High Acetone Concentrations throughout the 0–12 km Altitude Range over the Tropical Rainforest in Surinam

Airborne measurements of acetone were performed overthe tropical rainforest in Surinam(2°–7° N, 54°–58° W, 0–12 kmaltitude) during the LBA-CLAIRE campaign in March1998, using a novel proton transfer reaction massspectrometer (PTR-MS) that enables the on-linemonitoring of volatile organic compounds (VOC) with ahigher proton affinity than water. The measuredacetone volume mixing ratios ranged from 0.1 nmol/molup to 8 nmol/mol with an overall average of 2.6nmol/mol and a standard deviation of 1.0 nmol/mol. Theobserved altitude profile and correlations with CO,acetonitrile, propane and wind direction are discussedwith respect to potential acetone sources. No linearcorrelation between acetone and CO mixing ratios wasobserved, at variance with results of previousmeasurement campaigns. The mean acetone/CO ratio(0.022) was substantially higher than typical valuesfound before. The abundance of acetone appears to beinfluenced, but not dominated, by biomass burning,thus suggesting large emissions of acetone and/oracetone precursors, such as possibly 2-propanol, fromliving plants or decaying litter in the rainforest.     

The 1997/1998 mass mortality of corals: effects on fish communities on a Tanzanian coral reef

The abnormally high surface temperatures in the world's oceans during 1997/1998 resulted in widespread coral bleaching and subsequent coral mortality. An experiment was performed to study the effects of this coral mortality as well as the influence of the structural complexity on fish communities on a Tanzanian coral reef. Changes in fish communities were investigated on plots of transplanted corals after 88% of these corals had died. A distinct shift in fish community composition was found, although diversity was not affected. Fish abundance rose by 39% mostly due to an increase in herbivores, which seemed to benefit from enhanced algal growth on the dead corals. Fish abundance, species diversity and community composition were also strongly influenced by the structural complexity provided by the live and dead corals. This suggests that a coral reef can support abundant and diverse fish populations also after the corals have died as long as the reef structure is sustained.     

额济纳绿洲夏末典型晴天小气候特征分析

绿洲系统特有的地理地貌形成了绿洲特殊的小气候特征。利用额济纳绿洲2003年9月8～10日小气候观测资料，分析了绿洲柽柳林的小气候特征。在柽柳林内，地表和近地层大气温度有明显的日变化，日间地表给大气加热，大气温度呈超绝热递减率随高度递减；夜间大气给地表加热，大气为稳定层结。近地层空气湿度的日变化与温度相反。林内空气温度的垂直分布主要取决于冠层与地表吸收太阳辐射状况。在林冠顶层，白天以上升气流为主，夜间以下沉气流为主，绿洲荒漠环流效应已经不明显。绿洲上空大气浑浊度小，对太阳辐射的削减较少，绿洲具有很好的光资源背景。     

Petroleum inclusions and residual oils: constraints for deciphering petroleum migration

The analysis of petroleum inclusions (PI) in parallel to residual oils (=bitumens) provided specific constraints for petroleum migration processes in the Prague Basin. Whereas organic geochemical information from bitumens is limited due to alteration, additional high quality information was obtained from C_1–14-range compounds inside crystals. This was obtained by the application of a closed system for the decrepitation and thermal extraction of PI with subsequent gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). The resulting data not only show pristine live oils, gases, residual and precipitated bitumens and a broad variation of mixtures of the groups above, but also show that gas migration and fractionation processes played a major role in the Prague Basin.     

Spectral features of RZ Psc, a cool star with Algol-like brightness minima

We have determined the physical (T _eff, logg, ζ) and kinematic (V _e sini,V _r ) parameters and abundances for 14 chemical elements in the atmosphere of the “antiflare” variable RZ Psc, using medium-resolution spectra obtained with the Coudé spectrographs of the 6-m telescope of the Special Astrophysical Observatory and the Crimean Astrophysical Observatory 2.6-m Shain telescope. The chemical composition of the star is characterized by a slight metal deficiency; however, the iron and calcium abundances are consistent with the solar values within the errors. We also detected a peculiar dip (depression) of the continuum level near the H_α line. Assuming that this depression and the photospheric H_α line have independent origins, we calculated the hydrogen abundance X in the atmosphere of RZ Psc. The resulting value X=0.70 (of the solar value) implies a relative deficiency of hydrogen. Together with the spatial location of the star, these properties provide evidence that RZ Psc is an evolved star, most likely belonging to population II.     

Early Variscan magmatism in the Western Carpathians: U–Pb zircon data from granitoids and orthogneisses of the Tatra Mountains (Slovakia)

This study presents the first U–Pb zircon data on granitoid basement rocks of the Tatra Mountains, part of the Western Carpathians (Slovakia). The Western Carpathians belong to the Alpine Carpathian belt and constitute the eastern continuation of the Variscides. The new age data thus provide important time constraints for the regional geology of the Carpathians as well as for their linkage to the Variscides. U–Pb single zircon analyses with vapour digestion and cathodoluminescence controlled dating (CLC-method) were obtained from two distinct granitoid suites of the Western Tatra Mountains. The resulting data indicate a Proterozoic crustal source for both rock suites. The igneous precursors of the orthogneisses (older granites) intruded in Lower Devonian (405 Ma) and were generated by partial melting of reworked crustal material during subduction realated processes. In the Upper Devonian (365 Ma), at the beginning of continent–continent collision, the older granites were affected by high-grade metamorphism including partial melting, which caused recrystallisation and new zircon growth. A continental collision was also responsible for the generation of the younger granites (350–360 Ma). The presented data suggest multi-stage granitoid magmatism in the Western Carpathians, related to a complex subduction and collision scenario during the Devonian and Carboniferous. Received: 19 February 1999 / Accepted: 3 December 1999     

Experimental generation of shock‐induced pseudotachylites along lithological interfaces

Abstract— To understand the mechanism of formation of shock‐induced pseudotachylites and particularly the role that rock heterogeneities and interfaces play in their formation, shock recovery experiments were carried out on samples consisting of two distinct lithologies (dunite and quartzite). It was possible to generate melt veins of 1–6 μm width along lithological interfaces at moderate shock pressures (6 to 34 GPa). The magnitudes of displacement along the interface, strain rate, and the kinetic heat production indicate that friction is an important heat source that largely contributes to the energy budget of the melt veins. The experimentally produced veins resemble natural S‐type pseudotachylites. The geometry of the veins depends on the orientation of the interface with respect to the shock front and includes strong variations in thickness, formation of melt pockets and injection veins, sudden changes in vein orientation, and sharp vein margins. Two types of melt were observed: vesicle‐free and vesicular melts. Dense vesicle‐free melt rock is likely to represent high‐pressure melts. Vesicular melts were also generated during shock compression, but they remained in a molten state during pressure release and continued shearing. Intermingling of comminuted olivine and melt suggests that ultracataclasis of olivine induced by a dynamic tensile failure is a precursor stage to frictional melting. Shock wave interferences at the lithological interface provide the necessary stress conditions to start dynamic failure of olivine. The composition of the frictional melts ranges from olivine‐normative to enstatite‐normative and is, thus, largely determined by olivine melting. The validity of the sequence of friction melting susceptibilities of rock‐forming minerals inferred from tectonically‐produced pseudotachylites is confirmed and can now be applied to ultra‐high strain rates during shock compression.     

Petrogenesis of metatexite and diatexite migmatites determined using zircon U–Pb age,trace element and Hf isotope data,Higo metamorphic terrane,central Kyushu,Japan

Metatexite and diatexite migmatites are widely distributed within the upper amphibolite and granulite facies zones of the Higo low‐P/high‐T metamorphic terrane. Here, we report data from an outcrop in the highest grade part of the granulite facies zone, in which diatexite occurs as a 3 m thick layer between 2 m thick layers of stromatic‐structured metatexite within pelitic gneiss. The migmatites and gneiss contain the same peak mineral assemblage of biotite + plagioclase + quartz + garnet + K‐feldspar with retrograde chlorite ± muscovite and some accessory minerals of ilmenite ± rutile ± titanite + apatite + zircon + monazite ± pyrite ± zinc sulphide ± calcite. Calculated metamorphic P–T conditions are 800–900 °C and 9–12 kbar. Zircon in the diatexite forms elongate euhedral crystals with oscillatory zoning, but no core–rim structure. Zircon from the gneiss and metatexite forms euhedral–subhedral grains comprising inherited cores overgrown by thin rims. The overgrowth rims in the metatexite have lower Th/U ratios than zircon in the diatexite and yield a ²⁰⁶Pb/²³⁸U age of 116.0 ± 1.6 Ma, which is older than the 110.1 ± 0.6 Ma ²⁰⁶Pb/²³⁸U age derived from zircon in the diatexite. Zircon from the diatexite has variable REE contents with convex upward patterns and flat normalized HREE, whereas the overgrowth rims in the metatexite and gneiss have steep HREE‐enriched patterns; however, both types have similar positive Ce and negative Eu anomalies. ¹⁷⁶Hf/¹⁷⁷Hf ratios in the overgrowth rims from the metatexite are more variable and generally lower than values from zircon in the diatexite. Based on U–Pb ages, trace element and Hf isotope data, the zircon rims in the metatexite are interpreted to have crystallized from a locally derived melt, following partial dissolution of inherited protolith zircon during anatexis, whereas the zircon in the diatexite is interpreted to have crystallized from a melt that included an externally derived component. By integrating zircon and petrographic data for the migmatites and pelitic gneiss, the metatexite migmatite is interpreted to have formed by in situ partial melting in which the melt did not migrate from the source, whereas the diatexite migmatite included an externally derived juvenile component. The Cretaceous high‐temperature metamorphism of the Higo metamorphic terrane is interpreted to reflect emplacement of mantle‐derived basalts under a volcanic arc along the eastern margin of the Eurasian continent and advection of heat via hybrid silicic melts from the lower crust. Post‐peak crystallization of anatectic melts in a high‐T region at mid‐crustal depths occurred in the interval c. 116–110 Ma, as indicated by the difference in zircon ages from the metatexite and diatexite migmatites.     

Thermal evolution of the Tseel terrane,SW Mongolia and its relation to granitoid intrusions in the Central Asian Orogenic Belt

The timing and thermal effects of granitoid intrusions into accreted sedimentary rocks are important for understanding the growth process of continental crust. In this study, the petrology and geochronology of pelitic gneisses in the Tseel area of the Tseel terrane, SW Mongolia, are examined to understand the relationship between igneous activity and metamorphism during crustal evolution in the Central Asian Orogenic Belt (CAOB). Four mineral zones are recognized on the basis of progressive changes in the mineral assemblages in the pelitic gneisses, namely: the garnet, staurolite, sillimanite and cordierite zones. The gneisses with high metamorphic grades (i.e. sillimanite and cordierite zones) occur in the central part of the Tseel area, where granitoids are abundant. To the north and south of these granitoids, the metamorphic grade shows a gradual decrease. The composition of garnet in the pelitic gneisses varies systematically across the mineral zones, from grossular‐rich garnet in the garnet zone to zoned garnet with grossular‐rich cores and pyrope‐rich rims in the staurolite zone, and pyrope‐rich garnet in the sillimanite and cordierite zones. Thermobarometric analyses of individual garnet crystals reveal two main stages of metamorphism: (i) a high‐P and low‐T stage (as recorded by garnet in the garnet zone and garnet cores in the staurolite zone) at 520–580 °C and 4.5–7 kbar in the kyanite stability field and (ii) a low‐P and high‐T stage (garnet rims in the staurolite zone and garnet in the sillimanite and cordierite zones) at 570–680 °C and 3.0–6.0 kbar in the sillimanite stability field. The earlier high‐P metamorphism resulted in the growth of kyanite in quartz veins within the staurolite and sillimanite zones. The U–Pb zircon ages of pelitic gneisses and granitoids reveal that (i) the protolith (igneous) age of the pelitic gneisses is c. 510 Ma; (ii) the low‐P and high‐T metamorphism occurred at 377 ± 30 Ma; and (iii) this metamorphic stage was coeval with granitoid intrusion at 385 ± 7 Ma. The age of the earlier low‐T and high‐P metamorphism is not clearly recorded in the zircon, but probably corresponds to small age peaks at 450–400 Ma. The low‐P and high‐T metamorphism continued for c. 100 Ma, which is longer than the active period of a single granitoid body. These findings indicate that an elevation of geotherm and a transition from high‐P and low‐T to low‐P and high‐T metamorphism occurred, associated with continuous emplacement of several granitoids, during the crustal evolution in the Devonian CAOB.