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201.
202.
Adam M. Booth John Dehls Trond Eiken Luzia Fischer Reginald L. Hermanns Thierry Oppikofer 《Landslides》2015,12(4):745-756
203.
Gordon R. Osinski Adam B. Coulter Roberta L. Flemming Alexandra Ozaruk Annemarie E. Pickersgill Alaura C. Singleton 《Meteoritics & planetary science》2023,58(6):775-788
The ~5 km diameter Gow Lake impact structure formed in the Canadian Shield of northern Saskatchewan approximately 197 Myr ago. This structure has not been studied in detail since its discovery during a regional gravity survey in the early 1970s. We report here on field observations from a 2011 expedition that, when combined with subsequent laboratory studies, have revealed a wealth of new information about this poorly studied Canadian impact structure. Initially considered to be a prototypical central peak (i.e., a complex) impact structure, our observations demonstrate that Gow Lake is actually a transitional impact structure, making it one of only two identified on Earth. Despite its age, a well-preserved sequence of crater-fill impactites is preserved on Calder Island in the middle of Gow Lake. From the base upward, this stratigraphy is parautochthonous target rock, lithic impact breccia, clast-rich impact melt rock, red clast-poor impact melt rock, and green clast-poor impact melt rocks. Discontinuous lenses of impact melt-bearing breccia also occur near the top of the red impact melt rocks and in the uppermost green impact melt rocks. The vitric particles in these breccias display irregular and contorted outlines. This, together with their setting within crater-fill melt rocks, is indicative of an origin as flows within the transient cavity and not an airborne mode of origin. Following impact, a hydrothermal system was initiated, which resulted in alteration of the crater-fill impactites. Major alteration phases are nontronite clay, K-feldspar, and quartz. 相似文献
204.
Monin–Obukhov similarity theory (MOST) is commonly used to model the wind-speed profile at altitudes relevant to wind-power production (e.g. 10–200 m). Though reasonably accurate for unstable to weakly stable stratification, this approach becomes less accurate under increasingly stable stratification, largely due to the constant-flux surface layer assumed by MOST becoming shallower than the altitude range of interest. Furthermore, above the surface layer, the Coriolis force has a considerable influence on the wind-speed profile (in particular in the formation of low-level jets) that cannot be modelled using similarity theory. Our goal is to compare the accuracy of alternative extrapolation models that are more physically appropriate above the surface layer. Using data from the 213-m Cabauw meteorological tower in the Netherlands between July 2007 and June 2008, it is shown that MOST is accurate only at low altitudes and low stability, and breaks down at high altitudes and high stability. Local similarity is generally more accurate than MOST across all altitudes and stabilities, though the model requires turbulent flux data at multiple altitudes that is generally impractical. In contrast, a two-layer MOST–Ekman model is found to be comparable to the other models at low stability ranges and considerably more accurate in the high stability range, while requiring only a measure of surface stability and the geostrophic wind. 相似文献
205.
206.
B. Coldwell J. Adam T. Rushmer C. G. Macpherson 《Contributions to Mineralogy and Petrology》2011,162(4):835-848
Piston-cylinder experiments on a Pleistocene adakite from Mindanao in the Philippines have been used to establish near-liquidus
and sub-liquidus phase relationships relevant to conditions in the East Philippines subduction zone. The experimental starting
material belongs to a consanguineous suite of adakitic andesites. Experiments were conducted at pressures from 0.5 to 2 GPa
and temperatures from 950 to 1,150°C. With 5 wt. % of dissolved H2O in the starting mix, garnet, clinopyroxene and orthopyroxene are liquidus phases at pressures above 1.5 GPa, whereas clinopyroxene
and orthopyroxene are liquidus (or near-liquidus) phases at pressures <1.5 GPa. Although amphibole is not a liquidus phase
under any of the conditions examined, it is stable under sub-liquidus conditions at temperature ≤1,050°C and pressures up
to 1.5 GPa. When combined with petrographic observations and bulk rock chemical data for the Mindanao adakites, these findings
are consistent with polybaric fractionation that initially involved garnet (at pressures >1.5 GPa) and subsequently involved
the lower pressure fractionation of amphibole, plagioclase and subordinate clinopyroxene. Thus, the distinctive Y and HREE
depletions of the andesitic adakites (which distinguish them from associated non-adakitic andesites) must be established relatively
early in the fractionation process. Our experiments show that this early fractionation must have occurred at pressures >1.5 GPa
and, thus, deeper than the Mindanao Moho. Published thermal models of the Philippine Sea Plate preclude a direct origin by
melting of the subducting ocean crust. Thus, our results favour a model whereby basaltic arc melt underwent high-pressure
crystal fractionation while stalled beneath immature arc lithosphere. This produced residual magma of adakitic character which
underwent further fractionation at relatively low (i.e. crustal) pressures before being erupted. 相似文献
207.
Porphyry-type ore deposits sometimes contain fluid inclusion compositions consistent with the partitioning of copper and gold into vapor relative to coexisting brine at the depositional stage. However, this has not been reproduced experimentally at magmatic conditions. In an attempt to determine the conditions under which copper and gold may partition preferentially into vapor relative to brine at temperatures above the solidus of granitic magmas, we performed experiments at 800 °C, 100 MPa, oxygen fugacity () buffered by Ni-NiO, and fixed at either 3.5 × 10−2 by using intermediate solid solution-pyrrhotite, or 1.2 × 10−4 by using intermediate solid solution-pyrrhotite-bornite. The coexisting vapor (∼3 wt.% NaCl eq.) and brine (∼68 wt.% NaCl eq.) were composed initially of NaCl + KCl + HCl + H2O, with starting HCl set to <1000 μg/g in the aqueous mixture. Synthetic vapor and brine fluid inclusions were trapped at run conditions and subsequently analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Our experiments demonstrate that copper and gold partitioned strongly into the magmatic volatile phase(s) (MVP) (i.e., vapor or brine) relative to a silicate melt over the entire imposed range of . Nernst style partition coefficients between coexisting brine (b) and melt (m), Db/m (±1σ), range from 3.6(±2.2) × 101 to 4(±2) × 102 for copper and from 1.2(±0.6) × 102 to 2.4(±2.4) × 103 for gold. Partition coefficients between coexisting vapor (v) and melt, Dv/m range from 2.1 ± 0.7 to 18 ± 5 and 7(±3) × 101 to 1.6(±1.6) × 102 for copper and gold, respectively. Partition coefficients for all experiments between coexisting brine and vapor, Db/v (±1σ), range from 7(±2) to 1.0(±0.4) × 102 and 1.7(±0.2) to 15(±2) for copper and gold, respectively. Observed average Db/v at an of 1.2 × 10−4 were elevated, 95(±5) and 15 ± 1 for copper and gold, respectively, relative to those at the higher of 3.5 × 10−2 where Db/v were 10(±5) for copper and 7(±6) for gold. Thus, there is an inverse relationship between the and the Db/v for both copper and gold with increasing resulting in a decrease in the Db/v signifying increased importance of the vapor phase for copper and gold transport. This suggests that copper and gold may complex with volatile S-species as well as Cl-species at magmatic conditions, however, none of the experiments of our study at 800 °C and 100 MPa had a Db/v ? 1. We did not directly determine speciation, but infer the existence of some metal-sulfur complexes based on the reported data. We suggest that copper and gold partition preferentially into the brine in most instances at or above the wet solidus. However, in most systems, the mass of vapor is greater than the mass of brine, and vapor transport of copper and gold may become more important in the magmatic environment at higher , lower , or near the critical point in a salt-water system. A Db/v ? 1 at subsolidus hydrothermal conditions may also occur in response to changes in temperature, , , and/or acidity.Additionally, both copper and gold were observed to partition into intermediate solid solution and bornite much more strongly than into vapor, brine or silicate melt. This suggests that, although vapor and brine are both efficient at removing copper and gold from a silicate melt, the presence of Cu-Fe sulfides can sequester a substantial portion of the copper and gold contained within a silicate melt if the Cu-Fe sulfides are abundant. 相似文献
208.
Adam A. Monroe 《Geochimica et cosmochimica acta》2011,75(23):7585-7595
The Bells meteorite is a CM2 chondrite that has long been considered anomalous for having mineralogical and isotopic differences with CMs together with an overall affinity to CIs in its matrix. We extracted a fragment of the only Bells stone collected unweathered with water and solvents and studied the meteorite’s soluble organic composition. We found Bells to contain abundant organic compounds, which are predominantly O-containing such as hydroxy- and di-carboxylic acids, and a scarcity of amino acids and other N-containing compounds. Amines were not detected and ammonia is less abundant than in both the Murchison and Ivuna meteorites. Overall, Bells’ soluble organic composition is more similar to that of Ivuna than of Murchison. The observation that Bells’ amino acid suite shares a distinct distribution of characteristic molecular species with other stones that are thought to have experienced extensive parent body aqueous alteration, such as the Orgueil, Ivuna and recently analyzed GRO 95577 CR1 meteorites, seems to allow the suggestion that such a composition is secondary to prolonged aqueous alteration processes that superseded some of the initial compositional distinctions determined by the asteroidal environments. 相似文献
209.
Burial of organic carbon in Holocene sediments of the Zhujiang (Pearl River) and Changjiang (Yangtze River) estuaries 总被引:1,自引:0,他引:1
Shouye Yang Min Tang Wyss W.-S. Yim Yongqiang Zong Guangqing Huang Adam D. Switzer Yoshiki Saito 《Marine Chemistry》2011,123(1-4):1-10
The East Asian marginal seas are important sinks of terrigenous materials transported by large rivers. In this study two cores from the Changjiang (Yangtze River) and Zhujiang (Pearl River) estuaries and one core from the inner shelf off of Hong Kong were investigated to examine the burial of organic matter during the postglacial period and its possible links with paleoenvironmental changes. Based on a simple two end-member mixing model, the terrestrial organic matter supplied primarily from the Zhujiang and Changjiang dominates the estuarine areas while marine organic matter contributes more to the inner-mid shelf. The competing contributions of terrestrial and marine organic matter are responsible for the downcore variations of organic elemental compositions. The overall decreasing shifts of total organic carbon concentrations and total organic carbon to total nitrogen ratios in the Zhujiang estuarine sediments since 6.5 kaBP seems to support the notion that depth profiles of organic matter compositions deposited in the Zhujiang Estuary can aid in the reconstruction of monsoon history in the Holocene. Nevertheless, organic matter compositions in the Changjiang Estuary and inner shelf off of southeastern Hong Kong respond in a different and more complex way to freshwater discharges or precipitation changes (monsoon variability) in the catchments, owing to complex controls of deposition and preservation of organic matter in these estuarine and shelf environments. Caution is therefore needed in using organic elemental and isotopic compositions to decipher paleoenvironmental changes in East Asian continental shelves where intense river–sea interactions occur and sedimentary environments change drastically. 相似文献
210.
Adam A. Garde Anders Scherstén Iain McDonald Nynke Keulen 《Meteoritics & planetary science》2014,49(12):2129-2132