Evolution and properties of young oceanic crust: constraints from Poisson's ratio

SUMMARY The seismic velocity of the oceanic crust is a function its physical properties that include lithology, degree alteration and porosity. Variations in these are particularly significant young crust, but also occur with age as it evolves through hydrothermal circulation progressively covered sediment. While such variation may be investigated P-wave alone, joint analysis S-wave allows determination Poisson's ratio, which provides more robust insight into nature change properties. Here we describe independent modelling P- data sets, acquired along an ∼330-km-long profile traversing new to ∼8 Myr-old formed at intermediate-spreading Costa Rica Rift (CRR). Despite coverage being almost four-times lower than set, both models demonstrate correlations local variability long-wavelength increase distance, thus age, from ridge axis up 0.8 0.6 km s−1, respectively. Using Vp Vs calculate ratio (σ), reveals typical structure for generally high values uppermost decrease minimum 0.24 by 1.0–1.5 sub-basement, before increasing again throughout crust. observed upper crustal inσ most likely results sealing fractures, supported observations porosity depth (from ∼15 <2 per cent) dyke sequence Ocean Drilling Program borehole 504B. High (>0.31) north flank CRR and, whilst this falls within ‘serpentinite’ classification lithological proxies, morphological evidence pervasive surface magmatism limited tectonism suggests, instead, cause form fracturing thus, dominant control on newly South CRR, representative distance spreading centre, result mineralization increased fracture infill. This modelled 3-D anisotropy. Crustal segments during periods low half-spreading rate (<35 mm yr−1) relative background, indicating retention associated greater degrees time their formation. Across south find average 1 decreases ∼0.0084 Myr−1 prior thermal suggesting that, least ∼7 Myr, advective processes dominate early CRR-generated evolution, consistent heat flow measurements.