The role of crustal contamination in magma evolution of Neoproterozoic metaigneous rocks from Southwest Svalbard

Reports of shoshonitic rocks in Precambrian terrains are relatively rare. Pl-Grt amphibolites and Hbl-Bt mafic granulites occurring in the migmatitic gneisses of the Chhotanagpur Gneissic Complex (CGC) show calc-alkaline and shoshonitic characteristics. Relict porphyritic, sub-ophitic and poikilitic textures are noted in these rocks. Their parent magma was emplaced during the waning phase of the regional metamorphism. Geochemically, these metamafics are similar to the Group III potassic and ultrapotassic rocks of Foley et al. (1987). The magma was derived from the metasomatized subcontinental lithospheric mantle (SCLM). Subduction-related sediment melts metasomatized the SCLM. Compositionally, the SCLM is a metasomatized phlogopite-amphibole-spinel-bearing harzburgite. 1%-5% batch melting of the SCLM could produce the parental magma of the mafic granulites. Pressures and temperatures of metamorphic equilibration were carried out by pseudosection modeling. Peak metamorphic assemblage (M 1 : Grt-Cpx-Pl-Qz) in garnetiferous amphibolite equilibrated at 740º C and 8.7 kbar. The Cpx-Pl corona appeared around the garnet during decompression (M 2 : 655°C, 6 kbar). The Hbl-Pl symplectites around garnet formed during isobaric cooling (M 3 : 580°C and 5.9 kbar). The emplacement of shoshonitic magma and subsequent decompression happened at the slab break-off stage of continental collision (~990 Ma).

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“…Fig. 3c; after Gołuchowska et al, 2022), the analyzed samples disqualify a crustal assimilation trend.…”

Section: Role Of Crustal Contaminationmentioning

confidence: 90%

Discovery of Early Tonian Calc‐alkaline and Shoshonitic Metamafic Rocks from the North Purulia Shear Zone, Chhotanagpur Gneissic Complex, Eastern India: Implications of Proterozoic Sub‐continental Lithospheric Mantle

Goswami

Das

Basak

et al. 2023

Acta Geologica Sinica (Eng)

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Extension during the Liebig Orogeny: Revised tectonic setting of Paleoproterozoic central Australia

March,

Hand,

Morrissey

et al. 2024

Gondwana Research

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Apatite Chemistry as a Petrogenetic Indicator for Mafic Layered Intrusions

Kieffer,

Dare,

Namur

et al. 2024

Journal of Petrology

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Mafic layered intrusions constitute a natural laboratory to investigate petrogenetic processes using trace element variations in apatite chemistry. Although these intrusions are related to large igneous provinces, there is a wide range of parameters that can affect the chemistry of the primary melt (i.e., composition of the source, pressure, temperature, oxygen fugacity), followed by possible crustal contamination. In this study, we use a comprehensive dataset of analyses of cumulus and intercumulus apatite from a variety of mafic layered intrusions to demonstrate the use of apatite as a powerful petrogenetic indicator. The dataset (determined in this study and compiled from the literature) comprises electron microprobe and LA-ICP-MS analyses, as well as in-situ LA-MC-ICP-MS analyses of Sr isotopes in apatite from well documented layered intrusions (Sept-Iles, Skaergaard, Bushveld, Panzhihua) and the Sudbury Igneous Complex. For the first time, we show that high values of (La/Nd)N, Th, U, Pb, and As in apatite correlate with high (87Sr/86Sr)initial and are related to contamination with continental crust. An elevated (Gd/Yb)N ratio might indicate melting of a mantle source deep enough to retain Yb in garnet. We also confirm that increasingly negative Eu anomaly and decreasing Sr/Y ratio in apatite are indicators of fractional crystallisation of plagioclase, and that high Sr/Y is indicative of early saturation of apatite and/or delayed crystallisation of plagioclase. The reversal to more primitive compositions caused by magma mixing is expressed by higher Sr, V, Mg and Sr/Y ratio, and lower REE+Y, As and Na concentrations in apatite following magma replenishment. Lastly, we show that apatite signature can efficiently distinguish a mafic from a felsic intrusion using its REE and Sr content coupled to its Eu anomaly. It is also possible to further identify the more primitive from the more evolved parts of a mafic layered intrusion, using the Lu, Th, V and volatile (F/Cl) content to distinguish intercumulus from cumulus apatite, respectively. Finally, identifying a mafic magmatic system using detrital apatite in till will prove useful for provenance and mineral exploration studies.

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The role of crustal contamination in magma evolution of Neoproterozoic metaigneous rocks from Southwest Svalbard

Cited by 6 publications

References 93 publications

Discovery of Early Tonian Calc‐alkaline and Shoshonitic Metamafic Rocks from the North Purulia Shear Zone, Chhotanagpur Gneissic Complex, Eastern India: Implications of Proterozoic Sub‐continental Lithospheric Mantle

Discovery of Early Tonian Calc‐alkaline and Shoshonitic Metamafic Rocks from the North Purulia Shear Zone, Chhotanagpur Gneissic Complex, Eastern India: Implications of Proterozoic Sub‐continental Lithospheric Mantle

Extension during the Liebig Orogeny: Revised tectonic setting of Paleoproterozoic central Australia

Apatite Chemistry as a Petrogenetic Indicator for Mafic Layered Intrusions

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