Band 101, Heft 2

Magnesium isotope compositions of the bulk continental crust is a key to understand Mg isotope behaviors during crustal processes, and is the prerequisite to study mantle-crust material exchange/reaction by Mg isotopes. However, thus far, little is known about Mg isotopic compositions of the middle and lower continental crust. In the article by Yang et al. in this issue entitled “Magnesium isotopic composition of the deep continental crust,” the authors present high-precision Mg isotopic analyses of high-grade metamorphic terrane samples and granulite xenoliths from China, which represent the middle and lower continental crust, respectively. Large Mg isotopic variation is observed in the deep continental crust, reflecting the combination of several processes, such as continental weathering, involvement of supracrustal materials, and fluid metasomatism. In addition, this article also provides an average Mg isotope composition of the bulk continental crust, which is crucial to future applications of Mg isotopes.

To constrain the behavior of Mg isotopes during deep crustal processes and the Mg isotopic composition of the middle and lower continental crust, 30 composite samples from high-grade metamorphic terranee and 18 granulite xenoliths were investigated. The composites derive from eight different high-grade metamorphic terranee ill the two largest Archean cratons of China, including 13 TTG gneisses, 5 amphibolites, 4 felsic, 4 intermediate, and 4 mafic granulites. They have variable bulk compositions with SiO 2 ranging from 45.7 to 72.5%, representative of the middle crust beneath eastern China. The δ 26 Mg values of these samples vary from −0.40 to +0.12‰, reflecting heterogeneity of their protoliths, which could involve upper crustal sediments. The granulite xenoliths from the Cenozoic Hannuoba basalts also have a diversity of compositions with MgO ranging from 2.95 to 20.2%. These xenoliths equilibrated under high temperatures of 800–950 °C, corresponding to depths of the lower continental crust (>30 km). They yield a large δ 26 Mg variation of −0.76 to −0.24‰. The light Mg isotopic compositions likely result from interactions with isotopically light metamorphic fluids, probably carbonate fluids. Together with previously reported data, the average δ 26 Mg values of the middle and lower continental crusts are estimated to be −0.21 ±0.07‰ and −0.26 ±0.06‰, respectively. The bulk continental crust is estimated to have an average δ 26 Mg of −0.24 ±0.07‰, which is similar to the average of the mantle. The large Mg isotopic variation in the continental crust reflects the combination of several processes, such as continental weathering, involvement of supracrustal materials in the deep crust, and fluid metasomatism.

This is a review of the thermal and compressional behavior of cancrinite-group minerals with a description of the mechanisms, at the atomic scale, that govern their P-T -induced structure evolution. The open-framework structure of this group of feldspathoids is characterized by the [CAN] topology, which contains large parallel channels (confined by 12-membered rings of tetrahedra), surrounded by columns of cages. At least two structural “subgroups” can be identified according to the nature of the constituents filling the cages, irrespective of the channel population. The minerals of the “cancrinite subgroup” show [NaH 2 O] + clusters into the cages and those of the “davyne subgroup” contains [CaCl] + clusters. Beside a similar bulk compressibility and expansivity at room conditions for all the minerals of the group, a different elastic anisotropy, coupled with different deformation mechanisms of the tetrahedral framework, were found to be mainly controlled by the nature of the population filling the cages. The role played by the channel populations appears to be secondary. These experimental findings allow us to provide a model of the structure evolution in response to the different cage content, i.e., NaH 2 O + and CaCl + . The high-temperature studies of the hydrous members of the cancrinite subgroup reveal a slow dehydration process, often irreversible at the timescale of the experiments and leading to quasi-anhydrous high-temperature forms that keep their crystallinity even up to 800–900 K (at room P ). The experiments at high pressure on the cancrinite-group minerals show a high- P stability, at least up to 7–8 GPa (at room- T ), which is quite surprising if we consider their microporous nature. The P -induced stability is the effect of a pronounced structural flexibility, which in turn is based mainly on tilting of rigid tetrahedra around O atoms that behave as hinges. The character and the mechanisms that govern the P-T -induced P 6 3 -to- P 6 3 / m phase transition in the compounds of davyne subgroup are also discussed.

Nepheline crystallizes upon slow-cooling in some melts concentrated in Na 2 O and Al 2 O 3 , which can result in a residual glass phase of low chemical durability. Nepheline can incorporate many components often found in high-level waste radioactive borosilicate glass, including glass network ions (e.g., Si, Al, Fe), alkali metals (e.g., Cs, K, Na, and possibly Li), alkaline-earth metals (e.g., Ba, Sr,Ca, Mg), and transition metals (e.g., Mn, and possibly Cr, Zn, Ni). When crystallized from melts of different compositions, nepheline composition varies as a function of starting melt composition. Five simulated high-level nuclear waste borosilicate glasses shown to crystallize large fractions of nepheline on slow-cooling were selected for study. These starting melt compositions contained a range of Al 2 O 3 , B 2 O 3 , CaO, Na 2 O, K 2 O, Fe 2 O 3 , and SiO 2 concentrations. Compositional analyses of nepheline crystals in glass by electron probe micro-analysis (EPMA) indicate that nepheline is generally rich in silica, whereas boron is unlikely to be present in any significant concentration, if at all, in nepheline. Also, several models are presented for calculating the fraction of vacancies in the nepheline structure.

Pure larnite (β-Ca 2 SiO 4 ; Lrn) was synthesized at 6 GPa and 1473 K for 6 h by using a cubic press, its thermal expansivity was investigated up to 923 K by using an X-ray powder diffraction technique (ambient P ), and its compressibility was investigated up to ∼16 GPa by using a diamond-anvil cell coupled with synchrotron X-ray radiation (ambient T ). Its volumetric thermal expansion coefficient (α V ) and isothermal bulk modulus ( K T ) were constrained as α V = 4.24(4) × 10 −5 K −1 and K T = 103(2) GPa [the first pressure derivative KT′$K_{\rm{T}}^\prime $ obtained as 5.4(4)], respectively. Its compressibility was further studied with the CASTEP code using density functional theory and planewave pseudopotential technique. We obtained the K T values as 123(3) GPa (LDA; high boundary) and 92(2) GPa (GGA; low boundary), with the values of the KT′$K_{\rm{T}}^\prime $ as 4.4(9) and 4.9(5), respectively. The phonon dispersions and vibrational density of states (VDoS) of Lrn were simulated using density functional perturbation theory, and the VDoS was combined with a quasi-harmonic approximation to compute the isobaric heat capacity ( C P ) and standard vibrational entropy (S2980)$\left( {S_{298}^0} \right)$, yielding C P = 212.1(1) − 9.69(5) × 10 2 T −0.5 − 4.1(3) × 10 6 T −2 + 5.20(7) × 10 8 T −3 J/(mol.K) for the T range of ∼298–1000 K and (S2980) = 129.8(13)$\left( {S_{298}^0} \right)\, = \,129.8\left( {13} \right)$ J/(mol.K). The microscopic and macroscopic thermal Grüneisen parameters of Lrn at 298 K were calculated to be 0.75(6) and 1.80(4), respectively.

Vaterite is one of three non-hydrate calcium carbonate crystalline polymorphs and is formed as an initial phase under pseudo-biological conditions. However, biological hard tissues that use vaterite are rare; the reason for vaterite rarely appearing in vivo is still unclear. There is consensus that, in phosphate-containing solutions, vaterite barely forms and amorphous calcium carbonate (ACC), the precursor of crystalline calcium carbonate and considered as aggregation of growth unit of vaterite, is stabilized. In this study, to clarify the biomineralization process, we investigated how phosphate acts as an inhibitor of vaterite growth. We measured vaterite growth rates in situ and estimated the essential crystal growth parameter, edge free energy, in the Ca-CO 3 -PO 4 system in relation to the physico-chemical properties of ACC. The effects of PO 4 on the ACC structure and dynamics were also observed. Co-existed PO 4 reduced the growth rate of vaterite even when it was added in µM-scale concentrations. The surface free energy of vaterite increased with increasing PO 4 concentration and was 10× higher in a 10 μM PO 4 -containing solution than in a PO 4 -free solution. Spectroscopic analyses showed that the chemical bonds in ACC particles were drastically changed by the addition of μM-scale PO 4 , and the particles could no longer transform into vaterite. We conclude that PO 4 inhibits vaterite growth and changed the ACC structure. And the original growth units of vaterite were also modified to the other structures. Thus, vaterite crystals could not grow by association of these growth units, which resulted in an increase in the apparent surface free energy of vaterite.

Commingling between contemporaneous mafic and felsic magmas is now widely recognized in a broad range of intrusions and intrusive complexes. These interactions are important features for two main of reasons: (1) the rapidly chilled margins of mafic magma against silicic magma commonly preserve the compositions of mafic liquids, and (2) because the mafic magma solidifies rapidly, the resulting (final) configurations of mafic and felsic magmas can provide insights into physical processes and changing viscosity contrasts and rheologies of magmas and felsic crystal mush during crystallization of the mafic magma. Mingling of contrasted magmas was first recognized in the 1950s. Wider recognition of interactions between mafic and silicic liquids led to concepts of “net-veining” in the 1960s, “intramagmatic flows” (chilled basaltic layers separated by felsic cumulates) in the 1970s, and in the 1990s to “mafic-silicic layered intrusions” (MASLI), which could be as much as a few kilometers thick and more than 100 km 2 in area. It was quickly appreciated that these MASLI preserved stratigraphic records of mafic replenishments into silicic magma chambers floored by felsic crystal mush. Volcanic studies had anticipated the occurrence of this last type of intrusion on the grounds that extensive ponding of basaltic magmas beneath silicic chambers was seen to be essential to keep large silicic systems like Yellowstone active for millions of years. This paper looks at the history of changing perceptions and interpretations of magma mingling and whether or not “sill complexes” are distinct from mafic-silicic layered intrusions. The stratigraphy of mafic-silicic layered intrusions records changing magmatic compositions, events, and processes in a temporal framework comparable to that provided by coeval volcanic rocks. As a result, careful study of MASLI has great potential for linking plutonic and volcanic processes and events.

The >700 km 3 Peach Spring Tuff (PST), erupted at 18.8 Ma from the Silver Creek caldera in the southern Black Mountains volcanic center (SBMVC) of western Arizona, is the only supereruption-scale ignimbrite in the northern Colorado River Extensional Corridor. The SBMVC contains pre- and post-caldera volcanic rocks and caldera-related intrusions (∼19–17 Ma) that provide a detailed petrologic record of ignimbrite antecedence and aftermath. Whole-rock Sr-Nd-Pb-Hf isotopic data combined with complementary zircon O and Hf isotopic data from a suite of pre- through post-PST samples provide robust constraints on (1) how the SBMVC evolved with respect to magmatic sources and processes throughout its ∼2 Ma history and (2) the petrogenetic relationships between the PST and slightly younger intracaldera plutons. Both pre- and post-PST units have isotopic ranges (ε Nd = −8.3 to −11.6, ε Hf = −8.2 to −14.0, 87 Sr/ 86 Sr = 0.709–0.712; 206 Pb/ 204 Pb = 18.19–18.49, 207 Pb/ 204 Pb = 15.60–15.62, 208 Pb/ 204 Pb = 38.95–39.29) that fall within the spectrum of Miocene Colorado River Extensional Corridor rocks and are consistent with mixing of substantial fractions of Proterozoic (Mojave) crust and juvenile material derived from regional enriched mantle. Compared to the PST, which has relatively uniform isotopic ratios (ε Μ = −11.4 to −11.7, ε κ = −13.8 to −14.3, 87 Sr/ 86 Sr i =0.709–0.712; 206 Pb/ 204 Pb = 18.20–18.29, 207 Pb/ 204 Pb = 15.60–15.62, 208 Pb/ 204 Pb = 39.02–39.33), individual pre- and post-PST units are isotopically more variable and generally more primitive. Consistent with whole-rock isotopes, zircon ε Hf (−8 to −14) and oxygen δ 18 O (+4.5 to +7.2‰) for most pre- and post-PST units also have wider ranges and more mantle-like values than those of the PST (−12 to −15, +6.1 to +7.1‰). Moreover, zircon isotopic compositions decrease in post-PST samples. A few zircons from post-PST intrusions have δ 18 O values lower than mantle values (<+5‰), suggesting incorporation of hydrothermally altered rock. Whole-rock and zircon elemental and isotopic analyses indicate that (1) most pre- and post-PST units are less evolved and less homogenized than the PST itself; (2) intrusions in the Silver Creek caldera are petrogenetically distinct from the PST and therefore represent discrete magmatic pulses, not unerupted PST mush; (3) enriched mantle input increased in the SBMVC following the paroxysmal PST eruption; (4) post-PST history of the SBMVC was characterized by periodic influx of magmas with varying juvenile fractions into pre-existing mushy or solidified intrusions, resulting in variable and incomplete hybridization; and (5) melting and assimilation of hydrothermally altered crust played a relatively minor role in the generation and evolution of magmas in the SBMVC.

Hornblende in the Kuna Crest lobe (KCL) of the Tuolumne Intrusive Complex (TIC) and the upper zone of the Wooley Creek batholith (WCB) precipitated over a temperature range of ~835 to 700 °C, and thus has the potential to record magmatic processes. We measured trace element concentrations in hornblende from the WCB, from the KCL of the TIC, and from one sample from an adjacent interior unit of the TIC to compare and contrast magmatic processes in these two mid-crustal intrusions. In both systems the magmatic amphibole is magnesiohornblende in which Ti, Zr, Hf, Nb, Sr, Ba, and rare earth elements (REE) typically decrease from crystal interiors to rims, an indication of compatible behavior of these elements, and the size of the negative Eu anomaly decreases. In the Kuna Crest lobe, hornblende from individual mapped units differs in trace element abundances and zoning trends. Some samples contain at least two distinct hornblende populations, which is particularly evident in the shapes of REE patterns. In contrast, compositions of hornblende from all structural levels of the upper WCB and related dacitic roof-zone dikes form a single broad array and the REE patterns are essentially indistinguishable, regardless of rock type, from quartz diorite to granite. In the WCB, Zr/Hf ratios in hornblende are consistent with crystallization from a melt with chondritic Zr/Hf values. In contrast, most hornblende in the KCL has Zr/Hf values lower than expected from crystallization from a melt with chondritic values, suggesting that zircon fractionation occurred before and during crystallization of the hornblende. Simple fractional crystallization models indicate that REE, high field strength elements, Sr, and Ba were compatible in KCL and WCB magmas as hornblende grew; these trends require removal of hornblende + plagioclase + zircon ± ilmenite ± biotite. The uniform variations of trace element concentrations and patterns in the upper WCB and roof-zone dikes indicates crystallization from a large magma body that was compositionally uniform; probably stirred by convection caused by influx of mafic magmas at the base of the zone (Coint et al. 2013a, 2013b; cf. Burgisser and Bergantz 2011). In contrast, in the KCL, each analyzed sample displays distinct hornblende compositions and zoning patterns, some of which are bimodal. These features indicate that each analyzed sample represents a distinct magma and that individual magmas were variably modified by fractionation and mixing. Hornblende trace element contents and zoning patterns prove to be powerful tools for identification of magma batches and for assessing magmatic processes, and thereby relating plutonic rocks to hypabyssal and volcanic equivalents.

The active Lassen hydrothermal system includes a central vapor-dominated zone or zones beneath the Lassen highlands underlain by ~240 °C high-chloride waters that discharge at lower elevations. It is the best-exposed and largest hydrothermal system in the Cascade Range, discharging 41 ± 10 kg/s of steam (~115 MW) and 23 ± 2 kg/s of high-chloride waters (~27 MW). The Lassen system accounts for a full 1/3 of the total high-temperature hydrothermal heat discharge in the U.S. Cascades (140/400 MW). Hydrothermal heat discharge of ~140 MW can be supported by crystallization and cooling of silicic magma at a rate of ~2400 km 3 /Ma, and the ongoing rates of heat and magmatic CO 2 discharge are broadly consistent with a petrologic model for basalt-driven magmatic evolution. The clustering of observed seismicity at ~4–5 km depth may define zones of thermal cracking where the hydrothermal system mines heat from near-plastic rock. If so, the combined areal extent of the primary heat-transfer zones is ~5 km2, the average conductive heat flux over that area is >25 W/m2, and the conductive-boundary length <50 m. Observational records of hydrothermal discharge are likely too short to document long-term transients, whether they are intrinsic to the system or owe to various geologic events such as the eruption of Lassen Peak at 27 ka, deglaciation beginning ~18 ka, the eruptions of Chaos Crags at 1.1 ka, or the minor 1914-1917 eruption at the summit of Lassen Peak. However, there is a rich record of intermittent hydrothermal measurement over the past several decades and more-frequent measurement 2009-present. These data reveal sensitivity to climate and weather conditions, seasonal variability that owes to interaction with the shallow hydrologic system, and a transient 1.5-to twofold increase in high-chloride discharge in response to an earthquake swarm in mid-November 2014.

Maruyamaite, ideally K(MgAl 2 )(Al 5 Mg)Si 6 O 18 (BO 3 ) 3 (OH) 3 O, was recently approved as the first K-dominant mineral-species of the tourmaline supergroup. It occurs in ultrahigh-pressure quartzofeldspathic gneisses of the Kumdy-Kol area of the Kokchetav Massif, northern Kazakhstan. Maruyamaite contains inclusions of microdiamonds, and probably crystallized near the peak pressure conditions of UHP metamorphism in the stability field of diamond. Crystals occur as anhedral to euhedral grains up to 2 mm across, embedded in a matrix of anhedral quartz and K-feldspar. Maruyamaite is pale brown to brown with a white to very pale-brown streak and has a vitreous luster. It is brittle and has a Mohs hardness of ∼7; it is non-fluorescent, has no observable cleavage or parting, and has a calculated density of 3.081 g/cm 3 . In plane-polarized transmitted light, it is pleochroic, O = darkish brown, E = pale brown. Maruyamaite is uniaxial negative, ω = 1.634, ε = 1.652, both ±0.002. It is rhombohedral, space group R3m , a = 15.955(1), c = 7.227(1) Å, V = 1593(3) Å 3 , Z = 3. The strongest 10 X-ray dif- fraction lines in the powder pattern are [ d in Å( I )( hkl )]: 2.581(100)(051), 2.974(85)(1̄32), 3.995 (69)(2̄40), 4.237(59)(2̄31), 2.046(54)(1̄62), 3.498(42)(012), 1.923(36)(3̄72), 6.415(23)(1̄11), 1.595(22)(5̄.10.0), 5.002(21)(021), and 4.610(20)(030). The crystal structure of maruyamaite was refined to an R 1 index of 1.58% using 1149 unique reflections measured with Mo K α X-radiation. Analysis by a combination of electron microprobe and crystal-structure refinement gave SiO 2 36.37, Al 2 O 3 31.50, TiO 2 1.09, Cr 2 O 3 0.04, Fe 2 O 3 0.33, FeO 4.01, MgO 9.00, CaO 1.47, Na 2 O 0.60, K 2 O 2.54, F 0.30, B 2 O 3 (calc) 10.58, H 2 O(calc) 2.96, sum 100.67 wt%. The formula unit, calculated on the basis of 31 anions pfu with B = 3, OH = 3.24 apfu (derived from the crystal structure) and the site populations assigned to reflect the mean interatomic distances, is (K 0.53 Na 0.19 Ca 0.26 □ 0.02 ) ΣX=1.00 (Mg 1.19 Fe0.552+Fe0.053+${\rm{Fe}}_{0.55}^{2 + }{\rm{Fe}}_{0.05}^{3 + }$ Ti 0.14 Al 1.07 ) □Y=3.00 (Al 5.00 Mg 1.00 )(Si 5.97 Al 0.03 O 18 )(BO 3 ) 3 (OH) 3 (O0.602−${\rm{O}}_{0.60}^{2 - }$F 0.16 OH 0.24 ). Maruyamaite, ideally K(MgAl 2 ) (Al 5 Mg)(BO 3 ) 3 (Si 6 O 18 )(OH) 3 O, is related to oxy-dravite: ideally Na(MgAl 2 )(Al 5 Mg)(BO 3 ) 3 (Si 6 O 18 )(OH) 3 O, by the substitution X K → X Na.

The bond-valence model has recently been expanded to include a directional component, the vectorial bond-valence sum, which is useful for characterizing non-centrosymmetric distortions involving lone-pair and second-order Jahn-Teller effects. Here we show that the bond-valence sum and vectorial bond-valence sum are equivalent to monopole and dipole terms in a multipole expansion of the bond valence incident to an atom. We then extend the multipole expansion to include a quadrupole term, which describes the ellipsoidal deviation from spherical symmetry of the bonding environment, and is useful for characterizing centrosymmetric distortions, such as those caused by first-order Jahn-Teller effects. These distortions follow characteristic patterns in valence space, which depend upon factors that include the d -orbital configuration and size of the transition metal involved. This extended approach, called the Valence Multipole Model, should prove useful for modeling molecular and crystal structures, including those associated with spin transitions.

A suite of Ti-bearing garnets from magmatic, carbonatitic, and metamorphic rocks was studied by electron probe microanalysis (EPMA), X-ray powder diffraction (XRPD), single-crystal X-ray diffraction (SCXRD), Mössbauer spectroscopy, and secondary ion mass spectrometry (SIMS) to better characterize their crystal chemistry. The studied garnets show TiO 2 varying in the range of 4.9(1) to 17.1(2) wt% and variable Fe 3+ /ΣFe content. SIMS analyses allowed quantification of light elements yielding H 2 O in the range 0.091(7)–0.46(4), F in the range 0.004(1)–0.040(4), and Li 2 O in the range 0.0038(2)–0.014(2) wt%. Mössbauer analysis provided spectra with different complexity, which could be fitted to several components variable from one ( Y Fe 3+ ) to four ( Y Fe 2+ , Z Fe 2+ , Y Fe 3+ , Z Fe 3+ ). A good correlation was found between the Fe 3+ /ΣFe resulting from the Mössbauer analysis and that derived from the Flank method. X-ray powder analysis revealed that the studied samples are a mixture of different garnet phases with very close cubic unit-cell parameters as recently found by other authors. Single-crystal X-ray refinement using anisotropic displacement parameters were performed in the Ia 3 d space group and converged to 1.65 ≤ R 1 ≤ 2.09% and 2.35 ≤ wR 2 ≤ 3.02%. Unit-cell parameters vary in the range 12.0641(1) ≤ a ≤ 12.1447(1) Å, reflecting different Ti contents and extent of substitutions at tetrahedral site. The main substitution mechanisms affecting the studied garnets are: Y R 4+ + Z R 3+ ↔ Z Si + Y R 3+ (schorlomite substitution); Y R 2+ + Z R 4+ ↔ 2 Y R 3+ (morimotoite substitution); YR 3+ ↔ Y Fe 3+ (andradite substitution); in the above substitutions Y R 2+ = Fe 2+ , Mg 2+ , Mn 2+ ; Z R 4+ = Ti; YR 3+ = Fe 3+ , Al 3+ , Cr 3+ ;ZR 3+ = Fe 3+ , Al 3+ . Minor substitutions, such as 2 Y Ti 4+ + Z Fe 2+ ↔ 2 Y Fe 3+ + Z Si, (SiO 4 ) 4– ↔ (O4H 4 ) 4– , F – ↔ OH – , and Y R 4+ + X R + ↔ Y R 3+ + X Ca 2+ , with Y R 4+ = Ti, Zr; YR 3+ = Fe 3+ , Al, Cr 3+ ; X R + = Na, Li also occur.

The validity of the application of the n -alkylammonium method to carbonate-rich lithologies was checked by means of a double comparison: First, the method was applied to samples studied by XRD and HRTEM. Second, these results were compared with the chemical compositions obtained independently by analytical electron microscopy (AEM) from single grains of smectites and I/S. Marl and marly limestone samples corresponding to the R0 and R1 illite/smectite mixed-layer (I/S) stages of diagenetic evolution have been analyzed by the n -alkylammonium method. Forty samples were taken and analyzed by routine X-ray diffraction (XRD) methods. The complete series from n c :6 to n c :18 has been used for XRD determination on eight samples, yielding layer charges of 0.32 to 0.39 apfu for the expandable component [formula based on O 10 (OH) 2 ]. Lattice-fringe images have been obtained under TEM from four selected samples treated with n c :8 and n c :14 alkylammonium, which are the best chain lengths for discrimination, according to the XRD results. The same type of interlayer configuration (mono-, bi-, or pseudo-tri-layer) has been found by XRD and TEM in all cases. A comparison of the alkylammonium method layer charges with those calculated from formulas determined by AEM on single clay particles has revealed a good general agreement between the two independent methods; however, results from the alkylammonium method are 3 to 14% lower than those from AEM. This disparity is qualitatively in agreement with the literature, but the difference is clearly lower, presumably due to the use of specific in situ analyses (which are contamination-free) instead of whole analyses of separates. The good agreement among the three methods validates their use for carbonate-rich lithologies. Layer charge increases with depth through the R0 stadium, but stabilizes, with no further increase, when the R1 stadium is reached; this change in behavior may be related with qualitative differences in the transformation mechanism.

This study provides new insights into the relation between thermally induced structural reorganization and the macroscopic mechanical properties of radiation-damaged titanite. The natural sample contains ca. 30% amorphous fraction. Low-temperature annealing affects only slightly the sample stiffness and leads to a softening resulting from the defect annihilation in crystalline regions. In the high-temperature annealing regime, amorphous domains recrystallize and this leads to further recovery of defects, reduction of interfaces, grain growth, and, in general, an increase in the long-range order. The thermally induced recrystallization is accompanied by massive dehydration leading to considerable stiffening and hardening. This interpretation of the recrystallization process in titanite based on the correlation of new results from nanoindentation and Raman-spectroscopic measurements complementing previous investigations using thermogravimetric and gas analyses by Hawthorne et al. (1991) and infrared spectroscopy by Zhang et al. (2001). The new data combined with previous work leads to a detailed description of the annealing behavior of a radiation-damaged titanite, which is a complicated process that includes dehydration and atomic-scale structural reorganization. To minimize the influence of surface phenomena on the hardness measurements, the so-called “true” hardness was used instead of the standard hardness calculation (Oliver and Pharr 1992). A comparison shows that the Oliver and Pharr method clearly underestimates the hardness.

Synchrotron powder X-ray diffraction and scanning electron microscopy examinations of man-ganese oxide concretions/nodules (∼0.3-1.0 mm diameter) from ODP Site 1262 on Walvis Ridge in the Southeastern Atlantic Ocean revealed that they consist primarily of the layered Mn oxide phase jianshuiite [(Mg,Mn,Ca)Mn34+O7⋅3H2O]$[({\rm{Mg}},{\rm{Mn}},{\rm{Ca}}){\rm{Mn}}_3^{4 + }{{\rm{O}}_7} \cdot 3{{\rm{H}}_2}{\rm{O]}}$. The nodules are from an interval with severe carbonate dis-solution that represents the Paleocene/Eocene (P/E) thermal maximum (∼5 5.8 Ma). Most nodules from the middle of the carbonate dissolution interval contain internal open space, and consist almost entirely of euhedral plate-like jianshuiite crystals, 2–4 μm in diameter and ∼0.1–0.5 μm thick. Backscattered electron images and energy-dispersive X-ray analyses revealed stacks of interleaved Al-rich and Al-poor jianshuiite crystals in some nodules. The crystals in other nodules contain predominantly Mg (with trace K and Al) in addition to Mn and O, making them near “end-member” jianshuiite. Rietveld refinements in space group R 3̄ confirmed the isostructural relationship between jianshuiite and chalcophanite, with Mg occupying the interlayer position above and below the vacant sites in the Mn/O octahedral sheet, and coordinated to 3 octahedral layer O atoms (1.94 Å) and 3 interlayer water O atoms (2.13 Å). Final refined occupancy factors suggest that small quantities of Ni and possibly Mn 2+ are located on the Mg site. The transient appearance of the Mg-rich birnessite-like phase jianshuiite, probably abiotically produced, must indicate an exceptional transient change in the chemistry of the pore fluids within deep ocean sediments directly following the P/E boundary, possibly as a result of decreasing oxygen levels and pH, followed by a return to pre-event conditions.

Solubility experiments of Mn-columbite (MnNb 2 O 6 ) and Mn-tantalite (MnTa 2 O 6 ) were conducted under water-saturated conditions in synthetic haplogranitic melts containing different amounts of phosphorus at 800 °C and 100 MPa. All experiments were carried out in cold-seal rapid quenching pressure vessels (RQV) with water as a pressure medium. Experimental results show that: (1) the solubilities of MnNb 2 O 6 and MnTa 2 O 6 in peralkaline melts are higher than those in peraluminous melts; (2) phosphorus has strong influence on the solubilities of MnTa 2 O 6 and MnNb 2 O 6 in peralkaline melts, KSpNb${\rm{K}}_{{\rm{Sp}}}^{{\rm{Nb}}}$ and KSpTa${\rm{K}}_{{\rm{Sp}}}^{{\rm{Ta}}}$ decrease from 104.89 × 10 –4 mol 2 /kg 2 and 107.62 × 10 –4 mol 2 /kg 2 for melts without P 2 O 5 to 16.11 × 10 –4 mol 2 /kg 2 and 7.96 × 10 –4 mol 2 /kg 2 for melts containing ~4.00 wt% P 2 O 5 , respectively; (3) phosphorus has less influence on the solubilities of MnTa 2 O 6 and MnNb 2 O 6 in peraluminous melt, KSpNb${\rm{K}}_{{\rm{Sp}}}^{{\rm{Nb}}}$ decrease from 4.50 × 10 –4 mol 2 /kg 2 for melts without P 2 O 5 to 0.73 × 10 –4 mol 2 /kg 2 , and K Sp Ta from 3.57 × 10 –4 mol 2 /kg 2 to 0.14 × 10 –4 mol 2 /kg 2 for melts contaning ~5.00 wt% P 2 O 5 . Taking the structural role of phosphorus into account, P decreases the solubility of Mn-columbite and Mn-tantalite via competing for network modifiers.

A series of 1:1 silicate clays of the lizardite-nepouite series [Si 2 Mg 3–x Ni x O 5 (OH 4 ) with x = 0, 0.5, 1, 1.5, 2, 2.5, and 3] was synthesized at 220 °C during 7 days from coprecipitated gels in hydrothermal conditions. A clear relationship was evidenced between the d (06–33) and the Ni/Mg ratio of the synthesized samples following a Vegard’s law and suggested a random distribution of octahedral cations. For the first time, infrared spectra of this series were given in both near and mid-infrared spectral regions (250–7500 cm –1 ). Notably, the bands due to the OH stretching vibrations and those of their first overtones in the lizardite-nepouite series were attributed. The combination bands observed in the near infrared region for both end-members could be attributed thanks to combinations of two or three middle-infrared features. Some of the observed combination bands are clearly linked to combination of different vibrational groups. Infrared spectroscopy is simple to use and is a powerful tool to study the crystal chemistry of garnierites. More broadly, the improvement of band attributions especially in near infrared contributes to develop the infrared analyses in field geology and remote sensing.

The synthesis of 10 Å phase via the reaction of talc plus water at 8 GPa and 500 °C was studied by in situ Raman spectroscopy using a diamond-anvil cell. The initial fast (2 h) incorporation of interlayer H 2 O molecules into the talc structure is traced by gradual growth of new OH stretching bands at 3592 and 3621 cm -1 and the shift of several framework bands. Further monitoring at HP-HT conditions over 7 h reveals gradual weakening of the 3592 cm -1 band, which can probably be related to the onset of the formation of “long-run” 10 Å phase through the appearance of silanol groups following the model proposed by Pawley et al. (2010), influencing the interlayer hydrogen bonding.

To constrain the ternary K 2 CO 3 -CaCO 3 -MgCO 3 T-X diagram at 6 GPa and to expand upon the known K-Mg, K-Ca, and Ca-Mg binary systems we have carried out multi-anvil experiments along the K 2 CO 3 -Ca 0.5 Mg 0.5 CO 3 join. The diagram has primary phase fields for K 2 CO 3 , K 2 Mg(CO 3 ) 2 , K 2 Ca 0.1–0.5 Mg 0.9–0.5 (CO 3 ) 2 , K 4 CaMg(CO 3 ) 4 , Ca-magnesite, and dolomite. The system has two liquidus minima near 1000 °C. At one minimum, a liquid with the composition of 36 K 2 CO 3 ·64(Ca 0.65 Mg 0.35 )CO 3 is in equilibrium with three phases: Ca-magnesite, K 2 Ca 0.1–0.5 Mg 0.9–0.5 (CO 3 ) 2 , and K 6 Ca 2 (CO 3 ) 5 . The other minimum, a liquid with the composition of 62 K 2 CO 3 ·38Ca 0.72 Mg 0.28 CO 3 is in equilibrium with K 2 CO 3 , K 4 CaMg(CO 3 ) 4 , and K 6 Ca 2 (CO 3 ) 5 . At 900 °C, the ternary diagram contains two- and three-phase regions with Ca-magnesite, aragonite, K 2 Ca 3 (CO 3 ) 4 , K 2 Ca(CO 3 ) 2 , K 6 Ca 2 (CO 3 ) 5 , K 2 CO 3 , K 2 Ca 0.1–0.5 Mg 0.9–0.5 (CO 3 ) 2 solid solution, K 2 Mg 0.9 Ca 0.1 (CO 3 ) 2 , and K 4 CaMg(CO 3 ) 4 . We also expect an existence of primary phase fields for K 6 Ca 2 (CO 3 ) 5 , K 2 Ca 3 (CO 3 ) 4 and aragonite. We suggest that extraction of K from silicate to carbonate components should decrease the minimum melting temperature of dry carbonated mantle rocks up to 1000 °C at 6 GPa and yield ultrapotassic Ca-rich dolomite melt containing more than 10 mol% K 2 CO 3 . As temperature increases above 1200 °C the melt evolves toward an alkali-poor, dolomitic liquid if the bulk molar CaO/MgO ratio >1, or toward K-Mg-rich carbonatite if bulk CaO/MgO <1. The majority of compositions of carbonatite inclusions in diamonds from around the world fall within the magnesite primary field between the 1300 and 1400 °C isotherms. These melts could be formed by partial melting of magnesite-bearing peridotite or eclogite with bulk Ca/Mg <1 at temperatures ≤1400 °C. A few compositions revealed in the Ebelyakh and Udachnaya diamonds (Yakutia) fall within the dolomite primary field close to the 1200 °C isotherm. These melts could be formed by partial melting of dolomite-bearing rocks, such as carbonated pelite or eclogite with bulk Ca/Mg <1 at temperatures ≤1200 °C.

Natural kyanites with Cr 2 O 3 contents >1 wt% are very rare and known only from high- P environments, for example, eclogite-facies gabbroic cumulates containing Cr-spinel from the Pohorje Massif, Eastern Alps, Slovenia. In these rocks, turquoise-colored Cr-rich kyanites are present in two different textural types. A first type has formed as blocky crystals of several hundred micrometers in size around clusters of small drop-like Cr-spinels. This kyanite shows a highly irregular Cr distribution and may contain up to 15.6 wt% Cr 2 O 3 , which is one of the highest Cr 2 O 3 contents reported so far. A second type is present as part of reaction coronas around large red-brownish Cr-spinel and forms deep-blue needle-like crystals that rarely exceed 100 μm in size. This kyanite contains up to 8.2 wt% Cr 2 O 3 and is associated with Cr-rich corundum (≤9.1 wt% Cr 2 O 3 ) and Cr-Al-rich pargasite (≤3.9 wt% Cr 2 O 3 ). The formation of kyanite around Cr-spinel droplets is interpreted to be the result of increasing P-T conditions during prograde metamorphism where Cr-spinel and plagioclase or quartz react to Crkyanite, ±garnet, ±omphacite. In contrast, the formation of kyanite associated with Cr-rich corundum and Cr-rich pargasite within coronas around Cr-spinel occurred in an early stage of the retrogressive evolution of the gabbroic cumulates at eclogite-facies conditions of ~2.5 GPa and 750–800 °C triggered by the influx of H 2 O-rich fluids. The driving force for developing these coronas was an increase in the chemical potential of silica caused by the infiltrating hydrous fluid phase. P-T estimates using matrix mineral assemblage place the peak metamorphic conditions close to the quartz/coesite transition with temperatures in the range of 750–810 °C and pressures of ~2.9 GPa.

Ferri-kaersutite, ideally NaCa 2 (Mg 3 TiFe 3+ )(Si 6 Al 2 )O 22 O 2 , is a new oxo-amphibole from Harrow Peaks, Northern Victoria Land, Antarctica. It occurs as brown prismatic crystals, up to 200 μm in length, with a vitreous luster, and a perfect {110} cleavage. Ferri-kaersutite is associated with forsterite, diopside, and Cr-bearing spinel. Chemical analyses, by a combination of electron microprobe, SIMS, and 57 Fe Mössbauer spectroscopy, gave the following results (in wt%): SiO 2 41.69, TiO 2 5.30, Al 2 O 3 13.65, Cr 2 O 3 0.09, Fe 2 O 3 4.52, MgO 15.54, CaO 11.03, MnO 0.11, FeO 2.83, Na 2 O 2.88, K 2 O 0.96, H 2 O 0.70, F 0.24, Cl 0.08, O=(F,Cl) –0.12, sum 99.50. On the basis of 24 anions per formula unit, the formula is (Na0.816K0.179)∑0.995(Ca1.726Fe0.2582+Mn0.014)∑1.998(Mg3.383Fe0.0882+Ti0.582Fe0.4973+Al0.439Cr0.011)∑5.00${\left( {{\rm{N}}{{\rm{a}}_{0.816}}{{\rm{K}}_{0.179}}} \right)_{\sum {0.995} }}{\left( {{\rm{C}}{{\rm{a}}_{1.726}}{\rm{Fe}}_{0.258}^{2 + }{\rm{M}}{{\rm{n}}_{0.014}}} \right)_{\sum {1.998} }}{\left( {{\rm{M}}{{\rm{g}}_{3.383}}{\rm{Fe}}_{0.088}^{2 + }{\rm{T}}{{\rm{i}}_{0.582}}{\rm{Fe}}_{0.497}^{3 + }{\rm{A}}{{\rm{l}}_{0.439}}{\rm{C}}{{\rm{r}}_{0.011}}} \right)_{\sum {5.00} }}$ (Si 6.089 Al 1.911 )Σ 8.00 O 22 [O 1.187 (OH) 0.682 F 0.111 Cl 0.020 ] Σ2.00 . Ferri-kaersutite is monoclinic with space group C 2/ m . Its unit-cell parameters are a = 9.8378(8), b = 18.0562(9), c = 5.3027(4) Å, β = 105.199(9)°, V = 908.99(13) Å 3 , Z = 2. The five strongest reflections in its X‑ray powder diffraction pattern [ d in Å (relative visual intensity, hkl )] are: 8.4 (s, 110), 3.379 (ms, 131), 3.115 (ms, 310), 2.707 (s, 151), 2.598 (ms, 061). The crystal structure of ferri‑kaersutite has been refined on the basis of 1783 observed reflections [ F o > 4σ( F o )] with a final R 1 = 0.038. The relatively large equivalent isotropic displacement parameter at M (1), with respect to those at M (2) and M (3) sites, together with the short M (1)–O(3) distance, suggest the occurrence of Ti 4+ at the M (1) site, whereas the small octahedral distortion at this site suggests a low Fe 3+ occupancy. This element is mainly hosted at the M (2) and M (3) sites. The occurrence of amphiboles in the magma source region is notably relevant. The melting of Ti-rich amphibole in the lithosphere and subsequent degrees of melt/host peridotite reactions are able to produce melts that account for the compositional spectrum ranging from extreme alkaline lavas to the most common alkaline basalts. In particular, when this amphibole is formed by reaction between a peridotite matrix and metasomatic melts/fluids with high Fe 3+ /Fe tot ratio, its subsequent melting can influence primary volatile contents and ultimately magma rheology.

Despite claims to the contrary, the compositions of magnetite and ilmenite in the Bishop Tuff correctly record the changing conditions of T and f O 2 in the magma reservoir. In relatively reduced (ΔΝΝΟ <1) siliceous magmas (e.g., Bishop Tuff, Taupo units), Ti behaves compatibly (D Ti ≈ 2−3.5), leading to a decrease in TiO 2 activity in the melt with cooling and fractionation. In contrast, FeTioxides are poorer in TiO 2 in more oxidized magmas (ΔΝΝΟ > 1, e.g., Fish Canyon Tuff, Pinatubo), and the d ( a TiO 2 )/ dT slope can be negative. Biotite, FeTi-oxides, liquid, and possibly plagioclase largely maintained equilibrium in the Bishop Tuff magma (unlike the pyroxenes, and cores of quartz, sanidine, and zircon) prior to and during a mixing event triggered by a deeper recharge, which, based on elemental diffusion profiles in minerals, took place at least several decades before eruption. Equilibrating phases and pumice compositions show evolving chemical variations that correlate well with mutually consistent temperatures based on the FeTi-oxides, sanidine-plagioclase, and Δ 18 Ο quartz-magnetite pairs. Early Bishop Tuff (EBT) temperatures are lower (700 to ~780 °C) than temperatures (780 to >820 °C) registered in Late Bishop Tuff (LBT), the latter defined here not strictly stratigraphically, but by the presence of orthopyroxene and reverse-zoned rims on quartz and sanidine. The claimed similarity in compositions, Zr-saturation temperatures and thermodynamically calculated temperatures (730−740 °C) between EBT and less evolved LBT reflect the use of glass inclusions in quartz cores in LBT that were inherited from the low-temperature rhyolitic part of the reservoir characteristic of the EBT. LBT temperatures as high as 820 °C, the preservation of orthopyroxene, and the presence of reverse-zoned minerals (quartz, sanidine, zircons) are consistent with magma recharge at the base of the zoned reservoir, heating the cooler rhyolitic melt, partly remelting cumulate mush, and introducing enough CO 2 (0.4−1.4 wt%, mostly contained in the exsolved fluid phase) to significantly lower H 2 O-activity in the system.

Here we report on the coexistence between Na-rich ringwoodite and bridgmanite in the system MgSiO 3 −Na 2 CO 3 −Al 2 O 3 at 24 GPa and 1700 °C. In our experiments ringwoodite incorporates up to 4.4 wt% Na 2 O, with Na entering the octahedral site together with Si, according to the mechanism: Mg 2+ → ⅔Na + + ⅓Si 4+ . The volume of the unit cell increases along with the Na content. A similar behavior is observed for the unit-cell volume of Na-bearing bridgmanite, although the mechanism of Na incorporation into this structure remains unknown because of the lack of sufficient crystallographic data. Na 2 O is compatible in ringwoodite relative to bridgmanite with a partition coefficient (D) of 5 (+5/–4), but is incompatible in ringwoodite relative to carbonate-rich melt/fluid, with the D value ranging between 0.5 and 0.1. Al is highly enriched in bridgmanite relative to the other coexisting phases. Carbonatitic melt metasomatism in the deep transition zone may lead to local Na-enrichment, and ringwoodite may be an important host for Na in the deep transition zone. Subsequent convection or subduction of metasomatized mantle may lead to enrichment of alkaline elements in the upper and lower mantle.