Space radiation processing of sulfides and silicates in primitive solar systems materials: Comparative insights from in situ TEM ion irradiation experiments     

Roy CHRISTOFFERSEN  Lindsay P. KELLER 《Meteoritics & planetary science》2011,46(7):950-969

Abstract– Mineral grains that comprise dust particles in circumstellar, interstellar, and protostellar environments can potentially undergo amorphization and other solid‐state transformations from exposure to energetic ions from space plasmas. The Fe‐sulfide minerals troilite (FeS) and pyrrhotite (Fe_1?xS) are important known dust components, but their potential to undergo structural changes, including amorphization, from space radiation processing in dusty space environments has not been experimentally evaluated relative to silicates. We used a transmission electron microscope (TEM) with capabilities for in situ ion irradiation to precisely follow structural changes in troilite and pyrrhotite exposed to 1.0 MeV Kr⁺⁺ ions selected to optimize the probability of inducing amorphization from nuclear elastic collisional processes. No indication of amorphization was found in either mineral up to an experimentally practical ion dose of 1 × 10¹⁶ Kr⁺⁺ ions cm^?2, indicating that both structures can remain crystalline up to a modeled collisional damage level of at least 26 displacements‐per‐atom. This behavior matches that of some of the most radiation‐resistant nonmetallic phases known, and is two orders of magnitude higher than the levels at which Mg‐rich olivine and enstatite become amorphous under the same irradiation conditions. Although pyrrhotite retained short‐range crystalline order during irradiation, its longer range vacancy‐ordered superstructure is removed at modeled damage levels equivalent to those at which olivine and enstatite become amorphous. This suggests that space radiation conditions sufficient to amorphize olivine and enstatite in circumstellar and interstellar environments would convert coexisting pyrrhotite to its disordered structural form, thereby changing magnetic and possibly other properties that determine how pyrrhotite will behave in these environments.  相似文献   

Modelling surface drainage patterns in altered landscapes using LiDAR     

J.B. Lindsay  K. Dhun 《International journal of geographical information science》2013,27(3):397-411

The detailed topographic information contained in light detection and ranging (LiDAR) digital elevation models (DEMs) can present significant challenges for modelling surface drainage patterns. These data frequently represent anthropogenic infrastructure, such as road embankments and drainage ditches. While LiDAR DEMs can improve estimates of catchment boundaries and surface flow paths, modelling efforts are often confounded difficulties associated with incomplete representation of infrastructure. The inability of DEMs to represent embankment underpasses (e.g. bridges, culverts) and the problems with existing automated techniques for dealing with these problems can lead to unsatisfactory results. This is often dealt with by manually modifying LiDAR DEMs to incorporate the effects of embankment underpasses. This paper presents a new DEM pre-processing algorithm for removing the artefact dams created by infrastructure in sites of embankment underpasses as well as enforcing flow along drainage ditches. The application of the new algorithm to a large LiDAR DEM of a site in Southwestern Ontario, Canada, demonstrated that the least-cost breaching method used by the algorithm could reliably enforce drainage pathways while minimizing the impact to the original DEM.  相似文献   

A Review of “Taming the Disorderly City: The Spatial Landscape of Johannesburg After Apartheid”     

Lindsay Bremner 《The Professional geographer》2013,65(1):143-144

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Decoupled crystallization and eruption histories of the rhyolite magmatic system at Tarawera volcano revealed by zircon ages and growth rates   总被引：2，自引：2，他引：0  

Sonja?StormEmail author  Phil?Shane  Axel?K.?Schmitt  Jan?M.?Lindsay 《Contributions to Mineralogy and Petrology》2012,163(3):505-519

We obtained U–Th disequilibrium age data on zircons from each of the four rhyolite eruptions that built Tarawera volcano in the last 22 ka within the Okataina Volcanic Center (OVC), caldera, New Zealand. Secondary ion mass spectrometry analyses on unpolished euhedral crystal faces that lack resorption features show that crystal growth variously terminated from near-eruption age to ~100 ka prior to eruption. Age-depth profiling of crystals reveals long periods of continuous (~34 ka) and discontinuous growth (~90 ka). Growth hiatuses of up to ~40 ka duration occur, but do not all relate to obvious resorption surfaces. Age differences up to similar magnitude are found on opposing faces of some crystals suggesting episodes of partial exposure to melts. These features are best explained by periodic, complete, or partial, sub-solidus storage and/or inclusion in larger crystal phases, followed by rapid liberation prior to eruption. This is supported by high abundances of U and Th (~500 − >2,000 ppm) in some zircons consistent with periods of high crystallinity (>70%) in the magmatic system, based on crystal/melt partitioning. Contemporaneous but contrasting rim-ward trends of these elements within crystals, even in the same lava hand sample, require synchronous growth in separate melt bodies and little connectivity within the system, but also significant crystal transport and mixing prior to eruption. Many crystals record continuity of growth through the preceding ~60 ka OVC caldera-collapse and subsequent eruptions from Tarawera. This demonstrates a decoupling between eruption triggers, such as shallow crustal extension and mafic intrusion, and the crystallization state of the OVC silicic magmatic system. The data highlights the need to distinguish between the time for accumulation of eruptible magma and the long-term magma residence time based on the age of crystals with high closure temperatures, when assessing the potential for catastrophic eruptions.  相似文献   

The weathering of norite at Black Hill,South Australia     

J. T. Hutton  Dianne S. Lindsay  C. R. Twidale 《Australian Journal of Earth Sciences》2013,60(1-2):37-50

Black Hill is a boulder‐strewn residual of norite standing 45 m above the Murray Plains about 80 km northeast of Adelaide. Between the boulders, the crystalline rock has weathered to a dark‐brown terra rossa‐rendzina soil with calcite, illite, kaolin, and hematite as the principal secondary minerals. At one site on the smooth lower slopes of the outcrop, the material above the norite consists of partially weathered granular fragments with considerable dolomite and some calcite in nodular form. Below the surface, the rock has been weathered along joints to produce the clay mineral nontronite, and between each corestone and this plastic clay there is a zone of laminated but essentially unaltered rock 10–25 cm thick. Pieces of amorphous silica occur sporadically in some joints and on the surface.

The dark‐brown soil appears to be related to the present environment but the nontronite in the joint weathering, the dolomite, and the amorphous silica are all consistent with the norite having been inundated, possibly during the Miocene marine transgression.

Calculations based on the retention of elements such as aluminium, potassium, titanium, and iron have been used to predict quantitatively the amount of certain minerals such as quartz, calcite, and dolomite introduced to the weathering profiles.  相似文献   

Diversity and distribution of the Siphonophora (Cnidaria) in Sagami Bay, Japan, and their association with tropical and subarctic water masses     

Mary M. Grossmann  Dhugal J. Lindsay 《Journal of Oceanography》2013,69(4):395-411

Siphonophores were sampled using stratified 1.67-m²-mouth 330-μm mesh nets during both day- and nighttime in Sagami Bay (35°0.50′N, 139°20′E), off south-eastern Japan during a 9-day period in March 2006, when the Kuroshio Current was in an offshore non-large meander phase. The samples were collected at 50-m intervals spanning from 1,000 m depth to the surface. Fifty-eight species and 11 eudoxid forms of unknown parentage were collected, of which 5 represent first-time records from Japanese waters, and Clausophyes laetmata Pugh and Pagès 1993, Eudoxia cf. galathea Moser 1925 and Lensia panikkari Daniel 1970 were recorded for the first time not only from Japan but from the entire Pacific Ocean. The highest abundance and diversity was found below the thermocline during the day, and above it at night. A second peak in abundance, around 400 m depth, associated with a decrease in diversity, could be linked to the increase in abundance of a single species—Dimophyes arctica (Chun 1897). The siphonophore communities could be related to the different water masses in the Bay, with an important influence of lateral transport of both tropical and subarctic species into the Bay by the different water masses.  相似文献   

Biodiversity,land degradation,and climate change: Participatory planning in Romania     

Lindsay C. Stringer  S. Serban Scrieciu  Mark S. Reed 《Applied geography (Sevenoaks, England)》2009,29(1):77-90

This paper considers the role of stakeholder participation in drawing together the three Rio Conventions, exploring how participatory activities to combat desertification in southern Romania can both support and hinder efforts to conserve biodiversity and mitigate the effects of climate change. It suggests that Romania's growing civil society sector has a potentially vital role to play in promoting synergy through participation, and that participatory processes act as an important mechanism for harnessing multiple benefits. The paper argues that participation needs to be further institutionalised within the Romanian context and in doing so, should emphasise empowerment, equity, trust and learning, integrating different knowledge bases to allow the development of sustainable and synergistic environmental solutions.  相似文献   

Incorporating conceptual and interpretation uncertainty to mineral prospectivity modelling     

J.N.Burkin  M.D.Lindsay  S.A.Occhipinti  E.-J.Holden 《地学前缘(英文版)》2019,10(4):1383-1396

Prospectivity analyses are used to reduce the exploration search space for locating areas prospective for mineral deposits.The scale of a study and the type of mineral system associated with the deposit control the evidence layers used as proxies that represent critical ore genesis processes.In particular,knowledge-driven approaches(fuzzy logic)use a conceptual mineral systems model from which data proxies represent the critical components.These typically vary based on the scale of study and the type of mineral system being predicted.Prospectivity analyses utilising interpreted data to represent proxies for a mineral system model inherit the subjectivity of the interpretations and the uncertainties of the evidence layers used in the model.In the case study presented,the prospectivity for remobilised nickel sulphide(NiS)in the west Kimberley,Western Australia,is assessed with two novel techniques that objectively grade interpretations and accommodate alternative mineralisation scenarios.Exploration targets are then identified and supplied with a robustness assessment that reflects the variability of prospectivity value for each location when all models are considered.The first technique grades the strength of structural interpretations on an individual line-segment basis.Gradings are obtained from an objective measure of feature evidence,which is the quantification of specific patterns in geophysical data that are considered to reveal underlying structure.Individual structures are weighted in the prospectivity model with grading values correlated to their feature evidence.This technique allows interpreted features to contribute prospectivity proportional to their strength in feature evidence and indicates the level of associated stochastic uncertainty.The second technique aims to embrace the systemic uncertainty of modelling complex mineral systems.In this approach,multiple prospectivity maps are each generated with different combinations of confidence values applied to evidence layers to represent the diversity of processes potentially leading to ore deposition.With a suite of prospectivity maps,the most robust exploration targets are the locations with the highest prospectivity values showing the smallest range amongst the model suite.This new technique offers an approach that reveals to the modeller a range of alternative mineralisation scenarios while employing a sensible mineral systems model,robust modelling of prospectivity and significantly reducing the exploration search space for Ni.  相似文献   

Mineralogical,geochemical, and microbial investigation of a sulfide-rich tailings deposit characterized by neutral drainage     

Matthew B.J. Lindsay  Peter D. Condon  John L. Jambor  Kerry G. Lear  David W. Blowes  Carol J. Ptacek 《Applied Geochemistry》2009

Mineralogical, geochemical and microbial characterization of tailings solids from the Greens Creek Mine, Juneau, Alaska, was performed to evaluate mechanisms controlling aqueous geochemistry of near-neutral pH pore water and drainage. Core samples of the tailings were collected from five boreholes ranging from 7 to 26 m in depth. The majority of the 51 samples (77%) were collected from the vadose zone, which can extend >18 m below the tailings surface. Mineralogical investigation indicates that the occurrence of sulfide minerals follows the general order: pyrite [FeS₂] >> sphalerite [(Zn,Fe)S] > galena [PbS], tetrahedrite [(Fe,Zn,Cu,Ag)₁₂Sb₄S₁₃] > arsenopyrite [FeAsS] and chalcopyrite [CuFeS₂]. Pyrite constitutes <20 to >35 wt.% of the tailings mineral assemblage, whereas dolomite [CaMg(CO₃)₂] and calcite [CaCO₃] are present at ?30 and 3 wt.%, respectively. The solid-phase geochemistry generally reflects the mineral assemblage. The presence of additional trace elements, including Cd, Cr, Co, Mo, Ni, Se and Tl, is attributed to substitution into sulfide phases. Results of acid–base accounting (ABA) underestimated both acid-generating potential (AP) and neutralization potential (NP). Recalculation of AP and NP based on solid-phase geochemistry and quantitative mineralogy yielded more representative results. Neutrophilic S-oxidizing bacteria (nSOB) and SO₄-reducing bacteria (SRB) are present with populations up to 10⁷ and 10⁵ cells g⁻¹, respectively. Acidophilic S-oxidizing bacteria (aSOB) and iron-reducing bacteria (IRB) were generally less abundant. Primary influences on aqueous geochemistry are sulfide oxidation and carbonate dissolution at the tailings surface, gypsum precipitation–dissolution reactions, as well as Fe reduction below the zone of sulfide oxidation. Pore-water pH values generally ranged from 6.5 to 7.5 near the tailings surface, and from approximately 7–8 below the oxidation zone. Elevated concentrations of dissolved SO₄, S₂O₃, Fe, Zn, As, Sb and Tl persisted under these conditions.  相似文献   

An irregular triangle mesh buffer analysis method for boundary representation geological object in three-dimension     

Nan Li  Leon Bagas  Mark Lindsay  Daniel Wedge  Lin Bai  Xianglong Song 《Earth Science Informatics》2017,10(2):149-167

Three-dimensional (3D) buffer analysis is a basic function of spatial analysis used widely in 3D Geographic Information Systems (3DGIS). Current buffer analysis methods for spatial points and curves generally function well. One exception is buffer zone of surface. Previous researchers in this field have used voxel models to overcome this limitation; however, defects with voxel model buffer analysis include redundancies, approximations, and poor visualization characteristics. In this contribution, a surface buffer analysis method is presented for the boundary representation of geological objects. Exact geometric representation is achieved via the construction of irregular triangle meshes in 3D. The results can be used for 3D structural modeling and then form the basis for spatial analysis or model-based quantitative assessment in mineral potential mapping and resource evaluation. Three comparisons between existing voxel methods and our new method, evaluating visualization, precision and redundancy, are conducted. The comparisons show that our proposed method is robust and provides a higher quality output than voxel modeling. Finally, uncertainty analysis of buffer distance in different geological objects was discussed.  相似文献