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SUMMARY:Detachment-mode seafloor spreading and the tectonics of oceanic co
 re complexes - Antony Morris\, University of Plymouth
DTSTART:20141125T160000Z
DTEND:20141125T170000Z
UID:TALK54602@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:Seafloor spreading is a fundamental component of the plate tec
 tonic cycle\, responsible for producing two-thirds of the Earth’s surfac
 e\, but our understanding of this process is still far from complete. Rece
 nt exploration of slow and ultraslow spreading systems has revealed a styl
 e of spreading that is radically different from the “normal” magmatic 
 accretion seen at fast spreading rates. In these systems\, large-offset de
 tachment faults are responsible for accommodating plate divergence. These 
 faults exhume deep lithosphere\, forming oceanic core complexes that expos
 e lower oceanic crust and upper mantle rocks on the seafloor. Their widesp
 read occurrence in slow-spreading systems has led to the definition of a n
 ew “detachment-mode” of seafloor spreading\, representing a major adva
 nce in understanding plate tectonics. This talk will show how palaeomagnet
 ic analysis of core samples recovered from the footwalls of oceanic detach
 ment faults by scientific ocean drilling has allowed the tectonic evolutio
 n of oceanic core complexes to be determined. Using magnetic remanences ac
 t as a marker\, it has been possible to demonstrate that oceanic detachmen
 t faults initiate as steep normal faults at depth\, and shallow into low a
 ngle extensional faults through rotation of their footwalls. This characte
 ristic rolling-hinge style of rotation provides a key to recognizing this 
 important tectonic process in ophiolites\, allowing the record of detachme
 nt-mode seafloor spreading to be extended back beyond the age of the oldes
 t crust in the modern oceans. \n\nKey references:\n\nEscartín\, J. & Cana
 les\, J. P.\, 2011. Detachments in oceanic lithosphere: Deformation\, magm
 atism\, fluid flow\, and ecosystems. Eos Trans. AGU\, 92(4)\, 31\, doi:10.
 1029/2011EO040003.\n\nMaffione\, M.\, Morris\, A. & Anderson\, M. W.\, 201
 3. Recognizing detachment-mode seafloor spreading in the deep geological p
 ast. Scientific Reports 3\, doi:10.1038/srep02336.\n\nMorris\, A.\, Gee\, 
 J. S.\, Pressling\, N.\, John\, B. E.\, MacLeod\, C. J.\, Grimes\, C. B. &
  Searle\, R. C.\, 2009. Footwall rotation in an oceanic core complex quant
 ified using reoriented Integrated Ocean Drilling Program core samples. Ear
 th Planet. Sci. Lett. 287\, 217–228\, doi:10.1016/j.epsl.2009.08.007.\n\
 nSmith\, D. K\, Escartín\, J.\, Schouten\, H. & Cann\, J. R.\, 2008\, Fau
 lt rotation and core complex formation: Significant processes in seafloor 
 formation at slow spreading mid-ocean ridges (Mid-Atlantic Ridge\, 13–15
 ° N). Geochem. Geophys. Geosyst. 9\, doi:10.1029/2007GC001699.\n
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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