Growth of bultfonteinite and hydrogarnet in metasomatized basalt xenoliths in the B/K9 kimberlite, Damtshaa, Botswana: insights into hydrothermal metamorphism in kimberlite pipes

Buse, Ben; Schumacher, John C.; Sparks, R. S. J.; Field, M. Paul

doi:10.1007/s00410-010-0492-4

Cited by 33 publications

(19 citation statements)

References 60 publications

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“…The fabrics at the margins of the kimberlite have been presented in Brown et al (2008a). Optical microscopy, scanning electron microscopy and electron microprobe analysis were used to analyse the mineral assemblages in the individual geological units, noting that some of the mineralogical data and petrological descriptions have been presented in Buse et al (2010).…”

Section: Methodsmentioning

confidence: 99%

“…Dynamically steam generated in phreatomagmatic explosions can play the same role as release of gases from magmatic explosions as a cause of fluidisation. However, for BK9 the evidence of welding (Brown et al 2008a) and high emplacement temperature derived from metamorphic mineral assemblages (Buse et al 2010) indicate a largely magmatic event.…”

Section: Kimberlite Emplacementmentioning

confidence: 97%

“…4 in Brown et al 2009). The DVK units described here contain a distinctive hydrothermal assemblage as a result of abundant basalt accidental lithic clasts, which have a low-silica content (Buse et al 2010). This results in hydrogarnet forming as part of the hydrothermal assemblage and the absence of void-filling diopside, which is common in MVK .…”

Section: Kimberlite Emplacementmentioning

confidence: 97%

“…The DVK (c) of the central pipe does not contain coalesced igneoustextured patches and, together with the thinner envelopes of former melt on the pelletal clasts, suggest that the eruption dynamics were different from the other two pipes. All the deposits contain hydrothermal alteration minerals, which indicate emplacement temperatures of >400°C (Buse et al 2010) and the presence of agglutinated particles within the north and south pipes suggests temperatures where at least locally in excess of 600°C (Brown et al 2008a). These temperatures are consistent with a hot deposit fluidised by eruption of magmatic volatiles.…”

Section: Kimberlite Emplacementmentioning

confidence: 97%

“…The central pipe eruption ceased with one or more large-scale collapse events in rapid succession, followed by the passive infilling of the crater. In each pipe, as the deposits cooled to below 400°C, external water infiltrated and circulated through the deposits, resulting in the serpentinisation of the olivine, the formation of hydrogarnet and the infilling of the void space (Buse et al 2010).…”

Section: Summary: the Development Of The Bk9 Kimberlitementioning

confidence: 99%

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Geology of the BK9 kimberlite (Damtshaa, Botswana): implications for the formation of dark volcaniclastic kimberlite

Buse

Sparks

Field³

et al. 2011

Bull Volcanol

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The BK9 kimberlite consists of three overlapping pipes. It contains two dark varieties of massive volcaniclastic kimberlite, informally termed dark volcaniclastic kimberlite (DVK). DVK(ns) is present in the north and south pipes and is interbedded with lenses of basalt breccia at the margins of the pipes. DVK(c) is present within the central pipe where it is overlain by a sequence of basalt breccias with interbedded volcanogenic sediments. The features observed within the DVK units of the BK9 kimberlite provide strong evidence for gas fluidisation of the accumulating pyroclastic material. These include the massive interior of the pipes, marginal epiclastic units, welldispersed country-rock xenoliths and small-scale heterogeneities in lithic clast abundance. The upper portions of the central pipe provide a record of the transition from pyroclastic eruption and infill to passive epiclastic infilling of the crater, after the eruption has ceased. The wall-rock of the BK9 kimberlite dips inwards and is interpreted as post pipe-fill subsidence of the adjacent country rock. The two DVK units contain interstitial, silt-sized pyroclasts. The DVK(ns) has a higher fraction of former melt and displays evidence of incipient welding, as a result of differences in eruption dynamics. These units demonstrate that whilst DVK is comparable in many respects to MVK and forms part of a spectrum of volcaniclastic rocks formed by fluidisation, it differs in frequently containing silt-sized particles and including agglutinated and welded varieties with a high melt fraction. The DVK varieties, studied here, also have a distinctive hydrothermal assemblage, resulting from the abundance of low-silica accidental lithic clasts. Both the hydrothermal alteration and the abundance of silt-sized particles contribute to the DVKs distinctive dark colour.

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Section: Methodsmentioning

confidence: 99%

Section: Kimberlite Emplacementmentioning

confidence: 97%

Section: Kimberlite Emplacementmentioning

confidence: 97%

Section: Kimberlite Emplacementmentioning

confidence: 97%

Section: Summary: the Development Of The Bk9 Kimberlitementioning

confidence: 99%

See 3 more Smart Citations

Geology of the BK9 kimberlite (Damtshaa, Botswana): implications for the formation of dark volcaniclastic kimberlite

Buse

Sparks

Field³

et al. 2011

Bull Volcanol

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Hydrothermal alteration of kimberlite by convective flows of external water

Afanasyev

Melnik

Porritt

et al. 2014

Contrib Mineral Petrol

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Kimberlite volcanism involves the emplacement of olivine-rich volcaniclastic deposits into volcanic vents or pipes. Kimberlite deposits are typically pervasively serpentinised as a result of the reaction of olivine and water within a temperature range of 130–400 °C or less. We present a model for the influx of ground water into hot kimberlite deposits coupled with progressive cooling and serpentisation. Large-pressure gradients cause influx and heating of water within the pipe with horizontal convergent flow in the host rock and along pipe margins, and upward flow within the pipe centre. Complete serpentisation is predicted for wide ranges of permeability of the host rocks and kimberlite deposits. For typical pipe dimensions, cooling times are centuries to a few millennia. Excess volume of serpentine results in filling of pore spaces, eventually inhibiting fluid flow. Fresh olivine is preserved in lithofacies with initial low porosity, and at the base of the pipe where deeper-level host rocks have low permeability, and the pipe is narrower leading to faster cooling. These predictions are consistent with fresh olivine and serpentine distribution in the Diavik A418 kimberlite pipe, (NWT, Canada) and with features of kimberlites of the Yakutian province in Russia affected by influx of ground water brines. Fast reactions and increases in the volume of solid products compared to the reactants result in self-sealing and low water–rock ratios (estimated at <0.2). Such low water–rock ratios result in only small changes in stable isotope compositions; for example, δO18 is predicted only to change slightly from mantle values. The model supports alteration of kimberlites predominantly by interactions with external non-magmatic fluids.

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Djerfisherite in kimberlites and their xenoliths: implications for kimberlite melt evolution

Abersteiner

Kamenetsky

Goemann

et al. 2019

Contrib Mineral Petrol

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Growth of bultfonteinite and hydrogarnet in metasomatized basalt xenoliths in the B/K9 kimberlite, Damtshaa, Botswana: insights into hydrothermal metamorphism in kimberlite pipes

Cited by 33 publications

References 60 publications

Geology of the BK9 kimberlite (Damtshaa, Botswana): implications for the formation of dark volcaniclastic kimberlite

Geology of the BK9 kimberlite (Damtshaa, Botswana): implications for the formation of dark volcaniclastic kimberlite

Hydrothermal alteration of kimberlite by convective flows of external water

Djerfisherite in kimberlites and their xenoliths: implications for kimberlite melt evolution

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