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|Title:||Experimental alteration of monazite in granitic melt: Variable U–Th–Pb and REE mobility during melt-mediated coupled dissolution-precipitation|
|Citation:||Chemical Geology, 2020; 544:1-16|
|Jan Varga, Tom Raimondo, Nathan R.Daczko, John Adam|
|Abstract:||Monazite U–Th–Pb geochronology of high-temperature and melt-bearing metamorphic rocks sometimes produces a continuum of concordant ages (‘smear’) without well-defined age populations. In combination with textural and geochemical criteria, these datasets are typically interpreted to infer either variable Pb-loss between two discrete events or protracted metamorphism lasting >50 Myr. We experimentally react monazite with granitic melt (0.7 GPa and 750 °C) to produce a range of complex monazite textures and age patterns similar to those found in natural high-temperature rock samples. Our observations show that within a short duration (≤24 h experiment time), variable REE, Y, Th, U and Pb mobility is achieved via coupled dissolution-precipitation in a melt-bearing system. An ultra-local interface melt is saturated in dissolved components, including the U–Th–Pb isotopic character of the original monazite, such that newly precipitated monazite may copy or partly inherit the age of a precursor grain. This implies that monazite grown via coupled dissolution-precipitation may not faithfully record the age or duration of metamorphism in melt-bearing rocks typical of a variety of geodynamic settings.|
|Keywords:||Monazite; experimental petrology; U–Th–Pb; coupled dissolution-precipitation; metamorphism|
|Rights:||© 2020 Elsevier B.V. All rights reserved.|
|Appears in Collections:||Geology & Geophysics publications|
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