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Magmatic fluid degassing within shallow magma chambers underneath the ore bodies is critical to the formation of porphyry Cu-Au deposits (PCDs). Yet, it remains unclear how the fluid degassing influences the development of PCDs. Here, geochemical data of apatite, amphibole, and plagioclase from ore-bearing and coeval barren porphyries have been analyzed in Sanjiang metallogenic belt, China. The ore-bearing porphyries normally exhibit high and wide XF/XCl (31.76–548.12) and XF/XOH (0.779–7.370) ratios of apatites, which are evidently higher than those of the barren porphyries (XF/XCl of 1.03–26.58; XF/XOH of 0.686–3.602). Combined with the continuous variation features of Cl/OH ratios and H2O contents of melts calculated by amphiboles, as well as fluid migration models, we constrained the mechanisms of fluid degassing within shallow magma chambers underneath PCDs. There are three different ways of fluid degassing, while only fluid degassing via fluid channel stage can migrate and focus the metal-rich fluids effectively, conducive to the development of PCDs. The mechanisms of magmatic fluid degassing processes are further controlled by the storage depths of magma chambers and initial H2O contents of the magmas revealed by the compositions of amphibole, plagioclase, and thermodynamic modeling. Magmas with shallower storage depths and higher initial H2O contents are more likely to experience extensive and focused fluid degassing, leading to the generation of PCDs. This study demonstrates the potential utility of integrated mineral analyses and thermodynamic modeling for investigating the mechanisms of magmatic fluid degassing in porphyry systems, as well as for identifying prospective buried PCDs. [ABSTRACT FROM AUTHOR]

Small amounts of water (tens to hundreds of parts per million) can have a profound effect on the properties of mantle peridotites, including viscosities, conductivities, and melting temperatures. Measuring the water content of nominally anhydrous minerals (NAMs) has provided insight into the amounts of water contained within mantle rocks. However, converting from NAM water contents to the activity of H2O is non-trivial. Equilibria involving amphibole can be used to determine values of the activity of H2O (aH2O) at the time of mineral equilibration. This approach yields low values of the activity of H2O (<0.3) for four peridotite xenoliths from Southeastern Australia. These four xenoliths also record values of oxygen fugacity (fO2) that range from −0.2 to −1.2 log units below the fayalitemagnetite-quartz buffer. All these values of fO2 are inconsistent with the presence of a CH4-rich fluid (too oxidizing), and the lowest value of oxygen fugacity, as recorded by one sample, is inconsistent with the presence of a CO2-rich fluid. [ABSTRACT FROM AUTHOR]

Kumdykolite is a polymorph of albite that has been predominantly identified within crystallized melt inclusions in high-temperature metamorphic rocks. This study reports a new occurrence of kumdykolite that formed during internal mineral carbonation within amphibole-hosted fluid inclusions in post-collisional hornblendite from the Dabie orogen, central China. Amphibole in the hornblendite trapped CO2-rich fluid inclusions at the magmatic stage, and mineral carbonation, referring to the reaction of mineral rich in divalent cations and CO2 into carbonate, occurred in situ within the fluid inclusions due to the interaction between trapped CO2-rich fluids and host amphibole during cooling of the hornblendite. Kumdykolite was produced along with calcite, dolomite, chlorite, talc, a SiO2 phase (quartz or cristobalite), a TiO2 phase (rutile or anatase), and mica during internal mineral carbonation within the fluid inclusions. It is estimated that kumdykolite in the fluid inclusions crystallized under near-surface conditions, which are significantly different from the conditions of crystallization proposed in previous studies. It is further inferred that kumdykolite may crystallize metastably across the stability field of albite, and the presence of kumdykolite is not indicative of extreme thermobaric and fluid-absent conditions. [ABSTRACT FROM AUTHOR]

Amphibole and pyroxenes are the main reservoirs of rare earth elements (REEs) in the lithospheric mantle that has been affected by hydrous metasomatism. In this study, we developed semi-empirical models for REE partitioning between orthopyroxene and amphibole and between clinopyroxene and amphibole. These models were formulated on the basis of parameterized lattice strain models of mineral-melt REE partitioning for orthopyroxene, clinopyroxene, and amphibole, and they were calibrated using major element and REE data of amphibole and pyroxenes in natural mantle samples from intraplate settings. The mineral-melt REE partitioning models suggest that amphibole is not in equilibrium with coexisting pyroxenes in the mantle samples and that the amphibole crystallized at a lower temperature than that of the pyroxenes. We estimated the apparent amphibole crystallization temperature using major element compositions of the amphibole and established temperature- and composition-dependent models that can be used to predict apparent pyroxene-amphibole REE partition coefficients for amphibole-bearing peridotite and pyroxenite from intraplate lithospheric mantle. Apparent pyroxene-amphibole REE partition coefficients predicted by the models can be used to infer REE contents of amphibole from REE contents of coexisting pyroxenes. This is especially useful when the grain size of amphibole is too small for trace element analysis. [ABSTRACT FROM AUTHOR]

Nb and Ta are geochemical twins, yet their ratio varies considerably in igneous rocks. It is generally supposed that felsic melts coexisting with residual rutile will have elevated Nb/Ta ratios relative to their basalt precursors, which is pivotal to our understanding of deep crustal melting and continent formation throughout Earth's history. This study reports petrological, bulk-rock and mineral geochemical, and Sr-Nd-Mo-Hf isotopic data on Eocene adakitic rocks in central Tibet. These rocks can be petrologically and geochemically divided into an amphibole-bearing high-Nb/Ta and an orthopyroxene-bearing low-Nb/Ta group, which were formed by partially molten eclogitized lower crust based on the geochemistry of their early-crystallized minerals. The two groups have similar Sr–Nd–Hf isotope compositions and abundances of strong incompatible elements, suggesting that their source protoliths share identical compositions. Besides, the values of TiO 2 , Ba, Zr/Sm, and La/Yb are comparable between the two groups of rocks, eliminating the possibility of variations in Nb/Ta-sensitive minerals (e.g., rutile, amphibole, biotite, and titanite) in the source as the cause of their Nb/Ta variation. The contrasting mineral assemblages of the two group rocks, along with the higher Ce/Mo ratios and lower δ98/95Mo values in the low-Nb/Ta group, indicate the source of the low-Nb/Ta contains less water than that of the high-Nb/Ta group. These findings, combined with experimental results and trace element partial melting modeling, lead us to propose that the D rutile Nb/Ta responsible formation of the low-Nb/Ta group is higher than that of the high-Nb/Ta group, due to the decreased water content in the source. Thus, the central Tibetan adakitic rocks provide the first natural example demonstrating that the Nb/Ta ratios in felsic rocks derived from rutile-bearing eclogite depend on the physical conditions of source melting, which are not always higher than the protolith. Our study also highlights the potential of employing Mo isotopes in adakitic rocks to test this hypothesis for those that are not petrologically distinguishable. [ABSTRACT FROM AUTHOR]

The subduction-related Sunda-Banda arc hosts several giant and major Cu–Au–Mo porphyry and epithermal Au systems, making it one of the most important magmatic-related metallogenic belts in Indonesia. They are accompanied by a number of smaller systems, one of which is the recently discovered Randu-Kuning porphyry Cu-Au deposit on Java Island. The present study investigates the geochemical characteristics of this deposit through whole-rock and mineral geochemistry and mineral geothermobarometry, focusing on three sequential dioritic intrusions that make up the host igneous complex, two barren and the third mineralized. Moreover, a comparative analysis is performed between other porphyry deposits in the Sunda-Banda arc and with Grasberg in Papua. This study shows that the older porphyry deposits have mostly similar geochemical characteristics to the younger deposits, suggesting the same magma source, which is mantle-derived oxidized I-type magma. Amphibole geothermobarometry shows that the formation of syn-ore intrusion in the older porphyry was higher in temperature and pressure than those at the younger porphyry. The halogen and oxygen fugacities inferred from biotite and amphibole chemistry indicate an oxidized, water- and halogen-rich melt. Our study shows that combining amphibole and biotite chemistry and whole-rock geochemical data is useful to fingerprint the magmatic-hydrothermal processes, especially where multiple magmatic phases occur. This research also provides valuable insights into the magmatic-hydrothermal physiochemical conditions during the formation of the mineralized system. [ABSTRACT FROM AUTHOR]

This study explores the capability of amphibole in tracing the physicochemical process of magma mixing through spatially associated gabbros, mafic microgranular enclaves (MMEs) and granodiorites from central Tibet. These rocks share similar zircon ages as well as zircon Hf‐O and plagioclase Sr isotopes. However, the amphiboles within the gabbros and granodiorites have different Sr and B isotope compositions, while amphiboles with both heterogeneous isotopic imprints occur in the MMEs. According to data and modeling, significant mixing of two isotopically distinct magmas is recorded by amphibole but not by zircon and plagioclase. Based on a synthesis of petrography, geochemistry and thermobarometry, we interpret this inconsistency by the crystallization order of minerals and propose that magma mixing occurred after the parent magma was emplaced at ∼10 km and cooled to ∼750°C. Our study highlights that amphibole may be a more sensitive tracer of magma mixing relative to other commonly used methods. Plain Language Summary: Magma mixing significantly shapes the composition of silicic igneous rocks representing the major constituent of the upper continental crust. Since bulk‐rock composition may only bear the average of mixed sources, in situ techniques such as Hf‐O isotopes in zircon and Sr‐Pb isotopes in plagioclase are widely used to investigate the details of magma mixing. However, these methods cannot constrain how magma mixing operates in the deep crust. This study novelly uses in situ Sr‐B isotopes and trace elements in amphibole to trace the physicochemical process of magma mixing through spatially associated gabbros, mafic microgranular enclaves and granodiorites from the central Tibetan Plateau. Our data show that significant mixing of two isotopically distinct magmas is recorded by amphibole but not by zircon and plagioclase. We demonstrate that the amphibole geochemistry (i.e., trace element, Sr‐B isotope compositions) may be more sensitive in tracing magma mixing relative to traditional isotopic tools and has the potential to unravel the physicochemical process(es) of magma mixing in the deep crust. In addition, our work reinforces the use of B isotopes in amphibole to discern the nature (fluids released from altered oceanic crust vs. residual slab) of the slab components that metasomatized the supra‐subduction mantle. Key Points: The amphiboles in central Tibetan magmatic complex have contrasting geochemical and Sr‐B isotopic compositionsSignificant magma mixing is well recorded by amphibole but not by zircon and plagioclaseAmphibole is a more sensitive tracer of magma mixing relative to zircon and plagioclase [ABSTRACT FROM AUTHOR]

The Dalaku'an mafic–ultramafic intrusion, located in the western segment of the East Kunlun, presents conducive conditions for the magmatic Cu-Ni sulfide deposits. According to the detailed petrographic observation, the amphiboles within distinct rock types were analyzed by EPMA analysis. The crystallization conditions, such as temperature, pressure, oxygen fugacity, and water content of the magma, were calculated to explore the genesis of the intrusion. The amphiboles were divided into three types: Amp-I, characterized by low silicon content but enrichment of aluminum, titanium, and alkali, predominantly comprising Tschermakitic hornblende and Magnesio-hornblende with mantle-derived traits; Amp-II, exhibiting elevated silicon content but diminished levels of aluminum, titanium, and alkali, primarily constituted of Magnesio-hornblende; whereas Amp-III manifests as Actinolitic hornblende, indicative of crustal origins. The calculated temperatures of amphiboles ranged between Amp-I (955–880) °C, Amp-II (852–774) °C, and Amp-III (761–760) °C; the pressures ranged between Amp-I (454–274) MPa, Amp-II (194–93) MPa, and Amp-III (101–84) MPa; the oxygen fugacities (△NNO) ranged between Amp-I (0.93–2.17), Amp-II (1.55–2.52), and Amp-III (1.89); and the water contents (H2Omelt) ranged from (6.69–8.67) to (5.90–7.32). The magma experienced multiple stages of crystallization and underwent complex magma evolution at different depths. The high oxygen fugacity and water content could be attributed to the subduction of the oceanic crust. The magma source of the Dalaku'an intrusion was metasomatized by fluids from subducting plates, thereby originating within a post-collision extension. [ABSTRACT FROM AUTHOR]

Olivine, the most abundant mineral in the upper mantle, exhibits elastic anisotropy. Understanding the seismic anisotropy and flow patterns in the upper mantle hinges on the crystallographic preferred orientation (CPO) of olivine. Similarly, hydrous minerals, which also display elastic anisotropy, play a crucial role in explaining seismic anisotropy in numerous subduction zones. High-temperature and -pressure simple shear experiments reveal that the CPO of amphibole can lead to significant seismic anisotropy. In this study, peridotite samples originating from the southern end of the Mariana Trench, commonly containing amphibole, were analyzed. The microdeformation fabric and seismic anisotropy were examined. The results indicate a weak fabric strength in olivine, yet identifiable deformation fabrics of A/D, D, and AG were observed. Various dislocation structures suggest that olivine experiences complex deformation across various temperatures. Not only can the original slip system transform, but the melt/fluid resulting from melting also has a substantial impact on the peridotite. Deformation precedes the melt/rock interaction, resulting in a strong melt/rock reaction under near-static conditions. Furthermore, the modal content of amphibole significantly alters the seismic anisotropy of peridotite. An increase in amphibole content (types I, III, and IV) enhances seismic anisotropy, particularly for type I amphibole. Notably, the presence of type I fabric amphibole promotes the Vs1 polarization direction parallel to the trench in subduction zones, a phenomenon observed in other subduction zones. Therefore, when considering mantle peridotite regions rich in amphibole, the impact of amphibole on seismic anisotropy must be accounted for. [ABSTRACT FROM AUTHOR]

Here, we present a petrographic and microanalytical study of microinclusions in chromite from podiform chromitites hosted by the Sartohay ophiolitic mélange in west Junggar, northwestern China, to investigate the parental magma evolution and chromitite genesis. These silicate inclusions comprise olivine, enstatite, diopside, amphibole, and Na-phlogopite. Their morphological characteristics suggest that most inclusions crystallized directly from the captured melt, with a few anhydrous inclusions (olivines and pyroxenes) as solid silicates trapped during the chromite crystallization. Equilibrium pressure–temperature conditions of coexisting enstatite–diopside inclusions are 8.0–21.6 kbar, and 874–1048 °C. The high Na2O and TiO2 contents of hydrous minerals indicate that the parental magma of chromitites was hydrous and enriched in Mg, Na, Ca, and Ti. The calculated Al2O3 content and FeO/MgO ratio of the parental melts in equilibrium with chromite showed MORB affinity. However, the TiO2 values of parental melts, TiO2 contents of chromite, and estimated fO2 values for chromitites (1.3–2.0 log units above the FMQ buffer) evoked parental MORB-like tholeiitic melts. The composition of olivine inclusion was determined, and it was revealed that the primary melts of the Sartohay podiform chromitites had MgO contents of ~22.7 wt %. This aligns with the observed high magnesian signature in mineral inclusions (Fo = 96–98 in olivine, Mg# = 0.91–0.97 in diopside, and Mg# = 0.92–0.97 in enstatite). We propose that Sartohay podiform chromitites initially formed through the mixing/mingling of primary hydrous Mg-rich melt and the evolved MORB-like melt derived from the melt–peridotite reaction in the upper mantle. In this process, the continuous crystallization of chromite captured micro-silicate mineral inclusions, finally leading to the formation of the Sartohay podiform chromitites. [ABSTRACT FROM AUTHOR]

Magnesio-ferri-hornblende, ideally □Ca2(Mg4Fe3+)[(Si7Al)O22](OH)2, is a new mineral of the amphibole supergroup from the Husite granitic complex related to skarn-type Fe-Cu mineralization in the Western Tianshan, Xinjiang, northwestern China. The new species and the new name have been approved by the IMA-CNMNC (2021-100). Magnesio-ferri-hornblende is dark green to green-black with a vitreous luster and a pale gray-green to gray-white streak. It occurs mostly as subhedral-columnar crystals with lengths of 0.5 to 3 mm and shows well-developed {110} cleavage. It has a Mohs hardness of ~5 and a Vickers microhardness of 389–448 kg/mm2 (VHN load in 100 g) and is brittle with a conchoidal fracture. The measured and calculated densities are 3.275(6) and 3.204 g/cm3, respectively. In transmitted plane-polarized light, magnesio-ferri-hornblende is strongly pleochroic, X = pale yellow, Y = yellowish brown, Z = dark yellowish green. It is biaxial (−), α = 1.651(2), β = 1.658(2), γ = 1.662(2), 2V (meas) = 73 (1)° to 82 (1)°, and 2V (calc) = 73.9 (1)°, dispersion is r > v, medium to strong. The orientation is Y||b, X^a = 31.5° (β obtuse), Z^c = 16.5° (β acute). Magnesio-ferri-hornblende is monoclinic, space group C2/m, a = 9.8620(3), b = 18.1060(5), c = 5.30810(10) Å, β = 104.8480(10)°, V = 916.17(4) Å3, Z = 2. The seven strongest lines in the powder X-ray diffraction pattern are [d in Å(I)(hkl)]: 8.397(52)(110), 3.383(41)(150), 2.717(100)(151), 2.597(84)(061), 2.545 (61)(20 2), 1.854(49)(1 7 2), and 1.519(62)(6 2 2). Analysis by a combination of electron microprobe and Mössbauer spectroscopy gave SiO2 47.37, TiO2 1.51, Al2O3 7.07, Fe2O3 3.86, FeO 11.62, MgO 12.77, CaO 11.22, SrO 0.15, MnO 0.39, Na2O 1.54, K2O 0.78, Cl 0.15, F 0, H2Ocalc 2.01, Cl=O −0.03, sum 100.41 wt%. The empirical formula calculated on the basis of 24 (O+OH+F+Cl) with (QH+F+Cl) = 2 apfu is A(□0.62Na0.23K0.15)Σ1.00B(Ca1.76Na0.21Mn0.02Sr0.01)Σ2.00 C (M g 2.79 F e 1.42 2 + F e 0.43 3 + T i 0.17 A l 0.16 M n 0.03 ) Σ 5.00 T (S i 6.94 A l 1.06 ) Σ 8.00 O 22 W (O H 1.96 C l 0.04 ) Σ 2.00. The crystal structure of magnesio-ferri-hornblende was refined to an R1 of 3.95% using 2185 data (>2σ) collected with MoKα X-radiation. The A site is dominantly occupied by □ where A(Na+K+2Ca) ≥0.5. TAl is ordered at the T(1) site. M(1) and M(3) are dominantly occupied by Mg2+, and M(2) is occupied by both Mg2+ and high-charged cations. The new mineral occurs most commonly in the porphyry-skarn Fe-Cu-Mo-Au- and hydrothermal Au-mineralized granitoids with high oxygen fugacity but is rare or absent in barren intrusions. Its finding has important significance for magma fertility discrimination and can potentially be used in regional exploration for porphyry-skarn ore systems. [ABSTRACT FROM AUTHOR]

The first nitridic analog of an amphibole mineral, the quaternary nitridosilicate phosphate Cr5.7Si2.3P8N24 was synthesized under high‐pressure high‐temperature conditions at 1400 °C and 12 GPa from the binary nitrides Cr2N, Si3N4 and P3N5, using NH4N3 and NH4F as additional nitrogen source and mineralizing agent, respectively. The crystal structure was elucidated by single‐crystal X‐ray diffraction with microfocused synchrotron radiation (C2/m, a=9.6002(19), b=17.107(3), c=4.8530(10) Å, β=109.65(3)°). The elemental composition was analyzed by energy dispersive X‐ray spectroscopy. The structure consists of vertex‐sharing PN4‐tetrahedra forming zweier double chains and edge‐sharing (Si,Cr)‐centered octahedra forming separated ribbons. Atomic resolution scanning transmission electron microscopy shows ordered Si and Cr sites next to a disordered Si/Cr site. Optical spectroscopy indicates a band gap of 2.1 eV. Susceptibility measurements show paramagnetic behavior and support the oxidation state Cr+IV, which is confirmed by EPR. The comprehensive analysis expands the field of Cr−N chemistry and provides access to a nitride analog of one of the most prevalent silicate structures. [ABSTRACT FROM AUTHOR]

The major- and trace-element compositions of amphiboles in andesite from Quaternary Yufu Volcano, northeastern Kyushu, Japan were analysed to investigate the generation processes of andesitic magma from Yufu Volcano. The amphiboles in andesite from Yufu volcano can be divided into two groups based on major-element composition: pargasite and magnesio-hornblende. To estimate temperature, pressure, and major- and trace-element compositions of melts in equilibrium with amphiboles, we used the recently proposed methods that can calculate temperature, pressure, major element compositions, and partition coefficients of trace-element between amphibole and melt using only the major-element compositions of amphibole. The estimated temperature, pressure, and major-element composition of melt in equilibrium with the amphibole phenocrysts indicate that each group crystallised under different conditions. These differences suggest that two magma chambers at different depths existed beneath Yufu Volcano and that the andesitic magma of Yufu Volcano was formed by mixing of the two magmas. The trace-element compositions of melts in equilibrium with the pargasite and magnesio-hornblende, estimated by applying the partition coefficients calculated from major-element compositions of amphibole to trace-element compositions of amphiboles, indicate magma derived from slab melt and the partial melting of crustal material, respectively. Because magma is a mixture of minerals and melt, we estimate the chemical compositional ranges of the two end-member magmas on the Y versus SiO2 diagram from the mixing relationship between amphibole and estimated melt, as well as phenocrysts of plagioclase, clinopyroxene, and orthopyroxene. The overlap of the estimated compositional range with the trend of whole-rock composition represents the chemical compositions of the end-members of magma mixing, yielding estimates of the mafic (SiO2 ≈ 45 wt %) and felsic (SiO2 ≈ 68 wt %) end-member magmas. Furthermore, we estimate the concentrations of other elements in the end-member magmas by substituting the estimated SiO2 concentrations of the magmas into linear regression equations between the whole-rock contents of other elements and SiO2. The trace-element compositions of the mafic and felsic end-member magmas, as estimated in this study, have similar features to those of gabbroids and Cretaceous granitic rocks, respectively, that are presumed to lie beneath Yufu Volcano. These similarities could be explained by the possibility that the compositions of the end-member magmas were influenced by basement rocks. [ABSTRACT FROM AUTHOR]

Slave Province in Canada is an Archean granite–supracrustal terrane at the northwestern corner of the Canadian Shield. It is bordered by the Thelon–Taltson orogen (2.0 to 1.9 Ga) to the southeast and the Wopmay orogen (1.9 to 1.8 Ga) to the west. Acasta gneisses, exposed in the westernmost Slave Province, and the Wopmay rocks, located close to the gneisses, were systematically collected for K–Ar and laser step-heating 40Ar/39Ar single-crystal analyses of the biotite and amphibole. The K–Ar biotite ages of the four Wopmay samples range from 1816 ± 18 Ma to 1854 ± 26 Ma. The 40Ar/39Ar biotite analyses of the three Wopmay samples yield plateau ages of 1826 ± 21 Ma, 1886 ± 13 Ma, and 1870 ± 18 Ma. These ages fall within the reported U–Pb zircon age range of the Wopmay orogen. The K–Ar biotite ages of the fifteen Acasta gneisses range from 1779 ± 25 Ma to 1877 ± 26 Ma, except for one younger sample (1711 ± 25 Ma). The 40Ar/39Ar analyses of the biotite crystals from three samples give the plateau ages of 1877 ± 8 Ma, 1935 ± 14 Ma, and 1951 ± 11 Ma. The K–Ar amphibole ages from twelve samples range from 1949 ± 19 Ma to 1685 ± 25 Ma. Two samples of them give ages older than the zircon U-Pb age of Hepburn plutons. The 40Ar/39Ar analyses of the amphibole crystals show varied age relations. The two samples give plateau ages of 1814 ± 22 Ma and 1964 ± 12 Ma. Some samples exhibit apparent old ages of ~2000 Ma in the middle temperature fractions. These old fractions result from the amphibole crystals, originally formed in the Archean, being affected by the thermal events during the Wopmay orogeny but not fully resetting. These observations suggest that the K–Ar system ages of the biotite and amphibole in the Archean Acasta gneiss were rejuvenated during the Paleoproterozoic ages. The Discussion explores the possibility that the heat source rejuvenating the K–Ar system ages may have arisen due to asthenospheric extrusion into the wedge mantle, a process likely triggered by subduction rollback. [ABSTRACT FROM AUTHOR]

This article reports on the recent mining and production status of ruby in Longido, Tanzania. Faceted-grade rubies and their matrix from Longido Area, Tanzania, were investigated by standard gemological testing, including FTIR, UV-VIS, Raman spectra, and LA-ICP-MS. Microscopic observations revealed dense needle-like and triangular inclusions, distinct growth lines, and color banding as typical inclusions. In agreement with the Raman results, the transmission FTIR spectrum confirmed the presence of aluminum hydroxide. The Raman spectra identified associated minerals and inclusions, including zoisite, parasites, feldspar within the matrix, rutile, and diaspore in the ruby host. The chemistry analysis revealed a high amount of Cr and relatively low iron as a good indicator of geographic origin. [ABSTRACT FROM AUTHOR]

Metasomatized mantle xenoliths containing hydrous minerals, such as amphiboles, serpentine, and phlogopite, likely represent the potential mineralogical compositions of the metasomatized upper mantle, where low seismic velocities are commonly observed. This study presents the first experimentally determined single‐crystal elasticity model of an Fe‐free near Ca, Mg‐endmember amphibole tremolite at high pressure and/or temperature conditions (maximum pressure 7.3(1) GPa, maximum temperature 700 K) using Brillouin spectroscopy. We found that sound velocities of amphiboles strongly depend on the Fe content. We then calculated the sound velocities of 441 hydrous‐mineral‐bearing mantle xenoliths collected around the globe, and quantitatively evaluated the roles that amphiboles, phlogopite and serpentine played in producing the low velocity anomalies in the metasomatized upper mantle. Plain Language Summary: Amphiboles are the most widely distributed hydrous minerals resulting from metasomatism in the upper most mantle. We measured sound velocities of tremolite (Ca, Mg endmember of the amphibole series) at high pressures and high temperatures by Brillouin spectroscopy. Based on global hydrous‐mineral‐bearing mantle xenoliths record, we quantitively evaluated the contributions of amphiboles, serpentine, and phlogopite to low velocity anomalies and water storage in the upper most mantle. We found the existence of hydrous minerals (amphiboles, serpentine, and phlogopite) remains a viable explanation for the low velocity anomalies in the upper most mantle (e.g., mid‐lithosphere discontinuity). Compared to serpentine and phlogopite, although the amount of velocity reduction caused by amphibolization is moderate, the formation of amphiboles does not require K, Al, Si‐rich environments like phlogopite, or exceedingly water‐rich environments like serpentine. Key Points: The single‐crystal elasticity of tremolite is determined by Brillouin spectroscopy up to 7.3 GPa and 700 KSound velocities of uppermost mantle amphiboles mainly depend on Fe contentHydrous minerals (amphiboles, serpentine, phlogopite) are plausible causes of the low velocity anomalies in the uppermost mantle [ABSTRACT FROM AUTHOR]

Petrographic and thermobarometric data obtained on a blastolite lens hosted in sheared rocks of the Gonzhinskii block indicate that the lens contains four mineral assemblages: relict, main, an assemblage corresponding to biotitization, and that of retrograde alterations. The relict assemblage was likely eclogitic. The main mineral assemblage corresponds to zoisite amphibolite developing after eclogite. The P−T metamorphic parameters of this assemblage are P = 13.0−15.0 kbar and T = 580−670°C. However, if the calculations are done using the iron richest outer rim of amphibole 1, the P−T parameters are P = 13.0−17.0 kbar and T = 660−780°C. The mineral assemblage corresponding to the overprinted biotitization is clearly distinct texturally. The lines of the monomineral equilibria of the biotite assemblage plotted using various combinations of the composition of the garnet, biotite, and plagioclase well converge within a compact field of P = 12.5−13.2 kbar and T = 810−830°C. The latest assemblage of retrograde minerals includes low-Al amphibole 2. Our original Sm−Nd isotope date were used to calculate an isochron for a whole-rock sample, garnet, and two amphiboles. The isochron age of the rock is 171 ± 3 Ma and is interpreted as the age of the main mineral assemblage, i.e., its crystallization at the metamorphic peak. [ABSTRACT FROM AUTHOR]

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Abstract This study explores the capability of amphibole in tracing the physicochemical process of magma mixing through spatially associated gabbros, mafic microgranular enclaves (MMEs) and granodiorites from central Tibet. These rocks share similar zircon ages as well as zircon Hf‐O and plagioclase Sr isotopes. However, the amphiboles within the gabbros and granodiorites have different Sr and B isotope compositions, while amphiboles with both heterogeneous isotopic imprints occur in the MMEs. According to data and modeling, significant mixing of two isotopically distinct magmas is recorded by amphibole but not by zircon and plagioclase. Based on a synthesis of petrography, geochemistry and thermobarometry, we interpret this inconsistency by the crystallization order of minerals and propose that magma mixing occurred after the parent magma was emplaced at ∼10 km and cooled to ∼750°C. Our study highlights that amphibole may be a more sensitive tracer of magma mixing relative to other commonly used methods.

This paper presents the results of a study of isotopic systems in minerals and rocks in southern margin of the epi-Archean Karelian craton in the zone of its junction with the Svecofennian mobile belt. U-Pb, Sm-Nd and Rb-Sr mineral ages of metamorphic rocks allowed reconstructing a T-t trend during ~1.88–1.61 Ga, which reflects a wide-ranging cooling history of metamorphic rocks from the peak values of about 650–700 °C at 1.88–1.79 Ga (U-Pb age of monazites and apparent oldest Sm-Nd age of amphiboles) to 300–400 °C at 1.61 Ga (model Rb-Sr age of biotites) in zones of low- and medium-temperature metamorphism. The specificity of removal of deep-seated rocks to the present-day erosion surface and the reconstructed T-t trend comply with the development of thrust-nappe structures during the exhumation of the Svecofennids. It is also assumed that differential vertical block movements played a significant role during the post-orogenic extensional collapse and neorifting.

Abstract Metasomatized mantle xenoliths containing hydrous minerals, such as amphiboles, serpentine, and phlogopite, likely represent the potential mineralogical compositions of the metasomatized upper mantle, where low seismic velocities are commonly observed. This study presents the first experimentally determined single‐crystal elasticity model of an Fe‐free near Ca, Mg‐endmember amphibole tremolite at high pressure and/or temperature conditions (maximum pressure 7.3(1) GPa, maximum temperature 700 K) using Brillouin spectroscopy. We found that sound velocities of amphiboles strongly depend on the Fe content. We then calculated the sound velocities of 441 hydrous‐mineral‐bearing mantle xenoliths collected around the globe, and quantitatively evaluated the roles that amphiboles, phlogopite and serpentine played in producing the low velocity anomalies in the metasomatized upper mantle.

Coastal and river sand sequences of Holocene age at Orokolo Bay in Papua New Guinea are host to secondary titanomagnetite ore deposits. The resource developer (Mayur Resources) declares a measured orebody of 139 million tons at grades of 11.35% Fe, 1.94% Ti, and 712 ppm Zr. Orokolo Bay is located near the boundary between the Papuan Thrust and Fold Belt and the Aure Fold Belt. This region is characterized by sedimentary rocks of the Papuan Basin, which are intruded and overlain by a diverse array of magmatic intrusive and volcanic rocks, ranging from mafic alkaline to felsic calc‐alkaline types related to arc–continent collisions in the Cenozoic. The Vailala and Purari rivers located to the east and west of Orokolo Bay, respectively, are the main sediment pathways. Earlier provenance studies have suggested that the deposited sediments mainly come from the erosion of volcanic rocks found within the catchments of these two rivers. However, these studies did not specifically identify the primary source of the Fe‐Ti ores within this region. Here, we report on a potential primary source of the Fe‐Ti ores by examining the occurrence and chemical compositions for detrital titanomagnetites, and associated pyroxene and amphibole minerals. The purpose of this was to discern specific attributes of the primary source for its identification. Lithic sediments comprised of magnesio‐hornblende (Mhbl), tschermakaite (Tsr) and magnesio‐hastingsite (Mhst) amphiboles, clinopyroxene (Cpx), and Fe‐Ti oxide minerals dominate the heavy sands. Feldspar is more abundant than quartz, and Cr‐spinel is rare. Two primary titanomagnetite types were categorized based on their homogeneous grain textures and TiO2 content, Tmt1 (average 28 wt% TiO2) and Tmt2 (average 7 wt% TiO2). Pleonaste exsolutions and zircon inclusions distinguish Tmt1 from Tmt2, while apatite and quenched glass inclusions occur in both. A portion of both primary titanomagnetites exhibits hydrothermal overprinting, this subset was categorized as Tmt3 (average 12.5 wt% TiO2). Fe‐Ti oxides are associated with Cpx and amphiboles as inclusions, and as pseudomorphs in opacitic amphiboles. Tmt1 coexists predominantly with Mhst‐Tsr but also appears less frequently with Mhbl and Cpx. Tmt2 occurs almost exclusively with Mhbl and Cpx. Titanomagnetite chemistry is low in Cr, Mg, and V content suggesting crystallization from evolved melts. Tmt3 is shows enriched Si, Ca, Al, and Mg concentrations that are characteristic of late‐stage fluids derived from calcareous rocks. Amphibole and Cpx chemistry indicate they were derived from a subalkaline source magma of arc affinity. Fe‐Ti thermobarometry reveals Tmt1 (990 to 967°C, −0.51 to −0.18 ΔNNO) formed at higher temperatures and in less oxidized conditions than Tmt2 (834 to 689°C, 0.33 to 3.2 ΔNNO). Amphibole thermobarometry reveals Mhst‐Tsr and Mhbl formed under similar conditions as Tmt1 and Tmt2, respectively. The lack of Cr‐spinel, olivine, and the abundant occurrence of zircon and Mhbl indicate an evolved subalkaline source characterized by felsic rocks related to arc magmatism. The only volcanic source which aligns with these characteristics is Mount Yelia within the Vailala River catchment. Compositional variation between Tmt1 and Tmt2 titanomagnetites and associated silicate minerals is attributed to heterogeneous temperature and ƒO2 conditions within the melt during crystallization. The provenance of Ti‐rich titanomagnetite ores from sources related to arc magmatism indicates the potential of other areas associated with arc activity in Papua New Guinea to host secondary deposits rich in Fe‐Ti ores. [ABSTRACT FROM AUTHOR]

Compositional variations of amphibole stratigraphically recovered from multiple eruptions at a given volcano have a great potential to archive long-term magmatic processes in its crustal plumbing system. Calcic amphibole is a ubiquitous yet chemically and texturally diverse mineral at Mount St. Helens (MSH), where it occurs in dacites and in co-magmatic enclaves throughout the Spirit Lake stage (last ~4000 years of eruptive history). It forms three populations with distinct geochemical trends in key major and trace elements, which are subdivided into a high-Al (11–14.5 wt% Al2O3), a medium-Al (10–12.5 wt% Al2O3), and a low-Al (7.5–10 wt% Al2O3) amphibole population. The oldest investigated tephra record (Smith Creek period, 3900–3300 years BP) yields a bimodal amphibole distribution in which lower-crustal, high-Al amphibole cores (crystallized dominantly from basaltic andesite to andesite melts) and upper-crustal, low-Al amphibole rims (crystallized from rhyolitic melt) document occasional recharge of a shallow silicic mush by a more mafic melt from a lower-crustal reservoir. The sudden appearance of medium-Al amphiboles enriched in incompatible trace elements in eruptive periods younger than 2900 years BP is associated with a change in reservoir conditions toward hotter and drier magmas, which indicates recharge of the shallow silicic reservoir by basaltic melt enriched in incompatible elements. Deep-crystallizing, high-Al amphibole, however, appears mostly unaffected by such incompatible-element-enriched basaltic recharge, suggesting that these basalts bypass the lower crustal reservoir. This could be the result of the eastward offset position of the lower crustal reservoir relative to the upper crustal storage zone underneath the MSH edifice. Amphibole has proven to be a sensitive geochemical archive for uncovering storage conditions of magmas at MSH. In agreement with geophysical observations, storage and differentiation have occurred in two main zones: an upper crustal and lower crustal reservoir (the lower one being chemically less evolved). The upper crustal silicic reservoir, offset to the west of the lower crustal reservoir, has captured compositionally unusual mafic recharge (drier, hotter, and enriched in incompatible trace elements in comparison to the typical parental magmas in the region), resulting in an increased chemical diversity of amphiboles and their carrier intermediate magmas, in the last ~3000 years of MSH's volcanic record. [ABSTRACT FROM AUTHOR]

Scandian actinolite evolving to scandio-winchite (up to 5.45 wt% Sc2O3) has been found in chloritedominant xenoliths incorporated into marginal portion of a granitic pegmatite. The pegmatite intruded a blackwall schist zone developed around rodingite-type rocks exposed in a serpentinite quarry at Jordanów Śląski near Sobótka, ~30 km south of Wrocław, Lower Silesia, Poland. The amphiboles form irregular overgrowths around cascandite and represent a complex solid-solution series among actinolite and scandio-winchite end-members, with a trace contribution of "scandio-magnesio-hornblende." Structural studies of a scandian actinolite crystal with composition A[□0.995(2)K0.005(2)]Σ1B[Na0.24(5)Ca1.73(4)]Σ1.98(1) C M g 3.74 (7) F e 0.90 (3) 2 + M n 0.04 (1) S c 0.26 (3) A l 0.05 (1) Σ 4.99 (1) T S i 7.98 (2) A l 0.02 (2) Σ 8.00 O 22 (O H) 2 revealed monoclinic C2/m structure with unit-cell parameters a = 9.8517(3), b = 18.0881(6), c = 5.28501(18) Å, β = 104.809(4)°, in which scandium is located solely at the CM2 site. Scandian amphiboles are uncommon in geological environments, and invite comments on the origin of the observed Sc enrichment in the amphibole structure. Textural appearance of the chlorite-cascandite-amphibole clusters suggests that the formation of the amphiboles is related to the evolution of the country rocks followed by partial alteration of blackwall schist xenoliths by pegmatite-forming melt. [ABSTRACT FROM AUTHOR]

This article reports a protocol on the application of Amp-TB2 (single-amphibole thermobarometry) based on detailed electron-microprobe analyses performed on homogeneous natural standards and synthetic glasses, and amphibole crystals (mostly phenocrysts) of volcanic products erupted by the Bezymianny volcano during its activity through time. The application of this protocol is facilitated by a new version of the model (Amp-TB2.1.xlsx) including an equation to identify heterogeneous domains (disequilibrium; not suitable for thermobarometric constraints) and homogenous (equilibrium) zones within amphibole crystals, which can be used to quantify the physicochemical parameters (i.e., pressure, P; temperature, T; volatile content in the melt, H2Omelt; oxygen fugacity, fO2) of "steady-state" magmatic crystallization. Application examples of the protocol, showing detailed core–rim microprobe data and physicochemical parameter variations in representative amphibole phenocrysts of the Bezymianny are also reported. The depth (and P) estimated by Amp-TB2.1 for this volcano are compared to seismic tomography results. Amp-TB2.1 results mainly show (1) that the Bezymianny is characterized by a very dynamic feeding system where the magma is stored at shallow crustal levels before recent activity periods characterized by climatic events and (2) that the pre-eruptive depth of magma storage generally increases with the age of the investigated products. [ABSTRACT FROM AUTHOR]

The Patagonian batholith was formed through continuous subduction in the southwestern Gondwana margin, from the Early–Middle Jurassic to present times. This study presents a petrological analysis of the La Hoya pluton, an intrusive body located in the North Patagonian Andes near Esquel that is part of the Patagonian batholith. The La Hoya pluton consists of porphyritic biotite–amphibole granodiorites that grade into porphyritic biotite monzogranites, and both facies are associated with minor occurrences of gabbroic-to-tonalitic stocks and doleritic dikes. Amphibole dating yielded a new 40Ar–39Ar stepwise age of 161.5 ± 0.5 Ma for this shallow emplaced pluton. Field, petrographic, whole rock, and mineral geochemical data suggest and indicate that the petrogenetic evolution of the La Hoya pluton involved fractional crystallization, mafic and felsic magma interaction, and possibly mixing of multiple magma sources. Early formed brown resorbed amphibole and labradoritic plagioclase antecrysts crystallized in alkaline-to-transitional (alkaline-to-subalkaline) magmas with temperatures of 834–962 °C and pressures of ~ 2 kbar (up to ~ 7 km depth). Green amphiboles, plagioclases of andesine–oligoclase composition, and biotites crystallized in equilibrium with subalkaline magmas at lower temperatures and pressures (750–806 °C and of ~ 1 kbar; ~ 3.5 km depth). Actinolitic amphibole and albitic plagioclase formed during the hydrothermal alteration associated with the overprinting of post-emplacement solid-state deformation. The La Hoya pluton involved early formed alkaline-to-transitional magmas that progressively became more calc-alkaline with ongoing differentiation. [ABSTRACT FROM AUTHOR]

The amphiboles from Kakanui and Arenal are two natural minerals that have been used worldwide as microanalytical reference materials, but their compositions and crystal structures are still poorly constrained. In this paper, we report new data on H2O and trace element mass fractions and single‐crystal structural refinement of these two amphiboles. H2O mass fractions of the Kakanui and Arenal amphiboles determined via Karl‐Fischer titration are 0.92 ± 0.18 (2s) and 1.56 ± 0.22% m/m (2s), respectively; these values estimated based on crystal‐structure refinement are 0.86 and 1.46% m/m, respectively. Trace element mass fractions measured via LA‐ICP‐MS in two laboratories are in good agreement, and spots from five fragments for both Kakanui and Arenal amphiboles are generally consistent within reproducibility precision (2s). Our measurements indicate a better homogeneity for the amphiboles from Kakanui than that from Arenal. According to the latest scheme for amphibole classification and nomenclature (Hawthorne et al. 2012), the sample from Arenal is a (partially dehydrogenated) pargasite, and that from Kakanui is a kaersutite. The significant amount of oxo‐component and that CTi4+ content is strongly ordered at the M(1) site for both amphiboles indicate crystallisation under high fO2 conditions. [ABSTRACT FROM AUTHOR]

Fluorine-rich granites and rhyolites occur throughout the southern Rocky Mountains, but the origin of F-enrichment has remained unclear. We test if F-enrichment could be inherited from ancient mafic lower crust by: (1) measuring amphibole compositions, including F and Cl contents, of lower crustal mafic granulite xenoliths from northern Colorado to determine if they are unusually enriched in halogens; (2) analyzing whole-rock elemental and Sr, Nd, and Pb isotopic compositions for upper crustal Cretaceous to Oligocene igneous rocks in Colorado to evaluate their sources; and (3) comparing batch melting models of mafic lower crustal source rocks to melt F and Cl abundances derived from biotite data from the F-rich silicic Never Summer batholith. This approach allows us to better determine if the mafic lower crust was pre-enriched in F, if it is concentrated enough to generate F-rich anatectic melts, and if geochemical data support an ancient lower crustal origin for the F-rich rocks in the southern Rocky Mountains. Electron microprobe analyses of amphibole in lower crustal mafic granulite xenoliths show they contain 0.56–1.38 wt% F and 0.45–0.73 wt% Cl. Titanium in calcium amphibole thermometry indicates that the amphiboles equilibrated at high to ultrahigh temperature conditions (805 to 940 °C), and semiquantitative amphibole thermobarometry indicates the amphiboles equilibrated at 0.5 to 1.0 GPa prior to entrainment in magmas during the Devonian. Mass balance calculations, based on these new measurements, indicate parts of the mafic lower crust in Colorado are at least 3.5 times more enriched in F than average mafic lower crust. Intrusions coeval with the Laramide Orogeny (75 to 38 Ma) pre-date F-rich magmatism in Colorado and have Sr and Nd isotopic compositions consistent with mafic lower crust ± mantle sources, but many of these intrusions contain elevated Sr/Y ratios (>40) that suggest amphibole was a stable phase during magma generation. The F-rich igneous rocks from the Never Summer igneous complex and Colorado Mineral Belt also have Sr and Nd isotopic compositions that overlap with the lower crustal mafic granulite xenoliths, but they have lower Sr/Y, higher Nb and Y abundances, and distinctly less radiogenic 206Pb/204Pbi compositions than preceding Laramide magmatism. Batch melt modeling indicates low-degree partial melts derived from rocks similar to the mafic lower crustal xenoliths we analyzed can yield silicic melts with >2000 ppm F, similar to estimated F melt concentrations for silicic melts that are interpreted to be parental to evolved leucogranites. We suggest that F-rich silicic melts in the southern Rocky Mountains were sourced from garnet-free mafic lower crust, and that fluid-absent breakdown of amphibole in ultrahigh temperature metamorphic rocks was a key process in their generation. Based on the composition of high-F amphibole measured from lower crustal xenoliths, the temperature of amphibole breakdown and melt generation for these F-enriched source rocks is likely >100 °C higher than similar lower crust with low or average F abundances. As such, these source rocks only melted during periods of unusually high heat flow into the lower crust, such as during an influx of mantle-derived magmas related to rifting or the post-Laramide ignimbrite flare-up in the region. These data have direct implications for the genesis of porphyry Mo mineralization, because they indicate that pre-enrichment of F in the deep crust could be a necessary condition for later anatexis and generation of F-rich magmas. [ABSTRACT FROM AUTHOR]

Time-series experiments were carried out in a piston-cylinder apparatus at 0.8 GPa and 1030–1080 °C using a hydrous K-basalt melt as the starting material to determine the element partition coefficients between amphibole and silicate glass. Major, minor, and trace element compositions of amphibole and glass were determined with a combination of electron microprobe and laser ablation inductively coupled plasma mass spectrometry. Results show that the main mineral phase is calcic amphibole, and the coexisting glass compositions range from basaltic trachyandesite to andesite. We estimated the ideal radius, the maximum partition coefficient and the apparent Young's modulus of the A, M1-M2-M3, and M4-M4′ sites of amphibole. The influence of melt and amphibole composition, temperature, and pressure on the partition coeficients between amphiboles and glasses has also been investigated by comparing our data with a literature data set spanning a wide range of pressures (0.6–2.5 GPa), temperatures (780–1100 °C), and compositions (from basanite to rhyolite). Finally, we modeled a deep fractional crystallization process using the amphibole-melt partition coeficients determined in this study, observing that significant amounts of amphibole crystallization (>30 wt%) well reproduce the composition of an andesitic melt similar to that of the calc-alkaline volcanic products found in Parete and Castelvolturno boreholes (NW of Campi Flegrei, Italy). [ABSTRACT FROM AUTHOR]

Despite the first-order importance of crystallisation–differentiation for arc magma evolution, several other processes contribute to their compositional diversity. Among them is the remelting of partly crystallised magmas, also known as cumulate melting or 'petrological cannibalism'. The impact of this process on the plutonic record is poorly constrained. We investigate a nepheline-normative dyke suite close to the Blumone gabbros, a large amphibole-gabbro unit of the Tertiary Southern Alpine Adamello igneous complex. The compositions of the studied dykes are characterised by low SiO2 (43–46 wt. %), MgO (5.0–7.2 wt. %), Ni (18–40 μg/g), and high Al2O3 (20.2–22.0 wt. %) contents. Phenocrystic plagioclase in these dykes exhibits major, trace, and Sr isotope compositions similar to Blumone cumulate plagioclase, suggesting a genetic link between the nepheline-normative dykes and the amphibole-gabbro cumulates. We tested this hypothesis by performing saturation experiments on a nepheline-normative dyke composition in an externally heated pressure vessel at 200 MPa between 975 and 1100 °C at fO2 conditions close to the Ni–NiO buffer. Plagioclase and spinel are near-liquidus phases at and above 1050 °C, contrasting with the typical near-liquidus olivine ± spinel assemblage in hydrous calc-alkaline basalts. The alkaline nature of the dykes results from the abundance of amphibole in the protolith, consistent with melting of amphibole-gabbro cumulates. We modelled the heat budget from the repeated injection of basaltic andesite into a partly crystallised amphibole-gabbro cumulate. The results of this model show that no more than 7% of the cumulate pile reaches temperatures high enough to produce nepheline-normative melts. We propose that such nepheline-normative dykes are a hallmark of hydrous cumulate melting in subvolcanic plumbing systems. Therefore, ne-normative dykes in arc batholiths may indicate periods with high magma fluxes. [ABSTRACT FROM AUTHOR]

Although the evolution of residual melts in magmatic systems controls their eruptability and ore-forming potential, their compositions are obscured in plutonic rocks by a protracted near-solidus evolution and the absence of interstitial glass. Here, we trace the evolution of residual melt compositions in rocks from the Strontian Intrusive Complex, Scotland, using the trace element chemistry of amphiboles, and titanites which are intergrown with amphibole rims. Laser ablation mapping reveals an abrupt change in certain trace elements in the amphibole rims, with sharp increases in Eu/Eu* and Sr/Y, and decreases in rare earth elements, Ta, Nb, and Ta/Nb ratios. Core-rim variations in these elements in titanite show the same variations as in amphibole, but are more gradual. By reconstructing the crystallisation sequence of the Strontian magmas using textural observations and thermobarometric estimates, we determine that amphibole cores crystallised prior to titanite saturation, but amphibole rims crystallised simultaneously with titanite. Using the trace element composition of the mineral phases and their modal abundance in the rock, with comparison to the whole-rock chemistry, we determine that titanite hosts the majority of the rare earth and high field strength element budget of the rocks. We therefore propose that the onset of titanite crystallisation had a profound effect on the trace element composition of late-stage residual melts at Strontian, which were inherited by the amphibole rims and subsequent titanites. This is supported by Rayleigh fractional crystallisation modelling, which demonstrates that the composition of amphibole rims cannot be explained without the influence of titanite. We therefore show that the saturation of trace element-rich phases in magmas represents a significant geochemical event in the petrogenesis of intermediate to silicic magmas. This has implications for provenance studies that attempt to reconstruct bulk rock compositions from mineral compositions, as the residual melts from which those minerals crystallise can be driven to significantly different compositions from the host magma by late-stage accessory phase crystallisation. [ABSTRACT FROM AUTHOR]

The paper presents experimental data on the interaction of amphibole with NaCl–H2O and (K, Na)Cl–H2O solutions at varying salt content. When interacting with H2O–NaCl fluid, amphibole remains the predominant mineral in all experiments, and the newly formed minerals are Na-phlogopite, plagioclase, and nepheline/sodalite. At > 0.6, the amphibole melts. When amphibole interacts with H2O–NaCl–KCl fluid at < 0.40 and ХKCl/(ХKCl + ХNaCl) in the fluid, defined as ХNaCl = 0.506 – 0.84ХKCl, the amphibole is replaced by the association of nepheline with sodic plagioclase, sodalite, and biotite. At ХKCl/(ХKCl + ХNaCl) > 0.3, nepheline, sodalite, and plagioclase become unstable, K-feldspar is formed, and biotite, clinopyroxene, and amphibole remain stable. At ХKCl/(ХKCl + ХNaCl) > 0.5, the association Cpx + Bt + Kfs + Grt (grossular–andradite) is stable. Thus, grossular–andradite garnet is an indicator of a high potassium activity in the fluid, whereas nepheline testifies that the sodium activity was high. Na → K exchange is typical of the amphibole and biotite, and Ca → Na exchange occurs in the clinopyroxene, and all of these minerals (but neither nepheline nor garnet) remain generally stable within a wide range of the K/Na ratio in the fluid. Clinopyroxene in the experiments spans Ca–Fe–Mg compositions with a varying, sometimes high, Al content, and the amphiboles belong to the pargasite–hastingsite series. With an increase in ( > 0.57), i.e., a decrease in the gross salinity of the fluid, melts are generated, and their composition varies from trachyte to phonolite. An increase in the ХKCl/(ХKCl + ХNaCl) ratio in the fluids leads to a decrease in alumina content of the melts. An increase in the total salinity of the fluid leads to an increase in the content of potassium in the melt and a decrease in the content of chlorine in it. The experiments have shown that interaction between amphibole and fluids containing high NaCl and KCl concentrations results in mineral associations typically produced by alkaline metasomatism of amphibole-bearing rocks and concomitant HCl enrichment in the fluid phase. The substitution of highly saline fluids for highly acidic ones leads to the leaching of Ca, Mg, Fe from the metamorphic rocks, and the transport and redeposition of these components. It follows that significant removal of FeO, MgO, CaO from rocks is sometimes a consequence of the interaction of the host rocks with saline aqueous solutions. [ABSTRACT FROM AUTHOR]

To explore the flotation feasibility and flotation law of iron minerals from amphibole-type iron oxide ore with full-size minerals, a systematic study on the flotation behaviors of single minerals hematite, quartz, and amphibole was carried out with the anionic reverse flotation system. The effects of collectors, depressants, activators, and pH on the floatabilities of three single minerals was investigated. The flotation separations of binary mixed minerals and ternary mixed ores were carried out, respectively. The study results show that CaCl2 is adsorbed on the surfaces of quartz and amphibole, which can activate them. The hydroxyl groups of the starch molecular chain were adsorbed on the surfaces of the hematite and amphibole in the form of hydrogen bonds, but were hardly adsorbed on surface of the quartz. Therefore, both hematite and amphibole were depressed, resulting in a poor separation effect of the three single minerals in the anionic flotation system. [ABSTRACT FROM AUTHOR]

The Strandja Massif cropping out in NW Turkey is cut by Late Cretaceous intrusives. These are called Strandja Intrusives and they are felsic and mafic coeval intrusives. Felsic intrusives consist of granite, granodiorite, quartz monzonite and syenite, while mafic intrusives consist of diorite and gabbro composition. Main composition of felsic intrusives consists of quartz, alkali feldspar, plagioclase, biotite, amphibole ±pyroxene mineral association, while main composition of mafic ones consists of plagioclase, biotite, amphibole ±pyroxene ±olivine mineral association. Amphiboles hydrated double-chain mineral of the Strandja Intrusives observed in all rocks used as an index mineral in this study to understand the petrological evolution of the rocks. According to Confocal Raman Spectroscopy studies amphiboles were actinolite type and exhibited similar spectrum and results of mineral chemistry reveals that they were calcic/Mg-hornblende types. According to geothermobarometer calculations, amphiboles crystallize in felsic intrusives at a pressure range of 0.49-0.94 kbar and a temperature of 757.52-814.49oC temperature at a depth of approximately 1.34-4.93 km, while in mafic ones at 2.59 kbar pressure and 892.82oC temperature at 9.97 km depth. Different temperatures-depth conditions and overlaps in Raman shift obtained from amphiboles indicate that these intrusives are derived from different sources but crystallized in the same environment.

The southern part of the Kuril Island Arc is one of the world's most active modern volcanic zones, with widespread felsic caldera volcanism, but it has been less well studied compared with other arcs. The Mendeleev caldera-forming eruption (40 ka) on Kunashir Island, southern Kurils, is one of the most explosive Pleistocene eruptions to have occurred in this region. This study aimed to establish the origin and storage conditions of magma preceding the Pleistocene caldera eruption of Mendeleev volcano. Mineralogical and melt inclusion analyses reveal that the primary melts had felsic compositions and that the early stage of magmatic evolution involved amphibole breakdown into a two-pyroxene, plagioclase, and Fe–Ti oxide assemblage under pressure–temperature conditions of 107–314 MPa and 807–932°C. The caldera-forming products are represented by dacitic pumice composed of plagioclase + augite + hypersthene+ quartz + Fe–Ti oxides and melt with uniform low-K rhyolite composition. Pre-eruptive magma was stored in a reservoir at 77–195 MPa (3.0–7.6 km depth) and 830–890°C under H2O-saturated conditions. The mechanism of magmatic evolution implies the following two-step scenario: (1) generation of magma by the partial melting of an amphibole-bearing substrate accompanied by the formation of early Mg-rich clino- and orthopyroxene, plagioclase, Fe–Ti oxides, and peritectic rhyolitic melt; and (2) crystallization of late plagioclase and quartz directly from these partial melts. Local or regional extension during the Pleistocene, accompanied by increasing heat flow in the supra-subduction mantle, generated an active mafic intrusion into the upper crust. This process was accompanied by abundant subaerial eruptions of basaltic volcanoes and could have caused intense heating and partial melting of upper-crustal rocks. Our results indicate that the partial melting of amphibole-bearing substrates in island arcs may serve as a universal mechanism for the generation of silicic magmas during powerful caldera eruptions in young island arcs. [ABSTRACT FROM AUTHOR]

This article reports on the recent mining and production status of ruby in Longido, Tanzania. Faceted-grade rubies and their matrix from Longido Area, Tanzania, were investigated by standard gemological testing, including FTIR, UV-VIS, Raman spectra, and LA-ICP-MS. Microscopic observations revealed dense needle-like and triangular inclusions, distinct growth lines, and color banding as typical inclusions. In agreement with the Raman results, the transmission FTIR spectrum confirmed the presence of aluminum hydroxide. The Raman spectra identified associated minerals and inclusions, including zoisite, parasites, feldspar within the matrix, rutile, and diaspore in the ruby host. The chemistry analysis revealed a high amount of Cr and relatively low iron as a good indicator of geographic origin.

Seismic anisotropy is controlled by aligned rock‐forming minerals, which most studies attribute to solid‐state shear with less consideration for magmatic fabric in plutonic rocks (rigid‐body rotation of crystals in the presence of melt). Our study counters this traditional solid‐state bias by evaluating contributions from fossil magmatic fabric. We collected samples from various tectonic settings, identified mineral orientations with electron backscatter diffraction and neutron diffraction, and calculated their bulk rock elastic properties. Results indicate that magmatic fabric may lead to moderate to strong anisotropy (3%–9%), comparable to solid‐state deformation. Also, magmatically aligned feldspar may cause foliation‐perpendicular fast velocity, a unique orientation that contrasts with a fast foliation typical of solid‐state deformation. Therefore, magmatic fabric may be more relevant to seismic anisotropy than previously recognized. Accordingly, increased considerations of magmatic fabric in arcs, batholiths, and other tectonic settings can change and potentially improve the prediction, observation, and interpretation of crustal seismic anisotropy. Plain Language Summary: Seismic waves that travel through Earth have directionally varying velocities, which depend on the type and orientation of minerals that make up a rock. A common assumption is that the processes that align these minerals occur when the rock is solid, by either brittle fracturing or by plastic deformation at the subatomic scale. However, a similar alignment can form in a magmatic rock by the rotation of elongated crystals in a partially molten rock mush, prior to solidification, and that alignment remains after cooling. In this study, we measured the orientation of such magmatically aligned minerals in rocks and calculated how fast seismic waves travel through the rocks. In some cases seismic properties are similar, whether planar minerals like mica were aligned in the solid‐state or magmatic‐state, with faster seismic waves traveling parallel to the rock's planar fabric. However, where tabular feldspar is strongly aligned in magmatic rocks, seismic waves instead travel faster perpendicular to the rock's planar fabric. Scientists who use seismic stations on Earth's surface to measure differences in crustal seismic velocities can therefore make more accurate interpretations of subsurface rock fabric by considering whether minerals were aligned in a solid‐state or magmatic‐state. Key Points: Magmatic fabric may lead to moderate to strong (3%–9%) anisotropy, comparable to that commonly produced by solid‐state shear deformationMagmatically aligned feldspar causes foliation‐perpendicular fast velocities, contrasting to foliation‐parallel as typical of solid‐stateMagmatic fabrics provide complementary or alternative explanations (compared to solid‐state) for observed crustal anisotropy [ABSTRACT FROM AUTHOR]

Melt inclusions are of major significance because they can constrain the volatile abundances in magmas. Here, we report the discovery of the first melt inclusion in a martian apatite containing the first chloro-amphibole reported in Northwest Africa (NWA) 998, a sample that crystallized early from the nakhlite-source. The amphibole is also the first sodic-calcic amphibole in a nakhlite, identified as ferro-chloro-winchite (4.75 wt% Cl) by FIB-TEM. The melt inclusion is present in a euhedral, cumulus apatite grain (Cl/F = 2.11) and is surrounded by a shell of voids. Evidence indicates that the melt inclusion remained as a closed system although syn- and post-entrapment processes may have modified the chemical composition of the original trapped melt. The inclusion also contains Fe-rich, Ca-poor pyroxene and a residual silicate melt consisting of pyroxene and interstitial K-rich glass. Additionally, Cl-enriched apatite is present within the boundaries of the melt inclusion. This apatite could result from cracking of host-apatite during contraction of the melt inclusion glass or represent daughter apatite crystallizing on the walls of the inclusion. Given that Cl-enrichments are found in the host apatite outside the melt inclusion, it is inferred that a later, fluid alteration event locally modified the composition of the apatite in and/or around the melt inclusion. The calculated bulk composition of the melt inclusion is generally consistent with previous work in other nakhlites. Prior to this study, Cl-rich amphiboles have only been found within olivine- and pyroxene-hosted melt inclusions in the later-formed nakhlites. The present study thus demonstrates that (i) the nakhlites record magmatic mixing with a Cl-rich exogenous component that is absent within olivine-hosted melt inclusions in the chassignites, (ii) Cl-rich amphiboles were able to crystallize from the earliest nakhlite parent melt, and (iii) the presence of a Cl-rich fluid was not required to stabilize chloro-amphiboles. We also conclude that magmatic martian amphiboles likely stabilized at lower pressures (and temperatures) than terrestrial amphiboles due to their higher Cl contents. [ABSTRACT FROM AUTHOR]

The paper provides results of a detailed mineralogical study of some chromitite ores from two deposits in the Southern Urals of Kazakhstan: Almaz-Zhemchuzhina and Geofizicheskoe-VII. It is revealed that the main ore minerals are Cr-spinel with high Cr# (Cr/(Cr + Al) = 0.8–0.83), as well as serpentine and chlorite, replacing primary olivine. Chromium spinel grains contain mineral inclusions, which are distributed rather unevenly. The most common mineral inclusions are olivine (serpentine) and amphibole; phlogopite, pyroxenes, and base metal sulfides are rare. Olivine from inclusions in chromite is the highest in magnesium (Fo97–98), and is anomalously high in nickel (up to 1.8 wt.% NiO). The closure of exchange reactions between olivine and chromite occurred in the temperature range of 700–850 °C and in the oxygen fugacity range of −1.04 ... +2.8 ΔFMQ, which most likely corresponds to the upper mantle settings of the fore-arc basin. A few tens of monomineral grains and polymineral intergrowths of platinum group minerals (PGMs) were found in chromite aggregates. Notably, monomineral grains are mainly represented by Ru, Os, and Ir disulfides, while in polymineral inclusions, iridium prevails (with widespread native phases, sulfides, and sulfoarsenides). PGM grains included in chromite are often associated with hydrous silicates: amphibole, and less often with phlogopite or chlorite. Discussed in the paper is the possible genesis of ores and inclusions. As a preliminary conclusion, we suggest that the solid-phase processes played the most significant role in the crystallization of Cr-spinel in the investigated chromitite ores. [ABSTRACT FROM AUTHOR]

• P-T-t evolution was re-constructed for central Himalayan granulitized eclogites. • Zircons in eclogites record granulite/amphibolite facies overprinting at ∼14 Ma. • These zircons have low total REE in equilibrium with hornblende growth. • Zircon ages should be interpreted by distinguishing flat HREE vs. low total REE. Exhumation rates of high-pressure rocks are paramount in determining plate tectonic processes, which requires absolute chronology of metamorphic stages. U-Pb geochronology of zircon and other accessory minerals has proven successful in dating different metamorphic stages, thus constraining geological rates. A common strategy to link U-Pb ages to metamorphic stages uses rare earth element (REE) patterns in the dated minerals. In this study, the changes in the REE composition of accessory and rock-forming minerals in response to changing assemblages have been investigated in granulitized eclogites and gneisses from the Ama Drime Massif, central Himalaya. Phase equilibrium modelling shows that the eclogite-facies assemblage formed at 660–720 °C and 1.6–1.9 GPa (M1), was overprinted at high-pressure granulite-facies (M2) and then ultra-high temperature conditions of >900 °C and 0.8–1.1 GPa (M3) and finally re-equilibrated at conditions of 780–810 °C and 0.8–1.0 GPa (M4). In the countryrock orthogneisses, monazite records partial resetting during granulite-facies overprinting at 26–19 Ma and melt crystallisation at 16–13 Ma, supported by textures, mineral inclusions and trace elements. In the associated granulitized eclogites, zircon records only granulite/amphibolite facies overprinting at ∼14 Ma, and titanite and rutile record cooling to 580–630 °C at 12.5–9 Ma. Granulite/amphibolite facies zircon has a low total REE relative to the protolith zircon, primarily due to the growth of REE-rich hornblende (total REE 80–260 μg/g), which removed 67–92% of the REE from the system. The low total REE of granulite/amphibolite facies zircon is comparable to the flat HREE reported for garnet-rich eclogite-facies zircon, and distinguishing these zircon types requires quantitative mineral volume estimates and other criteria. These findings may imply slower exhumation rates for some eclogite-facies terranes, such as the Tso Morari Himalaya and Papua New Guinea, than previously reported. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Seismic anisotropy is controlled by aligned rock‐forming minerals, which most studies attribute to solid‐state shear with less consideration for magmatic fabric in plutonic rocks (rigid‐body rotation of crystals in the presence of melt). Our study counters this traditional solid‐state bias by evaluating contributions from fossil magmatic fabric. We collected samples from various tectonic settings, identified mineral orientations with electron backscatter diffraction and neutron diffraction, and calculated their bulk rock elastic properties. Results indicate that magmatic fabric may lead to moderate to strong anisotropy (3%–9%), comparable to solid‐state deformation. Also, magmatically aligned feldspar may cause foliation‐perpendicular fast velocity, a unique orientation that contrasts with a fast foliation typical of solid‐state deformation. Therefore, magmatic fabric may be more relevant to seismic anisotropy than previously recognized. Accordingly, increased considerations of magmatic fabric in arcs, batholiths, and other tectonic settings can change and potentially improve the prediction, observation, and interpretation of crustal seismic anisotropy.

The Matachel Basin is a tectono-stratigraphic unit of Ossa-Morena Zone (southern Iberian Massif) that encompasses an Upper Tournaisian – Viséan basaltic sequence, generated by effusive and explosive eruptions in a shallow submarine setting. A collection of 23 basaltic and gabbroic samples were selected for detailed petrographic descriptions, which included a mineral chemistry characterization by means of Electron Microprobe analysis in 9 rock samples. In this contribution a total of 501 mineral chemical data are presented, which correspond to plagioclase (208 analysis), clinopyroxene (202 analysis), amphibole (64 analysis), opaque minerals (18 analysis), and alkali feldspar (9 analysis). According to mineral classification diagrams analyzed rock samples are composed by albite-labradorite (An01-66), augite (Wo31–41En32–49Fs7–22), magnesiohornblende, ferrohornblende, ferropargasite, titanian magnesiohastingsite, orthoclase (Or93–97), titanomagnetite, and ilmenite. Presented dataset provides a robust information of the nature of the outpouring lava emissions in shallow-marine intra-continental basins, and would enhance a better understanding of eruptive dynamics in this type of tectonic settings.

The Fe3+/FeT ratios (Fe3+/[Fe2++Fe3+]) in minerals can be used to understand their crystallization and post-crystallization conditions. However, as natural minerals are often zoned and contain inclusions, bulk techniques, e.g., wet chemistry, may not provide accurate Fe3+/FeT values for a single phase of interest. We determined Fe3+/FeT ratios of amphiboles in different crystallographic orientations by single-crystal synchrotron Mossbauer spectroscopy (SMS) in energy and time domain modes from four volcanic localities (Long Valley Caldera, Mount St. Helens, Lassen Volcanic Center, U.S.A., and Mt. Pinatubo, Philippines). The high spatial resolution (as low as 12 x 12 ^m spot size) and standardfree nature of SMS allow the detection of intra-grain compositional heterogeneities in Fe3+/FeT with relatively low uncertainties. We combine SMS with major element compositions, water contents, and hydrogen isotope compositions to document the Fe3+/FeT ratios as a function of mineral composition and post-crystallization dehydrogenation. Spectra were fitted with up to five distinct sites: ferrous iron on M( 1), M(2), M(3), and ferric iron on M(2) and M(3), consistent with X-ray diffraction studies on single crystals of amphibole. The Fe3+/FeT ratios range from 0.14 ± 0.03 (Long Valley Caldera), 0.51 to 0.63 ± 0.02 (representing intra-grain heterogeneities, Mount St. Helens) to 0.86 ± 0.03 (Lassen Volcanic Center). The latter grain experienced post-crystallization dehydrogenation, shown by its low water content (0.6 ± 0.05 wt%) and its elevated hydrogen isotope composition (SD = +25 ± 3%o relative to SMOW). The Fe3+/FeT ratios of 0.62 ± 0.01 and 0.20 ± 0.01 of two Mt. Pinatubo grains correlate with high-Al2O3 cores and low-Al2O3 rims and smaller phenocrysts in the sample, respectively. This study shows that SMS is capable of distinguishing two different domains with dissimilar Fe3+/FeT values formed under different crystallization conditions, demonstrating that SMS in combination with major element, water, and hydrogen isotope compositions allows the interpretation of amphibole Fe3+/FeT ratios in the context of crystallization and post-crystallization processes. [ABSTRACT FROM AUTHOR]

The Kanarata albitized granite deposit is located on the NE periphery of the Sakar Upper Carboniferous granite batholith, immediately adjacent to its contact with the metamorphic framework. The porphyroid two-mica granites of the batholith are replaced by albite and quartz, and by magnesium-rich minerals in small amounts (some enriched in sodium): Mg-actinolite to Mg-hornblende and Mg-tremolite, phlogopite, chlorite, talc, saponite, as well as accessory rutile, probably titanite and apatite. The only relict mineral is zircon. The newly formed minerals are products of alkaline (magnesium-sodium) metasomatosis of possibly Alpine age. This has led to a change in the chemical composition of the granite, resulting in a decrease in the amount of silicon, iron, calcium, and especially potassium, and an increase in the amount of titanium, aluminum, magnesium, and especially sodium. [ABSTRACT FROM AUTHOR]

The Strandja Massif cropping out in NW Turkey is cut by Late Cretaceous intrusives. These are called Strandja Intrusives and they are felsic and mafic coeval intrusives. Felsic intrusives consist of granite, granodiorite, quartz monzonite and syenite, while mafic intrusives consist of diorite and gabbro composition. Main composition of felsic intrusives consists of quartz, alkali feldspar, plagioclase, biotite, amphibole ±pyroxene mineral association, while main composition of mafic ones consists of plagioclase, biotite, amphibole ±pyroxene ±olivine mineral association. Amphiboles hydrated double-chain mineral of the Strandja Intrusives observed in all rocks used as an index mineral in this study to understand the petrological evolution of the rocks. According to Confocal Raman Spectroscopy studies amphiboles were actinolite type and exhibited similar spectrum and results of mineral chemistry reveals that they were calcic/Mg-hornblende types. According to geothermobarometer calculations, amphiboles crystallize in felsic intrusives at a pressure range of 0.49-0.94 kbar and a temperature of 757.52-814.49o C temperature at a depth of approximately 1.34-4.93 km, while in mafic ones at 2.59 kbar pressure and 892.82o C temperature at 9.97 km depth. Different temperatures-depth conditions and overlaps in Raman shift obtained from amphiboles indicate that these intrusives are derived from different sources but crystallized in the same environment. [ABSTRACT FROM AUTHOR]

The existence of thermally-activated quasiparticles in amphiboles is an important issue, as amphiboles are among the main hydrous complex silicate minerals in the Earth's lithosphere. The amphibole structure consists of stripes of 6-membered TO4-rings sandwiching MO6 octahedral slabs. To elucidate the atomistic origin of the anomalous rock conductivity in subduction-wedge regions, we studied several Fe-containing amphiboles with diverse chemistry by using in situ, temperature-dependent, polarised Raman spectroscopy. The occurrence of resonance Raman scattering at high temperatures unambiguously reveal temperature-activated small polarons arising from the coupling between polar optical phonons and electron transitions within Fe2+O6 octahedra, independently of the amphibole chemical composition. The FeO6-related polarons coexist with delocalised H+; that is, at elevated temperatures Fe-bearing amphiboles are conductive and exhibit two types of charge carriers: electronic polarons with highly anisotropic mobility and H+ cations. The results from density-functional-theory calculations on the electron band structure for a selected amphibole compound with a relatively simple composition are in full agreement with experimental data. The polaron activation temperature, mobility, and polaron-dipole magnitude and alignment can be controlled by varying the mineral composition, which makes amphiboles attractive "geo-stripes" that can serve as mineral-inspired technology to design thermally-stable smart materials with anisotropic properties. [ABSTRACT FROM AUTHOR]

Episodic tremor and slow slip (ETS) downdip of the subduction seismogenic zone are poorly understood slip behaviors of the seismic cycle. Talc, a common metasomatic mineral at the subduction interface, is suggested to host slow slip but this hypothesis has not been tested in the rock record. We investigate actinolite microstructures from talc‐bearing and talc‐free rocks exhumed from the depths of modern ETS (Pimu'nga/Santa Catalina Island, California). Actinolite deformed by dissolution‐reprecipitation creep in the talc‐free rock and dislocation creep ± cataclasis in the talc‐bearing rock. This contrast results from stress amplification in the talc‐bearing rock produced by high strain rates in surrounding weak talc. We hypothesize that higher strain rates in the talc‐bearing sample represent episodic slow slip, while lower strain rates in the talc‐free sample represent intervening aseismic creep. This work highlights the need to consider fluid‐mediated chemical change in studies of subduction zone deformation and seismicity. Plain Language Summary: Episodic tremor and slow slip (ETS) are poorly understood styles of fault slip that occur just below the locked part of the megathrust fault where large subduction zone earthquakes occur. Chemical reactions at the depths of ETS can produce new and particularly weak minerals such as talc that change fault behavior but are rarely considered in studies of ETS. Modeling of rock deformation suggests that talc should host ETS fault slip, but this hypothesis has not been tested in the rock record. We investigated deformation of the mineral actinolite in talc‐free and talc‐bearing rocks exhumed from the depths of ETS in modern subduction zones on Pimu'nga/Santa Catalina Island (California) as a record of fault slip. Contrasting microstructures and deformation mechanisms in talc‐free and talc‐bearing rocks are best explained by differences in the rate of deformation (strain rate) between the two rock types. Lower strain rates in talc‐free rocks likely record background creeping (aseismic) deformation and higher strain rates in talc‐bearing rocks likely represent episodic slow slip events. This work suggests that talc may be a key host for slow slip and that future studies must account for new rock types formed by chemical reactions to accurately represent subduction zone deformation. Key Points: Contrasting actinolite microstructures in talc‐free and talc‐bearing subduction interface metasomatic rocks record stress variationsStress amplification in actinolite from talc‐actinolite schist results from high strain rate deformation of surrounding talcHigh strain rates reflect episodic slow slip localized in talc‐actinolite schist under high pore fluid pressures during metasomatism [ABSTRACT FROM AUTHOR]

Oxygen fugacity is an important but difficult parameter to constrain for primitive arc magmas. In this study, the partitioning behavior of Fe3+/Fe2+ between amphibole and glass synthesized in piston-cylinder and cold-seal apparatus experiments is developed as an oxybarometer, applicable to magmas ranging from basaltic to dacitic composition. The partitioning of Fe2+ is strongly dependent on melt polymerization; the relative compatibility of Fe2+ in amphibole decreases with increasing polymerization. The Fe2+/Mg distribution coefficient between amphibole and melt is a relatively constant value across all compositions and is, on average, 0.27. The amphibole oxybarometer is applied to amphibole in mafic enclaves, cumulates, and basaltic tephra erupted from Shiveluch volcano in Kamchatka with measured Fe3+/FeTotal. An average Fe3+/Fe2+ amphibole-glass distribution coeficient for basalt is used to convert the Fe3+/FeTotal of amphibole in samples from Shiveluch to magmatic oxygen fugacity relative to NNO. The fO2 of primitive melts at the volcano is approximately NNO+2 and is faithfully recorded in amphibole from an amphibole-rich cumulate and the basaltic tephra. Apparently, higher fO2 recorded by amphibole in mafic enclaves likely results from partial dehydrogenation of amphibole during residence in a shallow andesite storage region. We identify three pulses of mafic magma recharge within two weeks of, a month before, and two to three months before the eruption and find that, at each of these times, the host andesite was recharged by at least two magmas at varying stages of differentiation. Application of the amphibole oxybarometer not only gives insight into magmatic fO2 but also potentially details of shallow magmatic processes. [ABSTRACT FROM AUTHOR]