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

Research project: The nature and extent of seafloor basement weathering within the South Pacific Gyre

Currently Active: 
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IODP Exp 329 recovered sediment at 7 sites and basement from 3 sites spanning an entire ~100 Myr transect of the South Pacific Gyre (SPG). Our goal during IODP Exp 329 was to explore the nature and extent of sub-seafloor microbiological activity in one of the most biologically barren regions on Earth. Dr Christopher Smith-Duque played a key role in characterizing igneous basement and subsequent hydrothermal alteration.Samples of basement from the South Pacific Gyre are now being used to shed light on the nature of carbon uptake in the oceans, the timing of late stage hydrothermal alteration, and the factors that control the nature and extent of low temperature alteration within upper oceanic basement.

Site locations of Exp 329 with crustal age and gyre location, expressed in terms of chlorophyll abundance
Location of Exp 329 Sites

Scientific aims:

  1. Determine the timing of carbonate emplacement within upper oceanic crust by radiometric dating of calcium carbonate veins.
  2. Investigate the uptake of carbon in the ocean crust over a 100 Myr time scale and its relationship to past seawater cation compositions.
  3. Elucidate the environment of carbonate formation, in terms of source fluid composition and temperature.
  4. Determine the origins of upper oceanic basement across the SPG and what factors are controlling its alteration.
Processes and their potential controls and limits that relate to aging of the ocean crust (After Coggon, R.M)
Aging of ocean crust

Why explore this region?

  1. Prolonged period of low biological activity with crust exposed to seawater provide us with a great opportunity to learn what factors (such as crustal structure and sedimentation) influence the style and intensity of low temperature seafloor weathering.
  2. The research area, which represents over 40% of the Pacific ocean and spans over 100 Myrs of crustal evolution, allows us to observe how ocean crust might evolve over large timescales.
  3. Recovery of calcium carbonate veins from basement within the SPG may give us new insights into palaeoseawater cation chemistry.
  4. Calcium carbonate veins from within ancient oceanic crust presents a unique opportunity to understand the timing of late stage alteration.
Alteration of a basaltic lava flow boundary recovered from ~100 Ma Site U1365 during IODP Exp 329 (Credit: IODP).
Basement alteration

How are we going to do it?

  1. A comprehensive analysis of fresh and altered whole rock and secondary mineral compositions, including major element abundances, trace and REE abundances, and 87Sr/86Sr will allow us to assess the chemical fluxes associated with seafloor weathering. This will be used to help us assess the factors that are controlling alteration and help us better understand the effect of ridge flank alteration on global chemical budgets and fluxes.
  2. Precision U concentration and Pb-isotope ratios by ICP-MS and MC-ICP-MS together with measurements of 87Sr/86Sr, δ18O,cation ratios (Sr/Ca and Mg/Ca), and Major and trace element abundances will be used to determine the nature and timing of late stage alteration processes and provide new insights into recent palaeoseawater Sr/Ca and Mg/Ca estimates from calcium carbonate veins.

 

Key Contacts

Prof. Damon Teagle (Principal Investigator)
Dr. Christopher Smith-Duque (Researcher)

PhDs and Other Opportunities

Visit GSNOCS

Associated research themes

Formation and Evolution of the Ocean Crust

Hydrothermal Processes and Mineral Deposits

Past Present and Future Environmental Change

Related research groups

Geochemistry

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