Monazite geochronology in melt-percolated UHP meta-granitoids: An example from the Erzgebirge continental subduction wedge, Bohemian Massif

0539597 - GFÚ 2022 RIV NL eng J - Journal Article
Závada, Prokop - Štípská, P. - Hasalová, P. - Racek, M. - Jeřábek, P. - Schulmann, K. - Kylander-Clark, A. - Holder, R.
Monazite geochronology in melt-percolated UHP meta-granitoids: An example from the Erzgebirge continental subduction wedge, Bohemian Massif.
Chemical Geology. Roč. 559, January (2021), č. článku 119919. ISSN 0009-2541. E-ISSN 1872-6836
Institutional support: RVO:67985530
Keywords : monazite * Erzgebirge (U)HP province * REE * granulite * coesite * thorium
OECD category: Geology
Impact factor: 4.685, year: 2021
Method of publishing: Open access
https://www.sciencedirect.com/science/article/pii/S0009254120304587

Coupled age and trace element mapping in monazite grains using the Laser-Ablation Split-Stream ICP-MS technique was carried out for a sequence of samples from (U)HP crustal section in the Eger Crystalline Complex interpreted as a Variscan continental subduction wedge. The sampled section comprises banded orthogneiss with monazite protolith ages of 486 +/- 3 [10] Ma. The orthogneiss was heterogeneously transformed to migmatite, HP felsic granofels and U(HP) fine-grained Ky-Kfs granulite during coupled deformation and percolation of silicate melts in a subduction channel. Age of the (U)HP metamorphism and related melt percolation in the granulite is dated by Th-rich and HREE-poor monazite cores at 353.6 +/- 2.7[8] Ma, that are in equilibrium with HREE-rich garnets. Th-rich cores of monazites in the migmatite, granofels and granulite that lack the (U)HP signatures show younger ages of 347.8 +/- 3.4[8] Ma, 345.8 +/- 2.4[8] Ma and 339.3 +/- 1.3[7] Ma, respectively. The monazite rims with lower Th and higher HREE contents than the monazite cores are likely a result of (re)crystallization in equilibrium with melt that partly dissolved the HREE-rich prograde garnet during decompression. This (re) crystallization is constrained by ages of 344.2 +/- 1.6[8] Ma in (U)HP granulites and 338-340 +/- [8] Ma in migmatites, granofelses and granulites without the (U)HP signature. The groups of ages from 353 Ma to 338 Ma, are significantly different when only their in-run uncertainties (7-10 Ma) are compared and indicate a 15 +/- 3 Ma period of monazite (re)crystallization from burial/peak to exhumation.
Permanent Link: http://hdl.handle.net/11104/0317305