Polymineralic inclusions in kimberlite-hosted megacrysts: Implications for kimberlite melt evolution

Abersteiner, Adam; Kamenetsky, Vadim S.; Goemann, Karsten; Golovin, Alexander V.; Sharygin, Igor S.; Pearson, D. Graham; Kamenetsky, Maya B.; Gornova, M. A.

doi:10.1016/j.lithos.2019.04.004

Cited by 29 publications

(25 citation statements)

References 84 publications

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“…The formation of polymineralic inclusions in megacrysts has been attributed to a variety of metasomatic agents in the upper mantle, including the megacryst magma, which also crystallized the host megacrysts [43], primary or early kimberlite melt [44][45][46], mantle carbonatite with a subduction origin [47,48], or even diamond-forming fluids [49,50]. Here, the findings of previous studies on polymineralic inclusions in megacrysts from kimberlites are discussed.…”

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confidence: 89%

“…Polymineralic inclusions are typically located where fractures or veinlets in the host megacryst converge, and are usually surrounded by regions and trails of smaller melt inclusions and fluid inclusions (Figure 2). In a recent study by Abersteiner et al [46], the smaller melt inclusions were described as "micro-melt inclusions" (MMIs), and this term is adopted here. Polymineralic inclusions within clinopyroxene megacrysts are typically surrounded by "spongy rims" (i.e., regions where the clinopyroxene is altered and contains abundant fluid/melt inclusions), whereas polymineralic inclusions within garnets are typically lined by kelyphite ( Figure 2).…”

Section: Polymineralic Inclusions In Megacrysts-early Studies To Currmentioning

confidence: 99%

“…Based on reconstructed bulk compositions, the authors concluded that the primary kimberlite melt is carbonated silicate melt rather than carbonatite. Abersteiner et al [46] focused on the much smaller (<5 µm) melt inclusions (i.e., MMIs) surrounding polymineralic inclusions hosted in megacrysts from Lac de Gras and Jericho kimberlites in the Slave craton (Canada), as well as from the Udachnaya kimberlite in the Siberian craton (Russia). They suggested that polymineralic inclusions, and thus early kimberlite melt, may have been enriched in alkali-halogen-phases.…”

Section: Typical Mineralogy Of Polymineralic Inclusionsmentioning

confidence: 99%

“…Olivine also occurs within inclusions in all host minerals. It is often euhedral and sometimes described to have a "spinifex" texture (i.e., acicular or elongated crystals), which is indicative of fast cooling/quenching [46][47][48]. Olivine is typically partially serpentinized.…”

Section: Typical Mineralogy Of Polymineralic Inclusionsmentioning

confidence: 99%

“…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 inclusions in megacrysts has been attributed to a variety of metasomatic agents in the upper mantle, including the megacryst magma, which also crystallized the host megacrysts [43], primary or early kimberlite melt [44][45][46], mantle carbonatite with a subduction origin [47,48], or even diamond-forming fluids [49,50]. Here, the findings of previous studies on polymineralic inclusions in megacrysts from kimberlites are discussed.…”

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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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confidence: 89%

Section: Polymineralic Inclusions In Megacrysts-early Studies To Currmentioning

confidence: 99%

Section: Typical Mineralogy Of Polymineralic Inclusionsmentioning

confidence: 99%

Section: Typical Mineralogy Of Polymineralic Inclusionsmentioning

confidence: 99%

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

Bussweiler

2019

Minerals

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Can primitive kimberlite melts be alkali‐carbonate liquids: Composition of the melt snapshots preserved in deepest mantle xenoliths

Golovin

Sharygin

Korsakov

et al. 2019

J Raman Spectroscopy

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The study of kimberlite rocks is important as they provide critical information regarding the composition and dynamics of the continental mantle and are the principal source of diamonds. Despite many decades of research, the original compositions of kimberlite melts, which are thought to be derived from depths > 150 km, remain highly debatable due to processes that can significantly modify their composition during ascent and emplacement. Snapshots of the kimberlite‐related melts were entrapped as secondary melt inclusions hosted in olivine from sheared peridotite xenoliths from the Udachnaya‐East pipe (Siberian craton). These xenoliths originated from 180‐ to 220‐km depth and are among the deepest derived samples of mantle rocks exposed at the surface. The crystallised melt inclusions contain diverse daughter mineral assemblages (>30 mineral species), which are dominated by alkali‐rich carbonates, sulfates, and chlorides. The presence of aragonite as a daughter mineral suggests a high‐pressure origin for these inclusions. Raman‐mapping studies of unexposed inclusions show that they are dominated by carbonates (>65 vol.%), whereas silicates are subordinate (<13 vol.%). This indicates that the parental melt for the inclusions was carbonatitic. The key chemical features of this melt are very high contents of alkalis, carbon dioxide, chlorine, and sulfur and extremely low silica and water. Alkali‐carbonate melts entrapped in xenolith minerals likely represent snapshots of the primitive kimberlite melt. This composition is in contrast with the generally accepted notion that kimberlites originated as ultramafic silicate water‐rich melts. Experimental studies revealed that alkali‐carbonate melts are a very suitable diamond‐forming media. Therefore, our findings support the idea that some diamonds and kimberlite magmatism may be genetically related.

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Confocal Raman spectroscopic study of melt inclusions in olivine of mantle xenoliths from the Bultfontein kimberlite pipe (Kimberley cluster, South Africa): Evidence for alkali‐rich carbonate melt in the mantle beneath Kaapvaal Craton

Sharygin

Golovin

Tarasov

et al. 2021

J Raman Spectroscopy

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Identifying the composition of primary/primitive mantle melts is crucial for understanding the mantle's evolution and mantle‐derived magmatism. Melt inclusions in mantle xenoliths provide key information about such melts. This study used confocal Raman spectroscopy to characterize mineral assemblage of unexposed crystallized secondary melt inclusions in the olivine from the xenoliths of the sheared garnet peridotites from the Bultfontein kimberlite pipe (Kimberley cluster, Kaapvaal Craton, South Africa). The studied peridotites originated from 112‐ to 146‐km mantle depths. In total, 16 minerals were identified among daughter crysatls, which include carbonates (calcite, magnesite, dolomite), alkali carbonates (eitelite, nyerereite, gregoryite/natrite, K–Na–Ca–carbonate (K,Na)2Ca(CO3)2 (K analogue of nyerereite), alkali carbonates with additional anions (northupite, bradleyite, burkeite), alkali sulfates (glauberite, thenardite, aphthitalite), apatite, tetraferriphlogopite, and magnetite. Several more daughter minerals gave distinct Raman spectra, but they were not determined due to the lack of similar spectra in the databases. Carbonates are predominant among the daughter minerals in the melt inclusions. Many daughter minerals are rich in alkalis. These facts indicate that melt(s), parental for the inclusions, is alkali‐rich carbonate in composition. Two possible models were suggested for the origin of these melt inclusions: (1) in situ fracturing of olivine and the mantle melt infiltration shortly before the sheared peridotites were entrained by the ascending kimberlitic magma; (2) infiltration of the transporting kimberlite melt into xenoliths during ascent. Both models imply that the alkali‐rich carbonate melt(s) that interacted with peridotites originated at a greater depth than the entrapment level of studied xenoliths (>150 km), that is, at the base of the lithosphere or in the asthenosphere. This melt is genetically related to the kimberlite magmatism that formed the Bultfontein pipe and points at the alkali‐rich carbonate composition of primary kimberlite melt.

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Polymineralic inclusions in kimberlite-hosted megacrysts: Implications for kimberlite melt evolution

Cited by 29 publications

References 84 publications

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

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

Can primitive kimberlite melts be alkali‐carbonate liquids: Composition of the melt snapshots preserved in deepest mantle xenoliths

Confocal Raman spectroscopic study of melt inclusions in olivine of mantle xenoliths from the Bultfontein kimberlite pipe (Kimberley cluster, South Africa): Evidence for alkali‐rich carbonate melt in the mantle beneath Kaapvaal Craton

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