RCL (Rupturing Continental Lithosphere)

Over-Arching Themes:

(See Science Plans, page 24)

Rifting of continental lithosphere is a fundamental process in the growth and evolution of continents, and it has substantial societal relevance by virtue of the large petroleum reserves and sensitive environmental conditions recognized at rifted continental margins. In spite of this significance we lack a full understanding of the magnitude and cause of stresses that drive rifting, the deformational mechanisms of extension, and the key parameters that control this deformation. Basic questions persist about the style of lithospheric extension—whether it deforms symmetrically in pure shear, or asymmetrically in simple shear; about the roles of lower-crustal flow, magmatism, and sedimentation in evolving rift architecture; and about the sensitivity of rift evolution to variations in key parameters such as lithospheric strength and temperature, strain rate, and crustal thickness. Five over-arching themes for RCL were identified by the community:

Methods Of Studying RCL Processes:

(See detailed discussion in Science Plans, page 26)

Focus Sites and Focus Site Rationale:

(See detailed discussion in Science Plans, page 32)

Given the necessity to concentrate on both active and complete extensional systems, only a few areas around the world are suitable for consideration. Regions that were considered included:

  1. Gulf of Aden and Gulf of Tadjura (Arabia-Somalia)
  2. Gulf of California and Salton Sea region (Mexico/USA)
  3. Lena delta and Gakkel Ridge (Russia)
  4. Northern and central Red Sea and Gulf of Suez (Arabia-Nubia)
  5. Western Woodlark Basin (Papua New Guinea)

RCL Focus Site Criteria:

Scientific criteria:

Logistical criteria included:

In a series of two votes, consensus emerged supporting:

  1. The Gulf of California/Salton Sea (see Science Plans, page 33), a region partially within the U.S., optimal for investigating rifting of orogenic crust
  2. The northern Red Sea/Gulf of Suez (see Science Plans, page 42), optimal for studying cratonic continental extension.

Workshops in Mexico and Egypt were successfully completed and allowed U.S. scientists to inform and involve colleagues from these countries concerning the overall goals of the MARGINS program, the types of scientific problems to be addressed by the Rupturing of Continental Lithosphere initiative, and our need for meaningful collaborations and interactions with Mexican, Egyptian, and Saudi universities and institutes.

Workshops and TEIs:

Major Research Activities — Funding 2000 to Present:

(Proposal start dates in parentheses)

MARGINS-Funded Research Projects:

NSF-Funded MARGINS-Related Projects:

Political Complications:

RCL research has been slowed as a result of military instabilities in the Middle East, and by controversy over the impact of seismic acoustic systems on marine mammals in the Gulf of California. The situation with collaborators in the Red Sea area are discussed in the section on International Collaboration, below. Despite limitations, a fair bit of work has been completed to date, and potential PIs remain committed to the initiative.

Intellectual Progress During MARGINS:

Gulf of California - Salton Trough Focus Site:

Map (PDF) prepared by the MARGINS Office, showing the available information on where work has been funded to date in the Gulf of California focus area. (Click map for a larger version with explanatory caption.)

Central and Northern Red Sea Focus Site:   

Map (PDF) prepared by the MARGINS Office, showing the available information on where work has been funded to date in the Red Sea focus area. (Click map for a larger version with explanatory caption.)

Major Research Gaps (Practical and Intellectual):

Many of the scientific questions that motivate research in the Gulf of California-Salton Trough focus site remain unanswered at the writing of this document. This is due in part to the late initiation of RCL relative to other parts of the MARGINS program, and in part to delays in the offshore research that have resulted from the marine mammal and permitting issues. The fundamental questions of the RCL initiative—exactly how does extension stop and get replaced by seafloor spreading (the role of fluids, volatiles, and magmas), exactly how does the lithosphere thin by extension in space and time (regional partitioning of strain and oblique vs. orthogonal rifting) and exactly why rifts form where they do (strength of the lithosphere and the role of inherited crustal and lithosphere weaknesses)—remain the fundamental issues to be addressed by current and future RCL research. Since the RCL initiative has only recently commenced, answers to these questions are pending. However, recently funded (or delayed) projects of Lonsdale/Umhoefer and Gaherty/Collins, and the ongoing passive seismic experiment of the NARS-Baja project (Clayton and Ritsema), are still ramping up and are generating critical new data to address the above questions. Similarly for data acquisition and research in the Red Sea focus site, which hopefully will accelerate over the next year following successful negotiations with Egyptian colleagues in March 2004.

One concern is that part of the motivation behind RCL science—comparison and contrasting of style and behavior between orogenic and cratonic lithospheric extension systems—may be compromised if access to the central and northern Red Sea rift system is denied by the Egyptian authorities, and as a result NSF continues to discourage the submission of Red Sea RCL proposals. The Red Sea focus site is one of two regions of the world where cratonic lithosphere is being rifted apart to form oceanic lithosphere. The other is the southern Red Sea/Gulf of Aden region, previously dismissed by the MARGINS community because of political and social instability. A MARGINS delegation were recently engaged in efforts to strengthen ties with Egyptian scientists and explore ways to gain permission to conduct marine geophysical and geological surveys in the Red Sea region, in collaboration with Egyptian and Saudi Arabian colleagues. Meetings with Egyptian collaborators were very positive and suggest that joint U.S.-Egyptian-Saudi Arabian projects are feasible. Data sharing policies remain to be worked out. We hope that the concerns and objections voiced by NSF last year may be addressed adequately to open the way for RCL Red Sea proposal submission for the November 1, 2004 deadline.

International Collaborations:

Northern and Central Red Sea

In the Red Sea region, the Saudi Geological Survey (SGS) has strongly encouraged collaboration between U.S. researchers and itself. A general MOU was signed late last year between the MARGINS Office and the SGS, acknowledging the common research interests between the SGS and the objectives of the MARGINS RCL initiative. The MOU acknowledges that the SGS is the primary geologic survey agency in the Kingdom and the principal repository for Earth Science data. The MOU also outlines a number of agreements that will help facilitate collaborative research between U.S. and Saudi scientists. Under this MOU, Danny Stockli and G. I. Omar have secured full scientific and logistical support from the Saudi Geological Survey, providing a unique opportunity to study the geodynamic evolution of the eastern margin of the Red Sea rift system. Rob Reilinger is currently engaged in collaborations with Saudi Arabian scientists at KACST. Shared resources include Saudi magnetic and gravity data, access to published geological survey reports and geological, geophysical and topographic maps, access to demographic maps, and access to field equipment (e.g., Land cruisers), shallow drilling rigs, helicopters, and SGS field staff.

In Egypt, the National Research Institute of Astronomy and Geophysics (NRIAG) is a natural partner for much MARGINS geophysics and seismic work, as they run the country's seismic network, have experience with magnetic and microgravity surveys, and have well established facilities for processing and archiving earthquake data. Julie Morris, the current MARGINS Chair, made a recent trip to NRIAG, joined by scientists representing a potential proponent group from Lamont, University of Alabama and University of Hawaii. During this visit, NRIAG provided geological and topographic maps and summaries of recent seismic activity in Egypt, Gulf of Suez and the Red Sea, and initiated discussion on whether NRIAG seismic stations might be used to facilitate field work in Egypt. Policies of data access for American scientists were introduced, with continuing discussion needed.

Gulf of California

MARGINS and MARGINS-related research in the Gulf of California benefits from ongoing collaborations with Mexican scientists and students. Participating universities and research institutes include Universidad Nacional Autonoma de Mexico (UNAM), Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Universidad Autonoma de Baja California (UABC), and Universidad Autonoma de Baja California Sur (UABCS). The University of Utrecht (The Netherlands) is also represented in Gulf of California research. These collaborations are the result of long-term planning efforts that have included a number of international workshops and symposia, and they help to sustain the current climate of friendly scientific partnerships that benefit U.S., Mexican, and Dutch participants. Shared resources include use of a Mexican research vessel (CICESE's Francisco de Ulloa ; Stock and Steckler proposal), help with obtaining Mexican permits for marine geophysical work (Lizarralde, et al. ), and access to Mexican geophysical data, unpublished reports, topographic maps, air photos, etc.

RCL Presentations and Publications:

(See “Research” section)


(Proposal start dates in parentheses)