Multi-stage melt–rock interaction in the Mt. Maggiore (Corsica, France) ophiolitic peridotites: microstructural and geochemical evidence

Spinel and plagioclase peridotites from the Mt.Maggiore (Corsica, France) ophiolitic massif record a composite asthenosphere–lithosphere history of partial melting and subsequent multi-stage melt–rock interaction. Cpx-poor spinel lherzolites are consistent with mantle residues after low-degree fractional melting (F = 5–10%). Opx + spinel symplectites at the rims of orthopyroxene porphyroclasts indicate post-melting lithospheric cooling (T = 970–1,100°C); this was followed by formation of olivine embayments within pyroxene porphyroclasts by melt–rock interaction. Enrichment in modal olivine (up to 85 wt%) at constant bulk Mg values, and variable absolute REE contents (at constant LREE/HREE) indicate olivine precipitation and pyroxene dissolution during reactive porous melt flow. This stage occurred at spinel-facies depths, after incorporation of the peridotites in the thermal lithosphere. Plagioclase-enriched peridotites show melt impregnation microtextures, like opx + plag intergrowths replacing exsolved cpx porphyroclasts and interstitial gabbronoritic veinlets. This second melt–rock interaction stage caused systematic chemical changes in clinopyroxene (e.g. Ti, REE, Zr, Y increase), related to the concomitant effects of local melt–rock interaction at decreasing melt mass, and crystallization of small (<3%) trapped melt fractions. LREE depletion in minerals of the gabbronoritic veinlets indicates that the impregnating melts were more depleted than normal MORB. Preserved microtextural evidence of previous melt–rock interaction in the impregnated peridotites suggests that they were progressively uplifted in response to lithosphere extension and thinning. Migrating melts were likely produced by mantle upwelling and melting related to extension; they were modified from olivine-saturated to opx-saturated compositions, and caused different styles of melt–rock interaction (reactive spinel harzburgites, vs. impregnated plagioclase peridotites) depending on the lithospheric depths at which interaction occurred. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A new bivariate Gamma distribution generated from functional scale parameter with application to drought data

Univariate and bivariate Gamma distributions are among the most widely used distributions in hydrological statistical modeling and applications. This article presents the construction of a new bivariate Gamma distribution which is generated from the functional scale parameter. The utilization of the proposed bivariate Gamma distribution for drought modeling is described by deriving the exact distribution of the inter-arrival time and the proportion of drought along with their moments, assuming that both the lengths of drought duration (X) and non-drought duration (Y) follow this bivariate Gamma distribution. The model parameters of this distribution are estimated by maximum likelihood method and an objective Bayesian analysis using Jeffreys prior and Markov Chain Monte Carlo method. These methods are applied to a real drought dataset from the State of Colorado, USA.     

Identification and assessment of groundwater flow and storage components of the relict Schöneben Rock Glacier,Niedere Tauern Range,Eastern Alps (Austria)

More than 2,600 relict rock glaciers are known in the Austrian Alps but the knowledge of their hydraulic properties is severely limited. The relict Schöneben Rock Glacier (Niedere Tauern Range, Austria), with an extension of 0.17 km², was investigated based on spring data (2006–2014) and seismic refraction survey. Spring-discharge hydrographs and natural and artificial tracer data suggest a heterogeneous aquifer with a layered internal structure for the relict rock glacier. The discharge behavior exhibits a fast and a delayed flow component. The spring discharge responds to recharge events within a few hours but a mean residence time of several months can also be observed. The internal structure of the rock glacier (up to several tens of meters thick) consists of: an upper blocky layer with a few meters of thickness, which lacks fine-grained sediments; a main middle layer with coarse and finer-grained sediments, allowing for fast flow; and an approximately 10-m-thick basal till layer as the main aquifer body responsible for the base flow. The base-flow component is controlled by (fine) sandy to silty sediments with low hydraulic conductivity and high storage capacity, exhibiting a difference in hydraulic conductivity to the upper layer of about three orders of magnitude. The high storage capacity of relict rock glaciers has an impact on water resources management in alpine catchments and potentially regulates the risk of natural hazards such as floods and related debris flows. Thus, the results highlight the importance of such aquifer systems in alpine catchments.     

The geography of urban greenhouse gas emissions in Asia: A regional analysis

This paper aims to advance two objectives: (1) identify and explore greenhouse gas emissions from urban areas in Asia at the regional level; and (2) explore covariates of urban greenhouse gas emissions. We use the Emissions Database for Global Atmospheric Research estimates for carbon dioxide, methane, nitrous oxide, and sulfur hexafluoride from 14 source activities for the year 2000, which are allocated on a 1/10° global grid. We extract emissions for 3535 urban extents all with populations over 50,000, accounting for approximately 91% of the region's urban population. We use regression analysis to associate emissions with urban area and growth, economic, and biophysical characteristics. Our findings suggest that urban areas account for between 30 and 38% of total anthropogenic greenhouse gas emissions for the region and that emission per capita averages from urban areas are lower than those at the national level. Important covariates for total urban greenhouse gas emissions include population size, density and growth rate, income per capita, development status and elevation. This is a first and preliminary assessment of regional baseline trends using these data and this top-down analysis.     

Case studies on the origin of basalt

The simplified model of basalt genesis described in Part I of this series, equilibrium partial melting followed by Rayleigh-type fractional crystallization, is applied to a stratigraphically controlled sequence of basalt flows from Kohala volcano. Major-element compositions were determined for 52 samples and show a time-stratigraphic progression from tholeiites through transitional basalts to alkali basalts. Twenty-six of these samples were analyzed by isotope dilution for K, Rb, Cs, Sr, Ba and the REE, 13 for⁸⁷Sr/⁸⁶Sr, and 19 for Co, Cr, Ni and V by atomic absorption. After a simple, first-order correction for the effects of fractional crystallization (involving mostly olivine and aluminous clinopyroxene), the major element concentrations cluster tightly, and the incompatible trace elements show monotonic increases in concentration as a function of stratigraphic height. The process identification plot shows that all the (fractionation corrected) melt compositions can be explained by equilibrium partial melting of compositionally identical batches of source material. The REE and Sr are fractionated because of the presence of residual clinopyroxene. Garnet may also be present but in much smaller amounts. In this respect our results differ significantly from those of Leeman et al. (1980). The calculated chondrite-normalized REE patterns of the source are nearly flat to slightly convex upward. Therefore there is no need to invoke special mechanisms, such as metasomatic REE preenrichment of the source, in order to explain the petrogenesis of the suite of lavas. Specifically, Ce concentrations ranging from 20 to 250 times chondritic are all explained by the same calculated source pattern having a chondrite-normalized ratio of Ce/Sm=0.9±0.2. However, the normalized ratio Ce/Ba?2 shows that the source is not simply primitive mantle.     

Die Berechnung der Angströmschen Trübungskonstanten aus Sonnenstrahlungsmessungen in verschiedenen Filtergebieten

Zusammenfassung Zur Bearbeitung von mehreren hundert Messungen der direkten Sonnenstrahlung mit fünf verschiedenen Farbfiltern werden Neuberechnungen derAngstr?mschen Formel (Gleichung 1) für die einzelnen Wellenl?ngen mit insgesamt 144 verschiedenen Werten für die Luftmassem, den Wellenl?ngenexponenten α der Zerstreuungsfunktion, dem Trübungskoeffizienten β und dem WasserdampfgehaltW der Atmosph?re durchgeführt. Es wurde hierbei festgestellt, da? es m?glich ist, die Filterdifferenzen für die Spektralbereiche Blau, Gelb, Rot und zwei Infrarot durch einfache algebraische Formeln darzustellen (Gleichungen 3 und 5), aus denen α und β errechnet werden k?nnen (Gleichungen 6 und 7). Bezüglich des Wasserdampfgehaltes ergab sich, da? es nicht m?glich ist, die Wasserdampfabsorption durch ein einziges Gliedf(mW) darzustellen, das additiv zu dem Zerstreuungsterm derAngstr?mschen Formel hinzugefügt wird, wie es bisher meist geschah. Es wurde eine neue Fassung des additiven Gliedes für die Wasserdampfabsorptionf(α, β, m, mW) berechnet und durch eine Formel (12) wiedergegeben. Auf die Bedeutung der neuen Absorptionsfunktion des Wasserdampfes für die vom Verfasser kürzlich entwickelte Kalibrierung der Aktinometer aus dem Beobachtungsmaterial wird eingegangen (Gleichung 14). Zum Schlu? werden neue Gleichungen (20) entwickelt, die die Bestimmung von α im langwelligen Spektralgebiet der Sonnenstrahlung erm?glichen, in dem auch der Wasserdampf absorbiert. Dies ist wichtig, weil das α, das bisher nur aus dem kurzwelligen Teil des Sonnenspektrum bestimmt werden konnte, nicht notwendig übereinzustimmen braucht mit dem α im langwelligen Gebiet.

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Summary DeterminingAngstr?m’s turbidity constants from several hundred sets of readings of the solar radiation with five different glass filters,Angstr?m’s formula (equ. 1) was calculated for a total of 144 different values of air massesm, the wavelength exponent α of the scattering function, the turbidity coefficient β and water vapour content W of the atmosphere. It was found that it is possible to express the filter differences belonging to the spectral ranges blue, yellow, red, and two infrared ranges with simple algebraic formulae (equ. 3 and 5) which allow α and β to be calculated (equ. 6 and 7). With respect to the water vapour content it was pointed out that it is impossible to express, in the usual way, the water vapour absorption by a single termf(mW), which is added to the scattering term ofAngstr?m’s formula. A new form of the water vapour absorption was calculated and expressed as a formula (12). The significance of the new water vapour absorption function was discussed with reference to the author’s newly developed actinometer calibration from observational data (equ. 14). In conclusion new equations (20) were derived enabling to be determined in the long wave range of solar radiation, i.e. where the water vapour absorption exists. This is important because so far α could only be determined from the short wave range of solar radiation, which does not necessarily agree with that of the long wave range.

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Dr. Fritz H. W. Albrecht, 10, Belgravia Ave., Box Hill North E 12,Melbourne.     

Tri- and tetraterpenoid hydrocarbons in the Messel oil shale

The high molecular weight constituents of the branched and cyclic hydrocarbon fraction of the Messel oil shale (Eocene) have been examined by high resolution gas chromatography and combined gas chromatography-mass spectrometry. The following compounds are present: perhydrolycopene (1; lycopane), together with one or more unsaturated analogues with the same skeleton; a series of 4-methylsteranes (2c) in higher abundance than their 4-desmethyl analogues; two series of pentacyclic triterpanes, one series (C₂₇-C₃₂) based on the hopane structure (3a-e), and the other (C₂₇-C₃₁) based on the 17α-H hopane structure (3a-d, 17αH); and an intact triterpene hop-17 (21)-ene [3c, Δ 17(21)]. Only two additional triterpanes were detected in minor concentrations, viz. 30-normoretane (3b, 21αH) and a C₃₁ triterpane based on the hopane/lupane-type skeleton. The presence of these compounds suggests a significant microbial contribution to the forming sediment. Comparison of the tri- and tetraterpenoid hydrocarbons with those of the Green River Shale indicates differences in the organisms contributing to the two sediments.     

Fractionation corrections for mixed-isotope spikes of Sr, K, and Pb

Methods are given to correct for isotopic fractionation in the determination of the isotopic composition of mixed-isotope spikes. The simplest method, applicable to Sr, utilizes the fact that the fractionated, measured isotope ratios of a critical three-isotope mixture lie exactly on a tie line that connects the true compositions of spike and normal element. Three-isotope elements that do not have critical mixtures require independent determination of the weight ratio of spike to normal element. A new analytic solution together with a straightforward graphical representation is given to the four-isotope problem.