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Arc magmas, a major contributor to continental crust growth, are thought to be more oxidized than mid-ocean ridge basalts as reflected by an enrichment in ferric iron relative to ferrous iron. But how arc magmas become oxidized is hotly debated. It is acknowledged that the fractionation of common Fe-rich phases (e.g., amphibole) may change the Fe valence of the derivative melt. Amphibole has Fe-rich compositions commonly found in arc systems. We present high-precision (±0.01%) Fe valence data of amphibole and cumulates from the Kohistan arc determined by Mössbauer spectroscopy and bulk cumulate Fe3+/ΣFe ratios by wet chemistry. We evaluate the Fe3+/ΣFe trend of Fe-rich amphibole during arc magma fractionation. Our results show that bulk Fe3+/ΣFe ratio of cumulates in mature island arc settings is mainly controlled by amphibole due to its abundance and decreases (from 0.4 to 0.2) with decreasing Mg# as Fe3+/ΣFe ratios decrease in amphibole (from 0.35 to 0.2). Our modeling suggests that amphibole fractionation from parental arc magmas to Fe3+/ΣFe above 0.2 may lead to an increase in Fe3+/ΣFe ratios of middle–late stage residual melts by 0.1–0.3, and the partitioning of ferrous Fe into amphibole increases with the evolution of arc magmas. Our findings highlight the importance of petrological processes in the magma that contribute to the production of fertile arc crust. [ABSTRACT FROM AUTHOR]

Brown amphibole is a minor but common mineral component in lower oceanic crust. It is generally interpreted as products of migrating SiO2 and H2O-rich fluids or melts, which can be either residual melts from advanced magmatic differentiation of Mid-Ocean Ridge Basalt (MORB), or hydrothermal fluids including a seawater component. Within the lower oceanic crust exhumed at the Atlantis Bank Oceanic Core Complex, along the ultraslow Southwest Indian Ridge, brown amphibole is ubiquitous in all lithologies from olivine- to oxide-gabbros and diorites, including both undeformed and plastically deformed varieties. We here show the results of a systematic petrological study conceived to unravel the nature of the H2O-rich component recorded in brown amphiboles and document: (i) the evolution of migrating melts during the magmatic stage and (ii) different extents of melt-bearing deformation events recorded throughout the entire crustal transect. The low Cl contents and the light over heavy rare earth elements (LREE/HREE) ratios and high Ti contents in brown amphiboles indicate they crystallized from melts with a magmatic hydrous component. Consistently, their δ18O values are in equilibrium with Mid-Ocean Ridge Basalt (MORB) composition, except for diorite amphiboles that possibly record the local assimilation of altered minerals. In undeformed olivine gabbros, interstitial pargasite crystallized at hypersolidus conditions (~1000°C) from the melt residual after late stages of MORB differentiation. We speculate that before the olivine gabbro crystal mush reached fully solid state, some aliquots of residual melts were extracted and accumulated within discrete intervals. There, ferrobasaltic melts differentiated through the early crystallization of Fe-Ti oxides and clinopyroxene as liquidus phases, ultimately forming the oxide gabbros. This process promoted rapid Si enrichment and depletion in Fe, Ti, V in the residual melt, later extracted to form the crosscutting diorite veins. The mylonitic olivine gabbros record high-temperature plastic deformation (~900°C ± 50°C) under hypersolidus conditions, involving melts residual from previous crystallization of the gabbroic rock. Further solid-state plastic deformation led to substantial grain size reduction and, consequently, to an increase in porosity. This created pathways for subsequent melt focusing, which likely represent late-stage differentiated melts migrating throughout the lower crustal section. This study shows that brown amphibole in the Atlantis Bank lower oceanic crust is the crystallization product of melts residual from advanced magmatic differentiation, which are also locally involved in the plastic deformation events during crustal accretion. [ABSTRACT FROM AUTHOR]

Ferri-taramite (IMA CNMNC 2021-046), ideally A Na B (CaNa) C (Mg 3 Fe 23+)(Si 6 Al 2)O 22 W (OH) 2 , occurs in skarn from the Jakobsberg manganese mine, Värmland, Sweden. Associated minerals are celsian, phlogopite, aegirine-augite, andradite, hancockite, melanotekite, microcline (var. hyalophane), calcite, baryte, prehnite, macedonite and oxyplumboroméite. Conditions of formation, close to peak metamorphism (at circa 650 ∘ C and 0.4 GPa), include silica undersaturation, a slightly peralkaline character and relatively high oxygen fugacities. Ferri-taramite forms poikiloblastic crystals up to 5 mm and is dark brownish black with a yellowish grey streak. The amphibole is brittle with an uneven to splintery fracture. Cleavage parallel to {110} is good. Hardness (Mohs) is ∼ 6, and Dcalc=3.227(5) g cm -3. Holotype ferri-taramite has the experimental unit formula A (Na 0.79 K 0.16 Pb 0.01)Σ0.96 B (Ca 1.26 Na 0.72 Mn 0.022+)Σ2 C (Mg 2.66 Mn 0.582+ Fe 0.162+ Zn 0.02 Fe 1.263+ Al 0.26 Ti 0.06)Σ5.00 T(Al1.86 Si 6.14)Σ8 O 22 W(OH)2 , based on chemical analyses (EDS, laser-ablation ICP-MS) and spectroscopic (Mössbauer, infrared) and single-crystal X-ray diffraction data. The mineral is optically biaxial (–), with α=1.670(5) , β=1.680(5) and γ=1.685(5) in white light and 2 Vmeas=70(10) ∘ and 2 Vcalc=70.2 ∘. Ferri-taramite is distinctly pleochroic in transmitted light, with X pale yellow, Y dark brown, Z yellowish brown and absorption Y>Z>X. The eight strongest reflections in the X-ray powder pattern (d values (in Å), Irel , hkl) are 8.44, 60, 110; 3.392, 25, 131; 3.281, 39, 240; 3.140, 100, 310; 2.816, 45, 330; 2.7104, 38, 151; 1.3654, 26, 461; and 1.4451, 33, 6‾61. Refined unit-cell parameters from single-crystal diffraction data are a=9.89596(13) , b=18.015(2) , c=5.32164(7) Å, β=105.003(13) ∘ and V=916.38(2) Å 3 for Z=2. Refinement of the crystal structure yielded R=2.26 % for 2722 reflections with Io>2σ(I). The Mn 2+ and Fe 2+ ions show preference for the M 1 and M 3 octahedrally coordinated sites, whereas Fe 3+ is strongly ordered at M 2. The A -group cations, K and Na, are split over two subsites, A(m) and A (2), respectively. [ABSTRACT FROM AUTHOR]

The zircon-bearing Liushuzhuang Peridotite in the Tongbai Orogen provides insights into the composition and evolution of Paleozoic sub-arc lithospheric mantle between the North China and Yangtze cratons. This orogenic peridotite is dominated by clinopyroxene-free spinel facies harzburgite to dunite. The refractory nature is indicated by high olivine Mg# (up to 92.4), elevated spinel Cr# (74-87), and low orthopyroxene Al.sub.2O.sub.3 (mostly < 1.0 wt.%). The occurrence of zircon, amphibole, phlogopite, apatite, and LREE-enriched orthopyroxene, with Raman probe analyses showing amphibole and phlogopite inclusions in zircon, testifies to extensive fluid-driven metasomatism of the mantle at ca. 420 Ma (U-Pb zircon). The high spinel TiO.sub.2 contents (0.4-1.4 wt.%), the Cl-enriched apatite, and the hydrous secondary phases indicate that the metasomatic agent was volatile- (CO.sub.2 + H.sub.2O) and TiO.sub.2-rich. The elevated oxygen fugacity (âlogfO.sub.2 (FMQ) > 2.5) coupled with high spinel Cr# of peridotites suggest that they formed within highly oxidizing supra-subduction zone environment. In-situ.sup.87Sr/.sup.86Sr.sub.i amphibole and apatite data indicate that the metasomatic fluids were slightly to moderately radiogenic (0.7032-0.7090) and therefore likely partially derived from the subducted Shangdan oceanic crust that separated the North China and Yangtze cratons. The very low .sup.176Lu/.sup.177Hf (mostly < 0.0002) of metasomatic zircon and similar [epsilon].sub.Hf(t) to Tongbai Orogen arc-related magmas implies that zircon grew during modification of sub-arc mantle. Juxtaposition with the host gneisses occurred after 410 Ma and before U-Pb closure during apatite cooling at ~ 340 Ma. The Liushuzhuang Peridotite therefore records intense metasomatism of the Paleozoic sub-arc mantle wedge prior to collision of the North China and Yangtze cratons., Author(s): Tingting Wang [sup.1] [sup.3], Jianping Zheng [sup.1] [sup.2], James M. Scott [sup.3], Qing Xiong [sup.2], Xianquan Ping [sup.1] Author Affiliations: (1) grid.503241.1, 0000 0004 1760 9015, School of Earth [...]

• Partial melting experiments on amphibole-bearing arclogite at 2 GPa and 1040–1300 °C. • Arclogite begins melting at 1040–1080 °C to form alkali-, FeO-, and TiO 2 -rich magmas. • Arclogite melting is not a main mechanism of magmagenesis at thick-crusted arcs. • Arclogite melts geochemically resemble magmas within alkaline-silicate complexes. • Post-orogenic extension aids extraction of melts sourced from foundered arclogites. Magmatic processing in the lower crust of thick-crusted (>40 km) arcs generates garnet-rich clinopyroxenite residues (arclogites) that are denser than the underlying mantle and therefore susceptible to foundering. Arclogites, which can contain substantial amphibole, may undergo partial melting as they sink into the subarc mantle. To constrain the geochemical composition of arclogite-derived melts and the role of arclogite in magmagenesis, we conducted partial melting experiments on average amphibole-bearing arclogite ARC15 at 2 GPa from 1040 to 1300 °C. At subsolidus conditions, garnet and clinopyroxene coexist with lesser amounts of amphibole, ilmenite, and biotite. Hydrous ARC15 begins melting between 1040 and 1080 °C. Once amphibole and biotite are exhausted by 1140 and 1190 °C, respectively, garnet becomes the primary melting phase according to the reaction 0.8 Garnet + 0.2 Clinopyroxene = 1 Melt. At 1300 °C, ARC15 yields 18 wt.% melt, indicating an anomalously low melt productivity of 0.12%/°C and rendering it the least melt-productive of all experimental pyroxenites investigated at 2 GPa. Geochemically, melts sourced from ARC15 are predominantly basanitic with low SiO 2 (43–52 wt.%) and high FeO (10–17 wt.%), TiO 2 (2.5–3.7 wt.%), and alkali (Na 2 O + K 2 O = 3–6.5 wt.%) contents. Such compositions do not resemble magmas erupted at thick-crusted arcs, indicating that arclogites are not a dominant source of magmatism in these settings. Rather, the compositions of ARC15 melts more closely match those of magmas emplaced at post-collisional alkaline-silicate complexes, which form as a result of orogenic collapse and subsequent continental rifting and are common hosts of economic rare-earth element (REE) deposits. Trace element modeling further indicates derivation of alkaline-silicate magmas from variably metasomatized, light REE-enriched arclogite. Our results suggest a geodynamic model in which subduction beneath thickened crust leads to arclogite formation, foundering, and metasomatism as the material descends through the subduction-influenced mantle. During this stage, partial melts sourced from arclogite are likely modified by subduction-related secondary processes which dilute their diagnostic geochemical signatures. Subsequent collision and orogenic collapse induce extensional stresses that facilitate asthenospheric upwelling, leading to partial melting of the arclogite-bearing mantle and efficient extraction of primitive arclogite melts to the surface to form alkaline-silicate complexes and associated REE deposits. [ABSTRACT FROM AUTHOR]

The Menderes massif is a large metamorphic crystalline complex located in western Turkey. The massif consists of late Neoproterozoic basement (core) rocks and Palaeozoic - Cenozoic cover units that have undergone by high- and low-grade polyphase metamorphisms. Palaeozoic to Mesozoic cover units cropped out in the NE edge of the massif (east of Sivaslı) are overlaid tectonically by upper Cretaceous meta-ophiolitic rocks. The meta-ophiolitic unit comprises blocks mainly of metabasalt, metagabbro, metadiorite and metaultramafite within an intensively sheared serpentinite matrix. It also includes blocks of epidote-actinolite-schist and tremolite-actinolite-schist, which originated from basic rocks, as well as chlorite schist blocks, which originated from ultramafic rocks. Sodic-calcic amphiboles recorded in the samples of metabasalt block taken from the marble-metabasalt block boundary, at the tectonic contact where the meta-ophiolitic rocks overlap the underlying marble sequence. Sodic-calcic amphiboles were classified into winchite and ferri-winchite with relatively homogeneous TSi (7.35–8.01 a.p.f.u.), and X Mg (0.69–0.80) values. P-T conditions were estimated to be around 300–400 °C and 5–6 kb based on the mineral chemical analyses of the sodic-calcic amphiboles. According to these values, the NE edge of the Menderes Massif must have undergone metamorphism under a medium-pressure (MP) greenschist facies. • Metabasalts include winchite-ferri winchite at northeastern rim of the Menderes Massif. • Mineral chemistry data indicate a transition zone of MP greenschist-blueschist facies. • The metaophiolitic slice in question is probably related to the Cycladic belt. [ABSTRACT FROM AUTHOR]

• Petrochronological study of a high-P garnet amphibolite. • Multidisciplinary approach results indicate titanite petrogenesis during decompression. • Convergence of multiple thermobarometry methods support the decompression P-T-t path. • Integrated results indicate exhumation of a high-P nappe late during the Grenvillian Orogeny. In this contribution, we present new petrochronological results from samples collected the Shabogamo Domain, of the Grenville Province, Québec, Canada. The Shabogamo domain has a distinct geophysical signature and has been proposed to be linked with the well-studied allochthonous Manicouagan Imbricate Zone. We document a Pressure-Temperature-time (P-T-t) path for an amphibolite sample by combining several approaches including: i) an ordinary least square model able to estimate P-T conditions from amphibole composition using a previously semi-quantitative amphibole thermobarometer ii) titanite petrochronology; iii) phase equilibria modelling; iv) trace element thermometry. We show that single element thermobarometry on titanite and amphibole pairs yield the information necessary to reconstruct a decompression P-T path from peak P-T conditions of 1.8 GPa – 775 °C down to 1.2 GPa – 750 °C and are consistent with results of phase equilibria modelling. Titanite U-Pb geochronology results indicate growth between 987 ± 16 Ma and 969 ± 17 Ma. These results are consistent with U-Pb geochronology on zircon from a dyke that crosscuts the amphibolite and from a deformed leucosome sampled in the domain's footwall. Zircon from the crosscutting dyke appear to have grown at 985 ± 18 Ma without interaction with garnet, whereas zircon from the deformed leucosomes grew at 972 ± 16 Ma during high-pressure metamorphism. Integrating the results of this study into the regional context outlines the exhumation of a second high-P allochthonous nappe, most likely by ductile extrusion, coeval with the burial of the parautochthonous footwall. This study further supports the growing body of evidence for a major tectonic event during the later phase of the Grenvillian Orogeny. [ABSTRACT FROM AUTHOR]

• Progressive δ56Fe in the convergent margins magmas reflects continental crustal oxidation. • Fractionation of amphibole from magmas can controls the removal of the light Fe isotopes. • Control of amphibole fractionation on oxidation widely impacts worldwide arc magmas. • Amphibole can act synergistically to the formation of porphyry deposits. During the process of differentiation, the magmas in convergent margins undergo an increase of oxidized nature, accompanied by a decreased Fe content and concentration of heavy Fe isotopes. Garnet and amphibole are both Fe-rich minerals, which can be responsible for this phenomenon through fractional crystallization. One prevailing hypothesis suggests that Fe2+-rich garnet cumulates in the arc root as a "crustal redox filter." However, the stability of garnets is highly dependent on pressure conditions. In contrast, amphibole can crystallize under a broader range of temperature and pressure conditions and is a more common mineral phase in magmas. As such, the contribution of amphibole might have been underappreciated. Here, we conducted elemental composition, zircon trace element, and high-precision Fe isotope analyses on Miocene magmatic rocks from the Gangdese arc to trace the evolution of magmatic oxidation. The results indicate that the enrichment of heavy Fe isotopes in these magmas is primarily controlled by amphibole-dominated fractional crystallization rather than garnet. This also implies that amphibole fractional crystallization may play a role in enhancing the oxygen fugacity of the magmas. Taking a global perspective, we found a pervasive correlation between amphibole fractional crystallization and Fe isotope fractionation in magmatism at convergent plate margins, indicating its widely applicable influence on oxidation. The influence of garnet cannot be entirely neglected in some specific scenarios, such as within thickened continental arcs, but its impact is generally limited. Continuous amphibole fractional crystallization increases oxidation, facilitating the mobilization and concentration of Cu within the magma, thereby enhancing the potential for porphyry deposit formation. This impact is especially notable in spatiotemporally related magmatic events and could be decisive in determining the magmatic mineralization potential. [ABSTRACT FROM AUTHOR]

• Yaojialing are characterized by high Zn/Cu mineralization in proximal and distal. • Magma mixing resulting in generation of quartz monzonite porphyry parental magma. • Magma mixing increases water content and f O 2 of quartz monzonite porphyry magma. • Initial low f O 2 and Cu, Zn differential release result in the high Zn/Cu. The major factors especially the roles of the magma evolution controlling the Zn/Cu mineralization in skarn deposits are still controversial. Yaojialing is a large-sized skarn Zn polymetallic deposit (1.74 Mt Zn at 3.6 %, 30.4 t Au at 4.2 g/t and 24.8 t Cu at 0.83 %) located in the Tongling district of the Middle–Lower Yangtze belt (MLYB), both the proximal and distal areas of the deposit exhibit high Zn/Cu mineralization. The intrusions in Yaojialing primarily consist of quartz monzonite porphyry (QMP) and granodiorite porphyry (GDP), and the QMP is related to skarn mineralization. Both the QMP and GDP display relatively high (87Sr/86Sr) i values (0.707907 to 0.709390), low ε Nd (t) values (−9.05 to −8.17) and negative ε Hf (t) values (−8.51 to −11.72), suggesting that they originated from a mixed source of enriched mantle and lower crust. Both the QMP and GDP contain type I and type II amphiboles, while type III amphibole exists only in QMP. Type I amphibole is acicular crystals shape, type II amphibole is euhedral in shape and relatively large in size (0.6–2.0 mm), while type III amphibole crystallized around the margin of type II amphibole. The type I amphibole from QMP and GDP show similar calculated temperatures (948–1010 ℃), pressures (2.9–6.5 kbar, corresponding depths at 11.0 to 24.4 km), f O 2 (ΔFMQ = 0.2–1.9) and H 2 O content (4.2–6.8 wt%). Type II amphibole crystallized at 815–941 ℃, 1.2–2.9 kbar (corresponding to depth of 4.6–11.1 km), ΔFMQ = 0.7–2.1, and 4.4–5.7 wt% H 2 O. Type III amphibole have a lower temperature (679–795 ℃), pressure (<0.5 kbar) and water content (2.5–4.3 wt%) but higher f O 2 value (ΔFMQ = 3.1–3.8) compared to type I and type II amphiboles. Reverse zoning of plagioclase and higher Mg# (74 to 89) of type III amphibole in QMP are resulted from injection of mafic magma at shallow depths, which provide sufficient metal and favorable conditions for the formation of QMP parental magma. Modeling of magma H2O solubility indicates that QMP begins to exsolve fluid at depth of 6.2–11.1 km. Initial low oxygen fugacity and ore-forming element differential release during fluid exsolution process resulted in the high Zn/Cu mineralization at Yaojialing. [ABSTRACT FROM AUTHOR]

Paleoproterozoic tectonic evolution of the northern North China Craton has been a hot research topic. We firstly identified a 1.85 Ga hornblendite from the Gaositai mafic–ultramafic complex, in northern Hebei. Systematic studies of petrology, zircon U-Pb geochronology, and in situ mineral major and trace elements of hornblendite are the key to revealing the petrogenesis of the Paleoproterozoic ultramafic rock and the tectonic evolution of northern North China Craton. LA-ICP-MS zircon U-Pb dating suggests the Gaositai hornblendite formed at 1851 ± 44 Ma. The late Paleoproterozoic ultramafic rocks, together with coeval post-collisional granites, formed a bimodal igneous assemblage. Both hornblende and its equilibrium melt compositions show strongly fractionated HREE patterns, relative enrichments in LREEs and LILEs, and depletions in HREEs and HFSEs. The phlogopite-bearing hornblendite magma could have originated from a hydrous garnet-facies mantle source metasomatized by slab-derived silicate melt. Furthermore, the variations of major and trace elements in hornblende from core to rim also reveal the mineral fractional crystallization and magma recharge. Zircon trace elements, melt composition equilibrium with hornblendes, and the bimodal igneous assemblage suggest that the generation of the Gaositai Paleoproterozoic hornblendite was likely the product of post-collisional extension related to the collision between eastern and western North China blocks. [ABSTRACT FROM AUTHOR]

Aluminum-rich and Si-poor calcium amphibole [~3.9 Al atoms per formula unit (apfu) and ~5.5 Si apfu for 23 O] occur in the quartz-bearing eclogites from the Donghai area, Sulu ultrahigh-pressure metamorphic belt, eastern China. Most of the aluminous amphibole phases are retrograde products from the exhumation and hydration stage and are texturally divided into a mantle phase around a porphyroblastic garnet and a crack-filling (vein) phase of a garnet. Less aluminous amphibole occurs as symplectite phase with plagioclase after omphacite. The formation process of the aluminous amphibole in the quartz-bearing samples is discussed on the basis of the analytical data by EPMA, FIB-TEM, and EBSD. The mantle amphibole occurs between garnet and symplectite or quartz. A set of plagioclase and aegirinediopside/argirine-hedenbergite thin monomineralic bands forms at the boundary between the mantle amphibole and matrix quartz. However, these monomineralic bands do not occur at the mantle amphibole-symplectite boundary. These textural diferences indicate that the recrystallization of the aluminous amphibole around garnet was controlled by significant local reactions, and the size of equilibrate domains was probably several tens of micrometers or less. The mantle amphibole is composed of inner (garnet-side) and outer (matrix-side) zones. The inner zone is compositionally homogeneous, and its atomic Al/Si value is ~0.63–0.66 and similar to that of garnet. Atomic Ca/Si value in the inner zone is also almost uniform and is generally identical to that of garnet. The outer zone exhibits a monotonic decrease in the Al/Si and Ca/Si values outward, and its composition at the outermost margin is similar to that of the symplectitic amphibole. The crack-filling amphibole has a composition similar to the inner zone of the mantle amphibole. The CPO pattern of the crack-filling amphibole is diferent from that of the adjacent mantle amphibole, showing that the crack-filling amphibole is cut by the mantle amphibole. The textural relationship between the mantle and crack-filling amphibole phases and their compositional characteristics imply that: (1) the mantle type is a slightly later stage product than the crack-filling type, and (2) the boundary between the inner and outer zones of the mantle aluminous amphibole probably corresponds to the initial surface of the porphyroblastic garnet. The inner zone is considered to have grown inward by simple substitution of garnet, using the tetrahedral and octahedral cations of the garnet as the basic framework. On the other hand, most of the outer zone of the mantle-type amphibole grew outward in the matrix from the initial surface of the garnet porphyroblast. The mantle amphibole shows a CPO similar to that of amphibole in the adjacent symplectite domain, suggesting that these two types of amphibole formed almost simultaneously, sharing crystallographic orientation with each other. The formation of crack-filling aluminous amphibole was probably promoted by the hydraulic microfracturing process at an early stage of exhumation and hydration. The mantle and symplectitic amphibole phases formation was promoted by the subsequent infiltration of metamorphic fluid. The aluminous amphibole in the SiO2 phase-bearing eclogites probably recrystallized with the formation of a localized SiO2-undersaturated reaction domain because of rapid exhumation and subsequent rapid cooling of the Sulu UHP metamorphic belt. [ABSTRACT FROM AUTHOR]

To investigate the direct evidence for a number of physico-chemical processes related to pluton construction and growth, we examine the Buya pluton of West Kunlun in Northwestern China, which emplaced within the 455-460 Ma time frame. Field observations, geochemical data, and thermodynamic modeling show that mafic dikes of the Buya pluton were conduits for magma chamber replenishment during pluton construction. These mafic inputs, and the enclaves that resulted from them, induced compaction of the semi-consolidated, crystal-rich, felsic mushes below them. The accumulation of highly silicic, fine-grained granite at the top of the Buya pluton is the result of episodic melt segregation events from these mushes. This sequence of events may reflect a common process that promotes compositional variation in granite suites. Combined geochemical and Hf- and Nd-isotopic data suggest that parental magmas of the mafic sheet and enclave are similar to sanukitoid, which is potentially consistent with a mantle peridotitic source metasomatized by slab melts. These mafic magmas intruded the lower crust where the original magma was modified by mafic lower-crust melt. Following emplacement at shallow crustal levels of the mafic inputs (~3.7 kbar, ~5.3 km, constrained by amphibole geobarometry), the felsic mush evolved through the extraction of interstitial melts driven by hybridization with episodic inputs of mafic magmas as well as crystal consequent accumulation and fractional crystallization of plagioclase, hornblende, and accessory phases such as allanite, apatite, and zircon. This fractional crystallization process may also provide an explanation for the apparently high Sr/Y features in some silicic high-K, calc-alkaline magmas. [ABSTRACT FROM AUTHOR]

Garnet–kyanite–staurolite assemblages with large, late porphyroblasts of amphibole form garbenschists in Ordovician volcaniclastic rocks lying immediately south of the Pearya terrane on northernmost Ellesmere Island, Canada. The schist, which together with carbonate olistoliths makes up the Petersen Bay Assemblage (PBA), displays a series of parallel isograds that mark an increase in metamorphic grade over a distance of 10 km towards the contact with Pearya; however, a steep, brittle Cenozoic strike-slip fault with an unknown amount displacement disturbs the earlier accretionary relationship. The late amphibole growth, probably due to fluid ingress, is clear evidence of disequilibrium conditions in the garbenschist. In order to recover the P–T history of the schists, we construct isochemical phase equilibrium models for a nearby garnet–mica schist that escaped the fluid event and compare the results to quartz inclusion in garnet (QuiG) barometry for a garbenschist and the metapelitic garnet schist. Quartz inclusions are confined to garnet cores and the QuiG results, combined with Ti-in-biotite and garnet–biotite thermometry, delineate a prograde path from 480 to 600°C and 0.7 to 0.9 GPa. This path agrees with growth zoning in garnet deduced from X-ray maps of the spessartine component in garnet. The peak conditions obtained from pseudosection modelling using effective bulk composition and the intersection of garnet rim with matrix biotite and white mica isopleths in the metapelite are 665°C at ≤0.85 GPa. Three generations of monazite (I, II and III) were identified by textural characterization, geochemical composition (REE and Y concentrations) and U–Pb ages measured by ion microprobe. Monazite I occurs in the matrix and as inclusions in garnet rims and grew at peak P–T conditions at 397 ± 2 Ma (2σ) from the breakdown of allanite. Monazite II forms overgrowths on matrix Monazite I grains that are oriented parallel to the main schistosity and yield ages of 385 ± 2 Ma. Monazite III, found only in the garbenschist, is 374 ± 6 Ma, which is interpreted as the time of amphibole growth during fluid infiltration at lower temperature and pressure on a clockwise P–T path that remained in the kyanite stability field. These results point to a relatively short (≈12 Myr) Barrovian metamorphic event that affected the schists of the PBA. An obvious heat source is lacking in the adjacent Pearya terrane, but we speculate it was large Devonian plutons—similar to the 390 ± 10 Ma Cape Woods granite located 40 km across strike from the fault—that have been excised by strike-slip. Arc fragments that are correlative to the PBA are low grade; they never saw the heat and were not directly involved in Pearya accretion. [ABSTRACT FROM AUTHOR]

Keywords: Amphiboles; thermal expansion; X-ray diffraction; modeling EN Amphiboles thermal expansion X-ray diffraction modeling 1302 1312 11 07/05/22 20220701 NES 220701 Introduction In a recent paper, [20] reported thermal expansion results for a chemically diverse group of pyroxene minerals based on high-temperature X-ray powder diffraction data. [Extracted from the article]

Andesites are iconic of subduction zone magmatism. Yet intermediate magmas (57–66 wt % SiO2) are less abundant than generally thought in arc settings. A comparison of experimental hydrous liquid lines of descent, melt inclusions and bulk-rock compositions demonstrates the importance of polybaric crystallization–differentiation in producing the compositional range and dictating the relative abundance of arc melts, but also highlights the preponderant role of mixing (sensu lato) in producing andesitic magmas. Based on their P2O5 contents, at least 74% of the arc magmas with around 64 wt % SiO2 are inferred to be mixing products. In addition to their surprisingly low abundance, andesitic melt inclusions are characterized by relatively low H2O, Al2O3, ± Na2O contents compared to the ranges measured in mafic and silicic melt inclusions. These compositional characteristics suggest that there is a sweet spot for the production of andesitic melts delimited by the low-pressure stability limit of amphibole (<150 MPa) and the adiabatic ascent path of mafic melts, but that this low-pressure differentiation pathway plays a minor role in the production of silicic arc magmas that principally form along high-pressure hydrous liquid line of descents (>700 MPa) before decompression. The compositional bimodality recorded by the melt inclusions and in well-preserved intra-oceanic arc crustal sections is a fundamental characteristic of differentiation in transcrustal arc magmatic systems, with important consequences for the chemical evolution of the continental crust. We propose that the overall bimodality shown by arc melts does not relate to a compositional gap in the differentiation mechanisms but results from a combination of (1) the disparity in volume of differentiated magmas produced by low and high-pressure crystallization–differentiation and (2) the strong nonlinearity of the high-pressure liquid lines of descent in composition–temperature–crystallinity space related to crystallization of amphibole-rich assemblages. In this context, the compositional characteristics shared by andesitic magmas and the continental crust principally depict the central role of mixing and mass balance processes in producing andesitic compositions. The step in differentiation efficiency encountered by hydrous magmas entering the amphibole stability field at high pressure plays an important role in defining the silicic component involved in these scenarios. [ABSTRACT FROM AUTHOR]

The airborne Time-domain electromagnetic data acquired over the Ilesha Schist Belt in southwestern Nigeria were filtered, enhanced and analysed to generate ground conductivity responses at different time gates and employed to characterise the subsurface in terms of rock distribution, structural framework as well as evaluate the gold and base metal mineralisation potential of the region. The near-surface sensitive early time gate conductivity responses (EMZ1 – EMZ3) indicate relatively high subsurface conductivity distribution (60–120 mS/m) in amphibole schist and pegmatite terrain in the west while medium to low-conductivity (<5 mS/m) values were recorded in the east underlain by granitic rocks. Major and minor linear/sub-linear conductive features having conductivity in excess of 2 mS/m and trending NE-SW, NNE-SSW, NNW-SSE and ENE-WSW directions were delineated on the mid conductivity time gate responses (EMZ3 – EMZ5). One of which presents geometry and pattern consistent with the well-reported Ifewara – Iwaraja fault system that runs through the entire Ilesha Schist Belt. Very high anomalous conductivity (160–300 mS/m) responses at late conductivity time gates (EMZ10 – EMZ13) with characteristic long decay curves were obtained over isolated zones, especially along fractures and veins suggesting the occurrence of structurally controlled gold and base metal mineralisation. [ABSTRACT FROM AUTHOR]

Major and trace elements in omphacite, including hydrogen, were determined in eclogites from two Variscan basement complexes in Germany: Erzgebirge (EG) and Fichtelgebirge (FG). Erzgebirge eclogite is derived from three units, showing different peak pressure (P) and temperature (T) conditions (Unit 1: 840–920°C/≥30 kbar, Unit 2: 670–730°C/24–26 kbar, Unit 3: 600–650°C/20–22 kbar). The peak conditions of FG eclogite (690–750°C/25–28 kbar) resemble those of EG Unit 2. Coesite eclogite occurs in EG Unit 1, and quartz eclogite in all other units. Omphacite from all samples shows four infrared (IR) absorption bands. Two prominent, sharp bands occur at 3,455 ± 10 cm−1 (band II) and 3,522 ± 10 cm−1 (band III). Band II is usually more prominent than band III, except for few samples with low jadeite content. A further, broad band is centred between 3,270 and 3,370 cm−1 (band I) and a fourth, minor band at 3,611–3,635 cm−1 (band IV). Bands II and III are due to hydrogen bound as structural OH− ions in omphacite. In most cases, this also applies to band IV. However, some spectra with extremely large type IV bands reflect phengite inclusions. The ambiguous band I may be due to different H2O species (molecular water, structural OH, and water in phengite). Omphacite of quartz eclogite has lower contents of TiO2, Zr, Hf, and REE, compared with that from coesite eclogite. By contrast, omphacite in quartz eclogite from both EG (H2O sample averages: 465–852 ppm) and FG (546–1,089 ppm) contains the same amount of structural OH (concentrations given in wt.‐ppm H2O) as omphacite in coesite eclogite (492–1,140 ppm). The obtained difference in the garnet‐omphacite H2O partition coefficient between quartz (0.01–0.03) and coesite eclogite (0.08–0.11) results from different H2O contents in garnet (coesite eclogite: 50–150 ppm; quartz eclogite: <2–50 ppm; Gose & Schmädicke, 2018). The total content of structural OH in omphacite is unrelated to its major and trace element composition. However, treating the individual IR bands separately, a relation between OH and mineral composition is observed. The OH amount defined by band II is positively correlated to Ti and tetrahedral Al, and that of band III shows a positive correlation with Ca and a negative one with Na (and jadeite). Both the total OH content of omphacite and the partial contents deduced from individual IR bands are unrelated to PT conditions. This implies that omphacite incorporated its structural H2O mainly in the quartz stability field, presumably during initial omphacite growth. Conversely, most OH in garnet was derived from the final breakdown of the last remaining calcic amphibole close to or within the coesite stability field. Our data suggest that coesite eclogite is able to transport a significant amount of H2O (average 550 ppm, maximum 730 ppm), corresponding to that in 3–4 vol.% calcic amphibole, via subduction to depths beyond 100 km. However, the majority of water liberated by dehydration reactions during subduction, including the breakdown of 5–10 vol.% eclogite facies and >10 vol.% pre‐eclogitic hydrous minerals, is not preserved in eclogite but liberated to the mantle wedge. [ABSTRACT FROM AUTHOR]

Accessory and minor phases are frequently used to infer the composition and intensive parameters of magmas. In granites, the most common ferromagnesian phases are biotite and amphibole, which raises the question as to what compositional domains are present among these phases and how do those domains relate to granite composition. Here we present a characterization of biotite and amphibole compositions from S-, I-, and A-type granites. A database of biotite (1215 data points) and amphibole (525 data points) compositions from previously classified S-, I-, and A-type granites has been compiled. Three characteristics can be used to describe the variations in biotite composition including X Annite Bt (fraction of Fe2+ in the octahedral site), X Fe VI ∗ Bt (fraction of total iron in the octahedral site), and total aluminum (apfu). Three characteristics can also be used to describe variations in amphibole composition including, NK/CNK [i.e., (Na + K)/(Ca + Na + K)], Fe/(Fe + Mg), and total aluminum. Utilizing, for the first time, a random forest (machine learning) model the three characteristics for biotite and amphibole could discriminate the inferred source region of the granites with 82 and 96% accuracy, respectively. Biotite composition can also be used to broadly characterize f O 2 , f H 2 O f HF , f H 2 O f HCl , and f HF f HCl of each granite type at a given temperature and pressure. Thus, biotite and amphibole compositions can be used to further characterize granites; however, biotite and amphibole should not solely be used to infer the source of a granite. [ABSTRACT FROM AUTHOR]

A plausible origin of the seismically observed mid-lithospheric discontinuity (MLD) in the subcontinental lithosphere is mantle metasomatism. The metasomatized mantle is likely to stabilize hydrous phases such as amphiboles. The existing electrical conductivity data on amphiboles vary significantly. The electrical conductivity of hornblendite is much higher than that of tremolite. Thus, if hornblendite truly represents the amphibole varieties in MLD regions, then it is likely that amphibole will cause high electrical conductivity anomalies at MLD depths. However, this is inconsistent with the magnetotelluric observations across MLD depths. Hence, to better understand this discrepancy in electrical conductivity data of amphiboles and to evaluate whether MLD could be caused by metasomatism, we determined the electrical conductivity of a natural metasomatized rock sample. The metasomatized rock sample consists of ~87% diopside pyroxene, ~9% sodium-bearing tremolite amphibole, and ~3% albite feldspar. We collected the electrical conductivity data at ~3.0 GPa, i.e., the depth relevant to MLD. We also spanned a temperature range between 400 to 1000 K. We found that the electrical conductivity of this metasomatized rock sample increases with temperature. The temperature dependence of the electrical conductivity exhibits two distinct regimes. At low temperatures <700 K, the electrical conductivity is dominated by the conduction in the solid state. At temperatures >775 K, the conductivity increases, and it is likely to be dominated by the conduction of aqueous fluids due to partial dehydration. The main distinction between the current study and the prior studies on the electrical conductivity of amphiboles or amphibole-bearing rocks is the sodium (Na) content in amphiboles of the assemblage. Moreover, it is likely that the higher Na content in amphiboles leads to higher electrical conductivity. Pargasite and edenite amphiboles are the most common amphibole varieties in the metasomatized mantle, and our study on Na-bearing tremolite is the closest analog of these amphiboles. Comparison of the electrical conductivity results with the magnetotelluric observations constrains the amphibole abundance at MLD depths to <1.5%. Such a low-modal proportion of amphiboles could only reduce the seismic shear wave velocity by 0.4–0.5%, which is significantly lower than the observed velocity reduction of 2–6%. Thus, it might be challenging to explain both seismic and magnetotelluric observations at MLD simultaneously. [ABSTRACT FROM AUTHOR]

Geochemical and isotopic data are presented for ~ 32 Ma-old high-K andesites and dacites from the Alpine Chain. The samples consist of plagioclase, amphibole, titanomagnetite and rare biotite and quartz. Geochemical and isotope data indicate that slab-derived fluids, sediment melts and presumably AFC processes involving continental crust played a key role in the petrogenesis of the high-K rocks. A contribution of fluids is suggested based on the overall enrichment of large-ion lithophile elements and related high Ba/La, Ba/Zr, Ba/Th, Ba/Nb and Pb/Nd, sometimes distinctively higher than average continental crust. Positively correlated Ba/Nb-Th/Nb relationships, low Ce/Pb, low Nb/U and a negative correlation of Pb isotopes with Ce/Pb and Nb/U and positive â 7/4 and â 8/4 values similar to GLOSS imply the additional involvement of a sediment-derived melt. Negatively correlated Nb/Ta-Zr/Hf ratios at overall low Nb/Ta (13-7.5) are best explained by parental magma differentiation involving amphibole and biotite in a continental arc system. The samples have moderately unradiogenic Nd ([epsilon]Nd: - 2.0 to - 6.7) and radiogenic .sup.87Sr/.sup.86Sr isotope compositions (0.7085-0.7113), moderately radiogenic Pb isotope compositions (.sup.206Pb/.sup.204Pb: 18.50-18.72; .sup.207Pb/.sup.204Pb: 15.59-15.65; .sup.208Pb/.sup.204Pb: 38.30-38.67), and elevated [delta].sup.18O values (+ 6.5 to + 9.1 â°). Epsilon Hf isotope values range from + 2.5 to - 4.0. Negative [epsilon]Hf(t) and [epsilon]Nd(t) values and .sup.206Pb/.sup.204Pb ratios are correlated with elevated K.sub.2O abundances that indicate enrichment in K.sub.2O is related to AFC processes. The offset of [epsilon]Hf at a given [epsilon]Nd points to involvement of aged garnet-bearing crustal lithologies. The latter feature is qualitatively consistent with modification of unexposed primary basaltic andesites by AFC processes involving deep crustal material. In conclusion, in an Alpine context, inferred unexposed primitive high-K basaltic to andesitic melts are generated in the mantle wedge through fluid infiltration from the descending slab where fluids may have caused also partial melting of sedimentary rocks that mixed with evolving andesite-dacite compositions towards shallow-level intrusive and extrusive rocks. High-K and related trace element and isotope features thus result from a combination of already elevated values with participation of fluids and melts and probably AFC processes., Author(s): S. Jung [sup.1], J. A. Pfänder [sup.2], O. Nebel [sup.3], M. Willbold [sup.4], S. Hoernes [sup.5], J. Berndt [sup.6], A. Pack [sup.4] Author Affiliations: (1) grid.9026.d, 0000 0001 2287 [...]

Amphibole asbestos is related to lung fibrosis and several types of lung tumors. The disease-triggering mechanisms still challenge our diagnostic capabilities and are still far from being fully understood. The literature focuses primarily on the role and formation of asbestos bodies in lung tissues, but there is a distinct lack of studies on amphibole particles that have been internalized by alveolar epithelial cells (AECs). These internalized particles may directly interact with the cell nucleus and the organelles, exerting a synergistic action with asbestos bodies (AB) from a different location. Here we document the near-atomic- to nano-scale transformations induced by, and taking place within, AECs of three distinct amphiboles (anthophyllite, grunerite, "amosite") with different Fe-content and morphologic features. We show that: (i) an Fe-rich layer is formed on the internalized particles, (ii) particle grain boundaries are transformed abiotically by the internal chemical environment of AECs and/or by a biologically induced mineralization mechanism, (iii) the Fe-rich material produced on the particle surface does not contain large amounts of P, in stark contrast to extracellular ABs, and (iv) the iron in the Fe-rich layer is derived from the particle itself. Internalized particles and ABs follow two distinct formation mechanisms reaching different physicochemical end-states. [ABSTRACT FROM AUTHOR]

Ferro-papikeite, ideally NaFe22+(Fe32+Al2)(Si5Al3)O22(OH)2, is a new mineral of the amphibole supergroup from the Filipstad Municipality, Värmland County, Central Sweden, where it occurs in a medium-grade felsic metavolcanic rock. Ferro-papikeite is pale brown with a translucent luster, has a colorless to very pale-brown streak, and shows no fluorescence under long-wave or short-wave ultraviolet light. Grains are subhedral, 0.4–3.0 mm in size, and show well-developed {210} cleavage. It has a Mohs hardness of ~6 and is brittle with a splintery fracture, has the characteristic perfect {210} cleavage of orthorhombic amphiboles, intersecting at ~56°, and the calculated density is 3.488 g/cm3. In transmitted plane-polarized light, ferro-papikeite is moderately pleochroic X = very pale brown, Y = Z = honey brown; X < Y = Z. Ferro-papikeite is biaxial (+), α = 1.674(2), β = 1.692(2), γ = 1.716(2), 2Vmeas = 86.2(9) and 2Vcalc = 88.3°, dispersion is r < v, weak. The orientation is: X || a, Y || b, Z || c. Ferro-papikeite is orthorhombic, space group Pnma, a = 18.628(4), b = 17.888(4), c = 5.3035(11) Å, V = 1767.2(6) Å3, Z = 4. The strongest ten X‑ray diffraction lines in the powder pattern are [d in Å(I) (hkl)]: 8.255(100)(210), 3.223(39)(440), 3.057(68)(610), 2.824(28)(251), 2.674(41)(351), 2.572(56) (161,621), 2.549(38)(202), 2.501(50)(261,451), 2.158(25)(502), and 1.991(31)(661). Chemical analysis by electron microprobe gave SiO2 36.50, Al2O3 22.24, TiO2 0.09, FeO 31.54, MnO 0.65, MgO 5.48, CaO 0.08, Na2O 2.35, F 0.22, H2Ocalc 1.85, O=F –0.09, sum 100.91 wt%. The formula unit, calculated on the basis of 24 (O+OH+F) with (OH) = 2 apfu and Fe3+ = 0.13 apfu (determined from the distance) is A(Na0.70Ca0.01)B+C(Mg1.25Fe23.90+ Mn20.08+ Al1.62Fe30.13+ Ti40.01+)Σ6.99T(Si5.60Al2.40)Σ8O22(OH1.89F0.11)2. The crystal structure of ferro-papikeite was refined to an R-index of 3.60% using 2335 unique observed reflections collected with MoKa X-radiation. [4]Al3+ is ordered over the four T sites as follows: T 1B > T1A > T2B >> T2a, [6]Al3+ is completely ordered at M2, and Fe2+ is strongly ordered at M4. The A site is split with Na+ strongly ordered at A1. End-member ferro-papikeite is related to end-member gedrite, □Mg2(Mg3Al2)(Si6Al2)O22(OH)2, by the substitutions Na+ → □, Fe2+ → Mg, and Al3+ → Si4+. The description of ferro-papikeite as a new species further emphasizes the compositional similarities between the monoclinic calcium amphiboles and the orthorhombic magnesium-iron-manganese amphiboles. [ABSTRACT FROM AUTHOR]

Here we present new occurrences of amphibole in a suite of chromitites, dunites, and harzburgites from the mantle sequence of the Lycian ophiolite in the Tauride Belt, southwest Turkey. The amphibole occurs both as interstitial grains among the major constituent minerals and as inclusions in chromite grains. The interstitial amphibole shows generally decreasing trends in Na2O and Al2O3 contents from the chromitites (0.14–1.54 wt% and 0.04–6.67 wt%, respectively) and the dunites (0.09–2.37 wt%; 0.12–11.9 wt%) to the host harzburgites (<0.61 wt%; 0.02–5.41 wt%). Amphibole inclusions in chromite of the amphibole-bearing harzburgites are poorer in Al2O3 (1.12–8.86 wt%), CaO (8.47–13.2 wt%), and Na2O (b.d.l.–1.38 wt%) than their counterparts in the amphibole-bearing chromitites (Al2O3 = 6.13–10.0 wt%; CaO = 12.1–12.9 wt%; Na2O = 1.11–1.91 wt%). Estimated crystallization temperatures for the interstitial amphibole grains and amphibole inclusions range from 706 to 974 °C, with the higher values in the latter. A comparison of amphibole inclusions in chromite with interstitial grains provides direct evidence for the involvement of water in chromitite formation and the presence of hydrous melt/fluid metasomatism in the peridotites during initial subduction of Neo-Tethyan oceanic lithosphere. The hydrous melts/fluids were released from the chromitites after being collected on chromite surfaces during crystallization. Different fluid/wall rock ratios are thought to have controlled the crystallization and composition of the Lycian amphibole and the extent of modification of the chromite and pyroxene grains in the peridotites. Considering the wide distribution of podiform chromitites in this ophiolite, the link between chromitite formation and melt/fluid metasomatism defined in our study may be applicable to other ophiolites worldwide. [ABSTRACT FROM AUTHOR]

bstract: The mineral zoning of corundum-bearing rocks of the Belomorian mobile belt, whose genesis remains controversial, has been studied at one of the typical occurrences: Khitoostrov. Based on the estimates of the P–T parameters of the formation of corundum-bearing rocks by the multiequilibrium thermobarometry method, pseudosections were constructed using the Perple_X 6.9.0 software package in P–T, T–µ(SiO2), µ(SiO2)–µ(Na2O), and µ(SiO2)–µ(K2O) space, with CO2–H2O fluid, to model the metasomatic transformation of migmatized kyanite–garnet–biotite gneisses of the Chupa sequence. It has been established that the mineral zoning of the corundum-bearing rocks reflects the successive transition of SiO2, Na2O and K2O to a mobile state. Desilication in the outer zones led to the formation of' quartz-free associations, alkaline sodic metasomatism concurrent with ongoing desilication led to the formation of associations with staurolite and plagioclase, and K2O removal led to the replacement of biotite with calcium amphibole. Further desilication and sodic metasomatism resulted in mineral assemblages with corundum. This process is reflected in an increase in the sodium content in the calcic amphibole and variations in the Ca content of the garnet at a practically constant composition of the plagioclase. [ABSTRACT FROM AUTHOR]

The potential toxic effects of short chrysotile and amphibole asbestos fibers with lengths <5 to ∼10 µm have been debated over the years. This stems from the large database of epidemiology, toxicology, and in-vitro studies, each of which often provides different information in understanding and differentiating the effects of short fibers. The epidemiology studies in which the cancer potency estimates were based upon relatively high exposure concentrations provide a conservative assessment that shorter fibers would have little if any effect, especially under controlled exposure or environmental conditions that may occur today. The QSAR models have shown that fiber aspect ratio and Mg content are excellent predictors of cancer potency and that short fibers/particles of amphibole would have no effect. The studies of motor vehicle mechanics and in particular workers who serviced chrysotile containing brakes with the majority of the fibers being short provides evidence that motor vehicle mechanics, including workers who were engaged in brake repair, are not at an increased risk of mesothelioma. Several inhalation toxicology studies clearly differentiated that short chrysotile and amphibole asbestos fibers did not produce a significant carcinogenic effect in the lung or pleural cavity. Because of dosing and lack of sensitivity to biosolubility, in vitro studies can be difficult to interpret; however, a number have differentiated short chrysotile and amphibole asbestos fibers from long fibers. Integral to understanding the importance of fiber length in determining possible health effects is an understanding of the biological and physiological function of the respiratory system. Short asbestos fibers, like innocuous dust, can be cleared through the tracheobronchial ciliated mucous transport, phagocytized by macrophages and cleared via the bronchial tree, and can also be removed through the lymphatic system. While the first two methods can remove them from the lung, with lymphatic transport through one-way valves, fibers are removed from the active area of the lung where the fiber-related disease has been shown to develop and can accumulate in lymphatic sumps and lymph nodes. While short asbestos fibers are present in most occupational or environmental exposures, the large body of studies strongly supports that they do not contribute to the health effects of asbestos exposure. [ABSTRACT FROM AUTHOR]

We report new petrographic and geochemical observations on magmatic sulfides occurring in different enclave types, including hornblende and/or clinopyroxene‐rich cumulates, and in the host lavas, in Nisyros (South Aegean volcanic arc). We discuss our findings in the context of pre‐existing petrological and thermobarometry studies. Our results indicate that sulfides become less abundant and Cu‐richer (Cu median values) with magma differentiation at progressively lower pressure/P‐temperature/T‐depth conditions. Starting with high T‐P sulfide‐free pillow lavas and wehrilitic cumulates still representing a sulfide undersaturated system, passing to high T and lower P, deep‐forming sulfide‐rich and hornblende‐rich gabbroic enclaves (SiO2 = 53–55 wt.%, 4–5 × 10−5 area %, Cu = 260 μg/g) at the base of the crust (∼25–30 km), then to clinopyroxene‐rich gabbroic micro‐cumulates (2–3 × 10−5 area %, Cu = 570 μg/g) forming in shallower crustal levels (∼10 km), then to more evolved sulfide‐poor hybrid enclaves (SiO2 = 56–70 wt.%, 1 × 10−5 area %, Cu = 602 μg/g), and finally to even more sulfide‐poor rhyodacitic host lavas (SiO2 = 66–76 wt.%, <0.5 × 10−5 area %, Cu = 6.4 wt.%) differentiating at even shallower crustal levels (∼7 km). Sulfide‐free quenched basaltic andesitic enclaves differentiating near surface levels, carry no textural evidence of pre‐existing magmatic sulfides suggesting that the system returned to a sulfide‐undersaturated state. Finally, we point out two important processes for sulfide evolution, a reaction replacement of clinopyroxene by amphibole observed in the deep‐forming hornblende‐rich gabbroic enclaves triggering the onset of sulfide saturation, and an increased mafic input followed by magma mingling and enclave disaggregation leading to sulfide dissolution and Cu‐enrichment of the magmas. Plain Language Summary: In this study we investigate the occurrence and chemistry of magmatic sulfide minerals found within volcanic lavas, and within smaller rock inclusions (‐enclaves), of Nisyros active volcano, located in the Aegean arc. Sulfides are the main repositories of Cu and other precious metals and thus determine their availability in the residual ascending melt which in turn affects the potential of a system to produce an economic ore deposit. Meanwhile, enclaves offer a unique possibility to "access" different parts of a plumbing system, as they preserve the information corresponding to a specific depth range. Our results are discussed in the context of previous studies which have extensively studied the plumbing system of Nisyros. Understanding what triggers the formation of these sulfides, as well as how do they evolve from the roots to the surface of a well‐studied plumbing system can help to further constrain metal transport and concentration through the crust. Our results suggest that sulfides: (a) form at the base of the crust with the first occurrence of amphibole, (b) become less abundant and Cu‐richer with magma evolution at progressively lower crustal depths, and (c) dissolve, thus causing the release of metals back in the system. Key Points: Magmatic sulfide saturation is triggered at the base of the crust due to the replacement of clinopyroxene by amphiboleMagmatic sulfide abundance and composition vary according to magma evolution and the T‐P‐depth of magma differentiationIncreased mafic input followed by magma mingling and enclave disaggregation lead to sulfide dissolution and Cu‐enrichment of the magmas [ABSTRACT FROM AUTHOR]

The physical and chemical properties of magma govern the eruptive style and behaviour of volcanoes. Many of these parameters are linked to the storage pressure (P) and temperature (T) of the erupted magma, and the chemistry of the melt phase (X). However, reliable single-phase thermobarometers (P, T) and chemometers (X) which can recover this information remain elusive. We present a suite of new single-phase amphibole and clinopyroxene thermobarometers and chemometers, calibrated using random forest machine learning. These calibrations are used to track the range of pre-eruptive conditions, over the course of a millennial eruptive cycle, on an island arc volcano (Mount Liamuiga, Saint Kitts, Eastern Caribbean). We unpick the recent history of Mount Liamuiga, a stratovolcano that produces a dacitic eruption from the upper crust (~ 2 kbar) prior to the Lower Mansion Series eruptive sequence. This precedes a systematic increase in the temperature of crystallisation recovered by amphibole and clinopyroxene in the middle to upper crust (1.2 ± 0.5 to 5.6 ± 2.4 kbar), which correlates with a remarkable progression of matrix plagioclase chemistry to a less-evolved (more anorthitic) composition in time. Prediction of melt chemistry (SiO2, Al2O3, CaO, Na2O, K2O, FeO, MgO, TiO2) in equilibrium with clinopyroxene and amphibole delineate a liquid line of descent concordant with measured groundmass and whole rock chemistry. We also show that the regression strategy, as opposed to the abject insensitivity to pressure, has hindered previous calibrations of amphibole-only barometers. By applying our new calibrations, we construct a quantitative picture of the magma plumbing system beneath an arc volcano. [ABSTRACT FROM AUTHOR]

A peralkaline granite of the Ilímaussaq Complex, South Greenland, contains the rare mineral henrymeyerite [(Ba0.92Na0.05Ca0.03)1.0(Ti6.87Fe2+ 1.04Nb0.03)7.9O16], a low-Fe Ba titanate [(Ba0.74Ca0.02Na0.05)0.8 (Ti4.9oFe2+ 0.15 Nb0.04)5.1O11], and an unidentified Ba titanosilicate. Both titanates show the coupled substitution 2Na+ + Si4+ → Ba2+ + Ti4+. The minerals are present as tiny crystals fringing ilmenite inclusions in an amphibole crystal and are thought to have formed during the hydrothermal stage of the granite's evolution. [ABSTRACT FROM AUTHOR]

The present study focuses on the mineral chemistry data of Early–Cenozoic volcanic rocks in the south of the Tarom-Hashtjin magmatic zone. The Uchbolaq lavas in the north of Zanjan are a part of Oligocene eruptions within the Turkish-Iranian plateau. The microprobe analysis of the andesite-trachyandesites’ samples from this area indicates that the rocks under study composed of, labradorite (An55-66), augite (Wo44 En44 Fs12), Mg-hastangsite ((Na+K)A≥0.50 and Alvi0.3). Based on geo-thermometric calculations, the crystallization temperatures for amphiboles vary from 985 to 941 ºC, and for biotites from 770 to 758 ºC. According to geobarometric measurements, the pressure in amphiboles ranges between 5.3 and 6.5 kbar, and for biotites from 0.9 to1.9 kbar. The mineral chemistry datasets consisting of amphiboles' and biotites' data indicate that the investigated rocks are derived from a calk-alkaline magma with approximately high ƒO2, in a volcanic arc related to the subduction zone and the orogenic setting suites. [ABSTRACT FROM AUTHOR]

A new carbonatite body has been discovered from Gundlupet area, western Dharwar craton, southern India which is located at juncture of major shear zones namely, Kollegal shear zone to the east, Sargur shear zone to the west and Moyar shear zone to the south. The carbonatite and associated syenite have intruded into the peninsular gneissic complex. The southern margin of the syenite has a tectonic contact with the peninsular gneissic complex suggesting their emplacement is related to the splay shear of Moyar shear zone. The Gundlupet carbonatite is dominantly sövite with minor beforsite and iron rich carbonatite which are associated with phenocrystic magnetite, apatite, amphibole, pyroxene and monazite. Fenitisation is observed in local scale along the contact of carbonatite and syenite where metasomatic alterations took place to give rise to alkali amphibole and pyroxene rich rock. Geochemically, the carbonatite is characterised by high CaO content (48.86%–51.80%), P2O5 (0.35%–3.23%) and low SiO2 (3.09%–5.30%). The high Sr (5750–13445 ppm) content and low Ni, Cr, Zn and Cu content indicates that the melt has undergone some degree of fractionation before crystallization. Gundlupet carbonatite is enriched in LREE with values ranging from 5666 ppm to 7530 ppm and average LREE of 6248 ppm. [ABSTRACT FROM AUTHOR]

In comparison to the eastern Dharwar Craton, the mantle-derived xenocrysts/xenoliths are extremely rare or even unreported from the western Dharwar Craton, southern India. A Neoproterozoic (ca. 800–900 Ma) lamprophyre cropping out in the Mysuru area of southern India contains chrome-diopside xenocrysts (Cr2O3 content varying from 0.2–1.23 wt%) which provide important evidence about the pressure-temperature conditions and lithospheric thickness beneath the western Dharwar Craton. Studied chrome-diopsides show compositional zoning which is lacking in the liquidus phases (amphiboles and feldspars) of the lamprophyre which additionally favors a non-cognate origin of the former. Based on the compositional zoning, all the chrome-diopside xenocrysts can be divided into three groups: (i) Group I- which are euhedral and show reverse zoning with increasing Cr-content from core to rim; (ii) Group II- which are characterized by fractures and resorption textures, show complex reverse zoning and display up to three distinct compositional layers, and (iii) Group III- which evidence the reaction of chrome-diopsides with lamprophyric melt and are marked by alteration phases, such as actinolite and chlorite, together with relicts of some unaltered xenocrysts. High Cr2O3, moderate MgO and low Al2O3 content of all the three varieties of chrome-diopside suggest them to represent disaggregated xenocrysts of mantle-derived garnet peridotite. Temperature-pressure estimates for chrome-diopside xenocrysts ranges from 895–1026 °C (± 30 °C) and 32–38 kbar respectively and correspond to depth range of 106–127 km. The study reveals that lithospheric thickness during the Neoproterozoic beneath the western Dharwar craton was at least ∼115 km and is similar in composition to that of the cratonic lithosphere found in the other cratonic domains. [ABSTRACT FROM AUTHOR]

Context: Though some significant advances have been made in recent decades to evaluate the importance of size and morphology (habit) of elongate mineral particles (EMPs), further research is needed to better understand the role of each dimensional metric in determining the levels of cancer potency. Objective: To determine dimensional parameters most relevant for predicting cancer potency of durable elongate particles, specifically amphibole and durable silicate minerals generally. Methods: A database on dimensional and other relevant characteristics of elongate amphibole mineral particles was created, containing particle-by-particle information for 128 099 particles. Integral statistical characteristics on dimensionality of various amphibole types and morphological habits of EMPs were calculated, compared, and correlated with published mesothelioma and lung cancer potency factors. Results: The highest absolute Pearson correlation (r = 0.97, r2 = 0.94, p < 0.05) was achieved between mesothelioma potency (RM) and specific surface area. The highest correlation with adjusted lung cancer potency was found with particle aspect ratio (AR) (r = 0.80, r2 = 0.64, p < 0.05). Cluster analysis demonstrates that fractions of thin fibers (width less than 0.15 and 0.25 µm) also closely relate both to lung cancer and RM. Asbestiform and non-asbestiform populations of amphiboles significantly differ by dimensionality and carcinogenic potency. Conclusions: Dimensional parameters and morphological habits of EMPs are the main drivers for the observable difference in cancer potency among amphibole populations. [ABSTRACT FROM AUTHOR]

New petrographic, lithogeochemical and structural analyses were performed on the Upper Cretaceous lamprophyres emplaced in the Proterozoic basement rocks of the Resende sedimentary basin in SE Brazil. Field characteristics and petrographic data confirm their identification as alkaline lamprophyres. Geochemical variations were mainly controlled by fractional crystallization of clinopyroxene and olivine. Liquid immiscibility, rapid cooling and crustal assimilation may have occurred subordinately during the evolution of the Resende lamprophyres. Mantle and chondrite-normalized diagrams point to an enriched mantle as the lamprophyre's magma source. Th/Yb and Ta/Yb ratios confirm a within-plate enriched mantle source with residual carbonate and phlogopite/amphibole as suggested by LILE enrichment and the presence of carbonate and phlogopite/amphibole as primary phases. The predominance of an ENE-trend of the dykes is related to a prevalent NNW-SSW orientation of the minimum principal stress (σ3) orientation in an extensional regime during the emplacement of the Resende lamprophyres' dyke swarm. Frequent offsets produced by local dilation direction are parallel to the NNW-oriented extension of the main segments. WNW to NW secondary sets are controlled by previous discontinuities that were favored as pathways for the highly volatile lamprophyre magma. An NNW-SSE distension related to the Resende lamprophyre dyke swarm emplacement is consistent with the early stages of evolution of the Resende basin and uplift of its basement during the Late Cretaceous to the Paleocene. [ABSTRACT FROM AUTHOR]

Mineração de Boquira (Bahia) has treated a Pb and Zn ore for over thirty years. Its flotation plant produced about 4.5 million tons of tailings, containing more than 50% of amphiboles and significant levels of Pb, Zn and Cd. The results show that the tailings pollution index for Pb, Cd and Zn classifies the tailings dam region as a highly contaminated area. The results also show that the content of Pb and Cd in the tailings causes the area of the dam to have a high potential ecological risk factor. The potential risk of tailings in contributing to the development of non-carcinogenic diseases is high in children due to the high levels of Pb and Cd, however for adults only Pb can contribute significantly to the development of non-carcinogenic diseases. Based on current knowledge, the concentrations of heavy metals in the tailings do not significantly contribute to increasing the risk of carcinogenic diseases in this region. The presence of asbestos-amphibole in the tailings dam can represent a serious risk to the health of the population. The results of the present study indicate that the population of Boquira is exposed to the risks associated with mining waste, which includes potentially toxic metals (mainly Pb, Cd and Zn) and asbestos-amphibole. [ABSTRACT FROM AUTHOR]

Amphibole represents an important repository of water (among other volatiles, e.g., chlorine and fluorine) in the lithosphere in all those environments characterized by the circulation of fluids and hydrous melts, such as subduction zones and subcontinental lithospheric mantle. Therefore, detailed knowledge of the mechanisms ruling water incorporation in amphibole is essential to assess the amount of water that can be fixed in the lithosphere by this mineral and, ultimately, gain a better insight into the deep water cycle. Water is incorporated into the structure of amphibole as hydroxyl (OH -), which is hosted in the anion site O(3) , and the incorporation is mainly controlled by the oxo-substitution mechanism M(1) Ti 14++O(3) O 22- M(1) (Mg 2+ , Fe 2+)-1+ O(3) (OH -)-2-. However, the fluids and melts circulating in the lithospheric mantle can be variably enriched in halogens (Cl - and F -) that can substitute OH - in the anion site O(3) of amphibole, thus potentially affecting its water budget. The aim of this study is to evaluate the effect of Cl on the oxo-substitution and the incorporation of water in amphibole. End-loaded piston cylinder experiments were conducted at pressure and temperature conditions compatible with the upper-mantle depth (1.4 GPa and 1015–1050 ∘ C) in order to favor the crystallization of amphibole at equilibrium with the coexisting melt. Alkali basalt powder was used as starting material, and water doped with different contents of Cl was added to each experiment. Two ranges of oxygen fugacity (f O 2) were investigated at Δ FMQ = -2.6 (log f O 2 [experiment] - log f O 2 [FMQ buffer]) and Δ FMQ = +1.7 , where FMQ is fayalite–magnetite–quartz, in order to preliminarily identify the potential influence of the f O 2 on the water budget in amphibole. In this contribution, we propose a new method to quantify water in amphiboles using confocal micro-Raman spectroscopy. The H 2 O contents range from 2.20 ± 0.10 wt % to 5.03 ± 0.47 wt % in glasses and from 0.93 ± 0.08 wt % to 1.50 ± 0.12 wt % in amphiboles, resulting in a partition coefficient of water between amphibole and glass (Amph/L D H2O) ranging from 0.29 ± 0.06 to 0.52 ± 0.08. Our results show a positive correlation between the Cl content of amphibole (from 0.18 wt % to 0.88 wt %) and the Amph/L D H2O. This effect is ascribed to the incorporation of Cl at the anion site O(3) that influences the oxo-substitution mechanism by impeding the entrance of Ti 4+ at the M(1) sites and thus preventing the amphibole dehydrogenation. The effect of Cl reported in this study, which is related to a change in the amphibole crystal structure, highlights that high Cl concentrations in magmatic systems favor the incorporation of water in amphibole rather than in the coexisting melt, although the exchange coefficient between Amph/L D H2O and Amph/L D Cl supports a preferential incorporation of water over Cl in amphibole. Therefore, the presence of abundant Cl influences the hydration state of magmas evolving from upper-mantle conditions towards crustal roots with the crystallization of amphibole. [ABSTRACT FROM AUTHOR]

Granitoids are the main constituents of the continental crust, and an understanding of their petrogenesis is key to the origin and evolution of continents. Whether crystal fractionation is the dominant way to generate evolved magmas has long been debated, mostly because such processes would produce large volumes of complementary cumulates, which remains elusive. Mafic magmatic enclaves (MMEs) are ubiquitous in granitoids and their presence was initially recognized as cumulates. However, because many MMEs lack obvious evidence of accumulation, such as the classic cumulate textures and modal layering, the cumulate origin of MMEs has been abandoned and the model of magma mixing between mafic and felsic magmas has become popular. In this study, we conduct a combined study of amphibole composition and in situ O isotopes in zircons on three suites of orogenic granitoids with MMEs from the North Qilian Orogenic Belt (NQOB). We find that the MMEs and their host granodiorites show overlapping zircon δ18O values, affirming that they share the same parental magmas. The amphibole compositions indicate that amphiboles from the MMEs are not in equilibrium with a melt whose composition was that of the bulk-rock. These new data, together with the published bulk-rock data, suggest that the MMEs in our study have clear cumulate signatures and are thus of cumulate origin. Our study provides evidence for crystal accumulation in granitoids in the NQOB. This new understanding calls for re-examination on the petrogenesis of some intermediate magmatic rocks (granitoid/andesite) in discussing models of continental crustal growth. [ABSTRACT FROM AUTHOR]

The Mado Megamullion is an oceanic core complex (OCC) in the Shikoku back‐arc basin within the Philippine Sea Plate. Mantle peridotites (serpentinized) recovered by six dredge and submersible cruises exhibit signatures of extensive deformation. Amorphous pseudomorphs after plagioclase in many of the samples, as well as plagioclase‐spinel intergrowths, are clear evidence of melt stagnation and mantle reaction. Spinels show a wide range of compositions in terms of their Cr#, Mg#, and TiO2 content. The presence of apparently magmatic high‐temperature pargasitic amphibole in veins and as replacement of clinopyroxene suggests that it may be a primary or near‐primary mineral crystallized from a hydrous melt which is unusual for abyssal peridotites. Two trace‐element populations of clinopyroxenes are in equilibrium with depleted and enriched basaltic melts, respectively. Rare‐earth element (REE) in the most depleted clinopyroxenes are modeled by 10% fractional melting except for a ubiquitous La‐Ce "kick." Multiple models of open system melting combined with subsequent mixing of an enriched melt can explain the REE data. Broadly it appears that the peridotites underwent variable degrees of partial melting with moderate influx of enriched melts, which agrees with the other textural and chemical evidence of melt‐rock reaction and re‐fertilization. The compositions of the accumulated melts simulated by the open system models reproduce the enrichments in fluid mobile elements (Ba, U, and Pb) observed in basalts dredged from the Shikoku basin. Back‐arc basin peridotites at Mado Megamullion appear to have a unique petrographic and geochemical character that is distinct from those of peridotites exposed at the seafloor after formation from mid‐ocean ridges. Key Points: Partial melting and melt‐rock reaction in back‐arc basin peridotitesPresence of pargasitic amphiboles in the peridotites and crystallization in a hydrous environmentInflux of enriched melts which reproduces the enriched signatures in the Shikoku Basin basalts [ABSTRACT FROM AUTHOR]

We report new results of a comprehensive study into Carboniferous – Early Permian granite magmatism of the northern Taimyr Peninsula, Russia (southern part of the Kara Terrane). U-Pb zircon ages (SHRIMP and LA–ICP–MS) represent the crystallization ages of these intrusions and range from ca. 344.5 to 288.4 Ma, defining the onset of granite magmatism during the Early Carboniferous (Visean; ca. 344 Ma) and its termination in the Early Permian (Artinskian; ca. 288 Ma). Ar-Ar dating of micas and amphiboles indicates that Late Palaeozoic tectonic activity in northern Taimyr ceased during the Middle Permian (Roadian; ca. 272 Ma). Rb/Sr and Sm/Nd isotopic data from the same intrusions, show initial (87Sr/86Sr)i ratios of between 0.70288 and 0.71027, with εNd(t) values range between −3.3 and +3.1. The combined geochemical and isotopic compositions of the granites describe an affinity to peraluminous I-type granites, probably formed in an Andean-type active continental margin setting. Our new geochemical, isotopic, and geochronological data indicate the existence of a long-lived (ca. 56 Myr) Andean-type active continental margin along the southern edge of the Kara Terrane during the Late Palaeozoic. Furthermore, our study reveals a causal relationship between Late Palaeozoic magmatism across northern Taimyr and closure of the Uralian Ocean. [ABSTRACT FROM AUTHOR]

Amphibole plays an important role in the petrogenesis and evolution of arc magmas, but its role is not completely understood yet. Here, a field, petrological, geochronological and geochemical study is carried out on ultramafic–mafic arc cumulates with textural and chemical heterogeneities and on associated host diorites from the eastern Gangdese Batholith, southern Tibet to explore the problem. The cumulates occur as a large body in diorite host-rocks. The core of the body consists of coarse-grained Cpx hornblendite with a porphyritic texture. Towards the contact with the host diorite, the coarse-grained Cpx hornblendite grades to relatively homogeneous fine-grained melagabbro. Zircon U–Pb dating indicates that they all crystallized at 200 ± 1 Ma. Textural features and whole-rock and mineral chemical data reveal that both the Cpx hornblendite and the melagabbro are mixtures of two different mineral assemblages that are not in equilibrium: (1) brown amphibole and its clinopyroxene inclusions; (2) matrix clinopyroxene + green amphibole + plagioclase + quartz + accessory phases. Clinopyroxene and brown amphibole from the first assemblage are enriched in middle rare earth elements (MREE) relative to light REE (LREE) and heavy REE (HREE), and are weakly depleted in Ti, whereas clinopyroxene and green amphibole from the second assemblage are characterized by LREE enrichment over MREE–HREE and more marked Sr and Ti depletion. The higher Mg#, MgO and Cr of the late-formed green amphibole than the early formed brown amphibole suggest that the two assemblages are not on the same liquid line of descent. Given the close relations of the three rock types in the exposed crustal section, the cumulates are interpreted to have formed in an open system, in which an ultramafic cumulate body consisting of the first assemblage reacted with the host dioritic melt to form new clinopyroxene and amphibole of the second assemblage. The melt calculated to be in equilibrium with the first mineral assemblage resembles an average continental arc basalt, which is less evolved than the host dioritic melt, responsible for the second mineral assemblage. On the basis of whole-rock Sr–Nd–Hf isotopic similarity of the cumulates and a host diorite sample, we argue that the host diorites were formed through crystal fractionation from the parent melt of the first assemblage. Results of least-squares mass-balance calculations suggest that the quantities of the host dioritic melts, involved in the generation of these modified cumulates, vary from ~25 to ~44 %. The presence of magmatic epidote in the host diorites and Al-in-Hb geobarometry indicate that the reaction that occurred when the dioritic melts percolated through the cumulate body was at ~6 kbar. Both the brown and green amphiboles are enriched in MREE relative to HREE, and can impart to residual melts a strong geochemical signature of amphibole fractionation (low Dy/Yb). Thus, we conclude that fractional crystallization and melt–rock reaction are two mechanisms by which amphibole controls arc magma petrogenesis and evolution. [ABSTRACT FROM AUTHOR]

Amphiboles and diopside occur in several distinct mineral assemblages in banded carbonatite-like marbles from the Bližná graphite mine, Český Krumlov Unit, Moldanubian Zone. The carbonatite-like marble is interlayered with dominant ordinary metacarbonates as a single continuous stratabound layer, up to 3-4 m thick. It is enriched in elements typical for carbonatites (REE, Y, Th, Sr, Nb, Zr, and Mo) and contains accessory betafite-pyrochlore and uranothorite along with molybdenite, sulfides (e.g., pyrite, pyrrhotite) and oxides (e.g., magnetite, ilmenite). Detailed study of thin sections in optical microscope and BSE images as well as results of EMPA revealed three distinct mineral assemblages - richterite + forsterite (RF) assemblage (Rht + Fo + Cal - Dol - Phl + Di), Na-rich actinolite + diopside (AD) assemblage (Di + Act + Rht + Cal - Phl) and magnesio-hastingsite + diopside (HD) assemblage (Mhst + Di + Cal - Ab + Phl). The distinct amphibole species found within the individual assemblages exhibit complex textural relations and crystallized in several prograde and retrograde stages. The following amphibole species were recognized in the individual assemblages: RF - (richterite > ferri-winchite > tremolite, edenite), AD - (actinolite > ferri-winchite; richterite > ferri--katophorite; magnesio-riebeckite), HD - (magnesio-hastingsite; ferri-winchite, actinolite). They differ especially in Mg/(Mg + Fetot) ratio and concentrations of F. Diopside contains up to 17 mol. % of the aegirine component and albite is Fe, Ba-enriched (= 0.69 wt. % BaO and = 0.50 wt. % Fe2O3tot). The composition of amphiboles and pyroxenes indicates the alkaline environment of their formation; unusually high Fe2O3 contents in albite plagioclase have known counterparts in alkaline pegmatites and some carbonatite dykes. The following options of potential origin of the carbonatite-like marble from Bližná are discussed: (i) metacarbonates potentially with Na- and Na,Ca-carbonates and sulfate admixture; (ii) admixture of alkaline volcanodetritic component during carbonate sedimentation; (iii) metamorphosed carbonatites enclosed in ordinary sedimentary metacarbonate; (iv) Na-rich metasomatites characterized by mineral assemblages with Na,Fe,F-enriched amphiboles, diopside with high aegirine component and albite. With regard to the observed mineral assemblages, textures and composition of minerals, we can exclude (i) marine evaporates, whereas the other options (ii), (iii) and (iv) are, in general, possible. The amphiboles observed in the Bližná carbonatite-like marble are unique within the Bohemian Massif and distinctly different from amphiboles found in metacarbonates with evaporite component. [ABSTRACT FROM AUTHOR]

Naqadeh intrusive pluton is composed of two distinct sections of felsic (40 Ma age) and mafic (99 Ma age) rocks. The granitoid rocks of Naqadeh pluton have different types of mafic enclaves, including mafic microgranular enclaves (MME) and quartz + amphibole bearing enclaves. The MME has the same age to its host granitoids and could be divided into two types. The first type has similar Sr-Nd composition to the host rock (87Sr/86Sri = 0.7062 and εNdi= -0.89), and their trace amphibole composition is like host granitoids. These enclaves are cogenetic with the granitoid magma and formed by early crystal-melt segregations. Another type of MME shows the textural evidence of magma mixing and is characterized by different isotopic ratios from granitoids (87Sr/86Sri = 0.7042 and εNdi= +2.98). The trace element composition of this type of enclave is completely different from the other enclaves and the host rocks. The quartz + amphibole bearing enclave formed contemporaneous with mafic rocks of Naqadeh pluton (99 Ma), and displays the same isotopic ratios and amphibole composition. [ABSTRACT FROM AUTHOR]

Electronic probe analyses were performed on 343 and 406 sedimentary amphibole single-mineral samples extracted from five sampling points in the Huanghe River estuary and six in the Changjiang River estuary. The profiles of amphibole single-mineral major elements were determined for the two rivers using these samples. The cation coefficients and related parameters of 749 amphiboles were calculated based on 23 oxygen standards, and their crystal structure molecular formulae and related characteristic crystallochemical values were determined. The results show that the sedimentary amphiboles of the two estuaries belong to the calcic amphibole subgroup, where the majority is Magnesiohornblende, accounting for more than 70%, followed by Tschermakite. A genetic mineralogical analysis was carried out on the genesis type, magmatic source, and crystallization temperature and pressure environment of the amphiboles in the Huanghe River and Changjiang River estuaries, showing that most of the calcic amphiboles in these estuaries originated from metamorphic rocks, followed by magmatic rocks. Amphiboles of magmatic genesis in the Huanghe River and Changjiang River estuaries were largely crust-mantle type. Most of the metamorphic amphiboles originated in a metamorphic environment below moderate temperature and pressure. The amphiboles of the Huanghe River estuary mainly originate from the orogenic belt in the Northern Loess Plateau. The amphiboles of the Changjiang River estuary mainly originate from the middle and upper reaches of the Changjiang River, where the amphiboles mainly form as a result of magmatic and hydrothermal activity, as well as metamorphism. The chemical composition and characteristic values of sedimentary amphiboles in the Huanghe River and Changjiang River estuaries are stable, and can be used as standardized substances for terrestrial sediments. [ABSTRACT FROM AUTHOR]

Amphibole and biotite were the principal mafic minerals precipitated during the magmatic and post-magmatic (including hydrothermal) crystallisation stages of coeval metaluminous to slightly peraluminous syenogranites and peralkaline alkali-feldspar granites of the Mandira Granite Massif, in the post-collisional A-type Graciosa Province, S-SE Brazil. Magmatic calcic (ferro-ferri-hornblende and hastingsite) amphiboles occur in the metaluminous syenogranites, whereas calcic (ferro-edenite), sodic–calcic (ferro-ferri-winchite) and sodic (arfvedsonite and riebeckite) amphiboles occur in peralkaline alkali-feldspar granites. Rare earth element (REE) contents decrease from hornblende to winchite and riebeckite, and the partition coefficients indicate increasing compatibility from light rare earth elements (LREE) to heavy rare earth elements (HREE), with a marked preference for the HREE over the LREE in the sodic–calcic and, particularly, the sodic amphiboles. Post-magmatic calcic- (ferro-actinolite) and sodic- (riebeckite) amphiboles are also present in the peralkaline granites. Magmatic biotite (annite) is dominant in syenogranites, whereas post-magmatic annite and late-to post-magmatic annite evolving to siderophyllite occurs in the peralkaline granites. Typical hydrothermal phyllosilicates are chlorite (chamosite) in syenogranites and related greisens, and ferri-stilpnomelane which is present in both peralkaline granites and metaluminous syenogranites. Lithostatic pressure estimates suggest that the main granites were emplaced under pressures of ~93–230 MPa, with close-to-liquidus temperatures varying from ~830°C for syenogranites to ~900°C for the peralkaline granites. The original magmas crystallised mainly under relatively reduced (buffered at ~ –1 ≤ QFM ≤ 0), and more oxidising (somewhat above QFM) environments, respectively. Chlorite, replacing biotite in syenogranites and as the main mineral in the related greisens, permits the temperature of the main hydrothermal event to have taken place between 250 and 272°C. Estimated log (fHF/fHCl) values from biotite compositions vary from ~ –2 to –1 (syenogranites) and ~ –3.5 to –2 (peralkaline granites) and indicate F preference over Cl in the hydrothermal fluid phase. [ABSTRACT FROM AUTHOR]

Today, cancer is one of the main health issues faced in the workplace, with asbestos an important carcinogen in the occupational environment. Among the asbestos minerals, chrysotile is the main species of socio-economic and industrial relevance. Although chrysotile asbestos is classified as a "carcinogenic substance" by the International Agency for Research on Cancer (IARC), this fiber is still mined and used in Russia. The effective health hazard posed by the Russian commercial chrysotile has not been quantitatively assessed to date. In this work, the potential toxicity/pathogenicity of Russian chrysotile was quantitatively determined using the fiber potential toxicity index (FPTI) model. This model was applied to a representative commercial chrysotile from the Orenburg region, Russia, whose morphometric, crystal-chemical, surface activity, and biodurability related parameters were determined. We have quantitatively assessed that the toxicity/pathogenicity potential of Russian chrysotile (FPTI = 2.4) is lower than that of amphibole asbestos species but higher than the threshold limit set for "safe" mineral fibers (FPTI = 2.0), although it does not contain impurities of amphibole asbestos. Differences with other chrysotile samples were discussed, and it was found that the investigated Russian commercial chrysotile shares several features with the Italian Balangero chrysotile, indicating that widespread concern on commercial Russian chrysotile is justified. [ABSTRACT FROM AUTHOR]

Amphibole phenocrysts in post-1 ka lava domes deposits of Taranaki volcano, an andesite arc volcano in New Zealand, provide an opportunity to explore late-stage changes in melt composition and volatiles in the run up to eruption. Amphibole is a subordinate phase (0–7% of modal phenocrysts) and the phenocrysts display three types of growth history. Type 1 are large compositionally and texturally uniform phenocrysts that have low MgO (<13 wt%) and high K 2 O (∼1–1.4 wt%) contents. In contrast, Type 2 have similar cores but have been partially resorbed and overgrown by a mafic rim distinguished by high MgO (up to 15 wt%) and low K 2 O (<1.0 wt%) contents. Type 3 are the least common, and have either normal zoned or concentrically zoned interiors with respect to MgO and FeO. Overall, elemental substitutions and zonation patterns are related to periods of resorption and regrowth that are best explained by changes in melt composition. Based on calculated equilibrium melt compositions, the amphibole crystallisation is consistent with an incrementally grown andesitic to dacitic (SiO 2 58–67 wt%) crystal mush that was periodically recharged with more mafic magma (SiO 2 ∼ 55 wt%). The melts span a compositional gap (SiO 2 ∼ 60–65 wt%) that is not represented in eruption products from the last 8 ka. Such melts were likely brief stages during ongoing fractional crystallisation and magma mixing. Each recharge event disrupted an evolving system and mixed crystals from different parts of it. This concept supports triggering of eruptions by recharge of mafic melts, as also inferred from plagioclase zonation for some eruptions from Taranaki. The outermost rims (0–5 μm) of many amphibole phenocrysts are enriched in fluorine (up to 1.9 wt%) and surrounded by a thick opacitic decomposition growths. We interpret this as the result of slow magmatic ascent and extensive crystallisation that produced a late-stage halogen-rich interstitial melt. This likely extended the conditions for amphibole stability to lower pressure. If F enrichment was accompanied by comparable enrichments in other halogens that preferentially partition into an aqueous phase, then extensive degassing would have occurred during the dome extrusions. • Taranaki andesite dome amphiboles have diverse crystallisation histories. • Amphibole phenocrysts formed in cryptic melts that did not voluminously erupt. • Eruptions were preceded by mafic recharge into a silicic resident mush. • Extensive crystallisation produced late-stage fluorine rich melt. • The dome extrusions were likely associated with extensive degassing. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple generations of amphiboles were distinguished in the Haobugao deposit. • Amphiboles in the Haobugao deposit were formed from a fluid mixing magmatic fluid with meteoric water. • Amphibole geochemistry is useful for tracing fluid evolution and mineralization processes. The Haobugao Zn-Fe-Sn deposit is a typical skarn deposit in the southern Great Xing'an Range of NE China. Despite many advances in understanding its genesis, the detailed ore-forming processes of Zn, Fe and Sn are still unclear. Amphibole, a rock-forming mineral, has been well studied as an indicator of diverse magmatic and metamorphic processes; however, the geochemistry of hydrothermal amphibole has previously received less attention. The Haobugao deposit contains two generations of hydrothermal amphibole (Amp-I and Amp-Ⅱ), which provides a good opportunity to use amphibole geochemistry to trace the mineralization process. Early Amp-I coexists with cassiterite, magnetite and quartz, whereas late Amp-II coexists with quartz and sulfides and can be further divided into two subgroups: Amp-Ⅱa (in skarn) and Amp-Ⅱb (in the country rocks of siltstone). The oxygen isotopic compositions of the fluid (δ18O fluid 2.9‰) responsible for the Amp-I formation indicate that the amphiboles formed from mixed magmatic fluid with meteoric water. Amp-I is LREE-depleted and HREE-enriched with obvious negative Eu anomalies. Amp-Ⅱ is generally slightly LREE-depleted with negative or positive Eu anomalies and positive Ce anomalies. The incorporation of trace and rare elements is mainly controlled by the fluid composition. Detailed petrological observations and amphibole geochemistry, combined with previous research results, confirm that Sn, Fe, Pb and Zn mineralization occurred during a single mineralization event. From the oxide to the quartz sulfide stage, the ore-forming fluid evolved from high-temperature and oxidized conditions with enrichment of Sn, Li, Be and REEs to low-temperature and reduced or oxidized conditions with enrichment of Cu, Co and Zn. The concentrations of Cu, Co and Zn in different amphiboles vary with the mineral crystallization sequence. This study shows that amphibole geochemistry can be useful for tracing fluid evolution and mineralization processes in hydrothermal systems. [ABSTRACT FROM AUTHOR]

Copper, obtained from porphyry deposits formed in arc settings, is a critical resource, and is primarily sourced from magmas. However, the processes that shape the copper contents of arc magmas are up for debate. Existing models place emphasis on different petrological agents that explain large-scale trends in copper systematics. Previous studies have noted the 'Cu paradox,' where the magmas with high Sr/Y ratios, indicative of ore-forming potential, have the lowest copper concentrations. Here we compile a multidimensional database of volcanic whole rock compositions and couple it with simple petrological models to elucidate the controls on volcanic whole rock compositions with respect to Cu. We show that calc-alkaline, high Sr/Y magmas undergo major element modification caused by extensive amphibole and/or garnet fractionation, which promotes sulphide precipitation and copper depletion. We demonstrate the importance of amphibole fractionation as a globally important process that promotes both calc-alkaline differentiation and sulphide fractionation in arc magmas, as well as its role in signalling the right set of chemical conditions in magmas that ultimately feed copper porphyry deposits. This work also raises the possibility of amphibole as a geochemical and petrological indicator of potential porphyry-forming conditions in a magma, which we show should be readily detectable by a combination of different geochemical metrics. Despite their paucity in copper, high Sr/Y magmas are associated with porphyry deposits, implying that the propensity of magmas to form such deposits depends on factors other than a magma's bulk copper content. [ABSTRACT FROM AUTHOR]