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• U-Pb zircon and titanite dating yield a ca. 3.35 Ga age for the Bahalda Pluton. • U-Pb fluorapatite ages of ca. 3.27–3.05 Ga record metamorphic / hydrothermal event(s). • The fluorapatite and titanite trace element chemistry record a detailed magmatic and post-magmatic evolution. • Some of Earth's oldest known bedrock apatite U-Pb ages indicate an undisturbed crustal history for over 3 Gyr. The Archean Bahalda Pluton (Singhbhum Craton, eastern India) is an I-type mafic granodiorite, surrounded by Paleoarchean TTG and TTG-derived granites of the Singhbhum Suite. The Singhbhum Suite is highly unusual amongst Eo- and Paleo-Archean terranes because most of the Singhbhum Craton escaped post-Archean deformation and metamorphism. The Bahalda granodiorite contains accessory zircon, titanite, and fluorapatite, which are rarely studied together but are a powerful tool for exploring magmatic and post-magmatic processes. U-Pb zircon and titanite dating indicate a ca. 3.35 Ga emplacement age of the Bahalda granodiorite. Subsequent ca. 3.27–3.05 Ga U-Pb fluorapatite ages are interpreted as recording low-grade metamorphic or hydrothermal event(s). The Bahalda fluorapatite and titanite are LREE-enriched compared to the HREE. The complex zonation of fluorapatite suggests that primary igneous fluorapatite was recrystallised with the removal of REE and overgrown by REE-depleted rims. This is in agreement with the apatite trace element systematics which imply fluorapatite cores are of mafic I-type granitoid affinity, with rims of low- and medium-grade metamorphic / metasomatic affinity. No textural evidence of titanite alteration was detected, but some domains have minor REE depletion compared to crystal interiors. The titanite and fluorapatite data display similar trends in LREE vs Sr/Y space due to metamorphic/hydrothermal alteration. The evolution of the Bahalda Pluton, which did not exceed greenschist facies for 3 Gyr, invites comparison with other stabilized cratons from the Mesoarchean. [ABSTRACT FROM AUTHOR]

Phosphates from the Martian shergottite NWA 2975 were used to obtain insights into the source and subsequence differentiation of the melt/melts. The crystallization of two generations of fluorapatite (F > Cl~OH and F-rich), chlorapatite and ferromerrillite-merrillite were reconstructed from TEM (Transmission Electron Microscopy) and geochemical analyses. The research results indicated that the recognized volatiles budget of the two generations of fluorapatite was related to their magmatic origin. The apatite crystals crystallized from an evolved magma during its final differentiation and degassing stage. In turn, chlorapatite replaced ferromerrillite-merrillite and was not related to, mantle-derived shergottite magma. The relationship between merrillite and apatite indicates that apatite is most probably a product of merrillite reacting with fluids. REE (rare earth elements) pattern of Cl-apatite might point to an origin associated with exogenous fluids mixed with fluids exsolved from evolved magma. The study shows that, among the three types of apatite, only the fluorapatite (F > Cl~OH) is a reliable source for assessing the degree of Martian mantle hydration. The occurrence of apatite with merrillite requires detailed recognition of their relationship. Consequently, the automatic use of apatite to assess the water content of the magma source can lead to false assumptions if the origin of the apatite is not precisely determined. [ABSTRACT FROM AUTHOR]

We combined the focused ion beam sample preparation technique with polarized synchrotron-based FTIR (Fourier transform infrared) spectroscopy, laser-Raman spectroscopy, electron microprobe analysis ( EMPA), and transmission electron microscope ( TEM) analysis to identify and quantify structurally bound OH, F, Cl, and CO3 groups in fluorapatite from the Northwest Africa 2975 ( NWA 2975) shergottite. In this study, the first FTIR spectra of the OH-stretching region from a Martian apatite are presented that show characteristic OH-bands of a F-rich, hydroxyl-bearing apatite. Depending on the method of apatite-formula calculation and whether charge balance is assumed or not, the FTIR-based quantification of the incorporated OH, expressed as wt% H2O, is in variably good agreement with the H2O concentration calculated from electron microprobe data. EMP analyses yielded between 0.35 and 0.54 wt% H2O, and IR data yielded an average H2O content of 0.31 ± 0.03 wt%, consistent with the lower range determined from EMP analyses. The TEM observations implied that the volatiles budget of fluorapatite is magmatic. The water content and the relative volatile ratios calculated for the NWA 2975 magma are similar to those established for other enriched or intermediate shergottites. It is difficult to define the source of enrichment: either Martian wet mantle or crustal assimilation. Comparing the environment of parental magma generation for NWA 2975 with the terrestrial mantle in terms of water content, it displays a composition intermediate between enriched and depleted MORB. [ABSTRACT FROM AUTHOR]

Apatites from Martian nakhlites NWA 10153 and NWA 10645 were used to obtain insight into their crystallization environment and the subsequent postcrystallization evolution path. The research results acquired using multi-tool analyses show distinctive transformation processes that were not fully completed. The crystallization history of three apatite generations (OH-bearing, Cl-rich fluorapatite as well as OH-poor, F-rich chlorapatite and fluorapatite) were reconstructed using transmission electron microscopy and geochemical analyses. Magmatic OH-bearing, Cl-rich fluorapatite changed its primary composition and evolved toward OH-poor, F-rich chlorapatite because of its interaction with fluids. Degassing of restitic magma causes fluorapatite crystallization, which shows a strong structural affinity for the last episode of system evolution. In addition to the three apatite generations, a fourth amorphous phase of calcium phosphate has been identified with Raman spectroscopy. This amorphous phase may be considered a transition phase between magmatic and hydrothermal phases. It may give insight into the dissolution process of magmatic phosphates, help in processing reconstruction, and allow to decipher mineral interactions with hydrothermal fluids. [ABSTRACT FROM AUTHOR]