The city and its port—an economic appraisal

Following a brief examination of the role of ports as foci for industrial and urban development, this paper discusses four major changes—the scale of international trade, structural changes in port activities, port industrialization, and traffic origin and destination—which are acting to alter the relationship between ports and their urban areas. Attention is then focused on the redevelopment of docklands and the need to inform public and political opinion of the importance of port activities to the development of local, regional and national economies. The use of economic impact studies to highlight the multiplier effects of port activities is discussed.     

Subsidence breccias in kimberlite pipes—an application of fractal analysis

A particular variety of volcanogenic country rock breccia is described; a contact breccia that has been identified at Venetia, River Ranch and Wimbledon kimberlite pipes. The contact breccia is clast supported with no juvenile kimberlite component, has tightly packed, angular fragments (with occasional rounding of smaller particles), and has a shear-fabric dipping towards the center of each kimberlite pipe or volcanic event. Clasts have preferred orientations parallel to the fabric. Photographs of the breccia in the open pit face and measured data from drill core are analyzed specifically to quantify the clast size distributions and clast shapes by means of fractal analysis. The fractal dimension is one means of characterizing the breccia because the dimension can be specific to a fragmentation mechanism. Clast size distribution fractal dimensions in the coarser particles (greater than circa 3 cm) range from greater than 3 for nonsheared breccia, down to circa 2.3 for the sheared breccia. Breccia characterization based on this fractal analysis suggests that fragmentation occurred initially from confined high-energy explosions, followed by collapse and abrasion by subsequently gravity-induced rockmass subsidence. All studied contact breccias produced a distinctive fractal signature in the finer particles (<3 cm) of circa 1.6 that can be explained by a comminution fragmentation process in that particular particle size range. It is suggested that these subsidence breccias require a substantial volume deficit at depth within the volcanic pipe in order to explain their origin and size. The methodology used in this study could be used to characterize any other volcanic breccia and further model their origins.     

Critical shear stress for mechanical twinning of jadeite—an experimental study

Coarse-grained natural jadeitite samples from Myanmar were experimentally deformed in a Griggs-type solid-medium apparatus at strain rates of 2·10⁻⁵ and 5·10⁻⁶ s⁻¹ and temperatures of 900 and 1000 °C. The microfabrics of the deformed samples are investigated by scanning electron microscopy (SEM) using the electron backscatter diffraction (EBSD) technique. The critical shear stress for twinning in the (100) [001] system is derived from the orientation distribution of jadeite crystals with and without mechanical twins. The results indicate a homogeneous stress field within the sample and a critical shear stress of 150±25 MPa, which compares well to that determined by Kollé and Blacic [J. Geophys. Res. 87 (1982) 4019] for mechanical twinning of other clinopyroxenes. With the critical shear stress known, mechanical twinning of jadeite can be used as a paleopiezometer for high stress tectonic environments.     

Introduction to TETHYS—an interdisciplinary GIS database for studying continental collisions

The TETHYS GIS database is being developed as a way to integrate relevant geologic, geophysical, geochemical, geochronologic, and remote sensing data bearing on Tethyan continental plate collisions. The project is predicated on a need for actualistic model ‘templates’ for interpreting the Earth's geologic record. Because of their time-transgressive character, Tethyan collisions offer ‘actualistic’ models for features such as continental ‘escape’, collision-induced upper mantle flow magmatism, and marginal basin opening, associated with modern convergent plate margins. Large integrated geochemical and geophysical databases allow for such models to be tested against the geologic record, leading to a better understanding of continental accretion throughout Earth history. The TETHYS database combines digital topographic and geologic information, remote sensing images, sample-based geochemical, geochronologic, and isotopic data (for pre- and post-collision igneous activity), and data for seismic tomography, shear-wave splitting, space geodesy, and information for plate tectonic reconstructions. Here, we report progress on developing such a database and the tools for manipulating and visualizing integrated 2-, 3-, and 4-d data sets with examples of research applications in progress. Based on an Oracle database system, linked with ArcIMS via ArcSDE, the TETHYS project is an evolving resource for researchers, educators, and others interested in studying the role of plate collisions in the process of continental accretion, and will be accessible as a node of the national Geosciences Cyberinfrastructure Network—GEON via the World-Wide Web and ultra-high speed internet2. Interim partial access to the data and metadata is available at: http://geoinfo.geosc.uh.edu/Tethys/ and http://www.esrs.wmich.edu/tethys.htm. We demonstrate the utility of the TETHYS database in building a framework for lithospheric interactions in continental collision and accretion.     

New Mexico structural zone—an analogue of the Colorado mineral belt

Updated aeromagnetic maps of New Mexico together with current knowledge of the basement geology in the northern part of the state (Sangre de Cristo and Sandia–Manzano Mountains)—where basement rocks were exposed in Precambrian-cored uplifts—indicate that the northeast-trending Proterozoic shear zones that controlled localization of ore deposits in the Colorado mineral belt extend laterally into New Mexico. The shear zones in New Mexico coincide spatially with known epigenetic precious- and base-metal ore deposits; thus, the mineralized belts in the two states share a common inherited basement tectonic setting. Reactivation of the basement structures in Late Cretaceous–Eocene and Mid-Tertiary times provided zones of weakness for emplacement of magmas and conduits for ore-forming solutions. Ore deposits in the Colorado mineral belt are of both Late Cretaceous–Eocene and Mid-Tertiary age; those in New Mexico are predominantly Mid-Tertiary in age, but include Late Cretaceous porphyry-copper deposits in southwestern New Mexico.The mineralized belt in New Mexico, named the New Mexico structural zone, is 250-km wide. The northwest boundary is the Jemez subzone (or the approximately equivalent Globe belt), and the southeastern boundary was approximately marked by the Santa Rita belt. Three groups (subzones) of mineral deposits characterize the structural zone: (1) Mid-Tertiary porphyry molybdenite and alkaline-precious-metal deposits, in the northeast segment of the Jemez zone; (2) Mid-Tertiary epithermal precious-metal deposits in the Tijeras (intermediate) zone; and (3) Late Cretaceous porphyry-copper deposits in the Santa Rita zone. The structural zone was inferred to extend from New Mexico into adjacent Arizona. The structural zone provides favorable sites for exploration, particularly those parts of the Jemez subzone covered by Neogene volcanic and sedimentary rocks.     

Subsurface sequestration of carbon dioxide — an overview from an Alberta (Canada) perspective

To stabilize the atmospheric concentration of greenhouse gases (GHG), a huge reduction of carbon dioxide (CO₂) emissions is required. Although some people believe that this necessitates a considerable reduction in the use of fossil fuels or fuel switching, other options are available that allow the use of fossil fuels and reduce atmospheric emissions of CO₂. Sequestration of CO₂ from fossil fuel combustion in the subsurface could prevent the CO₂ from reaching the surface for millions of years. Geological sequestration of CO₂ in deep aquifers or in depleted oil and gas reservoirs is a mature technology. Despite the huge quantities of CO₂ that can be sequestered in this way, this approach does not provide any economic benefit. This paper discusses a third option, which consists of injecting CO₂ in deep coal seams to sequester the carbon and enhance the recovery of coalbed methane (CBM). Waste CO₂ from CBM-fueled power plants could be injected into CBM reservoirs to produce more methane (CH₄) for the power plant. The 2:1 coal-sorption selectivity for CO₂ over CH₄ supports the feasibility of operating fossil-fueled power plants without atmospheric CO₂ emissions. Other CO₂ sequestration technologies, such as ocean disposal and biofixation, are briefly discussed and the suitability of these approaches is evaluated for use in Alberta, Canada.     

Structure of the lithosphere along the deep seismic sounding profile: Tien Shan—Pamirs—Karakorum—Himalayas

During 1973–1977, as part of the International Geodynamic Project, some seismic investigations of the Earth's crust have been carried out by geotraverses of the Tien Shan—Pamirs—Karakorum—Himalayas. The seismic data obtained together with other geophysical information, allow the construction and interpretation of the lithospheric section through the Pamirs-Himalayas structure. This section includes thick crust with complex layering, supra-asthenospheric and asthenospheric layers of the upper mantle. The thickness of the Earth's crust increases from 50–55 km in the north, in the Ferghana depression (Tien Shan), to 70–75 km in the south, near the Karakul Lake (Northern Pamir). It varies within 60–65 km for the Central and Southern Pamir, Karakorum and the Inner Himalayas. Its thickness is least (35–37 km) in the south, under the outer margin of the Himalayan foredeep. Extreme gravity minima and depressions on the geoid surface correspond to the regions with maximum thickness of the Earth's crust. The centers of the disturbing masses on the geoid surface are located in the vicinity of the asthenosphere's upper layer; this determines the effect of the whole lithospheric layer, including its asthenospheric layer, at intense changes of gravity anomalies. The asthenospheric upper layer is recorded at a depth of about 120 km, its base at a depth of 200 km, in the northern and southern regions, and 300 km in its central part (Southern Pamir, Karakorum). In the middle asthenospheric layer, wave velocities decrease to 7.5 km/sec, under the base they increase to 8.4 km/sec and reach 9.4 km/sec at a depth of about 400 km. In the supra-asthenospheric layer of the upper mantle, longitudinal and shear wave-velocities slightly increase (by less than 0.1 km/sec) towards its base.     

Zircon—Earth's timekeeper

One of the earliest written references to zircon is from Lydgate's edition of Aesop's Fables from c.1400 where a zircon was found ‘hid in the dunghill’. Since the humble surroundings of this early record, zircon has become a popular and important mineral. The name zircon is believed to have derived from the Persian words ‘zar’ and ‘gun’ meaning gold and colour respectively. During the Middle Ages, it was believed that wearing zircon jewellery was a cure against insomnia and protected against disease. In more modern times, zircon has found uses in industrial processes and is a key mineral for geologists investigating the geological history of the Earth. It can incorporate uranium which undergoes radioactive decay to lead at a constant rate. By measuring the ratios of uranium and lead isotopes, geologists can calculate the age at which zircons formed. Physical and chemical durability makes zircon able to survive for long periods of geological time and record information about hallmark geological events in Earth history, including early crustal formation, mountain‐building events and mass extinctions. Indeed, the oldest known material on the planet is a zircon from Jack Hills in Western Australia, dated at 4.4 billion years old, a mere 0.15 billion years after the formation of the Earth. This remarkable durability has also led to zircon finding commercial applications in high‐temperature industrial processes, such as brick foundries, while its chemical inertness makes it a potential material for testing the impact of the radioactive products of nuclear waste on mineral structures.     

Carbonate concretions—explained

Carbonate concretions are common features of sedimentary rocks of all geological ages. They are most obvious in sandstones and mudstones as ovoid bodies of rock that protrude from natural outcrops: clearly harder or better cemented than their host rocks. Many people are excited by finding fossils in the centre of mudstone‐hosted concretions ( Fig. 1 ) but spend little time wondering why the fossils are so well preserved. While the study of concretions has benefitted from the use of advanced analytical equipment, simple observations in the field can also help to answer many questions. For example, in cliff sections, original sedimentary beds and sedimentary structures can be traced right through concretions ( Fig. 2 ): so it can be deduced that the concretion clearly formed after these depositional structures were laid down. In this article we explain how and where concretions form and discuss the evidence, ranging from outcrop data to sophisticated laboratory analyses, which can be used to determine their origins. The roles of microbes, decaying carcasses, compaction and groundwaters are highlighted. Concretions not only preserve fossils but can also subdivide oil, gas and water reservoirs into separate compartments.

Figure 1 Open in figure viewer PowerPoint An early diagenetic carbonate concretion split in half to reveal an ammonite retaining its original aragonite shell, from the Maastrichtian of Antarctica. Image courtesy of Alistair Crame (British Antarctic Survey, NERC). Lens cap is 6 cm.     

Untersuchungen mit der Elektronen-Mikrosonde an zonargebauten Mineralen der Pyromorphitgruppe

Zusammenfassung Natürliche Glieder der Pyromorphitgruppe wurden mit einer Elektronen-Mikrosonde untersucht. Bei allen untersuchten Proben tritt gegenseitige isomorphe Ersetzung des Phosphors, Arsens oder Vanadins auf. Die fast reinen Endglieder zeigen dabei einen ziemlich gleichmäßigen, geringfügigen Einbau der Nebenkomponente unabhängig vom optischen Zonarbau, während für die Mischglieder starke zonare Schwankungen in der chemischen Zusammensetzung in Abhängigkeit von den optisch erkennbaren Zonen typisch sind.In einem Falle wird zonar Blei isomorph durch Kalzium ersetzt. Der Chlorgehalt scheint von keiner der übrigen Komponenten abhängig zu sein und unterliegt nur z.T. zonaren Schwankungen. Zonarbau durch Farbänderungen und Einbau von Fremdpartikeln, fast nur bei den Mischgliedern zu finden, bedingt zumeist entsprechende zonare chemische Veränderungen der Phosphor-, Arsen- oder Vanadingehalte. Zonarbau infolge unterschiedlicher optischer Orientierung kann sowohl ohne chemische Zonen vorkommen (bei den Endgliedern), als auch mit gleichlaufenden Veränderungen der Komponenten bei den Mischgliedern.Zonarbau als Folge unterschiedlicher optischer Orientierung, Felderteilung und Zweiachsigkeit haben nach den vorliegenden Untersuchungen nicht isomorphen Ersatz als Ursache; Veränderungen der physikalischen Bedingungen während oder Sekundärvorgänge nach Beendigung des Wachstums der Kristalle könnten eine Rolle gespielt haben. In Frage kommt auch eine Abweichung von der hexagonalen Symmetrie; eine kürzlich von U. Keppler (Karlsruhe) durchgeführte Einkristall-Untersuchung einer Mimetesit-Zone ergab für diese eine monokline Symmetrie (im Druck).Das Auftreten von diffusen Reflexen oder Doppellinien in den Röntgendiagrammen der Mischglieder kann zwanglos durch die gegenläufigen Schwankungen der Phosphor-, Arsen- oder Vanadin-Gehalte gedeutet werden.

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Electron microprobe investigation of members of the pyromorphite group with zoned structure

Natural members of the pyromorphite group, pyromorphite Pb₅(PO₄)₃Cl, mimetite Pb₅(AsO₄)₃Cl, kampylite Pb₅(PO₄, AsO₄)₃Cl, and vanadinite Pb₅(VO₄)₃Cl were investigated by the electron microprobe method. Mutual isomorphic replacement of P, V and As was observed even in the purest available end members occurring in nature. The frequently appearing zoned structure, observed in thin sections, may or may not coincide with corresponding chemical changes with respect to the V, As or P contents, mainly for the intermediate members, while for the rather pure end members nearly no connection was found between optical zones and chemical composition (also as to the division of basal sections into six triangular areas).

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Den Herren Prof. Dr. F. Laves, Zürich, und Prof. Dr. H. Wondratschek, Karlsruhe, danken wir für die Ermöglichung dieser Arbeit und für das fördernde Interesse. Der Deutschen Forschungsgemeinschaft danken wir für die finanzielle Unterstützung dieser Arbeit durch eine Beihilfe.