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The studies conducted during 1990 to 1996 on igneous and metamorphic petrology, mineralogy and its chemistry, acoustic properties of minerals, clays, clastic sedimentology, and carbonates are discussed. Research findings on environmental mineralogy, remote sensing and in situ techniques are discussed. The progress in the field of the acoustic properties of minerals and seismology, and studies on high pressure metamorphism and carbonate sedimentation are also discussed.

High-pressure granulite assemblages have been produced as residues in partial melting experiments on a natural (alkalic basalt) amphibolite between pressures of 12 and 18 kbar. In particular, at 18 kbar, partial melting of the hornblende + plagioclase + or - quartz assemblage under fluid-absent conditions produces garnet + clinopyroxene + new albitic plagioclase + melt. Seismic velocities (V(sub P)) are estimated from the modal data for the experimental assemblages and range from 6.90 km/s for hornblende-bearing residues to 7.62 for the dominantly garnet-clinopyroxene residues. These values are typical for rock types in the lowermost crust, transitional to mantle. The experimental results help place additional pressure-temperature-a(H2O) constraints on the source region for the natural high-pressure granulites. The experimental residue assemblage formed at 18 kbar has been described in natural xenolith suites from the Delegate Pipes in Australia, where the pipes intrude Upper Ordovician and Lower Devonian continental crust, and in the Bearpaw Mountains, Montana, where the xenolith-bearing magmas intrude older crust of Archean age. The combination of these data shows that the xenoliths may indeed represent lowermost continental crust and furthermore helps interpret the nature of the crust-mantle boundary in these areas. The Delegate Pipes xenoliths suggest that the crust-mantle boundary may be the site for partial melting and assimilation, whereas the Bearpaw Mountains samples indicate that magmatic underplating may have been a major process in generating thick continental Archean crust. The experimental data and Bearpaw Mountains xenoliths suggest that the large range of rock types found in Archean granulite terranes may not be representative of the lowermost continental crust.

Six acidic dykes were discovered surrounding the Laiziling pluton, Xianghualing area, in the western Cathaysia Block, South China. A number of captured zircons are found in two of these acidic dykes. By detailed U–Pb dating, Lu–Hf isotopes and trace-element analysis, we find that these zircons have ages clustered at c. 2.5 Ga. Two acidic dyke samples yielded upper intersection point 206U/238Pb ages of 2505 ± 42 Ma and 2533 ± 22 Ma, and weighted mean 207Pb/206Pb ages of 2500 ± 30 Ma and 2535 ± 16 Ma. The majority of these zircons have high (Sm/La)N, Th/U and low Ce/Ce* ratios, indicating a magmatic origin, but some grains were altered by later hydrothermal fluid. Additionally, the magmatic zircons have high Y, U, heavy rare earth element, Nb and Ta contents, indicating that their host rocks were mainly mafic rocks or trondhjemite–tonalite–granodiorite rock series. Equally, their moderate Y, Yb, Th, Gd and Er contents also indicate that a mafic source formed in a continental volcanic-arc environment. These zircons have positive ϵHf(t) values (2.5–6.9) close to zircons from the depleted mantle, with TDM (2565–2741 Ma) and TDM2 (2608–2864 Ma) ages close to their formation ages, indicating that these zircons originated directly from depleted mantle magma, or juvenile crust derived from the depleted mantle in a very short period. We therefore infer that the Cathaysia Block experienced a crustal growth event at c. 2.5 Ga. [ABSTRACT FROM AUTHOR]

Subduction-related Quaternary volcanic rocks from Solander and Little Solander Islands, south of mainland New Zealand, are porphyritic trachyandesites and andesites (58.20-62.19 wt% Si[O.sub.2]) with phenocrysts of amphibole, plagioclase and biotite. The Solander and Little Solander rocks are incompatible element enriched (e.g. Sr ~931-2,270 ppm, Ba ~619-798 ppm, Th ~8.7-21.4 ppm and La ~24.3-97.2 ppm) with MORB-like Sr and Nd isotopic signatures. Isotopically similar quench-textured enclaves reflect mixing with intermediate (basaltic-andesite) magmas. The Solander rocks have geochemical affinities with adakites (e.g. high Sr/Y and low Y), whose origin is often attributed to partial melting of subducted oceanic crust. Solander sits on isotopically distinct continental crust, thus excluding partial melting of the lower crust in the genesis of the magmas. Furthermore, the incompatible element enrichments of the Solander rocks are inconsistent with partial melting of newly underplated mafic lower crust; reproduction of their major element compositions would require unrealistically high degrees of partial melting. A similar argument precludes partial melting of the subducting oceanic crust and the inability to match the observed trace element patterns in the presence of residual garnet or plagioclase. Alternatively, an enriched end member of depleted MORB mantle source is inferred from Sr, Nd and Pb isotopic compositions, trace element enrichments and ζHf [much greater than] 0 CHUR in detrital zircons, sourced from the volcanics. [sup.10]Be and Sr, Nd and Pb isotopic systematics are inconsistent with significant sediment involvement in the source region. The trace element enrichments and MORB-like Sr and Nd isotopic characteristics of the Solander rocks require a strong fractionation mechanism to impart the high incompatible element concentrations and subduction-related (e.g. high LILE/HFSE) geochemical signatures of the Solander magmas. Trace element modelling shows that this can be achieved by very low degrees of melting of a peridotitic source enriched by the addition of a slab-derived melt. Subsequent open-system fractionation, involving a key role for mafic magma recharge, resulted in the evolved andesitic adakites. Keywords Subduction * Slab fluid * Slab melt * Partial melting * Cosmogenic [sup.10]Be * Oxygen isotopes, Introduction Numerous geochemical (e.g. Defant and Drummond 1990; Kay and Kay 1993; Garrison and Davidson 2003), experimental (e.g. Sen and Dunn 1994a; Rapp and Watson 1995; Rapp et al. 1999) [...]