The effect of amphibolite facies metamorphism on the U-Th-Pb geochronology of accessory minerals from meta-carbonatites and associated meta-alkaline rocks

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Conditions for Early Cretaceous emerald formation at Dyakou, China: fluid inclusion, Ar-Ar, and stable isotope studies

The Dyakou emerald occurrence is located in Malipo County in the province of Yunnan, southern China. The occurrence lies in the northern part of the Laojunshan-Song Chay metamorphic core complex, which is exposed in an area of approximately 2,000 km2 and extends across the border between China and Vietnam. Emerald mineralization is hosted by pegmatite and associated quartz veins that intrude deformed Proterozoic biotite-muscovite granofels and schist. Hydrogen and oxygen isotope results from the emerald channel waters and emerald, respectively, are consistent with an igneous fluid source. The δ18O fractionation between emerald and quartz yields vein temperatures of 365° to 420°C. Fluid inclusions indicate that the emerald precipitated from saline brines ranging from almost pure water to 10.5 mass percent NaCl equiv. Fluid inclusion isochores intersected with δ18O data yield pressures changing along the geothermal gradient from 1,500 to 3,300 bars. Ar-Ar geochronology of biotite and muscovite from the emerald veins yields consistent ages of 124 ± 1 Ma. These constraints combined with field observations indicate that the Dyakou emerald deposit is consistent with the igneous-related model for emerald formation

Interfaces in metamict titanite: the macroscopic mechanical properties after stepwise annealing

Elastic material properties of metamict titanite (sample E2312) during thermally induced stepwise recrystallization are measured using nanoindentation. Changes of the elastic modulus (E) and the hardness (H) are related to increasing long-range order and vanishing amorphous interface areas. Metamict titanite shows H and E values close to titanite glass. H decreases on annealing until ca. 950 K to 9.08 GPa and increases at higher temperatures, while E increases continuously on annealing up to ca. 168.4 GPa at 1220 K. Crystalline titanite from Rauris shows strong anisotropy and H and E values are clearly larger than those of E2312