Sequential integrated inversion of refraction and wide-angle reflection traveltimes and gravity data for two-dimensional velocity structures

A new algorithm is presented for the integrated 2-D inversion of seismic traveltime and gravity data. The algorithm adopts the 'maximum likelihood' regularization scheme. We construct a 'probability density function' which includes three kinds of information: information derived from gravity measurements; information derived from the seismic traveltime inversion procedure applied to the model; and information on the physical correlation among the density and the velocity parameters. We assume a linear relation between density and velocity, which can be node-dependent; that is, we can choose different relationships for different parts of the velocity–density grid. In addition, our procedure allows us to consider a covariance matrix related to the error propagation in linking density to velocity. We use seismic data to estimate starting velocity values and the position of boundary nodes. Subsequently, the sequential integrated inversion (SII) optimizes the layer velocities and densities for our models. The procedure is applicable, as an additional step, to any type of seismic tomographic inversion.
We illustrate the method by comparing the velocity models recovered from a standard seismic traveltime inversion with those retrieved using our algorithm. The inversion of synthetic data calculated for a 2-D isotropic, laterally inhomogeneous model shows the stability and accuracy of this procedure, demonstrates the improvements to the recovery of true velocity anomalies, and proves that this technique can efficiently overcome some of the limitations of both gravity and seismic traveltime inversions, when they are used independently.
An interpretation of field data from the 1994 Vesuvius test experiment is also presented. At depths down to 4.5 km, the model retrieved after a SII shows a more detailed structure than the model obtained from an interpretation of seismic traveltime only, and yields additional information for a further study of the area.     

Hydrological and biogeochemical features of the Northern Adriatic Sea in the period 2003–2006

This paper reports on the main biogeochemical properties of the Northern Adriatic Sea in the period May 2003–November 2006 within the framework of the European program INTERREG III Italy‐Slovenia. Spatial and temporal distributions of water density, dissolved oxygen, nutrients (nitrogen, phosphorous and silicon) and chlorophyll a are presented. Multivariate methods such as fuzzy k‐means, self‐organising maps and cluster analysis were used to identify the different water masses and to characterise the temporal and spatial variability of the main biogeochemical features present in the area. The results confirm that the Po River outflows and the meteorological forcing factors are the main components triggering the alternation of stratification and mixing of the water column and that strongly affect the trophic state of the basin. In general, oligotrophic conditions dominate, and were more pronounced offshore, but mesotrophy occurred episodically in May 2004 and July 2005, when phytoplankton blooms were observed concomitant with vertical stability of the water column. A marked interannual variability was also observed, supporting the importance of maintaining long‐term observations of the basin.     

The application of a Marine Biotic Index to different impact sources affecting soft-bottom benthic communities along European coasts

Following the European Water Framework Directive (2000/60/EC), the authors proposed, in a previous contribution, a Marine Biotic Coefficient (BC) to establish the ecological quality of soft-bottom benthos within European estuarine and coastal environments. The present study examines the application of the BC to the Atlantic (North Sea; Bay of Biscay; South of Spain) and Mediterranean (Spain and Greece) European coasts. The investigation assesses also the usefulness of the BC, in relation to different impact sources (e.g. drilling cuts with ester-based mud, submarine outfalls, heavy metals, industrial and mining wastes, jetties and sewerage works). The results obtained are consistent with those obtained using several methods and parameters, such as richness, diversity, evenness, Abundance-Biomass comparison plots and univariate and multivariate statistical analyses. The BC values provide a simple and clearly defined way to establish the ecological quality of soft-bottom benthos, complementary to the above mentioned methods.     

Geology and ore enrichment factors at the Radiore mine,Quebec

The Radiore Cu-Zn massive sulfide deposit occurs in Archean metavolcanic rocks of the Abitibi greenstone belt in northwestern Quebec. The ore forms a stratiform lens between a massive rhyolite flow and a unit of mixed basaltic and intermediate flows. Intrusions of thick dykes of gabbro-diorite, quartz-diorite and granodiorite, and of the Bell River igneous complex, closely surround the ore lens. All the volcanic rocks, the quartz-diorite, grandiorite and the igneous complex are tholeiitic, whereas the gabbro-diorite is of calc-alkaline affinity. Sedimentary structures are prevalent in the ore, and heavily chloritized and biotitized rocks form a stratiform alteration zone mainly below the ore, indicating a distal-type deposit.Ore enrichment factors (wt % metal in ore/wt % metal in source rock) are calculated from analyses of ore and source rocks, assuming that seawater-derived brines leached ore materials from underlying rocks and precipitated them at the point of brine discharge onto the seafloor. Cd, Zn, Cu, Au and Ag are most highly enriched, followed by Bi, Pb, Sn, As and Co. Mo, W, V, Cr, Mn and Ni are not enriched at Radiore.     

西秦岭地区卡林-类卡林型金矿床及其成矿时间、构造背景和模式

秦岭造山带是世界第二大卡林-类卡林型金矿省,其地质背景与美国西部卡林-类卡林型金矿省明显不同,位于大陆内部的碰撞造山带,而非活动大陆边缘的盆岭省。秦岭卡林-类卡林型金矿主要赋存于板块缝合带及其前陆冲断带的海西-印支构造层中,以泥盆系和三叠系为主,主要岩性为瀉湖-浅海相的含碳细碎屑岩-碳酸盐岩建造,即碳硅泥岩系;成矿元素为Au-As-Sb-Hg-Ag,缺乏T1,共生矿种为Sb,Hg,Ag,U和重晶石等;成矿温度为160～300℃,流体盐度为4％～10％(NaClcq),压力为5～50MPa,深度约0．5～5km,属于中低温中浅成热液矿床,与内华达卡林-类卡林型金矿一致。成矿流体具有建造水特点,C2H6含量较高,显示了有机流体参与成矿。成矿同位素年龄介于220～100Ma之间,以170Ma为高峰,地球动力学背景属碰撞造山过程挤压-伸展转变期的减压增温体制,成矿构造模式为碰撞造山成岩成矿和流体作用模式。陆陆碰撞过程中,沿龙门山、阿坝-黑水-平青、若尔盖-文县、玛曲-勉县-略阳、白龙江、双河-公馆、凤县-镇安、安康等大型断裂带的陆内俯冲作用不仅导致了西秦岭地壳缩短增厚隆升,而且使俯冲板片变质脱水、熔融,派生成矿流体和相关熔体,流体和熔体的上升到仰冲板片次级构造带,形成了卡林-类卡林型和造山型金矿成矿系统。据此提出,西秦岭深部可能存在潜力巨大的造山型金矿省。     

天山-阿尔泰东部地区海西晚期后碰撞铜镍硫化物矿床:主要特点及可能与地幔柱的关系

天山—阿尔泰东部地区是中国重要的铜镍成矿区,近年来针对区内的铜镍矿床和相关岩体的研究不断取得进展,找矿也取得了一系列新突破,已经探明了十几个矿床和矿点。笔者基于以往研究成果,结合目前地质勘查和找矿评价的新进展,比较详细地全面总结了后碰撞铜镍硫化物矿床的基本特点、成矿规律和成矿过程,并建立了描述性成矿模型。这些矿床沿一组平行的走向近东西的深大断裂分布,与成矿有关的镁铁质—超镁铁质杂岩体一般不大于5km2,小的可为一个岩墙。矿化分两种类型:通道型和熔离型。成矿时代为298~270Ma,为中亚成矿带大规模成矿期的组成部分,形成于后碰撞伸展阶段。与这组铜镍硫化物矿床有关的镁铁质—超镁铁质杂岩体可能是早二叠世大面积喷溢岩浆的残留根部或通道部分,可能与地幔柱活动有关。另外,针对区内的地质特征,结合以往找矿的成功经验,对区内进一步的找矿工作提出了一些设想和建议。     

Implementation of the European water framework directive from the Basque country (northern Spain): a methodological approach

The European Water Framework Directive provides a challenge in the development of new and accurate methodologies. It addresses assessment of Ecological Quality Status within European rivers, lakes, groundwaters, estuaries and coasts. Although this directive is simple and flexible in its concept, it is necessary to develop an approach based upon scientific knowledge; however, at the same time it should be as simple as possible, in order to achieve both requirements and comparability of results throughout European waters. This contribution presents the first methodological approach to the problem, as used for estuaries and coasts of the Basque Country (northern Spain), in: selecting typologies and reference conditions; determining biological quality and ecological status; and identifying some problems in implementing the WFD. As such, the present paper could serve as the basis for a discussion document for other regions and countries, throughout Europe.     

A recipe for simulating the interannual variability of the Asian summer monsoon and its relation with ENSO

This study investigates how accurately the interannual variability over the Indian Ocean basin and the relationship between the Indian summer monsoon and the El Niño Southern Oscillation (ENSO) can be simulated by different modelling strategies. With a hierarchy of models, from an atmospherical general circulation model (AGCM) forced by observed SST, to a coupled model with the ocean component limited to the tropical Pacific and Indian Oceans, the role of heat fluxes and of interactive coupling is analyzed. Whenever sea surface temperature anomalies in the Indian basin are created by the coupled model, the inverse relationship between the ENSO index and the Indian summer monsoon rainfall is recovered, and it is preserved if the atmospherical model is forced by the SSTs created by the coupled model. If the ocean model domain is limited to the Indian Ocean, changes in the Walker circulation over the Pacific during El-Niño years induce a decrease of rainfall over the Indian subcontinent. However, the observed correlation between ENSO and the Indian Ocean zonal mode (IOZM) is not properly modelled and the two indices are not significantly correlated, independently on season. Whenever the ocean domain extends to the Pacific, and ENSO can impact both the atmospheric circulation and the ocean subsurface in the equatorial Eastern Indian Ocean, modelled precipitation patterns associated both to ENSO and to the IOZM closely resemble the observations.