Disturbance versus preservation of U–Th–Pb ages in monazite during fluid–rock interaction: textural, chemical and isotopic in situ study in microgranites (Velay Dome, France)

Didier, Amélie; Bosse, Valérie; Boulvais, Philippe; Bouloton, J.; Paquette, Jean‐Louis; Montel, Jean-Marc; Devidal, Jean‐Luc

doi:10.1007/s00410-012-0847-0

Cited by 79 publications

(57 citation statements)

References 63 publications

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“…274 ± 7 Ma for a Quatre-Vios granite, Caen-Vachette et al 1982) are now believed to reflect late isotopic disturbance: the Montasset granite ( Fig. 1) yielded pristine monazites with a LA-ICP-MS age of 307 ± 2 Ma, and fluid-altered monazites with scattered ages suggesting reopening of the isotopic system between 270 and 290 Ma (Didier et al 2013). …”

Section: Geological Settingmentioning

confidence: 97%

Temporal relationships between Mg-K mafic magmatism and catastrophic melting of the Variscan crust in the southern part of Velay Complex (Massif Central, France)

Couzinié¹,

Moyen²,

Villaros³

et al. 2014

Jour. Geosci.

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Mg-K mafic intrusive rocks are commonly observed during the late stages of the evolution of orogenic belts. The Variscan French Massif Central has many outcrops of these rocks, locally called vaugnerites. Such magmas have a mantle-derived origin and therefore allow discussion of the role of mantle melting and crust-mantle interactions during late-orogenic processes. In the Southern Velay area of the French Massif Central, LA-ICPMS U-Pb dating on zircons and monazites from three vaugnerites and four coeval granites reveals that the two igneous suites formed simultaneously, at c. 305 Ma. This major igneous event followed after an early, protracted melting stage that lasted for 20-30 My and generated migmatites, but the melt was not extracted efficiently and therefore no granite plutons were formed. This demonstrates that widespread crustal anatexis, melt extraction and granite production were synchronous with the intrusion of vaugneritic mantle-derived melts in the crust. The rapid heating and subsequent melting of the crust led to upward flow of partially molten rocks, doming and collapse of the belt.

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Section: Geological Settingmentioning

confidence: 97%

Temporal relationships between Mg-K mafic magmatism and catastrophic melting of the Variscan crust in the southern part of Velay Complex (Massif Central, France)

Couzinié¹,

Moyen²,

Villaros³

et al. 2014

Jour. Geosci.

Self Cite

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“…The alignment of the instrument and mass calibration were performed before every analytical session using the NIST SRM 612 reference glass by inspecting the 238 U signal and by minimizing the ThOþ/Thþ ratio (,1%). The analytical method for isotope dating is similar to that developed and described in Paquette & Tiepolo (2007) and Didier et al (2013) and detailed in Hurai et al (2010) A single analysis consisted of 30 s of background integration with the laser off, followed by 60 s integration with the laser firing, and a 20 s delay to wash out the previous sample and prepare for the next analysis.…”

Section: Methodsmentioning

confidence: 99%

Chronological Constraints On Tsavorite Mineralizations and Related Metamorphic Episodes In Southeast Kenya

Martelat¹,

Paquette²,

Bosse³

et al. 2017

Can Mineral

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Tsavorite is exclusively hosted in the Neoproterozoic Metamorphic Mozambique Belt (NMMB). The gemstone mines, widespread between Kalalani (Tanzania) and Mgama Ridge (Kenya), define a continuous corridor over a hundred kilometers in length. The tsavorite is hosted by a metasedimentary sequence defined as the Kurase tsavorite-bearing metasediments (Kurase-TB metasediments) that also hosts rubies. These metasediments underwent amphibolite-facies metamorphism and are surrounded by granulitic gneisses that are also of sedimentary origin (the Kurase high-temperature gneisses). All these rocks lie below the Kasigau Group, a unit dominated by granulite-facies metamagmatic rocks.To constrain the timing of events that led to this peculiar occurrence of tsavorite, we have performed geochronological analyses of thin sections and of separated grains of zircon, monazite, and rutile using LA-ICP-MS and ID-TIMS, as well as 40 Ar/ 39 Ar of muscovite and phlogopite from various lithologies. The results show that the different terranes were metamorphosed synchronously between 620-580 Ma but under different P-T strain conditions. The Kurase-HT gneisses and the rocks from the Kasigau Group are highly strained and underwent granulite-facies metamorphism with abundant partial melting and emplacement of felsic melts between 620 and 600 Ma. Textural observations also underlined a late regional water flux controlling the occurrence of V-free muscovite and monazite mineralizations at 585 Ma. The latter event can be related to the 1 activity of the Galana shear zone, in the east. The Kurase-TB metasediments escaped strain and partial melting. They record amphibolite-facies conditions with static heating, since initial sedimentary structures were locally preserved. The age of the tsavorite mineralization was inferred at 600 Ma from metamorphic zircon rims and monazite from the closest host-rocks, sampled in the mines. Hence, tsavorite crystallization occurred statically at the end of the metamorphic event, probably when the temperature and the amount of volatiles were at maximum levels.Conversely, the ruby formed by local metasomatism of felsic dikes and isolated ultramafic bodies. The rubies are older and zircons and monazites from a ruby-bearing felsic dike (plumasite) were dated at 615 Ma. Finally, data from rutile and micas indicate a global cooling below 430 8C of the whole region between 510 and 500 Ma.

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“…Bastnäsite is not a secondary mineral formed via alteration or replacement of a pre-existing REE mineral, but rather a primary LREE phase. Such a scenario does not discount the possibility of a precursor LREE mineral phase, such as monazite, that has since been altered or dissolved, with LREE "recycled" into synchysite (e.g., [56]) or bastnäsite. There is, however, no direct evidence of synchysite or bastnäsite replacing monazite or any other LREE-bearing mineral, apart from bastnäsite replacing synchysite.…”

Section: Formation Conditionsmentioning

confidence: 99%

Rare Earth Element Fluorocarbonate Minerals from the Olympic Dam Cu-U-Au-Ag Deposit, South Australia

et al. 2017

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Abstract:Olympic Dam is a world-class breccia-hosted iron-oxide copper-gold-uranium ore deposit located in the Gawler Craton, South Australia. It contains elevated concentrations of rare earth elements (REE) which occur as the REE minerals bastnäsite, synchysite, florencite, monazite, and xenotime. This is the first study to focus on the mineralogy and composition of the most abundant REE mineral at Olympic Dam, bastnäsite, and subordinate synchysite. The sample suite extends across the deposit and represents different sulfide mineralization styles (chalcopyrite-bornite and bornite-chalcocite) and breccias of various types, ranging from those dominated by clasts of granite, dykes, and hematite. The REE-fluorocarbonates (bastnäsite and synchysite) typically occur as fine-grained (<50 µm) disseminations in Cu-Fe-sulfides and gangue minerals, and also within breccia matrix. They are also locally concentrated within macroscopic REE-mineral-rich pockets at various locations across the deposit. Such coarse-grained samples formed the primary target of this study. Three general textural groups of bastnäsite are recognized: matrix (further divided into disseminated, fine-grained, and stubby types), irregular (sulfide-associated), and clast replacement. Textures are largely driven by the specific location and prevailing mineral assemblage, with morphology and grain size often controlled by the associated minerals (hematite, sulfides). Major element concentration data reveal limited compositional variation among the REE-fluorocarbonates; all are Ce-dominant. Subtle compositional differences among REE-fluorocarbonates define a spectrum from relatively La-enriched to (Ce + Nd)-enriched phases. Granite-derived hydrothermal fluids were the likely source of F in the REE-fluorocarbonates, as well as some of the CO 2 , which may also have been contributed by associated mafic-ultramafic magmatism. However, transport of REE by Cl-ligands is the most likely scenario. Stubby bastnäsite and synchysite may have formed earlier, coincident with hydrothermal alteration of granite releasing Ca from feldspars. Other categories of bastnäsite, notably those co-existing with sulfides, and reaching the top of the IOCG mineralization at Olympic Dam (chalcocite + bornite zone) are relatively younger. Such an interpretation is concordant with subtle changes in the REE patterns for the different categories. The common association of bastnäsite and fluorite throughout the deposit is typical of the hematite breccias and can be deposited from neutral, slightly acidic fluids (sericite stability) at T ≈ 300 • C.

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Disturbance versus preservation of U–Th–Pb ages in monazite during fluid–rock interaction: textural, chemical and isotopic in situ study in microgranites (Velay Dome, France)

Cited by 79 publications

References 63 publications

Temporal relationships between Mg-K mafic magmatism and catastrophic melting of the Variscan crust in the southern part of Velay Complex (Massif Central, France)

Temporal relationships between Mg-K mafic magmatism and catastrophic melting of the Variscan crust in the southern part of Velay Complex (Massif Central, France)

Chronological Constraints On Tsavorite Mineralizations and Related Metamorphic Episodes In Southeast Kenya

Rare Earth Element Fluorocarbonate Minerals from the Olympic Dam Cu-U-Au-Ag Deposit, South Australia

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