The Orapa and Jwaneng kimberlites are located along the western margin of the Kalahari Craton and the prevalence of eclogitic over peridotitic diamonds in both mines has recently been linked to lower P-wave velocities in the deep mantle lithosphere (relative to the bulk of the craton) to suggest a diamond formation event prompted by mid-Proterozoic growth and modification of preexisting Archean lithosphere (Shirey et al. 2002). Here we study peridotitic diamonds from both mines, with an emphasis on the style of metasomatic source enrichment, to evaluate their relationship with this major eclogitic diamond formation event. In their major element chemistry, the peridotitic inclusions compare well with a world-wide database but reveal differences to diamond sources located in the interior of the Western Terrane of the Kaapvaal block, where the classical mines in the Kimberley region are located. The most striking difference is the relative paucity of low-Ca (<2 wt% CaO in garnet) harzburgites and a low ratio of harzburgitic to lherzolitic garnets (2:1). This suggests that lithospheric mantle accreted to the rim of the Zimbabwe and Kaapvaal blocks was overall chemically less depleted. Alternatively, this more fertile signature may be assigned to stronger metasomatic re-enrichment but the trace element signature of garnet inclusions is not in favor of strong enrichment in major elements. For both mines the majority of lherzolitic and harzburgitic garnet inclusions are characterized by moderately sinusoidal REEN patterns and low Ti, Zr and Y contents, indicative of a metasomatic agent with very high LREE/HREE and low HFSE. This is consistent with metasomatism by a CHO-fluid or, as modeled by Burgess and Harte (2003), a highly fractionated, low-volume silicate melt from the MORB-source. In both cases, changes in the major element chemistry of the affected rocks will be limited. In a few garnets from Orapa preferential MREE enrichment is observed, suggesting that the percolating fluid/melt fractionated a LREE-phyllic phase (such as crichtonite). The overall moderate degree of metasomatism reflected by the inclusion chemistry is in stark contrast to lithospheric sections for Orapa and Jwaneng based on mantle xenocrysts and xenoliths, revealing extensive mantle metasomatism (Griffin et al. 2003). This suggests that the formation of peridotitic diamonds predates the intensive modification of the subcratonic lithosphere during Proterozoic rifting and compression, implying that diamonds may survive major tectonothermal events.

Magmas erupted at convergent margins consist of components from both mantle wedge and subducted slab. In an effort to quantify the relative contributions of these sources, we have determined 19 trace element partition coefficients (D values) for orthopyroxene and clinopyroxene, in equilibrium with spinel and hydrous high-MgO melt under conditions appropriate to melting in the mantle wedge, i.e., 1.3 GPa, 1245 degreesC, and f(o2) of NNO + 1. All trace elements are more incompatible in clinopyroxene during hydrous melting than during anhydrous melting of fertile and depleted peridotite. Orthopyroxene D values are relatively insensitive to pressure, temperature, and phase composition. The new D values are used to calculate the trace-element composition of the mantle wedge, which produced primitive South Sandwich Islands and St. Vincent (Lesser Antilles) arc basalts. Both sources correspond to previously depleted mantle that has been enriched in LILEs and LREEs by slab-derived fluids. In the case of the South Sandwich Islands, the calculated source is in very close agreement with dredged fore-arc therzolites. Our partitioning data confirm that hydrous melting of wedge peridotite itself cannot produce the characteristic enrichments of LILEs over REEs and HFSEs. Our estimates of the slab component in South Sandwich Islands and St. Vincent are consistent with estimates from other arcs, derived by alternative methods.

The partition coefficient (D) for any trace element in the mantle is a function of pressure, temperature and phase composition, the latter of which is controlled by the relative fertility of the peridotite. Models of mantle melting therefore require accurate determination of partition coefficients along the peridotite solidus. We have experimentally determined partition coefficients for clinopyroxene, orthopyroxene and olivine in equilibrium with melt, close to the anhydrous solidus of refractory Tinaquillo Lherzolite at 1.5 GPa, 1315 °C. All trace elements, apart from Sc, are incompatible in clinopyroxene, and the maximum DREE is DEr at 0.76. All trace elements are incompatible in orthopyroxene; the most compatible REE is Lu (DLu=0.18). Partition coefficients for olivine are generally <0.005, and only Ti and Li are moderately compatible (DTi=0.10;DLi=0.29). Compared to a previous study of trace element partitioning at the solidus of a more fertile peridotite (mid-ocean ridge basalt (MORB)-pyrolite-90, MPY-90) at 1.5 GPa, it is shown that, at fixed pressure, partition coefficients, especially for clinopyroxene, generally increase with increasing source fertility. DU/DTh for clinopyroxene is 0.86±0.02 and for orthopyroxene is 1.49±0.03, significantly lower than DU/DTh ratios previously determined for MPY-90 at 1.5 GPa. When compared with pyroxene partition coefficients experimentally determined on the MPY-90 solidus at 3.0 GPa, the partition coefficients for the majority of trace elements increase as pressure decreases along the mantle solidus. Notable exceptions are Li and Na which become more compatible as pressure increases along the solidus. The combined effects of pressure, temperature and source fertility mean that partition coefficients increase with decreasing pressure during decompression mantle melting beneath mid-ocean ridges. By expressing the variation in D as a function of melt fraction (F), the new data can be used to model decompression melting taking into account changes in partition coefficients as melting proceeds. We show that the trace element composition of residual (or "trapped") melts is sensitive both to source mineralogy (i.e. garnet–lherzolite versus spinel–lherzolite) and to the depth range over which melting occurs. The variation in partition coefficients during mantle melting therefore provides a valuable tool in the interpretation of melt inclusions. The variable partition coefficients have much less impact on the composition of aggregated melts.

The localization of strain in the continental crust during compressional tectonics is examined using the active structures at the Nanga Parbat massif, an exhumed tract of Indian continental crust in the Pakistan Himalaya. This large‐scale (∼40 km wavelength) structure is considered to involve the whole crust. Thrusting at the modern surface places gneisses of the Indian continental crust onto Holocene deposits. At the Raikhot transect, the thrust zone carries a relatively narrow (2 km wide) shear zone within which minor structures are asymmetric and the deformation apparently noncoaxial. However, modeling of foliation and augen preferred orientation/ellipticity suggests that the bulk deformation is a combination of relatively small simple shear strains (γ = 1) with larger stretching strains. Heterogeneous stretching within the shear zone was accommodated by localized shearing on metabasic layers so that strain is partitioned. Outside this shear zone on the transect there is penetrative deformation throughout the Nanga Parbat massif. This broadly distributed deformation shows no asymmetry or evidence of rotation. Rather this deformation is better described as near pure‐shear subvertical stretching. Augen ellipticities suggest subvertical stretches of greater than 200%. Consideration of plausible changes in crustal thickness during the amplification of the Nanga Parbat structure suggests the magnitude of vertical stretch decays with depth. Presumably these strains in the deep crust are more distributed but weaker than in the exposed middle crustal sections, assuming conservation of horizontal shortening displacement with depth. These studies suggest that penetrative vertical stretching through dominantly pure shear deformation is an effective mechanism for thickening the continental crust and that models which assume that simple shear zones penetrate the whole crust need not be of ubiquitous applicability.

Piston-cylinder cell assemblies experience inhomogeneous pressure distribution upon pressurization due to the variable compressibilities of the cell components. This results in the sample experiencing a pressure loader than expected, given the applied force of the piston. Although the effect is generally compensated for by applying a 'friction' correction. there have been wide variations in the corrections applied for some of the harder cell materials. We have determined friction correction factors for a range of cell assemblies commonly used in our laboratory, relative to select well-characterized phase equilibria. Single-sleeve NaCl cells require. using the piston-in technique, very small corrections of the order -0.05 GPa for 12.7 mm diameter. and less for larger diameter assemblies. Four separate calibrations of the single sleeve 12.7 mm BaCO3 cell show that it requires a correction of -9%. This factor is entirely independent Of temperature and pressure within the range 1000 to 1600degreesC and 1.5 to 3.2 GPa. This result is in contrast to the results of Fram and Longhi (1992) who claim that the correction for BaCO3 cells is highly dependent on pressure. For the assemblies included in this study there is an increase in the pressure Correction required in the order of 12.7 mm diameter NaCl-pyrex -3%; 19 mm talc-pyrex -3.6%; 12.7 mm BaCO3 -9% and 12.7 mm BaCO3-silica glass -13%.

Due to the retrograde cation exchange problems experienced by conventional geothermobarometers above their closure temperatures, petrogenetic grids are a potentially powerful alternative to unravelling the P–T evolution of ultrahigh‐T granulite terranes. A new qualitative KFMASH (K2O–FeO–MgO–Al2O3–SiO2–H2O) petrogenetic grid for Mg–Al rich metapelites containing K‐feldspar, sillimanite and quartzofeldspathic melt that successfully accounts for the majority of assemblages composed of variations of sapphirine, spinel, garnet, orthopyroxene, cordierite, biotite and quartz is developed. Univariant reactions are predicted utilizing a newly derived ‘melt projection’ and these reactions are entirely consistent with algebraically calculated reaction coefficients obtained using a set of standard phase compositions. Based upon observations of commonly associated mineral assemblages in natural lithologies the [Spr, Spl], [Qtz, Spl], [Bt, Spl], [Opx, Spr], [Opx, Qtz] and [Bt, Opx] invariant points are assumed to be stable, whilst the [Grt, Spr], [Grt, Qtz], [Spr, Qtz] and [Crd, Qtz] are assumed to be metastable. Biotite‐bearing assemblages are confined to the lowest temperatures, and sapphirine + quartz to the highest temperatures. Orthopyroxene + sillimanite ± quartz assemblages are confined to the highest pressures, whilst spinel‐bearing assemblages are stabilized by lower pressures. The alternative choice of invariant point stability leads to significant differences between this grid and previously proposed topologies. Spinel cannot be stable along with the orthopyroxene and sillimanite assemblage as previously proposed. Further, more subtle differences in topology result from the treatment of H2O in the chemographic projection used to deduce univariant reactions, and projecting from a water‐bearing quartzofeldspathic melt does not yield the same reaction coefficients as projection from H2O. The new grid allows reinterpretation of previously proposed evolutionary P–T paths for Mg–Al rich granulites from the Napier Complex and Rauer Group, East Antarctica, and In Ouzzal, Algeria.

A dual RF input high linearity power amplifier for PCS bands from 1850 to 1910 MHz has been developed for TDMA/CDMA applications. It features on die, input switching, active bias sensing and regulation, 50/spl Omega/ input matching and power down control. A single positive supply voltage is required. This amplifier is packaged in a low cost plastic super small SSOP-16 package. In digital operation adjacent channel power rejection is better then 30 dBc at 800 mW and 22 dB of gain. Maximum output power is 2 W. Typical high power added efficiency (PAE) is 40%.