The early Proterozoic gneiss-charnockites from Dharmapuri area, southern India are investigated to understand the crustal evolution processes of the area. The granulite facies metamorphism which converted the tonalitic gneisses to enderbites in the area was isochemical, except for the depletion of LIL elements. The enderbites of granulite zone have high K/Rb, Ba/Rb, K/U and K/Th but low U, Th, K/Sr, Rb/Sr and Th/U compared to the tonalitic gneisses of the transition zone. The petrochemical studies show a compositional continuum, without bimodal distribution pattern, from mafic gneisses to enderbites/tonalitic gneisses. Their variation suggests that the rocks were derived from igneous protoliths. The REE pattern of tonalitic rocks show LREE enrichment, HREE depletion and variable positive Eu anomalies. The REE concentrations, however, do not show any signs of fractionation with increasing grade of metamorphism. It is also observed that ages obtained from whole rock Rb-Sr and Sm-Nd systematics remain same, which probably suggests that the high grade metamorphism followed crustal generation processes within a short span. The protolithic orthogneisses were probably derived either by fractional crystallization of basaltic/dioritic magma involving hornblende, plagioclase and iron oxides as the major precipitating phases, or by partial melting of an amphibolite source leaving plagioclase and clinopyroxene as the main residual phases. A fractional crystallization model is more preferred because of the presence of horn-blende cumulate rocks and because there is a continuous compositional range from gabbro to granodiorite through tonalite.

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Temperature-chloride mixing diagrams at 500 and 1000 bars, and at vapor-saturated pressures, are calculated in order to demonstrate the mixing behavior of saline (up to 40 NaCl wt%) high-temperature solutions with 1 wt% low-temperature solutions, with the results applied to interpreting fluid inclusion data. The temperature of the initial saline solutions is 450°C at 500 bars, 600°C at 1000 bars, or 300°C at vapor-saturated pressures. The temperature of the diluent is 100° or 300°C at 500 and 1000 bars, and 100°C at the vapor-saturated pressure. Mixing diagrams at 500 and 1000 bars are recast onto the relation between homogenization temperature and chloride concentration of fluid inclusion using densities of NaCl solutions. Temperature-chloride mixing diagrams indicate that mixing of 40 wt% fluids with dilute solutions at 1000 bars is not linear, but shows a greater decrease in temperature with up to 3 wt% NaCl deviation. The deviations are larger (up to 9 wt%) with respect to homogenization temperature versus concentration relations. In contrast, mixing lines for 30 to 10 wt% initial fluids at 1000 bars and those for 40 to 10 wt% fluids at 500 bars are nearly linear with respect to temperature (or homogenization temperature) and NaCl concentration, within ±3 wt% deviations. At vapor-saturated pressures, 300°C and 25 to 5 wt% initial solutions show nearly linear mixing relationships under the condition that vapor/liquid volume ratios are less than 1. Potassium chloride solutions show almost identical temperature-chloride relations with sodium chloride solutions, up to 325°C, 500 bars, and 6 mole/kg, when the molalities of saline and dilute solutions are same for both solutes. The relations between homogenization temperature and concentration for KCl solutions show slightly smaller slopes than those for NaCl solutions. Application of these results to fluid inclusion data of the Ohe, Toyoha, and Fujigatani-Kiwada deposits in Japan indicates that high temperature and high salinity fluids (335°C and 6.3 wt% for the Ohe deposit; 325°C and 4.6 wt% for the Toyoha deposit; 360°C and 7.4 wt% for the Fujigatani-Kiwada deposits) mixed with low temperature and low salinity solutions (221°C and 1.6 wt% for the Ohe deposit; 209°C and 0.0 wt% for the Toyoha deposit; 250°C and 1.9 wt% for the Fujigatani-Kiwada deposits).

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Several chemical leaching experiments were carried out to characterize the REE distribution in four pelagic sediments which have negative Ce anomaly collected in Central Pacific. Extraction experiments indicate that the carrier of the negative Ce anomaly is phosphate phase. This result supports our hypothesis that a negative Ce anomaly is mainly due to fish bone debris in the Pacific equatorial pelagic sediments, in case of pelagic sediments far from the areas of hydrothermal activity. Furthermore, a positive Ce anomaly in pelagic sediments was confirmed by leaching experiment to be due to hydrogenous components (Mn-Fe oxides). The terrigenous component (silicate phase) has a low REE content and a flat shale-normalized REE pattern.

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Basalts (OKTB) from the Okinawa Trough (OKT), which is a now opening marginal back-arc basin, are chemically quite similar to those from the intra-oceanic back-arc basins such as the Mariana Trough. Both olivine-normative and quartz-normative basalts occur, and major and trace element concentrations show a systematic variation, probably derived by differentiation of the magma. D/H, ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios are almost identical in the dacite and basalts, and the ¹⁸O/¹⁶O ratio in the former is only slightly higher than in the latter, suggesting that the dacites are ultimately cognate with basalts. Concentrations of Al₂O₃, total iron, MgO, CaO, Na₂O, Ni, Cr, and V in OKTB are within the range of variation in normal type mid-ocean ridge basalts (N-MORB), whereas OKTB have significantly higher K₂O, Rb and Sr contents and D/H, ¹⁸O/¹⁶O and ⁸⁷Sr/⁸⁶Sr ratios and a lower ¹⁴³Nd/¹⁴⁴Nd ratio than N-MORB have. These chemical and isotopic features of OKTB can be well explained by the concept, which has been proposed by many authors for magma genesis in the intraoceanic back-arc basins, that the H₂O-rich primary magma is generated from normal-type mantle peridotite modified by component from the subducted slab. Compared with those from intra-oceanic back-arc basins, the rocks from the OKT have distinctly higher ⁸⁷Sr/⁸⁶Sr and lower ¹⁴³Nd/¹⁴⁴Nd ratios, reflecting the higher contribution of continent-derived sedimentary components to the magma source. Oxygen, Sr and Nd isotopic characteristics of the rocks of the OKT are fitted well with paired two-component mixing models: one for the source-mixing and another for the crustal contamination.

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