Sulfur-rich monazite with high common Pb in ore-bearing schists from the Schellgaden mining district (Tauern Window, Eastern Alps)
26
Citation
33
Reference
10
Related Paper
Citation Trend
Keywords:
Paragenesis
The Albion–Raft River–Grouse Creek metamorphic core complex of southern Idaho and northern Utah exposes 2.56-Ga orthogneisses and Neoproterozoic metasedimentary rocks that were intruded by 32–25-Ma granitic plutons. Pluton emplacement was contemporaneous with peak metamorphism, ductile thinning of the country rocks, and top-to-the-west, normal-sense shear along the Middle Mountain shear zone. Monazite and zircon from an attenuated stratigraphic section in the Middle Mountain were dated with U-Pb, using a SHRIMP-RG (reverse geometry) ion microprobe. Zircons from the deformed Archean gneiss preserve a crystallization age of Ma, while monazites range from to Ma. In the schist of the Upper Narrows, detrital zircons lack metamorphic overgrowths, and monazites produced discordant U-Pb ages that range from to Ma. From the structurally and stratigraphically highest unit sampled, the schist of Stevens Spring, narrow metamorphic rims on detrital zircons yield ages from 140–110 Ma, and monazite grains contained cores that yield an age of Ma, whereas rims and some whole grains ranged from to Ma. A boudinaged pegmatite exposed in Basin Creek is deformed by the Middle Mountains shear zone and yields a monazite age of Ma. We interpret these data to indicate two periods of monazite and metamorphic zircon growth: a poorly preserved Early Cretaceous period (∼140 Ma) that is strongly overprinted by Oligocene metamorphism (∼32–27 Ma) related to regional plutonism and extension.
Plutonism
Metamorphic core complex
Batholith
Geochronology
Leucogranite
Cite
Citations (37)
Abstract Metasedimentary rocks of the Archean Quetico subprovince of the Superior province in northeastern Minnesota contain monazite that has undergone low-grade hydrothermal alteration and disseminated sulfide mineralization. The area contains multiply deformed, metasedimentary rocks with abundant granitic veins that were subjected to deep burial, deformation, and syntectonic Barrovian metamorphism ranging from kyanite-staurolite grade to sillimanite-muscovite grade. Continued deformation and concomitant granitic intrusion produced rapid decompression and a well-developed high-temperature, low-pressure thermal aureole adjacent to the granitic intrusive bodies. This second metamorphic event is characterized by mineral assemblages containing cordierite or andalusite after staurolite. Subsequent reburial of the area produced prennite/pumpellyite facies regional metamorphism that is widespread but only locally recognized. The initial aim of this study was to determine the petrographic relationships between monazite, a light rare-earth phosphate, and the surrounding minerals as a basis for absolute age dating, by electron probe microanalyzer (EPMA), of deformation and related metamorphic events.
Staurolite
Sillimanite
Andalusite
Isograd
Muscovite
Cite
Citations (0)
Paragenesis
Greenschist
Pelite
Batholith
Cite
Citations (180)
Allanite
Massif
Pegmatite
Cite
Citations (18)
Geochronology
Cite
Citations (9)
Whole rock major element influences on monazite growth: examples from igneous and metamorphic rocks in the Menderes Massif, western Turkey Monazite (LREEPO 4 ) is a radiogenic, rare-earth bearing mineral commonly used for geochronology. Here we examine the control of major element chemistry in influencing the crystallization of monazite in granites (Salihli and Turgutlu bodies) and garnet-bearing metamorphic assemblages (Bozdag and Bayindir nappes) from the Menderes Massif, western Turkey. In S-type granites from the massif, the presence of monazite correlates to the CaO and Al 2 O 3 content of the whole rock. Granites with monazite only are low Ca (0.6-1.8 wt% CaO). As CaO increases (from 2.1-4.6 wt%), allanite [(Ce, Ca, Y) 2 (Al, Fe 3+ ) 3 (SiO 4 ) 3 (OH)] is present. Higher Al 2 O 3 (>15 wt%) rocks contain allanite and/or monazite, whereas those with lower Al 2 O 3 contain monazite only. However, examining data reported elsewhere for A-type granites, the correlation between major element chemistry and presence of monazite is likely restricted to S-type lithologies. Pelitic schists of the Menderes Massif show no correlation between major element chemistry and presence of monazite. One Bayindir nappe sample contains both prograde garnets and those affected significantly by diffusion. These rocks have likely experienced a complicated multi-stage tectonic history, which influenced their current mineral assemblages. The presence of monazite in a metamorphic rock can be influenced by the number, duration, and nature of events that were experienced and the degree to which fluids were involved. The source of monazite in the Bayindir and Bozdag samples was likely reactions that involved allanite. These reactions may not have significantly changed the bulk composition of the rock.
Allanite
Massif
Carbonatite
Migmatite
Pelite
Cite
Citations (14)
Staurolite
Isochron dating
Sillimanite
Pegmatite
Isograd
Cite
Citations (57)
Paragenesis
Cite
Citations (26)
Sericite
Geochronology
Allanite
Titanite
Radiometric dating
Cite
Citations (60)
Poly-metamorphism has been observed in many Precambrian metamorphic terranes. The metamorphic overprinting in the poly-metamorphic rocks makes it difficult to determine the timing and P − T path of each metamorphic event. In this study, in situ U–Pb dating of zircon, xenotime, and monazite, with simultaneously determination of trace element compositions, is utilized to provide new constraints on the timing of discrete metamorphic events involving reactivation of the Jiao-Liao-Ji Belt, the eastern edge of the North China Craton. Detrital zircons from metasandstones in the Gaixian Formation record a mixed provenance that includes late Neoarchean (ca. 2532 Ma) and middle Paleoproterozoic (ca. 2181 Ma). Xenotimes from the Gaixian pelitic schists yield an upper intercept age of 1906 ± 25 Ma, and this age is interpreted as the timing of greenschist-facies regional metamorphism. However, monazites from the same pelitic schists yield a distinctly younger age of 242 Ma, with late Paleoproterozoic inherited ages of 1894 and 1809 Ma, which are broadly consistent with the xenotime ages. In addition, magmatic zircons from a granitic mylonite vein yield a similar age of 245 Ma, making it coeval with the monazite. The interpretation of these ages is also reinforced by the mineral assemblage of inclusions in the dated accessory mineral grains. These new geochronological data, combined with published data from the Jiao-Liao-Ji Belt and the related regions, suggest that the Gaixian Formation in the Yanghe area was likely some time deposited at 2181–1900 Ma, and experienced both late Paleoproterozoic and Triassic low-grade metamorphic events related to two distinct orogenic phases in the eastern North China Craton.
Geochronology
Radiometric dating
Pelite
Greenschist
Cite
Citations (8)