The Kabanga Ni sulfide deposit, Tanzania: I. Geology, petrography, silicate rock geochemistry, and sulfur and oxygen isotopes   总被引：1，自引：0，他引：1  

Wolfgang D. Maier  Sarah-Jane Barnes  Arindam Sarkar  Ed Ripley  Chusi Li  Tim Livesey 《Mineralium Deposita》2010,45(5):419-441

The Kabanga Ni sulfide deposit represents one of the most significant Ni sulfide discoveries of the last two decades, with current indicated mineral resources of 23.23 Mt at 2.64% Ni and inferred mineral resources of 28.5 Mt at 2.7% Ni (Nov. 2008). The sulfides are hosted by a suite of ∼1.4 Ga ultramafic–mafic, sill-like, and chonolithic intrusions that form part of the approximately 500 km long Kabanga–Musongati–Kapalagulu igneous belt in Tanzania and Burundi. The igneous bodies are up to about 1 km thick and 4 km long. They crystallized from several compositionally distinct magma pulses emplaced into sulfide-bearing pelitic schists. The first magma was a siliceous high-magnesium basalt (approximately 13.3% MgO) that formed a network of fine-grained acicular-textured gabbronoritic and orthopyroxenitic sills (Mg# opx 78–88, An plag 45–88). The magma was highly enriched in incompatible trace elements (LILE, LREE) and had pronounced negative Nb and Ta anomalies and heavy O isotopic signatures (δ¹⁸O +6 to +8). These compositional features are consistent with about 20% contamination of primitive picrite with the sulfidic pelitic schists. Subsequent magma pulses were more magnesian (approximately 14–15% MgO) and less contaminated (e.g., δ¹⁸O +5.1 to +6.6). They injected into the earlier sills, resulting in the formation of medium-grained harzburgites, olivine orthopyroxenites and orthopyroxenites (Fo 83–89, Mg# _opx 86–89), and magmatic breccias consisting of gabbronorite–orthopyroxenite fragments within an olivine-rich matrix. All intrusions in the Kabanga area contain abundant sulfides (pyrrhotite, pentlandite, and minor chalcopyrite and pyrite). In the lower portions and the immediate footwall of two of the intrusions, namely Kabanga North and Kabanga Main, there occur numerous layers, lenses, and veins of massive Ni sulfides reaching a thickness of several meters. The largest amount of high grade, massive sulfide occurs in the smallest intrusion (Kabanga North). The sulfides have heavy S isotopic signatures (δ³⁴S wr = +10 to +24) that broadly overlap with those of the country rock sulfides, consistent with significant assimilation of external sulfur from the Karagwe–Ankolean sedimentary sequence. However, based partly on the relatively homogenous distribution of disseminated sulfides in many of the intrusive rocks, we propose that the Kabanga magmas reached sulfide saturation prior to final emplacement, in staging chambers or feeder conduits, followed by entrainment of the sulfides during continued magma ascent. Oxygen isotope data indicate that the mode of sulfide assimilation changed with time. The heavy δ¹⁸O ratios of the early magmas are consistent with ingestion of the sedimentary country rocks in bulk. The relatively light δ¹⁸O ratios of the later magmas indicate less bulk assimilation of the country rocks, but in addition the magmas selectively assimilated additional S, possibly through devolatization of the country rocks or through cannibalization of magmatic sulfides deposited in the conduits by preceding magma surges. The intrusions were tilted at ca. 1.37 Ga, during the Kibaran orogeny and associated synkinematic granite plutonism. This caused solid-state mobilization of ductile sulfides into shear zones, notably along the base of the intrusions where sulfide-hornfels breccias and lenses and layers of massive sulfides may reach a thickness of >10 m and can extend for several 10 s to >100 m away from the intrusions. These horizons represent an important exploration target for additional nickel sulfide deposits.  相似文献   

Combined influence of PDO and ENSO on northern Andean glaciers: a case study on the Cotopaxi ice-covered volcano,Ecuador     

Bijeesh Kozhikkodan Veettil  Éder Leandro Bayer Maier  Ulisses Franz Bremer  Sergio Florencio de Souza 《Climate Dynamics》2014,43(12):3439-3448

This paper describes the application of remote sensing in monitoring the fluctuations in one of the mountain glaciers in the Ecuadorean Andes during the past few decades using ASTER, EO-1 ALI, Landsat MSS, TM and ETM + images. Satellite images were used to calculate the snow line altitudes (SLAs) during the period 1979–2013. Cotopaxi ice covered volcano was studied as representative of Ecuadorian glaciers in the eastern cordillera. Precipitation and air temperature data from various gauging stations within the range of 30 km from the study site and monthly discharge and water level data from a gauging station were also utilized in this study. Anomalies in precipitation and temperature were found to be slightly different in the Cotopaxi region compared to nearby Antizana in the same cordillera and Chimborazo region in the western cordillera. An attempt to correlate the El Niño—southern oscillation phenomenon with the glacier fluctuations in Ecuadorian Andes was done successfully. Cold and warm regimes of Pacific Decadal Oscillation is also considered. The calculated glacier fluctuations obtained were similar to that performed on the nearby Antizana 15 in the eastern cordillera during 1995–2002. Precipitation and temperature anomalies were similar with Antizana 15. It is evident from the research that SLAs were highly fluctuated between the period of occurrence of El Niño and La Niña events. It is also seen that the glacier fluctuations show a negative mass balance trend in during the warm regime of Pacific Decadal Oscillation during the past three decades. Glaciated areas were advanced during the La Nina events in the cold regime of PDO during 1998–2002.  相似文献   

The freshwater lens of Benjamín Aceval,Chaco, Paraguay: a terrestrial analogue of an oceanic island lens     

Georg Houben  Ursula Noell  Sara Vassolo  Christoph Grissemann  Mebus Geyh  Susanne Stadler  Eduardo J. Dose  Sofia Vera 《Hydrogeology Journal》2014,22(8):1935-1952

The occurrence of a freshwater lens in the Paraguayan Chaco, 900 km away from the ocean, is reported. It is located underneath sandstone hills, surrounded by lowlands with predominantly saline groundwater. Its geometry was delineated using geoelectrical and electromagnetic investigations. The unusual height of the fresh groundwater level can be attributed to the presence of a confining layer at depth. The lens receives its recharge exclusively from rainfall during the hot and humid summer months. It predominantly contains water predating the atmospheric atomic bomb tests, some of it probably up to a thousand or more years old. The water balance shows that extraction currently does not exceed recharge in normal years. However, the available volume of groundwater leaves little room for a further increase of extraction in the future. Recharge is augmented by return flow from thousands of latrines and cess pits, and this has lead to widespread contamination of the groundwater by faecal bacteria.  相似文献   

Zircon evidence for a ~200 k.y. supereruption-related thermal flare-up in the Miocene southern Black Mountains,western Arizona,USA     

Susanne?M.?McDowellEmail author  Calvin?F.?Miller  Roland?Mundil  Charles?A.?Ferguson  Joseph?L.?Wooden 《Contributions to Mineralogy and Petrology》2014,168(1):1031

The Silver Creek caldera (southern Black Mountains, western Arizona) is the source of the 18.8 Ma, >700 km³ Peach Spring Tuff (PST) supereruption, the largest eruption generated in the Colorado River Extensional Corridor (CREC) of the southwestern United States. Within and immediately surrounding the caldera is a sequence of volcanics and intrusions ranging in age from ~19 to 17 Ma. These units offer a record of magmatic processes prior to, during, and immediately following the PST eruption. To investigate the thermal evolution of the magmatic center that produced the PST, we applied a combination of Ti-in-zircon thermometry, zircon saturation thermometry, and high-precision U–Pb CA–TIMS zircon dating to representative pre- and post-supereruption volcanic and intrusive units from the caldera and its environs. Similar to intracaldera PST zircons, zircons from a pre-PST trachytic lava (19 Ma) and a post-PST caldera intrusion (18.8 Ma) yield exceptionally high-Ti concentrations (most >20 ppm, some up to nearly 60 ppm), corresponding to calculated temperatures that exceed 900 °C. In these units, Ti-in-zircon temperatures typically surpass zircon saturation temperatures (ZSTs), suggesting the entrainment of zircon that had grown in hotter environments within the magmatic system. Titanium concentrations in younger volcanic and intrusive units (~18.7–17.5 Ma) decline through time, corresponding to an average cooling rate of 10^?3.5 °C/year. The ~200 k.y. thermal peak evident at Silver Creek caldera is spatially limited: elsewhere in the Miocene record of the northern CREC, Ti-in-zircon concentrations and ZSTs are much lower, suggesting that felsic magmas were generally substantially cooler.  相似文献   

Cross-basin differences in particulate organic carbon export and flux attenuation in the subtropical North Atlantic gyre     

Peer Helmke  Susanne Neuer  Michael W. Lomas  Maureen Conte  Tim Freudenthal 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(2):213-227

We compared in-situ and satellite-derived measures of the biological carbon pump efficiency at the two seemingly similar subtropical North Atlantic gyre time series sites, the Bermuda time series (BATS, Bermuda Atlantic time-series study and OFP, ocean flux program) in the western gyre and the ESTOC time series (European station for time-series in the ocean, Canary Islands) in the eastern gyre. Satellite-derived surface chlorophyll a was slightly lower at Bermuda compared to ESTOC (annual average of 0.10±0.04 vs. 0.14±0.05-mg-m^?3), as was satellite-derived primary production (annual average of 380±77 vs. 440±80-mg C-m^?2 d^?1). However, export production normalized to primary production (export ratio) was higher at Bermuda by a factor of 2–3 when estimated using mesopelagic traps moored at 500-m depth and by a factor of 3–4 when estimated using surface-tethered drifting traps. When averaged seasonally, flux at BATS was highest in spring (March, April, May) at all depths followed by summer (June, July, August) and decreasing towards fall, but this seasonality was less visible at ESTOC. Seasonal comparison showed the fastest flux attenuation at Bermuda in winter and spring, coinciding with the highest POC flux. POC/PIC ratios derived from the moored traps were significantly higher at BATS than at ESTOC in fall and winter, but this difference was not significant in spring (p>0.05). This study shows that while the western and eastern Atlantic subtropical gyres have similar rates of primary production, the biological carbon pump differs between the two provinces. Higher new nutrient input observed at Bermuda compared to ESTOC might explain part of the difference in export ratio but alone is insufficient. Greater winter mixed-layer depths and higher mesoscale eddy activity at Bermuda resulting in pulsed production events of labile organic matter might explain both the higher export flux and export ratios found at Bermuda.  相似文献   

Whipple telescope observations of LS I +61 303: 2004–2006     

A. Smith  R. W. Atkins  S. Bradbury  O. Celik  Y. C. K. Chow  P. Cogan  C. Dowdall  S. J. Fegan  P. Fortin  D. Gall  G. H. Gillanders  J. Grube  K. J. Gutierrez  T. A. Hall  D. Hanna  J. Holder  D. Horan  S. B. Hughes  T. B. Humensky  I. Jung  P. Kaaret  G. Kenny  M. Kertzman  D. B. Kieda  A. Konopelko  H. Krawczynski  F. Krennrich  M. J. Lang  S. Le Bohec  G. Maier  J. Millis  P. Moriarty  R. A. Ong  J. S. Perkins  K. Ragan  G. H. Sembroski  J. A. Toner  L. Valcarcel  V. V. Vassiliev  R. G. Wagner  S. P. Wakely  T. C. Weekes  R. J. White  D. A. Williams 《Astrophysics and Space Science》2007,309(1-4):299-303

In this paper we present the results of the past two years observations on the galactic microquasar LS I +61 303 with the Whipple 10 m gamma-ray telescope. The recent MAGIC detection of the source between 200 GeV and 4 TeV suggests that the source is periodic with very high energy (VHE) gamma-ray emission linked to its orbital cycle. The entire 50-hour data set obtained with Whipple from 2004 to 2006 was analyzed with no reliable detection resulting. The upper limits obtained in the 2005–2006 season covered several of the same epochs as the MAGIC Telescope detections, albeit with lower sensitivity. Upper limits are placed on emission during the orbital phases of 0→0.1 and 0.8→1, phases which are not included in the MAGIC data set.   相似文献   

Synthetic Spectra of Long-Period Variables: A First Comparison with ISO Observations     

Rita Loidl  Josef Hron  Susanne Höfner  Uffe G. ørgensen  Bernhard Aringer  Franz Kerschbaum 《Astrophysics and Space Science》1997,251(1-2):243-246

Exploratory synthetic spectra were computed for carbon-rich long-period variables. We used dynamic model atmospheres of Höfner &; Dorfi (1997) and calculated partial pressures, absorption- and scattering coefficients as input for the spectral synthesis code of Jørgensen et al. (1992). First ISO SWS-observations of the carbon-Mira T Dra are compared with our synthetic spectra.  相似文献   

A consistent combination of GNSS and SLR with minimum constraints   总被引：1，自引：1，他引：0  

Susanne Glaser  Mathias Fritsche  Krzysztof Sośnica  Carlos Javier Rodríguez-Solano  Kan Wang  Rolf Dach  Urs Hugentobler  Markus Rothacher  Reinhard Dietrich 《Journal of Geodesy》2015,89(12):1165-1180

  相似文献   

The Qso Hosts I Zw 1 and 3C 48: Prototypes of a Merger-Driven Quasar Evolution?     

Julia Scharwächter  Andreas Eckart  Susanne Pfalzner  Jens Zuther  Melanie Krips  Eva Schinnerer  Johannes Staguhn 《Astrophysics and Space Science》2005,295(1-2):101-106

I Zw 1 and 3C 48 are two neighboring template objects at a later stage of the hypothesized merger-driven evolutionary sequence from ultra-luminous infrared galaxies (ULIRGs) to quasi-stellar objects (QSOs). Since galaxy mergers are assumed to trigger the evolution, it is important to confirm the merger properties of transitionary objects. Using multi-wavelength observations and N-body simulations, the merger histories of I Zw 1 and 3C 48 have been investigated in two separate case studies. Here, the results from both studies are compared and their relevance for the evolutionary hypothesis is discussed.This research is partly based on observations with ISAAC at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) under projects 67.B-0009 and 67.B-0019.  相似文献   

Mare basalt units and the compositions of their magmas     

Alan B. Binder  Manfred A. Lange  Heinz-Jürgen Brandt  Susanne Kähler 《Earth, Moon, and Planets》1980,23(4):445-481

A synthesis of the majority of the available mare basalt data shows that basalts and glasses came from 28 different volcanic units. The compositions of the magmas of 12 of these units can be calculated with a high degree of confidence. Reasonable estimates can be made for the compositions of nine of the remaining units. In addition, the compositions of three general magma types can be obtained from data derived from the Luna 16, Luna 24, and Apollo 17 fines. The compositional data presented provide a firm basis for the further study of the characteristics of the mare basalt magma source region.  相似文献