Garnet‐controlled very low velocities in the lower mantle transition zone at sites of mantle upwelling          下载免费PDF全文

Thorsten J. Nagel  Erik Duesterhoeft  Christian Schiffer 《地学学报》2018,30(5):333-340

Deep mantle plumes and associated increased geotherms are expected to cause an upward deflection of the lower–upper mantle boundary and an overall thinning of the mantle transition zone between about 410 and 660 km depth. We use subsequent forward modelling of mineral assemblages, seismic velocities, and receiver functions to explain the common paucity of such observations in receiver function data. In the lower mantle transition zone, large horizontal differences in seismic velocities may result from temperature‐dependent assemblage variations. At this depth, primitive mantle compositions are dominated by majoritic garnet at high temperatures. Associated seismic velocities are expected to be much lower than for ringwoodite‐rich assemblages at undisturbed thermal conditions. Neglecting this ultralow‐velocity zone at upwelling sites can cause a miscalculation of the lower–upper mantle boundary on the order of 20 km.  相似文献   

Time constraints for low-angle shear zones in the Central Rhodopes (Bulgaria) and their significance for the exhumation of high-pressure rocks     

Silke Jahn-Awe  Jan Pleuger  Dirk Frei  Neven Georgiev  Nikolaus Froitzheim  Thorsten J. Nagel 《International Journal of Earth Sciences》2012,101(7):1971-2004

In the Central Rhodopes of southern Bulgaria, an eclogite-bearing rock sheet belonging to the Middle Allochthon (Starcevo Unit) is over- and underlain by eclogite-free, amphibolite-facies rock units along low-angle shear zones, the Borovica Shear Zone at the top and the Starcevo-Ardino Shear Zone at the base. The age of these shear zones is determined by U–Pb zircon dating of pre-, syn- and posttectonic magmatic rocks, mostly pegmatite veins, using LA–SF–ICP–MS. Zircons from pre- to syntectonic pegmatites within the Borovica Shear Zone yielded ages of ca. 45–43?Ma, indicating that the shear zone was active at that time, and zircons from a pretectonic pegmatite and a posttectonic granitoid body within the Starcevo-Ardino Shear Zone yielded ages of ca. 45 and ca. 36?Ma, respectively, giving a time frame for the activity of that shear zone which probably rather postdated the activity of the Borovica Shear Zone. By combining the ages with the kinematics of the shear zones and the metamorphic history of the rock units, the following scenario is sketched: Soon after the Starcevo Unit reached peak pressure (eclogite facies), it was exhumed to a mid-crustal level by top-to-the-north-west, extensional unroofing along the Borovica Shear Zone, in a kinematic framework of orogen-parallel extension. Beginning at ca. 40?Ma, the partly exhumed Starcevo Unit was underthrust from the south-west by continental crust of the foreland (Apulia), forming the Lower Allochthon of the Rhodopes, along the Starcevo-Ardino Shear Zone. These results underline the significance of orogen-parallel extension for the exhumation of high-pressure rocks. With respect to regional geology of the Hellenides and the Aegean, it is found that the tectonic architecture of the Rhodopes is essentially of Tertiary age. Cretaceous syn-metamorphic shear zones do exist but are largely restricted to higher levels of the nappe stack (Upper Allochthon). The Rhodopes do not represent an older essentially Mesozoic core of the Hellenides but are formed by the internal, higher-metamorphic portions of the same major nappe systems as occur in the Hellenides.  相似文献   

Comment on “Tank-reservoir drainage as a simulation of the recession limb of karst spring hydrographs”: paper published in Hydrogeology Journal (2011) 19:1009–1019, by Francesco Fiorillo     

Erick Carlier  Hussein Mroueh 《Hydrogeology Journal》2012,20(7):1427-1428

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Risk reduction at the ��Last-Mile��: an attempt to turn science into action by the example of Padang, Indonesia     

H. Taubenb?ck  N. Goseberg  G. L?mmel  N. Setiadi  T. Schlurmann  K. Nagel  F. Siegert  J. Birkmann  K.-P. Traub  S. Dech  V. Keuck  F. Lehmann  G. Strunz  H. Kl��pfel 《Natural Hazards》2013,65(1):915-945

More than ever before, the last decade revealed the immense vulnerability of the world??s cities to natural hazards. Neither the tsunami in the Indian Ocean in 2004, the hurricane Katrina in 2005, the cyclone Nargis in 2008 nor the earthquakes in Sichuan in 2008 or in Haiti 2010 found the people, the city administrations or the national or international organizations well prepared in the advent of anticipated but to a large extent disregarded natural disasters. It is evident that the lack of tailor-made disaster management plans and standard operational procedures are often the crucial point in proper risk reduction approaches. This study presents an approach to transfer knowledge of an extensive multidisciplinary scientific study on risk identification into recommendations for risk reduction strategies. The study has been conducted by means of a combination of experts from different scientific communities coming from civil and coastal engineering, remote sensing, social sciences, evacuation modelling and capacity development. The paper presents the results of this research approach and interweaves key findings with recent experiences from an eyewitness on a previous hazard event. Thus, necessary tsunami hazard and vulnerability information as well as valuable insights into preparedness activities have been derived for initiating updated infrastructural designs and practical recommendations for emergency management as well as strategic spatial planning activities at the local scale. The approach was applied in the context of tsunami early warning and evacuation planning in the coastal city of Padang, Western Sumatra, Republic of Indonesia.  相似文献   

Rethinking Geographies of Assimilation     

Caroline R. Nagel 《The Professional geographer》2013,65(3):400-407

This commentary argues for a reconsideration of the concept of assimilation in geographical research. Whereas critics of assimilation theory have often misrepresented assimilation research, those working within the assimilation framework have seldom explored societal understandings of “sameness.” This commentary advocates that geographers look at assimilation not only in terms of spatial patterns but also in terms of the discursive and material practices through which dominant and subordinate groups negotiate the terms of social membership. The need to arrive at a richer understanding of assimilation becomes more pressing as the assimilability of migrants becomes an increasingly salient topic of debate.  相似文献   

Arsenic remediation by Australian laterites     

Nasima Jahan  Huade Guan  Erick A. Bestland 《Environmental Earth Sciences》2011,64(1):247-253

The efficiency of Australian laterites in arsenic adsorption has been examined using three laterite samples collected from different locations in South Australia. The characteristics such as electrical conductivity, pH, mineral compositions, and isoelectric point of laterite samples have been measured. The laterite samples are mainly composed of iron and aluminum oxides, and rutile (TiO₂). Two batch experiments have been performed to compare the efficiencies of different laterites to remove AS (III) from water at two different doses, and to examine whether pH influences arsenic adsorption. For 50 mg/l arsenic solution, at doses 1,000 g (laterite)/l (arsenic solution) and 200 g/l, the laterites removed more than 97% and 87–97%, respectively. At the dose of 200 g/l, adsorption capacity has been found to be 200–243 mg/kg. Out of the laterite samples from three localities, the Kangaroo Island laterite performed the best. This is probably related to its high content of gibbsite. It has been found that arsenic adsorption by laterite is not significantly affected at the examined pH ranges of 4.7–10.0.  相似文献   

A model for the interior structure, evolution, and differentiation of Callisto     

K. Nagel 《Icarus》2004,169(2):402-412

The recently measured dimensionless moment of inertia (MoI) factor for Callisto of 0.3549±0.0042 (Anderson et al., 2001, Icarus, 153, 157-161) poses a problem: its value cannot be explained by a model in which Callisto is completely differentiated into an ice shell above a rock shell and an iron core such as its neighboring satellite Ganymede nor can it be explained by a model of a homogeneous, undifferentiated ice-rock satellite. We show that Callisto may be incompletely differentiated into an outer ice-rock shell in which the volumetric rock concentration is close to the primordial one at the surface and decreases approximately linearly with depth, an ice mantle mostly depleted of rock, and an about 1800 km rock-ice core in which the rock concentration is close to the close-packing limit. The ice-rock shell thickness depends on uncertain rheology parameters and the heat flow and can be roughly 50 to 150 km thick. We show that if Callisto accreted from a mix of metal bearing rock and ice and if the average size of the rocks was of the order of meters to tens of meters, then Callisto may have experienced a gradual, but still incomplete unmixing of the two components. An ocean in Callisto at a depth of 100-200 km is difficult to obtain if the ice is pure H₂O and if the ice-rock lithosphere is 100 km or more thick; a water ocean is more plausible for ice contaminated by ammonia, methane or salts; or for pure H₂O at a depth of 400-600 km.  相似文献   

A macroscopic elastoplastic constitutive law for multilayered media: Application to reinforced earth material     

Erick Pruchnicki  Isam Shahrour 《国际地质力学数值与分析法杂志》1994,18(7):507-518

This paper refers to the formulation of a macroconstitutive law for elastoplastic multilayered media, using both thermodynamical approach and homogenization procedure. The latter shows that both the microstress and strain tensors are constant in each constituent. This result permits the formulation of a macroconstitutive law involving the microplastic strains as internal parameters. Both the macrofree energy and dual dissipation potential are computed and used to derive explicit expressions for the macrocompliance tensor, yield surface and hardening rule. Finally, this law is used to analyse the behavior of a reinforced earth material under various loading paths.  相似文献   

International Pellet Watch: Global monitoring of persistent organic pollutants (POPs) in coastal waters. 1. Initial phase data on PCBs, DDTs, and HCHs   总被引：1，自引：0，他引：1  

Yuko Ogata  Kaoruko Mizukawa  Satoru Iwasa  Yukie Mato  Keiji Okuda  Michio Murakami  Ruchaya Booyatumanondo  Le Quang Dung  Carlos Miguez  Charles Moore  Steven Weerts  Erick Burres  Michael Van Velkenburg  Richard C. Lang  Brenda Danner  Richard C. Thompson 《Marine pollution bulletin》2009,58(10):1437-1446

Samples of polyethylene pellets were collected at 30 beaches from 17 countries and analyzed for organochlorine compounds. PCB concentrations in the pellets were highest on US coasts, followed by western Europe and Japan, and were lower in tropical Asia, southern Africa and Australia. This spatial pattern reflected regional differences in the usage of PCBs and was positively correlated with data from Mussel Watch, another monitoring approach. DDTs showed high concentrations on the US west coast and in Vietnam. In Vietnam, DDT was predominant over its metabolites (DDE and DDD), suggesting the principal source may be current usage of the pesticide for malaria control. High concentrations of pesticide HCHs were detected in the pellets from southern Africa, suggesting current usage of the pesticides in southern Africa. This study demonstrates the utility and feasibility of the International Pellet Watch approach to monitor POPs at a global scale.  相似文献   

Fractured bedrock and saprolite hydrogeologic controls on groundwater/surface-water interaction: a conceptual model (Australia)   总被引：1，自引：1，他引：0  

Edward W. Banks  Craig T. Simmons  Andrew J. Love  Roger Cranswick  Adrian D. Werner  Erick A. Bestland  Martin Wood  Tania Wilson 《Hydrogeology Journal》2009,17(8):1969-1989

Hydrologic conceptual models of groundwater/surface-water interaction in a saprolite-fractured bedrock geological setting often assume that the saprolite zone is hydraulically more active than the deeper bedrock system and ignore the contribution of deeper groundwater from the fractured bedrock aquifer. A hydraulic, hydrochemical, and tracer-based study was conducted at Scott Creek, Mount Lofty Ranges, South Australia, to explore the importance of both the deeper fractured bedrock aquifer system and the shallow saprolite layer on groundwater/surface-water interaction. The results of this study suggest that groundwater flow in the deeper fractured bedrock zone is highly dynamic and is an important groundwater flow pathway along the hillslope. Deep groundwater is therefore a contributing component in streamflow generation at Scott Creek. The findings of this study suggest that hydrologic conceptual models, which treat the saprolite-fractured bedrock interface as a no-flow boundary and do not consider the deeper fractured bedrock in hydrologic analyses, may be overly simplistic and inherently misleading in some groundwater/surface-water interaction analyses. The results emphasise the need to understand the relative importance of subsurface flow activity in both of these shallow saprolite and deeper bedrock compartments as a basis for developing reliable conceptual hydrologic models of these systems.  相似文献