The newly discovered ca. 1.5 Ga old Attu carbonatite dyke in central West Greenland is characterized by very high contents of rare earth elements (REE), Sr and Ba (up to 12.4 wt.% total REE, 14.6 wt.% SrO and 12.4 wt.% BaO). The carbonatite is primarily composed of carbonate minerals such as Sr-rich calcite (CaCO3) and dolomite (CaMg(CO3)2), huntite (Mg3Ca(CO3)4), strontianite (SrCO3), alstonite (CaBa(CO3)2), burbankite ((Na,Ca)3(Sr,Ba, Ce)3(CO3)5) and daqingshanite(-Ce) ((Sr,Ca,Ba)3(Ce, La)(PO4)(CO3)3−x(OH, F)x). In addition to the wide range of carbonate minerals, the carbonatite contains coarse-grained monazite(-Ce), apatite and magnetite. Barite occurs as discrete grains together with the rock-forming carbonates. Texturally, the carbonatite rock displays abundant intimately intergrown fine- to medium-grained Ca, Sr, Ba and REE carbonate minerals, which may exhibit prominent exsolution textures within calcite, burbankite, strontianite and dolomite hosts as well as in the apatite grains. Several different exsolution textures are observed: 1) alstonite in calcite; 2) daqingshanite in calcite; 3) daqingshanite(-Ce) in burbankite; 4) Mg-Ba carbonate in strontianite; 5) Mg-Ba carbonate in calcite and strontianite in dolomite; 6) strontianite in apatite; and 7) monazite(-Ce) in apatite. The carbonatite dyke is foliated and exsolution textures are observed internally in the foliation-defining minerals indicating that exsolution occurred after the main deformation event.The carbonatite magma intruded into Archaean basement gneisses that had been affected by the Nagssugtoqidian tectonometamorphic event at approximately 1850 Ma. Magmatic monazite(-Ce) crystals from the carbonatite yield a U-Pb age of 1565±53 Ma, which is the current best estimate of dyke emplacement. Monazite(-Ce) that exsolved from apatite and calcite yields a U-Pb age of 1492±33 Ma, which is within the analytical uncertainty of the primary magmatic monazite U-Pb age. However, the U-Pb age determinations suggest that mineral exsolution occurred a few million years after carbonatite magma emplacement, in response to further cooling of the deep-seated dyke (uplift?). Dyke emplacement may have occurred within an active ductile shear zone, which would help to explain the foliation of the carbonatite rock, predating cooling-related mineral exsolution. Country rock fenitisation by fluids that emanated from the carbonatite dyke intrusion is recorded by the increasing abundance of mafic silicates such as Ba-rich phlogopite at the contact zone.

Carbonatite

10.2139/ssrn.4675889

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The alleged carbonatitic-kimberlitic melt continuum: Contrary evidence from West Greenland

Geochimica et Cosmochimica Acta Supplement (2008)

Sebastian Tappe Agnete Steenfelt Larry M. Heaman Rolf L. Romer Antonio Simonetti

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Depositional history and provenance of cratonic “Purana” basins in southern India: A multipronged geochronology approach to the Proterozoic Kaladgi and Bhima basins

Geological Journal (2018)

Sojen Joy Sarbani Patranabis‐Deb Dilip Saha Hielke Jelsma Roland Maas

Peninsular India is a collage of Archaean cratonic domains separated by Proterozoic mobile belts. A number of cratonic basins, known as “Purana basins” in the Indian literature, formed in different parts of the Indian Peninsula during extensional tectonic events, from Paleoproterozoic through Neoproterozoic times. In this contribution, we present a diversity of new geochronological data for different units within the Kaladgi and the Bhima basins, which overlie the western and eastern Dharwar cratons, respectively. The new geochronology data are discussed in terms of depositional history and provenance of these poorly understood Proterozoic intracratonic basins. For the Kaladgi Group, a U–Pb baddeleyite age of 1,861 ± 4 Ma obtained for a dolerite dyke intruding the Yendigere Formation is used to constrain the minimum age of deposition of the lower Kaladgi Group. This result demonstrates that this part of the succession is comparable in age to the Papaghni Group of the Cuddapah Basin, heralding onset of Purana sedimentation at ~ 1,900 Ma. The detrital zircon populations from the clastic rocks of the Kaladgi and Bhima basins show unique and distinct age patterns indicating different source of sediments for these two basins. Palaeocurrent analysis indicates a change in provenance from south or southeast to west or northwest between the Kaladgi and Bhima clastic sedimentation. New U–Th–Pb and Rb–Sr radiometric dates of limestones and glauconite‐bearing sandstones of the Bhima Group (Bhima Basin) and the Badami Group (Kaladgi Basin) indicate deposition at around 800–900 Ma, suggesting contemporaneity for the two successions. Thus, the unconformity between the Kaladgi Group and the overlying Badami Group represents a time gap of up to 1,000 Myr. These new results demonstrate the complex multistage burial and unroofing history of the Archaean Dharwar Craton throughout the Proterozoic, with important implications for exploration of metal deposits and diamonds in Peninsular India.

Geochronology

Conglomerate

10.1002/gj.3415

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Calcium isotopes track volatile components in the mantle sources of alkaline rocks and associated carbonatites

Earth and Planetary Science Letters (2023)

Chunfei Chen Stephen F. Foley Sebastian Tappe Huange Ren Lanping Feng

The volatile components CO2 and H2O induce mantle melting and thus exert major controls on mantle heterogeneity. Primitive intraplate alkaline magmatic rocks are the closest analogues for incipient mantle melts and provide the most direct method to assess such mantle heterogeneity. Given the considerable Ca isotope differences among carbonate, clinopyroxene, garnet, and orthopyroxene in the mantle (up to 1 ‰ for δ44/40Ca), δ44/40Ca of alkaline rocks is a promising tracer of lithological heterogeneity. We present stable Ca isotope data for ca. 1.4 Ga lamproites, 590–555 Ma ultramafic lamprophyres and carbonatites, and 142 Ma nephelinites from Aillik Bay in Labrador, eastern Canada. These primitive alkaline rock suites are the products of three stages of magmatism that accompanied lithospheric thinning and rifting of the North Atlantic craton. The three discrete magmatic events formed by melting of different lithologies in a metasomatized lithospheric mantle column at various depths: (1) MARID-like components (mica-amphibole-rutile-ilmenite-diopside) in the source of the lamproites; (2) phlogopite-carbonate veins were an additional source component for ultramafic lamprophyres during the second event; and (3) wehrlites at shallower depths were an important source component for nephelinites during the final event. The Mesoproterozoic lamproites show lower δ44/40Ca values (0.58 to 0.66 ‰) than MORBs (0.84 ± 0.03 ‰, 2se). This cannot be explained by fractional crystallization or melting of the clinopyroxene-dominated source but can be attributed to a source enriched in the alkali amphibole K-richterite, which has characteristically low δ44/40Ca. The δ44/40Ca values of the ultramafic lamprophyre suite during the second rifting stage are remarkably uniform, with overlapping ranges for primary carbonated silicate melts (aillikite: 0.67 to 0.75 ‰), conjugate carbonatitic liquids (0.71 to 0.82 ‰) and silicate-dominated damtjernite liquid (primary damtjernite: 0.68 to 0.72 ‰). This suggests negligible Ca isotope fractionation during liquid immiscibility of carbonate-bearing magmas. Combined with previously reported δ44/40Ca values for carbonatites and kimberlites, our data suggest that carbonated silicate melts in Earth's mantle have δ44/40Ca compositions resolvably lower than those for MORBs (0.74 ± 0.02 ‰ versus 0.84 ± 0.03 ‰, 2se). The δ44/40Ca values of the Cretaceous nephelinites (0.72 to 0.78 ‰) are homogenous and similar to those of the 590–555 Ma ultramafic lamprophyres, suggesting that the wehrlitic source component for the nephelinites formed by mantle metasomatism during interaction with rising aillikite magmas during the second rifting stage. Our results highlight that both K-richterite and carbonate components in mantle sources can result in the systematically low δ44/40Ca values of alkaline magmas, which may explain previously reported low δ44/40Ca values of alkaline rocks and some carbonatites. Our study indicates that Ca isotopes are a robust tracer of lithological variation caused by volatiles in the Earth's upper mantle.

Carbonatite

Ultramafic rock

Phlogopite

Amphibole

Peridotite

Incompatible element

10.1016/j.epsl.2023.118489

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Calcium isotopic evidence for the mantle sources of carbonatites

Science Advances (2020)

Elsa Amsellem Fréderic Moynier Hervé Bertrand Amaury Bouyon João Mata

The origin of carbonatites-igneous rocks with more than 50% of carbonate minerals-and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.

Carbonatite

Isotopic signature

10.1126/sciadv.aba3269

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Citations (62)