Erupted cumulate fragments in rhyolites from Lipari (Aeolian Islands)     

Francesca?ForniEmail author  Ben?S.?Ellis  Olivier?Bachmann  Federico?Lucchi  Claudio?A.?Tranne  Samuele?Agostini  Luigi?Dallai 《Contributions to Mineralogy and Petrology》2015,170(5-6):49

Over the last ~267 ky, the island of Lipari has erupted magmas ranging in compositions from basaltic andesites to rhyolites, with a notable compositional gap in the dacite field. Bulk geochemical and isotopic compositions of the volcanic succession, in conjunction with major and trace elemental compositions of minerals, indicate that the rhyolites were dominantly generated via crystal fractionation processes, with subordinate assimilation. Radiogenic (Sr, Nd, and Pb) and stable (O) isotopes independently suggest ≤30 % of crustal contamination with the majority of it occurring in mafic compositions, likely relatively deep in the system. Within the rhyolites, crystal-rich, K₂O-rich enclaves are common. In contrast to previous interpretations, we suggest that these enclaves represent partial melting, remobilization and eruption of cumulate fragments left-over from rhyolite melt extraction. Cumulate melting and remobilization is supported by the presence of (1) resorbed, low-temperature minerals (biotite and sanidine), providing the potassic signature to these clasts, (2) reacted Fo-rich olivine, marking the presence of mafic recharge, (3) An_38–21 plagioclase, filling the gap in feldspar composition between the andesites and the rhyolites and (4) strong enrichment in Sr and Ba in plagioclase and sanidine, suggesting crystallization from a locally enriched melt. Based on Sr-melt partitioning, the high-Sr plagioclase would require ~2300 ppm Sr in the melt, a value far in excess of Sr contents in Lipari and Vulcano magmas (50–1532 ppm) but consistent with melting of a feldspar-rich cumulate. Due to the presence of similar crystal-rich enclaves within the rhyolites from Vulcano, we propose that the eruption of remobilized cumulates associated with high-SiO₂ rhyolites may be a common process at the Aeolian volcanoes, as already attested for a variety of volcanic systems around the world.  相似文献   

Uncertainty propagation in wildland fire behaviour modelling     

Andreas Bachmann  Britta Allgöwer 《International journal of geographical information science》2013,27(2):115-127

Rothermel's model is the most widely used fire behaviour model in wildland fire research and management. It is a complex model that considers 17 input variables describing fuel type, fuel moisture, terrain and wind. Uncertainties in the input variables can have a substantial impact on the resulting errors and have to be considered, especially when the results are used in spatial decision making. In this paper it is shown that the analysis of uncertainty propagation can be carried out with the Taylor series method. This method is computationally cheaper than Monte Carlo and offers easy-to-use, preliminary sensitivity estimations.  相似文献   

IVS contribution to ITRF2014   总被引：5，自引：4，他引：1  

Sabine Bachmann  Daniela Thaller  Ole Roggenbuck  Michael Lösler  Linda Messerschmitt 《Journal of Geodesy》2016,90(7):631-654

  相似文献   

U‐Th Zircon Dating by Laser Ablation Single Collector Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS)          下载免费PDF全文

Marcel Guillong  Jakub T. Sliwinski  Axel Schmitt  Francesca Forni  Olivier Bachmann 《Geostandards and Geoanalytical Research》2016,40(3):377-387

Zircon crystals in the age range of ca. 10–300 ka can be dated by ²³⁰Th/²³⁸U (U‐Th) disequilibrium methods because of the strong fractionation between Th and U during crystallisation of zircon from melts. Laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analysis of nine commonly used reference zircons (at secular equilibrium) and a synthetic zircon indicates that corrections for abundance sensitivity and dizirconium trioxide molecular ions (Zr₂O₃⁺) are critical for reliable determination of ²³⁰Th abundances in zircon. When corrected for abundance sensitivity and interferences, mean activity ratios of (²³⁰Th)/(²³⁸U) for nine reference zircons analysed on five different days averaged 0.995 ± 0.023 (95% confidence weighted by data‐point uncertainty only, MSWD = 1.6; n = 9), consistent with their U‐Pb ages > 4 Ma that imply equilibrium for all intermediate daughter isotopes (including ²³⁰Th) within the ²³⁸U decay chain. U‐Th zircon ages generated by LA‐ICP‐MS without mitigating (e.g., by high mass resolution) or correcting for abundance sensitivity and molecular interferences on ²³⁰Th are potentially unreliable. To validate the applicability of LA‐ICP‐MS to this dating method, we acquired data from three late Quaternary volcanic units: the 41 ka Campanian Ignimbrite (plutonic clasts), the 161 ka Kos Plateau Tuff (juvenile clasts) and the 12 ka Puy de Dôme trachyte lava (all eruption ages by Ar/Ar, with zircon U‐Th ages being of equal or slightly older). A comparison of the corrected LA‐ICP‐MS results with previously published secondary ion mass spectrometry (SIMS) data for these rocks shows comparable ages with equivalent precision for LA‐ICP‐MS and SIMS, but much shorter analysis durations (~ 2 min vs. ~ 15 min) per spot with LA‐ICP‐MS and much simpler sample preparation. Previously undated zircons from the Yali eruption (Kos‐Nisyros volcanic centre, Greece) were analysed using this method. This yielded a large age spread (~ 45 to > 300 ka), suggesting significant antecryst recycling. The youngest zircon age (~ 45 ± 10 ka) provides a reasonable maximum estimate for the eruption age, in agreement with the previously published age using oxygen isotope stratigraphy (~ 31 ka).  相似文献   

Crustal thickness,rift‐drift and potential links to key global events     

Timothy Paulsen  Chad Deering  Jakub Sliwinski  Snehamoy Chatterjee  Olivier Bachmann  Marcel Guillong 《地学学报》2021,33(1):12-20

Orogenic crustal thickening leads to increased continental elevation and runoff into the oceans, but there are fundamental uncertainties in the temporal patterns of thickening through Earth history. U‐Pb age and trace element data in detrital zircons from Antarctica are consistent with recent global analyses suggesting two dominant peaks in average crustal thickness from ~2.6 to 2.0 Ga and ~0.8 to 0.5 Ga. Shifts in marine carbonate ⁸⁷Sr/⁸⁶Sr ratios show two primary peaks that post‐date these crustal thickness peaks, suggesting significant weathering and erosion of global continental relief. Both episodes correlate well with zircon trace element and isotope proxies indicating enhanced crustal and fluid input into subduction zone magmas. Increased crustal thickness correlates with increased passive margin abundance and overlaps with snowball Earth glaciations and atmospheric oxygenation, suggesting a causal link between continental rift‐drift phases and major transitions in Earth's atmospheric and oceanic evolution.  相似文献   

Referate     

H. Bachmann 《Aquatic Sciences - Research Across Boundaries》1939,8(3-4):337-338

Ohne Zusammenfassung  相似文献   

Das Phytoplankton der Pioraseen nebst einigen Beiträgen zur Kenntnis des Phytoplanktons schweizerischer Alpenseen     

Hans Bachmann 《Aquatic Sciences - Research Across Boundaries》1928,4(3-4):50-103

Ohne Zusammenfassung  相似文献   

Redox and pH conditions in the water column and in the sediments of an acidic mining lake     

T. M. Bachmann  K. Friese  D. W. Zachmann   《Journal of Geochemical Exploration》2001,73(2)

Physico-chemical parameters of the acidic mining lake (ML) 111 in the Lusatian region (Germany) were determined in April and August 1997 using a multiparameter probe for the water column and punch-in pH and Eh electrodes for the sediment, respectively. Samples of the sediment profile were taken by a gravity corer. Besides determination of the physico-chemical parameters, grain size and water contents were determined after sediment slicing.Differences in the redox state of the water body, deduced from oxygen saturation between April and August, could not be inferred. However, a shift in pH to lower values was apparent. Data support the conclusion that the enhanced oxygen content was consumed for oxidation of ferrous iron to ferric iron (oxides/hydroxides) coupled with the release of protons.In the sediment, different buffer systems of iron compounds could be detected within separate zones with values below and above pH 3. At higher pH values, the redox conditions are controlled and stabilized by the presence of Fe-oxide-hydroxides and possibly Fe-sulfates.  相似文献   

Influence of time-domain dam–reservoir interaction on cracking of concrete gravity DAMS     

Dieter H. Wepf  Glauco Feltrin  Hugo Bachmann 《地震工程与结构动力学》1993,22(7):573-582

Based on a non-linear dam-reservoir interaction model, a study investigating the earthquake response of concrete gravity dams is presented. For the propagation of cracks in unreinforced mass concrete, a discrete crack approach formulation based on the finite element method is applied. A special crack element is used to follow a fictitious crack in order to account for a zone of microcracks developing at the crack tip. The reservoir is modelled using the boundary element method. At a fictitious boundary dividing the irregular finite part of the reservoir from the regular infinite part, the loss of energy due to pressure waves moving away towards infinity is taken into account rigorously. Analyses are performed on the tallest non-overflow monolith of the Pine Flat Dam located in Kern County, California. The interaction of a dam, which may exhibit cracks in mass concrete, with a reservoir domain of arbitrary geometry extending to infinity is studied. Some main parameters are investigated. The importance of tools capable of handling the non-linear dam-reservoir interaction is emphasized.  相似文献   

Hydrodynamic-stiffness matrix based on boundary elements for time-domain dam-reservoir-soil analysis     

Dieter H. Wepf  John P. Wolf  H. Bachmann 《地震工程与结构动力学》1988,16(3):417-432

For a reservoir with an arbitrary shape of the upstream dam face and of the bottom including an adjacent regular part of constant depth extending to infinity, the hydrodynamic-stiffness matrix in the frequency domain for a displacement formulation is derived using the boundary-element method. The fundamental solution takes the boundary condition at the free surface into account. The analytical solution of the semi-infinite reservoir is used to improve the accuracy. To be able to transform the hydrodynamic-stiffness matrix from the frequency to the time domain, the singular part consisting of its asymptotic value of ω ∞ is split off. It consists of an imaginary linear term in ω which can be interpreted as a damper with a coefficient per unit area equal to the product of the mass density and the wave velocity. This also applies for a reservoir bottom of arbitrary shape. The remaining regular part of the stiffness matrix is transformed numerically. The corresponding interaction force-displacement relationship involves convolution integrals. This boundary-element solution agrees well with analytical results and with those of other numerical procedures based on a time-stepping method. The method is also applied to an actual earthquake acting on a reservoir with an irregular part with an inclined bottom and a regular part extending to infinity. The results of the analysis in the time domain coincide with those determined in the frequency domain.  相似文献