Mineralogy and Petrology最新文献

The origin of magmatic microgranular enclaves has been investigated in the Mesoproterozoic granitoid Krasnopol intrusion (1.5 Ga), part of the AMCG (anorthosite–mangerite–charnockite–granite) Mazury Complex in the East European Craton (NE Poland). The granitoids are ferroan and metaluminous, and display the typical characteristics of A-type granites, with high contents of Zr, Nb, Ga and rare earth elements (REEs). The enclaves are metaluminous and have a broad compositional range with two groups distinguished: silica-poor (45–50 wt% SiO₂) and silica-rich (54 to 59 wt% SiO₂), the latter overlapping in composition with the granitoid samples. The silica-poor enclaves are enriched in REEs compared to the silica-rich type, while the silica-rich enclaves exhibit trace-element patterns similar to those of the granitoids. Initial whole rock ε_Nd values range between -3.8 and -4.0 for the granitoids and give a slightly wider range from -2.6 to -3.8 for the enclaves. The ⁸⁷Sr/⁸⁶Sr initial values vary from 0.7084 to 0.7138 for the granitoids and between 0.7052 and 0.7075 for the enclaves and indicate that the granitoids and enclaves are not isotopically identical. These may suggest that the two magmatic systems represented by the granitoid host rock and the enclaves, were probably derived from different sources, but with sufficient interaction, which led to a progressive change in the composition of the enclaves towards intermediate composition. We suggest that the mafic melts of the enclaves were generated at the base of the thickened crust through partial melting of the lower crustal source, with a significant contribution from mantle material. The increase in temperature resulted in anatexis of the lower crust and the formation of the granitoid parental magma.

The ca. 480 Ma Albești granite (Southern Carpathians, Romania) is characterized by the presence of color zoned blue quartz grains, and is part of the rather extensive European Cambro-Ordovician blue quartz landscape. The color is heat sensitive, fading at temperatures as low as 300℃, inconsistent with the thermally stable, light scattering, nanometric rutile/ilmenite inclusions cited in literature. Extensive X- and Q-band electron paramagnetic resonance (EPR) investigations were carried out, searching for distinctive features of the Albești quartz that are directly or indirectly involved in the generation of the blue coloration. The analyzed quartz grains were extracted from three granite samples of varying coloration and anisotropy, and the quartz from each rock sample was further separated into colored and colorless fractions. The paramagnetic E’ and [AlO₄]⁰ centers, as well as Mn²⁺ ions localized in traces of amorphous associated minerals at grain boundaries or fissure planes, were observed in all quartz samples. Broad EPR lines associated with the presence of magnetic clusters were observed in the spectra of the white quartz sample and the corresponding colorless one. Isochronal annealing up to 500℃ induced the correlated recombination of the E’ and [AlO₄]⁰ centers, the strong decrease of the Mn²⁺ spectrum and the formation of a minority iron oxide phase at the grain boundaries and/or fissure planes. The EPR signature was similar for the colored and the corresponding colorless quartz samples, before and after annealing, showing that the heat sensitive coloration of the Albești quartz does not directly involve the presence of paramagnetic defects and/or minority magnetic phases.

Seven experiments exploring the reaction of titanite with various hydrothermal solutions have been carried out at 700 °C and 200 MPa for a run duration of 16 days. In experiments involving fluids consisting of NaCl+H₂O, KCl+H₂O, CaCl₂+H₂O, 2M NaOH, or 2M KOH, no reaction of the titanite with the fluid was observed other than a slight dissolution of the titanite. Experiments involving NaF+H₂O and Ca(OH)₂+H₂O resulted in visible alteration of the titanite in texture and composition, coupled with the formation of perovskite. In the NaF+H₂O experiment, perovskite, enriched with rare earth elements (REE), formed as euhedral to subhedral crystals on the surface of the recrystallized titanite. In the Ca(OH)₂+H₂O experiment perovskite took in minor amounts of REE, and formed as a reaction rim partially replacing the titanite via a coupled dissolution-reprecipitation reaction. Wollastonite, along with minor calcite, and grossular garnet, formed as an outer rim on the perovskite. In the NaF+H₂O experiment major and trace elements were leached from the titanite, whereas in the Ca(OH)₂+H₂O experiment no leaching of major or trace elements was observed. Nb/Ta, Th/U, and Y/Ho were investigated as potential indicators of hydrothermal processes. While the Nb/Ta ratio was altered in the experimentally metasomatised titanite, the degree of alteration was the same for both fluids. In contrast, only small changes in the Th/U and Y/Ho ratios between the altered and original titanite were seen for either experiment. The formation of perovskite at the expense of titanite in NaF+H₂O or Ca(OH)₂+H₂O fluids demonstrates how titanite reacts with these fluids in simple, low silica activity systems under mid to upper crustal P-T conditions.

The Eocene Rasht-Abad volcanic rocks are located in the Alborz-Azerbaijan magmatic belt (including the Tarom-Hashtjin province) of NW Iran. Those are mainly mafic to intermediate with calc-alkaline affinities, comprising andesite, andesite-basalt, trachy-andesite, and dacite. Clinopyroxene ranging in composition from diopside to augite is the most significant mafic mineral of the basic rocks. Aluminum partitioning between tetrahedral and octahedral sites shows that those crystalized at low pressure. Ferric iron of clinopyroxene also indicates high oxygen fugacity for formation of crystal. Geothermobarometry using clinopyroxene-melt equilibrium calculations constrains the crystallization temperature and pressure of this mineral as 1100–1200 °C and 2–6 kbar. Ce/Pb values of the mafic lavas are lower than values expected for mantle-derived melts but do not support crustal contamination. Co-existing basalt to trachyandesite lavas display parallel and tight REE patterns that suggest these rocks originated from a common mantle source or parental magma. Tectonomagmatic discrimination diagrams and mineral compositions are consistent with the host volcanic rocks having the characteristics of continental margin arcs. Geochemical data are consistent with the parental magma of mafic-intermediate rocks of Rasht-Abad area being derived from a typical subcontinental lithospheric mantle which was enriched by subducted slab-derived fluids and melts during tectonic events in the active continental margin. The data support a model of Eocene flare-up magmatism associated with rollback of a flattened slab.

In this study, laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA–MC–ICP–MS) of apatites and LA–ICP–MS of zircons are used to collect U–Pb geochronological data, Rb–Sr isotope chronology is used to analyze alkaline feldspar and plagioclase, and archival apatite geochemistry data for the exposed Naitoushan basalt and Heishigou dike in the Changbaishan Tianchi volcano (CTV) are accessed to examine the petrogenesis and determine the origin of basaltic magmatism in the CTV. The Naitoushan basalt and Heishigou dike formed at 22.2–18.7 and 0.230–0.218 Ma, respectively. In situ oxides, volatiles, trace element geochemistry and Sr–Nd isotopes of apatite are reported for two samples. Most apatites are in the early crystallization phase and form inclusions in plagioclase that are euhedral or subhedral. They have higher MgO and K₂O/Na₂O concentrations; lower F and Cl concentrations; Ba, Sr, Nb, Ta, Zr, Hf, K, and Ti depletion; and Th, U, Ce, Pb, P, and Nd enrichment. All apatite samples are enriched in light rare earth elements (REEs) relative to heavy REEs and have relatively homogeneous Th/U, Zr/Hf, La/Sm, and Nd/Tb ratios and Sr–Nd isotopic compositions; thus, their host magmas potentially have the same magmatic origin as oceanic island basalt. The apatite La, Yb, and U contents, Eu/Eu* and La/Yb values, and high REE contents show a weak crystallization sequence in the mafic magma. This study demonstrates that the pre-shield and post-shield mafic magmas in the CTV were likely derived from an enriched mantle source with an I-type signature related to the rollback of the Pacific plate.

The Murun massif (Aldan shield, Russia) is particularly intriguing due to its group of alkali Ca-(K)-(Na) silicates, which includes many new and rare species. Additionally, it is also of interest for its beryllium mineralization. One of the unique beryllium Ca-(K)-(Na) silicates, odintsovite K₂Na₄Ca₃Ti₂Be₄Si₁₂O₃₈, was investigated in this study. The aim of this study is to provide new insights into the crystal chemistry and spectroscopic properties of odintsovite. DFT modelling was used to interpret the experimental IR and Raman spectra. Determining the crystal-chemical formula of odintsovite is challenging due to the presence of atoms in different structural positions with varying valence states. The distribution of cations was determined by combining electron probe microanalysis with the results of crystal structure refinement. Luminescence of Eu³⁺ was observed in odintsovite upon excitation at around 532 nm. Analysis of the luminescence band splitting is related to the 4f–4f transitions in Eu³⁺ ions. Additionally, upon excitation at around 370 nm, luminescence with a peak at around 410 nm, associated with 5d–4f transitions in Ce³⁺ ions, was observed.