Spitzer space telescope observations of SGR and AXP environments

Both Anomalous X-ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) are thought to be manifestations of magnetars. However, the specific physical characteristics that differentiate the two classes of objects remain unclear. There is some evidence that the progenitors of these sources and/or the environment in which they form might influence the type of phenomena the resulting magnetar displays. Several of the AXPs appear to be associated with supernova remnants, while embedded clusters of massive stars have been found in the immediate vicinity of some SGRs. Since both AXPs and SGRs are distributed close to the Galactic plane, high extinction makes studies in the optical difficult. We present early results from our Spitzer program aimed at probing the environmental factors that might contribute to the difference in the observed characteristics between AXPs and SGRs.     

Spatial and temporal patterns of the infaunal community near a major ocean outfall in Southern California

Effects of waste water discharge from a major ocean outfall in Southern California to the benthic infaunal community were examined during a 5-year monitoring programme. Natural features, primarily water depth, accounted for 82% of the variability in the infaunal community, while discharge-related effects represented less than 8% of the variability. The area immediately adjacent to the diffuser had the strongest outfall effects. Infaunal abundance showed a pattern of enhancement centred at the outfall. Diversity was also high, indicating that the area was not characterized by a degraded community.     

气象因素对飞行安全高度的影响

通过分析气象因素对气压式高度表测量高度的影响，求出了高度误差极值，说明了我国安全高度按高于航线两侧２５ｋｍ范围内的最大标高４００ｍ或６００ｍ存在一定误差，提出了４条预防措施。     

The relationship between the hawaiites and basalts of the itcha Volcanic Complex,central British Columbia

Volumetrically subordinate alkaline mafic lava flows form a late capping stage over the earlier felsic lavas that form the shield of the Itcha Volcanic Complex (IVC), of the Anahim Volcanic Belt (AVB) in central British Columbia (B.C.). The mafic capping stage of the IVC is dominated by hawaiites which are the earliest of the mafic lavas, and are succeeded by alkali olivine basalts (AOB) and then by basanites. The alkali olivine basalts can be subdivided into high-, intermediate- and low-MgO AOB groups, all of which share similar HFSE ratios (e.g. Nb/Zr) with the hawaiites. High Al contents and Sr/Zr ratios indicate that hawaiites and Fe-rich evolved AOB were derived from primitive AOB parental magmas by crystal fractionation of a wehrlitic assemblage at pressures on the order of 8 to 10 kbar. High Si and low Fe contents indicate that the majority of the evolved AOB lavas, however, do not represent an intermediate stage in the liquid line of descent to hawaiites, but were most likely produced by gabbroic fractionation from primitive AOB magmas at relatively low pressures. The parental magmas of the majority of these lavas were distinct from those of the observed high-MgO basalts, having higher HFSE contents and being more Si-under-saturated. The high Al, high Sr/Zr signature of high-pressure fractionation of a clinopyroxene-dominated assemblage in the IVC is shared by hawaiites of other alkaline volcanic suites of the Canadian Cordillera, such as the Edziza Volcanic Complex in northern B.C. and appears to be a feature of hawaiites in many localities, including Hawaii and Iceland. Viscosities calculated for both high- and low-pressure crystal fractionation models suggest that aphyric hawaiites are residual liquids escaped from a wehrlitic crystalline network, at elevated pressures, possibly at the base of the crust. Editorial responsibility: T.L. Grove     

Forum The observational side of volcanology

American Scientist , I think. One panel shows an Einstein-like figure in an easy chair with a pencil and pad of paper; this panel is labeled Big Science. The other panel shows the headquarters of a high-tech company and is labeled Little Science. Think about it. Science builds on testable ideas, often qualitative in nature, that commonly arise from observations of natural phenomena. Technology confirms or denies those ideas and helps to quantify them. Both are important, and there is considerable feedback, but fundamentally the ideas drive the technology. Hence the cartoonist had it right, despite society’s common perception of what is big and what is little. Big bucks do not equal big science. Volcanology is a science, the study of volcanoes. Ideas are key to our understanding of how and why volcanoes erupt. Many of these ideas are formulated from direct observations of volcanoes and their products before, during, and after eruptions. Observational volcanology may seem old-fashioned today but remains one of the most stimulating endeavors I know. If not big science, at least it is moderate science. And rather simple, too. All you need are your eyes, ears, nose, and brain, together with suitable equipment for the situation (often only a hammer or spade). In many instances simple observations and related measurements provide fundamental information about how volcanoes work. I described three such instances in Chapter 21 of USGS Bulletin 1966 and elaborated there my feelings about the importance of field observations for monitoring volcanoes and the concept of keeping monitoring, i.e., repeated direct observation, as simple as practical. I am disheartened by the recent deaths of volcanologists in the field but encouraged by the general understanding that the volcanologic community has shown. No one wants the death rate to continue unchecked, but no one is seriously suggesting cutting back on field observations by volcanologists either. The best way to reduce fatalities is to understand the volcano better. The best way to understand the volcano better involves field observations as well as electronic sensors. Meanwhile, it is well to remember that volcanology is the study of volcanoes, and that purely scientific, curiosity-driven motives are as justified as those designed purely to mitigate risks, and I think more valuable in the end. Curiosity leads to understanding, and understanding is the paramount goal of the science as well as the soundest basis for reducing risk. Volcanologists who are curious will get themselves into trouble and sometimes die because of it. It is often stated that we must weigh the potential benefits and risks before doing something that may be perceived as risky. Of course we must, but it is mathematically impossible to solve one equation with two unknowns, and generally the potential benefits and risks are both unknowns. In the end it comes down to common sense, which varies among individuals and in any case is far from foolproof. Let is be no other way, and let us praise the curious as we mourn the dead.     

Experimental study of liquid evolution in an Fe-rich,layered mafic intrusion: constraints of Fe-Ti oxide precipitation on the T-fO 2 and T-ϱ paths of tholeiitic magmas

The Newark Island layered intrusion, a composite intrusion displaying a similar fractionation sequence to the Skaergaard, has both dikes which preserved liquids fed into the intrusion and chilled pillows of liquids resident in the chamber. This study reports experimentally determined one atmosphere liquid lines of descent of these compositions as a function of oxygen fugacity which varies from QFM (quartz-fayalite-magnetite) to 0.5 log₁₀ units above IW (iron-wustite). These experiments reveal a strong oxygen fugacity dependence on the order of appearance and relative abundances of the Fe–Ti oxide minerals. Titanomagnetite saturates prior to ilmenite at QFM, but the order is reversed at lower oxygen fugacities. In the layered series of the Newark Island intrusion, ilmenite arrives shortly before titanomagnetite and the titanomagnetite/ilmenite ratio decreases monotonically after the cumulus appearance of titanomagnetite. Comparison of the crystallization sequence in the intrusion with that of the experiments requires that the oxygen fugacity in the intrusion increased relative to QFM before titanomagnetite saturation and decreased afterward, but always remained between the QFM and IW buffers. Similar trends in the modes of the Fe–Ti oxides (ilmenite and titanomagnetite) in the Skaergaard, Kiglapait, and Somerset Dam intrusions along with Fe₂O₃/FeO ratios in MORBs suggest that such a temperature-oxygen fugacity path may be typical of tholeiitic magma differentiation. Calculations of the temperature-density paths of the experimental liquids indicate that, at all possible oxygen fugacities, the density must have decreased abruptly after Fe–Ti oxide saturation. Accordingly, liquids replenishing the intrusion after Fe–Ti oxide saturation should pond at the bottom of the chamber, quenching against older cumulates. Field observation at the Newark Island intrusion confirm this prediction. The similarities in the fractionation paths of several other layered intrusions to that of the Newark Island intrusion suggest that the density of the liquids in these intrusions also decreased after Fe–Ti oxide saturation. Experiments on a suggested initial Skaergaard liquid are consistent with this model.     

Sr isotopic evidence for a multi-source origin of the potassic magmas in the neapolitan area (S. Italy)

New Sr isotopic data on lavas and xenoliths from Somma-Vesuvius and other nearby volcanic areas (Phlegrean Fields and Ischia) are presented. Chemical and isotopic evidences show that not all the Phlegrean Fields rocks belong to the low K series, but some of them may be interpreted as low pressure differentiates of Somma magmas, i.e. as a part of the high K series. Two rock groups are defined in the Ischia low K series, which are well identified both in time and in chemical and isotopic features, and cannot be derived from the same magma source. The low K series in the studied area generally has lower Sr isotopic values than the high K series.Historical Vesuvian lavas show two distinct linear trends with negative slopes when⁸⁷Sr/⁸⁶Sr ratios are plotted against their ages of eruption. Such trends are interpreted to result from mixing of magmas in two separate reservoirs. Evidence from the Vesuvian ejecta shows that Somma-Vesuvius magmas underwent high or low pressure fractionation, in connection with different events of the Vesuvian activity. Distinct magma reservoirs developed episodically at different depths. Isotopic and geochemical evidences do not favour large scale assimilation of crustal materials by Somma-Vesuvius magmas, but instead appear to reflect mantle characteristics.A minimum of three different (inhomogeneous) source regions is necessary to account for the isotopic features of the studied rocks.     

Fractionation paths of Atka (Aleutians) high-alumina basalts: Constraints from phase relations

An Aleutian high-alumina basalt from the island of Atka at one atmosphere crystallizes plagioclase (1275°C) followed by olivine (1170°C) and clinopyroxene (1115°C). At oxygen fugacities along NNO, magnetite crystallizes below 1070°C, but its liquidus increases to at least 1175°C at an oxygen fugacity two log units above NNO. Phase relations at two kilobars pressure of melts containing small amounts of water are similar, although orthopyroxene and magnetite are observed to follow clinopyroxene. Amphibole crystallizes at near-liquidus temperatures only at water contents of melts approaching 4.5%. Amphibole assumes the liquidus in melts containing 5% water.Anhydrous melts crystallize plagioclase to 19 kbar, where garnet and clinopyroxene assume the liquidus. Olivine yields to clinopyroxene as the highest-temperature subliquidus phase at about 9 kbar.The array of compositions of basaltic Atka rocks, as displayed on appropriate pseudoternary projections, can be interpreted as a crystal fractionation path at moderate pressure (8 kbar) and small melt-water contents. The interpreted fractionating minerals are olivine, clinopyroxene, plagioclase, and (probably) magnetite. (The actual phenocrysts in Atka basalts like AT-1, which lacks phenocrystic clinopyroxene, must have crystallized at pressure less than 8 kbar, however.) The compositions of two-pyroxene andesites from Atka can be interpreted to lie on a lower-pressure fractionation trend at melt water contents of 2–3%. Such water contents are consistent with the complete absence of amphibole in any Atka rocks and are suggestive that water contents of the basaltic magmas, if the basalts are parental to the andesites, were 1–2%.