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Active ocean-continent transform margins: seismic investigation of the Cayman Trough-Swan Island ridge-transform intersection

Peirce, C. and Grevemeyer, I. and Hayman, N.W. and Van Avendonk, H.J.A. (2022) 'Active ocean-continent transform margins: seismic investigation of the Cayman Trough-Swan Island ridge-transform intersection.', Geophysical Journal International .


The southern boundary of the Cayman Trough in theCaribbean is marked by the Swan Islands transform fault (SITF), which also represents the ocean-continent transition of the Honduras continental margin. This is one of the few places globally where a transform continental margin is currently active. The CAYSEIS experiment acquired an ~165 kmlong seismic refraction and gravity profile (P01) running across this transform margin, and along the ridge-axis of the Mid-Cayman Spreading Centre (MCSC) to the north. This profile reveals not only the crustal structure of an actively evolving transform continental margin, that juxtaposes Mesozoic-age continental crust to the south against zero-age ultraslow spread oceanic crust to the north, but also the nature of the crust and uppermost mantle beneath the ridge-transform intersection. The travel times of arrivals recorded by ocean-bottom seismographs (OBSs) deployed along-profile have been inverse and forward modelled, in combination with gravity modelling, to reveal an ~25 km-thick continental crust that has been continuously thinned over a distance of ~65 km to ~10 km adjacent to the SITF, where it is juxtaposed against ~3-4 km-thick oceanic crust. This thinning is primarily accommodated within the lower crust. Since Moho reflections are only sparsely observed, and, even then, only by a few OBSs located on the continental margin, the 7.5 km s -1 velocity contour is used as a proxy to locate the crust-mantle boundary alongprofile. Along the MCSC, the crust-mantle boundary appears to be a transition zone, at least at the seismic wavelengths used for CAYSEIS data acquisition. Although the travel-time inversion only directly constrains the upper crust at the SITF, gravity modelling suggests that it is underlain by a higher density (>3000 kg m-3 ) region spanning the width (~15 km) of its bathymetric expression, that may reflect a broad region of metasomatism, mantle hydration or melt-depleted lithospheric mantle. At the MCSC ridge-axis to the north, the oceanic crust appears to be forming in zones, where each zone is defined by the volume of its magma supply. The ridge tip adjacent to the SITF is currently in a magma rich phase of accretion. However, there is no evidence for melt leakage into the transform zone. The width and crustal structure of the SITF suggests its motion is currently predominantly orthogonal to spreading. Comparison to CAYSEIS Profile P04, located to the west and running across-margin and through 10 Ma MCSC oceanic crust, suggests that, at about this time, motion along the SITF had a left-lateral transtensional component, that accounts for its apparently broad seabed appearance westwards.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Publisher statement:AM: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Geophysical Journal International following peer review. The version of record for [C Peirce, I Grevemeyer, N W Hayman, H J A Van Avendonk, Active ocean-continent transform margins: seismic investigation of the Cayman Trough-Swan Island ridge-transform intersection, Geophysical Journal International, 2022;, ggac019,] is available online at:
Date accepted:14 January 2022
Date deposited:14 January 2022
Date of first online publication:18 January 2022
Date first made open access:14 January 2022

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