Summary:
 
 
 

Attending: Rodey Batiza (co-Chair), Joe Cann (co-Chair), Mathilde Cannat, Don Forsyth, Jeff Gee, Kathy Gillis, Ingo Grevemeyer, Peter Kelemen, Graham Kent, Eiichi Kikawa, Charles Langmuir, Rolf Pedersen, Philippe Pezard.

Jamie Allan (NSF), Bruce Malfait  (NSF) , Gene Pollard (TAMU Engineering Group), John Tarduno (Interiors SSEP).

Regrets: Georges Ceuleneer (ISSEP liason)
 
 

1. Welcoming Remarks, Logistics, Introductions (R. Batiza)

2. Approval of the Agenda- additional items

3. SCICOM-related matters
 Last SCICOM meeting (J. Cann)
 Post 2003 planning- letter of interest
 PPG Reporting
 Proposal Confidentiality and PPG Requests for Proposals
 
4. Report of ISSEP activities (J. Tarduno)
 Recent proposal Actions
 Other

5. Update on Engineering Developments (Gene Pollard)

6. Report of Long-Term Observatories (LTO) PPG Meeting (July 6,7  1998)- R. Batiza
 Interest in RABO
 InterRIDGE Connection (M. Cannat)
 
7. Update on Intact section -Guatemala Basin site survey cruise (G. Kent)

8. Update on Plutonic Foundations

  Layer 3
   735B  (535 Full)    (P. Kelemen)
   Hess Deep (551-Pre)    (K. Gillis)

  Mantle
   15°N MAR (525 Full)    (P. Kelemen)
   Detachments
    Kane (532-Pre2)   (J. Cann )
    Atlantis (512 Add)   (J. Cann )
   Intermediate Spreading Rate (531-Pre) (I. Grevemeyer)

9. Future Proposals

 a) Zero-age drilling
  EPR (proposal to be submitted by March 15, 1999)
  MAR (part of 4D architecture)

 b) Ridge Axis Borehole Observatories (RABO)
 
 c) Active Hydrothermal Sites

 d) Anatomy of a slow spreading segment
 

10. Report to ISSEP by Feb 15, 1999
 - how many more meetings?
 - how well are we fulfilling (have we fulfilled?) our mandate?
 

11. Next meeting? or Final PPG Report??
 

Meeting Minutes

1. Report of SCICOM Meeting: Joe Cann gave a report on the last SCICOM meeting. A general impression is that PPGs have a dual role: to insure that proposals addressing the important scientific questions listed in the ODP Long Range Plan are actually written and nurtured, and to create, via our reports to the SSEPs, a climate of opinion within the SSEPs and at SCICOM that favorably influences our PPGs scientific priorities. It is also clear that for both the SSEPs and SCICOM to react favorably to any proposal, the proposal must clearly spell out the importance of the objectives in a manner understandable to these scientifically very diverse groups. SCICOM has approved drilling on the Ontong Java plateau and the PacManus site.

2. Post-2003 Planning: The PPG reviewed the letters of interest that were submitted to JOIDES on topics of interest to the PPG. The group also discussed the ODP Town meeting at AGU and the upcoming COMPLEX meeting (May 26-29, Vancouver).

3. ISSEP Report from John Tarduno: John Tarduno discussed at length the proposal review process in which the SSEPs are engaged, results on specific proposals of interest to our PPG, and finally, what our PPG can do to help the SSEPs and advance the scientific themes of interest to our group. He stressed that successful drilling proposals must highlight the importance of the science, discuss testable hypotheses that drilling could help resolve, and in general communicate these items clearly to the multidisciplinary groups comprising the SSEPs and SCICOM. The SSEPs do not rank proposals, but rather, establish how the proposals address key science questions in the ODP Long Range Plan, determine through the review process which proposals are the strongest, and provide advocacy for all strong proposals within the mandated areas. SCICOM then assigns a watchdog to each proposal. The ISSEP considers proposal in areas including mantle dynamics, ocean crust formation, convergent margins, earthquake mechanics and active processes.
 Specific Proposals:
  522-Full (Superfast Ocean crust, Wilson et. al.)- The ISSEP decided that this proposal needed stronger scientific justification and results of the site survey before being sent out for review.
  535-Full (735 Deep-Slow spreading ridge, Dick et al.)- sent for external review
  551-Pre (Hess Deep, Gillis et al.)- not encouraged
  525-Full (15°20'N MAR peridotites, Kelemen et al.)- sent for external review- needs short addendum
  512 (Eastern Atlantis RTI, Blackman et al.)- awaits site survey results
  532-Pre (Kane megamullion, Tucholke et al.)- recommended for development to full proposal

 At its March meeting, SCICOM will review the progress of all the PPGs, including our AOL PPG. The most useful information that we can provide (to SSEPs and to SCICOM) is a discussion of how particular programs are related scientifically and how they comprise, as a group, a cohesive plan of attack on a particular scientific question up to and beyond 2003. Tarduno stressed that this was probably the most important role we could fulfill, not in ranking themes as we did at our last meeting in response to EXCOMs need to establish budgetary priorities.

4. PPG Reporting: Tarduno's discussion cleared up many of the questions we had concerning reporting.

5. Proposal Confidentiality: We reviewed the new JOIDES policy on confidentiality of drilling proposals. We can still obtain copies of drilling proposals, however we must obtain permission first from the lead PI of the proposal.

6. Long Term Observatories PPG (LTO PPG) Meeting: Batiza reported on the July 6-7, 1998 meeting of the LTO PPG. Later discussion considered the issues of our scientific overlap with the LTO PPG, for example in the study of hydrothermal cooling and alteration of ridge axes and flanks, and the issue of difficulties in drilling on zero-age crust.

7. Proposals for drilling zero-age crust: A group including R. Haymon and R. Batiza met during AGU to discuss the scientific objectives of drilling zero-age crust at the East Pacific Rise at 9°-10·N. There are plans to submit a drilling proposal, coordinated with TAMU engineers, in March. Discussion of zero-age drilling at slow spreading rates focused on a probable drilling proposal to be submitted for the Lucky Strike area.

8. Report by Gene Pollard (TAMU) on engineering developments: Gene Pollard presented a report including the latest drilling schedule, the test of the hammer drill-in casing, active heave compensation, diamond core barrel, measurement while drilling (MWD), and expected drilling times for deep multiple reentry holes into ocean crust. Gene offered to work with members of the PPG on detailed planning of zero-age and long reentry holes.

9. Proposal updates:

 522-Full (Superfast Ocean crust, Wilson et. al.)- The ISSEP decided that this proposal needed stronger scientific justification and results of the site survey before being sent out for review. The PPG discussed the upcoming site survey and the possibility that the Alijos Rock site could also be surveyed during the cruise. The Alijos Rock site was formed at a higher magnetic latitude than the Guatemala basin sites, and is therefore of great interest. We also discussed the fact that the magnetics community is very interested in drilling a polarity transition, in which case a higher magnetic latitude is important for obtaining unambiguous signals. Finally, we discussed the fact that there are presently no good tools available for obtaining well-oriented drill cores.

 551-Pre (Hess Deep, Gillis et al.)- The ISSEP did not encourage this proposal, so the PPG discussed possible next steps given the extreme importance of Hess Deep as the most likely site for obtaining plutonic lower crustal samples representative of fast spread crust. After considerable discussion, it was tentatively decided to appoint a small group of interested PPG members (K. Gillis, P. Kelemen, and R. Pederson) to take the lead in working with H. Dick and J. Natland to produce a site survey proposal and a new preproposal for drilling.

 525-Full (15°20'N MAR peridotites, Kelemen et al.)- The ISSEP sent the proposal out for external review- a  short addendum on peridotites will be provided by Kelemen. Kelemen noted that the NOBEL survey showed variable thickness of lower velocity material overlying the high velocity (presumably) fresh peridotites.

 535-Full (735 Deep-Slow spreading ridge, Dick et al.)- The ISSEP sent this proposal for external review. The recent site survey work was briefly discussed.
 

 512 (Eastern Atlantis RTI, Blackman et al.)- It was noted that recent work revealed high velocity material ~400-800m below the surface of the inferred detachment fault.

 532-Pre (Kane megamullion, Tucholke et al.)- The ISSEP recommended this program for development to full proposal. Recent work with the Shenkai 6500 found outcrops of basalt on the presumed detachment surface.

 531-Pre (CIR-Green Rock Hill- Peridotites from medium spreading ridge, Snow et al). This proposal is scientifically very interesting, however it may be several years before a site survey can be completed. Certainly, exploring the nature of possible detachment surfaces to understand their dynamics is justified at a wide range of spreading rates, from ultra-slow,  slow, and medium spreading rates

10. Future Proposals: The PPG discussed a variety of opportunities for future drilling proposals addressing key AOL topics:
 EPR zero-age drilling-  A proposal will be submitted March 15 for zero-age drilling in the 9°-10°N region.
 MAR zero-age drilling- There is a consensus that the most important drilling at zero age along slow ridges should be targeted on active hydrothermal systems. It is generally agreed that at the moment, what is needed for understanding the architecture of slow spread shallow ocean crust is more dredging  and mapping.
 MAR hydrothermal systems-  We discussed the fundamental importance of drilling the reaction zones of hydrothermal systems at slow ridges. There is an active proposal for additional drilling in the TAG area (proposal 507). In addition, there will probably be a pre proposal submitted for possible drilling at Lucky Strike, and possibly the Rainbow hydrothermal site.

11. Interim AOL PPG Report to SSEPs:  The AOL PPG has been asked to give a progress report to John Tarduno so that he and Ted Moore can provide a review of PPGs for SCICOM at their March meeting. Tarduno has requested our report by 15 February, 1999. Our Interim Report below is meant to provide a scientific context for the drilling proposals within our mandate and to show how each represents an integral part of our overall program for investigating the Architecture of Ocean lithosphere. In addition, we are asked how many meetings we have had and our evaluation of how well we have met or will meet our mandate:
 The AOL PPG has met twice so far: 1) 8-10 May, 1998 in La Jolla, CA. and 2) 11-12 December, 1998 in San Francisco. Minutes of both these meetings are availbale on the JOIDES Web site. Our Interim Report describes our long-term strategy for investigating the architecture of oceanic lithosphere formed at different spreading rates- the first point of our mandate. Overall, we feel that most of the proposals needed to form a coherent program have either been submitted or will be submitted in the near future. We have identified potential geographic areas as targets for drilling, as described in our Interim Report. The technological requirements necessary to achieve our objectives include, prior to 2003, a means of drilling deep holes into the upper oceanic crust produced at fast spreading rates, with the eventual goal of drilling an intact section through to the upper mantle. Active heave compensation, hammer drill-in casing, and new narrow-kerf bits all seem to offer the potential for achieving deep penetration of fast spread crust having a topmost  50-100m thick layer of rubbly basalt.  In the post- 2003 program, this goal will require a riser ~3500m long, or else well-control at the sea floor.
 We have in the past, and continue to organize and nurture the development of specific drilling proposals. We expect that these efforts will eventually succeed and that all the proposals needed to accomplish the overall program we propose will be in the system. Finally, the fifth point of our mandate is to communicate with the Long-Term Observatories PPG to assure that seafloor observatories are integrated into our long-term strategy. The principal area of overlapping interest of the AOL and LTO PPGs is in the area of fluid circulation. As fluid circulation in the crust, both at zero-age and on ridge flanks is an important area of concern of the AOL PPG, we expect that this aspect of our mandate will eventually be met successfully.

12. Next Meeting: The PPG members felt that there seemed to be no real need to schedule a  meeting at this time. When new developments warrant a meeting, we will schedule one. Meanwhile, the PPG will conduct its business via email.

 The architecture of oceanic crust at fast and slow spreading rates reflects contrasting modes of chemical, thermal, and physical interaction of materials from the mantle with those of the hydrosphere, atmosphere, and biosphere. Drilling provides a key role in understanding the architecture of ocean lithosphere and crust, as it is the only means available to achieve full answers to a variety of scientific questions related to four key sets of processes
  • Mantle Dynamics and Melt Extraction
  • Magmatic Accretion of the Crust at Fast and Slow Spreading Rates
  • Lithospheric extension
  • Fluid Circulation

 Fundamental advances  in these four process-oriented themes are required to achieve the overall goals of the program we propose for investigating the Architecture of Oceanic Lithosphere. These four themes comprise the cornerstones of our program, and define a scientific context for the individual drilling proposals needed to achieve our objectives.

Mantle Dynamics and Melt Extraction: Creation of the ocean lithosphere involves the upwelling and melting of mantle material, and the migration of melt toward the axes of mid-ocean ridges to form the crust. At the same time, the residue of mantle melting flows laterally away from the axis and becomes incorporated into the thickening ocean lithosphere. In order to investigate these fundamental processes, it is necessary to drill into and recover portions of the oceanic upper mantle and lower crust that preserve a record of these deep processes in their mineralogy, texture, and larger scale structure. Upper mantle peridotites preserve a variety of solid and melt flow indicators, allowing ridge-related mantle and melt flow fields to be directly mapped, given adequate recovery  from a network of drill holes. What are the directions and patterns of mantle flow at the segment level, and to what extent do these control segmentation patterns? How is melt extracted from this flowing mantle, and what are the forces that drive this melt flow? To what extent do diapiric structures mapped in ophiolites reflect the size and scale of mantle flow and how are the flow patterns influenced by spreading rate?
 There are strong indications from theoretical and experimental work that answers to the above fundamental questions will depend critically on the spreading rate. Patterns of mantle and melt flow are expected to be more focused below slow-spreading ridges and secondary flow patterns may be more apt to develop. For this reason, it is necessary to investigate drilled peridotites from both slow and fast spreading ridges to investigate the full range of behavior. This is one reason we feel that additional drilling at Hess Deep (successors to 551-Pre) is extremely important.- it represents the only viable drilling target for fast-spreading lithosphere in the pre-2003 timeframe. It is also why we advocate peridotite drilling at a variety of possible sites at the Mid-Atlantic Ridge and other slow-spreading ridges such as SWIR, including a return to site 735 (535-Full), peridotite drilling at the 15°20'N MAR site, and drilling into peridotites at windows provided by low angle detachment surfaces at the Kane FZ (532-Pre), and the Atlantis FZ (proposal 512).

Magmatic Accretion of the Crust at Fast and Slow Spreading Rates: Conductive and advective cooling of mantle-derived melt intruded at shallow levels is directly responsible for creating the layered oceanic crust. To what extent the deeper gabbroic crust is formed solely by cooling of shallow magma lenses in the upper crust (gabbro glacier model), or, as suggested by studies of the Oman ophiolite, also by melt intrusions near the base of the crust, is an important fundamental question that can only be answered by drilling gabbroic rocks from ocean crust produced at a variety of spreading rates. For this reason we strongly urge the sampling of intact sections of gabbro from fast (Hess Deep, again), and slow spreading centers (735B, 15°20'MAR, the Atlantis and Kane detachment surfaces). To what extent is lateral melt migration responsible for differences in crustal thickness detected at slow spreading segments with gravity "bull's eye" patterns? This basic question can also be answered by drilling of carefully selected gabbro sections in slow spread crust.
 Equally important is understanding the dynamics and behavior of shallow magma lenses and the extent to which their behavior regulates intrusion of dikes and eruptive activity. This is reflected by the compositional architecture and stratigraphic variation of volcanic rocks that build the uppermost layer of the crust. It is of fundamental importance to determine whether the seismic layer 2A corresponds to extrusive lavas because if so, then seismic imaging can be used to map this layer throughout the oceans. Drilling is the only way to make this determination for normal in situ ocean crust, and is a prime objective of drilling at the Guatemala Basin site (522-Full) and at zero-age crust at the East pacific Rise (proposal in preparation).

Lithospheric Extension: It is well-known that crustal accretion involves both magmatic and tectonic processes, but the interaction between the two is still poorly understood. New and very exciting studies at a variety of spreading rates indicate that in some cases, extension of the lithosphere may occur in the virtual absence of magmatic activity along low angle detachment surfaces commonly found near the inside corners of transform faults. These appear to represent the on-land structural equivalents of metamorphic core complexes that form also in extensional settings like the Cordillera. The manner in which these oceanic features form and develop is of fundamental importance to understanding the thermo mechanical response of ocean lithosphere and to basic tectonic issues of what controls the fracture mechanics of crustal rocks.  Drilling is required to test between competing models of the dynamics of oceanic  low angle detachment faults,. As an added bonus, these detachment surfaces also provide tectonic windows to the lower crust, providing thick and intact sections of oceanic gabbro and peridotite, such as at site 735. Drilling into detachments at the slow-spreading MAR (532-Pre and 512) is crucial for determining how and why detachments form and to what extent low angle faults serve as flow channels for hydrothermal fluids.

Fluid Circulation: Hydrothermal circulation in the ocean crust is the dominant mode of lithosphere cooling and plays a major role in global biogeochemical cycles of material and energy. Drilling provides the only means of investigating the deeper portions of active systems along the mid-ocean ridge system and on their flanks. It is of fundamental importance to determine the extent to which hydrothermal fluids advectively cool the lower crust and possibly even to some extent, the upper mantle. How do individual systems evolve and mature, and what are the physical and chemical processes that occur in the deep reaction zones? Firm answers to these questions require drilling into active systems at a range of spreading rates and tectonic settings, as there appear to major differences in the longevity, size, and metallogenetic processes occurring at fast (East Pacific Rise) and slow (e.g. Mid-Atlantic Ridge) systems, and among systems at mid-ocean ridges vs. back arc basins. Successful drilling of this type will require technological developments such as advances in bare-rock drilling, high temperature logging, and fluid sampling.

 Our proposed program will make important strides before 2003 with the existing platform, and in many cases, without new technology. Prior to 2003, we advocate starting a deep reentry hole in fast or superfast spread crust, with continuation to Moho with a multileg program after 2003. At the same time, and with existing technology, we propose direct sampling of the plutonic foundations of the oceanic crust at both fast and slow spreading rates. Conceivably, drilling into low angle detachment surfaces can simultaneously provide breakthroughs in understanding of mantle dynamics and melt migration, magmatic accretion of the crust, and lithosphere extension. This drilling does not require new technology and since many potential drill sites are in relatively shallow water (<2500m) this drilling can be continued with a short riser beyond 2003. This is also the case for zero-age drilling at the East Pacific Rise, although such drilling will probably require good active heave compensation, and possibly new casing and bit technology. A longer riser (~4000m) or alternative methods of well control for drilling in deep water will be needed in the post-2003 program to complete drilling through an intact section of fast spread ocean crust, drilling the deep reaction zones of active hydrothermal systems, and penetrating low angle detachment faults to the depth of the decollement.