Plate Tectonic Paradigm Research Articles

Syn‐Drift Plate Tectonics

AbstractThe paradigm of plate tectonics holds that ocean plates are rigid during drift and only experience tectonic deformation at subduction zones, but new findings from the Pacific challenge this idea. Geological and geophysical evidence from the Ontong Java, Shatsky, Hess, and Manihiki oceanic plateaux indicates that extensional deformation during plate drift is a widespread phenomenon across the Pacific plate. These anomalously thick oceanic plateaux are weaker regions of the ocean lithosphere and more prone to tectonic deformation. Numerical geodynamic models demonstrate that a slab pull force from distant subduction plate boundaries can be effectively transmitted to oceanic plateaux through strong ocean lithosphere and cause substantial extension during plate drift. Our findings reveal that a wide expanse of the Pacific has experienced syn‐drift plate tectonics linked to pull from the western Pacific subduction factory.

Carbon Tectonics: A new paradigm for Earth system science

<p indent="0mm">This paper puts forward a new scientific concept: Carbon tectonics. The original meaning of “tectonics” is the geotectonic process of the Earth, which is restrcited in the lithosphere. However, the actual tectonic process of the Earth can reach the lower mantle, and can be related to the atmosphere, and even involve the operation of other celestial bodies. It can be seen that the processes of each sphere of the Earth are closely related to the large-scale to micro-scale tectonic processes, that is to say, the tectonic process is a multisphere, multi-scale and multi-phase process, and a dominant process of the Earth system. Similarly, carbon is an important element of the inorganic and organic worlds of the Earth (including organic biomass and abiotic oil and gas hydrates), and it is constantly circulating and changing between different spheres of the Earth. “Carbon” and “tectonics” are closely combined or related processes, such as volcanic eruption, mantle plume upwelling, oil and gas accumulation process, which are collectively referred to as carbon tectonics in this paper. Carbon tectonics basically covers all aspects of the Earth system. It is a new generalization and in-depth understanding of the overall Earth system following the idea of the co-evolution of the biosphere and the geosphere by Верна́дский. It is also the best entry point for the construction of the Earth System Theory. It is expected to form a new research paradigm, and to open up a new research field, and to promote a series of large-scale interdisciplinary intersections. The paradigm of carbon tectonics surpasses the plate tectonics paradigm in geoscience, faces the non-linear system characteristics and overall emergence of the Earth system, frames the cross field between Earth science and life science, and puts forward to a series of new ideas and terms: carbon sink tectonics and carbon sequestration tectonics, carbon transport tectonics and carbon storage tectonics, geological carbon pump (including slab pump and magma pump, extension carbon pump and subduction carbon pump, eruption pump and intrusion pump, weathering pump and sedimentation pump, etc.), carbon chain and carbon path, carbon conveyor belt and others.

Terrestrial impact craters track the voyage of lithospheric plates

The paradigm of plate tectonics has aided in the identification of the journey of continents on the globe, their assembly into supercontinents, disruption, and re‐assembly. Here, we use meteorite impact craters as proxies for tracking the voyage of lithospheric plates. Employing the provisions in GPlates, an interactive geographic information system‐based plate tectonic reconstruction model, we were able to identify the palaeo‐position, and velocity of the 174 terrestrial impact craters, formed after 1,100 Ma, across the globe. These parameters of craters were evaluated for independent tectonic plates and were correlated with global tectonic events. For example, the similarity in the velocity of Beaverhead (900 Ma) and Holleford (550 Ma) craters since 550 Ma is traced to the connection between the Eastern Basin and North America Craton commencing 1,100 Ma, and through the South Basin and Range. Likewise, the drastic reduction in the velocity of Spider Crater (700 Ma) in Australia after 600 Ma can be attributed to the subduction between east and west Gondwana. The accelerated motion of the Indian Plate at 63 Ma, when the lithosphere was hovering over the Réunion hotspot, is also explained. With the advent of more improved plate tectonic models and the discovery of more impact craters, improvised interpretations will be possible.

Have the 1999 Izmit–Düzce earthquakes influenced the motion and seismicity of the Anatolian microplate?

SUMMARYIn the current plate tectonics paradigm, relative plate motions are assumed to remain unperturbed by temporal stress changes occurring during the seismic cycle, whereby stress slowly built up along tectonic plate boundaries is suddenly released by rapid fault slip during earthquakes. However, direct observations that could challenge such a tenet have not been identified so far. Here we show that the rigid motion of the whole Anatolian microplate, measured using space geodetic techniques, was altered by the stress released during the 1999 Izmit–Düzce earthquakes, which ruptured along the North Anatolian Fault. This kinematic change requires a torque change that is in agreement with the torque change imparted upon the Anatolian microplate by the Izmit–Düzce coseismic stress release. This inference holds across realistic ranges of data noise and controlling parameters, and is not hindered by active deformation in western Anatolia. These results suggest the existence of a whole-plate kinematic signal associated with the stress released by large earthquakes.

Some New Concepts in the Plate Tectonics Paradigm Fifty Years after Its Inception

AbstractWe have gained significant insights into the dynamic evolution of the earth, causes of geohazards, processes of continental growth, feedback mechanisms between tectonics, topography and cli...

Southward propagation of Nazca subduction along the Andes.

The Andean margin is the plate-tectonic paradigm for long-lived, continuous subduction, yet its geology since the late Mesozoic era (the past 100 million years or so) has been far from steady state. The episodic deformation and magmatism have been attributed to cyclic changes in the dip angle of the subducting slab, slab break-off and the penetration of the slab into the lower mantle; the role of plate tectonics remains unclear, owing to the extensive subduction of the Nazca-Farallon plate (which has resulted in more than 5,500 kilometres of lithosphere being lost to the mantle). Here, using tomographic data, we recreate the plate-tectonic geometry of the subducted Nazca slab, which enables us to reconstruct Andean plate tectonics since the late Mesozoic. Our model suggests that the current phase of Nazca subduction began at the northern Andes (5°S) during the late Cretaceous period (around 80 million years ago) and propagated southwards, reaching the southern Andes (40°S) by the early Cenozoic era (around 55 million year ago). Thus, contrary to the current paradigm, Nazca subduction has not been fully continuous since the Mesozoic but instead included episodic divergent phases. In addition, we find that foredeep sedimentation and the initiation of Andean compression are both linked to interactions between the Nazca slab and the lower mantle, consistent with previous modelling.

When will it end? Long-lived intracontinental reactivation in central Australia

The post-Mesoproterozoic tectonometamorphic history of the Musgrave Province, central Australia, has previously been solely attributed to intracontinental compressional deformation during the 580–520 Ma Petermann Orogeny. However, our new structurally controlled multi-mineral geochronology results, from two north-trending transects, indicate protracted reactivation of the Australian continental interior over ca. 715 million years. The earliest events are identified in the hinterland of the orogen along the western transect. The first tectonothermal event, at ca. 715 Ma, is indicated by 40Ar/39Ar muscovite and U–Pb titanite ages. Another previously unrecognised tectonometamorphic event is dated at ca. 630 Ma by U–Pb analyses of metamorphic zircon rims. This event was followed by continuous cooling and exhumation of the hinterland and core of the orogen along numerous faults, including the Woodroffe Thrust, from ca. 625 Ma to 565 Ma as indicated by muscovite, biotite, and hornblende 40Ar/39Ar cooling ages. We therefore propose that the Petermann Orogeny commenced as early as ca. 630 Ma. Along the eastern transect, 40Ar/39Ar muscovite and zircon (U–Th)/He data indicate exhumation of the foreland fold and thrust system to shallow crustal levels between ca. 550 Ma and 520 Ma, while the core of the orogen was undergoing exhumation to mid-crustal levels and cooling below 600–660 °C. Subsequent cooling to 150–220 °C of the core of the orogen occurred between ca. 480 Ma and 400 Ma (zircon [U–Th]/He data) during reactivation of the Woodroffe Thrust, coincident with the 450–300 Ma Alice Springs Orogeny. Exhumation of the footwall of the Woodroffe Thrust to shallow depths occurred at ca. 200 Ma. More recent tectonic activity is also evident as on the 21 May, 2016 (Sydney date), a magnitude 6.1 earthquake occurred, and the resolved focal mechanism indicates that compressive stress and exhumation along the Woodroffe Thrust is continuing to the present day. Overall, these results demonstrate repeated amagmatic reactivation of the continental interior of Australia for ca. 715 million years, including at least 600 million years of reactivation along the Woodroffe Thrust alone. Estimated cooling rates agree with previously reported rates and suggest slow cooling of 0.9–7.0 °C/Ma in the core of the Petermann Orogen between ca. 570 Ma and 400 Ma. The long-lived, amagmatic, intracontinental reactivation of central Australia is a remarkable example of stress transmission, strain localization and cratonization-hindering processes that highlights the complexity of Continental Tectonics with regards to the rigid-plate paradigm of Plate Tectonics.

Deep crustal cumulates reflect patterns of continental rift volcanism beneath Tanzania

Magmatism on Earth is most abundantly expressed by surface volcanic activity, but all volcanism has roots deep in the crust, lithosphere, and mantle. Intraplate magmatism, in particular, has remained enigmatic as the plate tectonic paradigm cannot easily explain phenomena such as large flood basalt provinces and lithospheric rupture within continental interiors. Here, I explore the role of deep crustal magmatic processes and their connection to continental rift volcanism as recorded in deep crustal xenoliths from northern Tanzania. The xenoliths are interpreted as magmatic cumulates related to Cenozoic rift volcanism, based on their undeformed, cumulate textures and whole-rock compositions distinct from melt-reacted peridotites. The cumulates define linear trends in terms of whole-rock major elements and mineralogically, can be represented as mixtures of olivine + clinopyroxene. AlphaMELTS modeling of geologically plausible parental melts shows that the end-member cumulates, clinopyroxenite and Fe-rich dunite, require fractionation from two distinct melts: a strongly diopside-normative melt and a fractionated picritic melt, respectively. The former can be linked to the earliest, strongly silica-undersaturated rift lavas sourced from melting of metasomatized lithosphere, whereas the latter is linked to the increasing contribution from the upwelling asthenospheric plume beneath East Africa. Thus, deep crustal cumulate systematics reflect temporal and compositional trends in rift volcanism, and show that mixing, required by the geochemistry of many rift lava suites, is also mirrored in the lavas’ cumulates.

Multiple convergences along an Archean craton margin: Clues from Proterozoic ophiolite remnants, granites and granulite domains along the SE margin of India

A collage of disparate tectonostratigraphic units intermittently stitched together in the Paleoproterozoic to Neoproterozoic constitutes the southeastern margin of the Archean Eastern Dharwar Craton (EDC). Two small ophiolitic slivers namely the 1.9 Ga Kandra Ophiolite Complex and the 1.33 Ga Kanigiri Ophiolitic Mélange (KOM) indicate two separate subduction-related intra-oceanic arcs outboard of the EDC margin in the Paleoproterozoic and the Mesoproterozoic, respectively. Post-tectonic granites intrusive into the KOM, adjoining domains of the Nellore Schist Belt and the Nallamalai Fold Belt add to the bulk of the collage which also includes the Ongole domain of the southern Eastern Ghats Belt. Generation of UHT granulite and migmatitic granite during 1.68-1.54 Ga probably indicating collision related tectonothermal activity, relate the Ongole domain to the Rayner complex of East Antarctica, which have similar isotopic signatures. The tectonic collage was welded with the EDC margin only in the Neoproterozoic as the intracratonic to cratonic marginal basins namely the Cuddapah Basin and the Kurnool Basin had open sea connections from the Paleoproterozoic to the Neoproterozoic. We re-examine the geological, structural and geochronological data in order to understand the applicability of a plate tectonic paradigm toward the growth of the EDC margin in the Proterozoic, and possible global connections.

Deciphering the Late Cretaceous‐Cenozoic Structural Evolution of the North Peruvian Forearc System

AbstractThe link between plate tectonics and the evolution of active margins is still an ongoing task to challenge since the acceptance of plate tectonic paradigm. This paper aims at deciphering the structural architecture and uplift history of the North Peruvian forearc system to better understand the evolution and the mechanics that govern the Late Cretaceous‐Cenozoic building of this active margin. In this study, we report surface structural geology data, interpretation of seismic reflection profiles, apatite fission track data, and the construction of two offshore‐onshore crustal‐scale balanced cross sections. The structure of the North Peruvian forearc system is dominated by an accretionary style with northwestward propagation of thrust‐related structural highs involving continental/oceanic basement rocks and off‐scrapped sediments. The thrust systems bound thick thrust‐top forearc depocenters mainly deformed by crustal normal to strike‐slip faults and thin‐skinned gravitational instabilities. The sequential restoration of the margin calibrated with apatite fission track data suggests a correlation between uplift, shortening, and plate convergence velocity during Late Cretaceous and Miocene. Pliocene‐Quaternary shortening and uplift of the coastal zone is rather related to the subduction of asperities during convergence rate decrease. The development of crustal normal to strike‐slip faulting and subsidence zones might be the consequence of slab flexure, local basal erosion along subduction fault, and/or oblique subduction associated with sediment loading control. We conclude that the evolution of the North Peruvian forearc system was controlled by subduction dynamics, strong sediment accumulation, and recent ridge subduction, and it recorded the orogenic loading evolution of the Andes over the Cenozoic.

Ancient Continental Lithosphere Dislocated Beneath Ocean Basins Along the Mid‐Lithosphere Discontinuity: A Hypothesis

AbstractThe documented occurrence of ancient continental cratonic roots beneath several oceanic basins remains poorly explained by the plate tectonic paradigm. These roots are found beneath some ocean‐continent boundaries, on the trailing sides of some continents, extending for hundreds of kilometers or farther into oceanic basins. We postulate that these cratonic roots were left behind during plate motion, by differential shearing along the seismically imaged mid‐lithosphere discontinuity (MLD), and then emplaced beneath the ocean‐continent boundary. Here we use numerical models of cratons with realistic crustal rheologies drifting at observed plate velocities to support the idea that the mid‐lithosphere weak layer fostered the decoupling and offset of the African continent's buoyant cratonic root, which was left behind during Meso‐Cenozoic continental drift and emplaced beneath the Atlantic Ocean. We show that in some cratonic areas, the MLD plays a similar role as the lithosphere‐asthenosphere boundary for accommodating lateral plate tectonic displacements.

A genetic link between transform and hyper-extended margins

The similarity between the geometry of the West African and South American coastlines is among one of the strongest natural observations supporting the plate tectonic paradigm. However, using classical plate tectonic approaches to model these conjugate transform margins results in a high degree of variability in palaeogeographic reconstructions. Using state-of-the-art 3D coupled thermo-mechanical numerical models, we simulate for the first time, crustal deformation at the onset of oceanisation along large offset oblique margins. Our models show that obliquity causes oceanic rift propagation to stall, resulting in an apparent polyphased tectonic evolution, and in some circumstances leads to the formation of hyper-extended margins. As a result, conjugate margins located at the edge of future fracture zones are highly asymmetric from rifting to spreading, with their lengths differing by a factor of 5 to 10, before the final phase of break-up occurs. Accounting for this discrepancy should ameliorate future palaeogeographic reconstructions.

Folding and necking across the scales: a review of theoretical and experimental results and their applications

Abstract. The shortening and extension of mechanically layered ductile rock generates folds and pinch-and-swell structures (also referred to as necks or continuous boudins), which result from mechanical instabilities termed folding and necking, respectively. Folding and necking are the preferred deformation modes in layered rock because the corresponding mechanical work involved is less than that associated with a homogeneous deformation. The effective viscosity of a layered rock decreases during folding and necking, even when all material parameters remain constant. This mechanical softening due to viscosity decrease is solely the result of fold and pinch-and-swell structure development and is hence termed structural softening (or geometric weakening). Folding and necking occur over the whole range of geological scales, from microscopic up to the size of lithospheric plates. Lithospheric folding and necking are evidence for significant deformation of continental plates, which contradicts the rigid-plate paradigm of plate tectonics. We review here some theoretical and experimental results on folding and necking, including the lithospheric scale, together with a short historical overview of research on folding and necking. We focus on theoretical studies and analytical solutions that provide the best insight into the fundamental parameters controlling folding and necking, although they invariably involve simplifications. To first order, the two essential parameters to quantify folding and necking are the dominant wavelength and the corresponding maximal amplification rate. This review also includes a short overview of experimental studies, a discussion of recent developments involving mainly numerical models, a presentation of some practical applications of theoretical results, and a summary of similarities and differences between folding and necking.

Phase change in subducted lithosphere, impulse, and quantizing Earth surface deformations

Abstract. The new paradigm of plate tectonics began in 1960 with Harry H. Hess's 1960 realization that new ocean floor was being created today and is not everywhere of Precambrian age as previously thought. In the following decades an unprecedented coming together of bathymetric, topographic, magnetic, gravity, seismicity, seismic profiling data occurred, all supporting and building upon the concept of plate tectonics. Most investigators accepted the premise that there was no net torque amongst the plates. Bowin (2010) demonstrated that plates accelerated and decelerated at rates 10−8 times smaller than plate velocities, and that globally angular momentum is conserved by plate tectonic motions, but few appeared to note its existence. Here we first summarize how we separate where different mass sources may lie within the Earth and how we can estimate their mass. The Earth's greatest mass anomalies arise from topography of the boundary between the metallic nickel–iron core and the silicate mantle that dominate the Earth's spherical harmonic degree 2 and 3 potential field coefficients, and overwhelm all other internal mass anomalies. The mass anomalies due to phase changes in olivine and pyroxene in subducted lithosphere are hidden within the spherical harmonic degree 4–10 packet, and are an order of magnitude smaller than those from the core–mantle boundary. Then we explore the geometry of the Emperor and Hawaiian seamount chains and the 60° bend between them that aids in documenting the slow acceleration during both the Pacific Plate's northward motion that formed the Emperor seamount chain and its westward motion that formed the Hawaiian seamount chain, but it decelerated at the time of the bend (46 Myr). Although the 60° change in direction of the Pacific Plate at of the bend, there appears to have been nary a pause in a passive spreading history for the North Atlantic Plate, for example. This, too, supports phase change being the single driver for plate tectonics and conservation of angular momentum. Since mountain building we now know results from changes in momentum, we have calculated an experimental deformation index value (1–1000) based on a world topographic grid at 5 arcmin spacing and displayed those results for viewing.

A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) 'The fit of the continents around the Atlantic'.

In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160 Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900 m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

Making it thick: a volcanic plateau origin of Palaeoarchean continental lithosphere of the Pilbara and Kaapvaal cratons

Abstract How and when continents grew and plate tectonics started on Earth remain poorly constrained. Most researchers apply the modern plate tectonic paradigm to problems of ancient crustal formation, but these are unsatisfactory because diagnostic criteria and actualistic plate configurations are lacking. Here, we show that 3.5–3.2 Ga continental nuclei in the Pilbara Craton, Australia, and the eastern Kaapvaal Craton, southern Africa, formed as thick volcanic plateaux built on a substrate of older continental lithosphere and did not accrete through horizontal tectonic processes. These nuclei survived because of the contemporaneous development of buoyant, non-subductable mantle roots. This plateau-type of Archean continental crust is distinct from, but complementary to, Archean gneiss terranes formed over shallowly dipping zones of intraoceanic underplating (proto-subduction) on a vigorously convecting early Earth with smaller plates and primitive plate tectonics.

Exhumation rates in the Archean from pressure–time paths: Example from the Skjoldungen Orogen (SE Greenland)

The discussions on the orogenic evolution during Earth's history converge to the question of a different thermal structure in the Archean compared to the Phanerozoic and the applicability of the plate tectonic paradigm. However, geothermal structures are transient in orogens and are difficult to translate into large-scale tectonics and exhumation rates. Therefore, we propose depth–time data in the Archean Skjoldungen Orogen (SE Greenland, North Atlantic Craton) that allow for reconstruction of an exhumation rate independent of geothermal gradients. The resulting exhumation rate of ca. 0.4km/Ma is similar to exhumation rates during erosion-controlled processes in modern orogens. These exhumation rates can only be established by erosion time constants similar to modern orogens. The occurrence of erosion-controlled exhumation is best explained by a stiff foreland promoting localized deformation in the orogen. Therefore, a switch from magmatic-dominated processes to localized deformation is proposed in the Skjoldungen Orogen area. This is supported by a change in magma composition and volume, from widespread granodiorite to localized alkaline intrusions. In addition, the involved metasedimentary rocks include detrital zircons of the only 50Ma older foreland, which also correspond to erosion and tectonics as in modern orogens, i.e. flysh-type sediments. Relatively fast exhumation rates and the structural-magmatic evolution of the Neoarchean Skjoldungen Orogen thus indicate modern-style tectonic processes where stiff Mesoarchean continental crust forms a foreland to a collisional orogen instead of typical accretionary tectonics of weak island arc-like terranes in granite-greenstone terranes.

John Tuzo Wilson: a man who moved mountains

Fifty years ago, the world’s Earth Scientists experienced the so-called “Revolution in the Earth Sciences”. In the decade from 1960 to 1970, a massive convergence took place from many diverse and contradictory theories about the tectonic processes operating on Earth (then loosely called “mountain building”) to a single widely accepted paradigm now called Plate Tectonics. A major player in leading the international “Revolution” was Canadian geophysicist J. Tuzo Wilson. This tribute reviews how he helped define and promote the Plate Tectonic paradigm, and also, from 1946 to 1967, how he led a rapid expansion of the role of geophysics in Canadian and international earth science. Wilson was a controversial figure before and during the “Revolution”, but his influence was large. It was not coincidental that earth science research in Canada grew by 1964 to the point where the National Research Council of Canada could add the Canadian Journal of Earth Sciences to its group of Canadian research journals.

John Tuzo Wilson: a Canadian who revolutionized Earth Sciences

John Tuzo Wilson (1908–1993) was one of the greatest Canadian scientists of the 20th century. His contributions to Earth Sciences, leading the formulation of the theory of plate tectonics, have revolutionized our understanding of how the planet Earth works and evolved over the past 4 billion years. This 50th anniversary special issue of the Canadian Journal of Earth Sciences is dedicated in honour of John Tuzo Wilson, who inspired tens of thousands of students all around the world to study the Earth. This special issue contains 12 papers dealing with various aspects of the “Wilson Cycle” in the geologic record, plate tectonics, mantle plumes, and how John Tuzo Wilson accepted “continental drift” and formulated the theory of plate tectonics. The contributions have mostly been made by geoscientists who directly or indirectly associated with John Tuzo Wilson and have contributed significantly to the plate tectonics paradigm.

Whither the supercontinent cycle?

The concept of episodicity in tectonic processes pre-dates acceptance of the plate tectonic paradigm (e.g., Umbgrove, 1940; Holmes, 1951; Sutton, 1963). It was specifi cally advocated by Wilson (1966) when he made the case that ocean basins repeatedly opened and closed, a process now known as “Wilson cycles” (Dewey and Burke, 1974). The relationship between tectonic episodicity and the supercontinent cycle was fi rst proposed by Worsley et al. (1982, 1984), who argued that episodic peaks in the number of continental collisions refl ect supercontinent amalgamation, and that episodes of rift-related mafi c dike swarms record supercontinent breakup. These authors identifi ed trends in tectonic activity, platform development, climate, life and stable isotopes that accompanied supercontinent amalgamation, breakup and dispersal (Nance et al. 2013). Although not universal (e.g., Stern, 2008), a broad consensus has emerged over the past 30 years that repeated cycles of supercontinent amalgamation and dispersal occurred since the late Archean, with profound effect on the evolution of the Earth’s geosphere, hydrosphere, atmosphere and biosphere. Statistical peaks in the age distributions of orogenic granites and detrital zircons, as well as negative e Hf excursions in zircons may match the timing of supercontinent amalgamation. As Hf is the more incompatible element, Lu/Hf is lower in the crust and higher in the depleted mantle relative to the bulk earth, and the crust therefore evolves towards negative eHf values. Whether these eHf data imply episodicity, a preservational bias, or a combination of both phenomena is debated (e.g., Roberts, 2012; Cawood et al., 2013; Nance et al., 2013). The mechanisms potentially responsible for the supercontinent