Two-feldspar geothermometry in granulite facies metamorphic rocks

A geothermometric technique based on equilibria between coexisting plagioclase and alkali feldspar was applied to quartzo-feldspathic granulites from Salvador, BA, Brazil. The conditions of metamorphism were determined to be in the range 750 ° C–800 ° C, 4–8 Kb, by comparison with experimental data on the stabilities of sapphirine, phlogopite and other minerals occurring in the associated rocks. Selected feldspar data gives temperatures near, but slightly below, this range. Several variants of the Wood and Banno model, as well as an empirical two-pyroxene geothermometer, were also tested and found to give temperatures which were apparently 50 °–100 ° high. The solubility of Al₂O₃ in orthopyroxene indicates temperatures which are about 200 ° to high, suggesting that Fe in the natural assemblages significantly changes relationships observed experimentally in MgO-Al₂O₃-SiO₂ systems.     

Fatty acids and Pb-210 geochronology of a sediment core from Buzzards Bay,Massachusetts

Four sections of a Pb-210 dated core of 62 cm length from Buzzards Bay, Massachusetts, were analyzed for fatty acids. A comparison of fatty acids extracted by Soxhlet extraction (unbound fatty acids) with fatty acids extracted by subsequent saponification extraction of the same sample (bound fatty acids) showed the former did not undergo diagenetic loss any faster than the latter. However, compositional differences between bound and unbound fatty acids were apparent in the top section of 1–2 cm and were less apparent in the 54–58 cm section. At least 14% of the bound fatty acids are esterified to non-solvent extractable material. The net conversion of fatty acids to other compounds is 32 μ/g dry weight sediment over the first 30 yr after deposition.     

Armalcolite stability as a function of pressure and oxygen fugacity

The stability of synthetic armalcolite of composition (Fe_0.5Mg_0.5Ti₂O₅ was studied as a function of total pressure up to 15 kbar and 1200°C and also as a function of oxygen fugacity (?O₂) at 1200°C and 1 atm total pressure. The high pressure experiments were carried out in a piston-cylinder apparatus using silver-palladium containers. At 1200°C, armalcolite is stable as a single phase at 10 kbar. With increasing pressure, it breaks down ($\text{dT}\text{dP}\text{= 20°C/}\text{kbar}$), to rutile, a more magnesian armalcolite, and ilmenite solid solution. At 14 kbar, this three-phase assemblage gives way ($\text{dT}\text{dP}\text{= 30°C/}\text{kbar}$) to a two-phase assemblage of rutile plus ilmenite solid solution.A zirconian-armalcolite was synthesized and analyzed; 4 wt % ZrO₂ appears to saturate armalcolite at 1200°C and 1 atm. The breakdown of Zr-armalcolite occurs at pressures of 1–2 kbar less than those required for the breakdown of Zr-free armalcolite. The zirconium partitions approximately equally between rutile and ilmenite phases.The stability of armalcolite as a function of ?O₂ was determined thermogravimetrically at 1200°C and 1 atm by weighing sintered pellets in a controlled atmosphere furnace. Armalcolite, (Fe_0.5Mg_0.5)-Ti₂O₅, is stable over a range ?O₂ from about 10^?9.5to 10^?10.5 atm. Below this range to at least 10^?12.8 atm, ilmenite plus a reduced armalcolite are formed. These products were observed optically and by Mössbauer spectroscopy, and no metallic iron was detected; therefore, some of the titanium must have been reduced to Ti³⁺. This reduction may provide yet another mechanism to explain the common association of ilmenite rims around lunar armalcolites.     

Late-Pleistocene and Holocene remains of Hysterocarpus traski (Tule Perch) from Clear Lake,California, and inferred Holocene temperature fluctuations

The remains of scales of Hysterocarpus traski Gibbons (Tule perch) were found throughout a 27.44-m core from Clear Lake. Most scales occurred between the mud surface and deposits approximately 11,000 years old. Changes in growth rates of the animals were examined by measuring scale annuli and applying an empirically established regression of fish length on scale radius. The data indicate a pattern of accelerating growth rates, reaching a peak between ?4000 and 2800 BP. After ?2800 BP, growth rates decline markedly. Because the growth rates of these animals are essentially dependent on temperature, the changes observed in the patterns of growth probably reflect changes in climate in the northern Coast Range. The general pattern of inferred temperature increase during the early and middle Holocene, ending between ?4000 and 2800 BP, is consistent with evidence from tree-line studies and palynology indicating higher temperatures in parts of the western United States during this period.     

Ferroan anorthosite: A widespread and distinctive lunar rock type

Eight of eleven Apollo 16 rake-sample anorthosites are very similar to each other, to hand-specimen Apollo 16 anorthosites, and to Apollo 15 anorthosites. They have feldspar An_96.6, both high- and low-Ca pyroxene with a restricted range of (low-magnesium) composition, minor olivine (～ Fo₆₀), traces of ilmenite and chromite, and originally coarse-grained, but now cataclastic texture. Such ferroan anorthosite is evidently a coherent, distinctive and widespread lunar rock type of cumulate origin which may not necessarily be very closely related genetically to other highland rock types.     

Distribution of nutrient salts in the southern North Sea during early 1974

Nutrient salt surveys in the southern North Sea have shown that the level of phosphate and nitrate off the continental coast during January, 1974 was two to three times higher than during the same period in 1962. The level of phosphate has also increased in the Thames Estuary but to a lesser degree. It is suggested that these increases are related to the discharge of waste material from terrestrial sources and that such changes must be considered in the context of eutrophication in the southern North Sea.     

Siltation analysis in the Neyyar reservoir and forest degradation in its catchment: a study from Kerala state, India

 Impact of catchment erosion and the resultant reservoir siltation from a tropical environment is reported here to discuss the effect of a reservoir in the natural degradation of an evergreen-forested segment. While an area of 8.01 km² has been affected by direct inundation at the full reservoir level, another 2.6 km² area once under thick forest cover, had also lost its identity over the last 38 years by indirect degradation. This zone mainly falls in the confluence of tributaries, namely Neyyar and Mullayar, with the reservoir. The capacity of the reservoir was found to be reduced by 28.8 Mm³ during this period and the annual average loss is calculated as 0.75 Mm³ (0.71%), indicating the intensity of erosion from the catchment zone. In case the proposed upper dam in the reservoir comes into existence, an additional area of 2.4 km² from the virgin forest would be submerged and more area would face degradation around the inundated zone. Received: 29 July 1998 · Accepted: 16 November 1998