Geochemistry and tectonic significance of peridotites from the South Sandwich arc–basin system, South Atlantic     

J. A. Pearce  P. F. Barker  S. J. Edwards  I. J. Parkinson  P. T. Leat 《Contributions to Mineralogy and Petrology》2000,139(1):36-53

Petrographic and geochemical studies of peridotites from the South Sandwich forearc region provide new evidence for the evolution of the South Sandwich arc–basin system and for the nature of interactions between arc magma and oceanic lithosphere. Peridotites from the inner trench wall in the north-east corner of the forearc vary from clinopyroxene-bearing harzburgites, through samples transitional between harzburgites and dunites or wehrlites, to dunites. The harzburgites are LREE depleted with low incompatible element abundances and have chromites with intermediate Cr# (ca. 0.40). Modelling shows that they represent the residues from 15–20% melting at oxygen fugacities close to the QFM buffer. The dunites have U-shaped REE patterns, low incompatible element abundances and high Cr# (0.66–0.77). Petrography and geochemistry indicate that the latter are the product of intense interaction between peridotite and melt saturated with olivine under conditions of high oxygen fugacity (QFM + 2). The transitional samples are the product of lesser interaction between peridotite and melt saturated with olivine ± clinopyroxene. The data demonstrate that the harzburgites originated as the residue from melting at a ridge (probably the early East Scotia Sea spreading centre), and were subsequently modified to transitional peridotites and dunites by interaction with South Sandwich arc magmas. The second dredge locality, near the South Sandwich Trench–Fracture Zone intersection, yielded rocks ranging from lherzolite to harzburgite that could similarly have resulted from a two-stage melting and enrichment process, but involving a more fertile mantle residue and a reacting melt that is transitional between MORB and island arc tholeiite. The South Sandwich peridotites have a similar petrogenetic history to those from Conical Seamount in the Mariana forearc in the sense that both involved interaction between arc magma and pre-existing mantle lithosphere of different provenance. However, the precise compositions of the magma and mantle components vary from location to location according to the precise tectonic setting and tectonic history. Overall, therefore, data from the South Sandwich and Izu–Bonin–Mariana systems emphasise the potential significance of peridotite geochemistry in unravelling the complex tectonic histories of forearcs past and present. Received: 31 August 1999 / Accepted: 3 December 1999  相似文献   

Understanding single-station ground motion variability and uncertainty (sigma): lessons learnt from EUROSEISTEST     

Olga-Joan Ktenidou  Zafeiria Roumelioti  Norman Abrahamson  Fabrice Cotton  Kyriazis Pitilakis  Fabrice Hollender 《Bulletin of Earthquake Engineering》2018,16(6):2311-2336

Accelerometric data from the well-studied valley EUROSEISTEST are used to investigate ground motion uncertainty and variability. We define a simple local ground motion prediction equation (GMPE) and investigate changes in standard deviation (σ) and its components, the between-event variability (τ) and within-event variability (φ). Improving seismological metadata significantly reduces τ (30–50%), which in turn reduces the total σ. Improving site information reduces the systematic site-to-site variability, φ _S2S (20–30%), in turn reducing φ, and ultimately, σ. Our values of standard deviations are lower than global values from literature, and closer to path-specific than site-specific values. However, our data have insufficient azimuthal coverage for single-path analysis. Certain stations have higher ground-motion variability, possibly due to topography, basin edge or downgoing wave effects. Sensitivity checks show that 3 recordings per event is a sufficient data selection criterion, however, one of the dataset’s advantages is the large number of recordings per station (9–90) that yields good site term estimates. We examine uncertainty components binning our data with magnitude from 0.01 to 2 s; at smaller magnitudes, τ decreases and φ _SS increases, possibly due to κ and source-site trade-offs Finally, we investigate the alternative approach of computing φ _SS using existing GMPEs instead of creating an ad hoc local GMPE. This is important where data are insufficient to create one, or when site-specific PSHA is performed. We show that global GMPEs may still capture φ _SS , provided that: (1) the magnitude scaling errors are accommodated by the event terms; (2) there are no distance scaling errors (use of a regionally applicable model). Site terms (φ _S2S ) computed by different global GMPEs (using different site-proxies) vary significantly, especially for hard-rock sites. This indicates that GMPEs may be poorly constrained where they are sometimes most needed, i.e., for hard rock.  相似文献   

A demographic model for Palaeolithic technological evolution: The case of East Asia and the Movius Line     

Stephen J. Lycett  Christopher J. Norton 《Quaternary International》2010,211(1-2):55-65

The Pleistocene record of East Asia continues to pose controversial questions for palaeoanthropology, especially with regard to Palaeolithic technological patterns. In recent years, an increased understanding of the effect of demography on cultural transmission has improved our understanding of the incidence, proliferation, and elaboration of technological traditions. Here, we present a generalised null model of Lower–Middle Palaeolithic technological evolution, which expressly links cultural transmission theory and demographic factors (i.e. population size, density, and social interconnectedness). Consistent with our model, Africa exhibits evidence of major technological innovations during the Early to Middle Pleistocene, due to a constant source of population and growth due to accumulation through time. In comparison, Pleistocene East Asian assemblages are dominated by Mode 1-type technologies, and only a few localized occurrences of bifacial technology are currently known. We detail evidence suggesting that during much of the Pleistocene a combination of biogeographical, topographical, and dispersal factors are likely to have resulted in relatively lower effective population sizes in East Asian hominins compared with western portions of the Old World, particularly Africa. Thus, the Movius Line – as is the case with its namesake ‘Wallace's line’ – must be examined in terms of its biogeographical context, if the divergent evolutionary trajectories of entities either side of it are to be understood. Most parsimoniously, the Movius Line sensu lato is thus a ‘line’ which represents the crossing of a demographic threshold. Under the parameters of our (testable) null model, geographically and temporally sporadic occurrences of bifacial technology in East Asia are the product of short-lived instances of technological convergence. As a consequence, the in situ evolution of Levallois (Mode 3) was inhibited in East Asia due to the constraints of relatively smaller effective population sizes.  相似文献   

GIS-based mineral potential modeling by advanced spatial analytical methods in the southeastern Yunnan mineral district,China     

《Ore Geology Reviews》2015

This paper demonstrates a modeling procedure of mineral potential mapping based on singularity theory, and further presents an idea to look into metallogeny of Sn–Cu polymetallic deposits in southeastern Yunnan mineral district, China by applying a localized regression method. Mineralization is a typical cascade process generally accompanied by irregular geological, geochemical and geophysical signatures. Singularity index as an efficient anomaly analytical tool helps to identify anomalies as well as characterize formation processes of these anomalies. In this study, the singularity-based mineral potential mapping method was utilized to characterize hydrothermal mineralization associated with magmatic, tectonic and sedimentary processes in this district. Based on the results, a mineral prospectivity model was constructed to delineate target areas. In addition to mineral prospectivity, controlling effects of geo-processes on mineralization are spatially non-stationary. Geographically-weighted regression analysis was thus employed to investigate these spatially-varied controlling effects and it has contributed to improve understanding to local metallogeny in the study area. Results of the spatial analysis presented can be used to guide following stages of mineral exploration in the district.  相似文献   

Financial services for small and medium-scale aquaculture and fisheries producers     

《Marine Policy》2013

This article summarises the results of case studies carried out in six developing countries. The case studies analyse the economics of small and medium-scale aquaculture and fisheries enterprises, in particular their capital requirement to cover investment and operating costs, and discuss the demand and supply of financial services. Given that capture fisheries face problems in many parts of the world due to stagnating or declining stocks, it is likely that in the future aquaculture, including mariculture, will have to play an increasing role in supply. In order to achieve sustainable growth in aquaculture businesses in sub-Saharan Africa a range of constraints—technical and financial—need to be overcome. Traditional financial instruments seem unable to meet the financial needs of small and medium-scale enterprises (SMEs) in the aquaculture and fisheries sector. Accordingly, innovative financial models for SMEs need to be developed to fill the gap between traditional banking and grant-based donor finance. One key characteristic of investment funds specialising in SMEs in Africa is the combination of investment funds with business development funds in order to ensure the economic growth of SMEs as well as the likelihood of prompt loan repayment.  相似文献   

Conserving Quaternary geoheritage in Northern Ireland     

《Proceedings of the Geologists' Association. Geologists' Association》2023,134(4):432-448

Northern Ireland has a rich and varied Quaternary geoheritage. Landforms and sediments from the last glacial phase of the Late Pleistocene are most prevalent, though the record extends from the last interglacial (MIS 5e) to the Holocene. The glacial record in the region continues to play a crucial role in the development of models of the last British-Irish Ice Sheet, with many sites having international significance. It is the role of the Northern Ireland Environment Agency to legally protect and conserve this important Quaternary heritage, and a programme of statutory designation of these sites as Areas of Special Scientific Interest (ASSIs) has been in place for over twenty years. ASSIs are selected from the Pleistocene and Holocene themes of the Earth Science Conservation Review, the process through which geological sites in Northern Ireland are assessed to determine their importance to science, and so to geoconservation. This produced a significant series of reports that have contributed much to the grey and white literature for the Quaternary in the United Kingdom and Ireland. Quaternary geoheritage is recognised in the local planning system and existing and potential UNESCO Global Geoparks further serve to promote and protect this aspect of Northern Ireland's natural heritage. This paper summarises the Quaternary history of Northern Ireland, how ASSIs are selected to reflect this and how they are monitored and managed. It also considers how to ensure continued protection and recognition for Quaternary sites and features in the region.  相似文献   

The Kula–Salihli UNESCO Geopark: Spectacular records of Quaternary volcanism,fluvial and landscape evolution and Quaternary environmental change     

《Proceedings of the Geologists' Association. Geologists' Association》2023,134(4):416-431

The Kula–Salihli UNESCO Geopark, western Turkey, is a tectonically and volcanically active region in which the most recent eruptions of basaltic lava, associated with scoria cone formation, were during the latest Pleistocene and the Holocene. Much older volcanism within the same volcanic province is also in evidence, with some of the older lavas capping mesa-style uplands, such that they have preserved underlying poorly consolidated sediments that would otherwise have been lost to erosion. Beneath these hill-capping lavas, above the Neogene sediments representing endorheic basin-fill, are the early gravels of the River Gediz system, forming narrowly separated terraces (separation by a few metres) thought to have been formed in response to the ~ 41 kyrs obliquity-driven climate cycles of the Early Pleistocene. The rarity of terrace preservation from this early part of the Quaternary makes this a very valuable part of the geopark, in which there is also evidence for the progressive incision into the landscape, and for periodic damming of the river system by lava eruptions, bringing about lacustrine phases that can be recognized from lake sediments and deltas that were built into the former lakes. The combination of volcanic and drainage evolutionary evidence has few if any parallels elsewhere. The geopark, which also contains sites of archaeological and historical importance, is managed sustainably in order to maximize its educational, economic, touristic and heritage value.  相似文献   

Bajsaphididae fam. nov., from the Lower Cretaceous of Baissa,Russia: A new family of aphids and its evolutionary significance     

《Cretaceous Research》2015

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The role of the marine sector in the Irish national economy: An input–output analysis     

《Marine Policy》2013

Recent research in Ireland has estimated both the national and regional economic value of the marine sector. However, economic activity does not exist in a vacuum. Activities in the marine sector not only directly affect the industries in the sector but also influence other sectors through inter-sectoral linkages. This paper uses an input–output (IO) methodology to examine the linkages and production effects of the Irish marine sector on the national economy. Disaggregating the Irish IO table for 2007 to include 10 additional marine sectors, this paper represents the first effort to quantify the inter-industry linkage effects, production-inducing effects and employment multipliers in the marine sector. This analysis found that a number of marine sectors, notably the maritime transportation sector, have an important economic role within the wider Irish economy.  相似文献   

Choosing a fishery’s governance structure using data poor methods     

《Marine Policy》2013

Multi-species fisheries are complex to manage and the ability to develop an appropriate governance structure is often seriously impeded because trading between sustainability objectives at the species level, economic objectives at the fleet level, and social objectives at the community scale, is complex. Many of these fisheries also tend to have a mix of information, with stock assessments available for some species and almost no information on other species. The fleets themselves comprise fishers from small family enterprises to large vertically integrated businesses. The Queensland trawl fishery in Australia is used as a case study for this kind of fishery. It has the added complexity that a large part of the fishery is within a World Heritage Area, the Great Barrier Reef Marine Park, which is managed by an agency of the Australian Commonwealth Government whereas the fishery itself is managed by the Queensland State Government. A stakeholder elicitation process was used to develop social, governance, economic and ecological objectives, and then weight the relative importance of these. An expert group was used to develop different governance strawmen (or management strategies) and these were assessed by a group of industry stakeholders and experts using multi-criteria decision analysis techniques against the different objectives. One strawman clearly provided the best overall set of outcomes given the multiple objectives, but was not optimal in terms of every objective, demonstrating that even the “best” strawman may be less than perfect.  相似文献