The “plate” model for the genesis of melting anomalies

Abstract

The Plate Tectonic Processes, or "Plate" model for the genesis of melting anomalies ("hot spots") 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 "hot spots" 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 "hot spots" and "hot spot tracks" exhibit extreme variability. This 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 precursory-, contemporaneous-or post-emplacement uplift or subsidence. The total volume erupted ranges from trivial in the case of minor seamount chains to ~ 10 8 km 3 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 underway and are stimulating an unprecedented and healthy degree of critical debate regarding the results. Determining seismologically the physical conditions beneath melting anomalies are 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 at large igneous provinces requires knowledge of the volume and timescale of emplacement, which are often unclear. Although ocean-island-basalt-type geochemistry is generally agreed to be derived from recycled near-surface materials, the specifics are not yet agreed. 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-progressive 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-teari...

Formation and evolution of Shatsky Rise oceanic plateau: Insights from IODP Expedition 324 and recent geophysical cruises

“…It is unclear, however, that these traits are inherent to the plume model. In contrast, the plate model argues that subduction can strand crustal material in the upper mantle and can later melt to provide heterogeneous magmas (Foulger, 2007;Anderson and Natland, 2014), so that neither recycled crust nor heterogeneity is explained only by the plume model.…”

“…The former model envisages plateau formation resulting from a massive, thermal diapir arising from the deep mantle (Richards et al, 1989;Duncan and Richards, 1991;Coffin and Eldholm, 1994), whereas the latter explains excess volcanism by the melting of particularly fertile (lower melting point) upper mantle material owing to decompression caused by plate extension (Foulger, 2007;Anderson and Natland, 2014). This dichotomy and the interest that it sparked, led to several recent studies of Shatsky Rise, including coring of the igneous pile by Integrated…”

“…Based on the plume head hypothesis of the mid-1990s (Richards et al, 1989;Duncan and Richards, 1991;Coffin and Eldholm, 1994;Campbell, 2007) and the subsequent questioning of the plume hypothesis (Anderson et al, 1992;Anderson, 1995;Foulger, 2007), there were two competing end-member models to explain oceanic plateau formation (Fig. 2).…”

“…Much of the motivation for studying Shatsky Rise was to determine whether this oceanic plateau could be explained by either of two end-member models: the thermal plume head (e.g., Richards et al, 1989;Duncan and Richards, 1991;Coffin and Eldholm, 1994) or decompression above fertile, shallow mantle (the plate model) (Foulger, 2007;Anderson and Natland, 2014). Such a test seemed feasible because Shatsky Rise was noted to have characteristics that fit both models (Sager, 2005).…”

IODP Expedition 324: Ocean Drilling at Shatsky Rise Gives Clues about Oceanic Plateau Formation

“…Subsequent volcanoes (Ori and Shirshov massifs) are significantly smaller (each ~25% the size of Tamu Massif), and together with a low volcanic ridge at the north end of the plateau, they may imply a transition from plume head to tail . Apropos of plate-edge genesis, Shatsky Rise displays a connection with tions come from decompression melting of unusually fusible upper mantle at plate edges (Foulger, 2007). This explanation is bolstered by the observation that many plateaus formed near ocean ridges, especially at triple junctions, a situation that is unlikely if the volcanism results from deep mantle convection independent of plate tectonics (Sager, 2005).…”