Monazite-(Ce)-huttonite solid solutions in granulite-facies metabasites from the Ivrea-Verbano Zone, Italy

Abstract

Composite populations of monazite-group minerals of both metamorphic and metasomatic origin have been discovered in thin layers of granulite-facies metabasites interlayered with metapelites, located in the Val Strona di Omegna region of the Ivrea-Verbano Zone, Italy. In addition to monazite-(Ce), which is uncommonly poor in Th and is probably formed by incongruent dissolution of apatite, these populations include members of the monazite~uttonite series. The latter minerals contain between 13 and 30.1 mol.% ThSiO4 [= huttonitic monazite-(Ce)], and are known from only half a dozen other occurrences worldwide. We propose that breakdown of primary monazite-(Ce) in the metapelites during granulite-facies metamorphism mobilized Th and the REEs, which were then transported by high-grade metamorphic fluids into the metabasite layers to form the Th-rich minerals of the monazitehuttonite series.

Pseudotachylyte as field evidence for lower-crustal earthquakes during the intracontinental Petermann Orogeny (Musgrave Block, Central Australia)

“…For a simplified geological map covering the same area, and an interpreted synthetic NS cross section, see Wex et al (2017). levels during the earlier granulite facies metamorphism, with the breakdown of apatite and monazite resulting in partitioning of incompatible elements, such as Th, into the melt phase (Förster and Harlov, 1999). Consequently, low Th concentrations can be used to indicate that the crust experienced granulite facies metamorphism (Lambert and Heier, 1968;Scharbert et al, 1976).…”

“…Kohlstedt et al, 1995). The simplest assumption of competing brittle and viscous behaviour at constant strain rate results in a typical "Christmas tree" 1-D representation of strength variation with depth (Goetze and Evans, 1979). One basic form of the strength profile for the continental lithosphere is the so-called "jelly sandwich" model, with a quartz-and feldspar-rich wet, weak, and viscously flowing lower crust sandwiched between a strong, brittle upper crust and a dry, strong, brittle upper mantle with olivine rheology (e.g.…”

Multiple Stage Ore Formation in the Chadormalu Iron Deposit, Bafq Metallogenic Province, Central Iran: Evidence from BSE Imaging and Apatite EPMA and LA-ICP-MS U-Pb Geochronology

“…However, leached REE were incorporated into other mineral inclusions, LREE preferentially incorporate into monazite and HREE into xenotime ( Figure 13) Similar REE-depleted, dark domains within apatite, accompanied by monazite inclusions, are reported by [53] from the Kirunavaara deposit, northern Sweden. The occurrence of fine monazite and/or xenotime inclusions in apatite and its grain boundaries have also been reported from metamorphosed rocks (e.g., [14,59,60]). The occurrence of monazite and xenotime in REE-depleted apatites has been observed in some other Bafq district magnetite-apatite deposits [18,20,28,35,36,52].…”

Stability and isotopic dating of monazite and allanite in partially molten rocks: examples from the Central Alps

“…Despite the variable compositions of the protoliths, the newly formed partial melts are relatively similar in composition (Johannes & Holtz 1996 and literature therein). A better understanding of the stability of allanite and monazite requires new thermodynamic data (Janots et al 2007), but petrographic data on natural samples are also helpful (e.g., Petrik et al 1995;Franz et al 1996;Förster 1998;Förster et al 1999;bea & Montero 1999;broska et al 2000).…”