Conodont geothermometry in pyroclastic kimberlite: constraints on emplacement temperatures and cooling histories

Kimberlite pipes from Chidliak, Baffin Island, Nunavut, Canada host surface-derived Paleozoic carbonate xenoliths containing conodonts. Conodonts are phosphatic marine microfossils that experience progressive, cumulative and irreversible colour changes upon heating that are experimentally calibrated as a conodont colour alteration index (CAI). CAI values permit us to estimate the temperatures to which conodont-bearing rocks have been heated. Conodonts have been recovered from 118 samples from 89 carbonate xenoliths collected from 12 of the pipes and CAI values within individual carbonate xenoliths show four types of CAI distributions: (1) CAI values that are uniform throughout the xenolith; (2) lower CAIs in core of a xenolith than the rim; (3) CAIs that increase from one side of the xenolith to the other; and, (4) in one xenolith, higher CAIs in the xenolith core than at the rim. We have used thermal models for post-emplacement conductive cooling of kimberlite pipes and synchronous heating of conodont-bearing xenoliths to establish the temperature–time history of individual xenoliths within the kimberlite bodies. Model results suggest that the time-spans for xenoliths to reach the peak temperatures recorded by CAIs varies from hours for the smallest xenoliths to 2 or 3 years for the largest xenoliths. The thermal modelling shows the first three CAI patterns to be consistent with in situ conductive heating of the xenoliths coupled to the cooling host kimberlite. The fourth pattern remains an anomaly.

     

Metal-enriched nanoparticles and black carbon: A perspective from the Brazil railway system air pollution

Having a better understanding of air pollutants in railway systems is crucial to ensure a clean public transport. This study measured, for the first time in Brazil, nanoparticles (NPs) and black carbon (BC) on two ground-level platforms and inside trains of the Metropolitan Area of Porto Alegre (MAPA). An intense sampling campaign during thirteen consecutive months was carried out and the chemical composition of NPs was examined by advanced microscopy techniques. The results showed that highest concentrations of the pollutants occur in colder seasons and influenced by variables such as frequency of the trains and passenger densities. Also, internal and external sources of pollution at the stations were identified. The predominance of NPs enriched with metals that increase oxidative stress like Cd, Fe, Pb, Cr, Zn, Ni, V, Hg, Sn, and Ba both on the platforms and inside trains, including Fe-minerals as hematite and magnetite, represents a critical risk to the health of passengers and employees of the system. This interdisciplinary and multi-analytical study aims to provide an improved understanding of reported adverse health effects induced by railway system aerosols.     

Recent and fossil resins from New Zealand and Australia

The carbon-13 nuclear magnetic resonance spectra of fossil resins from New Zealand and Australia have been compared with those of modern and semifossilized materials. The great majority of the fossilized samples have strong spectral similarities to modern Agathis resins and to North American fossil resins, which have been attributed to Agathis. The Agathis-related spectra are different from those of modern Hymenaea and Araucaria. A small subgroup of Late Cretaceous resins from Australia and Papua New Guinea appears to derive from a different botanical source and shows strong resemblances to Claiborne amber from Arkansas. The spectral resonances of the exomethylene carbons degrade over time and on average provide an approximate measure of the geological age of Agathis-related fossil resins. © 1993 John Wiley & Sons, Inc.     

Jenniferann.com,regional development,and realising the aspirations of mana whenua in Pōkeno

During the 1990s, the township of Pōkeno was held up as an example of a declining rural Aotearoa/New Zealand. By‐passed from the national state highway, it lost its status as a service hub and drastic measures were introduced to revitalise the town, including renaming the town “ Jenniferann.com .” Pōkeno has since undergone an unlikely transformation, with foreign investment and its location within an extended Auckland commuter zone meaning that the township has grown exponentially. This article describes the transformation of Pōkeno and uncovers what has been missing from discussions about Pōkeno's reinvention, namely, the place of mana whenua.     

A high-precision heuristic model to detect home and work locations from smart card data

Smart card-automated fare collection systems now routinely record large volumes of data comprising the origins and destinations of travelers. Processing and analyzing these data open new opportunities in urban modeling and travel behavior research. This study seeks to develop an accurate framework for the study of urban mobility from smart card data by developing a heuristic primary location model to identify the home and work locations. The model uses journey counts as an indicator of usage regularity, visit-frequency to identify activity locations for regular commuters, and stay-time for the classification of work and home locations and activities. London is taken as a case study, and the model results were validated against survey data from the London Travel Demand Survey and volunteer survey. Results demonstrate that the proposed model is able to detect meaningful home and work places with high precision. This study offers a new and cost-effective approach to travel behavior and demand research.     

Nutrient flux into an intense deep chlorophyll layer in a mode-water eddy

An intense deep chlorophyll layer in the Sargasso Sea was reported near the center of an anticyclonic mode-water eddy by McGillicuddy et al. [2007. Eddy–wind interactions stimulate extraordinary mid-ocean plankton blooms, Science, accepted]. The high chlorophyll was associated with anomalously high concentrations of diatoms and with a maximum in the vertical profile of ¹⁴C primary productivity. Here we report tracer measurements of the vertical advection and turbulent diffusion of deep-water nutrients into this chlorophyll layer. Tracer released in the chlorophyll layer revealed upward motion relative to isopycnal surfaces of about 0.4 m/d, due to solar heating and mixing. The density surfaces themselves shoaled by about 0.1 m/d. The upward flux of dissolved inorganic nitrogen, averaged over 36 days, was approximately 0.6 mmol/m²/d due to both upwelling and mixing. This flux is about 40% of the basin wide, annually averaged, nitrogen flux required to drive the annual new production in the Sargasso Sea, estimated from the oxygen cycle in the euphotic zone, the oxygen demand below the euphotic zone, and from the ³He excess in the mixed layer. The observed upwelling of the fluid was consistent with theoretical models [Dewar, W.K., Flierl, G.R., 1987. Some effects of wind on rings. Journal of Physical Oceanography 17, 1653–1667; Martin, A.P., Richards, K.J., 2001. Mechanisms for vertical nutrient transport within a North Atlantic mesoscale eddy. Deep-Sea Research II 48, 757–773] in which eddy surface currents cause spatial variations in surface stress. The diapycnal diffusivity at the base of the euphotic zone was 3.5±0.5×10⁻⁵ m²/s. Diapycnal mixing was probably enhanced over more typical values by the series of storms passing over the eddy during the experiment and may have been enhanced further by the trapping of near-inertial waves generated within the eddy.     

Lead and Mg isotopic age constraints on the evolution of the HED parent body

The large collection of howardite‐eucrite‐diogenite (HED) meteorites allows us to study the initial magmatic differentiation of a planetesimal. We report Pb‐Pb ages of the unequilibrated North West Africa (NWA) 4215 and Dhofar 700 diogenite meteorites and their mass‐independent ²⁶Mg isotope compositions (²⁶Mg*) to better understand the timing of differentiation and crystallization of their source reservoir(s). NWA 4215 defines a Pb‐Pb age of 4484.5 ± 7.9 Myr and has a ²⁶Mg* excess of +2.3 ± 1.6 ppm whereas Dhofar 700 has a Pb‐Pb age of 4546.4 ± 4.7 Myr and a ²⁶Mg* excess of +25.5 ± 1.9 ppm. We interpret the young age of NWA 4215 as a thermal overprint, but the age of Dhofar 700 is interpreted to represent a primary crystallization age. Combining our new data with published Mg isotope and trace element data suggests that approximately half of the diogenites for which such data are available crystallized within the first 1–2 Myr of our solar system, consistent with a short‐lived, early‐formed magma ocean undergoing convective cooling. The other half of the diogenites, including both NWA 4215 and Dhofar 700, are best explained by their crystallization in slowly cooled isolated magma chambers lasting over at least ~20 Myr.     

Two metallogenic maps for North America

Part of the interior of the North American continent is covered by relatively undisturbed sedimentary rocks not available to the entrance of ore-bearing fluids from depths, but a wide belt along the Pacific Coast, a narrower belt along the Atlantic Coast, and most of the north-east quadrant of the continent have been mineralized. If we plot all the known ore deposits in these latter areas, we find considerable differences in the densities of occurrences but no well defined patterns except a crowding along most of the area near the Pacific Coast. If, on the other hand, we plot only the major occurrences, we can see some linear patterns transverse to the edges of the continent.Transverse ore deposit patterns in an ENE direction are conspicuous in western United States and northern Mexico and in Ontario and Quebec of Canada but are almost unknown in British Columbia and Alaska. East-west patterns (within 5 degrees of a 90degree azimuth) are much more rare: one in southern British Columbia, one in Quebec and Ontario, one in Missouri, and one in Tennessee. No north-south patterns of any great length can be recognized.In addition to these rich ridges there are many inhomogeneities in the distribution of the major ore deposits, and these I think are due to subcrustal inhomogeneities in the distribution of metals, presumably in the upper mantle and probably of a late stage in the formation of the earth. I will attempt to show that the large ore deposits of North America form belts bounded approximately by parallels of latitude, separated by gaps in which no large deposits occur. Without undue distortions I have been able to draw outlines to include all the approximately 250 major ore deposits, except in the area north of latitude 60 where recorded occurrences are at present too sparse and too widely distributed.The localization of ore deposits in North America is thus the result of linear zones, probably deep crustal or sub-crustal fracture zones, crossing latitudinal belts of anomalous concentrations of metals probably of pre-crustal age.I have no explanations for the processes that formed either the transverse patterns or the latitudinal belts. They are not prominent and will be judged by many to be nonexistent. The lack of an explanation must not, however, be used to deny their existence— an attitude that surely limits the progress of metallogenic theory. Correlations with similar studies on other continents will be most useful.

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Zusammenfassung Ein Teil des Inneren des Nordamerikanischen Kontinents ist mit relativ ungestörten Sedimentgesteinen bedeckt, die ein Eindringen von Erz-bringenden Lösungen aus der Tiefe verhinderten. Dagegen sind ein breiter Streifen entlang der Pazifikküste, ein schmalerer Streifen entlang der Atlantikküste und der größte Teil des Nordostquadranten des Kontinentes mineralisiert. Wenn wir alle bekannten Erzlagerstätten in diese Gebiete eintragen, so finden wir auffällige Unterschiede in der Verteilung der Punkte, aber kein regelmäßiges Muster, ausgenommen das Gebiet nahe der Pazifikküste. Wenn wir dagegen nur die größeren Vorkommen auftragen, so ergeben sich lineare Anordnungen, die quer auf die Ecken des Kontinentes zulaufen.Quer verlaufende Muster in ENE-Richtung sind auffallend in den westlichen Vereinigten Staaten, in Nord-Mexico, in Ontario und Quebec; diese Richtung ist jedoch in British Columbia und in Alaska unbekannt.E-W-Muster mit±5° Schwankungen sind sehr viel seltener. Eines finden wir im südlichen British Columbia, eines in Quebec und Ontario, eines in Missouri und Tennessee, N-S-streichende Lineationen sind unbekannt.Über die Anordnung in reichen Zonen hinaus finden wir viele Inhomogenitäten in der Verteilung der wichtigsten Erzlagerstätten; diese sind meiner Meinung nach von subkrustalen Inhomogenitäten in der Verteilung der Metalle bestimmt. Vielleicht spielt hier eine frühe Verteilung im oberen Mantel zur Zeit der Entstehung der Erde eine Rolle. Ich will versuchen zu zeigen, daß die großen Erzlagerstätten an Zonen gebunden sind, die annähernd parallel zu den Breitengraden verlaufen und durch erzfreie Zonen getrennt sind. Ohne Schwierigkeiten lassen sich Umgrenzungen mit dieser Orientierung aufzeigen, die alle 250 größeren Erzlagerstätten umfassen, ausgenommen im Gebiet nördlich des 60. Breitengrades, wo die Dichte der Lagerstätten zu gering ist.Die Anordnung der Erzlagerstätten Nordamerikas ist auf lineare Zonen zurückzuführen, die wahrscheinlich auf Bruchstrukturen der Unterkruste oder des oberen Mantels begründet sind. Die Konzentration der Metalle in Querstrukturen zu den Breitenkreisen ist vermutlich eine Auflage, die vor der Bildung der Kruste entstanden ist. Ich habe keine Erklärung für die Prozesse, die zu dieser Metallkonzentration geführt haben. Viele mögen eine derartig vorgegebene Anordnung ablehnen; man sollte jedoch bedenken, daß das Fehlen einer Erklärung noch nicht zur Ablehnung auffälliger Phänomene berechtigt. Es sollten auch andere Kontinente daraufhin untersucht werden.

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Résumé Une partie de l'intérieur du continent Nord Américain est couverte par des roches sédimentaires peu dérangées et défavorables à l'accès de fluides minéralisants venus de la profondeur. Par contre une large ceinture le long de la côte pacifique, un ceinture plus étroit de long de la côte atlantique, et la majeure partie du quadrant Nord-Est du continent ont été minéralisées. Si l'on reporte sur carte tous les dépôts connus dans ces domaines, on trouve des différences considérables dans les »densités d'occurrences« mais aucun réseau bien défini, à l'exception d'un fort peuplement dans presque tout le domaine proche du Pacifique. Si, d'autre part, on ne reporte que les occurrences majeures, on voit apparaître des lignes directrices transversales sur les bordures du continent.De telles transversales dirigées ENE apparaissent dans l'Ouest des Etats-Unis, le Nord du Mexique, l'Ontario et le Québec (Canada) mais sont presque inconnues en Colombie britannique et en Alaska.Des directions Est-Ouest (avec une variation de 5) sont beaucoup plus rares: une dans le Sud de la Colombie britannique, une dans le Québec et l'Ontario, une dans le Missouri et une dans le Tennessee. Aucune direction Nord-Sud de grande longueur ne peut être reconnue.En plus de ces »arêtes riches« existent beaucoup d'inhomogénéités dans la distribution des gisements importants, et celles-ci sont dues, à mon avis, à des hétérogénéités souscrustales de la distribution des métaux, probablement au niveau du manteau supérieur et remontant à une étape tardive de la formation de la Terre. Je désire essayer de montrer que les grands gisements métallifères de l'Amérique du Nord s'intègrent dans des ceintures approximativement limitées par des parallèles de latitude et séparées par des intervalles dépourvus de grands dépôts. Ainsi, sans distorsions abusives, j'ai pu tracer des enveloppes englobant environ 250 gisements majeurs, sauf dans une aire située au Nord du parallèle 60 Nord, où les occurrences jusqu'ici enregistrées sont encore trop rares et disséminées.La localisation des gisements métallifères de l'Amérique du Nord est donc due à des zones linéaires, probablement des zones de fractures crustales profondes ou sous-crustales, croisant des ceintures latitudinales de concentrations anormales de métaux, elles-mêmes probablement précrustales.Je n'offre pas d'explication pour les processus qui ont formé les ceintures latitudinales et les transversales. Les unes et les autres ne sont pas fortement apparentes, et beaucoup estimeront qu'elles n'existent pas. Cette absence d'explication ne doit cependant pas être utilisée pour nier leur existence, attitude qui limiterait certainement les progrès des théories métallogéniques. Des comparaisons avec des ètudes similaires sur d'autres continents seraient certainement très utiles.

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