Ancient mantle metasomatism recorded in subcalcic garnet xenocrysts: Temporal links between mantle metasomatism, diamond growth and crustal tectonomagmatism

Shu, Qin; Brey, Gerhard P.

doi:10.1016/j.epsl.2015.02.038

Cited by 75 publications

(47 citation statements)

References 60 publications

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“…Published reports of pyrope garnets formed by isochemical exsolution are abundant in the literature. A small number of pyrope garnets with ultradepleted major-and/or trace-element compositions have been found in mantle peridotites from the Tanzanian and Kaapvaal cratons (Gibson et al, 2013;Lazarov et al, 2009Lazarov et al, , 2012Shu and Brey, 2015), and also in xenocryst suites from the Siberian, North Atlantic and Superior cratons (Grütter and Tuer, 2009;Ziberna et al, 2013). They are distinguished by their very low CaO contents (<2 wt.%; Grütter et al, 2004).…”

Section: Fig 2 Cao Vsmentioning

confidence: 99%

On the nature and origin of garnet in highly-refractory Archean lithospheric mantle: constraints from garnet exsolved in Kaapvaal craton orthopyroxenes

Gibson

2017

Mineral. mag.

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The widespread occurrence of pyrope garnet in Archean lithospheric mantle remains one of the 'holy grails' of mantle petrology. Most garnets found in peridotitic mantle equilibrated with incompatible-trace-element enriched melts or fluids and are the products of metasomatism. Less common are macroscopic intergrowths of pyrope garnet formed by exsolution from orthopyroxene. Spectacular examples of these are preserved in both mantle xenoliths and large, isolated crystals (megacrysts) from the Kaapvaal craton of southern Africa, and provide direct evidence that some garnet inthe sub-continental lithospheric mantle formed initially by isochemical rather than metasomatic processes. The orthopyroxene hosts are enstatites and fully equilibrated with their exsolved phases (low-Cr pyrope garnet ± Cr-diopside). Significantly, P-T estimates of the postexsolution orthopyroxenes plot along an unperturbed conductive Kaapvaal craton geotherm and reveal that they were entrained from a large continuous depth interval (85 to 175 km). They therefore represent snapshots of processes operating throughout almost the entire thickness of the sub-cratonic lithosphericmantle.New rare-earth element (REE) analyses show that the exsolved garnets occupy the full spectrum recorded by garnets in mantle peridotites and also diamond inclusions. A key finding is that a few low-temperature exsolved garnets, derived from depths of ∼90 km, are more depleted in light rare-earth elements (LREEs) than previously observed in any other mantle sample. Importantly, the REE patterns of these strongly LREE-depleted garnets resemble the hypothetical composition proposed for pre-metasomatic garnets that are thought to pre-date major enrichment events in the sub-continental lithospheric mantle, including those associated with diamond formation. The recalculated compositions of pre-exsolution orthopyroxenes have higher Al2O3 and CaO contents than their post-exsolution counterparts and most probably formed as shallow residues of large amounts of adiabatic decompression melting in the spinel-stability field. It is inferred that exsolution of garnet from Kaapvaal orthopyroxenes may have been widespread, and perhaps accompanied cratonization at ∼2.9 to 2.75 Ga. Such a process would considerably increase the density and stability of the continental lithosphere.

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Section: Fig 2 Cao Vsmentioning

confidence: 99%

On the nature and origin of garnet in highly-refractory Archean lithospheric mantle: constraints from garnet exsolved in Kaapvaal craton orthopyroxenes

Gibson

2017

Mineral. mag.

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“…High-chromium pyropes of harzburgitic and lherzolitic parageneses with sinusoidal REE patterns have been well documented among all kimberlite provinces worldwide and are the main types of garnet inclusions in diamonds [12,13,28]. These pyropes are now generally accepted to have initially formed in a highly-depleted (>35-50%) mantle source (clinopyroxene-free harzburgites) under the influence of C-H-O melts/fluids with high LREE/HREE ratios [12,13,28], most likely due to carbonatite composition [34]. According to recent experimental results [35], the crystallization of high-chromium harzburgitic pyropes occurs under subsolidus conditions by the reaction of orthopyroxene and spinel in the presence of a fluid phase.…”

Section: Origin Of Pyropesmentioning

confidence: 99%

Diamond-Bearing Root Beneath the Northern East European Platform (Arkhangelsk Region, Russia): Evidence from Cr-Pyrope Trace-Element Geochemistry

2019

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In this study, we reconstruct the composition and metasomatic evolution of the lithospheric mantle beneath the poorly-studied southern Arkhangelsk region, based on the geochemistry of 145 Cr-pyrope grains recovered from samples of modern rivers and stream sediments, to evaluate the diamond exploration potential of these territories. Based on the concentrations of Cr2O3, CaO, TiO2, and rare earth elements (REEs), the garnets are divided into four groups: (1) low-chromium lherzolitic pyropes with fractionated heavy REE patterns; (2) low- to medium-chromium pyropes of lherzolitic and megacryst associations with flat heavy REE patterns; (3) high-chromium lherzolitic pyropes with “humped” REE patterns; and (4) high-chromium and low-chromium lherzolitic and harzburgitic pyropes with sinusoidal REE patterns. The pyrope geochemistry suggests a multi-stage model for the evolution of the lithospheric mantle, including partial melting to different degrees and further metasomatic overprints by silicate and carbonatite melts. The results confirm that the lithospheric mantle beneath the study area is suitable for the formation and preservation of diamonds. The significant percentage of diamond-associated pyropes (15%) emphasizes the likelihood of high diamond contents in kimberlites to be discovered within the study area.

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“…Mantle xenoliths rarely enclose carbonate phases [41][42][43][44][45][46][47][48], though crystalline carbonates [26,[49][50][51] and crystallized carbonated melts often occur as inclusions in xenolith minerals [52][53][54][55][56] and in macrocrysts/megacrysts/xenocrysts associated with kimberlites [57][58][59][60][61]. A wealth of implicit evidence indicates metasomatic effects of carbonated melts in mantle xenoliths [62][63][64][65]. The stability of carbonatitic and alkali-carbonatitic melts in the mantle is further supported by numerous high-pressure experimental studies [66][67][68][69][70][71][72].…”

Section: Introductionmentioning

confidence: 99%

Metasomatic Evolution of Coesite-Bearing Diamondiferous Eclogite from the Udachnaya Kimberlite

et al. 2020

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A coesite-bearing diamondiferous eclogite from the Udachnaya kimberlite (Daldyn field, Siberian craton) has been studied to trace its complex evolution recorded in rock-forming and minor mineral constituents. The eclogite sample is composed of rock-forming omphacite (60 vol%), garnet (35 vol%) and quartz/coesite (5 vol%) and contains intergranular euhedral zoned olivine crystals, up to 200 µm long, coexisting with phlogopite, orthopyroxene, clinopyroxene (secondary), K-feldspar, plagioclase, spinel, sodalite and djerfisherite. Garnet grains are zoned, with a relatively homogeneous core and a more magnesian overgrowth rim. The rim zones further differ from the core in having higher Zr/Y (6 times that in the cores), ascribed to interaction with, or precipitation from, a kimberlite-related melt. Judging by pressure-temperature estimates (~1200 °C; 6.2 GPa), the xenolith originated at depths of ~180–200 km at the base of the continental lithosphere. The spatial coexistence of olivine, orthopyroxene and coesite/quartz with K-Na-Cl minerals in the xenolith indicates that eclogite reacted with a deep-seated kimberlite melt. However, Fe-rich olivine, orthopyroxene and low-pressure minerals (sodalite and djerfisherite) likely result from metasomatic reaction at shallower depths during transport of the eclogite by the erupting kimberlite melt. Our results demonstrate that a mixed eclogitic-peridotitic paragenesis, reported previously from inclusions in diamond, can form by interaction of eclogite and a kimberlite-related melt.

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Ancient mantle metasomatism recorded in subcalcic garnet xenocrysts: Temporal links between mantle metasomatism, diamond growth and crustal tectonomagmatism

Cited by 75 publications

References 60 publications

On the nature and origin of garnet in highly-refractory Archean lithospheric mantle: constraints from garnet exsolved in Kaapvaal craton orthopyroxenes

On the nature and origin of garnet in highly-refractory Archean lithospheric mantle: constraints from garnet exsolved in Kaapvaal craton orthopyroxenes

Diamond-Bearing Root Beneath the Northern East European Platform (Arkhangelsk Region, Russia): Evidence from Cr-Pyrope Trace-Element Geochemistry

Metasomatic Evolution of Coesite-Bearing Diamondiferous Eclogite from the Udachnaya Kimberlite

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