bluuebunny/crossref_metadata_2025 huggingface dataset:
Melt-Peridotite Interactions in Shallow Mantle at the East Pacific Rise: Evidence from ODP Site 895 (Hess Deep)
Authors: Edwards Stephen J. , Malpas John
Published: December 2006

Ocean Drilling Program (ODP) Leg 147 recently drilled at Site 895 in Hess Deep (eastern Equatorial Pacific), where a structurally dissected section of the East Pacific Rise (EPR) is preserved, and intersected the mantle-crust transition zone of a fast-spreading centre for the first time. The core from Hole 895D (latitude 2°16.635′N, longitude 101°26.777′W) revealed that harzburgite is predominant over dunite in the top section of the Hole, but the reverse relationship is found lower in the section where dunite is closely associated with gabbroic rocks (gabbro and troctolite). Texture, mineralogy and mineral chemistry suggest a two-stage evolution for harzburgite preserved at the transition zone. Harzburgite with a porphyroclastic texture was produced by partial melting of peridotite to, or beyond the clinopyroxene-out phase boundary before or during asthenospheric (>1000°C) flow, which suggests a higher degree of mantle melting than normally expected below mid-ocean ridges. Subsequently, basaltic melt(s) interacted with this refractory harzburgite (olivine + orthopyroxene + spinel), which resulted in dissolution of orthopyroxene, re-equilibration and formation of olivine and spinel, and formation of clinopyroxene ± plagioclase, this is manifested as a progressive conversion of harzburgite to gabbroic rock through an intermediate dunite. At low melt/peridotite ratios, harzburgite was refertilised as the plagioclase component of the melt completely reacted with the peridotite matrix to produce clinopyroxene-spinel intergrowths and Al enrichment in ferromagnesian minerals. At high ratios, orthopyroxene completely dissolved incongruently, plagioclase appeared, and spinel was partially to completely resorbed; this produced olivine-bearing and olivine-free gabbroic rocks. Residual minerals in peridotites adjacent to gabbroic zones were enriched in Fe and Ti and depleted in Al.
Metasomatism in the North Qôroq centre, South Greenland: apatite chemistry and rare-earth element transport
Authors: Rae David A. , Coulson Ian M. , Chambers Andrew D.
Published: December 2006

The North Qôroq syenite centre forms part of the Gardar Province of South Greenland. Extensive metasomatism, associated with the evolution of syenitic magmas, has resulted in redistribution of the rare-earth elements (REE), originally concentrated by magmatic processes, in both the syenites and surrounding granite-gneiss and quartzite country rocks. An important host for REE is apatite which can occur in significant quantities. Metasomatic apatites show complex, concentric, but irregular patterns of zonation, clearly seen using CL and BSE imaging. This zonation is related to successive pulses of metasomatising fluids. Electron microprobe analysis confirms the presence of significant quantities of REE in the apatites. The dominant cation exchange mechanism proposed is Ca2+ + P5+ ⇌ REE3+ + Si4+. In contrast to apatites from the nearby Ilímaussaq intrusion, there is no significant Na present in the structure and exchange reactions involving Na+ and REE3+ for Ca2+ have not occurred.

Apatites from the quartzite are fluor-apatites, while those from the granite-gneiss are more Cl-rich. These differences reflect the fact that granite-gneiss apatites are original and modified by metasomatism, whereas, those in the quartzite are metasomatic in origin. REE were probably transported as carbonate, fluoride or fluor-carbonate complexes, and reflect the activity of a F−-rich, CO2−3-rich fluid phase.
Geochemistry of late Caledonian minettes from Northern Britain: implications for the Caledonian sub-continental lithospheric mantle
Authors: Canning Jason C. , Henney P. J. , Morrison M. A. , Gaskarth J. W.
Published: December 2006

The geochemistry of late Caledonian minettes from across the orogenic belt is compared in order to constrain the composition of the Caledonian sub-continental lithospheric mantle (SCLM). All the minettes are similar petrographically and chemically and several samples have characteristics typical of near primary mantle melts. Samples from the Northern Highlands and the Caledonian foreland show enrichment in many trace elements (notably LILE and LREE) relative to those from the Grampians, the Southern Uplands and northern England, coupled with distinct Nd and Sr isotope characteristics. Processes such as fractional crystallization, crustal assimilation, and partial melting played a negligible role in creating the differences between the two groups which reflect long-term, time-integrated differences in the compositions of their SCLM sources. The Great Glen Fault appears to represent the boundary between these two lithospheric mantle domains. Other currently exposed Caledonian tectonic dislocations cannot be correlated directly with compositional changes within the SCLM. The chemical provinciality displayed by the minettes shows some resemblance to that within other late Caledonian igneous suites, including the newer granites, suggesting that the minettes may represent the lithospheric mantle contributions to these rocks.
Intergrowths of hexagonal and monoclinic pyrrhotites in some sulphide ores from norway
Authors: Lianxing Gu , Vokes Frank M.
Published: December 2006

Pyrrhotites in polished sections from more than twenty stratabound massive sulphide and magmatic nickel-copper deposits in Norway were studied under the microscope using the magnetic colloid method. In both types of deposits, two distinct styles of intergrowths between monoclinic and hexagonal pyrrhotites were found: crystallographically-controlled lamellar intergrowths and fissure-controlled irregular intergrowths.

Lamellar intergrowths consist of crystallographically oriented monoclinic lamellae occurring in a hexagonal matrix and were produced originally by exsolution from hexagonal pyrrhotite on cooling. Irregular intergrowths comprise blades and patches of monoclinic pyrrhotite occurring along fissures and grain boundaries of hexagonal pyrrhotite, and were formed by interactions between hexagonal grains and sulphur-rich hydrothermal solutions.

Increase in lamella thickness and spacing, development of lamella zonations, wedge-shaped composite ends, boxworks and composite lamellae were caused by progressive lamellae coarsening and maturation during natural annealing, which could have been promoted by anisotropic stress. Metamorphic recrystallization and annealing tend to homogenize pyrrhotite and erase preexisting exsolution lamellae.
Temperature gradients in large cold-seal pressure vessels
Authors: Dalton J. A. , Gibb F. G. F.
Published: December 2006

Radial and longitudinal temperature gradients within cold-seal pressure vessels can contribute significantly to the total temperature unccrtainty in any one experiment and it is important to calibrate such gradients before experiments are undertaken. We have measured temperature gradients in vertically mounted large cold-seal vessels at 1 atm and 1 kbar and in the temperature range 500–800°C Radial gradients were measured with the vessel at various positions within the furnace by recording the temperature difference between a thermocouple in the internal bore of the vessel and one in a well in the top of the vessel. We find that when the vessel is at a certain position in the furnace, the temperatures read by these two thermocouples are equivalent to within 1°C. The contribution of radial gradients to temperature uncertainty can be thus be substantially minimized if experiments are undertaken with the vessel in this position. Longitudinal gradients of 2.8°C/cm at 500°C and 3°C/cm at 800°C were recorded at 1 kbar. These profiles are significantly steeper than those recorded at 1 atm. Not to calibrate temperature gradients at the experimental conditions or failure to calibrate vessels at all could lead to large temperature uncertainties.
Minor and trace element chemistry of carbonates, apatites and magnetites in some African carbonatites
Authors: Dawson J. B. , Steele I. M. , Smith J. V. , Rivers M. L.
Published: December 2006

In calcites and dolomites in seven African carbonatites, SrO, FeO and MnO occur in concentrations from 1 to 2 wt.%, whereas Ce, Y, Cu and Zn occur only at the ppm level. Sr, Ce and Y partition preferentially into calcite relative to co-existing dolomite, whereas Fe and Mn favour dolomite. Sr partitions preferentially into calcite relative to co-exisiting apatite, but the light rare-earth elements partition into apatite. Magnetite from Kerimasi contains up to 13 wt.% MgO and 6 wt.% MnO, extending the known ranges in composition of magnetites from carbonatites.
The stabilities of secondary tin minerals. Part 2: The hydrolysis of tin(II) sulphate and the stability of Sn3O(OH)2SO4
Authors: Edwards R. , Gillard R. D. , Williams P. A.
Published: December 2006

Tritin(II)dihydroxyoxosulphate, Sn3O(OH)2SO4, is a rare corrosion product found on the surfaces of certain tin alloys. A new synthesis based on the hydrolysis of SnSO4 is described. The stability constant determination of Sn3O(OH)2SO4,s, at 298.2K and 105Pa is determined using direct measurements via electrodes, of the activities of tin(II) and sulphate ions. ΔfG0(298.2K) is equal to −1563.1 ± 0.9 KJ mol−1.
Nb-rich baotite in carbonatites and fenites at Haast River, New Zealand
Authors: Cooper Alan F.
Published: December 2006

Baotite occurs as an accessory mineral in carbonatites, fenites, and carbothermal veins associated with a lamprophyre dyke swarm in the Haast River area of south Westland, New Zealand. Carbonatites are petrogenetically evolved, with assemblages dominated by ankerite, siderite and Ba-Sr-REE carbonates. Microprobe analysis indicates baotite compositions more Nb-rich than previously recorded, with compositions close to Ba4[Ti3(Nb,Fe)5]Si4O28Cl. Ti must be partially replaced in both crystallographically-independent octahedral sites. Compositional zoning, and stoichiometric considerations suggest that the dominant octahedral substitution is the same as that described in rutile, namely 3Ti4+ ⇌ 2Nb5+ + Fe2+. Contrary to previous suggestions, Fe in the octahedral site should, therefore, be dominated by Fe2+.

The presence of baotite further documents the involvement of halogens in carbonatite magmas. In the New Zealand occurrences it is suggested that the chlorine originates from associated phonolitic magmas and is partitioned into carbonatite during liquid immiscibility.
Prismatine: revalidation for boron-rich compositions in the kornerupine group
Authors: Grew Edward S. , Cooper Mark A. , Hawthorne Frank C.
Published: December 2006

Kornerupine and prismatine were introduced independently by Lorenzen in 1884 (but published in 1886 and 1893) and by Sauer in 1886, respectively. Ussing (1889) showed that the two minerals were sufficiently close crystallographically and chemically to be regarded as one species. However, recent analyses of boron using the ion microprobe and crystal structure refinement, indicate that the boron content of one tetrahedral site in kornerupine ranges from 0 to 1. Kornerupine and prismatine, from their respective type localities of Fiskenæsset, Greenland and Waldheim, Germany, are distinct minerals, members of an isomorphic series differing in boron content. For this reason, we re-introduce Sauer’s name prismatine for kornerupines with B > 0.5 atoms per formula unit (p.f.u.) of 22(O,OH,F), and restrict the name kornerupinesensu strictoto kornerupines with B < 0.5 p.f.u. Kornerupinesensu latois an appropriate group name for kornerupine of unknown boron content. Kornerupinesensu strictoand prismatine from the type localities differ also in Fe2+/Mg ratio, Si − (Mg + Fe2++ Mn) content, Al content, F content, colour, density, cell parameters, and paragenesis. Both minerals formed under granulite-facies conditions with sapphirine and phlogopite, but kornerupinesensu strictois associated with anorthite and hornblende or gedrite, whereas prismatine is found with oligoclase (An9–13), sillimanite, garnet, and/or tourmaline. Occurrences at other localities suggest that increasing boron content extends the stability range of prismatine relative to that of kornerupinesensu stricto.
Larnitic kirschsteinite from the Kotakonda kimberlite, Andhra Pradesh, India
Authors: Chalapathi Rao N. V. , Reed S. J. B. , Pyle D. M. , Beattie P. D.
Published: December 2006

Olivines from igneous rocks generally have low calcium contents. However, olivines crystallized from strongly silica-undersaturated magmas occasionally contain large amounts of kirschsteinite (Ki" CaFeSiO4) and monticellite (Mo: CaMgSiO4) components. The purpose of this note is to report the first natural occurrence of kirschsteinite crystals that have lamite (La: CazSiO4) in the mineralogical norm.
Petrographic relationships between mineral phases and bitumen in the Oklo Proterozoic natural fission reactors, Gabon
Authors: Parnell John
Published: December 2006

Several of the Proterozoic natural fission reactors at Oklo, Gabon contain abundant organic matter (bitumen), with which much of the reactor uranium is associated. An understanding of the petrography of the bitumen is important in assessing its role in element retention following fissiogenic reactions. The bitumen is replacive and includes vestiges of detrital grains and clays of the host sandstones. It also contains several generations of mineral phases related to the migration of uranium and daughter lead, and other elements mobilized by hydrothermal activity in the reactor zones. The minerals include (primary) uraninite precipitated after reduction of uranium by organic matter, silicates concentrated in radiation halos around the uraninite, and native lead, galena and further uraninite which migrated from the primary uraninite. The silicates are illitic clays in the immediate vicinity of the reactors, and chloritic more distant from the reactors. Authigenic clays in radiation halos are compositionally distinct from earlier host rock clays. Local migration of uranium and lead is evident as dispersion of the elements through the radiation halos; cross-cutting veinlets of uraninite, native lead and galena, including veinlets extending directly from the primary uraninite crystals; and concentrations of the elements at the margins of bitumen masses. The limit of observed uranium dispersion is within clay immediately beyond the bitumen margins.
Twinning in an orthorhombic aluminate sodalite, Ca8[Al12O24] (CrO4)2
Authors: Hassan Ishmael
Published: December 2006

Transmission electron microscopy (TEM) was used to study the aluminate sodalite, Ca8[Al12O24](CrO4)2. This aluminate sodalite has four polymorphs: one cubic, one modulated, one tetragonal, and an orthorhombic cell that arise from ordering of [Ca4·CrO4]6+ clusters that occur in the cages of the structure. The transition temperatures are 432, 453, and 610 K. The cell parameters for the orthorhombic phase, with the cubic cell parameter of a = b = c = 9.222 Å, are 3a × 2b × c. Transformation twins are formed at 432 K during the transition from the tetragonal to the orthorhombic phase. The twin plane is {110} in the cubic cell, and {320} in the orthorhombic cell.
An unusual ruby-sapphire-sapphirine-spinel assemblage from the Tertiary Barrington volcanic province, New South Wales, Australia
Authors: Lin Sutherland F. , Coenraads Robert R.
Published: December 2006

Ruby-sapphire-sapphirine-spinel forms small, corroded, crystalline aggregates in corundum bearing alluvials shed from the Tertiary Barrington basalt shield volcano. Sapphirine is near a 7:9:3 (MgO-Al2O3-SiO2) composition and, together with the corundum, shows reaction rims of pleonaste spinel. Spinel in the aggregates has a compositional range Sp 68–73 Hc 27–29 Cm 0–3. The aggregates give new insights into the ruby-sapphire source rocks. Potential origins include metamorphic recrystallization of aluminous material (below 1460°C) or high temperature-high pressure crystallization reactions related to lamprophyric or basaltic magmas (up to 1300°C and 20 kbar). Sapphirine-spinel thermometry suggests final crystallization temperatures for the aggregates around 780 to 940°C and reaction with host magmas at over 1000°C.

The Barrington gemfield includes two distinct corundum suites. One, typical in eastern Australia, is dominated by blue-green, well-crystallized, growth-zoned sapphire, commonly containing rutile silk and Ferich spinel inclusions (Hc 51–73, Mt 18–35, Mf 6–8, Usp 2–6). The other, an unusual suite, is dominated by ruby and pastel coloured sapphires, with little crystal shape or growth zonation and restricted mineral inclusions, mostly chromian pleonaste and pleonaste. The ruby-sapphire-sapphirine-spinel aggregates provoke new thoughts on the origin of rubies and sapphires and their indicator minerals in eastern Australian and southeastern Asian volcanic gemfields.
Phosphatian coffinite with rare earth elements and Ce-rich françoisite-(Nd) from sandstone beneath a natural fission reactor at Bangombé, Gabon
Authors: Janeczek Janusz , Ewing Rodney
Published: December 2006

Spontaneous fission reactions occurred in several uranium deposits in SE Gabon approximately two billion years ago. The reactor zones, between 10 to 50 cm thick, are found in Proterozoic sandstones and consist of high-grade uranium ore mantled by illite and/or chlorite (Gauthier-Lafaye et al., 1989). During a mineralogical study of sandstones (quartz arenites) underlying a natural fission reactor at Bangombé (20 km south of the Oklo uranium deposit), we have found several grains of a uranous silicate, coffinite, with unusually high concentrations of phosphorous and enriched in light rare earth elements (LREE).
Mineral chemistry and geochronology of the potassic alkaline ultramafic Inagli complex, Aldan Shield, eastern Siberia
Authors: Mues-Schumacher U. , Keller J. , Kononova V. A. , Suddaby P. J.
Published: December 2006

The Inagli complex, one of several Mesozoic intrusive complexes of the Aldan Shield (Siberian Platform), exhibits a concentric structure comprising several alkaline ultramafic rock-types. A central dunite body is surrounded by olivine- and phlogopite-clinopyroxenites forming an inner rim. The outer rim consists of different shonkinitic and malignitic rocks. The K-Ar ages obtained for the whole complex vary around 132 Ma.

The dunites and clinopyroxenites are characterized by cumulate textures. With increasing modal abundances of clinopyroxene and subordinate phlogopite, the rocks develop to olivine-clinopyroxenite, shonkinite, and malignite with intercumulus potassium feldspar. Mineralogical characterization of the rocks suggests they evolved by fractional crystallization. The highly forsteritic olivines (Fo up to 95) require a melt as magnesian as mg# 87.1, representing ±26 wt.% MgO. The parental melt is likely to be an olivine-, H2O- and K2O-rich picritic liquid of shoshonitic character. Major and trace element systematics show highLILE/LREEandLREE/HFSEratios indicating the involvement of a subduction zone component in the genesis of these rocks.
Solubility and spectrochemical characteristics of synthetic chernikovite and meta-ankoleite
Authors: Van Haverbeke Laurent , Vochten Renaud , Van Springel Karel
Published: December 2006

Chernikovite and meta-ankoleite were synthesized with a relatively high crystallinity and the compounds were identified by means of chemical analysis and X-ray diffraction. The infrared spectra were recorded and the bands assigned. From the luminescence spectra, the band-gap energy for both compounds was calculated as 2.35 eV, indicating that they must be considered as insulators. The dependence of the solubilities of these compounds on the acidity of the solution was studied, and the dominant ionic species were determined. The pKsp values of chernikovite and meta-ankoleite were found to be 22.73±0.24 and 24.30±0.81 respectively.
Wesselsite, SrCu[Si4O10], a further new gillespite-group mineral from the Kalahari Manganese Field, South Africa
Authors: Giester G. , Rieck B.
Published: December 2006

Wesselsite, SrCu[Si4O10], is a new mineral species from the Wessels mine, Kalahari Manganese Field, South Africa, and it belongs to the gillespite group. Wesselsite is tetragonal, space group P4/ncc; the unit cell parameters, refined from Gandolfi film data, are a = 7.366(1), c = 15.574(3) Å V = 845.01 Å3. The strongest lines are (dobs/lobs/hkl) (7.79/35/002), (4.33/20/112), (3.89/20/004), (3.44/40/104), (3.33/100/202), (3.12/55/114), (3.03/50/212), (2.68/25/204), (2.61/30/220) and (2.32/30/116). Wesselsite is associated with hennomartinite, embedded in a matrix of sugilite, xonotlite, quartz and pectolite. Microprobe analyses of 111 samples show that it is the end-member of a solid solution series with effenbergerite, BaCu[Si4O10], with substitutions of Sr by Ba up to 50 mol.%. Wesselsite forms tiny subhedral plates in sizes not exceeding 50 × 50 × 5 µm, arranged in clusters of up to 200 µm. It shows a perfect cleavage parallel to {001}, has blue colour, white to light blue streak, and is uniaxial negative with ω = 1.630(2), ε = 1.590(5), strongly pleochroic from blue (ω) to pale blue (ε). The calculated density is 3.32 g cm−3, the measured density is 3.2(1) g cm−3.
MgSiO3 perovskite: a HRTEM study
Authors: Hassan Ishmael , Kudoh Yasuhiro , Buseck Peter R. , Ito Eui
Published: December 2006

Selected-area electron diffraction patterns for the [110] zone of MgSiO3 perovskite are consistent with the orthorhombic unit cell obtained by X-ray diffraction (a = 4.775, b = 4.929, c = 6.897 Å). Various areas of a crystal fragment show diffuse streaking along c*, and well-developed satellite reflections that give a 3-fold repeat along [10]*. Another fragment shows doubled cell dimensions when viewed down [30]. The variable occurrence of the satellite reflectioncs and diffuse streaking indicate subtle variations in ordering, chemistry, or both. Images obtained by high-resolution transmission electron microscopy contain perfectly ordered regions, out-of-phase boundaries, and intergrowths of the two orthorhombic forms of perovskite.
Microwave techniques for the synthesis and deuteration of minerals, with particular reference to scorodite, FeAsO4.2H2O
Authors: Baghurst David R. , Barrett Jack , Coleyshaw Esther E. , Griffith William P. , Mingos D. Michael P.
Published: December 2006

Microwave dielectric heating methods for the preparation of a number of arsenate, phosphate, vanadate, molybdate and carbonate minerals and their deuterated analogues are reported; rapid and efficient syntheses of these have been achieved. The application of this to the study of vibrational spectroscopy of minerals is discussed, with particular reference to scorodite.
Cellular precipitates of iron oxide in olivine in a stratospheric interplanetary dust particle
Authors: Rietmeijer Frans J. M.
Published: December 2006

The petrology of a massive olivine-sulphide interplanetary dust particle shows melting of Fe,Ni-sulphide plus complete loss of sulphur and subsequent quenching to a mixture of iron-oxides and Fe,Ni-metal. Oxidation of the fayalite component in olivine produced maghemite discs and cellular intergrowths with olivine and rare andradite-rich garnet. Cellular reactions require no long-range solid-state diffusion and are kinetically favourable during pyrometamorphic oxidation. Local melting of the cellular intergrowths resulted in three dimensional symplectic textures. Dynamic pyrometamorphism of this asteroidal particle occurred at ∼1100°C during atmospheric entry flash (5–15 s) heating.
Iridescent anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland composition, exsolution, age
Authors: Rodgers K. A. , Kinny P. D. , McGregor V. R. , Clark G. R. , Henderson G. S.
Published: December 2006

Golden iridescent, <1–100 mm crystals of alternating lamellae of anthophyllite and gedrite constitute the bulk of orthoamphibolite pods within quartz-cordierite gneisses of the Akulleq terrane at Simiuttat, SW Greenland. X-ray powder diffraction powder gavea= 18.526(7),b= 17.979(15),c= 5.285(23) Å; a single crystal hasa= 18.546(7),b= 17.950(16),c= 5.280(1) Å, space groupPnmawith some reflections being notably broader than others. Spot EMPA yielded composite analyses: AlIV= 0.89–1.3, Mg/(Mg+Fe2+) = 0.57–0.61, Na/AlIV= 0.22–0.26. AFM imaging of {210} cleavage surfaces, showed a uniform corrugated morphology parallel to [001]; wavelength was 190–350 nm, mean 250 nm, amplitude 3 nm. A plan view resembles TEM images of (010)-parallel exsolution textures of orthoamphiboles. A second set of corrugations may crosscut the [001]-parallel ridges at 20–25°, akin to reported lamellar intergrowths developed parallel to both (010) and (120). Unequivocal evidence linking topography with lamellae is absent. In contrast to the conventional multi-layer reflector model, the ridged surface provides an additional origin for iridescence, acting as a diffraction grating. Included zircons, 50–10 μm, have Hf/Zr = 0.008–0.012, Hf+FeIIc. 0.16.207Pb/206Pb ages are from 2690 to 2770 Ma, averaging 2732±10 Ma. Coexisting, included Th-, La-, Ce-, Pr-, Nd-, Gd-, Y-monazites have207Pb/206Pb ages from 2680 to 2720 Ma, averaging 2707±12 Ma. The included crystals grew during a late Archaean metamorphism that produced overgrowths on zircons within gneisses to the north, but with Simiuttat grains showing a more complex history. The lamellae may have developed at the same time, or during a reheatingc. 2550 Ma, or in a subsequent Proterozoic metamorphism.
Application of MAS NMR spectroscopy to poorly crystalline minerals: viséite
Authors: Kim Yeongkyoo , James Kirkpatrick R.
Published: December 2006

Viséite is a poorly crystalline mineral which is difficult to study by X-ray diffraction pattern. NMR is a very useful technique to study such poorly crystalline minerals, and 31P, 27Al, and 29Si MAS NMR in conjunction with powder XRD results show that at least our Viséite sample is not a single phase with a structure analogous to that of analcime as previously reported. Rather, it is very disordered with a structure similar to that of crandallite and includes other phases including an undefined aluminophosphate, opal, and a framework aluminosilicate, probably a zeolite. The previously reported variations in the Si content of Viséite are probably due to variable amounts of opal and the framework aluminosilicate.
A neutron powder diffraction determination of the thermal expansion tensor of crocoite (PbCrO4) between 60 K and 290 K
Authors: Knight Kevin S.
Published: December 2006

The thermal expansion tensor of crocoite has been determined from high-resolution neutron time-of-flight powder diffraction data. The temperature dependence of the lattice constants between 4.5 K and 290 K have been fitted to a quasi-harmonic Einstein model, and the temperature dependence of the thermal expansion tensor has been calculated for 60 K ≤ T ≤ 290 K. The magnitudes of the principal expansivities and their orientation exhibit saturation behaviour for temperatures above 300 K. The predicted saturated expansion coefficients are α11= 33.1(1) × 10−6K−1, α22= 15.72(3) × 10−6K−1, α33= 3.36(1) × 10−6K−1, with α22parallel to b and α11lying at an angle of −37.86(5)° to c for theP21/nsetting of the crystal structure. The direction of maximum expansion is approximately parallel to bothand the least-squares line passing through the projection of the chromium atoms on (010). The direction of minimum expansion lies approximately parallel to [101]. No evidence was found for either a structural or magnetic phase transition between 4.5 K and 300 K.
The geometry and evolution of magma pathways through migmatites of the Halls Creek Orogen, Western Australia
Authors: Oliver N. H. S. , Barr T. D.
Published: December 2006

In the Halls Creek Orogen of north-western Australia, the distance of melt migration through migmatitic metasedimentary rocks and adjacent metabasites is partly constrained by relationships of leucosomes and small mafic magma veins to rock boundaries and structural elements. Stromatic leucosomes in metasediments are cut by a network of small extensional fractures and shear zones, oriented steeply during melt migration. These shear zones allowed cm- to 10 m-scale migration of felsic magma derived by in situ anatexis. In the adjacent metabasite layers, a similar shear array allowed injection of H2O-undersaturated mafic to ultramafic magma, locally dehydrating and chemically modifying these rocks. However, these mafic to ultramafic veinlets are too mafic to be explained by in situ anatexis, necessitating an external magma source. Also, the lack of felsic veinlets cutting metabasites, and mafic veinlets cutting metasediments, requires that vertical inter-connectivity of these fracture systems was restricted. We propose along-layer migration of mafic to ultramafic magma through the metabasite, assisted by horizontal connection of the shear zones. This migration occurred independantly of metre-scale felsic magma migration in the adjacent metasediments, even though these two deformation-assisted magma migration systems may have been operating at the same time.
Crustal anatexis and melt extraction during deformation in the restitic xenoliths at El Joyazo (SE Spain)
Authors: Cesare B. , Salvioli Mariani E. , Venturelli G.
Published: December 2006

The dacite of El Joyazo contains abundant metapelitic xenoliths. These can be divided into two main types: garnet-biotite-sillimanite and spinel-cordierite xenoliths. In the xenoliths the widespread occurrence of rhyolitic glass as interstitial films, foliation-parallel layers and primary melt inclusions in all mineral phases indicates that these assemblages developed in the presence of a melt phase, i.e. during anatexis. The composition of the interstitial glass is comparable to that of the melt inclusions, suggesting that melt was locally produced. Phase equilibria indicate that anatexis occurred at P-T conditions of 5–7 kbar and 850±50°C.

Several microstructural lines of evidence show that melt extraction was assisted by deformation during foliation development, and that on the scale of the xenoliths (up to 50 cm) melt escaped mainly by flow along foliation planes. The development of a syn-anatectic foliation also suggests that metapelitic rocks were involved in high-grade metamorphism and partial melting prior to fragmentation and dispersion in the host dacite.

Mass balance calculations, based on the chemical composition of interstitial glass and melt inclusions in minerals, the bulk xenoliths and representative samples of potential pelitic sources support a model wherein the xenoliths represent restites after the extraction of 30 to 55 wt.% melt from graphitic metapelite protoliths similar to the rocks constituting the surrounding Alpujarride metamorphic complex.
Interactions between deformation, magmatism and hydrothermal activity during active crustal thickening: a field example from Nanga Parbat, Pakistan Himalayas
Authors: Butler Robert W. H. , Harris Nigel B. W. , Whittington Alan G.
Published: December 2006

The Nanga Parbat massif is a rapidly eroding, thrust-related antiform that is distinct from other regions of the Himalayan orogen in being both intruded by Late Miocene-Pliocene anatectic granites and permeated by a vigorous hydrothermal system. Exhumation is achieved by erosion during thrusting along the Liachar thrust in the apparent absence of extensional tectonics. At depths in excess of 20 km, small batches of leucogranitic melt have been generated by fluid-absent breakdown of muscovite from metapelitic lithologies. These melts ascend several kilometres prior to emplacement, aided by low geothermal gradients at depth and by interaction with meteoric water as they reach shallow levels. At intermediate depths (∼15 km) limited fluid infiltration is restricted to shear zones resulting in localised anatexis. Within the upper 8 km of crust, magmatic and meteoric fluid fluxes are channelised by active structures providing a feedback mechanism for focusing deformation. Leucogranite sheets show a range of pre-full crystallization and high-temperature crystal-plastic textures indicative of strain localisation onto these sheets and away from the country rocks. At subsolidus temperatures meteoric fluids promote strain localisation and may trigger cataclastic deformation. Since near-surface geothermal gradients are unusually steep, the macroscopic transition between distributed shearing and substantial, but localised, cataclastic deformation occurred at amphibolite-facies conditions (∼600°C). Even with the greatest topographic relief in the world, the meteoric system of Nanga Parbat is effectively restricted to the upper 8 km of the crust, strongly controlled by active structures.
An SEM examination of the chalcopyrite disease texture and its genetic implications
Authors: Nagase Toshiro , Kojima Shoji
Published: December 2006

Back-scattered electron imaging with a scanning electron microscope was applied to the intimate association of fine chalcopyrite grains and sphalerite (‘chalcopyrite disease’) in synthesized products and natural specimens, in order to distinguish between diagnostic features of two formation mechanisms: replacement and coprecipitation. In the synthetic chalcopyrite disease in Fe-bearing sphalerite formed by a replacement reaction, chalcopyrite occurs as fine lamellae, which are also observed in relatively Fe-rich growth bands of the natural zoned sphalerite. Ellipsoidal to lens-like habits of chalcopyrite appear in sphalerite that has undergone extensive replacement reactions. These textures may have grown steadily from the lamellar chalcopyrite by consuming the FeS component dissolved in the sphalerite. All the sphalerite samples formed by the coprecipitation mechanism are Fe-poor, hosting triangular or irregularly bleb-like inclusions of chalcopyrite. This variety of chalcopyrite morphology could be attributed to diffusion rates and variations in fluid saturation, and their effect on the rate of crystal growth. Thus, in both replacement and coprecipitation the chalcopyrite habit depends strongly both on the FeS content of the host sphalerite and on kinetic factors, and is significant when interpreting chalcopyrite disease textures in natural samples.
Petrochemistry of a Late Precambrian garnetiferous granite, pegmatite and aplite, southern Israel
Authors: Bogoch R. , Bourne J. , Shirav M. , Harnois L.
Published: December 2006

Garnet is a widespread minor accessory mineral in the Late Proterozoic Elat-Quarry granite of southern Israel and is more abundant in the associated pegmatite and aplite. All garnets are dominated by almandine and spessartine end-members. Granite-hosted garnets are zoned with relative enrichment of Mn in the core and Fe in the rim. The chemistry of the garnet in the pegmatite and aplite are comparable to the rim compositions of garnets in the granite, but with a slight Fe-depletion at the rims. Geochemical parameters for the granite indicate fractional crystallization largely of an S-type source magma to a peraluminous composition.

In the highly evolved granite magma, Fe is relatively diminished, and only small amounts of biotite can crystallize. Manganese becomes a compatible element forming Mn-rich garnet (cores), and reducing the Mn content in the magma, subsequently leading to Fe-enriched rims. The greater abundance of garnet in the pegmatite and aplite (and its larger crystal-size in the former) relate to the enhanced presence of a hydrous fluid within the magma. The tendency for garnet crystals to concentrate in bands is much more developed in the pegmatite than in the granite, and is associated with the effects of hydrofracturing (fracture-filling), and the crystallization of coarse-grained alkaline feldspars.
Closed system fractionation in a large magma chamber: mineral compositions of the websterite layer and lower mafic succession of the Great Dyke, Zimbabwe
Authors: Wilson A. H. , Chaumba J. B.
Published: December 2006

The Lower Mafic Succession of the Great Dyke is a 700 m thick sequence of gabbroic rocks which shows remarkably regular mineral compositional trends and trace element contents in whole rocks. Such chemical trends are strongly indicative of undisturbed fractionation having taken place within the magma chamber and contrast with the major development of cyclic units which characterize the underlying Ultramafic Sequence of the Great Dyke. The style of fractionation is quite different to that in the equivalent Main Zone of the Bushveld Complex with the latter possibly reflecting a ‘leaky’ input system, whereas in the Great Dyke the magma chamber was sealed. Major compositional reversals at the interface between the websterite layer (the topmost unit of the Ultramafic Sequence) and the base of the Lower Mafic Succession indicate a change in crystallization conditions at this level. Modal percentages of plagioclase and Al2O3 content of pyroxenes show the same trends indicating a strong control by temperature and magma composition.

Modelling of the fractionation processes and the influence of trapped liquid was carried out for Mg#, Cr2O3, and NiO in pyroxenes and for Zr in whole rock. The lowermost gabbroic rocks are adcumulates with effectively zero trapped liquid which contrasts with 10–15% trapped liquid in the underlying websterite There is a gradual rise in the amount of trapped liquid upwards in the Lower Mafic Succession. These results have implications for the mechanisms by which porosity is reduced in mafic cumulates. An injection of a small amount (10%) of new magma at the interface of the Ultramafic-Mafic Sequences of the Great Dyke was of a composition slightly different to that which gave rise to the cyclic units of the Ultramafic Sequence.
Graphite-bearing peraluminous dacites from the Erlend volcanic complex, Faeroe-Shetland Basin, North Atlantic
Authors: Kanaris-Sotiriou Raymond
Published: December 2006

Strongly peraluminous, cordierite-bearing anatectic dacites from the offshore Tertiary Erlend volcanic centre, north of the Shetland Isles, are shown to contain graphite which is interpreted as being essentially a restite phase inherited from carbonaceous pelitic source rocks. The form and characteristics of the graphite are documented and graphite geothermometry applied to establish that the graphite records a minimum peak temperature of ∼800°C, confirming that temperatures at which anatexis occurs were attained. The different morphological forms of graphite observed suggest the possibility that minor amounts of fluid-deposited graphite may also be present. The chemistry of the Erlend dacites is compared with that of other known examples of graphite-bearing peraluminous silicic igneous rocks and briefly with experimentally generated peraluminous liquid compositions. The Erlend source rocks were probably subjected to a higher degree of partial melting than has occurred in the petrogenesis of many other anatectic peraluminous silicic rocks.
Rare earth chemistry of perovskite group minerals from the Gardiner Complex, East Greenland
Authors: Campbell Linda S. , Henderson Paul , Wall Frances , Nielsen Troels F. D.
Published: December 2006

Perovskite group minerals, general formulaABX3, from the intrusive ultramafic alkaline Gardiner Complex, East Greenland, range from almost pure CaTiO3(perovskite,sensu stricto), to the rare earth element (REE) variety, loparite-(Ce). Chemical zonation in the perovskites (sensu lato), is described by the substitutions 2Ca2+= (Na++REE3+) on theA-site and 2Ti4+= (Fe3++ Nb5+) on theB-site. Other trace elements detected include Th, Sr, Al, Si, Zr, Ta and Sn. Excellent agreement was found between the determinations of theREEby electron microprobe and neutron activation analysis. Chondrite-normalizedREEpatterns display enrichment in the light rare earths for perovskite, loparite, apatite, melilite and diopside. Mean perovskite/apatite partition coefficients from four of the Gardiner rocks were calculated as La = 10.4, Ce = 13.8, Nd = 13.9, Sm = 9.9, Eu = 7.7, Gd = 5.2, Tb = 5.6, Tm = 5.5, Yb = 2.7 and Lu = 1.6, indicating that perovskite concentrates allREEto a much greater extent than apatite. Light-REEenrichment occurs in both perovskite and apatite.
Synchronous intracrystalline δ13C and δ18O differences in natural calcite crystals
Authors: Dickson J. A. D.
Published: December 2006

New intersectorial isotope data are presented for two calcites. Mendip calcite shows no detectable δ13C and δ18O differences between synchronous {214} and {014} sectors. Nottingham calcite shows a δ13C difference of 1.0‰ and a δ18O difference of 0.5‰ between synchronous {401} and {0001} sectors. Data now available for 5 different calcites show the magnitude of intersectorial fractionation is variable; the effect on δ13C is twice that on δ18O. All five natural calcites also show erratic isotopic differences between symmetrically-equivalent synchronous sectors. Intersectorial isotopic fractionation is probably widespread but its cause and quantification require further work. Synchronous intracrystalline isotopic differences should be accommodated in the interpretation of isotopic data and should influence future sampling strategy.
REE-bearing minerals in the albitites of central Sardinia, Italy
Authors: Carcangiu G. , Palomba M. , Tamanini M.
Published: December 2006

Recent studies on albitite rocks located in the granodiorite complex of Central Sardinia have revealed that epidote has a widespread occurrence as a light rare-earth element (LREE)-bearing accessory common phase. Titanite has been recorded as a heavy rare earth element (HREE)-bearing mineral. The Hercynian granodiorite complex of Central Sardinia is composed chiefly of quartz, Ca-plagioclase, K-feldspar and biotite and of a wide variety of secondary assemblages, mainly allanite, titanite and zircon. Albitic plagioclase and quartz are the main mineral components of the albitites. Additional minerals include, besides allanite and epidote, a more calcic-plagioclase (oligoclase), K-feldspar, chlorite, titanite and more rarely muscovite. The mineral assemblages and REE-bearing minerals of albitites were analysed by wavelength dispersive spectrometry (WDS). Chemical data suggest that there is a near complete solid-solution between epidote and allanite whereas little variations in HREE of titanites were detected. In epidote-group minerals a pronounced zoning in REE was observed while titanite was recorded unzoned. Textural relations were studied by SEM to distinguish primary from secondary epidotes. Chemical criteria to recognize magmatic from alteration epidotes were also applied. The alteration epidotes mainly occur and generally originate from plagioclase alteration and from leaching of magmatic allanite. Comparison of textures using both the SEM technique and EPMA data showed that the characteristic ‘patchy zoning’, observed in epidotes, corresponds with different amounts of REE in these minerals.

The schematic model proposed for the epidote-forming reactions during the metasomatic processes that affected the granodiorites involves: (i) the instability of the anorthitic component of plagioclase; (ii) the simultaneous formation of albite; (iii) the leaching of the magmatic allanite with a redistribution of REE in the epidotes of the albitites.
Nomenclature of Amphiboles; Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names
Authors: Leake Bernard E. , Woolley Alan R. , Arps C. E. S. , Birch W. D. , Gilbert M. C. , Grice J. D. , Hawthorne F. C. , Kato A. , Kisch H. J. , Krivovichev V. G. , Linthout K. , Laird J. , Mandarino J. , Maresch W. V. , Nickel E. H. , Rock N. M. S. , Schumacher J. C. , Smith D. C. , Stephenson N. C. N. , Ungaretti L. , Whittaker E. J. W. , Youzhi G.
Published: December 2006

The International Mineralogical Association's approved amphibole nomenclature has been revised in order to simplify it, make it more consistent with divisions generally at 50%, define prefixes and modifiers more precisely and include new amphibole species discovered and named since 1978, when the previous scheme was approved. The same reference axes form the basis of the new scheme and most names are little changed but compound species names like tremolitic hornblende (now magnesiohornblende) are abolished and also crossite (now glaucophane or ferroglaucophane or magnesioriebeckite or riebeckite), tirodite (now manganocummingtonite) and dannemorite (now manganogrunerite). The 50% rule has been broken only to retain tremolite and actinolite as in the 1978 scheme so the sodic calcic amphibole range has therefore been expanded. Alkali amphiboles are now sodic amphiboles. The use of hyphens is defined. New amphibole names approved since 1978 include nyböite, leakeite, kornite, ungarettiite, sadanagaite and cannilloite. All abandoned names are listed. The formulae and source of the amphibole end member names are listed and procedures outlined to calculate Fe3+and Fe2+when not determined by analysis.
Dawson's Oldoinyo Lengai calciocarbonatite: a magmatic sövite or an extremely altered natrocarbonatite?
Authors: Gittins J. , Harmer R. E.
Published: December 2006

In 1962 Dawson described a calcite carbonatite (specimen BD83) from the Tanzanian volcano Oldoinyo Lengai as a sövite, thus implying that at an earlier stage in its evolution this volcano had crystallized magmatic calciocarbonatites as well as the highly alkalic natrocarbonatite lava that has been erupted in more recent times. This proposition is difficult to reconcile with the currently fashionable hypothesis whereby the natrocarbonatite lava separated immiscibly from a type of nephelinite magma, most recently thought to be a wollastonite nephelinite. In 1993 Dawson sought to discredit the magmatic origin of this sövite specimen by arguing that it was derived from natrocarbonatite lava through extreme alteration (calcitization) in which process the original nyerereite was replaced by calcite in near-perfect pseudomorphs. We suggest that the arguments advanced in support of this concept are unconvincing and that the specimen is exactly what it was originally described as, namely a magmatic sövite in which the calcite crystallized from a magma rather than having replaced nyerereite. We do not seek to discredit the liquid immiscibility hypothesis but do believe that whatever process is responsible for the Oldoinyo Lengai natrocarbonatites and silicate rocks must also allow for the crystallization of calciocarbonatite.
C2/c pyroxene from two alkaline sodic suites (Western Ross Embayment – Antarctica): crystal chemical characterization and its petrologic significance
Authors: Salviulo Gabriella , Secco Luciano , Antonini Paolo , Piccirillo Enzo Michele
Published: December 2006

Two C2/c pyroxene suites from sodic alkaline rocks (Basanite-Phonolite: B-Ph and Alkali basalt-Trachyphonolite: AB-T) belonging to the McMurdo Volcanic Group (Mt. Melbourne province and Mt. Erebus, Antarctica) were investigated by single-crystal X-ray diffraction combined with electron probe microanalysis which together provide accurate site occupancy and site configuration parameters. Variations in site volumes distinguish the clinopyroxenes belonging to the more alkaline B-Ph suite from those of the AB-T suite. The former have higher VM2 and, for similar cell volume, lower VM1 and higher VT. In these C2/c pyroxenes, the bond lengths of M1 depend on R3+ content, necessary to balance AlIV in the T site. M1 geometric variations are similar for both B-Ph and AB-T suites. However, the M2 site is crucial for variations in polyhedral configurations. The increase in AlIV affects the shortest M2-O bond lengths in different ways depending on (Ca+Na) contents in the M2 site. Thus, the clinopyroxenes were distinguished in two different groups not related to the two suites. The first group is characterized by (Ca+Na) higher than 0.90 atoms per formula unit but shows a good positive correlation between the shortest M2-O bond lengths and AlIV content, at quite constant (Ca+Na). The second group has (Ca+Na) less than 0.90 atoms per formula unit but shows a poor correlation between the shortest M2-O bond lengths and AlIV content. In general, shortening of the longest M2-O bond lengths is associated with increase in AlIV. The cell and M1 volumes suggest that the clinopyroxenes, including the larger and sometimes resorbed macrocrysts, crystallized at a pressure lower than 5 kbar, fitting the petrography and evolved character of the rocks in question.