Unraveling plate tectonics: From mantle plumes to subduction dynamics

On the great plume debate

The existence, spatial distribution, and style of volcanism on terrestrial planets is an expression of their internal dynamics and evolution. On Earth a physical link has been proposed between hot spots, regions with particularly persistent, localized, and high rates of volcanism, and underlying deep mantle plumes. Such mantle plumes are thought to be constructed of large spherical heads and narrow trailing conduits. This plume model has provided a way to interpret observable phenomena including the volcanological, petrological, and geochemical evolution of ocean island volcanoes, the relative motion of plates, continental breakup, global heat flow, and the Earth's magnetic field within the broader framework of the thermal history of our planet. Despite the plume model's utility the underlying dynamics giving rise to hot spots as long‐lived stable features have remained elusive. Accordingly, in this review we combine results from new and published observational, analog, theoretical, and numerical studies to address two key questions: (1) Why might mantle plumes in the Earth have a head‐tail structure? (2) How can mantle plumes and hot spots persist for large geological times? We show first that the characteristic head‐tail structure of mantle plumes, which is a consequence of hot upwellings having a low viscosity, is likely a result of strong cooling of the mantle by large‐scale stirring driven by plate tectonics. Second, we show that the head‐tail structure of such plumes is a necessary but insufficient condition for their longevity. Third, we synthesize seismological, geodynamic, geomagnetic, and geochemical constraints on the structure and composition of the lowermost mantle to argue that the source regions for most deep mantle plumes contain dense, low‐viscosity material within D″ composed of partial melt, outer core material, or a mixture of both (i.e., a “dense layer”). Fourth, using results from laboratory experiments on thermochemical convection and new theoretical scaling analyses, we argue that the longevity of mantle plumes in the Earth is a consequence of the interactions between plate tectonics, core cooling, and dense, low‐viscosity material within D″. Conditions leading to Earth‐like mantle plumes are highly specific and may thus be unique to our own planet. Furthermore, long‐lived hot spots should not a priori be anticipated on other terrestrial planets and moons. Our analysis leads to self‐consistent predictions for the longevity of mantle plumes, topography on the dense layer, and composition of ocean island basalts that are consistent with observations.

The true driving force behind drifts in plate tectonics is still a topic open for discussion. Currently, slab pull is taken as the dominant driving force. From the energy perspective, heat from the Earth’s interior is the main source of power maintaining plate tectonics. The organized release of heat is the key to transforming static energy into kinetic energy. Here we propose a Magma Engine model. According to this model, heat is changed to potential energy through magmatism, and this consequently drives movements in plate tectonics through gravity. New oceanic crust is formed continuously at the mid-Ocean ridges, and then cools down gradually. The newly formed oceanic crust is lighter and thinner than the older ones, resulting in tilted plates sitting on the asthenosphere mantle. Given that the mantle has a high viscosity of 1019−1021 in the asthenosphere, and even higher values further down, the oceanic plate would lie on a big slope, with a height difference of around 80 kilometers. The highest plate sliding forces reach 1.4 ´ 1014 N/m, which is an order of magnitude larger than the estimated value of slab pull. It is therefore the primary driving force of plate tectonics. Mantle plume is another type of Magma Engine. Large plume heads may elevate the overlying continental crust in kilometer scales, due to high temperatures and the bouncy of large amounts of plume magma. Such uplifting may lead to the overlying plate sliding away from the center of the plume. This may initiate plate subduction along weaker belts in case the plume is big enough and the overlying plate is strong enough. This is likely the main mechanism that initiated plate tectonics in the early history of the Earth. Under the plate tectonic system, the plume head plays a major role in the opening of new ocean basins, acting as an “igniter” of mid-ocean Magma Engines. There are two types of subduction initiations, spontaneous and induced (or forced). Spontaneous subduction initiation usually occurs in old ocean basins, forming double-track subductions on either side of the ocean basin. In contrast, induced subduction initiation usually occurs in young ocean basins, forming single-track subduction. The closures of Neo-Tethys Oceans were likely associated with induced subduction initiation, which always forms northward subductions. The Magma Engine works mainly on plates that are directly connected to spreading ridges and/or mantle plumes. For others, the energy for plate movement and deformation comes from plate interactions.

Stagnant lid tectonics: Perspectives from silicate planets, dwarf planets, large moons, and large asteroids

Role of the overriding plate in the subduction process

Did the Neoproterozoic Revolution Extend to the Deep Mantle?

When Did Plate Tectonics Begin on the North China Craton? Insights from Metamorphism

<p indent="0mm">Established in the mid-1960s and regarded as a revolution in Earth sciences, the plate tectonics theory can reasonably interpret nearly all geological phenomena, processes, and events that happened during post-Archean time (from 2.5 billion years ago to the present), and has also been applied to explain the formation and evolution of continents. According to the plate tectonics theory, the mafic lower crust and the felsic upper crust of continents can develop from an island arc that formed by subduction of one oceanic crust beneath another, where the mafic lower crust of continents can be extracted from the mantle through the partial melting of the mantle wedge in the subduction zone, whereas the felsic upper crust of continents can form by the partial melting of the already-formed mafic lower crust. However, such an island arc model under a plate tectonic regime cannot well explain the magmatic, metamorphic and structural features of Archean (&gt;2.5 billion years) continents. For example, island arc models fail to explain the presence of ~1600°C komatiites, absence of andesites that is dominant in post-Archean arcs, nearly coeval and craton-scale emplacement of tonalite-trondhjemite-granodiorite (TTG) rocks, dominancy of dome-and-keel structures, and lack of ultrahigh-pressure rocks, paired metamorphic belts and ophiolites, etc. All of these imply that Archean continents may not have been formed under plate tectonic regimes, but were originated from some pre-plate tectonics (non-plate tectonics). So far, researchers have proposed a number of pre-plate tectonics models, of which the most representative ones are mantle plumes, sagduction, heat-pipes and stagnant lids. Although each of these pre-plate tectonics models can satisfactorily interpret some features of Archean cratons, none of them is successful in explaining all lithological, structural and metamorphic features of Archean cratons. For example, although the mantle plume-derived oceanic plateau models can well explain many features of Archean cratons, oceanic plateaus formed by mantle plumes may not provide enough water (H₂O) for aqueous partial melting of basaltic rocks to create TTG magmas. It is the same case with heat-pipe models. As the sagduction models assume the existence of an old felsic continental crust, they are not suitable for discussing the origin of Archean continents. As for stagnant lids, they just describe the state of a single lithosphere plate which itself cannot provide any geodynamic mechanisms for making a mafic crust be partially melt to form TTG magmas. Therefore, none of available pre-plate tectonics models proposed so far has been successfully applied to interpret the origins of Archean continents. Thus, a number of research groups in the world are conducting extensive and comprehensive investigations on this important scientific conundrum. Although Chinese geologists missed a chance to have made contributions to establishing plate tectonic theory in the 1960s, they have a great potential for breakthroughs in establishing a pre-plate tectonics theory since they have done tremendous work on the early geodynamic mechanisms for the formation and evolution of Archean continents and produced large amounts of new data and competing interpretations in the past four decades.

The existence of mantle plumes was first proposed in the 1970s to explain intra-plate, hotspot volcanism, yet owing to difficulties in resolving mantle upwellings with geophysical images and discrepancies in interpretations of geochemical and geochronological data, the origin, dynamics and composition of plumes and their links to plate tectonics are still contested. In this Review, we discuss progress in seismic imaging, mantle flow modelling, plate tectonic reconstructions and geochemical analyses that have led to a more detailed understanding of mantle plumes. Observations suggest plumes could be both thermal and chemical in nature, can attain complex and broad shapes, and that more than 18 plumes might be rooted in regions of the lowermost mantle. The case for a deep mantle origin is strengthened by the geochemistry of hotspot volcanoes that provide evidence for entrainment of deeply recycled subducted components, primordial mantle domains and, potentially, materials from Earth’s core. Deep mantle plumes often appear deflected by large-scale mantle flow, resulting in hotspot motions required to resolve past tectonic plate motions. Future research requires improvements in resolution of seismic tomography to better visualize deep mantle plume structures at smaller than 100-km scales. Concerted multi-proxy geochemical and dating efforts are also needed to better resolve spatiotemporal and chemical evolutions of long-lived mantle plumes.

In early Permian, a mantle plume heated up the Tarim block and formed the Tarim large igneous province. It is an interesting phenomenon to explore the interaction between mantle plume and a thick continent lithosphere, because mantle plume has been proposed to be an important route of material and energy transportation in the earth. Currently, the Tarim block is surrounded by Tibetan plateau to its south edge and Tian Shan orogeny to its north edge. The combined effects of both mantle plume activity and plate tectonics should have significantly changed the structure and composition of the Tarim block because of its amalgamations in Neoproterozoic. Seismic imaging plays a key role on revealing the deep structure of the Earth, which could help unravel the questions mentioned before. However, the harsh natural environment in the central part of the Tarim basin, the Taklimakan desert—the largest desert in China—has seriously hampered the broadband seismological observation. From July 2017 to November 2019, the Institute of Geology and Geophysics, Chinese Academy of Sciences deployed a 2D broadband seismic array named the Tarim seismic Array for lithoSpheric signaTure of mantle plumE (TASTE) over the inner part of the Tarim basin with an averaged spacing of 60–70 km. The primary target of this project is to obtain a detailed lithospheric structure to resolve the possible lithospheric signatures of Permian mantle plume activity. Here we introduce the basic information of the TASTE network and the performance of these instruments by analyzing the background noise level. Preliminary results of receiver function and ambient noise analyses are also shown, which may suggest a thick sedimentary layer, as well as complicated crust and lithospheric feature.

The Abitibi and Wawa subprovinces of the southern Superior Province differ in terms of the extent of pre-existing 2750 Ma sialic crust and relationships between mantle plume type (tholeiitic basalt – komatiite) and arc type (tholeiite to calc-alkaline basalt – andesite – dacite – rhyolite) volcanic successions but evolved in close proximity to each other. Isotopic data, evidence from the Kapuskasing uplift, continuation of major structures associated with large gold deposits from the Abitibi into the Wawa subprovince and the related occurrence of diamonds in lamprophyric rocks in both subprovinces point to a common evolution prior to and during orogeny. Differences preserved in supracrustal sequences of the two subprovinces suggest that the main petrogenetic controls on orogenic gold deposits and lamprophyre-hosted diamond deposits lay in the lower crust and upper mantle. Similar processes must also have been active where gold and diamonds are associated on other Archean cratons, such as the Slave and possibly the Kaapvaal craton. Based on evidence preserved in the Abitibi–Wawa orogen, rapid crustal growth at ∼2.7 Ga was linked to the interplay between plate tectonics and mantle plumes. Key indicators in the model developed for the Abitibi–Wawa arc are the co-existence of plume-related rock types, modern-style adakites, major gold deposits, and lamprophyre-hosted diamond occurrences, at least in cases where shoshonitic host magmas can ascend rapidly through the crust. All of these indicators are now identified on the Kaapvaal craton by 3.1 Ga and many recur together in Paleoproterzoic and younger terranes, suggesting a common mechanism for rapid crustal growth through much of Earth’s history. The variety of granitoid types found within the Abitibi–Wawa orogen demonstrates that local tectonic factors, rather than a hotter average upper mantle, were important in controlling the type of magmas formed. Based on the geodynamic history of the subprovince, mantle plume interaction with an existing volcanic arc and the subduction of oceanic plateau crust played an important role in the formation of magmas similar to Cenozoic adakites. Flat subduction beneath a mantle wedge was probably responsible for the generation of the adakites and also promoted diamond stability at shallow depths while enhancing the reservoirs for subsequent orogenic gold deposits. The history of magmatism and mineralization in the Abitibi and Wawa subprovinces precludes an early or gradual development of a cratonic keel, which instead must have coupled with crust during the latest stages of orogeny.

On the cause of continental breakup: A simple analysis in terms of driving mechanisms of plate tectonics and mantle plumes

The link between great earthquakes and subduction dynamics across a wide range of scales remains a crucial, yet elusive, tenet of the seismotectonics of convergent margins. Here, we show high-performance computational simulations of the three-dimensional Sunda subduction zone dynamics matching plate motions, tectonics and current deformation, thereby providing insights into the stress regime of the Java-Sumatra-Andaman margin. Testing various tectonic forces reveals the primary control of the Java slab pull and induced mantle flow on the whole margin tectonics, driving northward-increasing oblique convergence, Sumatran trench advance and increased tectonic coupling along this segment. The modelled deviatoric stresses reproduce the geodetically-constrained interseismic compression in Sumatra and megathrust stress orientations notably consistent with the seismic P-axes, with magnitude comparable to static stresses on seismogenic faults. We map the frictional strength along the Sumatra-Andaman megathrust, identifying critical thresholds at key seismogenic depths, which remarkably correlate with the location of great earthquakes. Our outcomes show how subduction dynamics may critically prime the conditions for seismicity along the Sunda margin.

The evolution of modern plate tectonics is described by the Wilson cycle, which portrays the dynamics of the supercontinental cycle through the interaction of the oceanic plate with the continental plate over periods of hundreds of millions of years. This cycle is characterized by a phase of supercontinent assembly and enhanced orogenic collision, followed by a phase of supercontinent fragmentation and dispersal, as shown by the geological record. The dynamics of the Wilson cycle is intrinsically linked to mantle convection and subduction dynamics. While the assembly phase appears to follow a degree-2 mantle convection style, the mechanism responsible for supercontinent fragmentation is still debated. We hypothesize that the dispersal phase is mostly governed by trench roll-back from subductions and mantle plumes. To test this hypothesis, we have built a series of 2D and 3D geodynamic models of the Earth on a global scale using the ASPECT code. We have tested different scenarios in which we prescribe the distribution of the supercontinent Rodinia at 1Ga or Pangea at 250 Ma and let the models evolve self-consistently.&amp;#160; In some model variants, the strength of the supercontinent and that of the surrounding oceanic area is changed. We will present our preliminary results and discuss the dynamics of continental dispersal and its link to subduction and mantle dynamics. In particular, 3D models will demonstrate how regional plume-induced retreating subduction zones evolve into a global network of subduction zones and tectonics plate boundaries which ultimately leads to the break-up of the supercontinent.

Plate tectonics describes the horizontal motions of lithospheric plates, the Earth’s outer shell, and interactions among them across the Earth’s surface. Since the establishment of the theory of plate tectonics about half a century ago, considerable debates have remained regarding the driving forces for plate motion. The early “Bottom up” view, i.e., the convecting mantle-driven mechanism, states that mantle plumes originating from the core-mantle boundary act at the base of plates, accelerating continental breakup and driving plate motion. Toward the present, however, the “Top down” idea is more widely accepted, according to which the negative buoyancy of oceanic plates is the dominant driving force for plate motion, and the subducting slabs control surface tectonics and mantle convection. In this regard, plate tectonics is also known as subduction tectonics. “Top down” tectonics has received wide supports from numerous geological and geophysical observations. On the other hand, recent studies indicate that the acceleration/deceleration of individual plates over the million-year timescale may reflect the effects of mantle plumes. It is also suggested that surface uplift and subsidence within stable cratonic areas are correlated with plume-related magmatic activities over the hundred-million-year timescale. On the global scale, the cyclical supercontinent assembly and breakup seem to be coupled with superplume activities during the past two billion years. These correlations over various spatial and temporal scales indicate the close relationship and intensive interactions between plate tectonics and plume tectonics throughout the history of the Earth and the considerable influence of plumes on plate motion. Indeed, we can acquire a comprehensive understanding of the driving forces for plate motion and operation mechanism of the Earth’s dynamic system only through joint analyses and integrated studies on plate tectonics and plume tectonics.