The recent discovery of ultrahigh-pressure (UHP) mineral parageneses in the far-transported (greater than 400 km) Seve Nappe Complex of the Swedish Caledonides sheds new light on the subduction system that dominated the contracting Baltoscandian margin of continental Baltica during the Ordovician and culminated in collision with Laurentia in the Silurian to Early Devonian. High-grade metamorphism of this Neoproterozoic to Cambrian rifted, extended, dike-intruded outer-margin assemblage started in the Early Ordovician and may have continued, perhaps episodically, until collision of the continents at the end of this period. The recent discovery of UHP kyanite eclogite in northern Jämtland (west-central Sweden) yields evidence of metamorphism at depths of 100 km. Although UHP rocks are only locally preserved from retrogression during the long-distance transport onto the Baltoscandian platform, these high-pressure parageneses indicate that deep subduction played an important role in the tectonothermal history of the complex. Based on existing isotopic age data, this UHP metamorphism occurred in the Late Ordovician, shortly before, or during, the initial collision between the continents (Scandian orogeny). In some central parts of the complex, migmatization and hot extrusion occurred in the Early Silurian, giving way to thrust emplacement across the Baltoscandian foreland basin and platform that continued into the Early Devonian. Identifi cation of HP/UHP metamorphism at different levels within the Scandian allochthons, defi nition of their pressure-temperature-time paths, and recognition of their vast transport distances are essential for an understanding of the deeper structural levels of the orogen in the hinterland (e.g., the Western Gneiss Region), where the attenuated units were reworked together during the Early Devonian.
Abstract. The safety of using meat and bone meal (MBM) in mammal feed was studied in view of BSE, by quantifying the risk of BSE transmission through different infection routes. This risk is embodied in the basic reproduction ratio R 0 of the infection, i.e. the average number of new infections induced by one initial infection. Only when R 0 is below 1, will the disease die out with certainty and the population will become free from BSE. Unfortunately this is a slow process due to the slow progression of the disease.We calculate R 0 explicitly from basic ingredients taking several different transmission routes into account. Several of the basic ingredients are functions of age or of infection-age. We also calculate the exponential growth rate r in terms of the same basic ingredients.Next we quantify the ingredients from available data and compute the effects on R 0 of various scenario's for controlling BSE, with examples for the UK and the Netherlands.
Rocks of the Lok Ulo Complex crop out over a small area in the vicinity of Karangsambung in central Java. They are part of a belt of Cretaceous accretionary-collision complexes that appear sporadically in an arc extending from Java to Kalimantan and Sulawesi. The complex consists of dismembered ophiolites, sedimentary rocks, and crystalline schists and gneisses occurring as tectonic slabs in a black-shale matrix tectonic mélange. High-pressure rocks such as eclogite, glaucophane rock and blueschist crop out in a thin zone between the low-grade schists and a serpentinite zone along the Muncar and Gua rivers. Some of the eclogite blocks contain tourmaline, which is restricted to the outer shells of-and veins in-such blocks.The early metamorphic stage (stage I) of the Lok Ulo eclogites comprises garnet (core) and omphacite + Ca-Na amphibole + phengite + rutile + epidote inclusions in the garnet core. Stage II is characterized by garnet (rims of porphyroblasts) + omphacite + rutile + phengite + Ca-Na amphibole. The matrix constituents, which are similar to those of stages I and II, are related to stage III (late or "peak" eclogitic stage). The blueschist overprint of the eclogites occurred during stage IV. The corresponding assemblage is Na amphibole + chlorite + albite + epidote + quartz + titanite + ilmenite. Subsequently, poikiloblastic tourmaline and apatite grew at the expense of chlorite, epidote, and other minerals in some eclogites (stage V).The P-T path of tourmaline-bearing eclogites is characterized by rising pressures at decreasing temperatures (stage I to stage III: P = 22.5 kbar and T = 365°C), whereas the normal eclogites show rising temperatures at increasing pressure (stage III: P = 20.5 kbar and T = 410°C). Thus, these eclogites were subducted to ~70 km depth at a geothermal gradient of ~6 C°/km. Stage IV is limited to the P-T range of 8-10 kbar and 350-400°C for both eclogite types. The different P-T paths (counterclockwise and clockwise) are explained by metamorphism within a subduction channel. The low geothermal gradient is probably due to a high rate of subduction of a cold oceanic plate.
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