Alteration of crystalline zircon solid solutions: a case study on zircon from an alkaline pegmatite from Zomba–Malosa, Malawi

Soman, Aneesh; Geisler, Thorsten; Tomaschek, Frank; Grange, Marion; Berndt, Jasper

doi:10.1007/s00410-010-0514-2

Cited by 70 publications

(33 citation statements)

References 65 publications

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“…e.g. Soman et al 2010). Taking these discordant data at face value suggests that a hydrothermal alteration event is substantially (*900 Ma) younger than the magmatism.…”

Section: Zircon Occurrence and Compositionmentioning

confidence: 89%

Independent ages of magmatic and hydrothermal activity in alkaline igneous rocks: The Motzfeldt Centre, Gardar Province, South Greenland

McCreath

Finch

Simonsen

et al. 2011

Contrib Mineral Petrol

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The Motzfeldt Centre is one of four major alkaline centres belonging to the Igaliko complex, part of the Mid-Proterozoic Gardar province of South Greenland. Motzfeldt comprises syenites and nepheline syenites displaying complex magmatic and subsolidus histories. Ta, Nb and REE-rich zones are associated with a pervasive hydrothermal alteration process in the North and East of the complex, part of a subdivision of the Centre called the Motzfeldt Sø Formation (MSF). The zircons from the MSF show textures that are both magmatic and altered, whereas the textures of pyrochlore have a predominantly subsolidus chemistry. We compare and contrast the radiogenic isotope geochemistry of the zircon and pyrochlore to obtain independent age estimates of the magmatic and hydrothermal episodes. Selected analyses of magmatic zircons are concordant with an age of 1,273 ± 6 Ma. Altered zircons are normally discordant with one intercept at 1,261 ± 28 Ma and the other at 349 ± 49 Ma. This younger age would appear on face value to date the hydrothermal event at Motzfeldt to *900 Ma after the magmatism. However, the Pb-Pb isotope systematics from altered pyrochlore define an isochron age of 1,267 ± 6 Ma for isotopic closure of the pyrochlore following alteration during the subsolidus. There is no known magmatic event in Southern Greenland at *350 Ma and discordant points have high common lead. We therefore infer that the younger intercept age is spurious. The overlap between the magmatic U-Pb zircon and the Pb-Pb pyrochlore age suggests that alteration of the Motzfeldt centre occurred shortly after magmatism.

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“…e.g. Soman et al 2010). Taking these discordant data at face value suggests that a hydrothermal alteration event is substantially (*900 Ma) younger than the magmatism.…”

Section: Zircon Occurrence and Compositionmentioning

confidence: 89%

Independent ages of magmatic and hydrothermal activity in alkaline igneous rocks: The Motzfeldt Centre, Gardar Province, South Greenland

McCreath

Finch

Simonsen

et al. 2011

Contrib Mineral Petrol

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“…The rather untypical PL pattern may hence be considered to reflect the unusual trace-element composition of this sample (for details on the geological setting of the Mt. Malosa alkaline complex see Woolley and Jones, 1992;Soman et al, 2010). Another unusual example is shown in Fig.…”

Section: Zirconmentioning

confidence: 96%

Laser-induced REE3+ photoluminescence of selected accessory minerals — An “advantageous artefact” in Raman spectroscopy

et al. 2015

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Keywords:Zircon Xenotime Monazite Titanite Laser-induced REE photoluminescence Raman artefact Laser-induced photoluminescence of trivalent rare-earth elements (REEs), which is obtained as analytical artefacts in Raman spectra of selected accessory minerals, was studied. Spectra of natural titanite, monazite-(Ce), xenotime-(Y), and zircon samples from various geological environments were compared with emission spectra of synthetic, flux-grown analogues doped with REEs. The latter is of great importance to identify potentially mistakable bands as either Raman or PL signal, and to assign them to certain REE centres. In the samples investigated, various REE centres are excited selectively using 473, 514, 532, 633, and 785 nm laser excitation. Their assignment was verified by photoluminescence-excitation experiments. Luminescence spectral patterns of zircon and titanite vary in dependence of trace-REE concentrations, hence reflecting geochemical growth conditions. "REE artefacts" in Raman spectra of accessory minerals may be used as fingerprint tool for mineral phaseidentification. The distribution of REE emission-intensities, revealed by hyperspectral mapping, opens up the opportunity to visualise mineral textures, complementary to cathodoluminescence imaging-techniques.

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“…The abundances of certain non-formula elements are high: P 2 O 5 ≤ 8.24 wt.%, CaO ≤3.02 wt.%; ΣREE 2 O 3 ≤22.44 wt.%; FeO* 4.05 wt.%, and TiO 2 ≤2.05 wt.%, the REE being dominated by the LREE. These elements are known to be incorporated into ThSiO 4 during interaction with hydrothermal fluids (Lumpkin and Chakoumakos 1988;Pointer et al 1988;Johan and Johan 2005;Förster 2006;Berger et al 2008;Uher et al 2009;Soman et al 2010;Piilonen et al 2013). The proportion of OH in the formulae was calculated from charge balance and ranged from 0.0 to 2.4 (Supplementary Table 2b).…”

Section: Thsiomentioning

confidence: 99%

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

et al. 2015

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The results are presented of a textural and mineral chemical study of a previously undescribed type of hydrothermal alteration of chevkinite-(Ce) which occurs in a syenitic pegmatite from the Vishnevye Mountains, Urals Region, Russia. The progressive alteration of the chevkinite to a bastnäsite-(Ce)-ilmenite-columbite-(Fe) assemblage through a series of texturally complex intermediate stages is described and electron microprobe analyses are given of all the major phases. Unusual Nb±Th-rich phases formed late in the alteration sequence provide evidence of local Nb mobility. The main compositional fluxes are traced, especially of the REE, HFSE, Th and U. It appears that almost all elements, with the exception of La, released from the chevkinite-(Ce) were reincorporated into later phases, such that they did not leave the alteration crust in significant amounts. The hydrothermal fluids are inferred to have been F-and CO 2 -rich, with variable levels of Ca activity, and with fO 2 mainly between the nickelnickel oxide and magnetite-hematite buffers. This occurrence represents a new paragenesis for a columbite-group mineral.

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Alteration of crystalline zircon solid solutions: a case study on zircon from an alkaline pegmatite from Zomba–Malosa, Malawi

Cited by 70 publications

References 65 publications

Independent ages of magmatic and hydrothermal activity in alkaline igneous rocks: The Motzfeldt Centre, Gardar Province, South Greenland

Independent ages of magmatic and hydrothermal activity in alkaline igneous rocks: The Motzfeldt Centre, Gardar Province, South Greenland

Laser-induced REE3+ photoluminescence of selected accessory minerals — An “advantageous artefact” in Raman spectroscopy

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

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