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The University of Southampton
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Ocean and Earth Science, National Oceanography Centre Southampton

Research project: The Accretion of Lower Oceanic Crust

Currently Active:
Yes

Ocean crust formed at fast spreading rates (8cm/yr full rate) has a relatively simple layered stratigraphy, the upper crust is formed of basaltic lava flows and sheeted dikes (1-2km) and the lower crust is formed of gabbroic plutonic rocks (~5km). Despite representing a large proportion of ocean crust, the formation of the lower ocean crust remains poorly understood. Our current understanding of the lower oceanic crust is based on observation from ophiolites (pieces of ocean crust obducted onto continents) and geophysical observation because of the lack of direct sampling.

Fig 1: Cartoon representations of the end member models (From IODP Proceedings Exp 335)
Accretion models

Theoretical models of accretion

Two end member theoretical models have been developed based on geophysical and ophiolite observations (Figure 1):

  • Gabbro glacier model (Henstock et al., 1993., Phipps Morgan & Chen 1993., Quick & Denlinger 1993):
    All of the lower crust crystallises in a high level melt lens and subsequently subsides downwards and away from the ridge axis.
  • Multiple sills model (Boudier et al., 1996., Korenaga & Kelemen 1997., MacLeod & Yoauancq 2000):
    The lower crust forms by the intrusion of multiple melt lenses throughout the lower crust

Alternatively, the lower oceanic crust may form by a combination of these processes.

Fig 2: Cartoon representation of the predicted differences for various parameters between the end member models (from IODP Proceedings Exp335)
Modelling

Testing models of accretion

With suitable samples, the different theoretical models generate testable hypotheses for the accretion of the lower crust. These include addressing the following:

  • Geohemical variation in bulk rock composition
  • Strain rate variation with depth
  • Depth, distribution and magnitude of hydrothermal circulation
  • Cooling rate through the lower crust
Hydrothermally altered gabbro from IODP Hole 1256D.
Altered Gabbro

Current work

Using recently recovered samples from ODP/IODP Hole 1256 (Fig 3) and Hess Deep, we are applying two approaches to understand the accretion of the lower oceanic crust:

  1. Combined petrographic, isotope and geochemical study to investigate the magnitude and distribution of hydrothermal circulation.
  2. Trace element partitioning geospeedometry to determine the cooling rate in gabbroic rocks

Key Contacts

Prof. Damon Teagle (Principal Investigator)
Dr. Michelle Harris (Post Doctoral Researcher)

PhDs and Other Opportunities

Visit GSNOCS

Associated research themes

Formation and Evolution of the Ocean Crust

Volcanic Processes

Hydrothermal Processes and Mineral Deposits

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