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Book Chapter

The “plate” model for the genesis of melting anomalies

By
Gillian R. Foulger
Gillian R. Foulger
1
Department of Earth Sciences, Durham University, Durham DH1 3LE, UK
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Published:
January 01, 2007

The plate tectonic processes, or “plate,” model for the genesis of melting anomalies (“hotspots”) attributes them to shallow-sourced phenomena related to plate tectonics. It postulates that volcanism occurs where the lithosphere is in extension, and that the volume of melt produced is related primarily to the fertility of the source material tapped. This model is supported in general by the observation that most present-day “hotspots” erupt either on or near spreading ridges or in continental rift zones and intraplate regions observed or predicted to be extending. Ocean island basalt-like geochemistry is evidence for source fertility at productive melting anomalies. Plate tectonics involves a rich diversity of processes, and as a result, the plate model is in harmony with many characteristics of the global melting-anomaly constellation that have tended to be underemphasized. The melting anomalies that have been classified as “hotspots” and “hotspot tracks” exhibit extreme variability. This variability suggests that a “one size fits all” model to explain them, such as the classical plume model, is inappropriate, and that local context is important. Associated vertical motion may comprise pre-, peri-, or post-emplacement uplift or subsidence. The total volume erupted ranges from trivial in the case of minor seamount chains to ∼108 km3 for the proposed composite Ontong Java–Manihiki–Hikurangi plateau. Time progressions along chains may be extremely regular or absent. Several avenues of testing of the hypothesis are being explored and are stimulating an unprecedented and healthy degree of critical debate regarding the results. Determining seismologically the physical conditions beneath melting anomalies is challenging because of problems of resolution and interpretation of velocity anomalies in terms of medium properties. Petrological approaches to determining source temperature and composition are controversial and still under development. Modeling the heat budget in large igneous provinces requires knowledge of the volume and time scale of emplacement, which is often poorly known. Although ocean island basalt–type geochemistry is generally agreed to be derived from recycled near-surface materials, the specifics are still disputed. Examples are discussed from the Atlantic and Pacific oceans, which show much commonality. Each ocean hosts a single, currently forming, major tholeiitic province (Iceland and Hawaii). Both of these comprise large igneous provinces that are forming late in the sequences of associated volcanism rather than at their beginnings. Each ocean contains several melting anomalies on or near spreading ridges, both time- and non-time-progressive linear volcanic chains of various lengths, and regions of scattered volcanism several hundred kilometers broad. Many continental large igneous provinces lie on the edges of continents and clearly formed in association with continental breakup. Other volcanism is associated with extension in rift valleys, back-arc regions, or above sites of slab tearing or break-off. Specific plate models have been developed for some melting anomalies, but others still await detailed application of the theory. The subject is currently developing rapidly and poses a rich array of crucial but challenging questions that need to be addressed.

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Contents

GSA Special Papers

Plates, Plumes and Planetary Processes

Gillian R. Foulger
Gillian R. Foulger
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Donna M. Jurdy
Donna M. Jurdy
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Geological Society of America
Volume
430
ISBN print:
9780813724300
Publication date:
January 01, 2007

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