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51.
Evidence for adiabatic decompression melting in the Southern Mariana Arc from high-Mg lavas and melt inclusions 总被引:1,自引:1,他引:1
Edward J. Kohut Robert J. Stern Adam J. R. Kent Roger L. Nielsen Sherman H. Bloomer Matthew Leybourne 《Contributions to Mineralogy and Petrology》2006,152(2):201-221
Unusually magnesian (Mg# ∼76) basalts have been sampled from a small submarine volcano situated on the Mariana arc magmatic front. Total alkalis range from 1.7 to 1.94%, Al2O3 from 9.09 to 10.3% and CaO from 13.9 to 14.09%. These lavas can be classified based on mineralogy as picrite and ankaramite. Olivine-hosted melt inclusions (MIs) have median MgO contents of 17.17–17.86 wt%, 0.35–0.5% TiO2, 42–50% SiO2 and 1.66–3.43% total alkalis, which suggest that the parental magmas were primitive mantle melts. Trace element concentrations for both MIs and lavas are arc-like, although more depleted than most arc lavas. Chlorine (182–334 ppm) and H2O contents (0.11–0.64 wt%) in the MIs are consistent with the estimated median oxygen fugacities (log ΔFMQ of + 1.53–1.66) which lie at the low end of the range estimates for arc basalts and picrites (ΔFMQ = + 1 to + 3). Isotopic compositions of Sr, Nd, Hf and Pb are similar to those of other Mariana arc lavas and indicate derivation from an Indian Ocean mantle domain. The averaged magmatic temperature estimate from several geothermometers was 1,367°C at 1–1.5 GPa. We propose that high-Mg magmagenesis in this region results from the adiabatic decompression melting of relatively anhydrous but metasomatized mantle wedge. This melting is attributed to enhanced upwelling related to unusual tectonics on the over-riding plate related to a tear or other discontinuity on the subducted slab.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
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Vulnerability and adaptive capacity of community food systems in the Peruvian Amazon: a case study from Panaillo 总被引:1,自引:1,他引:0
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The derivation and history of the frequently cited aeolian transport model of White are considered in light of the continued replication of an error in the original expression. The error may have escaped notice because the expression is still dimensionally correct and it yields predictions that appear reasonable in comparison with both the predictions of other models with field data. The incorrect expression has come to be identified as a distinct model. However, the correct formulation of the ‘White model’ is, in fact, a rearrangement of the Kawamura model with a slightly smaller (c.6%) empirical coefficient. © 1997 John Wiley & Sons, Ltd. 相似文献
55.
We used the Digital Faults geoinformation system that we developed to propose an algorithm for quantitative estimation of
seismic activity on faults. The resulting technique was used to study the spatiotemporal patterns in the present-day activity
of faults in Central Asia. Fault activity was found to vary at frequencies of a few years and cannot be explained by changes
in the regional stress fields. We studied the tendency of seismic events to be localized to areas of dynamic influence due
to faults. The active faults were grouped by the criteria of seismicity organization in the influence areas of these faults.
It was shown that fault activity and its comparatively high frequency on real time scales are caused by strain waves, which
may be generated by interplate and interblock movements in the brittle lithosphere. Judging by the speed of strain waves,
the active faults are classified into groups that differ in their geological and geophysical parameters. They can be used
to estimate the directions of strain wave fronts and to identify areas of dominant fault activation over intervals of real
(geologically speaking) time. We give a map showing active faults in Central Asia, plots of a quantitative index of their
seismic activity, and the directivity vectors of strain waves that excite fault activity. The methods we developed for classifying
active faults by the quantitative index of seismic activity and for determining the vectors of strain waves that excite fault
activity are all tools that significantly expand our possibilities when developing tectonophysical models of the seismic process
in earthquake-generating zones of the lithosphere and open new methods for attacking problems in intermediate-term earthquake
prediction. 相似文献
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Doklady Earth Sciences - 相似文献
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A total of 3086 samples, both marine (2916) and freshwater creeks/outfall samples (170) were collected and analyzed for enterococci during October 2002-April 2005, from 52 designated beaches in Oregon. A total of 3.2% (99/3086) of the samples at 21 beaches exceeded 158 most probable number (MPN)/100 milliliters (mL). The average enterococci levels of these 99 exceedances was 559 MPN/100 mL, with a maximum of 4352 MPN/100 mL (Otter Rock and Ona) and a minimum of 160 MPN/100 mL (Sunset Bay State Park, Bastendorff, and Mill). For marine water, 77/2916 (2.6%) exceeded 158 MPN/100 mL. For freshwater, 22/170 (12.9%) exceeded 158 MPN/100 mL, with a maximum of 587 MPN/100 mL at Sunset Bay. Sixty percent of the marine and 9% of freshwater exceedances occurred during the winter. Seventy-two percent (55/77) of the marine exceedances occurred after rainfall events (0.01-60.0 mm). At Harris and Mill Beaches, cumulative rainfall was highly correlated with bacterial densities, R = 0.7. Rainfall, at both beaches, explained about one-half the variation in log10 bacteria density (R2 = 0.5). Additional monitoring is warranted to further characterize bacterial contamination in Oregon waters. 相似文献