The Great Plume Debate: The Origin and Impact of LIPs and Hot Spots
Ben Nevis Hotel, Fort William, Scotland
Sunday, 28 August – Thursday, 01 September 2005
Registration and Information
Introduction: It is forty years since J. Tuzo Wilson first suggested that the Hawaiian Islands were produced by the oceanic lithosphere moving over a stationary "hot spot" in the mantle, and thirty years since W. Jason Morgan suggested that thermal plumes exist in the Earth's mantle and may play an important role in convection. Flood basalts, volcanic continental margins, large oceanic plateaus and age-progressive aseismic ridges, along with smaller-volume seamount and ocean-island chains, have all been attributed to mantle plumes.
The tendency over the last decade has been to focus research on those features of large igneous provinces (LIPs) and "hot spots" that can be explained by plume theory and to ignore those features that cannot. Many papers published have treated the plume hypothesis as an a-priori assumption, and little in the way of questioning of the hypothesis has been taught in schools and universities. Recently, however, there has been significant critical thought on the subject and a global debate is now in progress concerning the viability of alternative models, the number of deep mantle plumes and even whether any plumes at all exist in Earth (see, for example, http://www.mantleplumes.org/ ). Strong cases have been presented on both sides of the argument (see, for example, http://www.geolsoc.org.uk/template.cfm?name=NakedEmperor ).
Plume theory: The fluid mechanics of low-Reynolds-number plumes is well understood. A mantle starting plume is predicted to consist of a large spherical head followed by a small tail. When it reaches the top of its ascent the head flattens to form a disk with a diameter twice that of the spherical head. Plume heads have been proposed to be responsible for Earth's major flood basalts and plume tails for aseismic ridges and island chains that connect the flood basalt to the current position of the hot spot. Plume theory makes the following testable predictions:
All of the predicted phenomena have been observed in large igneous provinces. The length of thickened oceanic crust associated with opening on the North Atlantic, above the postulated Iceland plume head, is 2,400 km as expected, uplift has been documented prior to most flood volcanism, most flood volcanic provinces are associated with high-temperature picrites, especially during the early phase of volcanism, and recent seismic studies have followed plume tails to the core-mantle boundary. The agreement between theory and observations has convinced the "true believers" that plume theory is soundly based.
Alternatives: The quest for alternative theories is inspired by diverse observations at "hot spots" that are not predicted by the original classical plume model. These include observations that suggest that "hot spots" may not be hot, that age progressions are often complicated and not linear, and that the deep-mantle structures expected beneath large volcanic provinces are not observed. Enigmatic co-locations of "hot spots" with unusual surface tectonic features are viewed by many as being unlikely to be mere coincidences. Many variants of the original classical plume hypothesis have been invoked to take account of such observations, but this approach has been criticized on the grounds that it sacrifices scientific objectivity and renders the theory invulnerable.
Alternative models for "hot spots" include shallow magmatic, and propagating crack models, local convection and recycling of subducted slabs, Rayleigh-Taylor instability of the lithosphere for continental flood basalts, impacts, variations in stress at the junction of tectonic features and EDGE-driven convection. It has been suggested that much "hot spot" volcanism traditionally attributed to deep mantle plumes is, instead, controlled by shallow processes driven ultimately by plate tectonics. Regardless of the ultimate outcome of these individual theories, shallow or extra-terrestrial models for "hot spots" represent a fresh field of investigation that is likely to stimulate innovative ideas and experiments and lead to significant advances in our understanding.
Questions: The time is ripe for a zero-level reconsideration of the status of "hot spot" science that may provide a clear basis from which to move forward. Questions that need to be clearly thought through include:
Breadth of discipline: The Conference will be inter-disciplinary and will include a wide range of Earth scientists working in tectonophysics, seismology, fluid dynamics, geochemistry, geochronology, volcanology, petrology, sedimentology and field geology.
The Conference will span five days, with formal activities scheduled from 8.30 am to 5.00 pm daily. Previous experience has shown that the most successful format involves allocating ~ 1/3 of the time to formal addresses with 2/3 of the time reserved for free discussion from the floor. Attendees will be encouraged to bring overheads to illustrate points they wish to make during the discussion. Day 1 will be devoted to formally laying out the plume and alternative hypotheses and stating their predictions. The morning will be devoted to the plume hypothesis and the afternoon to alternative hypotheses. Each half-day will include four 20-min keynote talks, each with 25 min of associated discussion. Days 2, 3, 4 and the morning of Day 5 will focus on individual subjects important to understanding "hot spots". Each half-day session will include six 10-min invited talks, each with 20 min of associated discussion. The afternoon of Day 5 will be devoted to discussion and synthesis, structured around key questions identified in the light of the previous four days' proceedings.
Attendance will be limited to 100 participants.
Preliminary Schedule [PDF, 42Kb]
Details of the planned sessions are as follows. Oral presentations will be equally divided between plume-advocate and alternative presentations.
Attendees will be invited to bring posters. Opportunities will be given to poster authors to give 3-minute presentations introducing their posters during the meeting.
Two half-day local field trips will be organized during the week-long meeting. In addition, the following three pre- and post-meeting trips will be offered. These field trips are offered on a first come, first served basis. If you are interested, please contact the Gillian Foulger or Melissa Ficek to reserve your space.
The abstract submission deadline, 31 May 2005, has passed.
Application Deadline: 31 May 2005 has passed.
The conference will be held at the Ben Nevis Hotel & Leisure Club, Fort William, Scotland. For more information, see http://www.strathmorehotels.com/bennevis_site/index.htm.
A suitable travel schedule might involve flying to Glasgow Saturday, 27 August, and traveling by train (3 1/2 hours) from Glasgow to Fort William, which is ~ 170 km north of Glasgow. There are several trains on Saturdays but only one on Sundays.
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