent effective medium theory (EMT) predictions of VP and VP/VS as a function of porosity for a given aspect ratio (dashed lines), or as a function of aspect ratio for a given porosity (solid lines). Dotted green lines with labels correspond to predictions for a non-porous peridotite as a function of serpentinization fraction82 (labeled in 20% increments). Rock matrix is a, unaltered peridotite; b, 50% serpentinized peridotite; c, fully serpentinized peridotite.
Extended Data Fig. 9 Estimates of porosity, crack aspect ratio, and extent of serpentinization along profile 112.
a-c, Endmember models in which the matrix rock is allowed to reach the maximum extent of serpentinization (up to 100%). d-f, Intermediate models in which the maximum extent of serpentinization is limited at 50%. g-i, Endmember models in which the matrix rock is forced to be unaltered peridotite (0% serpentinization).
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Jian, H., Canales, J.P., Dunn, R. et al. Hydrothermal flow and serpentinization in oceanic core complexes controlled by mafic intrusions. Nat. Geosci. (2024). https://doi.org/10.1038/s41561-024-01444-y
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DOI: https://doi.org/10.1038/s41561-024-01444-y