4-D Architecture of the Oceanic Lithosphere

Chair: Jian Lin

Working Group Members:
UK - Simon Allerton
USA - Donna Blackman
France - Mathilde Cannat
France - Jerome Dyment
France - Pascal Gente
Canada - Kathryn M. Gillis
Spain - Eulalia Gracia
USA - Peter Kelemen
UK - Lindsay Parson
Japan - Nobukazu Seama
UK - Martin C. Sinha
USA - Maya Tolstoy

This working group was active between 1996 and 2004 and had hte objective to promote international efforts to constrain the composition and structure of the oceanic lithosphere, and their along- and across-axis variability.

1999 - 4-D Architecture WG update

by Jian LIn, Chair

This working group was established in 1996 to promote international collaboration in studying the structure, composition, and tectonics of the oceanic lithosphere, especially its accretionary processes at mid-ocean ridges. The InterRidge community in this research area has a strong tradition of international cooperation, as shown by frequent occurrence of researchers from one country participating in sea-going programs of the other countries. In the last decade, for example, much of the progress in understanding the segmentation processes of the northern Mid-Atlantic Ridge has been the result of research cruises and shore-based programs from multiple InterRidge countries including the US, France, UK, Japan, Russia, and others. Clearly such impressive progress could not have been achieved by one or two countries alone.

In 1999 Jian Lin of the Woods Hole Oceanographic Institution (USA) took over as Chair of this working group. The working group would like to express sincere gratitude to the founding Chair Lindsay Parson for his exceptional leadership and dedication during the first three years of the group - thanks, Lindsay! The working meet group met in Dec. 8, 1998 during the Fall AGU meeting in San Francisco, California to discuss several issues related to lithospheric programs in the coming years as detailed below. The group seeks comments, suggestions, feedbacks, and information exchanges from the wide InterRidge community on all issues related to studies of oceanic lithosphere. Comments and information can be submitted to intridge@ori.u-tokyo.ac.jp and/or jlin@whoi.edu.

InterRidge Theoretical Institute (IRTI)
During discussion within both the 4-D Architecture and Hydrothermal Fluxes working groups, it was felt that the time is ripe for InterRidge to host a focused meeting on the "Thermal Regime of Ocean Ridges and the Dynamics of Hydrothermal Circulation". A 4-day meeting with lectures and discussion was envisioned sometime in year 2000 to gather researchers in the InterRidge community to review, debate, and discuss progress in this active research subject. The InterRidge Steering Committee recommended that the meeting be called an InterRidge Theoretical Institute (IRTI) in keeping with the terminology used by the US RIDGE program. The planning of the meeting is currently underway.

Recent Meetings
The 4-D Architecture working group seeks to actively promote the exchange of the latest results of lithospheric studies at various national and international meetings. Members of the working group has sponsored special sessions on "Magma Focusing and the Segmentation of Mid-Ocean Ridges at all Spreading Rates" at the Fall AGU meeting in Dec. 1998; "Extensional Tectonics in the Oceanic Lithosphere from Continental Margins to Mid-Ocean Ridges" at the EUG meeting in April 1999; and "Evolution of Oceanic Spreading Centers and Their Discontinuities" at the spring AGU meeting in June 1999. In addition, InterRidge will be a co-sponsor (with the Geological Society of London and the Geological Society of America) of a meeting in March 2000 on "The Nature and Tectonic Significance of Fault Zone Weakening".

Drilling the Oceanic Lithosphere
The 4-D Architecture working group is coordinating with ODP in promoting oceanic lithosphere drilling programs. In spring 1998 ODP established a Program Planning Group (PPG) on the "Architecture of the Oceanic Lithosphere" to update and implement the drilling plan outlined in the 1996 Woods Hole Workshop on "The Ocean Lithosphere and Scientific Drilling". J. Cann and R. Batiza are the Co-Chairs of the ODP PPG and three of its members (M. Cannat, K. Gillis, and P. Kelemen) are also members of the InterRidge 4-D Architecture working group. Since its first meeting in May 1998, the ODP PPG has interacted with the PIs of drilling proposals that address lithosphere priorities, and has helped putting together new proposals. It has made recommendations in terms of priorities for ODP technological development. The PPG is also mandated to contribute to the planning process for post-2003 scientific ocean drilling.

The second meeting of the ODP PPG was held in Dec. 1998. In the period up until 2003, the PPG recommends two main thrusts for litho-spheric drilling. First, a start should be made on the drilling of an intact section of fast spreading ocean crust. This is likely to take place in three stages, a preliminary stage of pilot drilling, a second stage using current technology that would drill to about 3000 m penetration, and a third stage using riser technology which would complete the task. The first two stages are achievable with current drilling technology and may be planned before 2003. Possible locations for the deep drilling site were considered against a list of 11 essential and 6 desirable criteria. The Guatemala Basin, for which there is already a proposal in the system, fits most of these criteria. The PPG is currently working with the proposal PIs to promote site survey and improve the proposal.

Second, a major thrust should be made before 2003 to develop further our understanding of the dynamics of the plutonic foundations of the oceanic lithosphere. In fast spreading crust, the plutonic foundations are rarely brought close to the surface. Hess Deep is one place where this happens, and results from a previous drilling leg are now the basis for petrological interpretations of magmatic processes in fast spreading oceanic crust. A letter of intent has been submitted for further drilling. But new site surveys are required to unravel the complex tectonic history of the proposed drill sites. The PPG is currently interacting with PIs of both the drilling letter of intent and the site survey cruise proposals in order to improve and promote both. In slow spreading crust, there are a number of drilling proposals in the ODP system. A proposal for drilling an area close to 151/4N in the Atlantic, where peridotite seems to make up a large part of the surface layer, has recently received good reviews in the ODP system and is in good position for drilling before 2003. A proposal for new drilling around site 735B in the SW Indian Ocean Ridge is also in good shape.

Three preliminary proposals and letters of intent were submitted to ODP for drilling detachment faults of the Atlantic and Indian Oceans. This generic objective is seen as a very high priority by the ODP PPG for pre-2003 drilling of the oceanic litho-sphere. The PPG is in contact with PIs to help produce at least one good full proposal by the end of 1999 in order to have it ranked and scheduled prior to the end of ODP in 2003.

4-D Architecture-related Meetings and Workshops

June 19-22, 1996 - FARA-InterRidge Mid-Atlantic Ridge Symposium: Results from 15°N to 40°N, Reykjavik, Iceland

May 26-29, 1996 - ODP-InterRidge-IAVCEI Symposium: The Oceanic Lithosphere & Scientific Drilling into the 21st Century, North Falmouth and Woods Hole, MA, USA

May 26, 1996 - Meso-Scale WG Workshop: 4-D Architecture of the Oceanic Lithosphere, North Falmouth, MA, USA

Sept. 23-24, 1994 - Meso-Scale WG Workshop: 4-D Architecture of the Oceanic Lithosphere, Boston, MA, USA

Sept. 22-25, 1993 - Meso-Scale WG Workshop: Segmentation and Fluxes at Mid-Ocean Ridges: A Symposium and Workshops, Durham, UK