Polymetamorphic garnet micaschists from the Austroalpine Saualpe Eclogite Unit (Kärnten, Austria, Eastern Alps) display complex microstructural and mineral–chemical relationships. Automated scanning electron microscopy routines with energy dispersive X‐ray (EDX) spectral mapping were applied for monazite detection and garnet mineral–chemical characterization. When the Fe, Mg, Mn and Ca element wt% compositions are used as generic labels for garnet EDX spectra, complex zonations and porphyroblast generations can be resolved in complete thin sections for selective electron‐microprobe analyses. Two garnet porphyroblast generations and diverse monazite age populations have been revealed in low‐Ca and high‐Al‐metapelites. Garnet 1 has decreasing Mn, constant Ca and significantly increasing Mg from cores to rims. Geothermobarometry of garnet 1 assemblages signals a crystallization along a M1 prograde metamorphism at ~650 °C/6–8 kbar. Sporadic monazite 1 crystallization started at c. 320 Ma. Subsequent pervasive 300–250 Ma high‐Y and high‐Gd monazite 1 formation during decompression coincided with the intrusion of Permian and Early Triassic pegmatites. Monazite 1 crystallized along the margin of garnet 1. Coronas of apatite and allanite around the large 320–250 Ma monazite signal a retrogressive stage. These microstructures suggest a Carboniferous‐to‐Early‐Permian age for the prograde M1 event with garnet 1. Such a M1 event at an intermediate‐P/T gradient has not yet been described from the Saualpe, and preceded a Permo‐Triassic low‐P stage. The M2 event with garnet 2 postdates the corona formation around Permian monazite. Garnet 2 displays first increasing XCa at decreasing XMg, then increasing XCa and XMg, and finally decreasing XCa with increasing XMg, always at high Ca and Mg, and low Mn. This records a P–T evolution which passed through eclogite facies conditions and reached maximum temperatures at ~750 °C/14 kbar during decompression‐heating. A monazite 2 population (94–86 Ma) with lower Y and Gd contents crystallized at decreasing pressure during the Cretaceous (Eo‐Alpine) metamorphism M2 at a high‐P/T gradient. The Saualpe Eclogite Unit underwent two distinct clockwise metamorphic cycles at different P–T conditions, related to continental collisions under different thermal regimes. This led to a characteristic distribution pattern of monazite ages in this unit which is different from other Austroalpine basement areas. 相似文献
Underground geological storage of CO2 (GSC) requires a high level of subsurface understanding that is often hindered by a lack of data. This study demonstrates the use of stratigraphic forward modelling (SFM) in generating and characterising a static reservoir model using limited well data, with multiple potential applications within the GSC workflow. Sedsim SFM software was used to create a static model of the Surat Basin, including a high‐resolution nested model of the EPQ‐7 GSC tenement within the basin. Deposition and burial of the Jurassic Precipice Sandstone, Evergreen Formation and Hutton Sandstone were simulated. Modelling results show a close match with gamma‐ray well logs in the tenement area, and the model can be considered a credible model of the subsurface. The Sedsim‐predicted formation thicknesses and porosity and permeability distributions meet criteria set for GSC, suggesting that the EPQ‐7 tenement may be a prospective GSC location. 相似文献
Olivine in kimberlites can provide unique insights into magma petrogenesis, because it is the most abundant xenocrystic phase and a stable magmatic product over most of the liquid line of descent. In this study we examined the petrography and chemistry of olivine in kimberlites from different tectonic settings, including the Slave craton, Canada (Ekati: Grizzly, Koala), the Brasilia mobile belt (Limpeza-18, Tres Ranchos-04), and the Kaapvaal craton, South Africa (Kaalvallei: Samada, New Robinson). Olivine cores display a wide range of compositions (e.g., Mg# = 78–95). The similarity in olivine composition, resorption of core zones and inclusions of mantle-derived phases, indicates that most olivine cores originated from the disaggregation of mantle peridotites, including kimberlite-metasomatised lithologies (i.e. sheared lherzolites and megacrysts). Olivine rims typically show a restricted range of Mg#, with decreasing Ni and increasing Mn and Ca contents, a characteristic of kimberlitic olivine worldwide. The rims host inclusions of groundmass minerals, which implies crystallisation just before and/or during emplacement. There is a direct correlation between olivine rim composition and groundmass mineralogy, whereby high Mg/Fe rims are associated with carbonate-rich kimberlites, and lower Mg/Fe rims are correlated with increased phlogopite and Fe-bearing oxide mineral abundances. There are no differences in olivine composition between explosive (Grizzly) and hypabyssal (Koala) kimberlites. Olivine in kimberlites also displays transitional zones and less common internal zones, between cores and rims. The diffuse transitional zones exhibit intermediate compositions between cores and rims, attributed to partial re-equilibration of xenocrystic cores with the ascending kimberlite melt. In contrast, internal zones form discrete layers with resorbed margins and restricted Mg# values, but variable Ni, Mn and Ca concentrations, which indicates a discrete crystallization event from precursor kimberlite melts at mantle depths. Overall, olivine exhibits broadly analogous zoning in kimberlites worldwide. Variable compositions for individual zones relate to different parental melt compositions rather than variations in tectonic setting or emplacement mechanism.
On 22 March 2014, a massive, catastrophic landslide occurred near Oso, Washington, USA, sweeping more than 1 km across the adjacent valley flats and killing 43 people. For the following 5 weeks, hundreds of workers engaged in an exhaustive search, rescue, and recovery effort directly in the landslide runout path. These workers could not avoid the risks posed by additional large-scale slope collapses. In an effort to ensure worker safety, multiple agencies cooperated to swiftly deploy a monitoring and alerting system consisting of sensors, automated data processing and web-based display, along with defined communication protocols and clear calls to action for emergency management and search personnel. Guided by the principle that an accelerating landslide poses a greater threat than a steadily moving or stationary mass, the system was designed to detect ground motion and vibration using complementary monitoring techniques. Near real-time information was provided by continuous GPS, seismometers/geophones, and extensometers. This information was augmented by repeat-assessment techniques such as terrestrial and aerial laser scanning and time-lapse photography. Fortunately, no major additional landsliding occurred. However, we did detect small headscarp failures as well as slow movement of the remaining landslide mass with the monitoring system. This was an exceptional response situation and the lessons learned are applicable to other landslide disaster crises. They underscore the need for cogent landslide expertise and ready-to-deploy monitoring equipment, the value of using redundant monitoring techniques with distinct goals, the benefit of clearly defined communication protocols, and the importance of continued research into forecasting landslide behavior to allow timely warning.
The compression of cordierite (Mg, Fe)2Al4Si5O18·n (H2O, CO2; Na+, K+) has been studied up to 30 kbar (25° C) by volumetric measurements with a piston cylinder apparatus and by X-ray measurements with a diamond-anvil cell. Natural cordierite of intermediate Mg-Fe composition and synthetic Mg-cordierite served as samples. Two discontinuities at 2.2±0.3 and 9.0±0.6 kbar which are correlated with very small volume changes (0.3?0.05%) have been found. The X-ray data indicate, however, no symmetry change of the crystal structure. The two discontinuities are interpreted as phase transitions. The two discontinuities establish three pressure dependent phases referred to as low-pressure (LP)-, first high-pressure (HP1)- and second high-pressure (HP2)-phase. The gross compressibility of cordierite decreases from 1.1 Mbar?1 at low pressure to 0.7 Mbar?1 at 30 kbar for the intermediate Mg-Fe cordierite, and to 0.4 Mbar?1 for Mg-cordierite. Depending on the pressure transmitting medium used in the two different compression techniques, two kinds of compression behavior are observed for cordierite. The measurements with the piston cylinder apparatus where lead is used as quasihydrostatic pressure medium indicate normal compression properties. The X-ray data, however, obtained with the diamond anvil cell where a methanol-ethanol mixture provides hydrostatic pressure conditions yield, e.g. for the HP1-phase a dramatic decrease in compressibility to almost zero. IR-spectra from samples of augmenting experiments with methanol, deuteromethanol and D2O as pressure media indicate that pressure media of which the molecule size is comparable with the dimensions of the cordierite channels may be incorporated in the structure. This suggests that under such hydrostatic conditions the compression of cordierite is modified by a structure internal component which is acting via the channel system. 相似文献
Alkaline rocks were intruded into the Precambrian basement in southern West Greenland during at least five separate episodes. The Tupertalik carbonatite intrusion was emplaced around or before 2650 m.y.; it is now metamorphosed in granulite facies but is recognisable by its trace element content. Lamprophyre dykes were intruded at ca. 1800 m.y. and again at ca. 1200 m.y. At ca. 600 m.y. the Sarfartôq carbonatite intrusion and extensive kimberlite dykes were emplaced in the Holsteiborg-Strømfjord region. At 225-115 m.y. the Qaqarssuk carbonatite complex was emplaced in the Sukkertoppen region, and numerous lamprophyre and kimberlite dykes were emplaced between Fishenasset and Ivigtut. All these episodes are correlatable with contemporaneous alkaline activity in Canada and Scandinavia and substantiate the periodicity of carbonatite emplacement. The Mesozoic suite of intrusions is related to rifting prior to continental break-up and the formation of the North Atlantic Ocean. The Eocambrian suite of 600 m.y. is thought to have formed under similar conditions during continental break-up and the formation of the Iapetus ocean. 相似文献