What’s rate got to do with it?: Oceanic core complex evolution and serpentinized mantle exhumation at the Mid-Cayman Spreading Center.

Hayman, Nicholas W., Van Avendonk, Harm J., Harding, Jennifer, Peirce, Christine and Grevemeyer, Ingo (2018) What’s rate got to do with it?: Oceanic core complex evolution and serpentinized mantle exhumation at the Mid-Cayman Spreading Center. [Invited talk] In: AGU Fall Meeting 2018. , 10.-14.12.2018, Washington, D.C., USA .

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Abstract

The world’s slow and ultraslow spreading centers host oceanic core complexes and exhume extensive tracts of mantle to the seafloor. Oceanic core complexes (OCCs) are several km-high, detachment-fault-bounded massifs of lower crust and upper mantle materials and appear to form when magmatic accretion and tectonic stretching are somewhat proportional. Mantle exhumation at ultraslow spreading rates may be due to passive upwelling leading to a thicker lithospheric lid, lower mantle potential temperature, and an anomalously thin oceanic crust. The ultraslow spreading (~15 mm/yr full rate) Mid-Cayman Spreading Center (MCSC) poses some interesting challenges to these global relationships. The spreading center itself is in some ways similar to slow-spreading (>20 mm/yr) centers, and especially the Mid-Atlantic Ridge (MAR): faulting and magmatic intrusion are “killing” the Cayman OCCs in one place causing hydrothermal venting, basalts have similar Mg# compositions to those along the MAR, and seismicity also defines a relatively shallow (<6-10 km) brittle-ductile transition. Yet, the MCSC has some conspicuous differences from slow spreading centers: axial bathymetry is far deeper, from >6 km in the deep areas of the rift and ~2.5 km on the OCC summit, crustal thickness is thin, <3 km away from OCCs and ~5 km within them, and incompatible element concentrations in basalt are consistent with low mantle potential temperature. As Cayman OCCs were spread off the MCSC axis they were dismembered by normal faults forming curvilinear scarps, and OCCs formed in the same overall positions as the previous one as the “footwall domain” persistently spread to the west. Most remarkably, there is an apparent increase in the amount of exhumed serpentinized mantle across a ~10-Ma isochron without any significant change in spreading rate. The Cayman Trough thus illustrates that spreading rate alone does not govern many of the characteristics attributed to ultraslow spreading centers, and indeed no one petrological or structural model captures all of the heterogeneity exhibited in systems such as the Cayman Trough. Mantle heterogeneity, unexpected dynamics in asthenosphere-lithosphere relationships, and complicated crustal strain patterns all are significant controls on slower spreading MOR systems.

Document Type: Conference or Workshop Item (Invited talk)
Additional Information: T32C-01
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Date Deposited: 11 Dec 2018 08:32
Last Modified: 11 Dec 2018 08:32
URI: https://oceanrep.geomar.de/id/eprint/44911

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