Dynamical Initialization of Boundary-Layer Data

A procedure for the dynamic initialization of wind and temperature fields within the atmospheric boundary layer (ABL) is presented. The procedure uses transilient turbulence theory to assess the turbulent fluxes from observed wind and temperature data, which are used to estimate the eddy transfer coefficients, so enabling a local closure ABL model to be integrated forward in time to a new steady state. The method has been applied to initialize kytoon data taken at Kharagpur (22.3° N, 87.2° E) during the MONTBLEX field programme. Results of a case study for 17 June 1990 are discussed.     

Caledonian eclogite-facies metamorphism of Early Proterozoic protoliths from the North-East Greenland Eclogite Province

High-pressure metamorphic assemblages occur in mafic, ultramafic and a few intermediate rocks in a gneiss complex that covers an area of approximately 400 × 100 km in the North-East Greenland Caledonides. Detailed petrologic and geochronologic studies were carried out on three samples in order to clarify the P-T-t evolution of this eclogite province. Geothermobarometry yields temperature estimates of 700–800 °C and pressure estimates of at least 1.5 GPa from an eclogite sensu stricto and as high as 2.35 GPa for a garnet websterite. The eclogite defines a garnet-clinopyroxene-amphibole-whole rock Sm-Nd isochron age of 405 ± 24 Ma (MSWD 0.9). Isofacial garnet websterites define garnet-clinopyroxene-orthopyroxene-amphibole-whole rock-(biotite) ages of 439 ± 8 Ma (MSWD =2.1) for a coarse-grained sample and 370 ± 12 Ma (MSWD=0.6) for a finer-grained variety. Overgrowths on zircons from the fine-grained pyroxenite and the eclogite give a pooled ²⁰⁶Pb/²³⁸U SHRIMP age of 377 ± 7 Ma (n=4). Significantly younger Rb-Sr biotite ages of 357 ± 8, 330 ± 6 and 326 ± 6 agree with young Rb-Sr, K-Ar and ⁴⁰Ar/³⁹Ar mineral ages from the gneiss complex and indicate slow cooling of the eclogitic rocks. High-pressure metamorphism may have been at least 439 Ma old (Siluro-Ordovician) with cooling through amphibolite-facies conditions in the Devonian and continued crustal thinning and exhumation well into the Carboniferous. Sm-Nd whole rock model ages indicate the eclogite protoliths are Early Proterozoic in age, while ²⁰⁷Pb/²⁰⁶Pb SHRIMP ages of 1889 ± 18 and 1981 ± 8 from anhedral zircon cores probably reflect Proterozoic metasomatism. The samples have negative ɛ_Nd values (−5 to −16) and elevated ⁸⁷Sr/⁸⁶Sr ratios (0.708–0.715), consistent with field evidence that the eclogite protoliths were an integral part of the continental crust long before Caledonian metamorphism. The presence of a large Caledonian eclogite terrane in Greenland requires modification of current tectonic models that postulate subduction of Baltica beneath Laurentia during the Caledonian orogeny. Received: 9 October 1996 / Accepted: 7 July 1997     

The role of rock and clast fabric in the physical performance of crushed-rock aggregate

Crushed rock aggregate responds in a rational and predictable manner to the two tests designed by British Standards for assessing aggregate strength, i.e., Aggregate Impact (IV) and Crushing Values (ACV). The values obtained in both tests are influenced by intrinsic geological factors namely, petrology, petrography, rock and clast fabric. The Impact Value is affected further by procedural variables which have been identified and evaluated. When the effects of all these variables are known it is possible to understand the meaning of variation in test values within and between rock groups.Two new indices Impact and Aggregate Crushing Value Residues were introduced to probe more deeply the effects of cataclasis during testing. These have proved to be sensitive indicators of the geological variables like petrology and clast shape.In view of the rational behaviour of aggregate in the predictive tests it is possible to erect a new and more utilitarian classification of roadstone materials based on mechanical factors rather than the mineralogical-chemical basis of existing classifications. An outline of such a classification is presented.     

Climate Suitability: For Stable Malaria Transmission in Zimbabwe Under Different Climate Change Scenarios

As climate is one factor determining the potential range of malaria, climate change may work with or against efforts to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission is based on the MARA/ARMA model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using sixteen projections of climate in 2100. The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while the lowveld and areas currently limited by precipitation show varying degrees of change, depending on climate sensitivity and greenhouse gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used within or across other African countries. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geochemistry of newly discovered quaternary Shiribeshi Volcano,Northeast Japan Sea

Summary Shiribeshi Seamount is located to the east of the Okushiri Ridge, in the northeast Japan Sea. Whole rock K-Ar age of olivine-augite andesite dredged from the Seamount was determined to be 0.9 ± 0.2 Ma (Tsuchiya et al., 1989), indicating that Shiribeshi Seamount is a Quaternary volcano in the back-arc region off the junction of the Northeast Japan and Kurile arcs. Shiribeshi volcano is composed of basalt to rhyolite, which show a typical island arc calc-alkaline nature on the basis of petrographical characteristics of 95 samples dredged from four sites. Abundances of incompatible elements including K, Rb, Sr, Nb, P, Ti, Y and Zr in 16 representative rocks are discussed, together with those in the Quaternary volcanic rocks from the NE Japan and Kurile arcs in terms of compositional variation across the arcs. The estimated composition of the primary magma of Shiribeshi volcano is characterized by higher incompatible element contents and a higher Zr/Y ratio than primary magmas in the volcanic front side. Based on HFS element concentrations the degree of partial melting for three primary magmas of Oshima-Oshima, Shiribeshi and Rishiri volcanoes in the northeast Japan Sea may decrease gradually with increasing distance from the volcanic front. However, LIL element contents, especially K and Rb are lower in the primary magma of Rishiri volcano located far from the volcanic front than in the remaining two primary magmas, which would imply that LIL/HFS ratios (or degree of contribution of LIL elements originating from the subducted oceanic crust) become minimal at Rishiri volcano. One basalt and three andesites from Shiribeshi volcano have the restricted range of low⁸⁷Sr/⁸⁶Sr ratios of 0.70297–0.70300, which indicates that the magma source for Shiribeshi volcano may be slightly more enriched in Sr isotopic compositions than theN-type MORB source.

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Geochemie des neuentdeckten quartären submarinen Vulkans Shiribeshi im Nordöstlichen Japanischen Meer

Zusammenfassung Der Shiribeshi Seamount liegt östlich des Okushiri Rückens im nordöstlichen Japanischen Meer. Gesamtgesteins K-Ar Alter von Olivin-Augit-Andesiten von diesem Seamount ergeben Werte von 0,9 ± 0,2 Ma (Tsuchiya et al., 1989), und weisen darauf hin, daß Shiribeshi ein quartärer Vulkan im back-arc Bereich nahe dem Kreuzungspunkt des nordostjapanischen und des Kurilen-Inselbogens ist. Er besteht aus Gesteinen, deren Zusammensetzung von Basalt bis Rhyolit reicht. Petrographische Daten von 25 Proben, die von vier submarinen Lokationen durch Dredging aufgesammelt wurden, weisen auf eine typische kalk-alkalische Inselbogenzusammensetzung hin. Die Verbreitung von inkompatiblen Elementen, die unter anderem K, Rb, Sr, Nb, P, Ti, Y und Zr umfassen, in 16 representativen Proben wird zusammen mit denen von quartären vulkanischen Gesteinen aus dem nordöstlichen Japanischen und den Kurilen-Inselbogen diskutiert; dabei wird Variationen der Zusammensetzung über die Bögen hinweg besondere Beachtung geschenkt. Die so ermittelte Zusammensetzung des primären Magmas des Shiribeshi Vulkans wird durch höhere inkompatible Elementgehalte und höhere Zr/Y Verhältnisse charakterisiert, wenn man sie mit primären Magmen an der vulkanischen Stirn des Inselbogens vergleicht. HFS Element-Konzentrationen lassen erkennen, daß der Grad teilweiser Aufschmelzung für drei primäre Magmen von Oshima-Oshima, Shiribeshi und Rishiri im nordöstlichen Japanischen Meer graduell mit zunehmender Entfernung von der vulkanischen Stirm abnimmt. Die Gehalte an LIL Elementen und besonders an K und Rb sind in dem primären Magma des Rishiri Vulkans, der weit von der vulkanischen Front entfernt liegt, höher als in den zwei anderen primären Magmen. Dies weist darauf hin, daß LIL/HFS Verhältnisse (oder der Beitrag von LIL Elementen, die aus subduzierter ozeanischer Kruste stammen) am Rishiri Vulkan ein Minimum erreichen. Ein Basalt und drei Andesite von Shiribeshi zeigen⁸⁷Sr/⁸⁶Sr Verhältnisse von 0,70297 bis 0,70300; dies läßt erkennen, daß die Quelle des Magmas für Shiribeshi etwas mehr an⁸⁷Sr angereichert war, als dieN-Typ Quelle.

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With 7 Figures     

The southern agglomeration zone of the GDR — Regional structure and development

Agglomeration areas in the GDR are those regions, which are characterized by an above average level of regional concentration of productive forces and their conditions of reproduction. The economic potential concentrated in these regions represents a large part of the national economy. It is possible to describe the territorial structure of these agglomeration areas by general indices (agglomeration core — agglomeration field — agglometation fringe; polycentric node-band-structure), but also the individual features of each one of these regions are to be attended. They are expressed for the first time by several forms of localization of plants and by the structure of settlements and settlement networks. The present main tendencies in the development of the agglomeration regions are:

They succeeded in minimizing the regional disparities of productivity between different agglomeration regions and within them, and in stabilizing the economic position of these regions by systematic measures for investment and rationalization and the hereby influenced structural changes.

At present and up to 1990 the completion of housing programme is of foremost importance by which the main activities will shift from the urban fringe to the centres of the cities; provincial towns and smaller settlements will also participate in this programme.

The main target of these activities is to remove imperfect structures and other burning problems of the agglomeration regions step by step. Geographical Institutes are dealing with the management of these tasks too.     

The OSIRIS‐REx target asteroid (101955) Bennu: Constraints on its physical,geological, and dynamical nature from astronomical observations

We review the results of an extensive campaign to determine the physical, geological, and dynamical properties of asteroid (101955) Bennu. This investigation provides information on the orbit, shape, mass, rotation state, radar response, photometric, spectroscopic, thermal, regolith, and environmental properties of Bennu. We combine these data with cosmochemical and dynamical models to develop a hypothetical timeline for Bennu's formation and evolution. We infer that Bennu is an ancient object that has witnessed over 4.5 Gyr of solar system history. Its chemistry and mineralogy were established within the first 10 Myr of the solar system. It likely originated as a discrete asteroid in the inner Main Belt approximately 0.7–2 Gyr ago as a fragment from the catastrophic disruption of a large (approximately 100‐km), carbonaceous asteroid. It was delivered to near‐Earth space via a combination of Yarkovsky‐induced drift and interaction with giant‐planet resonances. During its journey, YORP processes and planetary close encounters modified Bennu's spin state, potentially reshaping and resurfacing the asteroid. We also review work on Bennu's future dynamical evolution and constrain its ultimate fate. It is one of the most Potentially Hazardous Asteroids with an approximately 1‐in‐2700 chance of impacting the Earth in the late 22nd century. It will most likely end its dynamical life by falling into the Sun. The highest probability for a planetary impact is with Venus, followed by the Earth. There is a chance that Bennu will be ejected from the inner solar system after a close encounter with Jupiter. OSIRIS‐REx will return samples from the surface of this intriguing asteroid in September 2023.     

Patterns of Nd and Sr isotopic ratios produced by magmatic and post-magmatic processes in the Shiant Isles Main Sill, Scotland

The Shiant Isles Main Sill of the British Tertiary Igneous Province is a classic example of a differentiated, alkaline basic sill. Four separate intrusions, each emplaced internally in rapid succession, form a 165-m-thick sill hosted by Lower Jurassic sedimentary rocks. Extensive Nd and Sr isotopic studies were conducted on samples from a vertical section through the sill where the relationships of samples to one another are well defined. The results illuminate patterns of modification of isotopic ratios and clarify the petrogenesis (magma sources, crustal contamination), magmatic processes (bulk mixing, interstitial liquid mixing), and post-magmatic alteration (hydrothermal effects on Sr and Nd). Overall, the whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios range from ∼0.7037 to 0.7061 while initial ¹⁴³Nd/¹⁴⁴Nd ratios vary from ∼0.51243 to 0.51286 (ɛ_Nd∼−0.7 to +5.7) – values that contrast markedly with those of the country rock. Acid leaching (HCl) of the whole-rock samples that removes analcime indicates that most of the scatter in the ⁸⁷Sr/⁸⁶Sr is caused by the ubiquitous sub-solidus, aqueous alteration during which more-radiogenic Sr was introduced into the sill, especially along the margins, and also reveals magmatic isotopic ratios. In contrast, Nd was immobile during fluid interaction so that the sill ¹⁴³Nd/¹⁴⁴Nd ratios were not affected, even <1 m from the country-rock contact. Using leached rock values, ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios are inversely correlated from magmatic processes. Magmas with two distinct isotopic compositions were involved: a more primitive one with ¹⁴³Nd/¹⁴⁴Nd ∼0.51285 and ⁸⁷Sr/⁸⁶Sr ∼0.7035 that produced the first two intrusions and a more evolved one (with 0.51252 and 0.7048) that produced the third intrusion. Mixing of the two magmas was very limited, restricted to near contacts between units, and apparently occurred by interstitial melt migration. The more evolved crinanitic magma was probably produced from a batch of the more primitive picritic melt by a small degree of crustal contamination and crystal fractionation during a short crustal residence prior to ascent and emplacement. Received: 20 December 1999 / Accepted: 5 May 2000     

Earthquake swarms preceding the 2000 eruption of Miyakejima volcano, Japan

The first sign of magma accumulating beneath Miyakejima, an island volcano in the northern Izu islands, Japan, came at around 18:00 on 26 June 2000, when a swarm of earthquakes was detected by a volcano seismic network on the island. Earthquakes occurred initially beneath the southwest flank near the summit and gradually migrated west of the island, where a submarine eruption occurred the next morning. Earthquakes then migrated further to the northwest between Miyakejima and Kozushima, another volcanic island and developed to the most intense earthquake swarm ever observed in and around Japanese archipelago. To better image how the initial magma intrusion occurred, we relocated hypocenters by using a station-correction method and a double-difference method. The relocated epicenters are generally concentrated near the upper bound of dyke intrusions inferred from geodetic studies throughout the initial stages of the 2000 eruption at Miyakejima from 26 to 27 June 2000. As for seismic activity westward off Miyakejima in the morning on 27 June, hypocenters from both a nationwide seismic network that were relocated by the double-difference method, and those from the volcano seismic network relocated by the station-correction method, formed a very shallow cluster that ascended slowly with time as it propagated northwestward from Miyakejima. This suggests that the dykes have both a radial and upward component of movement.Editorial responsibility: S. Nakada, T. Druitt