Paleomagnetic determination of emplacement temperatures of pyroclastic deposits: an under-utilized tool

Paleomagnetic data from lithic clasts collected from Mt. St. Helens, USA, Volcán Láscar, Chile, Volcán de Colima, Mexico and Vesuvius, Italy have been used to determine the emplacement temperature of pyroclastic deposits at these localities and to highlight the usefulness of the paleomagnetic method for determining emplacement temperatures. At Mt. St. Helens, the temperature of the deposits (T _dep ) at three sites from the June 12, 1980 eruption was found to be ≥532°C, ≥509°C, and 510–570°C, respectively. One site emplaced on July 22, 1980 was emplaced at ≥577°C. These new paleomagnetic temperatures are in good agreement with previously published direct temperature measurements and paleomagnetic estimates. Lithic clasts from pyroclastic deposits from the 1993 eruption of Láscar were fully remagnetized above the respective Curie temperatures, which yielded a minimum T _dep of 397°C. Samples were also collected from deposits thought to be pyroclastics from the 1913, 2004 and 2005 eruptions of Colima. At Colima, the sampled clasts were emplaced cold. This is consistent with the sampled clasts being from lahar deposits, which are common in the area, and illustrates the usefulness of the paleomagnetic method for distinguishing different types of deposit. T _dep of the lower section of the lithic rich pyroclastic flow (LRPF) from the 472 A.D. deposits of Vesuvius was ~280–340°C. This is in agreement with other, recently published paleomagnetic measurements. In contrast, the upper section of the LRPF was emplaced at higher temperatures, with T _dep ~520°C. This temperature difference is inferred to be the result of different sources of lithic clasts between the upper and lower sections, with the upper section containing a greater proportion of vent-derived material that was initially hot. Our studies of four historical pyroclastic deposits demonstrates the usefulness of paleomagnetism for emplacement temperature estimation.     

Growth of complex sheeted zones during recycling of older magmatic units into younger: Sawmill Canyon area,Tuolumne batholith,Sierra Nevada,California

In Sawmill Canyon, located near the eastern margin of the Tuolumne batholith, central Sierra Nevada, California, a series of petrologically and structurally complex, magmatic sheeted zones intrude older granodioritic units (Kuna Crest and equigranular Half Dome) and in one case truncate these units along a sharp contact. These sheeted zones (a) consist of numerous batches of (now frozen) magma, (b) display clear outward growth directions, (c) were actively deforming during and after emplacement resulting in magmatic folds, faults and multiple magmatic mineral fabrics, and (d) are the location of numerous, but localized magma flow structures (schlieren-bounded tubes, troughs, megacryst-rich pipes) and instabilities (load casts, flame structures, slumps, diapirs, ridge and pillar structures). Geochemical data indicate that the sheeted zones largely consist of magmas derived from the Half Dome granodiorite with some late Cathedral Peak granodiorite pulses, and with fractionation and flow sorting forming widespread layering in the above structures.     

Transdisciplinary co-operation for an ecosystem approach to fisheries: A case study from the South African sardine fishery

Integrative approaches that involve natural and social scientists are needed to manage fisheries, but these are difficult to achieve. The process of developing a prototype, knowledge-based, electronic decision support tool for the South African sardine Sardinops sagax fishery provided a platform for fostering collaboration and achieving active participation of many stakeholders. The aim of the decision support tool is to assist managers in evaluating how effectively an ecosystem approach to fisheries (EAF) has been implemented for this fishery. The collaborative process involved a series of meetings during which knowledge was elicited from fisheries scientists, social scientists, resource managers and fishing industry representatives. Conceptualisations of the different stakeholder perspectives were developed in terms of objectives and indicators following the hierarchical tree approach recommended by FAO. This paper describes the collaborative process. Hierarchies of objectives, indicators and data sets for the human dimension of an EAF in the South African sardine fishery are introduced. The value of a transdisciplinary approach towards an EAF in South Africa is discussed.     

A novel shear vane used to determine the evolution of hydraulic dredge tracks in sub-tidal marine sediments

A novel shear vane is described which can be used to record the shear strength of discrete depth horizons of a variety of marine sediment types in situ. This vane, or modifications of it, has great potential in allowing measurement of in situ shear strength without requiring any samples to be removed from the sea bed, a process which can often destroy the fine structure of the sediment. The vane was used to monitor the change in sediment shear strength caused by a hydraulic dredge, which was used to fish razor clams (Ensis arcuatus) in a sheltered bay within the Clyde Sea area, Scotland. Data collected using this apparatus provided valuable and immediate information on the stratification of the sea bed post-dredging and allowed the evolution of the dredge track to be regularly monitored by divers over a period of 100 d.     

Early presence of Bythotrephes cederströmii (Cladocera: Cercopagidae) in lake sediments in North America: evidence or artifact?

Journal of Paleolimnology - The spiny water flea (Bythotrephes cederströmii), a freshwater crustacean considered to be the world’s best-studied invasive zooplankter, was first recorded...     

How late are K-feldspar megacrysts in granites?

Various petrologists have suggested that K-feldspar megacrysts grow in granites that are extensively crystallized, even at subsolidus conditions. However, experimental evidence indicates that, though K-feldspar nucleates relatively late in the crystallization history, abundant liquid is available for development of large crystals. A great deal of evidence, involving many different factors, favours a magmatic/phenocrystic origin for K-feldspar megacrysts in granites, namely simple twinning, oscillatory zoning, euhedral plagioclase inclusions, and concentric, crystallographically controlled arrangements of inclusions. In addition, abundant evidence has been presented of (1) mechanical accumulation of K-feldspar megacrysts in granites, (2) alignment of megacrysts and megacryst concentrations in magmatic flow foliations, (3) involvement of megacrysts in zones of magma mixing in granite plutons, and (4) occurrence of megacrysts in some volcanic rocks, implying that the megacrysts were suspended in enough liquid to be moved without fracturing or plastic deformation. Detailed trace element and isotopic data also indicate that megacrysts can move between coexisting felsic and more mafic magmas. Irregular overgrowths on megacrysts are consistent with continued magmatic growth after euhedral megacrystic growth ceased, the overgrowths being impeded by simultaneously crystallizing quartz and feldspar grains.     

Place-Based Pathways to Proenvironmental Behavior: Empirical Evidence for a Conservation–Recreation Model

This study expands existing models of proenvironmental behavior (PEB) to examine the potentially important and interacting influences of nature-based recreation and sense of place on participation in conservation-oriented activities. We tested hypothesized relationships using a structural equation modeling approach that accounted for common behavioral antecedents within a sample of 1,124 nature-based recreationists and property owners in rural counties of New York, USA. We found that place attachment played an important role in strengthening connections between nature-based recreation and PEB. Birdwatching and hunting participation contributed independently and significantly to PEB, both directly and indirectly through effects on place meanings and place attachment. While birdwatching appeared to influence place attachment by impacting environmental place meanings, hunting exerted similar effects by affecting sociocultural place meanings. Ultimately, our synthesis results in the articulation of a comprehensive conservation–recreation model that could help researchers and practitioners identify and explore novel pathways to PEB.