Foreword to special issue: Inverse Theory in the Earth Sciences     

Ute Christina Herzfeld 《Mathematical Geology》1996,28(2):133-135

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Two magma series and associated ore deposit types in the Permian Emeishan large igneous province, SW China   总被引：29，自引：0，他引：29  

Mei-Fu Zhou  Nicolas T. Arndt  John Malpas  Christina Yan Wang  Allen K. Kennedy 《Lithos》2008,103(3-4):352-368

The Late Middle Permian ( 260 Ma) Emeishan large igneous province in SW China contains two magmatic series, one comprising high-Ti basalts and Fe-rich gabbroic and syenitic intrusions, the other low-Ti basalts and mafic–ultramafic intrusions. The Fe-rich gabbros are spatially and temporally associated with syenites. Each series is associated with a distinctive type of mineralization, the first with giant Fe–Ti–V oxide ore deposits such as Panzhihua and Baima, the second with Ni–Cu–(PGE) sulfide deposits such as Jinbaoshan, Limahe and Zhubu. New SHRIMP zircon U–Pb isotopic data yielded 263 ± 3 Ma for the Limahe intrusion, 261 ± 2 Ma for the Zhubu intrusion and 262 ± 2 Ma for a syenitic intrusion. These new age dates, together with previously reported SHRIMP zircon U–Pb ages, suggest that all these intrusions are contemporaneous with the Emeishan flood basalts and formed during a major igneous event at ca. 260 Ma.The oxide-bearing intrusions have higher Al₂O₃, FeO (as total iron) and total alkalis (Na₂O + K₂O) but lower MgO than the sulfide-bearing intrusions. All intrusions are variably enriched in LREE relative to HREE. The oxide-bearing intrusions display positive Nb- and Ti-anomalies and in certain cases negative Zr–Hf anomalies, whereas the sulfide-bearing intrusions have obvious negative Nb- and Ti-anomalies, a feature of crustal contamination. Individual intrusions have relatively small ranges of Nd(t) values. All the intrusions, however, have Nd(t) values ranging from − 3.9 to + 4.6, and initial ⁸⁷Sr/⁸⁶Sr ratios from 0.7039 to 0.7105. The syenites have very low MgO (< 2 wt.%) but highly variable Fe₂O₃ (2.5 to 13 wt.%) with initial ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7039 to 0.7089. Magmas from both series could have derived by melting of a heterogeneous mantle plume: the high-Ti series from a Fe-rich, more fertile source and the low-Ti series from a Fe-poor, more refractory source. In addition, the low-Ti series underwent significant crustal contamination. The two magma series evolved along different paths that led to distinct mineralization styles.  相似文献   

Platinum-group minerals from the Jinbaoshan Pd–Pt deposit,SW China: evidence for magmatic origin and hydrothermal alteration     

Christina Yan Wang  Hazel M. Prichard  Mei-Fu Zhou  Peter C. Fisher 《Mineralium Deposita》2008,43(7):791-803

The Jinbaoshan Pt–Pd deposit in Yunnan, SW China, is hosted in a wehrlite body, which is a member of the Permian (∼260 Ma) Emeishan Large Igneous Province (ELIP). The deposit is reported to contain one million tonnes of Pt–Pd ore grading 0.21% Ni and 0.16% Cu with 3.0 g/t (Pd + Pt). Platinum-group minerals (PGM) mostly are ∼10 μm in diameter, and are commonly Te-, Sn- and As-bearing, including moncheite (PtTe₂), atokite (Pd₃Sn), kotulskite (PdTe), sperrylite (PtAs₂), irarsite (IrAsS), cooperite (PtS), sudburyite (PdSb), and Pt–Fe alloy. Primary rock-forming minerals are olivine and clinopyroxene, with clinopyroxene forming anhedral poikilitic crystals surrounding olivine. Primary chromite occurs either as euhedral grains enclosed within olivine or as an interstitial phase to the olivine. However, the intrusion has undergone extensive hydrothermal alteration. Most olivine grains have been altered to serpentine, and interstitial clinopyroxene is often altered to actinolite/tremolite and locally biotite. Interstitial chromite grains are either partially or totally replaced by secondary magnetite. Base-metal sulfides (BMS), such as pentlandite and chalcopyrite, are usually interstitial to the altered olivine. PGM are located with the BMS and are therefore also interstitial to the serpentinized olivine grains, occurring within altered interstitial clinopyroxene and chromite, or along the edges of these minerals, which predominantly altered to actinolite/tremolite, serpentine and magnetite. Hydrothermal fluids were responsible for the release of the platinum-group elements (PGE) from the BMS to precipitate the PGM at low temperature during pervasive alteration. A sequence of alteration of the PGM has been recognized. Initially moncheite and atokite have been corroded and recrystallized during the formation of actinolite/tremolite, and then, cooperite and moncheite were altered to Pt–Fe alloy where they are in contact with serpentine. Sudburyite occurs in veins indicating late Pd mobility. However, textural evidence shows that the PGM are still in close proximity to the BMS. They occur in PGE-rich layers located at specific igneous horizons in the intrusion, suggesting that PGE were originally magmatic concentrations that, within a PGE-rich horizon, crystallized with BMS late in the olivine/clinopyroxene crystallization sequence and have not been significantly transported during serpentinization and alteration.  相似文献   

Determination of the ionospheric foF2 using a stand-alone GPS receiver     

Dudy D. Wijaya  Haris Haralambous  Christina Oikonomou  Wedyanto Kuntjoro 《Journal of Geodesy》2017,91(9):1117-1133

The critical frequency of ionospheric F2 layer (foF2) is a measure of the highest frequency of radio signal that may be reflected back by the F2 layer, and it is associated with ionospheric peak electron density in the F2 layer. Accurate long-term foF2 variations are usually derived from ionosonde observations. In this paper, we propose a new method to observe foF2 using a stand-alone global positioning system (GPS) receiver. The proposed method relies on the mathematical equation that relates foF2 to GPS observations. The equation is then implemented in the Kalman filter algorithm to estimate foF2 at every epoch of the observation (30-s rate). Unlike existing methods, the proposed method does not require any additional information from ionosonde observations and does not require any network of GPS receivers. It only requires as inputs the ionospheric scale height and the modeled plasmaspheric electron content, which practically can be derived from any existing ionospheric/plasmaspheric model. We applied the proposed method to estimate long-term variations of foF2 at three GPS stations located at the northern hemisphere (NICO, Cyprus), the southern hemisphere (STR1, Australia) and the south pole (SYOG, Antarctic). To assess the performance of the proposed method, we then compared the results against those derived by ionosonde observations and the International Reference Ionosphere (IRI) 2012 model. We found that, during the period of high solar activity (2011–2012), the values of absolute mean bias between foF2 derived by the proposed method and ionosonde observations are in the range of 0.2–0.5 MHz, while those during the period of low solar activity (2009–2010) are in the range of 0.05–0.15 MHz. Furthermore, the root-mean-square-error (RMSE) values during high and low solar activities are in the range of 0.8–0.9 MHz and of 0.6–0.7 MHz, respectively. We also noticed that the values of absolute mean bias and RMSE between foF2 derived by the proposed method and the IRI-2012 model are slightly larger than those between the proposed method and ionosonde observations. These results demonstrate that the proposed method can estimate foF2 with a comparable accuracy. Since the proposed method can estimate foF2 at every epoch of the observation, it therefore has promising applications for investigating various scales (from small to large) of foF2 irregularities.  相似文献   

Reply to R. F. Shurtz'' comment and R. M. Srivastava''s and E. H. Isaaks'' reply     

Ute Christina Herzfeld 《Mathematical Geology》1992,24(2):225-226

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Recovery of Danish Coastal Ecosystems After Reductions in Nutrient Loading: A Holistic Ecosystem Approach     

Bo Riemann  Jacob Carstensen  Karsten Dahl  Henrik Fossing  Jens W. Hansen  Hans H. Jakobsen  Alf B. Josefson  Dorte Krause-Jensen  Stiig Markager  Peter A. Stæhr  Karen Timmermann  Jørgen Windolf  Jesper H. Andersen 《Estuaries and Coasts》2016,39(1):82-97

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Bayesian estimation of reservoir properties—effects of uncertainty quantification of 4D seismic data     

Kjersti Solberg Eikrem  Geir Nævdal  Morten Jakobsen  Yan Chen 《Computational Geosciences》2016,20(6):1211-1229

This paper shows a history matching workflow with both production and 4D seismic data where the uncertainty of seismic data for history matching comes from Bayesian seismic waveform inversion. We use a synthetic model and perform two seismic surveys, one before start of production and the second after 1 year of production. From the first seismic survey, we estimate the contrast in slowness squared (with uncertainty) and use this estimate to generate an initial estimate of porosity and permeability fields. This ensemble is then updated using the second seismic survey (after inversion to contrasts) and production data with an iterative ensemble smoother. The impact on history matching results from using different uncertainty estimates for the seismic data is investigated. From the Bayesian seismic inversion, we get a covariance matrix for the uncertainty and we compare using the full covariance matrix with using only the diagonal. We also compare with using a simplified uncertainty estimate that does not come from the seismic inversion. The results indicate that it is important not to underestimate the noise in seismic data and that having information about the correlation in the error in seismic data can in some cases improve the results.  相似文献   

Does the High School Geography Experience Influence Enrollment in University Geography Courses?     

Joseph Leydon  Christina McLaughlin  Heather Wilson 《The Journal of geography》2017,116(2):79-88

The literature suggests that owing to profound difficulties with high school geography curricula, teachers play a vital role in stimulating student interest and in providing a platform for continuation in the study of geography at university. Yet, with little empirical evidence offered in support, it is unclear why students select geography at university and if their high school experience informs their decision. Through a survey of students enrolled in an introductory geography course at an Ontario university, this research questions the relationship between students' high school experience and their enrollment in the course and ponders the implications for the health of the discipline.  相似文献   

Effects of hypoxia on gene and protein expression in the blue crab, Callinectes sapidus     

Brouwer M  Larkin P  Brown-Peterson N  King C  Manning S  Denslow N 《Marine environmental research》2004,58(2-5):787-792

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Marine seismics with a pulsed combustion source and Pseudo Noise codes     

Bjørn Askeland  Halvor Hobæk  Rolf Mjelde 《Marine Geophysical Researches》2007,28(2):109-117

There has been a long-standing debate concerning how dangerous seismic surveys are with respect to marine life. Marine seismic work today is dominated by airgun technology, where high energy is generated by a release of compressed air into the water. The objective of the “Time coded impulse seismic technique” project is to examine whether a new low energy acoustic source can be used for seismic purposes. If the method turns out to be successful, the low output energy and continuous operation will make the source suitable in environmental sensitive areas. The Low level Acoustic Combustion Source (LACS) is a petrol driven pulsed underwater acoustic source. It operates at a few meters depth, and each shot can be digitally controlled from the surface by a computer located in the mother vessel. A presentation of the recorded LACS signal characteristics, the modulation, the Pseudo Noise coding/decoding principles and field test results, is given. The importance of using an optimized code with fine resolution and of using the near field recording as a correlator sequence is demonstrated. Clear correlation peaks could then be seen from the bottom and sub bottom reflectors.  相似文献