The Petrology and Origin of the Tertiary Lundy Granite (Bristol Channel, UK)

The British Tertiary Volcanic Province (BTVP) comprises within-platecentral igneous complexes associated with plateau lavas andregional dyke swarms. Lundy is the southernmost complex of theBTVP and comprises granite ({small tilde}90%) emplaced intodeformed Devonian sedimentary rocks within the Hercynian Cornubiangranite province of southwest England. The complex is intrudedby a northwest-southeast trending dyke swarm. In common withother BTVP igneous complexes, Lundy is associated with positivegravity and magnetic anomalies which are interpreted in termsof the presena of an underlying basic intrusion at shallow depth,with a volume exceeding that of the overlying granite. The Lundy intrusion is a coarse-grained megacrystic granitecontaining up to 20% alkali feldspar megacrysts in a coarse-grainedgroundmass composed of alkali feldspar, quartz, lithium-bearingmuscovite, and ‘biotite’ (lithian siderophyllite),with a range of aaxssory minerals. The main granite has a coarse-grained(locally miarolitic) pegmatitic facies and is intruded by thinsheets and veins of fine-grained aplite and microgranite. Themineralogy indicates crystallization of the Lundy granite froma highly fractionated H₂O- and halogen-rich magma at a relativelyshallow crustal level. The main Lundy granite is a peraluminous leucogranite with Na₂O=3–4%,K₂O{small tilde}5%, low TiO₂, MeO, CaO, Zr, and Sr, and highRb and Rb/Sr in comparison with many other peralurninous granites,including those from the Cornubian batholith and the BTVP. Anew Rb-Sr whole-rock isochron for the granite yields an ageof 58?7?1?6 Ma with an initial ⁸⁷Sr/86Sr of 0?715?0?006. _Ndvalues for the granite (–0?9 to –1?9) plot betweencontemporaneous mantle (positive _Nd and Cornubian granites (_Nd=ca.–11). The trace element data (Rb, Y, Nb) show affinities with syn-collisionand within-plate granites. As the Sr isotope data indicate amajor crustal component, and the Nd isotope data suggest bothmantle and crustal components, we propose that the Lundy graniteis derived from a parental magma comprising crustal components(derived from a similar source to that of the Cornubian granitebatholith) and a mantle-derived component (derived from a differentiateof contemporaneous basaltic magma This magma experienced fractionalcrystallization of plagioclase, alkai feldspar, Fe-Mg minerals,and REE-bearing accessory minerals before emplacement, and theLundy granite experienced further in situ fractional crystallization,associateded with crustal contamination by the Devonian shaleafter emplacement.     

Geochemical characteristics of sphagnum brown coal — A possible oil-generating precursor

A preliminary study of newly discovered sphagnum brown coal from the Jingsuo Basin, Yunnan Province, China, which is quite rich in montan wax, indicates the predominance of highern-alkane homologues and aromatized triterpenoid components. Aromatic hydrocarbons are composed mainly of pentacyclic and tetracyclic di-, tri- and tetra-aromatic components, which are obviously diagenetically related to higher plant-derived triterpenoids naturally occurring in the biosphere. Because the sphagnum brown coal still remains in the highly immature stage, it seems that the progressive diagenetic aromatization of the higher plant-derived triterpenoids may start at a very early stage.     

Recycling in the Puerto Rican mantle wedge, Greater Antilles Island Arc

Abstract The initial volcanic phase of Cretaceous island arc strata in central Puerto Rico, at the eastern end of the extinct Greater Antilles Arc, comprises a 6‐km thick pile of lava and volcanic breccia (Río Majada Group). Preserved within the sequence is a conspicuous shift in absolute abundances of the more incompatible elements, including Th, Nb, and the light rare earth elements (LREE: La, Ce, Pr and Nd). The compositional shift is marked by a decrease in La/Sm from averages of 2.11 in the lowest third of the pile (Formation A) to 1.48 at the top (Formation C), and by a distinctive flattening of LREE segments of chondrite‐normalized REE patterns. i⁸⁷Sr/⁸⁶Sr and ?_Nd average about 0.7035 and 8.2, respectively, in early Formation A basalts. These ranges normally overlap samples from later Formations B and C. Isotope compositions of the latter group are more variable, however, and several samples are considerably more radiogenic than Formation A basalts, such that i⁸⁷Sr/⁸⁶Sr averages almost 0.7042 while ?_Nd‐values decrease to 7.5 in Formation B and C basalts. Theoretical models of non‐modal melting processes in both amphibole peridotite and spinel lherzolite sources provide insight into the origin of depleted Th, Nb, and LREE abundances in Puerto Rican basalts. Low Nb concentrations less than normal mid‐oceanic ridge basalts in Formation A basalts indicate the wedge was slightly depleted by low‐volume decompression fusion due to induced convection in the back‐arc region prior to entry of the source into the arc melting zone. However, depleted patterns in Formation C basalts cannot be generated by relatively greater degrees of decompression fusion in the back‐arc, because addition of the La‐enriched slab‐derived component to more depleted source material invariably produces elevated rather than decreased La/Sm. Refluxing of Formation A harzburgitic residua is similarly precluded. In contrast, the observed patterns are readily reproduced by multistage melting models involving hybridized sources containing normal Formation A lherzolite source material blended with recycled, unrefluxed harzburgite residua. Successful models require hybrid sources containing large volumes of recycled harzburgite (up to 50%) during generation of Formation C basalts. Slightly elevated radiometric Sr and Nd isotopes in a few flows from Formation C are attributed to partial refluxing of the hybrid sources within the wedge.     

U-Pb isotopic dating of zircons (SHRIMP-II) from granulites of the Ol’khon region of Western Baikal area

Doklady Earth Sciences -     

The fast variable maser source IRAS 05338-0624

A new OH maser was detected in January 2008 toward the infrared source IRAS 05338-0624 in the dark cloud L1641N. The observations were carried out on the Nan cay Radio Telescope (France) in the 1667 and 1665 MHz OH lines. In the spectra of both lines, thermal OH emission from the surrounding molecular cloud is present at radial velocities V _LSR = 6–9 km/s. In addition, a narrow maser feature is present in both lines at V _LSR = 2 km/s in the profiles obtained on January 7, 2008; the peak flux densities at 1667 and 1665 MHz are 1.5 and 0.4 Jy, respectively. No OH maser emission was detected in February–July 2008. Then, a maser feature was again observed in the 1665 MHz line on August 20, 2008, at the same velocity as in January, V _LSR = 2 km/s, with a peak flux density of 0.4 Jy. No 1667 MHz counterpart was observed with an upper limit of ～0.1 Jy. Emission in both OH lines was again absent on September 18. The source was also observed in the H₂O line at λ = 1.35 cm on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) on February 7 and 13, 2008. In both cases, a maser feature was detected at V _LSR = 9 km/s, with peak flux densities of 35 and 15 Jy, respectively. After the its apparent absence in April, H₂O maser emission reappeared on May 14, 2008, at V _LSR = 7 km/s with a flux density of about 15 Jy. The history of previous observations of the object in the OH and H₂O lines is traced. The maser displays strong and rapid flux variability in the lines of both molecules, as is typical of young low-luminosity stellar objects at early stages of their evolution.     

Distribution and possible sources of organochlorine residues in sediments of a large urban estuary,Port Jackson,Sydney

Sydney Harbour is surrounded by a large capital city of about four million people and its highly urbanised (86%) catchment supports a substantial industrial base and an extensive transport infrastructure. Large commercial and naval ports occupy the waterway and the harbour is an important recreational area. Surficial sediment in Sydney Harbour contains high concentrations of PCBs, HCB, total chlordane, total DDT, aldrin, dieldrin, heptachlor and heptachlor‐epoxide, but low concentrations of lindane. PCBs, total chlordane, and to a lesser extent dieldrin, are most elevated in sediment in creeks on the southern shores of the harbour suggesting sources within older, highly urbanised/industrialised catchments of western‐central Sydney. There are high concentrations of total DDT and HCB in sediments of the upper harbour and Homebush Bay suggesting that chemical industries on the shores of the estuary in this area are sources of these contaminants. Although no sediment quality guidelines apply in Australia, empirically derived biological effects criteria suggest that sediment over extensive areas of Sydney Harbour may have an adverse impact on biota. Especially of concern are sediments containing high concentrations of chlordane and DDT.     

Groundwater acidification in Triassic sandstones: prediction with MAGIC modelling

 Acidification of groundwater lags behind acid deposition due to the relatively long water residence time in conjunction with various buffering processes in the soil zone and deeper aquifer (chemical weathering, cation exchange, sulfate sorption, and N uptake by the biomass). Extensive field data from eight forested catchments in the Bunter Sandstone of the Black Forest, including results from water budget studies and hydrochemical analysis of stream and spring waters, were used to simulate the future evolution of ground-water acidification with the MAGIC model. The present acid deposition exceeds the “critical load” (here meaning buffering due to chemical weathering and protonation of organic acids) in six of eight catchments. Two catchments are well buffered because they contain carbonate-bearing layers in the Upper Bunter sandstone. Transient buffering (i.e., cation exchange, N uptake, the sulfate sorption) thus far prevents worse acidification, but this effect will decline in the future. For one of the poorly buffered catchments (Seebach), a two-layer simulation was carried out, based on extensive data from 10 years of measurements. Validation of the long-term simulations by hydrochemical and soil data was hampered by strong annual variations but generally supported by paleolimnological studies. In the future, reductions in the S deposition by 20% and the N deposition by 10% up to the year 2030 are assumed as the most probable scenario. N uptake through soil and vegetation will come to an end as suggested by decreasing C/N ratios of the organic matter. This process is arbitrarily included in the simulations. In the periglacial soil layer, acidification will decrease until the year 2030 and then approach a steady-state condition. In the fractured aquifer, acidification will also proceed at a decreasing rate; however, sulfate desorption up to the year 2130, the end of simulated period, will prevent earlier remediation. Despite a significant reduction in S deposition since the mid-1980s, further efforts are necessary to reduce the emission of acidifying substances. Liming in the recharge area is partially effective to ameliorate “shallow” groundwater but largely fails to ameliorate “deeper” groundwater in the sandstone aquifer. Received: 30 July 1996/Accepted: 23 January 1997     

Geology and geochemistry of archaean felsic metavolcanic rocks of the Eastern Part of the Kolar greenstone belt, Dharwar craton, India: Implications for their petrogenesis and geodynamic setting

In the Kolar greenstone belt of the Dharwar craton, felsic metavolcanics are encountered prominently in its eastern region around Surapalli and Marikoppa. These felsic volcanic rocks are essentially homogeneous and their bulk mineralogy is almost the same. They consist of phenocrysts of quartz and feldspar, set in a fine-grained quartzo-feldspathic groundmass. They are calc-alkaline rhyolite in composition, and are characterized by high SiO₂ (av. 75.74 wt.%), moderate Al₂O₃ (av. 11.84 wt.%), Na₂O (av. 3.55 wt.%), K2O (av. 3.26 wt%) contents and low Mg# (av. 6.07), Cr (av. 8 ppm), Ni (av. 8 ppm), Sr (av. 331 ppm.), Y (av. 7 ppm), Yb (av. 0.87 ppm) and Nb/Ta (av. 6.40) values, suggesting Tonalite-Trondhjemite-Granodiorite (TTG) affinity for these felsic volcanics. They are strongly fractionated [(La/Yb)_N? = 14.41–48.70] with strong LREE enrichment [(La/Sm)_N = 2.50-3.59] and strong HREE depletion [(Gd/Yb)_N = 1.34–2.77] with positive Eu anomaly. The regional geological set-up, petrographic and geochemical characteristics suggest that these felsic volcanics probably were derived by partial melting of a subducting basalt slab at shallow depth without much involvement of mantle wedge in an island arc geodynamic setting.     

Predicted changes in fire weather suggest increases in lightning fire initiation and future area burned in the mixedwood boreal forest

Forecasting future fire activity as a function of climate change is a step towards understanding the future state of the western mixedwood boreal ecosystem. We developed five annual weather indices based on the Daily Severity Rating (DSR) of the Canadian Forest Fire Weather Index System and estimated their relationship with annual, empirical counts of lightning fire initiation for 588 landscapes in the mixedwood boreal forest in central-eastern Alberta, Canada from data collected between 1983 and 2001 using zero-inflated negative binomial regression models. Two indices contributed to a parsimonious model of initiation; these were Seasonal Severity Rating (SSR), and DSR-sequence count. We used parameter estimates from this model to predict lightning fire initiation under weather conditions predicted in 1 × CO₂ (1975–1985), 2 × CO₂ (2040–2049) and 3 × CO₂ (2080–2089) conditions simulated by the Canadian Regional Climate Model (CRCM). We combined predicted initiation rates for these conditions with existing empirical estimates of the number of fire initiations that grow to be large fires (fire escapes) and the fire size distribution for the region, to predict the annual area burned by lightning-caused fires in each of the three climate conditions. We illustrated a 1.5-fold and 1.8-fold increase of lightning fire initiation by 2040–2049 and 2080–2089 relative to 1975–1985 conditions due to changes in fire weather predicted by the CRCM; these increases were calculated independent of changes in lightning activity. Our simulations suggested that weather-mediated increases in initiation frequency could correspond to a substantial increase in future area burned with 1.9-fold and 2.6-fold increases in area burned in 2040–2049 and 2080–2089 relative to 1975–1985 conditions, respectively. We did not include any biotic effects in these estimates, though future patterns of initiation and fire growth will be regulated not only by weather, but also by vegetation and fire management.     

Changes in current regime and turbidity in response to a freshwater pulse in the eastmain estuary

In September 1984, the freshwater input to the Eastmain River (James Bay, Canada) was increased by a factor of 50 over a 6-d period during a controlled reservoir discharge. Changes to the current, salinity and turbidity regimes were monitored during the peak runoff. Estuarine salinity values fell rapidly with increasing mean flow, as did the amplitude of the semi-diurnal tidal currents. A large increase in bottom shear stress dispersed the settled suspension layer into the water column, raising concentrations of suspended matter in the estuary by a factor of 4 in 3 d. The peak values exceeded 150 mg I^?1. This led to erosion of the river silt deposits, with the export of an estimated 6 × 10⁴ metric tons of sediments. After the reduction of discharge, current values returned to their normal range within a day, whereas upstream salinity intrusion occurred at a slower rate. Horizontal diffusivities of about 100 m² s^?1 were required to match the observed lag.