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101.
Paul R. Renne Alan L. Deino Willis E. Hames Matthew T. Heizler Sidney R. Hemming Kip V. Hodges Anthony A.P. Koppers Darren F. Mark Leah E. Morgan David Phillips Brad S. Singer Brent D. Turrin Igor M. Villa Mike Villeneuve Jan R. Wijbrans 《Quaternary Geochronology》2009,4(5):346-352
Data reported in 40Ar/39Ar geochronology studies are commonly insufficient to allow computation of ages. This deficiency renders it difficult to compare ages based on different standards or constants, and often hinders critical evaluation of the results. Herein are presented an enumeration of the data that should be reported in all 40Ar/39Ar studies, including a discussion in support of these requirements. The minimum required data are identified and distinguished from parameters that are useful but may be derived from them by calculation. Finally, recommendations are made for metadata needed to document age calculations (e.g., from age spectrum or isochron analyses). 相似文献
102.
Michael O. Garcia Ken H. Rubin Marc D. Norman J. Michael Rhodes David W. Graham David W. Muenow Khalil Spencer 《Bulletin of Volcanology》1998,59(8):577-592
Samples of basalt were collected during the Rapid Response cruise to Loihi seamount from a breccia that was probably created
by the July to August 1996 Loihi earthquake swarm, the largest swarm ever recorded from a Hawaiian volcano. 210Po–210Pb dating of two fresh lava blocks from this breccia indicates that they were erupted during the first half of 1996, making
this the first documented historical eruption of Loihi. Sonobuoys deployed during the August 1996 cruise recorded popping
noises north of the breccia site, indicating that the eruption may have been continuing during the swarm. All of the breccia
lava fragments are tholeiitic, like the vast majority of Loihi's most recent lavas. Reverse zoning at the rim of clinopyroxene
phenocrysts, and the presence of two chemically distinct olivine phenocryst populations, indicate that the magma for the lavas
was mixed just prior to eruption. The trace element geochemistry of these lavas indicates there has been a reversal in Loihi's
temporal geochemical trend. Although the new Loihi lavas are similar isotopically and geochemically to recent Kilauea lavas
and the mantle conduits for these two volcanoes appear to converge at depth, distinct trace element ratios for their recent
lavas preclude common parental magmas for these two active volcanoes. The mineralogy of Loihi's recent tholeiitic lavas signify
that they crystallized at moderate depths (∼8–9 km) within the volcano, which is approximately 1 km below the hypocenters
for earthquakes from the 1996 swarm. Taken together, the petrological and seismic evidence indicates that Loihi's current
magma chamber is considerably deeper than the shallow magma chamber (∼3–4 km) in the adjoining active shield volcanoes.
Received: 21 August 1997 / Accepted: 15 February 1998 相似文献
103.
104.
Pragmatic experimental design requires objective consideration of several classes of information including the survey goals, the range of expected Earth responses, acquisition costs, instrumental capabilities, experimental conditions and logistics. In this study we consider the ramifications of maximizing model parameter resolution through non-linear experimental design. Global optimization theory is employed to examine and rank different EM sounding survey designs in terms of model resolution as defined by linearized inverse theory. By studying both theoretically optimal and heuristic experimental survey configurations for various quantities of data, it is shown that design optimization is critical for minimizing model variance estimates, and is particularly important when the inverse problem becomes nearly underdetermined. We introduce the concept of robustness so that survey designs are relatively immune to the presence of potential bias errors in important data. Bias may arise during practical measurement, or from designing a survey using an appropriate model. 相似文献
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107.
David J. Dunlop Hironobu Hyodo Todd Knight Alan G. Steele 《Geophysical Journal International》1985,83(3):699-720
Summary. After thermal and alternating field (AF) cleaning, the characteristic high blocking temperature A component of natural remanent magnetization (NRM) of the Tudor gabbro of southern Ontario has a mean direction D = 326°, I =–46° ( k = 132, α95 = 4.8°, N = 8 sites). The corresponding palaeopole, 133°E, 12°N ( dp = 4°, dm = 6°), confirms the palaeopole 137°E, 17°N (α95 = 8.4°) reported earlier by Palmer & Carmichael, based on AF cleaning only. The A NRM has unblocking temperatures > 515–525°C which exceed the estimated 500°C peak temperature reached locally during ∼ 1050 Ma Grenvillian regional metamorphism. The A NRM therefore predates metamorphism and is probably a primary thermoremanence (TRM). The age of the Tudor NRM has previously been taken to be about 675 Ma, but recent 40 Ar/39 Ar dating by Baksi has shown that this is the time of post-metamorphic cooling to 200–250°C. Hornblendes record initial cooling of the intrusion to 590±20°C at 1110 Ma and this is the best estimate of the age of the A remanence. Successful Thellier-type palaeointensity determinations on 11 Tudor samples confirm that the A NRM is a TRM and indicate a palaeofield at this time of 18–27 μT, about 50–70 per cent of the present field intensity at 27° magnetic latitude. The anomalous Tudor A palaeopole, which lies well to the west of both 1000–800 Ma Grenvillian palaeopoles and 1100–1050 Ma poles from Interior Laurentia, is interpreted as recording divergence between Grenvillia and Interior Laurentia just before the Grenvillian orogeny, rather than a post-metamorphic extension of the apparent polar wander path as previously assumed. 相似文献
108.
Cinema can be considered a useful tool for understanding different geographic concepts, showing physical and human factors and the interactions between them. Andres Wood's film Football Stories explores the Chilean territory allowing the observation of the differences between the north and south of the country. Geographic components such as landscapes, architectures, the impact of anthropogenic activities, social inequalities, ways of life, and city and countryside differences are analyzed, as well as the importance of location, the spatial environment, and cinematic narration. The study of geography through films could contribute to understanding of our world and to spatial knowledge. 相似文献
109.
In recent years, the urban political landscape has become infused with a potent and incendiary mixture of popular-democratic, anti-globalisation, and separatist rhetoric. One central process driving this has been the problematic relations between the nation-state and the city. This Debates and Interventions forum aims to prompt a debate about where the city should be situated intellectually in respect of the nation-state. Four questions are addressed: (1) How do contemporary processes of urban development reflect changing national geopolitical priorities? (2) To what extent are struggles around immigration, citizenship and recognition conducted within cities rather than around the nation-state? (3) To what degree does the city (as e.g. a physical form, social environment or discourse) help to mobilise, propel and/or contest this new urban politics? And (4) Is the concept of a “post-national” global order appropriate for understanding the city and urban politics today? 相似文献