Location of Repository

An alternative approach using integrated gamma-ray and geochemical data to estimate the inputs to subduction zones from ODP Leg 185, Site 801

By S. Révillon, S. R. Barr, T. S. Brewer, P. K. Harvey and J. Tarney

Abstract

The goal of the subduction factory project is to obtain a better understanding of processes occurring at convergent margins and performs mass balance calculations for tracer elements. As part of this project, a major objective of ODP Leg 185 is to determine the chemical composition of the inputs to the West Pacific Subduction Factory for use in calculations of elemental mass balance across the subduction zone. To understand such elemental budgets, it is critical to know the lithological diversity and chemical characteristics of the down going oceanic plate. Hole 801C, located ocean-ward of the Mariana island arc system, is the most complete section of old oceanic crust sampled to date but, core recovery in basement holes is often poor (e.g., <30%) resulting in a bias such that the less altered material is preferentially recovered. Integration of drilled cores and downhole wire line logging data was performed to reconstruct a complete section of the drilled basement. Furthermore we integrate gamma ray logging data with the geochemical analyses of recovered cores to estimate the average composition, in terms of potassium and uranium, of the volcanic section in Hole 801C. We used FMS (Formation MicroScanner) images to relocate the samples with respect to the logging depth and to directly compare the logging data and the geochemical data. We demonstrate that the logging tool is well calibrated for K and U in the basement and that differences observed between K2O and U contents measured by the tool and by geochemistry are strongly dependent on the nature of the samples. The average K2O concentration of Hole 801C basement section is 0.34 wt.% using core-derived proportions, 0.51 wt.% using log-derived proportions and 0.47 wt.% using the gamma ray data. In the same manner the average U concentrations are respectively 0.34 ppm, 0.39 ppm and 0.42–0.5 ppm. This implies that K and U budgets recycled in the Mariana subduction zone are 20–50% higher than previously reported. These results demonstrate that a careful core-log-geochemical integration is essential to accurately estimate the composition of a drilled section and in order to better constraint chemical fluxes into subduction zones

Year: 2002
DOI identifier: 10.1029/2002GC000344
OAI identifier: oai:lra.le.ac.uk:2381/2227
Journal:

Suggested articles

Preview

Citations

  1. (1992). Across-arc variation of lava chemistry in the Izu-Bonin arc: Identification of subduction components, doi
  2. (1998). Alteration and mineralizaion of an oceanic forearc and the ophiolite-ocean analogy, doi
  3. (1998). Applications of FMS images in the Ocean Drilling Program: An overview, in The Geological Evolution of Ocean Basins: Results From the Ocean Drilling Program, edited by A. Cramp et al.,
  4. (1998). Borehole images of the ocean crust: Case histories from the Ocean Drilling Program, in Borehole Imaging: Applications and Case Histories, edited by M. doi
  5. (1998). Causes of spatial compositional variations in Mariana arc lavas: Trace element evidence, doi
  6. (1996). Continental crust, crustal underplating, and low-Q upper mantle beneath an oceanic island arc, doi
  7. (2002). Determining the inputs to the Mariana Subduction Factory: Using core-log integration to reconstruct basement lithology at ODP Hole 801C, doi
  8. Effect of relative plate motion on the deep structure and penetration depth of slabs below the Izu-Bonin and Mariana island arcs, doi
  9. (1997). Element transport from subducted slab to volcanic front at the Mariana Arc, doi
  10. (1990). Enriched back-arc basin basalts from the northern Mariana Trough: Implications for the magmatic evolution of back-arc basins, doi
  11. (2001). Fall Meeting Suppl., F1147,
  12. Funding for this research was provided by a grant from the Natural Environment Research Council (NERC,
  13. Geochemical fluxes during seafloor alteration and the basaltic upper oceanic crust: doi
  14. (1992). Geochemistry and petrography of Cretaceous sills and lava flows, doi
  15. (2000). Group, ODP Logging manual: An electronic guide to ODP logging services, Lamont Doherty Earth Obs. of Columbia Univ.,
  16. (1992). Isotope geochemistry of Leg 129 basalts: Implications for the origin of the widespread Cretaceous volcanic event in the Pacific, doi
  17. (1995). Large scale isotopic Sr, Nd, O isotopic anatomy of altered oceanic crust: DSDP/ODP sites 417/418, Earth Planet. doi
  18. (1996). Mantle anisotropy beneath northwest Pacific subduction zones, doi
  19. (1999). Mariana blueschist mud volcanism: Implications for conditions within the subduction zone, doi
  20. (2001). Pacific Microplate and the Pangea supercontinent in the Early to Middle Jurassic, doi
  21. (1992). Radiometric ages of basaltic basement recovered at Sites 800, 801, and 802, Leg 129, western Pacific Ocean, doi
  22. (1998). Summary Subduction Factory project, paper presented at the SubFac workshop,
  23. (1998). The chemical composition of subducting sediment: Implications for the crust and mantle, doi
  24. (1995). The estimation of modal mineralogy: A problem of accuracy in core-log calibration, in Core-Log Integration, edited by P.
  25. (1996). The Geological Interpretation of Well Logs, Whittles Publishing, Caithness,
  26. (1998). The Subduction Factory Science Plan,
  27. (1999). The uptake of carbon during alteration of oceanic crust, doi
  28. (1999). Two isotopically distinct fluid components involved in the Mariana Arc: Evidence from Nb/B ratios and B, Sr, Nd, and Pb isotope systematics, doi

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.