Bubble nucleation as a trigger for xenolith entrapment in mantle melts

Lensky, Nadav G.; Niebo, Ron W.; Holloway, John; Lyakhovsky, Vladimir; Navon, O.

doi:10.1016/j.epsl.2005.11.064

Cited by 57 publications

(38 citation statements)

References 34 publications

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“…Residual kimberlite melt that crystallized Mg-silicates, however, is capable of dissolving all observed CO 2 and providing the CO 2 supersaturation necessary to nucleate bubbles and degas. A supersaturation of 1-3 kbar is needed, for example, for nucleation of CO 2 bubbles in alkaline basaltic melts (Lensky et al, 2006), which are good proxies for kimberlites. Deep fragmentation as a result of volatile supersaturation and 70% vesiculation (e.g., Sparks et al, 2006), therefore, is not inevitable in the kimberlite magma if it has an opportunity to evolve.…”

Section: Discussionmentioning

confidence: 99%

Searching for parental kimberlite melt

Kopylova

Matveev

Raudsepp

2007

Geochimica et Cosmochimica Acta

144

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Section: Discussionmentioning

confidence: 99%

Searching for parental kimberlite melt

Kopylova

Matveev

Raudsepp

2007

Geochimica et Cosmochimica Acta

144

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“…High over-pressures in the fluid-wetted crack-tip rise to the point that the overlying mantle lithosphere is damaged and, then, fails creating another dyke propagation event (∼10-70 MPa; Wilson and Head, 2007). Repeated failure and dyke propagation allows for simultaneous and continual sampling of mantle xenoliths (e.g., Rubin, 1995;Lensky et al, 2006;Sparks, 2013). Rapid ascent of the gas-rich head facilitates the break-up of the mantle xenoliths over short (∼5 km) transport distances by decompression (Fig.…”

Section: Fluidization Processesmentioning

confidence: 98%

The ascent of kimberlite: Insights from olivine

Brett

Russell

Andrews

et al. 2015

Earth and Planetary Science Letters

106

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Available online xxxx Editor: J. Brodholt Keywords: kimberlite olivine ascent decompression cracks carbonatite turbulent flowOlivine xenocrysts are ubiquitous in kimberlite deposits worldwide and derive from the disaggregation of mantle-derived peridotitic xenoliths. Here, we provide descriptions of textural features in xenocrystic olivine from kimberlite deposits at the Diavik Diamond Mine, Canada and at Igwisi Hills volcano, Tanzania. We establish a relative sequence of textural events recorded by olivine during magma ascent through the cratonic mantle lithosphere, including: xenolith disaggregation, decompression fracturing expressed as mineral-and fluid-inclusion-rich sealed and healed cracks, grain size and shape modification by chemical dissolution and abrasion, late-stage crystallization of overgrowths on olivine xenocrysts, and lastly, mechanical milling and rounding of the olivine cargo prior to emplacement. Ascent through the lithosphere operates as a "kimberlite factory" wherein progressive upward dyke propagation of the initial carbonatitic melt fractures the overlying mantle to entrain and disaggregate mantle xenoliths. Preferential assimilation of orthopyroxene (Opx) xenocrysts by the silica-undersaturated carbonatitic melt leads to deep-seated exsolution of CO 2 -rich fluid generating buoyancy and supporting rapid ascent. Concomitant dissolution of olivine produces irregular-shaped relict grains preserved as cores to most kimberlitic olivine. Multiple generations of decompression cracks in olivine provide evidence for a progression in ambient fluid compositions (e.g., from carbonatitic to silicic) during ascent. Numerical modelling predicts tensile failure of xenoliths (disaggregation) and olivine (cracks) over ascent distances of 2-7 km and 15-25 km, respectively, at velocities of 0.1 to >4 m s −1 . Efficient assimilation of Opx during ascent results in a silica-enriched, olivine-saturated kimberlitic melt (i.e. SiO 2 >20 wt.%) that crystallizes overgrowths on partially digested and abraded olivine xenocrysts. Olivine saturation is constrained to occur at pressures <1 GPa; an absence of decompression cracks within olivine overgrowths suggests depths <25 km. Late stage (<25 km) resurfacing and reshaping of olivine by particle-particle milling is indicative of turbulent flow conditions within a fully fluidized, gas-charged, crystal-rich magma.

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“…However, if rapid ascent from the mantle and, in particular, crack propagation is driven by exsolution of volatiles (e.g. Spera 1984;Lensky et al 2006), it is still surprising that certain kimberlite magmas can stall or pond so close to the surface to form hypabyssal intrusions. Sometimes these even Fig.…”

Section: Introductionmentioning

confidence: 98%

The volatile content of hypabyssal kimberlite magmas: some constraints from experiments on natural rock compositions

et al. 2011

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Kimberlites are volatile rich magmas that ascend from deep in the mantle at high velocities, then as they reach a 'root zone' at 1-3 km in depth they either discharge explosively through to the surface or stall to form dykes and sills. Understanding this eruptive behaviour is difficult due to a lack of data on volatile solubility, particularly at conditions where the magmas enter the 'root zone' . In this study, we perform experiments on some putative primary kimberlite magma compositions to assess the amount of CO 2 and H 2 O retained if these compositions represent magma as it enters the root zone. At the conditions investigated (100-200 MPa and 1,275-1,100°C) the results suggest that none of these particular kimberlite compositions reproduce a magma that can retain the observed high volatile content when intruded at these pressures (∼4-8 km). In our experiments, the low volatile retention is due to a combination of factors including a high proportion of solid phases, none of which are volatilebearing, and inadequate volatile solubilities in the subordinate amounts of melt present. Modelled solubilities also suggest that the dissolved volatile contents remain too low even at super-liquidus temperatures (i.e. 100% melt). For water, the higher values observed in natural rocks can be explained by the addition of H 2 O associated with ubiquitous post-emplacement serpentinization. The high CO 2 contents in hypabyssal rocks are unlikely to be related to alteration. We suggest that most kimberlites originally had lower SiO 2 contents and as such may have been 'transitional' between silicate and carbonate melts. This results in both higher CO 2 solubilities and lower liquidus temperatures. For such compositions, it is possible that both CO 2 and water solubility may first decrease and then increase as magmas decompress and crystallize. Such unusual behaviour can help explain why kimberlite magmas can be very explosive or form shallow hypabyssal intrusions.

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Bubble nucleation as a trigger for xenolith entrapment in mantle melts

Cited by 57 publications

References 34 publications

Searching for parental kimberlite melt

Searching for parental kimberlite melt

The ascent of kimberlite: Insights from olivine

The volatile content of hypabyssal kimberlite magmas: some constraints from experiments on natural rock compositions

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