Chondritic meteorites, consisting of the materials that have formed in the early solar system (ESS), have been affected by late thermal events and fluid activity to various degrees. Determining the timing of fluid activity in ESS is of fundamental importance for understanding the nature, formation, evolution and significance of fluid activity in ESS. Previous investigations have determined the relative ages of fluid activity with short-lived isotope systematics. Here we report an absolute 207Pb/206Pb isochron age (4,450±50 Ma) of apatite from Dar al Gani (DaG) 978, a type ∼3.5, ungrouped carbonaceous chondrite. The petrographic, mineralogical and geochemical features suggest that the apatite in DaG 978 should have formed during metamorphism in the presence of a fluid. Therefore, the apatite age represents an absolute age for fluid activity in an asteroidal setting. An impact event could have provided the heat to activate this young fluid activity in ESS.
Two species of X-site-vacant tourmalines, foitite and rossmanite, occur in the Koktokay No. 3 granitic pegmatite dyke, Altai, northwestern China, a spodumene-subtype pegmatite. Foitite-schorl crystals develop as fillings in the interstices among Fe-rich dravite crystals in the endocontact zone between the pegmatite dyke and the metagabbro country-rock. The evolution of the tourmaline crystals in the endocontact zone occurred in two stages. The first stage is typified by the formation of Fe-rich dravite with variable compositions described by substitutions
The Yichun topaz-lepidolite granite is the youngest and most evolved unit of the Yichun granitic complex, southern China, and is well known by virtue of the unusual development of Ta-Nb-Li mineralization and enrichment in cesium in a granite. Three petrographic zones are recognized from the bottom upward: K-feldspar-rich facies, albite-rich facies, and albite-and K-feldsparrich facies. The Cs contents increase with fractional crystallization of the magma, and reach a maximum in the middle part of the albite-rich facies (1709 ppm). Two principal carriers of Cs are observed in this facies: pollucite and the Cs-dominant analogue of polylithionite. In the middle part of this facies, both minerals occur as small inclusions within quartz or K-feldspar phenocrysts, indicative of a magmatic origin. However, in the upper part of this facies, pollucite appears interstitially among tabular crystals of albite around K-feldspar phenocrysts, suggesting that this type of pollucite postdates the rock-forming minerals, but formed prior to complete crystallization of the silicate melt. In addition, Cs-rich replacement zones typify the rim of lepidolite flakes in the groundmass. Lepidolite may contain up to 25.8 wt% Cs 2 O, or ~0.9 Cs apfu (based on O = 11). Such lepidolite may be considered a Cs-dominant analogue of polylithionite. According to their distribution and compositional characteristics, pollucite and the Cs-dominant analogue of polylithionite seem to have formed at the late-magmatic or magmatic to hydrothermal transition stage of evolution of the leucogranitic magma at Yichun.
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