Ar-Ar geochronology and petrogenesis of the Mushgai–Khudag alkaline‑carbonatite complex (southern Mongolia)

Nikolenko, Anna M.; Doroshkevich, A. G.; Ponomarchuk, A. V.; Redina, Anna A.; Prokopyev, Ilya; Vladykin, N. V.; Николаева, И. В.

doi:10.1016/j.lithos.2020.105675

Cited by 5 publications

(15 citation statements)

References 62 publications

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“…This event was associated with a transition from subductionrelated, through post-collisional to extensional magmatism (Wang et al, 2015). Numerous alkaline-carbonatite complexes were formed at this time (Nikiforov and Yarmolyuk, 2019), of which the most important are those in southern Mongolia, including the Mushghai Khudag, Bayan Khoshuu and Ulgii Khiid complexes, all of which are REE-enriched (Nikolenko et al, 2020(Nikolenko et al, , 2018Baatar et al, 2013). These complexes have commonly been described as rift-related, but several features, including enrichment in Ba, Sr, F, K and the LREE, are consistent with derivation from a mantle source that has been affected by subduction (Feng et al, 2020;Nikolenko et al, 2020).…”

Section: Mesozoicmentioning

confidence: 99%

Carbonatites and Alkaline Igneous Rocks in Post-Collisional Settings: Storehouses of Rare Earth Elements

et al. 2021

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The rare earth elements (REE) are critical raw materials for much of modern technology, particularly renewable energy infrastructure and electric vehicles that are vital for the energy transition. Many of the world’s largest REE deposits occur in alkaline rocks and carbonatites, which are found in intracontinental, rift-related settings, and also in syn- to post-collisional settings. Post-collisional settings host significant REE deposits, such as those of the Mianning-Dechang belt in China. This paper reviews REE mineralisation in syn- to post-collisional alkaline-carbonatite complexes worldwide, in order to demonstrate some of the key physical and chemical features of these deposits. We use three examples, in Scotland, Namibia, and Turkey, to illustrate the structure of these systems. We review published geochemical data and use these to build up a broad model for the REE mineral system in post-collisional alkaline-carbonatite complexes. It is evident that immiscibility of carbonate-rich magmas and fluids plays an important part in generating mineralisation in these settings, with REE, Ba and F partitioning into the carbonate-rich phase. The most significant REE mineralisation in post-collisional alkaline-carbonatite complexes occurs in shallow-level, carbothermal or carbonatite intrusions, but deeper carbonatite bodies and associated alteration zones may also have REE enrichment.

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Section: Mesozoicmentioning

confidence: 99%

Carbonatites and Alkaline Igneous Rocks in Post-Collisional Settings: Storehouses of Rare Earth Elements

et al. 2021

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“…A drill core and field investigation showed that carbonatitic and apatite-bearing ores are the two dominant types of REE ore [12]. Carbonatites are ubiquitously associated with fluorite mineralization and contain numerous fluorite veins [13]. The ages of K-Ar in the Mushgai Khudag complex vary widely between 179 and 121 Ma, which might reflect secondary processes [11].…”

Section: Geological Backgroundmentioning

confidence: 99%

“…The ages of K-Ar in the Mushgai Khudag complex vary widely between 179 and 121 Ma, which might reflect secondary processes [11]. The newly obtained Ar-Ar dating of the magnetite-apatite-enriched rocks and associated silicate rocks (e.g., melanephelinte and alkaline syenite) narrowed the measured age range to 145-133 Ma [13]. The Rb-Sr age of the syenite was shown by Baatar et al [6] to be 139.9 ± 5.9 Ma.…”

Section: Geological Backgroundmentioning

confidence: 99%

“…Andreeva et al [12] inferred that the complex is formed by fractional crystallization and silicate-salt liquid immiscibility based on the chemical compositions of fluid and melt inclusions hosted by silicate minerals (e.g., diopside, garnet, and K-feldspar) in alkaline igneous rocks. Nikolenko et al [13] presented new Sr-Nd-Pb isotopic compositions as well as geochemical data (LILE/HFSE values), which implies that the parental melts of Mushgai-Khudag were derived from a lithospheric mantle source affected by a mixture of subducted oceanic crust and its sedimentary components. The major and trace element compositions of alkaline silicate rocks suggest that these rocks were formed by fractional crystallization of the nephelinitic parental magma [13].…”

Section: Introductionmentioning

confidence: 99%

“…Nikolenko et al [13] presented new Sr-Nd-Pb isotopic compositions as well as geochemical data (LILE/HFSE values), which implies that the parental melts of Mushgai-Khudag were derived from a lithospheric mantle source affected by a mixture of subducted oceanic crust and its sedimentary components. The major and trace element compositions of alkaline silicate rocks suggest that these rocks were formed by fractional crystallization of the nephelinitic parental magma [13].…”

Section: Introductionmentioning

confidence: 99%

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Combined In Situ Chemical and Sr Isotopic Compositions and U–Pb Ages of the Mushgai Khudag Alkaline Complex: Implications of Immiscibility, Fractionation, and Alteration

et al. 2021

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The Mushgai Khudag complex consists of numerous silicate volcanic-plutonic rocks including melanephelinites, theralites, trachytes, shonkinites, and syenites and also hosts numerous dykes and stocks of magnetite-apatite-enriched rocks and carbonatites. It hosts the second largest REE–Fe–P–F–Sr–Ba deposit in Mongolia, with REE mineralization associated with magnetite-apatite-enriched rocks and carbonatites. The bulk rock REE content of these two rock types varies from 21,929 to 70,852 ppm, which is much higher than that of syenites (716 ± 241 ppm). Among these, the altered magnetite-apatite-enriched rocks are characterized by the greatest level of REE enrichment (58,036 ± 13,313 ppm). Magmatic apatite from magnetite-apatite-enriched rocks is commonly euhedral with purple luminescence, and altered apatite displays variable purple to blue luminescence and shows fissures and hollows with deposition of fine-grained monazite aggregates. Most magmatic apatite within syenite is prismatic and displays oscillatory zoning with variable purple to yellow luminescence. Both magmatic and altered apatite from magnetite-apatite-enriched rocks were dated using in situ U–Pb dating and found to have ages of 139.7 ± 2.6 and 138.0 ± 1.3 Ma, respectively, which supports the presence of late Mesozoic alkaline magmatism. In situ 87Sr/86Sr ratios obtained for all types of apatite and calcite within carbonatite show limited variation (0.70572–0.70648), which indicates derivation from a common mantle source. All apatite displays steeply fractionated chondrite-normalized REE trends with significant LREE enrichment (46,066 ± 71,391 ppm) and high (La/Yb)N ratios ranging from 72.7 to 256. REE contents and (La/Yb)N values are highly variable among different apatite groups, even within the same apatite grains. The variable REE contents and patterns recorded by magmatic apatite from the core to the rim can be explained by the occurrence of melt differentiation and accompanying fractional crystallization. The Y/Ho ratios of altered apatite deviate from the chondritic values, which reflects alteration by hydrothermal fluids. Altered apatite contains a high level of REE (63,912 ± 31,785 ppm), which are coupled with increased sulfur and/or silica contents, suggesting that sulfate contributes to the mobility and incorporation of REEs into apatite during alteration. Moreover, altered apatite is characterized by higher Zr/Hf, Nb/Ta, and (La/Yb)N ratios (179 ± 48, 19.4 ± 10.3, 241 ± 40, respectively) and a lack of negative Eu anomalies compared with magmatic apatite. The distinct chemical features combined with consistent Sr isotopes and ages for magmatic and altered apatite suggest that pervasive hydrothermal alterations at Mushgai Khudag are most probably being induced by carbonatite-evolved fluids almost simultaneously after the alkaline magmatism.

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Late Mesozoic Carbonatite of Central Asia

Никифоров

2023

Petrology

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Ar-Ar geochronology and petrogenesis of the Mushgai–Khudag alkaline‑carbonatite complex (southern Mongolia)

Cited by 5 publications

References 62 publications

Carbonatites and Alkaline Igneous Rocks in Post-Collisional Settings: Storehouses of Rare Earth Elements

Carbonatites and Alkaline Igneous Rocks in Post-Collisional Settings: Storehouses of Rare Earth Elements

Combined In Situ Chemical and Sr Isotopic Compositions and U–Pb Ages of the Mushgai Khudag Alkaline Complex: Implications of Immiscibility, Fractionation, and Alteration

Late Mesozoic Carbonatite of Central Asia

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