Petrological and geochemical characteristics of Mesoproterozoic dyke swarms in the Gardar Province, South Greenland: Evidence for a major sub-continental lithospheric mantle component in the generation of the magmas

AbstractThe Mesoproterozoic Gardar Province in South Greenland developed in a continental rift-related environment. Several alkaline intrusions and associated dyke swarms were emplaced in Archaean and Ketilidian basement rocks during two main magmatic periods at 1300–1250 Ma and 1180–1140 Ma. The present investigation focuses on mafic dykes from the early magmatic period ('Older Gardar') and the identification of their possible mantle sources.The rocks are typically fine- to coarse-grained dolerites, transitional between tholeiitic and alkaline compositions with a general predominance of Na over K. They crystallized from relatively evolved, mantle-derived melts and commonly show minor degrees of crustal contamination. Selective enrichment of the large ion lithophile elements Cs, Ba and K and the light rare-earth elements when compared to high field-strength elements indicate significant involvement of a sub-continental lithospheric mantle (SCLM) component in the generation of the magmas. This component was affected by fluid-dominated supra-subduction zone metasomatism, possibly related to the Ketilidian orogeny ∼500 Ma years prior to the onset of Gardar magmatism. Melt generation in the SCLM is further documented by the inferential presence of amphibole in the source region, negative calculated εNd(i) values (–0.47 to –4.40) and slightly elevated87Sr/86Sr(i) (0.702987 to 0.706472) ratios when compared to bulk silicate earth as well as relatively flat heavy rare-earth element (HREE) patterns ((Gd/Yb)N= 1.4 –1.9) indicating melt generation above the garnet stability field.The dyke rocks investigated show strong geochemical and geochronological similarities to penecontemporaneous mafic dyke swarms in North America and Central Scandinavia and a petrogenetic link is hypothesized. Considering recent plate reconstructions, it is further suggested that magmatism was formed behind a long-lived orogenic belt in response to back-arc basin formation in the time interval between 1290–1235 Ma.

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

Mineralogical Magazine ◽

10.1180/minmag.2016.080.158 ◽

2017 ◽

Vol 81 (4) ◽

pp. 781-809 ◽

Cited By ~ 11

Author(s):

Sally A. Gibson

Keyword(s):

Rare Earth ◽

Lithospheric Mantle ◽

Incompatible Trace Element ◽

Mantle Xenoliths ◽

Kaapvaal Craton ◽

Depth Interval ◽

Stability Field ◽

Full Spectrum ◽

Continental Lithospheric Mantle ◽

Peridotitic Mantle

AbstractThe 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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Mantle xenoliths from the Komsomolskaya-magnitnaya kimberlite pipe (Upper Muna kimberlite field, Siberian Craton) Evidences of the composition of the SCLM

10.5194/egusphere-egu2020-12666 ◽

2020 ◽

Author(s):

Igor Iakovlev ◽

Vladimir Malkovets ◽

Anastasiya Gibsher

Keyword(s):

Rare Earth ◽

Lithospheric Mantle ◽

Kimberlite Pipe ◽

Mantle Xenoliths ◽

Coarse Grained ◽

Peridotite Xenoliths ◽

Rare Earth Element Distribution ◽

Group 2 ◽

Kimberlite Field ◽

Group 1

Peridotite xenoliths from kimberlites provide important information about the composition, structure and thermal regime of the lithospheric mantle of ancient cratons. In this paper, we present the results of mineralogical studies of peridotite xenoliths from kimberlites of the Upper Muna field. The Middle Paleozoic (D3-C1) high diamondiferous kimberlite pipe Komsomolskaya-Magnitnaya was chosen as the object of research.We studied a collection of 180 peridotite xenoliths of the Komsomolskaya-Magnitnaya pipe, of which 104 belong to dunite-harzburgite paragenesis, 74 to lherzolite and 4 websterites.The chemical composition of basic minerals from xenoliths was determined using JEOL JXA-8100 electron microprobe. Chemical analysis of xenolith garnet compositions was also performed using the Agilent 7700cs LAM-ICPMS method.Based on a study of the collection of deep xenoliths, we found that the lithospheric mantle under the Upper Muna kimberlite field is composed mainly of garnet-bearing and chromite-bearing dunites and harzburgites, as well as coarse grained garnet lherzolites.The olivine Mg# varies from 88.4 to 94.12%, while the magnitude of the majority (60%) of the studied olivines does not exceed 92% and 30% of olivines have Mg#> 93%. We identified 2 groups according Mg # olivine from xenoliths. Group 1 with &#8220;typical&#8221; mantle values Mg # 88.39-90.70mol%, it is characteristic for fertile peridotites. And group 2 with highly depleted compositions Mg # 91.20-94.12mol%. A high proportion (~ 30%) of peridotites with high magnesian olivines (Mg #> 93 mol%) indicates the presence of a block of highly depleted rocks in the lithospheric mantle beneath the Upper Muna kimberilte field.According to the distribution of calcium and chromium in garnets, 10 out of 35 studied garnets from xenoliths belong to diamondiferous harzburgite-dunite paragenesis. According to the distribution of rare-earth elements, we distinguish two groups of garnets. Group 1 includes garnets with typical rare earth element distribution spectra typical for fertile garnets, and group 2 garnets with S-shaped spectra that are characteristic of garnet mineral inclusions in diamonds. We noted a high proportion of garnets with S-shaped REE distribution spectra (~ 66%), as well as garnets belonging to the harzburgite-dunite paragenesis, it indicate a moderate role of metasomatic changes associated with silicate melts, as well as interaction with carbonatite melts enriched in LREE.Using clinopyroxene monomineral thermobarometry, we found that the &#8220;diamond&#8221; window in the lithosphere mantle beneath the Upper Muna field, at the time of kimberlite magmatism (~ 360 Ma) was significant (about 95 km) and was located at a depth of 125 to 220 km.The study was supported by the Russian Science Foundation (grant No. 18-17-00249).

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Light oxygen isotopes in mantle-derived magmas reflect assimilation of sub-continental lithospheric mantle material

Nature Communications ◽

10.1038/s41467-021-26668-z ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jing-Yao Xu ◽

Andrea Giuliani ◽

Qiu-Li Li ◽

Kai Lu ◽

Joan Carles Melgarejo ◽

...

Keyword(s):

Oxygen Isotope ◽

Lithospheric Mantle ◽

Secondary Ion Mass Spectrometry ◽

Crustal Contamination ◽

Alternative View ◽

Crustal Material ◽

Mantle Material ◽

Oxygen Isotope Ratios ◽

Continental Lithospheric Mantle ◽

Lower Crustal

AbstractOxygen isotope ratios in mantle-derived magmas that differ from typical mantle values are generally attributed to crustal contamination, deeply subducted crustal material in the mantle source or primordial heterogeneities. Here we provide an alternative view for the origin of light oxygen-isotope signatures in mantle-derived magmas using kimberlites, carbonate-rich magmas that assimilate mantle debris during ascent. Olivine grains in kimberlites are commonly zoned between a mantle-derived core and a magmatic rim, thus constraining the compositions of both mantle wall-rocks and melt phase. Secondary ion mass spectrometry (SIMS) analyses of olivine in worldwide kimberlites show a remarkable correlation between mean oxygen-isotope compositions of cores and rims from mantle-like 18O/16O to lower ‘crustal’ values. This observation indicates that kimberlites entraining low-18O/16O olivine xenocrysts are modified by assimilation of low-18O/16O sub-continental lithospheric mantle material. Interaction with geochemically-enriched domains of the sub-continental lithospheric mantle can therefore be an important source of apparently ‘crustal’ signatures in mantle-derived magmas.

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Petrogenesis of Quaternary Shoshonitic Volcanism in NE Iran (Ardabil): Implication for Postcollisional Magmatism

Journal of Geological Research ◽

10.1155/2013/735498 ◽

2013 ◽

Vol 2013 ◽

pp. 1-11 ◽

Cited By ~ 1

Author(s):

Habib Shahbazi Shiran

Keyword(s):

Trace Elements ◽

Rare Earth ◽

Mantle Source ◽

Lithospheric Mantle ◽

Volcanic Rocks ◽

Enriched Mantle ◽

Low Degree ◽

Continental Lithospheric Mantle ◽

Ne Iran ◽

Postcollisional Magmatism

Trachyandesites, trachytes, andesites, and pyrocalstic rocks, with shoshonitic signature, are the main Quaternary volcanic rocks in the Sabalan region (Ardabil). Plagiocalse, K-feldspar, biotite associated with clinopyroxene, and glass are the main constituents of these lavas. Plagioclases are andesine to labradorite while clinopyroxenes have augitic composition. The Sabalan volcanic rocks show enrichment in LREEs (relative to HREEs) and are characterized by enrichment in LILEs and depletion in HFSEs. Petrological observations, along with rare earth and trace elements geochemistry, suggest shoshonitic signature for Sabalan lavas. This signature highlights derivation from a subduction-related source. The Sabalan volcanic rocks are isotopically characterized by derivation from an enriched mantle source with a tendency to plot in the fields defined by island-arc basalts (IAB) and OIBs (in εNd versus 87Sr/86Sr diagram). The geochemical and isotopic characteristics of the Sabalan lavas suggest that their magma has been issued via low degree partial melting of a subduction-metasomatized continental lithospheric mantle. The formation of these lavas is related to slab steepening and breakoff in a postcollisional regime.

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Depletion, metasomatism and refertilisation in the Sub-Continental Lithospheric Mantle beneath northern Victoria Land (Antarctica): a review

10.5194/egusphere-egu21-8450 ◽

2021 ◽

Author(s):

Massimo Coltorti ◽

Costanza Bonadiman ◽

Federico Casetta ◽

Barbara Faccini ◽

Pier Paolo Giacomoni ◽

...

Keyword(s):

Lithospheric Mantle ◽

Large Scale ◽

Ross Sea ◽

Mantle Xenoliths ◽

Rift System ◽

Stability Field ◽

Alkaline Magmatism ◽

Metasomatic Process ◽

Victoria Land ◽

Continental Lithospheric Mantle

Assessing the nature and evolution of the Sub-Continental Lithospheric Mantle (SCLM) is crucial to understand the dynamics of Earth&#8217;s interior and the global scale tectono-magmatic processes. The study of ultramafic xenoliths brought to the surface in specific context, such as northern Victoria Land (Antarctica), is a key to investigate how the SCLM bear witness of large-scale geodynamic episodes. Indeed, the Antarctica lithosphere was involved into three main tectono-magmatic episodes since Paleozoic, i.e. the 550-110 Ma Ross subduction, the Jurassic (~182 Ma) Ferrar magmatism and the Cenozoic alkaline magmatism responsible for the opening of the West Antarctic Rift System (WARS).In this study, a review of the petrological and geochemical features of >200 mantle-derived and cumulate xenoliths brought to the surface at Baker Rocks, Greene Point, Handler Ridge, Harrow Peaks, Browning Pass and Mount Overlord enabled us to reconstruct the main depletion and enrichment processes that took place in the Antarctica SCLM. Strong depletion is recorded by Greene Point lherzolites and harzburgites (18-21%), which likely began melting in the garnet facies and terminated in the spinel facies (Perinelli et al. 2006), whereas mild melt extraction in the spinel stability field was hypothesized at Baker Rocks and Handler Ridge (12-16% and 7-13% melting, respectively). The onset of the Jurassic Ferrar large magmatic event is testified by both the refertilisation in Greene Point-Baker Rocks peridotites and the appearance of cumulate orthopyroxenites/olivine-websterites at Harrow Peaks and Baker Rocks. Late enrichment process/es took place in concomitance with the Cenozoic alkaline magmatism of the WARS, resulting in both cryptic and modal metasomatism and overprinting earlier chemical modifications. This metasomatism was particularly effective at Baker Rocks, as shown by the increase of clinopyroxene abundance, its trace element enrichment and the formation of amphibole disseminated and in veins. Clinopyroxene composition in Cenozoic cumulate rocks matches the enrichment path observed in the peridotites, supporting the link between the last metasomatic process and the recent alkaline magmatism.Among mantle xenoliths populations, Greene Point record the highest T-P (870-1059 &#176;C; 0.8-1.6 GPa) and the least oxidized conditions (fO2 down to -2/-3 &#916;FMQ). Cumulate rocks yield the highest fO2 (up to +1.5 &#916;FMQ), at T varying between 900 and 1150&#176;C, approximating the conditions of crystallizing melts. No discrepancies in fO2 emerged between amphibole-bearing and amphibole-free peridotites, ruling out a strict correlation between amphibole stability, H2O activity and fO2. Nevertheless, the alkaline metasomatic event, which led to amphibole formation, caused a remarkable increase in the H2O content of the system. In fact, anhydrous peridotites preserve bulk H2O contents &#8804;128 ppm, while lherzolites with disseminated amphibole and hornblendites have H2O contents as up to 354-1120 ppm and 1.42 wt%, respectively.&#160;Perinelli, C., et al. 2006. Geochemical and O-isotope constraints on the evolution of lithospheric mantle in the Ross Sea rift area (Antarctica). Contributions to Mineralogy and Petrology, 151(3), 245-266.

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