HR: 1330h
AN: T42A-0281    [PDF]
TI: Physical Properties of the Interface between a Mineral Inclusion and the Host Mineral: Monazite Inclusions in Fluorapatite
AU: * Harlov, D E
EM: dharlov@gfz-potsdam.de
AF: GeoForschungsZentrum, Section 4.1 Experimental Geochemistry and Mineral Physics Telegrafenberg, Potsdam, D-14473 Germany
AU: Wirth, R
EM: wirth@gfz-potsdam.de
AF: GeoForschungsZentrum, Section 4.1 Experimental Geochemistry and Mineral Physics Telegrafenberg, Potsdam, D-14473 Germany
AU: Foerster, H
EM: forhj@gfz-potsdam.de
AF: GeoForschungsZentrum, Section 4.1 Experimental Geochemistry and Mineral Physics Telegrafenberg, Potsdam, D-14473 Germany
AU: Foerster, H
EM: forhj@gfz-potsdam.de
AF: Institute of Earth Sciences, University of Potsdam, Potsdam, D-14415 Germany
AB: The (Y+REE) chemistry of many metamorphic and igneous rocks is primarily controlled by phosphate-bearing accessory minerals such as fluorapatite and monazite. Studies of natural fluorapatite (Harlov and Foerster (2002) J Petrol 43, 801) as well as experimental investigations of chlorapatite (Harlov et al. (2002) Am Mineral 87, 245) and fluorapatite (Harlov et al. (2003) Am Mineral, 88, 1209) indicate that Th- and U-poor monazite, as inclusions in apatite, originate from the (Y+REE) budget available in the apatite as a product of mass transfer during fluid-triggered metasomatic alteration. Monazite inclusions form only in metasomatized regions of the apatite which have undergone fluid-induced dissolution-reprecipitation of the original apatite (Putnis (2002), Min Mag 66, 689) generally to an altered composition lower in (Y+REE+Na+Si). Dissolution-reprecipitation also results in a large increase in the micro-porosity throughout the metasomatized areas. The micro-pores provide natural nucleation sites for the growth of monazite inclusions via dissolution-precipitation as well as provide natural pathways for fluid movement and mass transfer throughout these metasomatized regions. TEM investigation of monazite inclusions in fluorapatite crystallized from late stage evolved magmas (Kiruna magnetite-apatite ore deposit, N. Sweden; Harlov et al. (2002) Chem Geol 191, 47) and in fluorapatite metamorphosed under granulite facies conditions in the presence of low H$_{2}$O activity fluids (Val Strona traverse, Ivrea-Verbano Zone, N. Italy; Harlov and Foerster (2002) J Petrol 43, 769), indicate that the interface between the monazite inclusion and the fluorapatite host tends to consist of either a 10-50 nm thick, continuous, amorphous layer surrounding the entire inclusion or a series of small, isolated voids, 10 - 20 nm in size, randomly scattered along the contact between the monazite inclusion and the surrounding host. These voids most likely represent fluid pathways. Chemically, the monazite inclusions are characterized by an enrichment in Cl along their rims in contact with the amorphous interface suggesting the presence of Cl-rich fluids. The composition of the amorphous layer consists of elements generally incompatible with the crystal chemistry of Th- and U-poor monazite. These include predominantly SiO$_{2}$ followed by MgO, FeO, CaO, and F; in essence all by-product elements not required by the monazite grains during metasomatically induced growth.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3630 Experimental mineralogy and petrology
DE: 3660 Metamorphic petrology
DE: 3900 MINERAL PHYSICS
DE: 3947 Surfaces and interfaces
SC: Tectonophysics [T]
MN: 2003 Fall Meeting