Geology of the Gahcho Kué kimberlite pipes, NWT, Canada: root to diatreme magmatic transition zones

Hetman, C.; Smith, B. Holly; Paul, Joanne L.; Winter, F H

doi:10.1016/j.lithos.2004.03.051

Cited by 80 publications

(30 citation statements)

References 6 publications

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“…Root zones are incompletely studied, and unfortunately are poorly understood. Most root zones are characterized from drill core as irregular bodies of hypabyssal intrusive rock having various forms of gradational transitions through breccia with volcanic components, to brecciated country rock and finally to undisturbed country rock (e.g., Hetman et al, 2004). One reason for the limited detail available is that although dikes with associated breccias inferred to represent incipient root zones are not uncommon, we know of no natural exposures clearly revealing the upper transition from root zone to unbedded or bedded diatreme fill.…”

Section: Root Zone: Dike-lower Diatreme Transitionmentioning

confidence: 99%

Maar-diatreme volcanoes: A review

White

Ross

2011

Journal of Volcanology and Geothermal Research

345

251

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Maar-diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock. A maar is the crater cut into the ground and surrounded by an ejecta ring, while the diatreme structure continues downward and encloses diatreme and root zone deposits. Here we attempt an evenhanded review of maardiatreme volcanology that extends from mafic to kimberlitic varieties, and from historical maar eruptions to deeply eroded or mined diatreme structures. We conclude that maar-diatreme eruptions are episodic. Ejecta rings provide invaluable insight into eruption processes and sequence, but are incomplete records of diatreme formation. Deposits within the diatreme structure include, in varying proportions, lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially, and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere. A basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock; root zones are irregular in form, and the clastic deposits are typically intruded by contorted dikes. Irregular root zone-like chaotic breccias cut by contorted dikes are also present within diatreme deposits, where they represent intra-diatreme fragmentation zones and record changes in the location of the explosion locus during eruption.

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Section: Root Zone: Dike-lower Diatreme Transitionmentioning

confidence: 99%

Maar-diatreme volcanoes: A review

White

Ross

2011

Journal of Volcanology and Geothermal Research

345

251

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“…One clast type characteristic of kimberlite deposits are round or sub-round ash-to lapilli-sized "pelletal" clasts (e.g., Mitchell, 1997;Hetman et al, 2004). These non-vesicular or poorly vesicular juvenile fragments are often cored by large crystal grains.…”

Section: Intra-vent and Vent-proximal Transport Of Hot Sticky Particlesmentioning

confidence: 99%

The importance of the transport system in shaping the growth and form of kimberlite volcanoes

McClintock¹,

Ross

White

2009

Lithos

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Understanding the range of transport styles recorded by kimberlite deposits is key to describing the type and style of eruptions. Building a clear picture of the processes that shape deposits is essential for selecting exploration targets and evaluating the grade and value of diamond-bearing kimberlites. Variations in grade reflect differences in the diamond content of different magma parcels erupted during the lifetime of the kimberlite volcano, sorting during transport of eruption products, or re-working of diamonds during crater growth, cone collapse and erosion.The form of the kimberlite volcano is largely determined when the magma arrives near the surface. If magma comes into contact with external water, transport will be driven by a combination of magmatic gases + steam. From a diamond exploration perspective, the resulting deep diatremes make the most attractive targets because they survive erosion and form large geophysical anomalies. If water is too abundant, a tuff cone or tuff ring with no diatreme or a shallow one will form. On the other hand, if external water is very limited or if the conduit is rapidly sealed by chilled melt, the transport system will be driven by magmatic gases alone. The result will then be a spatter cone or cinder cone underlain by a dike, possibly with a related lava flow, but with no diatreme.

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“…The transition zone is several to tens of metres wide, over which there is an almost continuous gradation of textural characteristics, both macroscopic and microscopic, from coherent kimberlite to MVK. Hetman et al (2004) interpreted the transition zone as representing a 'frozen' degassing and fragmentation front within the intruding magma, an idea also discussed by Field and Scott Smith (1999) and Skinner and Marsh (2004). It is, however, considered very unlikely that such a fragmentation front could be preserved in a deposit because fragmentation is a highly dynamic process .…”

Section: Coherent and Transitional Kimberlitementioning

confidence: 94%

“…Hawthorne 1975;Mitchell 1986;Scott Smith 1996), where it commonly underlies MVK (Clement 1982;Clement and Skinner 1985;Field and Scott Smith 1998). Hetman et al (2004) studied the fragmental and coherent facies of the Gaucho Kué kimberlites, Canada, and recognised a textural gradation between the two types termed the transition zone. Skinner and Marsh (2004) described transition facies kimberlite (TFK) from the Kamfersdam, Premier and Venetia pipes in Southern Africa.…”

Section: Coherent and Transitional Kimberlitementioning

confidence: 99%

The influence of complex intra- and extra-vent processes on facies characteristics of the Koala Kimberlite, NWT, Canada: volcanology, sedimentology and intrusive processes

Porritt

Fernand

2011

Bull Volcanol

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The Koala kimberlite, Northwest Territories, Canada, is a small pipe-like body that was emplaced into the Archean Koala granodiorite batholith and the overlying Cretaceous to Tertiary sediments at~53 Ma. Koala is predominantly in-filled by a series of six distinct clastic deposits, the lowermost of which has been intruded by a late stage coherent kimberlite body. The clastic facies are easily distinguished from each other by variations in texture, and in the abundance and distribution of the dominant components. From facies analysis, we infer that the pipe was initially partially filled by a massive, poorly sorted, matrix-supported, olivine-rich lapilli tuff formed from a collapsing eruption column during the waning stage of the pipe-forming eruption. This unit is overlain by a granodiorite cobble-boulder breccia and a massive, poorly sorted, mud-rich pebbly-sandstone. These deposits represent post-eruptive gravitational collapse of the unstable pipe walls and mass wasting of tephra forming the crater rim. The crater then filled with water within which~20 m of non-kimberlitic, wood-rich, silty sand accumulated, representing up to 47,000 years of quiescence. The upper two units in the Koala pipe are both olivine rich and show distinct grain-size grading. These units are interpreted to have been deposited sub-aqueously, from pyroclastic flows sourced from one or more other kimberlite volcanoes. The uppermost units in the Koala pipe highlight the likelihood that some kimberlite pipes may be only partially filled by their own eruptive products at the cessation of volcanic activity, enabling them to act as depocentres for pyroclastic and sedimentary deposits from the surrounding volcanic landscape. Recognition of these exotic kimberlite deposits has implications for kimberlite eruption and emplacement processes.

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Geology of the Gahcho Kué kimberlite pipes, NWT, Canada: root to diatreme magmatic transition zones

Cited by 80 publications

References 6 publications

Maar-diatreme volcanoes: A review

Maar-diatreme volcanoes: A review

The importance of the transport system in shaping the growth and form of kimberlite volcanoes

The influence of complex intra- and extra-vent processes on facies characteristics of the Koala Kimberlite, NWT, Canada: volcanology, sedimentology and intrusive processes

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