“Satellite monazites” in polymetamorphic basement rocks of the Alps: Their origin and petrological significance

Finger, Friedrich; Krenn, Erwin; Schulz, Bernhard; Harlov, Daniel E.; Schiller, David

doi:10.2138/am-2016-5477

Cited by 32 publications

(20 citation statements)

References 44 publications

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“…Harlov, 2011Harlov, , 2015Harlov et al, 2002Harlov et al, , 2005Harlov and Förster, 2003). Experimental results Budzyń et al, 2017) are consistent with natural observations that fluid activity is just as important as changes in P-T conditions for monazite breakdown reactions (Finger et al, 1998(Finger et al, , 2016Janots et al, 2008;Ondrejka et al, 2012Ondrejka et al, , 2016. The formation of monazite micro-inclusions in apatite may not be coeval with the breakdown of granoblastic monazite to apatite-allanite; the former may have been produced at different temperatures by fluids that were also responsible for monazite resetting at ca.…”

Section: Petrographic Considerations In Accessory Mineral Datingsupporting

confidence: 81%

Peak to post-peak thermal history of the Saglek Block of Labrador: A multiphase and multi-instrumental approach to geochronology

et al. 2018

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A B S T R A C TThe Saglek Block of coastal Labrador forms the western margin of the North Atlantic Craton, where Archean gneisses and granulites have been reworked during the Paleoproterozoic. Previous work has established that the block is a composite of Eoarchean to Mesoarchean protoliths metamorphosed to upper amphibolite and granulite facies at around 2.8-2.7 Ga. New in-situ microbeam dating of accessory minerals in granoblastic gneisses reveals a complex peak to post-peak thermal history. Zircon growth at ca. 3.7-3.6 Ga provides the age of formation of the tonalitic protoliths to the gneisses. Further zircon growth in syn-tectonic granitic gneiss and monazite growth in a variety of orthogneisses confirm peak metamorphic conditions at ca. 2.7 Ga, but also reveal high-temperature conditions at ca. 2.6 Ga and 2.5 Ga. The former is interpreted as the waning stages of the 2.7 Ga granulite event, whereas the latter is associated with a younger phase of granitic magmatism. In addition, apatite ages of ca. 2.2 Ga may represent either cooling associated with the 2.5 Ga event or a previously unrecognized greenschist-facies metamorphism event that predates the Torngat Orogeny.

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Section: Petrographic Considerations In Accessory Mineral Datingsupporting

confidence: 81%

Peak to post-peak thermal history of the Saglek Block of Labrador: A multiphase and multi-instrumental approach to geochronology

et al. 2018

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“…Similar conclusions have been made for natural examples of the partial-to complete replacement of monazite by a sequence of apatite, allanite, and epidote zones in metamorphosed granitic rocks and pelites (e.g. Broska and Siman 1998;Finger et al 1998;Broska et al 2005;Majka and Budzyń 2006;Petrík et al 2006;Budzyń et al 2010;Ondrejka et al 2012;Budzyń and Jastrzębski 2016;Finger et al 2016;Lo Pò et al 2016). The occurrence of ThSiO 4 or ThO 2 only in the inner zone mantling the monazite, as inclusions in apatite (Finger et al 1998;Ondrejka et al 2012;Budzyń et al 2010), indicates that Th transport occurs over a much more limited distance from the monazite compared to the REEs.…”

Section: Experiments With Xenotime-(y) and Na 2 Si 2 O 5 + H 2 Osupporting

confidence: 72%

“…Temperature conditions controlling monazite-allanite phase relations have been constrained to~400-450°C in metapelites, where progressive metamorphic reactions involve the breakdown of monazite to form allanite (Smith and Barreiro 1990;Wing et al 2003;Janots et al 2006Janots et al , 2008. In some cases these breakdown reactions were later followed by a reversed reaction resulting in the formation of monazite at the andalusite or kyanite isograd (Wing et al 2003) or under temperature conditions of~550-650°C (Janots et al 2008;Finger et al 2016). Thermodynamic modeling by Spear (2010), utilizing Shaw's (1956) average pelite bulk composition, predicted that increasing CaO from 2.17 to 4.34 wt.% would shift the allanite-(Ce) to monazite-(Ce) transition from 400°C at 200 MPa and 550°C at 1000 MPa, to 480°C at 200 MPa and 750°C at 1000 MPa (Fig.…”

Section: Interpretation Of the Experimental Results: Runs With Xenotimentioning

confidence: 99%

Experimental constraints on the relative stabilities of the two systems monazite-(Ce) – allanite-(Ce) – fluorapatite and xenotime-(Y) – (Y,HREE)-rich epidote – (Y,HREE)-rich fluorapatite, in high Ca and Na-Ca environments under P-T conditions of 200–1000 MPa and 450–750 °C

et al. 2016

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The relative stabilities of phases within the two systems monazite-(Ce)fluorapatiteallanite-(Ce) and xenotime-(Y)-(Y,HREE)-rich fluorapatite-(Y,HREE)-rich epidote have been tested experimentally as a function of pressure and temperature in systems roughly replicating granitic to pelitic composition with high and moderate bulk CaO/Na 2 O ratios over a wide range of P-T conditions from 200 to 1000 MPa and 450 to 750°C via four sets of experiments. These included (1) monazite-(Ce), labradorite, sanidine, biotite, muscovite, SiO 2 , CaF 2 , and 2 M Ca(OH) 2 ; (2) monazite-(Ce), albite, sanidine, biotite, muscovite, SiO 2 , CaF 2 , Na 2 Si 2 O 5 , and H 2 O; (3) xenotime-(Y), labradorite, sanidine, biotite, muscovite, garnet, SiO 2 , CaF 2 , and 2 M Ca(OH) 2 ; and (4) xenotime-(Y), albite, sanidine, biotite, muscovite, garnet, SiO 2 , CaF 2 , Na 2 Si 2 O 5 , and H 2 O. Monazite-(Ce) breakdown was documented in experimental sets (1) and (2). In experimental set (1), the Ca high activity (estimated bulk CaO/Na 2 O ratio of 13.3) promoted the formation of REE-rich epidote, allanite-(Ce), REE-rich fluorapatite, and fluorcalciobritholite at the expense of monazite-(Ce). In contrast, a bulk CaO/ Na 2 O ratio of~1.0 in runs in set (2) prevented the formation of REE-rich epidote and allanite-(Ce). The reacted monazite-(Ce) was partially replaced by REE-rich fluorapatite-fluorcalciobritholite in all runs, REE-rich steacyite in experiments at 450°C, 200-1000 MPa, and 550°C, 200-600 MPa, and minor cheralite in runs at 650-750°C, 200-1000 MPa. The experimental results support previous natural observations and thermodynamic modeling of phase equilibria, which demonstrate that an increased CaO bulk content expands the stability field of allanite-(Ce) relative to monazite-(Ce) at higher temperatures indicating that the relative stabilities of monazite-(Ce) and allanite-(Ce) depend on the bulk CaO/ Na 2 O ratio. The experiments also provide new insights into the re-equilibration of monazite-(Ce) via fluid-aided coupled dissolution-reprecipitation, which affects the Th-U-Pb system in runs at 450°C, 200-1000 MPa, and 550°C, 200-600 MPa. A lack of compositional alteration in the Th, U, and Pb in monazite-(Ce) at 550°C, 800-1000 MPa, and in experiments at 650-750°C, 200-1000 MPa indicates the limited influence of fluid-mediated alteration on volume diffusion under high P-T conditions. Experimental sets (3) and (4) resulted in xenotime-(Y) breakdown and partial replacement by (Y,REE)rich fluorapatite to Y-rich fluorcalciobritholite. Additionally, (Y,HREE)-rich epidote formed at the expense of xenotime-(Y) in three runs with 2 M Ca(OH) 2 fluid, at 550°C, 800 MPa; 650°C, 800 MPa; and 650°C, 1000 MPa similar to the experiments involving monazite-(Ce). These results confirm that replacement of xenotime-(Y) by (Y,HREE)-Editorial handling: L. Nasdala

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“…The microstructure of Cretaceous satellite monazite (Fig. 3i) has so far been described only by Finger et al (2016). These monazite satellite grains should have crystallized during an increase in temperature after the formation of allanite-apatite coronas surrounding the monazite.…”

Section: Monazite Crystallization and Decompositionmentioning

confidence: 98%

Polymetamorphism in garnet micaschists of the Saualpe Eclogite Unit (Eastern Alps, Austria), resolved by automated SEM methods and EMP–Th–U–Pb monazite dating

Schulz

2016

Journal Metamorphic Geology

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Polymetamorphic garnet micaschists from the Austroalpine Saualpe Eclogite Unit (Kärnten, Austria, Eastern Alps) display complex microstructural and mineral–chemical relationships. Automated scanning electron microscopy routines with energy dispersive X‐ray (EDX) spectral mapping were applied for monazite detection and garnet mineral–chemical characterization. When the Fe, Mg, Mn and Ca element wt% compositions are used as generic labels for garnet EDX spectra, complex zonations and porphyroblast generations can be resolved in complete thin sections for selective electron‐microprobe analyses. Two garnet porphyroblast generations and diverse monazite age populations have been revealed in low‐Ca and high‐Al‐metapelites. Garnet 1 has decreasing Mn, constant Ca and significantly increasing Mg from cores to rims. Geothermobarometry of garnet 1 assemblages signals a crystallization along a M1 prograde metamorphism at ~650 °C/6–8 kbar. Sporadic monazite 1 crystallization started at c. 320 Ma. Subsequent pervasive 300–250 Ma high‐Y and high‐Gd monazite 1 formation during decompression coincided with the intrusion of Permian and Early Triassic pegmatites. Monazite 1 crystallized along the margin of garnet 1. Coronas of apatite and allanite around the large 320–250 Ma monazite signal a retrogressive stage. These microstructures suggest a Carboniferous‐to‐Early‐Permian age for the prograde M1 event with garnet 1. Such a M1 event at an intermediate‐P/T gradient has not yet been described from the Saualpe, and preceded a Permo‐Triassic low‐P stage. The M2 event with garnet 2 postdates the corona formation around Permian monazite. Garnet 2 displays first increasing XCa at decreasing XMg, then increasing XCa and XMg, and finally decreasing XCa with increasing XMg, always at high Ca and Mg, and low Mn. This records a P–T evolution which passed through eclogite facies conditions and reached maximum temperatures at ~750 °C/14 kbar during decompression‐heating. A monazite 2 population (94–86 Ma) with lower Y and Gd contents crystallized at decreasing pressure during the Cretaceous (Eo‐Alpine) metamorphism M2 at a high‐P/T gradient. The Saualpe Eclogite Unit underwent two distinct clockwise metamorphic cycles at different P–T conditions, related to continental collisions under different thermal regimes. This led to a characteristic distribution pattern of monazite ages in this unit which is different from other Austroalpine basement areas.

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“Satellite monazites” in polymetamorphic basement rocks of the Alps: Their origin and petrological significance

Cited by 32 publications

References 44 publications

Peak to post-peak thermal history of the Saglek Block of Labrador: A multiphase and multi-instrumental approach to geochronology

Peak to post-peak thermal history of the Saglek Block of Labrador: A multiphase and multi-instrumental approach to geochronology

Experimental constraints on the relative stabilities of the two systems monazite-(Ce) – allanite-(Ce) – fluorapatite and xenotime-(Y) – (Y,HREE)-rich epidote – (Y,HREE)-rich fluorapatite, in high Ca and Na-Ca environments under P-T conditions of 200–1000 MPa and 450–750 °C

Polymetamorphism in garnet micaschists of the Saualpe Eclogite Unit (Eastern Alps, Austria), resolved by automated SEM methods and EMP–Th–U–Pb monazite dating

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