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This work has been supported by the Marsden Fund grant VUW0813 (Royal Society of New Zealand to C.J.N.W.), a James Cook Fellowship (Royal Society of New Zealand) to C.J.N.W., and the ECLIPSE Programme, funded by the N.Z. Ministry of Business, Innovation and Employment. G.F.C. is supported by a NERC Standard Grant (NE/T000317/1), M.L.M. is supported by an NSF CAREER grant (EAR 2042662) and S.J.B. acknowledges Marsden Fund grant VUW1627.

The chemical and isotopic compositions of volcanic arc lavas often show evidence for involvement of a sedimentary component during magma genesis. Determining where this sedimentary component is added to arc magmas is of vital importance for constraining the extent to which sediments and volatiles are recycled at subduction zones. Lavas from Martinique in the Lesser Antilles arc have wide ranging isotopic compositions extending to highly radiogenic values (e.g. 87/Sr/86Sr up to ∼0.710) that could, in principle, be explained by sediment addition to the mantle source or by crustal assimilation in the upper plate. We use Sr isotopic compositions of plagioclase from Martinique plutonic xenoliths to provide evidence supporting the crustal assimilation hypothesis. Plagioclase from plutonic xenoliths formed in the mid-crust (∼12 km) show a restricted range of unradiogenic Sr isotope ratios (87Sr/86Sr = 0.7041–0.7042) whereas plagioclase from upper crustal plutonic xenoliths (∼6 km) show greater intra-sample variation and more radiogenic Sr isotopic compositions up to 87Sr/86Sr = 0.7047. This trend is also observed in plutonic xenolith whole rock 87Sr/86Sr. Combined, these results indicate that the range of Sr isotope compositions becomes larger and more radiogenic in Martinique magmas as a result of sediment assimilation at shallow crustal levels. This is supported by Assimilation-Fractional Crystallization modeling, which shows that assimilation of chemically and isotopically heterogenous crustal sediments can produce the isotopic variation in Martinique plutonic xenoliths and lavas. Our results highlight the importance of constraining crustal contributions from the upper plate before using arc lava geochemistry to quantify sediment and volatile recycling at subduction zones and assessing potential heterogeneity of arc mantle sources.

We present a high‐resolution 2‐D P‐wave velocity model from a 225‐km‐long active seismic profile, collected over ~60–75 Ma central Atlantic crust. The profile crosses five ridge segments separated by a transform and three nontransform offsets. All ridge discontinuities share similar primary characteristics, independent of the offset. We identify two types of crustal segment. The first displays a classic two‐layer velocity structure with a high gradient Layer 2 (~0.9 s$^{−1}$) above a lower gradient Layer 3 (0.2 s$^{−1}$). Here, PmP coincides with the 7.5 km s$^{−1}$ contour, and velocity increases to >7.8 km s$^{−1}$ within 1 km below. We interpret these segments as magmatically robust, with PmP representing a petrological boundary between crust and mantle. The second has a reduced contrast in velocity gradient between the upper and lower crust and PmP shallower than the 7.5 km s$^{−1}$ contour. We interpret these segments as tectonically dominated, with PmP representing a serpentinized (alteration) front. While velocity‐depth profiles fit within previous envelopes for slow‐spreading crust, our results suggest that such generalizations give a misleading impression of uniformity. We estimate that the two crustal styles are present in equal proportions on the floor of the Atlantic. Within two tectonically dominated segments, we make the first wide‐angle seismic identifications of buried oceanic core complexes in mature (>20 Ma) Atlantic Ocean crust. They have a ~20‐km‐wide “domal” morphology with shallow basement and increased upper crustal velocities. We interpret their midcrustal seismic velocity inversions as alteration and rock‐type assemblage contrasts across crustal‐scale detachment faults.

We have used multiple-regression methods to calibrate new, pressure-independent empirical chemometric equations to calculate the major element composition of basanitic to rhyolitic melts in equilibrium with calcic amphibole. The equations are based on amphibole stoichiometric formula components ± temperature from published experimental P-T-X data and avoid some problems of previous studies associated with uncertainties in pressure determination. Compared with the pressure-dependent equations of Ridolfi and Renzulli (2012), tests run using an independent data set indicate that the new equations yield improved precision and accuracy, in particular for SiO2, TiO2, CaO, and K2O. The results are only marginally more precise when temperature is used as a dependent variable, demonstrating that temperature has a relatively minor role in controlling amphibole crystal chemistry compared with melt composition. This allows us to accept a small decrease in precision in excluding temperature from the analysis, which is very convenient for application of the equations to natural amphiboles where temperature is typically unknown. Using the new chemometric equations, reconstructed melt compositions in equilibrium with the rims of amphiboles in pumice clasts of the Ongatiti ignimbrite are in good agreement with coexisting matrix glass compositions, lending support for our analysis. The compositionally variable cores of the amphiboles give predicted melt compositions with large compositional variations from andesitic (63 wt% SiO2) to high-Si rhyolite. These compositional variations in the predicted melt compositions suggest that there may be a range of heterogeneous melts undergoing progressive differentiation within a major crustal magma storage region underneath the volcano. The results support the existence of genuine intermediate composition melts within the storage region. Interaction between these stored melts, disaggregating mush fragments and replenishing magmas gives rise to the chemical complexity observed in erupted magmas. We also used our multiple regression model to predict the compositions of melts that were in equilibrium with amphiboles in plutonic nodules from Grenada lavas. The predicted melts cover a wide range of compositions, perhaps as a result of in situ fractionation, but are consistent with melt inclusions hosted in those cumulates, as reported by Stamper et al. (2014). Overall, our new pressure- and temperature-independent equations resolve issues associated with previous pressure-dependent studies and represent a useful tool for further investigation of crustal processes at subduction zones.

Numerous studies have provided insights into one of the key problems of the Earth Sciences: subduction zone initiation (SZI). The insights into SZI are both numerous and diverse with evidence from multiple disciplines in Earth Sciences. SZI studies exploit the geological record, reconstruct regional or global plate motion back in time, interpret seismic tomography to identify the tip depth of sunken plate portions, and diagnose theoretical and numerical models of rock and plate deformation based on known physics.Getting and keeping an overview over the many discipline-specific advances is challenging for many reasons: one being the dispersed sources of information, another being the missing communication across the individual disciplines. The latter shortcoming also arises from the multiple incompatible scientific jargons currently in use.The SZI database now unifies the scientific jargon, and brings together old and new insights relating to SZI into a common, community-wide platform online (www.SZIdatabase.org). The SZI database builds bridges between individual communities, opening a community-wide discussion by making SZI data readily available and understandable. This keeps data and knowledge up-to-date, and can therefore provide the most complete picture of our current understanding of SZI.In this presentation, we outline where to find, how to use, and why to contribute to the SZI database. This community-wide project has already yielded interesting results regarding the fascinating question about how and where SZI occurs on present-day Earth and back to around 100 Ma. Work thus far suggests ‘subduction breeds subduction’, highlighting the beginning of crucial insights from these ongoing cross-disciplinary efforts.

Oceanic lithosphere carries volatiles, notably water, into the mantle through subduction at convergent plate boundaries. This subducted water exercises control on the production of magma, earthquakes, formation of continental crust and mineral resources. Identifying different potential fluid sources (sediments, crust and mantle lithosphere) and tracing fluids from their release to the surface has proved challenging

Quantifying the storage conditions and evolution of different magmatic components within sub-volcanic plumbing systems is key to our understanding of igneous processes and products. Whereas erupted magmas represent a portion of the eruptible volcanic system, plutonic xenoliths provide a complementary record of the mushy roots of the plumbing system that cannot be mobilised easily to form lavas and consequently offer a unique record of magma diversity within the sub-volcanic plumbing system. Here, we present a detailed petrological and geochemical study of erupted plutonic xenoliths from the island of Sint Eustatius (Statia), in the northern Lesser Antilles volcanic arc. The plutonic xenoliths are predominantly gabbroic, but vary in texture, mineral assemblage and crystallisation sequence. We report major, trace and volatile (H2O and CO2) concentrations of xenolith-hosted melt inclusions (MIs) and interstitial glass. The MIs have a very large range in major element (49–78 wt% SiO2 and 0.1–6.1 wt% MgO) and trace element concentration (72–377 ppm Sr, 32–686 ppm Ba, 39–211 ppm Zr). Their chemistry varies systematically with host phase and sample type. Significantly, it shows that (1) plutonic xenoliths record a complete differentiation sequence from basalt to rhyolite (2) apatite, but not zircon, saturation was reached during crystallisation, (3) amphibole breakdown reactions play a role in the genesis of shallow gabbronorite assemblages, and (4) mixing between crystal cargos and multiple discrete bodies occurred. Residual melt volatile contents are high (≤ 9.1 wt% H2O and ≤ 1350 ppm CO2), returning volatile saturation pressures of 0–426 MPa. Multiple reaction geobarometry and experimental comparisons indicate that equilibration took place in the upper-middle crust (0–15 km). We infer that the Statia plutonic xenoliths represent portions of a large heterogeneous crystal mush within which a great diversity of melts was stored and mixed prior to eruption. Our data show that compositional variations in magmatic plumbing systems exceed those observed in volcanic products, a likely consequence of the blending that occurs prior to and during eruption. Electronic supplementary material The online version of this article (10.1007/s00410-019-1576-4) contains supplementary material, which is available to authorized users.

In this Article, authors Michael J. Kendall and David Schlaphorst of the VoiLA consortium were incorrectly listed as being at the Department of Earth Sciences, Durham University, Durham, UK (affiliation 2), instead of at the School of Earth Sciences, University of Bristol, Bristol, UK (affiliation 1). This error has been corrected online.

Volcanism is the surface expression of magma intrusion, crystallization, assimilation and hybridization processes operating throughout the crust over a range of time periods. Many magmas, including those erupted at subduction zones, have complex textures that reflect these processes. Here, we use textural and geochemical characteristics of calcic amphiboles to help identify multiple ingredients of subduction zone magmatism at Mt Lamington volcano, Papua New Guinea. Our approach uses existing trace element partitioning schemes to calculate the compositions of amphibole equilibrium melts (AEMs). The AEM compositions show that Mt Lamington andesites and plutonic enclaves are dominated by fractionation of amphibole + plagioclase + biotite, with assimilation of plagioclase and zircon. Magnesiohastingsite crystals in the andesite and diktytaxitic mafic enclaves reflect multiple episodes of recharge by more primitive, geochemically variable melts. The andesite also contains clots with rounded grains and melt on grain boundaries. These features indicate slow crystallization, and the retention of melt films could significantly enhance the potential for remobilization of crystals by infiltrating melts or during magma mixing. Variations in crystallization conditions could thus significantly affect the mush microstructure. We suggest that this could result in a significant bias of the volcanic record towards the preferential incorporation of more slowly cooled plutonic material from the lower crust or from more thermally mature plumbing systems. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

Volcanoes at subduction zones reside above complex magma plumbing systems, where individual magmatic components may originate and interact at a range of pressures. Because whole-rock compositions of subduction zone magmas are the integrated result of processes operating throughout the entire plumbing system, processes such as mixing, homogenisation and magma assembly during shallow storage can overprint the chemical signatures of deeper crustal processes. Whereas melt inclusions provide an effective way to study the uppermost 10–15 km of the plumbing system, challenges remain in understanding magma intrusion, fractionation and hybridisation processes in the middle to lower crust (15–30 km depth), which commonly involves amphibole crystallisation. Here, we present new insights into the mid-crustal plumbing system at Mount St. Helens, USA, using multiple regression methods to calculate trace element partition coefficients for amphibole phenocrysts, and thus infer the trace element compositions of their equilibrium melts. The results indicate vertically distributed crystal fractionation, dominated by amphibole at higher pressures and in intermediate melts, and by plagioclase at lower pressures. Variations in Nb, Zr and REE concentrations at intermediate SiO2 contents suggest repeated scavenging of partially remelted intrusive material in the mid-crust, and mixing with material from geochemically diverse sources. Amphibole is an effective probe for deep crustal magmatism worldwide, and this approach offers a new tool to explore the structure and chemistry of arc magmas, including those forming plutonic or cumulate materials that offer no other constraints on melt composition.

The Ongatiti ignimbrite (> ~ 500 km3 DRE) was erupted at 1.21 ± 0.04 Ma from the Mangakino volcanic centre (Taupo Volcanic Zone, New Zealand). The ignimbrite is crystal rich (20–30%), of rhyodacite to low-silica rhyolite composition and lacks any consistent compositional zonation. Pumice whole-rock and glass compositions and crystal rim chemistries imply that the final erupted magma body was, to a first order, homogeneous, with the only variations reflecting crystal:glass proportions in analysed clasts. Crystals from pumices can be divided into two populations based on textural and chemical signatures: those that are inferred to have grown within the final erupted magma body (82% of plagioclase, 88% of orthopyroxene, 17% of amphibole), and those that originated in a chemically heterogeneous mush zone (18% of plagioclase, 12% of orthopyroxene, 83% of amphibole). Crystal-rich microcrystalline clasts, and clots within pumices, provide direct samples of parts of this heterogeneous source region. Amphibole model temperatures and pressures, coupled with in-situ trace element concentrations suggest that the mush region extended to ~ 15 km depth, near the base of the quartzofeldspathic crust and was rich in amphibole. Amphibole plus subordinate plagioclase and orthopyroxene, as well as antecrystic zircon were extracted from the crystal mush and ascended to a final storage region. Model temperatures and pressures from amphibole rims and Fe–Ti oxide model temperatures imply that the final erupted magma body was stored between 770 and 840 °C at 4–6 km depths. Homogenisation of the magma body occurred through convective stirring accompanying gradually rising temperatures induced by less-evolved magma(s) emplaced at deeper levels. Plagioclase records a steady core-to-rim increase in An content, implying that a gradual heating and/or increase in H2O in the final erupted magma body occurred over some significant period prior to the eruption. No signals of a rapid defrosting or rejuvenation event that could be considered as an eruption trigger are recorded by the crystal phases. The Ongatiti ignimbrite has features both common to, and distinct from crystal rich ‘monotonous intermediates’ and crystal-poor compositionally zoned rhyolites. As such, the Ongatiti ignimbrite demonstrates that ‘monotonous rhyolites’ can also be developed on a large scale.

The Lesser Antilles Volcanic Arc is remarkable for the abundance and variety of erupted plutonic xenoliths. These samples provide a window into the deeper crust and record a more protracted crystallisation history than is observed from lavas alone. We present a detailed petrological and in situ geochemical study of xenoliths from Martinique in order to establish their petrogenesis, pre-eruptive storage conditions and their contribution to construction of the sub-volcanic arc crust. The lavas from Martinique are controlled by crystal–liquid differentiation. Amphibole is rarely present in the erupted lavas, but it is a very common component in plutonic xenoliths, allowing us to directly test the involvement of amphibole in the petrogenesis of arc magmas. The plutonic xenoliths provide both textural and geochemical evidence of open system processes and crystal ‘cargos’. All xenoliths are plagioclase-bearing, with variable proportions of olivine, spinel, clinopyroxene, orthopyroxene and amphibole, commonly with interstitial melt. In Martinique, the sequence of crystallisation varies in sample type and differs from other islands of the Lesser Antilles arc. The compositional offset between plagioclase (~An90) and olivine (~Fo75), suggests crystallisation under high water contents and low pressures from an already fractionated liquid. Texturally, amphibole is either equant (crystallising early in the sequence) or interstitial (crystallising late). Interstitial amphibole is enriched in Ba and LREE compared with early crystallised amphibole and does not follow typical fractionation trends. Modelling of melt compositions indicates that a water-rich, plagioclase-undersaturated reactive melt or fluid percolated through a crystal mush, accompanied by the breakdown of clinopyroxene, and the crystallisation of amphibole. Geothermobarometry estimates and comparisons with experimental studies imply the majority of xenoliths formed in the mid-crust. Martinique cumulate xenoliths are inferred to represent crystal mushes within an open system, through which melt can both percolate and be generated. Electronic supplementary material The online version of this article (doi:10.1007/s00410-016-1299-8) contains supplementary material, which is available to authorized users.

The Kidnappers [∼1200 km 3 dense rock equivalent (DRE)] and Rocky Hill (∼200 km 3 DRE) caldera-forming events in the Taupo Volcanic Zone, New Zealand, were erupted in close succession from the Mangakino volcanic centre. They have identical radiometric ages at ∼1 Ma, yet erosion along the contact between the two deposits suggests that some years to decades separated the two eruptions. Field constraints and the similarities of crystal textures and compositions and glass chemistries of both eruption deposits demonstrate that they came from one overall magmatic system with a common crystal mush source. However, second-order variations in these parameters confirm that the Kidnappers and Rocky Hill deposits represent distinct events and are not the products of a single zoned magma chamber. The systematically zoned Kidnappers fall deposits provide evidence for the tapping of three discrete magma bodies, whereas the succeeding Kidnappers ignimbrite is compositionally more diverse. The transition from fall to flow deposition marks a change in the style of caldera collapse and the simultaneous evacuation of discrete but compositionally diverse melts, each of which underwent a distinct evolution and was held at slightly different P–T conditions prior to eruption. Contrasting plagioclase and orthopyroxene zonation patterns are present in pumices originating from three discrete magma bodies. Less evolved mafic melts interacted with the system, which mobilized portions of the final erupted melt through heating and volatile or chemical exchange in the mush. The two largest Kidnappers melt-dominant bodies were re-tapped in modified form, or re-established from their common mush source, prior to the Rocky Hill event. Rocky Hill pumices contain common, fluid-affected antecrystic crystal clots derived from chamber wall material. Amphibole compositions from each eruption reflect melt evolution processes and, in particular, the contemporaneous crystallization of biotite and breakdown of orthopyroxene. Plagioclase and orthopyroxene from Rocky Hill pumices share common zonation patterns with those from the two largest magma bodies in the Kidnappers. The rapid production of new melt-dominant bodies and the triggering of the Rocky Hill eruption reflect the ability of the magmatic system to rejuvenate on a geologically short timescale. The Mangakino centre did not follow a typical cycle of decreased activity after the supervolcanic Kidnappers event, instead producing a second caldera-forming eruption, within years to decades from the same system.

The 1.0 Ma Kidnappers supereruption (~ 1200 km3 DRE) from Mangakino volcanic centre, Taupo Volcanic Zone, New Zealand, produced a large phreatomagmatic fall deposit followed by an exceptionally widespread ignimbrite. Detailed sampling and analysis of glass shards and mineral phases have been undertaken through a proximal 4.0 m section of the fall deposit, representing the first two-thirds of erupted extra-caldera material. Major and trace element chemistries of glass shards define three distinct populations (types A, B and C), which systematically change in proportion through the fall deposit and are inferred to represent three magma types. Type B glass and biotite first appear at the same level (~ 0.95 m above base) in the fall deposit suggesting later tapping of a biotite-bearing magma. Plagioclase and Fe–Ti oxide compositions show bimodal distributions, which are linked to types A and B glass compositions. Temperature and pressure (T–P) estimates from hornblende and Fe–Ti oxide equilibria from each magma type are similar and therefore the three magma bodies were adjacent, not vertically stacked, in the crust. Most hornblende model T–P estimates range from 770 to 840 °C and 90 to 170 MPa corresponding to storage depths of ~ 4.0–6.5 km. Hornblende model T–P estimates coupled with in situ trace element fingerprinting imply that the magma bodies were individually well mixed, and not stratified. Compositional gaps between the three glass compositional types imply that no mixing between these magmas occurred. We interpret these data, coupled with the systematic changes in shard compositional proportions through the fall deposit, to reflect that three independent melt-dominant bodies of magma contributed large (A, ~ 270 km3), medium (B, ~ 90 km3) and small (C, ~ 40 km3) volumes (as reflected in the fall deposits) and were systematically tapped during the eruption. We propose that the systematic evacuation of the three independent magma bodies implies that there was tectonic triggering and linkage of eruptions. Our results show that supereruptions can be generated by near simultaneous multiple eruptions from independent magma chambers rather than the evacuation of a large single unitary magma chamber.

Mangakino, the oldest rhyolitic caldera centre delineated in the Taupo Volcanic Zone of New Zealand, generated two very large (super-sized) ignimbrite eruptions, the 1.21 ± 0.04 Ma >500 km3 Ongatiti and ~1.0 Ma ~1,200 km3 Kidnappers events, the latter of which was followed after a short period of erosion by the ~200 km3 Rocky Hill eruption. We present U/Pb ages and trace-element analyses on zircons from pumice clasts from these three eruptions by Secondary Ion Mass Spectrometry (SIMS) using SHRIMP-RG instruments to illustrate the evolution of the respective magmatic systems. U–Pb age spectra from the Ongatiti imply growth of the magmatic system over ~250 kyr, with a peak of crystallisation around 1.32 Ma, ~100 kyr prior to eruption. The zircons are inferred to have then remained stable in a mush with little crystallisation and/or dissolution before later rejuvenation of the system at the lead-in to eruption. The paired Kidnappers and Rocky Hill eruptions have U–Pb zircon ages and geochemical signatures that suggest they were products of a common system grown over ~200 kyr. The Kidnappers and Rocky Hill samples show similar weakly bimodal age spectra, with peaks at 1.1 and 1.0 Ma, suggesting that an inherited antecrystic population was augmented by crystals grown at ages within uncertainty of the eruption age. In the Kidnappers, this younger age peak is dominantly seen in needle-shaped low U grains with aspect ratios of up to 18. In all three deposits, zircon cores show larger ranges and higher absolute concentrations of trace elements than zircon rims, consistent with zircon crystallisation from evolving melts undergoing crystal fractionation involving plagioclase and amphibole. Abundances and ratios of many trace elements frequently show variations between different sectors within single grains, even where there is no visible sector zoning in cathodoluminescence (CL) imaging. Substitution mechanisms, as reflected in the molar (Sc + Y + REE3+)/P ratio, differ in the same growth zone between the sides (along a-axis and b-axis: values approaching 1.0) and tips (c-axis: values between 1.5 and 5.0) of single crystals. These observations have implications for the use of zircons for tracking magmatic processes, particularly in techniques where CL zonation within crystals is not assessed and small analytical spot sizes cannot be achieved. These observations also limit applicability of the widely used Ti-in-zircon thermometer. The age spectra for the Ongatiti and Kidnappers/Rocky Hill samples indicate that both magmatic systems were newly built in the time-breaks after respective previous large eruptions from Mangakino. Trace element variations defining three-component mixing suggest that zircons, sourced from multiple melts, contributed to the population in each system.

Presented here are preliminary results on a resonant gyroscope that is very simple to fabricate. It is made using both silicon and glass substrates, and involves the minimum of mask steps. Actuation and detection are all achieved via capacitive means. The minimum rotation rate that has been able to be sensed is 300 degrees/s; improvements in the manufacturing process could reduce this to as low as 0.07 degrees/s before the rate detection would become limited by electrical noise.

The behaviour of microengineered devices is routinely modelled using finite element analysis (FEA). Whilst this is becoming increasingly sophisticated, the values of the material data used in FEA packages have considerable associated uncertainty. In particular, there is no general technique to measure localized strain: the FEA is done using an average value taken from, for instance, a displacement measurement followed by calculations on bending stresses. The aim of this paper is to show how Raman spectroscopy can be used to assess localized strain, by first using the technique to calibrate doping profiles in silicon: doping itself being a major contributor to the strain in a device. Localized results are important because many applications require heavily doped silicon structures: in high concentrations the dopant will distort the silicon lattice considerably. In addition, dopants are known to aggregate at certain crystal defects such as dislocations. Thus the distribution of the dopant, and the associated strain, will depend on the original crystal quality and its processing history prior to dopant incorporation. Results have previously been reported on Raman spectroscopy of boron doped silicon [1], using a destructive etch technique to obtain a through-wafer doping profile. To our knowledge no results have been published on localized measurement of doping with the spatial resolution (,1 μm) proposed here, and using a nondestructive technique. There is an additional benefit from the work. Some microengineered devices, in particular those which require resonant motion, may have long term failure mechanisms which are caused by localized strain maxima. The ability to map the distribution of strain within a device, and then correlate this data with points of failure, should lead to more reliable design and manufacturing. The principles of this technique have been reported elsewhere, e.g. [2], as have details of the microline focus spectrometer (MiFS) used in our experiments [3]. Fig. 1 is a schematic of the instrument. Both the band shift and band half-width can be plotted as a function of position to give a direct two-dimensional picture. The established strain induced shift in orientated single crystal silicon and other materials points to the use of shifts in the doped silicon phonon frequency to determine relative strain distributions in the fabricated structures. As a result, strain peaks in the device, including overlays, can be observed. The instrumentation is capable of obtaining spectra with sub-micron resolution and can generate profiles and images representing intensity (species concentration), frequency (stress) and bandwidth (crystallinity). Applied mechanical stresses will result in phonon frequency changes, and structural alterations will change the phonon density of states population and thus the band shape. In the case of silicon these spectral responses to stress have been published [4], although the manifestation of all the theoretically predicted spectral changes has not been observed. A (1 0 0) n-type silicon wafer, of 10 U cm resistivity, was used as the starting material. After cleaning and etching to remove the top 3 μm of the wafer surface, the substrate was loaded into a diffusion furnace alongside a solid source of boron. Diffusion was carried out at 1100 8C for two hours. This is enough to produce a heavily doped p-type surface layer, with a concentration in excess of 3 3 10 ions cmy3 at a depth of 2 μm; confirmation is provided by this process being used to produce an etch stop layer in an ethylenediamine pyrocatechol (EDP)-based process. Substantial changes to the phonon spectrum of silicon in boron-diffused material have been ob

The design and operation of a micromechanical gyroscope based on a vibrating diaphragm loaded with an inertial mass is described. Capacitive actuation and sensing methods are employed. Preliminary results are presented which show that mechanical and electrical coupling limit current performance which could be improved to give noise equivalent rate of turn better than 0.14/spl deg//s.