Møre Margin: Crustal structure from analysis of Expanded Spread Profiles

Analysis in both the x—t and —p domains of high-quality Expanded Spread Profiles across the Møre Margin show that many arrivals may be enhanced be selective ray tracing and velocity filtering combined with conventional data reduction techniques. In terms of crustal structure the margin can be divided into four main areas: 1) a thicker than normal oceanic crust in the eastern Norway Basin; 2) expanded crust with a Moho depth of 22 km beneath the huge extrusive complex constructed during early Tertiary breakup; 3) the Møre Basin where up to 13–14 km of sediments overlie a strongly extended outer part with a Moho depth at 20 km west of the Ona High; and 4) a region with a 25–27 km Moho depth between the high and the Norwegian coast. The velocity data restricts the continent-ocean boundary to a 15–30 km wide zone beneath the seaward dipping reflector wedges. The crust west of the landward edge of the inner flow is classified as transitional. This region as well as the adjacent oceanic crust is soled by a 7.2–7.4 km s^–1 lower crustal body which may extend beneath the entire region that experienced early Tertiary crustal extension. At the landward end of the transect a 8.5 km s^–1 layer near the base of the crust is recognized. A possible relationship with large positive gravity anomalies and early Tertiary alkaline intrusions is noted.     

Water temperature behaviour in the River Loire since 1976 and 1881

Analysis of monthly mean river temperatures, recorded on an hourly basis in the middle reaches of the Loire since 1976, allows reconstruction by multiple linear regression of the annual, spring and summer water temperatures from equivalent information on air temperatures and river discharge. Since 1881, the average annual and summer temperatures of the Loire have risen by approximately 0.8?°C, this increase accelerating since the late 1980s due to the rise in air temperature and also to lower discharge rates. In addition, the thermal regime in the Orleans to Blois reach is considerably affected by the inflow of groundwater from the Calcaires de Beauce aquifer, as shown by the summer energy balance. To cite this article: F. Moatar, J. Gailhard, C. R. Geoscience 338 (2006).     

Une approche innovante pour modéliser la biodégradation des composés organochlorés volatils en aquifères poreux

The goal of this study was to develop an innovative chloroethene biodegradation module based on biological, thermodynamical and mechanistic concepts. The biodegradation scheme was based on the postulate that in each part of an aquifer only one degradation mechanism is dominant: the one involving the most energetic electron acceptor. Thus, the selection of the active degradation mechanism was a function of the concentration of different electron acceptors. Modified Monod-type kinetics was used in order to take into account the possible influence of some compounds on the biodegradation of a given organic compound. The numerical model developed was applied to a simple test case, whose results are presented here. To cite this article: F. Nex et al., C. R. Geoscience 338 (2006).     

Characterization of cristobalite in ash and dome rock from the Soufriere Hills volcano, Montserrat： Implications for respiratory health hazards

A link between the inhalation of respirable silicas （SiO2） and respiratory diseases such as silicosis is widely recognized. Ash from dome collapse eruptions on Montserrat has been found to contain high levels （〉20%） of silicas in the form of cristobalite, tridymite, quartz and/or amorphous silica. The toxicity of these silica polymorphs varies widely. Cristobalite and quartz （tridymite less well established） are viewed as carcinogenic to humans whereas amorphous silica generally shows a reduced biological response. In assessing the potential health effects of volcanic ash particulates it is vital to determine the types and concentration of silicas as well as their size （respirable fraction）, shape and surface properties. The aim of this study is to develop methods to assess potentially toxic respirable airborne silicas in the dome collapse ash （applicable to a range of ash types） and to develop a model to predict the levels and types of respirable silicas from future eruptions. The model is being developed by comparing dome rock with related ash from a series of previous eruption events. Mineralogical assessment using conventional scanning X-ray diffraction （XRD） was hampered by difficulties in differentiating characteristic peaks for cristobalite and tridymite in complex multi-component ash samples （containing high levels of plagioclase）. These difficulties have been largely overcome using an Enraf-Nonius PDS120 diffractometer with curved （120 degrees 20） position sensitive detector （PSD）. The determination of size, shape and elemental characteristics of ash particulate and dome rock samples has been carried out using automated analytical scanning electron microscopy. The quantification of mineral proportions using PSD-XRD was highly successful with an accuracy of 1 to 2 wt%. However, the determination of phase proportions using automated analytical SEM was problematic due to scattering effects and the multiphase nature of many of the particles.     

Genesis of monazite and Y zoning in garnet from the Black Hills, South Dakota

The paragenesis of monazite in metapelitic rocks from the contact aureole of the Harney Peak Granite, Black Hills, South Dakota, was investigated using zoning patterns of monazite and garnet, electron microprobe dating of monazite, bulk-rock compositions, and major phase mineral equilibria. The area is characterized by low-pressure and high-temperature metamorphism with metamorphic zones ranging from garnet to sillimanite zones. Garnet porphyroblasts containing euhedral Y annuli are observed from the garnet to sillimanite zones. Although major phase mineral equilibria predict resorption of garnet at the staurolite isograd and regrowth at the andalusite isograd, textural and mass balance analyses suggest that the formation of the Y annuli is not related to the resorption-and-regrowth of garnet having formed instead during garnet growth in the garnet zone. Monazite grains in Black Hills pelites were divided into two generations on the basis of zoning patterns of Y and U: monazite 1 with low-Y and -U and monazite 2 with high-Y and -U. Monazite 1 occurs in the garnet zone and persists into the sillimanite zone as cores shielded by monazite 2 which starts to form in the andalusite zone. Pelites containing garnet porphyroblasts with Y annuli and monazite 1 with patchy Th zoning are more calcic than those with garnet with no Y annuli and monazite with concentric Th zoning. Monazite 1 is attributed to breakdown of allanite in the garnet zone, additionally giving rise to the Y annuli observed in garnet. Monazite 2 grows in the andalusite zone, probably at the expense of garnet and monazite 1 in the andalusite and sillimanite zones. The ages of the two different generations of monazite are within the precision of chemical dating of electron microprobe. The electron microprobe ages of all monazites from the Black Hills show a single ca. 1713 Ma population, close to the intrusion age of the Harney Peak Granite (1715 Ma). This study demonstrates that Y zoning in garnet and monazite are critical to the interpretation of monazite petrogenesis and therefore monazite ages.     

Alpujarride attribution of the supposed ‘Almagride Complex’ (Betic Internal Zone,Almerı́a Province,Spain)Appartenance Alpujarride du prétendu « Complexe almagride » (Zones internes bétiques,province d'Almeria,Espagne)

The differentiation of units in the Sierra de Almagro has been a source of controversy. There were defined the Almagride and Ballabona–Cucharón complexes, the former considered by several authors as part of a Subbetic metamorphosed and outcropping in a tectonic window. In this study, the units of Ballabona, Almagro and Cucharón are integrated into a single one, that of Tres Pacos, because they correspond to different parts of the same stratigraphic series. This unit is tectonically over the Nevado–Filabride Complex. The existence of the Almagride and Ballabona–Cucharón complexes is discarded and their units form part of the Alpujarride Complex. To cite this article: C. Sanz de Galdeano, F.J. Garc??a Tortosa, C. R. Geoscience 334 (2002) 355–362.     

Soulèvement et plissement tectoniques révélés par analyse mathématique empirique de profils longitudinaux de rivières : un cas à TaiwanEmpirical mathematical analysis of longitudinal river profiles reveals tectonic uplift and folding: a case in Taiwan

We analyse longitudinal river profiles in southwestern Taiwan. As all necessary data are not available, a physical modelling of river erosion would be subject to large uncertainties. We thus shortcut this modelling and adopt simple empirical exponential equations giving riverbed elevation as a function of downstream distance. We identify a positive altimetric anomaly, which reveals active uplift of an anticline at the front of the fold-and-thrust belt. To cite this article: J. Angelier, R.-F. Chen, C. R. Geoscience 334 (2002) 1103–1111.     

Post-caldera activity in the Alban Hills volcanic district (Italy): 40Ar/39Ar geochronology and insights into magma evolution

We present 24 ⁴⁰Ar/³⁹Ar ages for the youngest volcanic products from the Alban Hills volcanic district (Rome). Combined with petrological data on these products, we have attempted to define the chronology of the most recent phase of activity and to investigate the magma evolution of this volcanic district. The early, mainly explosive activity of the Alban Hills spanned the interval from 561±1 to 351±3 ka. After approximately 50-kyr of dormancy, a mainly effusive phase of activity took place, accompanied by the strombolian activity of a small central edifice (Monte delle Faete). This second phase of activity spanned the interval 308±2 to 250±1 ka. After another dormancy period of approximately 50-kyr, a new, hydromagmatic phase of activity started at 200 ka at several centers located to the southwest of the Monte delle Faete edifice. After an initial recurrence period of approximately 50-kyr, which also characterized this new phase of activity, the longest dormancy period (approximately 80-kyr) in the history of the volcanic district preceded the start of the activity of the Albano and Giuturna centers at 70±1 ka. Results of our study suggest a quasi-continuous magmatic activity feeding hydromagmatic centers with a new acme of volcanism since around 70 ka. Based on data presented in this paper, we argue that the Alban Hills should not be considered an extinct volcanic district and a detailed re-assessment of the volcanic hazard for the area of Rome is in order. Published online: 4 April 2003 Editorial responsibility: J. Donnelly-Nolan     

Paléoenvironnements et caractérisation des roches mères pétrolières des séries pré-salifères du bassin intérieur du Gabon

The Interior Basin of Gabon, created during the break-up between South America and Africa, displays thick Neoproterozoic to Aptian p.p. fluvio-lacustrine deposits overlain by Aptian to Albian marine facies. Rock–Eval analyses from outcrop and drillhole samples show high content in organic matter (up to 25%) related to types I and II. These intervals are encountered within Permian, Neocomian–Barremian as well as Aptian siliciclastic succession. They constitute fairly good to excellent potential petroleum source rocks, which are most probably at the origin of oil indices recognized both in drillholes and in surface.     

Flood Damage Reduction Program (FDRP) in Québec: Case Study of the Chaudiére River

This study presents the evolution of agreements between the governments of Canadaand Québec on flood damage reduction. In Québec, the implementation of a regulation about building in floodplains came about in 1983–1984. Today, this regulation takes the form of a policy called ``Policy of shores, littoral and floodplain protection'. Municipalities must adopt rules that concur with the principles of this policy.The Chaudiére River basin was selected for analysis of urban developmentduring the period following the application of building rules in flood-risk areas.Despite the ban on building in the strong current zone (0–20 year return periodflood zone), many buildings, essentially residential, have been erected in thiszone. These new constructions generally account for a low percentage of thetotal property value in the 0–100 year flooding area, but are legal since theyare connected to a water and sewage network that existed prior to the officialfloodplain regulation.Flood damage along the Chaudiére River will tend to increase for two reasons.Firstly, while respecting the policy mentioned above, sites are still available infloodplains for future development. Secondly, no structural flood protection workshave been erected in view of the fact they are only marginally profitable from anbenefit-cost point of view.