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F. Zeb Page Lora S. Armstrong Eric J. Essene Samuel B. Mukasa 《Contributions to Mineralogy and Petrology》2007,153(5):533-555
Quantitative thermobarometry of inclusions in zoned garnet from a Franciscan eclogite block record a counter-clockwise P–T path from blueschist to eclogite and back. Garnet retains prograde zoning from inclusion-rich Alm52Grs30Pyp6Sps12 cores to inclusion-poor Alm62Grs25Pyp12Sps1 mantles, with overgrowths of highly variable composition. Barometry using the Waters–Martin version of the garnet–phengite–omphacite
thermobarometer yields conditions of 7–15 kbar, 400–500°C (garnet cores), 18–22 kbar, ∼550°C (mantles), and 10–14 kbar, 350–450°C
(overgrowths), in agreement with clinozoisite–sphene–rutile–garnet–quartz barometry. These pressures are ∼10–15 kbar less
than those obtained using more recent, fully thermodynamic calibrations of the phengite–omphacite–garnet thermobarometer.
Low early temperatures suggest that the block was subducted in a thermally mature subduction zone and not at the inception
of subduction when prograde temperature is expected to be higher. Franciscan high-grade blocks likely represent crust subducted
throughout the history of this convergent margin, rather than only at the inception of the subduction zone. 相似文献
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Justin C. Stout Ian Rutherfurd James Grove J. Angus Webb Adrian Kitchingman Zeb Tonkin 《地球表面变化过程与地形》2017,42(4):647-656
Reporting uncertainty in environmental measurements and estimates is important for cross‐comparison and inter‐comparison of sites and other spatial units. One such measure is the load of large in‐stream wood in river systems. In this paper we propose the use of the Weibull distribution to describe the central tendency and variability of wood loads along a river reach. We illustrate the link between the average wood load and the central tendency or scale parameter of the Weibull distribution. The shape of the Weibull distribution is strongly related to the ability of rivers to transport and rearrange the wood in a reach. We use six Victorian rivers to test the fit of the Weibull distribution, showing that the Weibull is a useful and flexible distribution that provides common reporting metrics useful for future studies. Using common reporting metrics provides a stronger tool for comparisons of wood loads between rivers and with reaches. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Rodrigo Scalise Horodyski Michael Holz Yngve Grahn Elvio Pinto Bosetti 《International Journal of Earth Sciences》2014,103(1):367-380
The Eifelian–Givetian (Middle Devonian) transition constituted an important paleoenvironmental event for the Malvinokaffric Realm in the Apucarana Sub-basin (Paraná Basin). This study highlights integration between taphonomy and sequence stratigraphy, and four depositional sequences are identified during the transition. In Sequence 1, the presence of a typical normal-sized Malvinokaffric fauna is recorded. In the transgressive systems tract (TST) of Sequence 2, no benthic fossils are present, and this is interpreted as a stratigraphic marker of an event of significant paleoenvironmental change (KA?ÁK Event). In Sequence 3, the TST has abundant bioclasts, which become rarer toward the top of the section, i.e., within the transgressive systems tract. The original habitat of this autochthonous to parautochthonous fauna was a low-energy environment between the fair weather wave base and the storm wave base of the Devonian epicontinental sea. In the highstand systems tract of this sequence, the presence of normal-sized Pennaia paulianna and lingulids demonstrates the return of more ambient conditions. Sequence 4 is of Carboniferous age. Its limit is a second-order sequence boundary recording a lowstand systems tract formed by a fluvial depositional system. The low diversity and the disappearance of taxa are not the result of a taphonomic bias, but reflect the post-KA?ÁK Event. 相似文献
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Yngve Öhman 《Solar physics》1973,28(2):399-402
Some comments are presented on the important observations of faint prominences made recently by Dr Jean-Louis Leroy at the Pic du Midi Observatory. The writer draws attention to the very probable connection with faintly luminous H obscuring prominences which appear sometimes as dark lanes and markings in ordinary prominences. 相似文献
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Yngve Öhman 《Solar physics》1979,62(2):407-412
Attention is drawn to a very simple instrumental arrangement for eclipse observations of the spectra of the chromosphere and prominences using a plane grating as polar heliostat and a short focus camera. A discussion is made of an infrared chromospheric spectrum showing traces of Thomson-scattered Ca ii absorption lines in the continuous spectrum. If the effect is real, it indicates a temperature of the order of 5000 K. A simple vector formula is presented describing various types of Doppler effects appearing in radiation scattered by moving particles. 相似文献
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Yngve Öhman 《Solar physics》1968,3(2):354-356
Observations are reported of an H filament clearly visible in the image of the chromosphere at the limb as well as in the H spectrum of the same part of the chromosphere. Observations of this kind may give valuable information about the absorption mechanism at work in filaments. 相似文献
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Zircons from kimberlite: New insights from oxygen isotopes, trace elements, and Ti in zircon thermometry 总被引：5，自引：0，他引：5
F. Zeb Page Bin Fu John Fournelle Daniel J. Schulze Miguel A.S. Basei 《Geochimica et cosmochimica acta》2007,71(15):3887-3903
Zircons found in mantle-sourced kimberlite provide probes into the isotopic chemistry of the asthenosphere and subcontinental lithospheric mantle. However, little is known about the conditions of formation of these zircons. A suite of 88 zircons found in kimberlites from Africa, Siberia, Brazil, and the United States have been analyzed for their Ti concentration and selected zircons were analyzed for their Rare Earth Element (REE) concentrations by ion microprobe. In addition, precise and accurate laser-fluorination oxygen isotope data were obtained for zircons from Brazil (5.1 ± 0.3‰, 1SD) and the Midwest United States (5.3 ± 0.3‰), yielding mantle-like δ18O values similar to published data for Africa (5.2 ± 0.3‰) and Siberia (5.3 ± 0.2‰). Most megacrysts in this study preserve fine-scale, oscillatory zoning in CL and are generally homogenous in oxygen isotopic composition, consistent with preservation of primary compositions. A few zircons from Brazil show some evidence of chemical zoning due to recrystallization. The Ti content of mantle zircon is in general low with average compositions from each locality of 13 ± 8.4 ppm (1SD, Kaapvaal craton), 12 ± 8.7 ppm (Siberian platform), 18 ± 11 ppm (Brazil), and 4.8 ±4.3 ppm (United States). The recently calibrated Ti in zircon thermometer yields an average temperature of 744 ±62 °C (1SD) for the average of 13 ± 9 ppm Ti, with no correction for pressure, aTiO2, or aSiO2. The Ti content of zircons found within rutile nodules from the Orapa kimberlite (Kaapvaal craton) is almost indistinguishable from those with no constraint on aTiO2, suggesting that reduced aTiO2 is not responsible for lower than expected mantle temperatures. The average temperature in this study corresponds to ∼3 GPa on a 40 mW/m2 cratonic geotherm. If correct, this would suggest that zircon megacrysts from all four cratons formed in the shallow lithospheric mantle. However, there are several possibly confounding effects to this thermometer, including: a pressure correction and disequilibrium zircon growth. Zircons from rutile nodules have REE contents that span the range of mantle zircon REE and are similar to both zircon megacrysts and zircons from metasomatic assemblages. 相似文献