The petrogenesis of the Edough amphibolites, Annaba, NE Algeria: two unrelated basic magmas and the lherzolite-harzburgite residue of a possible magma source

Summary The conditions of metamorphism and petrogenesis of Kef Lakhal amphibolites and associated amphibolite and olivine-rich lenses are discussed. The Kef Lakhal amphibolites contain plagioclase ranging from An₈₅ and An₁₂ and Ca-poor normally zoned garnet (< 9 wt% CaO) and were last metamorphosed to upper amphibolite facies. The amphibolite lenses invariably contain calcic plagioclase (An_97-78) and Ca-rich (up to 14 wt% CaO) doubly zoned garnets. Based on garnet zoning, it is found that the lenses experienced the three metamorphisms recorded elsewhere in the massif whereas the main amphibolites suffered only the last two metamorphisms, the last of which reached conditions of about T= 700 ± 80 °C and P= 8–10 Kb. This agrees with two unrelated igneous suites and is supported by the chemistry of the rocks and quantitative modelling. The Kef Lakhal amphibolites were formed by olivine-dominated fractional crystallisation processes from melts derived by partial melting of a homogeneous source and preserve MORB affinities. The amphibolite lenses were also evolved by fractional processes dominated by olivine but from a less homogeneous source and have island arc characteristics. The associated olivine-rich lenses are lherzolite-harzburgite mantle residua which suffered up to 35% melting. Bearing in mind the lack of isotopic and structural information, the data presented in this study indicate that fractional crystallisation of liquids produced through non model melting of these residua does not reproduce the composition of either of the amphibolites. Fractionation of melts similar to those derived from the Ronda peridotites yield compositions similar to the Edough amphibolites.

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Die Entstehung der Edough Amphibolite, Annaba, NE Algerien; zwei basische Magmen und das Lherzolit-Harzburgit-Residuum einer möglichen Magmenquelle

Zusammenfassung Die Metamorphosebedingungen und die Petrogenese der Amphibolite von Kef Lakhal und der mit ihnen assoziierten Amphibolit- und Olivin-reichen Linsen werden diskutiert. Die Kef Lakhal-Amphibolite enthalten Plagioklas, dessen Zusammensetzung von An₈₅ bis An₁₂ schwankt, und Ca-armen, normal zonierten Granat (< 9 Gew % CaO). Sie wurden unter Bedingungen der obenen Amphibolitfacies metamorphosiert. Die Amphibolit-Linsen führen stets Ca-reichen (An_97-78) Plagioklas und doppelt zonierten Granat (bis zu 14 Gew % Ca0). Die Granatzonierung läßt erkennen, daß die Linsen drei Metamorphose-Phasen, die auch sonst in dem Massiv nachgewiesen wurden, ausgesetzt waren. Die letzte Phase erreichte Bedingungen von ungefähr T = 700 ± 80 °C und P = 8–10 kb. Dies weist auf zwei, miteinander nicht verwandte magmatische Gesteinsabfolgen hin; dieses Konzept wird durch die chemische Zusammensetzung und durch quantitative Modellierung unterstützt. Die Kef Lakhal-Amphibolite wurden durch Olivin-dominierte fraktionierte Kristallisation aus Schmelzen gebildet, die durch partielle Aufschmelzung einer homogenen Quelle entstanden sind und MORB-Charakteristik haben. Die Amphibolit-Linsen gehen auch auf Olivin-dominierte Fraktionierungs-Prozesse zurück, hatten aber eine weniger homogene Quelle und zeigen Inselbogen-Charakteristika. Die assoziierten Olivin-reichen Linsen sind Lherzolit-Harzburgit Mantel-Residua, die von bis zu 35% Aufschmelzung betroffen waren. Obwohl zu berücksichtigen ist, daß isotopengeologische und strukturelle Daten fehlen, zeigen die Ergebnisse, daß fraktionierte Kristallisation von Schmelzen, die durch Non-Modell Aufschmelzung der Residua entstanden sind, nicht die Zusammensetzung der Amphibolite reproduzieren können. Hingegen liefert Fraktionierung von Schmelzen, die denen des RondaPeridotits ähnlich sind, Zusammensetzungen, die denen der Edough Amphibolite ähnlich sind.

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With 11 Figures     

三江地区高吉碱性岩体的岩石化学特征

三江地区的碱性岩有其独特的地质、岩石学与岩石化学特征；这些特征所记录的信息，不仅提供了高吉碱性岩区别于邻区及其它地方同类碱性岩的证据，而且也给出了识别碱性岩的标志与判定其所处的板块构造位置。     

Silicon isotope fractionation in bamboo and its significance to the biogeochemical cycle of silicon

A systematic investigation on silica contents and silicon isotope compositions of bamboos was undertaken. Seven bamboo plants and related soils were collected from seven locations in China. The roots, stem, branch and leaves for each plant were sampled and their silica contents and silicon isotope compositions were determined. The silica contents and silicon isotope compositions of bulk and water-soluble fraction of soils were also measured. The silica contents of studied bamboo organs vary from 0.30% to 9.95%. Within bamboo plant the silica contents show an increasing trend from stem, through branch, to leaves. In bamboo roots the silica is exclusively in the endodermis cells, but in stem, branch and leaves, the silica is accumulated mainly in epidermal cells. The silicon isotope compositions of bamboos exhibit significant variation, from −2.3‰ to 1.8‰, and large and systematic silicon isotope fractionation was observed within each bamboo. The δ³⁰Si values decrease from roots to stem, but then increase from stem, through branch, to leaves. The ranges of δ³⁰Si values within each bamboo vary from 1.0‰ to 3.3‰. Considering the total range of silicon isotope composition in terrestrial samples is only 7‰, the observed silicon isotope variation in single bamboo is significant and remarkable. This kind of silicon isotope variation might be caused by isotope fractionation in a Rayleigh process when SiO₂ precipitated in stem, branches and leaves gradually from plant fluid. In this process the Si isotope fractionation factor between dissolved Si and precipitated Si in bamboo (α_pre-sol) is estimated to be 0.9981. However, other factors should be considered to explain the decrease of δ³⁰Si value from roots to stem, including larger ratio of dissolved H₄SiO₄ to precipitated SiO₂ in roots than in stem. There is a positive correlation between the δ³⁰Si values of water-soluble fractions in soils and those of bulk bamboos, indicating that the dissolved silicon in pore water and phytoliths in soil is the direct sources of silicon taken up by bamboo roots. A biochemical silicon isotope fractionation exists in process of silicon uptake by bamboo roots. Its silicon isotope fractionation factor (α_bam-wa) is estimated to be 0.9988. Considering the distribution patterns of SiO₂ contents and δ³⁰Si values among different bamboo organs, evapotranspiration may be the driving force for an upward flow of a silicon-bearing fluid and silica precipitation. Passive silicon uptake and transportation may be important for bamboo, although the role of active uptake of silicic acid by roots may not be neglected. The samples with relatively high δ³⁰Si values all grew in soils showing high content of organic materials. In contrast, the samples with relatively low δ³⁰Si values all grew in soil showing low content of organic materials. The silicon isotope composition of bamboo may reflect the local soil type and growth conditions. Our study suggests that bamboos may play an important role in global silicon cycle.     

Origin and evolution of the Steamboat Springs siliceous sinter deposit, Nevada, U.S.A.

Siliceous hot spring deposits from Steamboat Springs, Nevada, U.S.A., record a complex interplay of multiple, changing, primary environmental conditions, fluid overprinting and diagenesis. Consequently these deposits reflect dynamic geologic and geothermal processes. Two surface sinters were examined—the high terrace, and the distal apron-slope, as well as 13.11 m (43 ft) of core material from drill hole SNLG 87-29. The high terrace sinter consists of vitreous and massive-mottled silica horizons, while the distal deposit and core comprise dominantly porous, indurated fragmental sinters. Collectively, the three sinter deposits archive a complete sequence of silica phase diagenetic minerals from opal-A to quartz. X-ray powder diffraction analyses and infrared spectroscopy of the sinters indicate that the distal apron-slope consists of opal-A and opal-A/CT mineralogy; the core yielded opal-A/CT and opal-CT with minor opal-A; and the high terrace constitutes opal-C, moganite, and quartz. Mineralogical maturation of the deposit produced alternating nano–micro–nano-sized silica particle changes. Based on filament diameters of microbial fossils preserved within the sinter, discharging thermal outflows fluctuated between low-temperatures (< 35 °C, coarse filaments) and mid-temperatures ( 35–60 °C, fine filaments). Despite transformation to quartz, primary coarse and fine filaments were preserved in the high terrace sinter. AMS ¹⁴C dating of pollen from three horizons within core SNLG 87-29, from depths of 8.13 to 8.21 m (26′8″ to 26′11″), 10.13 to 10.21 m (33′3″ to 33′6″), and 14.81 to 14.88 m (48′7″ to 48′10″), yielded dates of 8684 ± 64 years, 11,493 ± 70 years and 6283 ±60 years, respectively. In the upper section of the core, the stratigraphically out-of-sequence age likely reflects physical mixing of younger sinter with quartzose sinter fragments derived from the high terrace. Within single horizons, mineralogical and morphological components of the sinter matrix were spatially patchy. Overall, the deposit was modified by sub-surface flow of alkali-chloride thermal fluids depositing a second generation of silica, and periodically, by acidic steam condensate formed during periods when the water table was low. Local faulting produced considerable fracturing of the sinter. Hence, the Steamboat Springs sinter experienced a complex history of primary and secondary hydrothermal, geologic and diagenetic events, and their inter-relationships and effects are locked within the physical, chemical and biological signatures of the deposit.     

U–Pb SHRIMP zircon geochronology and T–t–d history of the Kampa Dome, southern Tibet

Structural, petrographic and geochronologic studies of the Kampa Dome provide insights into the tectonothermal evolution of orogenic crust exposed in the North Himalayan gneiss domes of southern Tibet. U–Pb ion microprobe dating of zircons from granite gneiss exposed at the deepest levels within the dome yields concordia ²⁰⁶Pb/²³⁸U age populations of 506 ± 3 Ma and 527 ± 6 Ma, with no evidence of new zircon growth during Himalayan orogenesis. However, the granite contains penetrative deformation fabrics that are also preserved in the overlying Paleozoic strata, implying that the Kampa granite is a Cambrian pluton that was strongly deformed and metamorphosed during Himalayan orogenesis. Zircons from deformed leucogranite sills that cross-cut Paleozoic metasedimentary rocks yield concordant Cambrian ages from oscillatory zoned cores and discordant ages ranging from ca. 491–32 Ma in metamict grains. Since these leucogranites clearly post-date the metasedimentary rocks they intrude, the zircons are interpreted as xenocrysts that are probably derived from the Kampa granite. The Kampa Dome formed via a series of progressive orogenic events including regional ~ N–S contraction and related crustal thickening (D₁), predominately top-to-N ductile shearing and crustal extension (D₂), top-to-N brittle–ductile faulting and related folding on the north limb of the dome, localized top-to-S faulting on the southern limb of the dome, and crustal doming (D₃), and continued N–S contraction, E–W extension and doming (D₄). Structural and geochronologic variability amongst adjacent North Himalayan gneiss domes may reflect changes in the magnitude of crustal exhumation along the North Himalayan antiform, possibly relating to differences in the mid-crustal geometry of the exhuming fault systems.     

云南腾冲热泉金的有机地球化学研究——Ⅰ生物标志物浅析

本文主要通过对比分析研究热泉软泥中的金含量与有机质及含硫化合物的相关性。并测定泉水及软泥中含金量和软泥中有机碳含量，以及对抽提物中的饱和烃和芳烃族组分进行色谱—质谱分析，最后得出的结论：有机质的沉积环境为还原—强还原，有机质属于腐泥－腐殖型，接近和达到了成熟阶段。软泥中金含量与有机质的性质无明显相关关系，与有机碳含量也无明显相关关系，而与其成熟度相关密切。样品分析证实软泥中含硫化合物与金含量呈正相关性。对比分析了水及软泥中金含量，认为两者之间也无明显相关关系     

新疆阿尔曼太蛇绿岩时代的Nd—Sr同位素地质研究

本文通过测定采自新疆阿尔曼太兔子泉一带蛇绿岩的堆晶辉长岩、辉绿岩和安山玢岩,获得Ｓｍ－Ｎｄ等时年龄为５６１±４１Ｍａ,εＮｄ（ｔ）＝６．１,Ｒｂ－Ｓｒ等时年龄为３９２±１７Ｍａ,（８７Ｓｒ／８６Ｓｒ）ｉ＝０．７０４１,前者为蛇绿岩的形成时代,后者为蛇绿岩遭受后期变质作用的时间。札河坝－阿尔曼太蛇绿岩的形成环境可能是古亚洲洋向南俯冲引起的弧后盆地     

Barium-rich fluids and melts in a subduction environment (La Corea and Sierra del Convento mélanges,eastern Cuba)

Whole-rock compositions of muscovite-bearing amphibolite, trondhjemite, pegmatite and quartz-muscovite rocks from Sierra del Convento and La Corea mélanges (eastern Cuba), as well as mineralogy, record complex circulation of Ba-rich fluids and melts in the subduction environment. Partial melting of fluid-fluxed, MORB-derived amphibolite produced trondhjemite magmas that crystallized at depth, in some cases evolving into pegmatites. Qtz-Ms rocks probably crystallized from primary fluids derived from subducted sediments. All these rocks have elevated concentrations of large-ion lithophile elements, especially Ba (up to 11,810 ppm), presumably released from slab sediments by fluids and/or melts. Fluid–rock interaction produced crystallization of phengite in parental amphibolites. The phengite crystallized in all types of rocks is rich in Ba, with concentric zoning, characterized by Ba-rich cores and Ba-poor rims, indicating a compatible behaviour of Ba in the studied systems. Zoning in phengite is governed primarily by the celadonite (tschermak) exchange vector ((Mg,Fe)Si-(Al)_-2), with more moderate contributions of the celsian (BaAl-(KSi)_-1) and paragonite (NaK_-1) exchange vectors. Late remobilization of Ba at relatively low temperature formed retrograde celsian. The compatible behaviour of Ba in the studied rocks strengthens the importance of the stability of phengite for the transfer of LIL elements from the subduction to the volcanic arc environments.     

Geochemical characterization of surface water and spring water in SE Kashmir Valley,western Himalaya: Implications to water–rock interaction

Water samples from precipitation, glacier melt, snow melt, glacial lake, streams and karst springs were collected across SE of Kashmir Valley, to understand the hydrogeochemical processes governing the evolution of the water in a natural and non-industrial area of western Himalayas. The time series data on solute chemistry suggest that the hydrochemical processes controlling the chemistry of spring waters is more complex than the surface water. This is attributed to more time available for infiltrating water to interact with the diverse host lithology. Total dissolved solids (TDS), in general, increases with decrease in altitude. However, high TDS of some streams at higher altitudes and low TDS of some springs at lower altitudes indicated contribution of high TDS waters from glacial lakes and low TDS waters from streams, respectively. The results show that some karst springs are recharged by surface water; Achabalnag by the Bringi stream and Andernag and Martandnag by the Liddar stream. Calcite dissolution, dedolomitization and silicate weathering were found to be the main processes controlling the chemistry of the spring waters and calcite dissolution as the dominant process in controlling the chemistry of the surface waters. The spring waters were undersaturated with respect to calcite and dolomite in most of the seasons except in November, which is attributed to the replenishment of the CO₂ by recharging waters during most of the seasons.     

A Two-Dimensional Alfvén-Wave-Driven Solar Wind Model

This paper presents a two-dimensional, Alfvén-wave-driven solar wind model, in which the wave energy is assumed to cascade from the low-frequency Alfvén waves to high-frequency ion cyclotron waves and to be transferred to the solar wind protons by cyclotron resonance at the Kolmogorov rate. A typical structure in the meridional plane consisting of a coronal streamer near the Sun, a fast wind in high latitudes, and a slow wind across the heliospheric current sheet, is found. The fast wind obtained in the polar region is essentially similar to that derived by previous one-dimensional flow-tube models, and its density profile in the vicinity of the Sun roughly matches relevant observations. The proton conditions at 1 AU are also consistent with observations for both the fast and slow winds. The Alfvén waves appear in the fast- and slow-wind regions simultaneously and have comparable amplitudes, which agrees with Helios observations. The acceleration and heating of the solar wind by the Alfvén waves are found to occur mainly in the near-Sun region. It is demonstrated in terms of one-dimensional calculations that the distinct properties of the fast and slow winds are mainly attributed to different geometries of the flow tubes associated with the two sorts of winds. In addition, the 2-D and 1-D simulations give essentially the same results for both the fast and the slow winds.