Porosity Distribution Simulation and Impure Inclusion Analysis of Porous Crystal Layer Formed via Polythermal Process

In this work, we investigated the porosity distribution and separation property of the porous crystal layer formed via the polythermal process. The proposed porosity distribution model, considering both the cooling profile and the crystal settling effect, provided simulative results that met the MRI analysis experimental results with suitable agreement. Significant porosity variation from the top to the bottom of the crystal layer (ϕ from 0.75 to 0.55 under rapid cooling profile) was detected. Meanwhile, the vertical supersaturation degree gradient induced by the fluid fluctuation could impact nucleation and crystal growth kinetic along with crystal particle settling. The resulting crystal layer possessed various impurity inclusion conditions. Under a moderate cooling profile (0.4 K·min−1), the volume fraction of closed pores against overall pores decreased from 0.75 to 0.36. The proposed model and experimental analysis approach were demonstrated to be helpful for porosity distribution simulation and impure inclusion analysis of layer crystallization.

Felsic Mineral Inclusions in Zircon from the Port Leyden Nelsonite, Western Adirondack Highlands, New York: A Product of Magma Mixing?

The Port Leyden nelsonite is small magnetite-apatite-ilmenite ore body occurring in Mesoproterozoic metapelitic gneiss on the western margin of the Adirondack Highlands. It is unusual in that no compositionally adequate parent magma (e.g. jotunite or oxide-apatite gabbronorite) has been identified in the area (Darling and Florence, 1995).The nelsonite typically contains elevated levels of Zr (1400 to 2500 ppm) largely present in abundant modal zircon. The Zr abundances are considerably higher than normal levels of Zr solubility in non-peralkaline melts and suggests that some of the zircon modal fraction is inherited (Hanchar and Harrison, 2003).The zircon grains display both euhedral, oscillatory zoned cores (interpreted as igneous) and anhedral, irregular, compositionally homogeneous rims (interpreted as metamorphic or igneous). The oscillatory zoned cores contain small (2-10 micrometer), solid inclusions that have energy-dispersive X-ray spectra (EDS) consistent with quartz, K-feldspar, plagioclase, biotite, and apatite. Remarkably, no low-silica mafic mineral inclusions (e.g. orthopyroxene, clinopyroxene, olivine) were observed in zircon.Felsic mineral inclusions in zircon from an igneous rock that has mafic magma affinities provides further evidence that the included cores of zircons in the Port Leyden nelsonite are inherited. This unusual occurrence may be possible considering that the mafic igneous rocks described above are part of the bimodal anorthosite-mangerite-charnockite-granite (AMCG) magmatic complex in the Adirondacks (McLelland et al, 1988). It is conceivable that during magma mixing, zircon from granite or charnockite may have become incorporated into coeval jotunite or oxide-apatite gabbronorite. Subsequently, the latter magma experienced either unmixing (Philpotts, 1967) or crystal settling (Dymek and Owens, 2001) to produce the Port Leyden nelsonite.