Complex isotopic-geochemical (Sm-Nd,U-Pb) study of Salma eclogites

Doklady Earth Sciences -     

Sub-parsec structure of binary supermassive black holes in active galactic nuclei

Long-term, multi-frequency monitoring of the radio fluxes of the four BL Lac objects 3C 120, OJ 287, 1308+326, and BL Lac is considered. Harmonic components of the flux variability on scales from one year to decades are determined. The observational data used were obtained at the Radio Astronomy Laboratory of the Crimean Astrophysical Observatory (Ukraine) and the University of Michigan Radio Astronomy Observatory (USA). These data are used to construct kinematic models for active galactic nuclei using values for the orbital and precessional periods of binary systems consisting of supermassive black holes. The derived speeds of the companions in their orbits lie in the narrow range 3000–4000 km/s. The orbital radii for the binary supermassive black holes also lie in a narrow range, 10¹⁷–10¹⁸ cm, providing evidence that observed prominent examples of active galactic nuclei are fairly close binary systems. The parameters of the mediumin which the components of the binary systems are moving are estimated, as well as the rates at which the systems are losing orbital angular momentum and their lifetimes to coalescence.     

Population Structure of White Sea Harp Seals (<Emphasis Type=Italic>Pagophilus groenlandicus</Emphasis>) as an Adaptation to Habitat Conditions

The spatiotemporal distribution of harp seal pups around breeding grounds in the White Sea is considered. It is shown that spatial localization of groups of females with different terms of mass pup birth takes place. This somewhat confirms the data on the gregarious structure of White Sea harp seal population. It is possible to explain the structure of this adaptation of the seal population to different living conditions in different feeding areas.     

The earthquake of 6 September 2002 and the seismic history of Palermo (Northern Sicily,Italy): Implications for the seismic hazard assessment of the city

On September 6, 2002, a M_L = 5.6 earthquake, occurring some tens of kilometres offshore from the Northern Sicilian coast (Southern Tyrrhenian Sea), slightly damaged the city of Palermo and surroundings (degree 6 in the European Macroseismic Scale 1998). The macroseismic investigation of the shock and a detailed study of effects of the main earthquakes which affected Palermo in the past have been performed in order to evaluate the seismic response of the city. Moreover, the comparison of the recent event, which is instrumentally constrained, with historical earthquakes allows us to infer new insights on the seismogenic sources of the area, that seem located offshore in the Tyrrhenian sea.In the last 500 years, Palermo has never been completely destroyed but has suffered effects estimated between intensities 6 and 8 EMS-98 many times (1693, 1726, 1751, 1823, 1940, 1968, 2002). The damage scenarios of the analysed events have shown that damage distribution is strongly conditioned by soil response in the different parts of the city and by a high building vulnerability, mainly in the historical centre and in the south-eastern zone of the modern city. As a matter of fact, Palermo has always suffered greater effects than those reported for other nearby localities. The hazard assessment obtained using observed site intensities has shown that the probability of occurrence for intensity 8 (the strongest intensity observed in Palermo) exceeds 99% for 550 years, while the estimated mean return period is 152 ± 40 years. These results, in connection with building vulnerability due to the urban expansion before the introduction of seismic code, suggest that the city is exposed to a relatively high seismic risk.This paper has not been submitted elsewhere in identical or similar form, nor will it be during the first 3 months after its submission to Journal of Seismology.     

新丰江水库上游氮磷污染的时空变化

新丰江水库流域是广东省最大的饮用水源保护区,对东江下游和香港地区的用水安全有十分重要的作用,水质长期保持在国家地表水I类标准。但随着经济的发展,水库上游地区人类活动加剧,对水质和水量造成潜在威胁。通过2007、2008年对新丰江水库上游流域采样分析氮磷质量分数,发现总氮和总磷超过地表水Ⅱ类标准的采样点比例分别为48%和12%。与总磷相比,新丰江水库上游总氮的污染要更加严重,丰水期超标点明显少于枯水期,而枯水期氮-磷正相关关系较好（P＜0.000 1,R²＝0.868 3）,污染物可能为同一污染源或同期释放。空间上超标点多位于新丰、连平县城和大型城镇居民点如马头、忠信、灯塔镇附近,河流污染主要来自生活污水和养殖废水等人为点源污染。尽管目前新丰江水库库区的水质情况总体较好,但上游水质也存在恶化风险,可能导致水库自净能力降低,水体富营养化加剧,因此需要对新丰江水库上游的水质进行定期监测,通过控制内、外源性氮磷措施,以减少饮用水源安全风险和保证新丰江水库水质长期稳定。     

Flood basalts and metallogeny: The lithospheric mantle connection

Continental flood basalts, derived from mantle plumes that rise from the convecting mantle and possibly as deep as the core–mantle boundary, are major hosts for world-class Ni–Cu–PGE ore deposits. Each plume may have a complex history and heterogeneous composition. Therefore, some plumes may be predisposed to be favourable for large-scale Ni–PGE mineralisation (“fertile”).Geochemical data from 10 large igneous provinces (LIPs) have been collected from the literature to search for chemical signatures favourable for Ni–PGE mineralisation. The provinces include Deccan, Kerguelen, Ontong Java, Paraná, Ferrar, Karoo, Emeishan, Siberia, Midcontinent and Bushveld. Among these LIPs, Bushveld, Siberia, Midcontinent, Emei Mt and Karoo are “fertile”, hosting magmatic ore deposits or mineralisation of various type, size and grade. They most commonly intruded through, or on the edges of, Archaean–Paleoproterozoic cratonic blocks. In contrast, the “barren” LIPs have erupted through both continental and oceanic crustal terranes of various ages.Radiogenic isotopic signatures indicate that almost all parental LIP magmas are generated from deep-seated mantle plumes, and not from the more widespread depleted asthenospheric mantle source: this confirms generally accepted plume models. However, several important geochemical signatures of LIPs have been identified in this study that can discriminate between those that are “fertile” or “barren” in terms of their Ni–PGE potential.The fertile LIPs generally contain a relatively high proportion of primitive melts that are high in MgO and Ni, low in Al₂O₃ and Na₂O, and are highly enriched in most of the strongly incompatible elements such as K, P, Ba, Sr, Pb, Th, Nb, and LREE. They have relatively high Os contents (≥ 0.03 to 10 ppb) and low Re/Os (< 10). The fertile LIP basalts display trends of Sr–Nd–Pb isotopic variation intermediate between the depleted plume and an EM1-type mantle composition (and thus could represent a mixing of these two source types), and have elevated Ba/Th, Ba/Nb and K/Ti ratios. These elemental and isotopic signatures suggest that interaction between plume-related magmas and ancient cratonic lithospheric mantle with pre-existing Ni- and PGE-rich sulfide phases may have contributed significantly to the PGE and Ni budget of the fertile flood basalts and eventually to the mineralisation. This observation is consistent with the location of fertile LIPs adjacent to deep old lithospheric roots (as inferred from tectonic environment and also seen in global tomographic images) and has predictive implications for exploration models.Barren LIPs contain fewer high-MgO lavas. The barren LIP lavas in general have low Os contents (mostly ≤ 0.02 ppb) with high Re/Os (10–≥ 200). They show isotopic variations between plume and EM2 geochemical signatures and have high Rb/Ba ratios. These signatures may indicate involvement of deep recycled material in the mantle sources or crustal contamination for barren LIPs, but low degrees of interaction with old lithospheric-type roots.