On the geodynamic setting of kimberlite genesis

doi:10.1016/0012-821X(84)90043-8

Earth and Planetary Science Letters

Volume 67, Issue 1, January 1984, Pages 109-122

https://doi.org/10.1016/0012-821X(84)90043-8 Get rights and content

Abstract

The emplacement of kimberlites in the North American and African continents since the early Palaeozoic appears to have occurred during periods of relatively slow motion of these continents. The distribution of kimberlites in time may reflect the global pattern of convection, which forces individual plates to move faster or slower at different times. Two-dimensional numerical experiments on a convecting layer with a moving upper boundary show two different regimes: in the first, when the upper boundary velocity is high, heat is transferred by the large-scale circulation and in the second, when the upper boundary velocity is lower, heat is predominantly transferred by thermal plumes rising from the lower boundary layer. For a reasonable mantle solidus, this second regime can give rise to partial melting beneath the moving plate, far from the plate boundaries. The transition between these modes takes place over a small range of plate velocities; for a Rayleigh number of 10⁶ it occurs around 20 mm yr⁻¹. We suggest that the generation of kimberlite magmas may result from thermal plumes incident on the base of a slowly moving plate.

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Cited by (36)

Origins of kimberlites and carbonatites during continental collision – Insights beyond decoupled Nd-Hf isotopes
2020, Earth-Science Reviews
During the past two decades significant progress has been made in understanding the origin and evolution of kimberlites, including relationships to other diamondiferous magma types such as lamproites and aillikites. However, the association of kimberlites and carbonatites on continental shields remains poorly understood, and two opposing ideas dominate the debate. While one school of thought argues that primary carbonatite melts transform into hybrid carbonated silicate magmas akin to kimberlites by assimilation of cratonic mantle material, others use geochemical evidence to show that carbonatite magmas can evolve from near-primary kimberlite melts within the cratonic lithosphere.
The 1.15 Ga Premier kimberlite pipe on the Kaapvaal craton in South Africa hosts several kimberlite and carbonatite dykes. Reconstructions of magma compositions suggest that up to 20 wt.% CO₂ was lost from near-primary kimberlite melts during ascent through the cratonic lithosphere, but the carbonatite dyke compositions cannot be linked to the kimberlite melts via differentiation. Geochemical evidence, including mantle-like δ¹³C compositions, suggests that the co-occurring kimberlite and carbonatite dykes represent two discrete CO₂-rich magma batches derived from a mixed source in the convecting upper mantle. The carbonatites probed a slightly more depleted source component in terms of Sr-Nd-Hf isotopic compositions relative to the peridotitic matrix that was more effectively tapped by the kimberlites (⁸⁷Sr/⁸⁶Sr_i = 0.70257 to 0.70316 for carbonatites vs. 0.70285 to 0.70546 for kimberlites; εNd_i = +3.0 to +3.9 vs. +2.2 to +2.8; εHf_i = -2.2 to +0.7 vs. -5.1 to -1.9).
Platinum-group element systematics suggest that assimilation of refractory lithospheric mantle material by the carbonatite melts was negligible (<1 vol.%), whereas between 5 – 35 vol.% of digested cratonic peridotite account for the kimberlite compositions, including the low ¹⁸⁷Os/¹⁸⁸Os signature (_ƔOs_i = -12.7 to -4.5). The kimberlite and carbonatite dykes show similarly strong Nd-Hf isotope decoupling (ΔεHf_i = -10.7 to -7.6 vs. -8.8 to -6.1), regardless of the variable lithospheric mantle imprints. This observation suggests a common sublithospheric origin of the negative ΔεHf signature, possibly linked to ancient recycled oceanic crust components in the convecting upper mantle to transition zone sources of CO₂-rich magmatism.
Mesoproterozoic kimberlite and carbonatite magmatism at Premier was coeval with subduction and collision events along the southern Kaapvaal craton margin during the 1,220 –1,090 Ma Namaqua-Natal orogeny associated with Rodinia supercontinent formation. Thermochronology suggests that the entire Kaapvaal craton was affected by this collisional tectonic event, and it appears that the changing lithospheric stress-field created pathways for deep-sourced kimberlite and carbonatite magmas to reach Earth’s surface. We find that collision-induced (e.g., Premier) and continental breakup-related (e.g., Kimberley) kimberlite magmas are compositionally indistinguishable, with the inference that plate tectonic processes aid solely in the creation of magma ascent pathways without a major influence on deep mantle melting beneath cratons. It follows that on-craton kimberlite magmatism in the hinterland of collision zones is not necessarily more likely to entrain large sublithospheric diamonds than kimberlite eruptions linked to continental breakup. This implies that Premier’s world-class endowment with ‘ultradeep’ Type-II diamonds is not causally related to its setting behind an active orogenic front.
Geodynamics of kimberlites on a cooling Earth: Clues to plate tectonic evolution and deep volatile cycles
2018, Earth and Planetary Science Letters
Citation Excerpt :
However, it is reasonable to conclude that enhanced rifting and drifting of tectonic plates with associated far-field stresses that propagate into cratonic continental interiors provided effective pathways to drain deep-sourced kimberlite and related magmas during supercontinent cycles. England and Houseman (1984) proposed that periods of strong kimberlite magmatic activity in North America and Africa during the Phanerozoic correlate with the slowest respective plate motions. However, the improved paleomagnetic and geochronological database for Africa suggests the opposite; that is, prominent peaks in kimberlite magmatic activity at 140–130 Ma and 100–80 Ma correspond to periods of fast acceleration of the African tectonic plate during Pangea breakup (Fig. 8).
Kimberlite magmatism has occurred in cratonic regions on every continent. The global age distribution suggests that this form of mantle melting has been more prominent after 1.2 Ga, and notably between 250–50 Ma, than during early Earth history before 2 Ga (i.e., the Paleoproterozoic and Archean). Although preservation bias has been discussed as a possible reason for the skewed kimberlite age distribution, new treatment of an updated global database suggests that the apparent secular evolution of kimberlite and related CO₂-rich ultramafic magmatism is genuine and probably coupled to lowering temperatures of Earth's upper mantle through time.
Incipient melting near the CO₂- and H₂O-bearing peridotite solidus at >200 km depth (1100–1400 °C) is the petrologically most feasible process that can produce high-MgO carbonated silicate melts with enriched trace element concentrations akin to kimberlites. These conditions occur within the convecting asthenospheric mantle directly beneath thick continental lithosphere. In this transient upper mantle source region, variable CHO volatile mixtures control melting of peridotite in the absence of heat anomalies so that low-degree carbonated silicate melts may be permanently present at ambient mantle temperatures below 1400 °C. However, extraction of low-volume melts to Earth's surface requires tectonic triggers. Abrupt changes in the speed and direction of plate motions, such as typified by the dynamics of supercontinent cycles, can be effective in the creation of lithospheric pathways aiding kimberlite magma ascent.
Provided that CO₂- and H₂O-fluxed deep cratonic keels, which formed parts of larger drifting tectonic plates, existed by 3 Ga or even before, kimberlite volcanism could have been frequent during the Archean. However, we argue that frequent kimberlite magmatism had to await establishment of an incipient melting regime beneath the maturing continents, which only became significant after secular mantle cooling to below 1400 °C during post-Archean times, probably sometime shortly after 2 Ga. At around this time kimberlites replace komatiites as the hallmark mantle-derived magmatic feature of continental shields worldwide.
The remarkable Mesozoic–Cenozoic ‘kimberlite bloom’ between 250–50 Ma may represent the ideal circumstance under which the relatively cool and volatile-fluxed cratonic roots of the Pangea supercontinent underwent significant tectonic disturbance. This created more than 60% of world's known kimberlites in a combination of redox- and decompression-related low-degree partial melting. Less than 2% of world's known kimberlites formed after 50 Ma, and the tectonic settings of rare ‘young’ kimberlites from eastern Africa and western North America demonstrate that far-field stresses on cratonic lithosphere enforced by either continental rifting or cold subduction play a crucial role in enabling kimberlite magma transfer to Earth's surface.
Planation surfaces as a record of mantle dynamics: The case example of Africa
2018, Gondwana Research
There are two types of emerged relief on the Earth: high elevation areas (mountain belts and rift shoulders) in active tectonic settings and low elevation domains (anorogenic plateaus and plains) characteristic of the interior of the continents i.e. 70% of the Earth emerged relief. Both plateaus and plains are characterized by large erosional surfaces, called planation surfaces that display undulations with middle (several tens of kilometres) to very long (several thousands of kilometres) wavelengths, i.e. characteristic of lithospheric and mantle deformations respectively.
Our objective is here (1) to present a new method of characterization of the very long and long wavelength deformations using planation surfaces with an application to Central Africa and (2) to reconstruct the growth of the very long wavelength relief since 40 Ma, as a record of past mantle dynamics below Central Africa.
(i) The African relief results from two major types of planation surfaces, etchplains (weathering surfaces by laterites) and pediplains/pediments. These planation surfaces are stepped along plateaus with different elevations. This stepping of landforms records a local base level fall due to a local tectonic uplift.
(ii) Central Africa is an extensive etchplain-type weathering surface – called the African Surface – from the uppermost Cretaceous (70 Ma) to the Middle Eocene (45 Ma) with a paroxysm around the Early Eocene Climatic Optimum. Restoration of this surface in Central Africa suggests very low-elevation planation surfaces adjusted to the Atlantic Ocean and Indian Ocean with a divide located around the present-day eastern branch of the East African Rift.
(iii) The present-day topography of Central Africa is younger than 40–30 Ma and records very long wavelength deformations (1000–2000 km) with (1) the growth of the Cameroon Dome and East African Dome since 34 Ma, (2) the Angola Mountains since 15–12 Ma increasing up to Pleistocene times and (3) the uplift of the low-elevation (300 m) Congo Basin since 10–3 Ma. Some long wavelength deformations (several 100 km) also occurred with (1) the low-elevation Central African Rise since 34 Ma and (2) the Atlantic Bulge since 20–16 Ma. These very long wavelength deformations record mantle dynamics, with a sharp increase of mantle upwelling around 34 Ma and an increase of the wavelength of the deformation and then of mantle convection around 10–3 Ma.
A new approach to computing steady-state geotherms: The marginal stability condition
2016, Tectonophysics
A necessary physical condition for steady-state mantle convection is the marginal stability of convective boundary layer (CBL) accommodating the transition from conductive lithosphere to convective mantle. We incorporate the marginal stability condition (MSC) of the CBL into the lithosphere thermal modeling using it instead of the heat flow boundary condition specified on the surface. For the oceanic region, the MSC-based approach allows to calculate rather than postulate the thickness of the oceanic lithosphere beneath old oceanic crust areas. The model allows to estimate the potential temperature and to predict the depth at which the suboceanic CBL base occurs. The latter agrees well with the seismologically observed lithosphere-asthenosphere boundary. In the continental region, the CBL is immediately adjacent to the base of the chemical boundary layer comprising a crust and a melt-depleted continental keel. A deep segment of the MSC-based continental geotherm is almost independent of the uncertainty of the crustal heat production in the sense that two geotherms corresponding to the same lithosphere thickness and potential temperature but different crustal heat production converge at depth. Besides, the solution may be additionally adjusted so that the calculated surface heat flow matches observations without affecting the properties of the deeper geotherm segment. The model predicts quantitative relations between the chemical boundary layer thickness, the potential temperature of convecting mantle, and the lithospheric geotherm. The predictions correlate with the lithospheric geotherms documented using the kimberlite xenolith/xenocryst thermobarometry.
Synchroneity of cratonic burial phases and gaps in the kimberlite record: Episodic magmatism or preservational bias?
2015, Earth and Planetary Science Letters
A variety of models are used to explain an apparent episodicity in kimberlite emplacement. Implicit in these models is the assumption that the preserved kimberlite record is largely complete. However, some cratons now mostly devoid of Phanerozoic cover underwent substantial Phanerozoic burial and erosion episodes that should be considered when evaluating models for global kimberlite distributions. Here we show a broad temporal coincidence between regional burial phases inferred from thermochronology and gaps in the kimberlite record in the Slave craton, Superior craton, and cratonic western Australia. A similar pattern exists in the Kaapvaal craton, although its magmatic, deposition, and erosion history differs in key ways from the other localities. One explanation for these observations is that there is a common cause of cratonic subsidence and suppression of kimberlite magmatism. Another possibility is that some apparent gaps in kimberlite magmatism are preservational artifacts. Even if kimberlites occurred during cratonic burial phases, the largest uppermost portions of the pipes would have been subsequently eroded along with the sedimentary rocks into which they were emplaced. In this model, kimberlite magmatism was more continuous than the preserved record suggests, implying that evidence for episodicity in kimberlite genesis should be carefully evaluated in light of potential preservational bias effects. Either way, the correlation between burial and kimberlite gaps suggests that cratonic surface histories are important for understanding global kimberlite patterns.
The Cameroon Line: Analysis of an intraplate magmatic province transecting both oceanic and continental lithospheres: Constraints, controversies and models
2014, Earth-Science Reviews
Citation Excerpt :
A regional pattern of topographic and bathymetric swells and irregularly shaped basins has long been a recognized peculiarity of the African plate (Holmes, 1944; Nyblade and Robinson, 1994; Burke, 1996; Doucouré and de Wit, 2003; Fig. 1a). Many researchers have interpreted this to reflect shallow-upper mantle convection (e.g., Burke and Wilson, 1972; McKenzie and Weiss, 1975; England and Houseman, 1984). However, the resolution of the present tomographic images of upper mantle and lithosphere variations across Africa is not yet of a quality to confidently model the effects of the mantle in dynamically supporting topography (e.g., Fishwick and Bastow, 2011; Raveloson et al., in press).
The near 1700 km long Cameroon Line (CL) is an African intraplate ‘fan-shaped’ alkaline volcano-plutonic rift zone of variable width (< 200 km), with a ca. 66 Ma history of magmatic activity without any systematic internal pattern of age variation. Although the CL features prominently in discussions about active rift tectonics and magmatism during the growth of the African Plate and the opening of the Central Atlantic Ocean, there is a significant diversity of opinions about its local geometry, origin and evolution. Here, we review various geodynamic models for the CL based on large data-sets of field geology, petrology, geochemistry and geochronology. Results indicate that the Line traverses both oceanic and continental domains, extending NE–SW for about 700 km on oceanic lithosphere of the Gulf of Guinea (ca. 80–120 Ma), cutting obliquely across oceanic transform faults and across the ocean–continent boundary (OCB), and then continuous for ~ 1000 km (to Kapsiki), with a significant bifurcation at about 320 km, to the Adamawa and the Biu Plateaus along complex Neoproterozoic continental lithosphere of Central and West Africa (500–800 Ma, with embedded fragments of Paleoproterozoic–Archean crust). The continental lithosphere is transected by a dense network of major late Neoproterozoic shear zones (500–650 Ma) that were linked to conterminous extensions in South America before the opening of the Atlantic Ocean. The shear zones define a “Cameroon Block” to which the continental sector of the Cameroon Line is confined, but neither this continental tectonic anisotropy, nor its oceanic transform faults, appear to have influenced the geometry of the CL. Geochemical data confirm that the mostly alkaline CL magmas originate from deep mantle upwelling with variable input from at least four different mantle end-members (DMM, HIMU, FOZO and EM-I), and with different degrees of partial melts derived from above the 410-discontinuity. These melts then interacted diversely with lithospheric mantle, but without extensive crustal contamination. The oldest igneous activity is documented on the continent at the far end of the CL by the Late Cretaceous–Early Paleocene (on the Kapsiki Plateau at Golda Zuelda), and by the Miocene, contemporaneous volcanic activity spread along the oceanic and continental sectors. The intraplate magmatism along the CL is coincident with continent-wide extensional tectonics across central and northern Africa during the Cretaceous and throughout the Cenozoic, a time during which the African Plate experienced rotation of ~ 7° and slow but variable rates of convergence with Europe, involving several episodic changes in the pole of rotation between the African and South American plates that affected the opening of the South-Central Atlantic. The CL reflects a unique long-lived geodynamic setting and there appears to be no simple explanation for its origin.

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On the geodynamic setting of kimberlite genesis

Abstract

Sci. Lett.

Tectonophysics

Earth Planet. Sci. Lett.

Earth Sci. Rev.

Phys. Chem. Earth

Peridotite xenoliths and the dynamics of kimberlite intrusion

Kimberlites: strange bodies

EOS Trans. Am. Geophys. Union

Order-disorder kinetics of ferromagnesian silicates, and the cooling history of rocks

EOS Trans. Am. Geophys. Union

Kimberlites and Their Xenoliths

The kimberlites of the continental United States: a review

J. Geol.

The kimberlites of the U.S.S.R.

Origin of kimberlite pipes by diapiric upwelling in the upper mantle

Nature

Chemical plumes in the mantle

Geol. Soc. Am. Bull.

Kimberlites and plate tectonics in Africa

Nature

An alternative hypothesis for the origin of west African kimberlites

Nature

Plate movement and continental magmatism

Nature

KAr and RbSr ages of some alkalic intrusives from central and eastern United States

Am. J. Sci.

Structural setting of kimberlites in southeastern Australia

Drift of major continental blocks since the Devonian

Nature

Paleopoles and paleolatitudes of North America, and speculations about displaced terrains

Can. J. Earth Sci.