Orthopyroxene survival in deep carbonatite melts: implications for kimberlites

Stone, Rebecca S; Luth, Robert W.

doi:10.1007/s00410-016-1276-2

Cited by 64 publications

(29 citation statements)

References 43 publications

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“…We can therefore confirm that the relationships quantified in this study parallel those attending the ascent of kimberlite magma (Merle, 2015). However, it should be noted that the natural estimates are based upon minimum values; at shallower crustal depths where CO 2 is liberated as a supercritical fluid and later a gaseous phase, the kimberlite density will decrease, and ascent velocity will increase (e.g., Russell et al, 2012;Stone and Luth, 2016), further supporting attrition.…”

Section: Scaling Experiments To Kimberlite Ascentsupporting

confidence: 76%

“…We suggest that at these early ascent stages mechanical cargo modifications are trivial and chemical processes dominate. Carbonate-rich kimberlite parental melts can be induced to exsolve a CO 2 dominated fluid phase in the mantle (∼3.5 and 2.5 GPa) by assimilation of mantle silicate minerals, especially orthopyroxene (Russell et al, 2012Stone and Luth, 2016). Importantly, the production of a CO 2 fluid continually increases the melt's rise velocity (Russell et al, 2012).…”

Section: Discussionmentioning

confidence: 99%

“…Resulting deposits have olivine (and other indicator minerals) that are less rounded than those observed in deposit 2. and ). Thirdly, surface-derived chips are highly amenable to rapid dissolution into the melt which facilitates an assimilation-induced transition in melt composition from more carbonatitic to kimberlitic and enhances the opportunity for early exsolution of a fluid phase (Russell et al, 2012Stone and Luth, 2016). Lastly, textural observations on the solid cargo (i.e., crystals, xenoliths, xenocrysts) can inform on their transport and eruption history (Campbell et al, 2013;Jones et al, 2014;Brett et al, 2015) including estimates on ascent velocities (>4 m s −1 ; Sparks et al, 2006), style of flow (turbulent or transitional), transit times (10's of h), and average concentrations of solid particles.…”

Section: Discussionmentioning

confidence: 99%

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Modification of Mantle Cargo by Turbulent Ascent of Kimberlite

2019

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Kimberlite magmas transport cratonic mantle xenoliths and diamonds to the Earth's surface. However, the mechanisms supporting the successful and efficient ascent of these cargo-laden magmas remains enigmatic due to the absence of historic eruptions, uncertainties in melt composition, and questions concerning their rheology. Mantle-derived xenocrystic olivine is the most abundant component in kimberlite and is uniquely rounded and ellipsoidal in shape. Here, we present data from a series of attrition experiments designed to inform on the transport of low-viscosity melts through the mantle lithosphere. The experimental data suggest that the textural properties of the mantle-derived olivine are records of the flow regime, particle concentration, and transport duration of ascent for kimberlitic magmas. Specifically, our results provide evidence for the rapid and turbulent ascent of kimberlite during their transit through the lithosphere; this transport regime creates mechanical particle-particle interactions that, in combination with chemical processes, continually modify the mantle cargo and facilitate mineral assimilation.

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Section: Scaling Experiments To Kimberlite Ascentsupporting

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Modification of Mantle Cargo by Turbulent Ascent of Kimberlite

2019

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“…Reaction with/dissolution of orthopyroxene and olivine may play a role as well. However, experimental studies have shown that the dissolution of orthopyroxene in ascending carbonate-rich melts is not effective until pressures of <3.5 GPa [76] and that decarbonation does not occur until depths of <100 km [77]. Yet, the dissolution of orthopyroxene is also a function of the primary melt composition, and other experimental studies suggested that in a Na 2 CO 3 melt this process would occur sooner and could result in the formation of a homogeneous silicate-carbonate melt at 5.0 GPa and 1200 • C [78].…”

Section: Composition Of the Original Meltmentioning

confidence: 99%

Polymineralic Inclusions in Megacrysts as Proxies for Kimberlite Melt Evolution—A Review

Bussweiler

2019

Minerals

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Polymineralic inclusions in megacrysts have been reported to occur in kimberlites worldwide. The inclusions are likely the products of early kimberlite melt(s) which invaded the pre-existing megacryst minerals at mantle depths (i.e., at pressures ranging from 4 to 6 GPa) and crystallized or quenched upon emplacement of the host kimberlite. The abundance of carbonate minerals (e.g., calcite, dolomite) and hydrous silicate minerals (e.g., phlogopite, serpentine, chlorite) within polymineralic inclusions suggests that the trapped melt was more volatile-rich than the host kimberlite now emplaced in the crust. However, the exact composition of this presumed early kimberlite melt, including the inventory of trace elements and volatiles, remains to be more narrowly constrained. For instance, one major question concerns the role of accessory alkali-halogen-phases in polymineralic inclusions, i.e., whether such phases constitute a common primary feature of kimberlite melt(s), or whether they become enriched in late-stage differentiation processes. Recent studies have shown that polymineralic inclusions react with their host minerals during ascent of the kimberlite, while being largely shielded from processes that affect the host kimberlite, e.g., the assimilation of xenoliths (mantle and crustal), degassing of volatiles, and secondary alteration. Importantly, some polymineralic inclusions within different megacryst minerals were shown to preserve fresh glass. A major conclusion of this review is that the abundance and mineralogy of polymineralic inclusions are directly influenced by the physical and chemical properties of their host minerals. When taking the different interactions with their host minerals into account, polymineralic inclusions in megacrysts can serve as useful proxies for the multi-stage origin and evolution of kimberlite melt/magma, because they can (i) reveal information about primary characteristics of the kimberlite melt, and (ii) trace the evolution of kimberlite magma on its way from the upper mantle to the crust.Here, the focus is on fully-crystallized melt inclusions, so-called "polymineralic inclusions", contained within megacrysts from kimberlites. The term "megacryst" applies to mantle minerals that are >1 cm in size. Common megacryst phases are clinopyroxene, garnet, olivine, ilmenite, phlogopite, and zircon [26][27][28]. Based on their composition, megacrysts can be divided into a Cr-poor and a Cr-rich suite [29][30][31]. The origin of megacrysts themselves has long been debated. Some studies have advocated for a genetic link between a kimberlitic or "proto-kimberlitic" melt [29,[32][33][34][35][36][37][38], whereas others considered the megacryst parental melt to be unrelated to kimberlites [26,39,40]. In the scenario that megacrysts are linked to crystallization from proto-kimberlitic melts in the lithospheric mantle, the spectrum of Cr-poor to Cr-rich megacrysts has been proposed to be a function of variable interaction with the surrounding mantle [30,41,42].The formation of polymineralic ...

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“…CO 2 degassing can be triggered by dissolution of silicate-rich material in carbonate-rich magma. Reaction between mantle orthopyroxene and kimberlite melt can start as deep as at 2.5 -3.5 GPa (Stone et al, 2016). Reaction of kimberlite magma with silicic crustal xenoliths through the tens of kilometers of crust would depend on the volume of crustal xenoliths entrained and assimilated by different portions of the rising kimberlite.…”

Section: The Role Of Fluidmentioning

confidence: 99%