Introduction
A craton is the long-lived, tectonically stable portion of the continental lithosphere that commonly forms the structural core of continents. The word derives from the Ancient Greek kratos, “strength,” and is pronounced variously (e.g., /ˈkreɪtɒn/, /ˈkrætɒn/, /ˈkreɪtən/), reflecting its role as a resilient continental nucleus. Cratons consist of ancient crystalline basement rocks capped by younger sedimentary successions; this stratigraphic arrangement preserves a prolonged record of surface and subsurface geological evolution. Structurally they are distinguished by thick continental crust and deep lithospheric “roots” or keels that extend into the mantle, commonly to depths of several hundred kilometres. Most cratonic crust formed during the Archaean and Proterozoic eons, with a substantial proportion assembled in the Archaean, and these domains host the oldest preserved continental lithosphere on Earth. In a plate-tectonic framework cratons typically occupy plate interiors, having survived multiple cycles of continental assembly and breakup, although rifting can isolate cratonic fragments and produce passive margins. A classic example of such continuity followed by fragmentation is the correspondence between South American and African cratons when both were contiguous within Pangea during the Triassic and later separated by Mesozoic rifting.
In global tectonic usage, a craton denotes the long‑lived, internally stable portion of continental crust that contrasts with adjacent, more tectonically active regions. Cratons are characterized by prolonged resistance to significant internal deformation and thus serve as the ancient structural cores of continents (Bleeker & Davis 2004). Archaean cratons in particular are commonly described as relatively flat, undeformed crustal domains that have persisted since the Precambrian and form the nuclei around which later continental growth accreted (King 2005).
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Morphologically and stratigraphically, cratons are conventionally divided into two principal components: the cratonic basement—an old, coherent assemblage of crystalline and high‑grade metamorphic rocks that provides the structural framework—and the platform, a laterally extensive, comparatively undeformed sedimentary cover that overlies and conceals much of the basement in many regions. Where basement rocks are exposed at the surface the term shield is applied; where they are buried beneath sedimentary cover the term platform is used. These labels are primarily physiographic descriptors of surface expression and cover relationships rather than independent tectonic units, and meaningful tectonic interpretation requires integration with subsurface and structural data.
Broader geologic‑province schemes, such as the USGS legend, treat shields and platforms alongside other domain types (e.g., orogen, basin, large igneous province, extended crust) within continental and oceanic classifications, and they also distinguish oceanic crust by age classes (0–20 Ma, 20–65 Ma, >65 Ma). The modern term “craton” derives from early 20th‑century usage: Leopold Kober’s German “Kratogen” (paired with “orogen”) was subsequently shortened by Hans Stille to “Kraton,” giving rise to the contemporary English term.
Examples
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Cratons are the long-lived, internally coherent cores of continental lithosphere that underlie much of the planet’s continental architecture and provide the rigid foundation onto which younger mobile belts and sedimentary covers have been accreted. Representative cratons occur on virtually every continent: the Dharwar Craton in southern India, the North China Craton in East Asia, and the East European Craton across much of Eastern Europe (Eurasia) each exemplify major stable continental nuclei in their regions. In the Southern Hemisphere, the Kaapvaal Craton of southern Africa and the Gawler Craton of South Australia are enduring blocks within their respective continental frameworks, while the Amazonian Craton constitutes a principal ancient core of South America. North America’s cratonic heart is commonly referred to as the North American or Laurentia Craton, reflecting the frequent use of alternative or historical names for these large crustal provinces. Collectively, these named examples illustrate the global distribution and fundamental role of cratons as the ancient, rigid nuclei of continents.
Structure
Cratons are underlain by anomalously cold, chemically depleted lithospheric roots that extend to depths commonly exceeding ~200 km—more than twice the typical thickness of mature oceanic or non‑cratonic continental lithosphere. Mantle tomography shows that the low‑velocity zone usually present within the asthenosphere beneath transient lithosphere is weak or missing beneath these keels, indicating a colder, mechanically stronger mantle column that penetrates into the asthenosphere. This cold, depleted mantle has a low intrinsic density and correspondingly neutral to positive buoyancy; that buoyancy counteracts density increases from secular cooling and thereby helps prevent cratons from sinking into the deeper mantle. The result is exceptional preservation: cratonic lithosphere can survive for up to ~4 billion years, in stark contrast to oceanic plates whose ages rarely exceed ~180 million years.
Direct constraints on the composition and physical state of cratonic roots come from mantle xenoliths carried to the surface in magmas—most notably peridotite nodules in kimberlite pipes. These xenoliths record extensive melt extraction and chemical depletion: harzburgite and related peridotites represent residue after removal of basalt‑ to komatiite‑like melts, producing the high‑Mg, low‑Ca and low‑Fe signature characteristic of cratonic mantle and contributing to its low density. Water contents in these peridotites are anomalously low, a dryness that substantially increases rheological strength relative to wetter mantle. Together, depletion by high‑degree melting, low volatile content, and the resultant thermochemical structure explain the density, buoyancy, strength, and extraordinary longevity of cratonic lithosphere.
Formation
An idealized lithospheric cross‑section frames cratons as stable continental interiors with pronounced lateral and vertical contrasts in thickness, composition and tectonic behavior. Exposed portions of cratons appear as shields, while platforms are cratonic regions blanketed by younger sedimentary cover; associated features such as cratonic basins, large igneous provinces and mid‑ocean ridges further illustrate the heterogeneity of lithospheric architecture and its interactions with surrounding tectonic domains.
Cratons are distinguished by unusually deep, long‑lived lithospheric roots that conserve ancient mantle and crustal materials. The recovery of diamonds from these roots provides a direct chronology of cratonic stability: diamonds are almost invariably older than 2 Ga and frequently exceed 3 Ga, attesting to extremely ancient origins for many cratonic cores.
The process that produced these robust continental nuclei is termed cratonization, a sequence of geodynamic and petrogenetic events that formed the first continents. Despite extensive study, the precise mechanisms, rates and timing of cratonization remain poorly resolved and are a continuing focus of debate within the geosciences.
Stratigraphic and crustal‑mass estimates indicate that the earliest cratonic lithosphere formed in the Archean, yet Archean rocks now account for only about 7% of present cratons. More comprehensive reconstructions that allow for erosion and crustal destruction place the fraction of continental crust generated during the Archean between roughly 5 and 40%, implying substantial post‑Archean crustal growth and reworking. Cratonization itself appears to have been largely accomplished by the Proterozoic; thereafter, continental growth proceeded mainly by peripheral accretion—addition of terranes, magmatic material and sedimentary cover at continental margins—rather than by wholesale formation of new cratonic cores.
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Root origin
The prevailing model for the origin of cratonic roots derives from Thomas H. Jordan’s 1978 proposal that very high degrees of partial melting of an anomalously hot Archean upper mantle produced the first stable continental keels. Extraction of roughly 30–40% of the source peridotite preferentially removed basaltic/komatiitic components and left a residue strongly enriched in magnesium and depleted in heavier, iron-bearing components. This chemical depletion reduced the intrinsic density of the residual peridotite, imparting a buoyant compositional effect that partially counterbalanced thermal contraction as the lithosphere cooled; the net result is a cold cratonic root whose physical density approaches that of the surrounding, hotter mantle.
Depletion also altered physical properties important for longevity: the residue has an elevated solidus and markedly higher viscosity, and its mineral phases (notably very dry olivine in xenoliths) are less prone to remelting or entrainment. These changes inhibit thermal and compositional reequilibration with adjacent undepleted mantle and help explain why cratonic lithosphere can persist for billions of years. Jordan envisaged subduction-related settings as the principal locus for such high-degree melting, with flood-basalt–type events as a secondary mechanism capable of producing large melt volumes.
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Petrological and geochemical observations lend qualified support to this melt-extraction framework. Continental xenoliths record low geothermal gradients beneath shields compared with oceanic domains, olivine in cratonic roots is anomalously dry (consistent with high viscosity), and Re–Os isotopes in xenoliths date major melting events to the early–middle Archean. Field and geochronological data also indicate that cratonization was protracted: stabilization of lithospheric roots continued into the late Archean and coincided with episodic, voluminous mafic magmatism rather than a single instantaneous event.
However, the melt-extraction model has important limitations. Jordan estimated that shallow high-degree melting could construct depleted roots only to depths of order ~200 km; many cratonic keels extend substantially deeper, implying additional processes are required. Experimental petrology shows that 30–40% melting at pressures of ~4–10 GPa produces komatiitic magma and a residue compositionally similar to Archean lithospheric mantle, yet the volume of komatiite exposed on shields is much smaller than this simple prediction. This discrepancy could mean that much komatiitic melt was emplaced at depth and never reached the surface, or that other mechanisms—tectonic juxtaposition of depleted fragments, metasomatic modification, delamination, chemical stratification, or yet-unidentified processes—contributed to root growth and thickening.
Because high-degree melt extraction alone cannot account simultaneously for the full depth, composition and long-term preservation of many cratonic keels, multiple competing hypotheses persist. Any satisfactory model must reconcile the observed low geothermal gradients, the presence of dry, high-viscosity olivine, Archean Re–Os ages of depletion, limited komatiite exposures at the surface, and the ~200 km depth constraint of simple melt-extraction scenarios.
Jordan’s repeated‑collision model explains cratonization as the cumulative effect of successive continental orogenies that progressively thicken continental crust and thereby build long‑lived, tectonically stable continental interiors. Each collision adds material and structural complexity to the crust, driving the system toward a thicker, more buoyant crust–mantle assemblage.
Isostatic balance governs the mass exchange between crust and mantle in this scenario: as the crustal column grows, it is compensated by the development of a low‑density, buoyant lithospheric root so that the combined crust and underlying keel remain in gravitational equilibrium. This compensatory thickening concentrates buoyant material beneath the evolving craton.
Mechanically, Jordan envisages repeated collisions producing pervasive ductile reworking of the lithosphere, allowing vertically directed material redistribution. Buoyancy forces promote upward mobilization of lower‑density components and downward segregation of higher‑density material, a process that differentiates and mechanically hardens the mantle portion of the lithosphere.
The net result is the formation of deep, compositionally and rheologically distinct lithospheric keels beneath cratons—mantle roots that can extend to depths on the order of several hundred kilometers (up to ~400 km). These thick, buoyant, and mechanically strong roots provide the fundamental support for the long‑term stability of continental cratons.
In the molten-plume model, buoyant mantle upwellings deliver heat and partial melt to the base of the lithosphere, producing thermal doming, magmatic addition and crustal growth. Plume-derived melts both add igneous material to the crust and thermally weaken and uplift the crustal column, thereby modifying crustal thickness and the local isostatic balance above the upwelling.
Sustained or repeated melt extraction from such upwellings leaves a residue of mantle that is depleted in fusible basaltic components, incompatible elements and volatiles. This refractory, compositionally impoverished layer beneath continents tends to be more buoyant and mechanically strong than fertile mantle. A thick refractory mantle root beneath cratons therefore increases effective lithospheric thickness, produces elevated seismic velocities and characteristic mantle xenolith and isotopic signatures, and helps stabilize continental blocks over geological time. By imposing contrasts in density and thermal structure with the surrounding asthenosphere, these roots influence lithosphere–asthenosphere coupling, long‑term buoyancy and surface topography, and thus play a central role in cratonization.
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Subducting ocean slab model
The subducting-slab model envisions that repeated episodes of oceanic lithosphere descent generate multiple downgoing slabs that stall at the base of an emergent continental nucleus rather than penetrating into the deep mantle. These mechanically trapped slabs accumulate at the lithosphere–asthenosphere boundary beneath a proto-craton, producing a stacked underplate of former oceanic lithosphere. During or after emplacement this material undergoes partial melting and extraction of melts, leaving a residue dominated by refractory, peridotitic mantle rather than fertile basaltic lithology.
This residual mantle is chemically depleted—low in incompatible trace elements and enriched in refractory phases—and thus records signatures of prior melt extraction (high Mg#, depleted radiogenic isotope compositions). Such characteristics are expected in mantle xenoliths, peridotites and other samples derived from subcontinental lithospheric mantle (SCLM) formed by this process, distinguishing underplated residues from more fertile or recently accreted oceanic material.
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Physically, accumulation of depleted slabs thickens and stiffens the SCLM, raising seismic shear‑wave velocities and effective viscosity while reducing conductive heat flow. The result is a cold, buoyant lithospheric root that is mechanically robust and resistant to subsequent deformation. Repeated underplating through prolonged or episodic subduction can thus progressively transform portions of oceanic lithosphere into a thick, chemically depleted subcontinental mantle root, providing a viable pathway for the formation, stabilization and long-term preservation of cratonic lithosphere.
Impact origin model
A 2015 hypothesis argues that continental cratons may have arisen from impact-driven, large-volume magmatism comparable to the processes that form crustal plateaus on Venus. According to this model, exceptionally large early-Earth asteroid impacts delivered sufficient energy to penetrate into the upper mantle and produce melt volumes vastly exceeding those of typical volcanic eruptions. These melts ponded within impact basins to form extensive, long-lived magma bodies; as they cooled and underwent fractional crystallization, they would differentiate to produce a thick, refractory, buoyant lithospheric keel. Such a differentiated root could supply the compositional and mechanical contrast needed for prolonged stability, offering an explanation for cratons’ longevity. By analogizing Earth’s cratons to Venusian plateaus, the model links planetary-scale cratering and subsequent large-volume magmatism to the development of stable continental interiors in Earth’s early history.
Evidence from seismic tomography beneath the North American craton reveals a vertically stratified lithospheric keel comprised of an upper layer shallower than ~150 km (93 mi) and a deeper layer between ~180 and 240 km (110–150 mi). The shallow layer is consistent with an ancient, strongly depleted refractory “cap” that formed in the Archean and persists as a mechanically and chemically distinct lid, whereas the deeper unit appears younger and less depleted, behaving as a stagnated thermal boundary layer accreted or modified against the pre‑existing root.
Compositional data from mantle xenoliths sampled in cratonic domains complement the seismic picture and more closely align with accretional assembly models in which discrete lithospheric packages were added to build the root, rather than with a single-stage, plume‑driven construction. Conversely, other geochemical datasets (independent of xenolith and tomographic constraints) retain signatures consistent with mantle plume activity, producing a genuine tension between different observational lines and their preferred process models.
An alternative explanation invoked for cratonic keel formation is a large‑impact mechanism that can produce rootlike lithospheric structures without requiring plumes or stepwise accretion; this hypothesis need not be mutually exclusive with plume or accretional processes and can be compatible with aspects of those models. All proposed scenarios, however, invoke the same fundamental physical requirement: geodynamic segregation in which buoyant, viscous mantle material separates from a denser residual phase under flow, driven by contrasts in buoyancy, viscosity and convective transport.
Given the complementary and at times conflicting evidence, the most parsimonious interpretation is pluralistic: accretional addition, plume influence, impact effects and mantle‑flow–driven segregation likely played varying roles in constructing and subsequently modifying the North American cratonic root.
Erosion (cratonic regime)
The cratonic regime denotes a model of long‑term denudation affecting ancient continental cores in which sustained surface lowering and extensive planation produce broad, low‑relief landscapes commonly termed peneplains. Over multi‑million to billion‑year intervals these landscapes evolve through alternating episodes of slope retreat and weathering‑driven stripping rather than by a single uniform process; the cyclic alternation of these modes is intrinsic to the cratonic erosion regime.
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Two principal planation mechanisms are recognized within this regime. Pediplanation, typical of arid to semi‑arid settings, operates through mechanical breakdown and upslope retreat of slopes that expand and coalesce into extensive pediments. Etchplanation, dominant under humid conditions, is controlled by deep chemical weathering that reduces relief by preferentially removing altered material and exposing a subdued surface. Despite their different operative processes, both pathways commonly converge on similarly low‑relief, near‑planar surfaces.
Because cratons persist through major climate swings, their peneplains are often polygenetic: composite surfaces that record successive intervals of pediplanation and etchplanation as climatic regimes oscillate. Superimposed on these climatic cycles are fluctuations in relative sea level; intervals of higher relative sea level increase marine influence and coastal inundation, whereas lower sea levels favor more continental, subaerial denudation regimes. The interplay of climatic change and sea‑level variability thus drives the alternating erosional signatures preserved on cratonic surfaces.
Many cratons retain subdued topography that can be traced back to Precambrian times, reflecting the cumulative effect of repeated planation episodes and generally limited tectonic rejuvenation. For example, the Yilgarn Craton of Western Australia had already attained a notably flat character by the Middle Proterozoic, indicating an early onset of long‑lived planation. Likewise, parts of the Baltic Shield were reduced to low relief by the Late Mesoproterozoic; the contemporaneity of this planation with rapakivi granite intrusion demonstrates that major plutonism can occur alongside or subsequent to deep, long‑term surface lowering.