Monazite as a monitor of melting, garnet growth and feldspar recrystallization in continental lower crust

Abstract

Monazite is a common accessory phase in felsic granulite ribbon mylonites exposed in the Upper Deck domain of the Athabasca granulite terrane, western Canadian Shield. Field relationships, bulk rock geochemistry and phase equilibria modelling in the Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 -Fe 2 O 3 system are consistent with the garnet-rich rocks representing the residual products of ultrahigh temperature melting of biotite-bearing paragneisses driven by intraplating of mafic magma in continental lower crust. The c. 2.64-2.61 Ga Y-rich resorbed monazite cores included in garnet are interpreted as relicts of detrital grains deposited on the Earth's surface after c. 2.61 Ga. Yttrium-poor monazite domains in garnet are depleted in Sm and Gd and linked to fluid-absent melting of biotite + plagioclase + quartz AE sillimanite during a prograde loading path from ≤0.8 to ≥1.4 GPa. The c. 2.61-2.55 Ga Y-depleted, Th-rich monazite domains crystallized in the presence of garnet + ternary feldspar AE orthopyroxene + peraluminous melt. The c. 2.58-2.52 Ga monazite rims depleted in Th + Ca and enriched in Eu are linked to localized melt extraction synchronous with growth of high-pressure (HP) grossular-rich garnet at the expense of plagioclase during crustal thickening, culminating at >950°C. Re-heating and dextral transpressive lower crustal reactivation at c. 1.9 Ga resulted in syn-kinematic growth of (La + Ce)-enriched monazite and a second generation of garnet, concurrent with recrystallization of feldspar and orthopyroxene at 1.0-1.2 GPa and 600-700°C. Monazite grains in this study are marked by positive Eu-anomalies relative to chondrite. A direct link is implied between Y, Sm, Eu and Gd in monazite and two major phases in continental lower crust: garnet and plagioclase. Positive Eu-anomalies in lower crustal monazite associated with modally abundant garnet appear to be directly related to Eu-enrichment and depletions of Y, Sm and Gd that are consequences of garnet growth and plagioclase breakdown during HP melting of peraluminous bulk compositions.

Phase equilibria modelling of residual migmatites and granulites: An evaluation of the melt‐reintegration approach

“…This issue was circumvented by reintegrating a certain amount of melt to the residuum composition and by performing phase equilibria modelling of the new model protolith composition to reconstruct the probable prograde history (see White, Powell, & Halpin, ). The melt‐reintegration approach has become an increasingly routine method among metamorphic petrologists and various ways of calculating and reintegrating the extracted melt have been developed and applied (Anderson, Kelsey, Hand, & Collins, ; Boger, White, & Schulte, ; Cai et al., , ; Chen, Ye, Liu, & Sun, ; Diener, White, & Hudson, ; Diener, White, Link, Dreyer, & Moodley, ; Diener, White, & Powell, ; Dumond, Goncalves, Williams, & Jercinovic, ; Fitzherbert, ; Groppo, Rolfo, & Indares, ; Groppo, Rolfo, & Mosca, ; Groppo, Rubatto, Rolfo, & Lombardo, ; Guilmette, Indares, & Hébert, ; Hallett & Spear, ; Hasalová et al., ; Jiang et al., ; Kelsey & Hand, ; Kohn, ; Korhonen, Brown, Clark, & Bhattacharya, ; Indares, White, & Powell, ; Lasalle & Indares, ; McGee, Giles, Kelsey, & Collins, ; Morrissey, Hand, Kelsey, & Wade, ; Nahodilová, Faryad, Dolejš, Tropper, & Konzett, ; Nicoli, Stevens, Moyen, & Frei, ; Palin et al., ; Redler, White, & Johnson, ; Shrestha, Larson, Guilmette, & Smit, ; Skrzypek, Štípská, & Cocherie, ; Štípská, Schulmann, & Powell, ; Taylor, Nicoli, Stevens, Frei, & Moyen, ; Tian, Zhang, & Dong, ; Tucker, Hand, Kelsey, & Dutch, ; Wang & Guo, ; White et al., ; Yakymchuk et al., ; Yin et al., ; Zhang et al., ; Zou et al., ). Furthermore, the reconstruction of a plausible protolith composition is essential to assess the likely melt productivity of rocks (White et al., ) which, in turn, allows the potential role of loss and redistribution of melt in the evolution of the deeper crust to be explored (Diener & Fagereng, ; Diener et al., ; Korhonen, Saito, Brown, & Siddoway, ; Korhonen et al.,…”

Using monazite and zircon petrochronology to constrain the P–T–t evolution of the middle crust in the Bhutan Himalaya

“…The high concentrations of Th and U in the monazite mantle support a suggestion of crystallization in the presence of melt (e.g. Dumond et al ., ). The mantles are slightly enriched in HREE and are characterized by low Gd/Lu ratios (100–400, Fig.…”

“…There has been recent concerted effort into linking ‘age’ to ‘stage’ using trace elements as reaction ‘fingerprints’ (e.g. Möller et al ., ; Rubatto et al ., , ; Dumond et al ., ; Holder et al ., ).…”

Speculations Linking Monazite Compositions to Origin: Llallagua Tin Ore Deposit (Bolivia)

“…The LA-ICP-MS data are difficult to evaluate due to the lack of the Sm measurement, but the electron microprobe results suggest the grains record a positive Eu anomaly. Monazite with positive Eu anomalies has been reported from banded iron formations [44], carbonatites [87], lower crustal rocks [88,89], and in metamorphic rocks as inclusions in plagioclase [90]. Fluids with strongly positive Eu anomalies are characteristic of highly reducing conditions [91][92][93][94], including back arc basin settings like the Llallagua deposit [95].…”