Geochemistry of streams, soils, and permafrost and the geochemical effects of climate change in a continuous permafrost region, Arctic Alaska, United States

Keller, Kate A University of Michigan 2006 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Climate warming can impact arctic ecosystems by altering watershed geochemistry through permafrost degradation and increased mineral weathering. This dissertation evaluated the importance of these changes in arctic Alaska by examining permafrost and soil geochemistry, mineral weathering, and changes in stream geochemistry. Elemental and 87Sr/86Sr geochemistry of streams and soils, permafrost, and soil parent materials from glacial deposit surfaces of varying ages were evaluated. Carbonate content increases with soil depth across all surfaces, and exchangeable P, K, and Ca concentrations are significantly (p<0.05) greater in permafrost than in active-layer mineral soil. These results suggest that increasing thaw depth will increase carbonate alkalinity, Ca, K, and P supply to soils and streams across the region. Elemental depletion factors for a subset of these soils forming a chronosequence indicate that carbonate weathering is the dominant weathering process, and long-term weathering rates are 0.5-11 meq m-2 yr-2. Based on increasing Ca/Na and Ca/Ba and decreasing 87Sr/ 86Sr with depth in soils and permafrost, elemental ratios and 87Sr/86Sr in an arctic stream were used as tracers of the maximum depth of soil water flow and therefore changes in integrated thaw depth across the watershed. From 1994 to 2004, mean 87Sr/ 86Sr values in low-discharge late summer stream water decreased from 0.7122 to 0.7119 (R2=0.62, p=0.012), and Ca/Na and Ca/Ba showed significant increasing trends that were consistent with increasing depth of soil water flowpaths. These trends provide new evidence for increasing thaw depth, despite the lack of measured increases using traditional thaw probe techniques. The effects of an in-stream thermokarst feature on stream chemistry were also investigated. Solute concentrations, alkalinity, and conductivity were elevated downstream from the thermokarst. Estimates suggest geochemical changes may be detectable downstream in rivers up to 100 times the size of the original affected stream. These data further support the use of stream geochemistry as an indicator of spatially heterogeneous permafrost degradation. This research suggests that permafrost degradation on the Alaskan North Slope is exposing previously frozen carbonate minerals to weathering, thereby influencing stream geochemistry. These geochemical changes are an important consideration when examining the overall impact of climate change on arctic ecosystems.

The Role of Upper Mantle Heterogeneity and Plume-Ridge Interaction Along the Central Indian Ridge from 7°S and 18°S : a multidisciplinary investigation based on MORB geochemistry, bathymetry, and gravity analysis

클레망 서울대학교 대학원 2024 국내박사

The mid-ocean ridges (MOR) are the largest volcanic system on Earth, generating the oceanic lithosphere that covers 65% of the Earth’s surface through seafloor spreading. This phenomenon is due to the tectonic plates moving away from each other, which induces the underlying mantle to rise and melt. The resultant buoyant melt erupts along the ridge axis in the form of mid-oceanic ridge basalts (MORB), and the geochemistry signature of these lavas are an important source of information on the melting conditions and the geochemical characteristics of the less accessible upper mantle. A multitude of parameters such as the spreading rate, the influence of mantle plume on the ridge or even the presence of heterogeneity embedded in the upper mantle may have an impact on morphology and/or geochemistry variations along portions of mid-ocean ridge. Variations of the spreading style, ridge morphology, and MORB geochemical signature will then reflect the nature of the mantle and the upwelling dynamics beneath the ridge. In this dissertation, the geochemical and isotopic signature of MORB sampled along the Central Indian Ridge axis between 8°and 17°S were investigated to better understand the different mantle source melting. The new trace element and isotopic analysis show that the MORB geochemical signature differs between segments along the studied portion of the ridge. The CIR portion between 12°and 17°S, especially the segment between 14°and 16°S show enriched MORB that can be explained by the presence of three mantle end-members: the depleted Indian-type MORB mantle, Réunion Plume, and Seychelles/Madagascar-like continental crust components. Moreover, the geophysical analysis of the enriched segment between 14°and 16°S reveals a correlation between its structural characteristics, gravity anomalies, and MORB enrichment variations. This correlation is best explained by the presence of a fertile heterogeneity in the melting regime which influences the melt production along a portion of this segment delimited by ridge discontinuities. Furthermore, this multidisciplinary analysis suggests that the magmatic accretion occurring along this segment is most certainly following the model of buoyancy-driven focused mantle upwelling. Another portion of the CIR formed by two segments between 8°and 12°S was investigated and their MORB geochemistry highlights the presence of a different enriched mantle component beneath this ridge area. This enriched source has a FOZO-like signature and its presence can be explained by the influence of an asthenospheric anomaly: the Mascarene Basin Asthenosphere Reservoir. Furthermore, it is proposed in this study that this plume-like anomaly is an aborted plume originally linked to a broad upwelling structure rooted in the lower mantle, in the African LLSVP. Thus, this study offers valuable insights into the geodynamics of the Indian Ocean mantle and its impact on MORB geochemistry and spreading processes along the CIR but also about processes affecting MOR in general. Keyword : Central Indian Ridge, Mantle upwelling, Seafloor spreading, Mantle heterogeneity, Mid-ocean ridge basalt, Isotope geochemistry, Ocean floor, Ridge segmentation Student Number : 2017-31049 중앙해령(Mid-Ocean Ridges, MOR)은 지구 표면의 65%를 구성하는 해양 지각을 해저면 확장을 통해 형성하는 지구에서 가장 큰 규모의 화산 활동이다. 이 현상은 지각판들이 서로 멀어지면서 그 아래에 존재하는 맨틀이 상승하여 용융한 결과물이며, 용융된 맨틀 물질은 해령의 축을 따라 중앙해령 현무암(Mid-Ocean Ridge Basalts, MORB)의 형태로 분출된다. 분출된 용암의 지구화학적 특성을 이해하는 것은 다른 방법으로는 접근하기 어려운 상부 맨틀에서의 용융 조건과 지구화학적 특성에 대한 중요한 정보를 제공한다. 판의 확장 속도, 해령에 대한 맨틀 플룸의 영향, 또는 상부 맨틀에 내재된 구성적 이질성과 같은 다양한 요소들이 해령의 일부분에서 그 형태학적 특성 및 지구화학적 변화를 초래할 수 있다. 그러므로 해저 확장의 방식, 해령의 형태학, MORB의 지구화학적 특성은 맨틀과 그 상승 과정의 동역학에 대한 정보를 제공한다. 이 연구에서는 남위 8°에서 17° 사이의 인도양 중앙해령(Central Indian Ridge, CIR) 을 따라 획득한 MORB의 지구화학적 특성과 및 동위원소 구성을 조사하여 서로 다른 맨틀 근원의 용융을 연구하였다. 새로운 미량 원소와 동위원소 분석 결과는 연구 지역의 해령의 각 구간에서 MORB의 지구화학적 특성이 서로 다르다는 것을 지시한다. 남위 12°에서 17° 사이, 특히 남위 14°에서 16° 사이에 위치한 구역에서는 세 가지 근원맨틀 성분들(결핍된 인도양 MORB 맨틀, 레위니옹 플룸, 세이셸/마다가스카르 대륙 지각)로 설명될 수 있는 부화된 MORB를 확인하였다. 또한, 동 구역에 대한 지구물리학적 연구를 통해 구역의 지구조적 특성, 중력 이상, 그리고 MORB 부화 정도가 가지는 상관 관계를 규명하였다. 이 상관 관계는 해령의 불연속적 단절에 의해 구분되는 구역의 한 구간에서 맨틀 부화도의 이질성이 용융에 미치는 영향에 의해 잘 설명될 수 있다. 더 나아가, 이러한 지구화학 및 지구물리학을 통한 다학제적 분석 결과는 이 구역에서 발생하는 마그마 축적이 주로 부력에 의해 집중된 맨틀 용승 모델을 따르고 있음을 시사한다. 남위 8°에서 12° 사이에서 두 구역으로 나뉘어진 인도양 중앙해령의 또 다른 구간에서의 MORB의 지구화학적 특성은 추가적인 부화된 근원 맨틀 성분의 존재를 나타낸다. 이 부화된 근원 맨틀 성분은 FOZO와 유사한 특성을 가지고 있으며, 이는 연약권 변칙성(마스카렌 분지 연약권 저장소, Mascarene Basin Asthenosphere Reservoir)의 영향으로 설명될 수 있다. 본 연구에서는 이러한 유사-플룸 변칙성이 하부 맨틀에 위치한 아프리카 LLSVP로부터 기원하는 광범위한 상승 구조와 연결된 중단된 플룸 현상이라고 제안한다. 따라서 이 연구는 인도양 맨틀에서의 지구동역학 및 MORB의 지구화학적 특성에 미치는 영향, 인도양 중앙해령을 따라 일어나는 해저면 확장에 대한 영향 뿐만이 아니라중앙해령에 영향을 미치는 다양한 요소들에 대한 전반적 통찰을 제공한다.

Advances in Calcium Isotope Geochemistry: Method Development and Application in a Multi-Proxy Investigation of Alaskan Arctic Watersheds

Lehn, Gregory O Northwestern University ProQuest Dissertations & T 2016 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The research presented in this dissertation improves double-spike isotope dilution techniques for measuring calcium isotope abundance variations (delta 44/40Ca and delta44/42Ca) by Multi Collector Thermal Ionization Mass Spectrometry (MC-TIMS). In combination with other elemental and isotopic proxies, high precision Ca isotope measurements are applied to the study of mountain and tundra watersheds underlain by continuous permafrost on the North Slope of Alaska to understand how seasonal freeze/thaw cycles of the active layer influence stream geochemistry. I developed a Monte Carlo error model to optimize analysis of delta 44/40Ca values using a 43Ca-42Ca double-spike. The model maximizes precision and throughput, while minimizing Faraday collector damage and instrumental drift. I implemented the new method to analyze four common Ca isotope standards and found good agreement with model predictions. The global, long-term external reproducibility for the method is +/-0.041‰ (2sigmaSD), which represents a two- to ten-fold improvement over previous Ca isotope methods. Next, I modified the Monte Carlo error model to optimize simultaneous analysis of delta44/40Ca and delta44/42Ca values using a 48Ca-43Ca double-spike. I used the method to analyze five common Ca isotope standards and found that measured precisions were significantly worse than model predictions, contrary to optimization of the 43Ca-42Ca double-spike technique. Patterns in measured data revealed that mixing of multiple Ca reservoirs on the filament hampered attainment of high-precision results expected from model predictions. Moreover, I observed that mixing had a multi larger effect with the 48Ca-43Ca double-spike compared to the 43Ca- 42Ca double-spike. I employed a filament reservoir-mixing model to examine how different double-spike pairs (i.e., 48Ca- 43Ca, 48Ca-42Ca, 46Ca- 43Ca, and 43Ca-42Ca) magnify propagation of these errors. Measured and modeled data confirmed existence of an "average mass rule," namely that the highest precision data are obtained when the average mass of the double-spike pair is similar to the average mass of the target measurement ratio. By identifying mixing as the dominant source of error for many Ca double-spike pairs, future research can focus on minimizing the effect. At current levels of filament mixing, the best precisions can only be achieved with a 43Ca-42Ca double-spike for delta44/40Ca and a 46Ca-43Ca double-spike for delta44/42Ca. Finally, I used multiple proxies (major ions, delta34S SO4, delta13CDIC, 87Sr/ 86Sr, and delta44/40Ca) to quantify seasonal controls on the geochemistry of streams draining continuous permafrost on the North Slope of Alaska. The major ion, delta34SSO4 and delta 13CDIC geochemistry indicates the overall dominance of carbonate weathering by carbonic and sulfuric acids, with additional seasonal influences from silicate weathering by carbonic acid, atmospheric deposition, plant decay, and sulfate salt dissolution. While all rivers experience shifts in major ion ratios and delta13CDIC values that coincide with seasonal permafrost thaw and downward expansion of the active layer, streams that predominantly drain bare bedrock in the Brook Range experience a dramatic transition from carbonate weathering in the spring and summer to sulfate salt dissolution in the fall. Riverine delta34S SO4 values confirm the sulfate salts are secondary precipitates rather than primary, bedrock forming marine evaporites. Results suggest that cryoconcentration in soils during the late fall and winter forces precipitation of secondary salts at depth, and exposure during subsequent thaw season yields the observed stream water signals. Streams draining tundra north of the Brooks Range lack definitive evidence for sulfate salt dissolution, presumably because thick peat soils limit the weathering of underlying glacial sediment where the salts are expected to form and dissolve. Appearance of a sulfate salt dissolution signal in tundra streams may correlate with future permafrost degradation. Carbonate weathering dominates riverine 87Sr/86Sr ratios, but the compositional heterogeneity of bedrock and secondary salts limit interpretation of the data. Riverine delta44/40Ca values are higher than those for bedrock, likely due to plant uptake of lighter Ca isotopes. In the tundra watersheds, freshet delta44/40Ca values are 0.10‰ to 0.20‰ lower than summer and fall values. These trends could reflect contributions from plant decay or radiogenic 40Ca contributions from the weathering of old silicate minerals with high K/Ca ratios.

Petrography, Cr-spinel Chemistry, and Whole Rock Geochemistry of the Cretaceous Icheonri Formation in Korea : Implications for Provenance and Tectonic Setting

양희선 국립부경대학교 대학원 2025 국내석사

Integrating Metagenomics and Geochemistry: Functional Evolution and Taxonomic Classification of Hot Spring Communities

Alsop, Eric Bennie Arizona State University 2014 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The taxonomic and metabolic profile of the microbial community inhabiting a natural system is largely determined by the physical and geochemical properties of the system. However, the influences of parameters beyond temperature, pH and salinity have been poorly analyzed with few studies incorporating the comprehensive suite of physical and geochemical measurements required to fully investigate the complex interactions known to exist between biology and the environment. Further, the techniques used to classify the taxonomic and functional composition of a microbial community are fragmented and unwieldy, resulting in unnecessarily complex and often non-consilient results. This dissertation integrates environmental metagenomes with extensive geochemical metadata for the development and application of multidimensional biogeochemical metrics. Analysis techniques including a Markov cluster-based evolutionary distance between whole communities, oligonucleotide signature-based taxonomic binning and principal component analysis of geochemical parameters allow for the determination of correlations between microbial community dynamics and environmental parameters. Together, these techniques allow for the taxonomic classification and functional analysis of the evolution of hot spring communities. Further, these techniques provide insight into specific geochemistry-biology interactions which enable targeted analyses of community taxonomic and functional diversity. Finally, analysis of synonymous substitution rates among physically separated microbial communities provides insights into microbial dispersion patterns and the roles of environmental geochemistry and community metabolism on DNA transfer among hot spring communities. The data presented here confirms temperature and pH as the primary factors shaping the evolutionary trajectories of microbial communities. However, the integration of extensive geochemical metadata reveals new links between geochemical parameters and the distribution and functional diversification of communities. Further, an overall geochemical gradient (from multivariate analyses) between natural systems provides one of the most complete predictions of microbial community functional composition and inter-community DNA transfer rates. Finally, the taxonomic classification and clustering techniques developed within this dissertation will facilitate future genomic and metagenomic studies through enhanced community profiling obtainable via Markov clustering, longer oligonucleotide signatures and insight into PCR primer biases.

Dreissenid-Mediated Energy and Nutrient Cycling in Profundal Regions of the Laurentian Great Lakes

Huff, Audrey University of Minnesota ProQuest Dissertations & T 2023 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

In the Laurentian Great Lakes, invasive zebra and quagga (dreissenid) mussels have dramatically altered biotic community structure, primary productivity, and biogeochemistry since their introduction in the 1980s. Recently, quagga mussel (Dreissena rostriformis bugensis) populations have been expanding deeper into profundal regions of Lakes Michigan, Huron, and Ontario. These dense offshore populations have substantially altered offshore energy and nutrient cycling, but there are key gaps in our understanding of deep-water quagga mussel physiology and their impacts on pelagic biogeochemistry. Specifically, there is a lack of information on (1) quagga mussel tissue nutrient sequestration and regeneration rates, including variability in tissue stoichiometry (C:N:P molar ratios) and its influence on mussel excretion rates and excretion stoichiometry, (2) quagga mussel impact on offshore sediment geochemistry, including sediment mixing rate, sediment oxygen penetration, and dissolved nutrient dynamics at the sediment-water interface, and (3) quagga mussel population dynamics, including size distribution and growth rates, in deep, offshore lake regions. Presented here are the results of field (chapter 2), experimental (chapter 3), and modelling (chapter 4) studies I conducted to address these knowledge gaps about quagga mussel physiology and ecological impacts.To determine variability of quagga mussel tissue stoichiometry and its impact on mussel excretion (chapter 2), I measured mussel tissue and excretion carbon, nitrogen, and phosphorus content along depth (20 – 130m) and trophic gradients in Lakes Michigan and Huron during spring mixing and summer stratification periods of 2019. I found that mussel tissue C:N:P ratios varied substantially in Lakes Michigan and Huron, suggesting that quagga mussels have flexible internal homeostasis. I also found that tissue C:N:P stoichiometry was a significant driver of mussel excretion rates and excretion stoichiometry. When mussels had lower tissue C:P ratios than available seston, excretion C:nutrient (C:N and C:P) ratios decreased. Next, to investigate the influence of quagga mussels on offshore sediment geochemistry (chapter 3), I conducted a sixweek microcosm experiment. I incubated quagga mussels, Diporeia spp. (previously the dominant Great Lakes’ macroinvertebrate), and oligochaete worms (the second most common benthic macroinvertebrate in the Great Lakes). Species were incubated separately and in combination to determine varying organism impacts on sediment mixing and biogeochemistry as well as potential community interaction effects. To simulate deep, offshore conditions, I used low particulate organic matter (POM) sediment in the microcosms and kept them in the dark and at 4°C. I found that sediment mixing depth and intensity varied significantly among species, but that there were no significant differences in sediment oxygen penetration depth or nutrient dynamics. Additionally, I found no evidence for species interaction effects. Finally, I used a Dynamic Energy Budget (DEB) model to explore quagga mussel physiology and growth rates under variable temperatures and food quantities (chapter 4). First, I simulated quagga mussel growth at annual temperatures and food availability representative of oligotrophic, mesotrophic, and eutrophic conditions in nearshore, mid-depth, and offshore regions of the Great Lakes. I then simulated mussel growth under three climate warming scenarios (+0.5°C, +1°C, and +2°C water temperatures). Corresponding changes in lake stratification regime under warming scenarios included an increase in the duration of summer stratification and a decrease in the duration of winter stratification. I found that quagga mussel growth increased with warmer water temperatures and altered stratification regimes. I also found that relative importance of water temperature and food availability varied over trophic status and mussel age, with mussel sensitivity to food limitation increasing as mussels grew larger over time.The combined results from these three studies indicate that quagga mussel impacts on pelagic energy and nutrient dynamics are mostly due to direct mechanisms – including carbon and nutrient ingestion, sequestration, and regeneration – rather than altered sediment geochemistry. My results provide detailed information on quagga mussel physiology, including variability of internal stoichiometry and growth under a wide range of environmental conditions, which strongly influences mussel nutrient recycling. Together, these results improve the current understanding of quagga mussel biology and will help to inform estimates of quagga mussel impacts on biogeochemical cycling in the Great Lakes and other invaded ecosystems.

강원도 양양 지역에 분포하는 섬장암에 대한 암석화학적 연구

이원섭 강원대학교 대학원 2012 국내석사

경기육괴 북동부에 위치하는 강원도 양양군 서면 장승리 일원에는 시대미상의 섬장암류가 양양철광 중앙부를 중심으로 남북방향을 장축으로 하는 타원체로 분포한다. 본 연구지역의 섬장암은 선캄브리아기의 편마암내에 발달한 단층대와 접촉해 있으며, 북부에는 중생대 화강암류의 관입에 의해 그 규모가 크게 축소된다. 양양지역에 분포하는 섬장암의 암석화학적 특성을 고찰하기 위하여 야외지질조사를 통해 채취한 시료 중 18개의 시추코어 및 노두 시료에 대해 박편제작과 편광현미경 관찰 등을 통한 암석기재 및 주성분원소, 미량원소 및 희토류원소에 대한 지화학 분석을 실시하였다. 연구지역의 섬장암은 회색 또는 담홍색의 암색을 나타내며, 조직은 주로 반상을 보이나 간혹 괴상을 나타내기도 한다. 전체적인 암색은 알칼리장석의 함유량에 따라 지배되어, 장석에 의한 전체적인 암색을 보인다. 반정의 크기 또한 보편적인 크기에서 신장되어 크게 발달되어 있는 것 등 다양한 범위를 나타낸다. 또한 편광현미경으로 살펴보면 주 구성광물은 알칼리장석(정장석, 미사장석), 사장석, 각섬석, 흑운모 등이며, 부 구성광물로는 석영, 스핀, 인회석, 저어콘, 불투명광물을 비롯하여 2차광물인 견운모, 녹니석, 녹렴석 등이 수반되며, 그리고 시추 코어 시편에서는 방해석의 세맥 등도 관찰된다. 각 주성분 원소의 변화 경향을 살펴보면 SiO2의 함량증가에 따라 TiO2, Fe2O3T, MnO, MgO, CaO, P2O5는 뚜렷하게 감소하는 경향을, Al2O3, Na2O는 명확하지는 않으나 감소하는 경향을, K2O는 증가하는 경향을 보인다. 미량원소의 성분변화는 V, Sc, Ba, Zn, Sr, Ni, Co, Cr, Y는 SiO2 증가에 따라 감소하고, Rb, Th, U, Pb는 증가하는 경향을 보여준다. 따라서 이들 주성분 원소, 미량 원소들의 함량변화에 대한 경향성은 단일암체의 분화경향에 잘 일치됨을 알 수 있다. 양양지역의 섬장암 시료들을 QAP diagram에 도시하여 IUGS에 의해 분류해 보면 섬장암과 석영섬장암 영역에 해당된다. 섬장암의 희토류원소 패턴도에서 보이는 희토류원소의 거동을 보면, 모든 시료에서 La에서 Sm까지는 급격한 감소를 보이며, Gd에서 Lu까지는 완만한 감소추세와 Eu 부(-)이상을 뚜렷하게 나타낸다. Eu의 부(-)이상과 표준화값 등으로 보아 장석의 분별결정작용이 있었음을 나타낸다. SiO2에 대한 Na2O+K2O의 상관 관계도에서 Alkaline series에 해당되며, AFM 삼각도에서는 전형적인 칼크-알카리 계열에 도시된다. 대표시료의 Al 포화지수(Molar A/CNK)는 0.91∼1.1로서 대부분의 시료들이 중알루미나형(Metaluminous)에서 점진적으로 고알루미나형(Peraluminous)으로 변화하여 분화가 진행될수록 더 알루미나화 됨을 볼 수 있다. A/CNK vs. A/NK의 상관도에서도 대부분의 시료가 중알루미나형에서 고알루미나형으로 도시되며, I-type 영역에 포함되며, I-type 암석의 특징과 연구지역 섬장암의 지화학적 특징이 잘 일치하는 것을 알 수 있다. The rocks in the vicinity of the Yangyang iron mine consist of Pre-Cambrian gneiss and metasediments, syenite of unknown age, and intrusive rocks of Cretaceous period, which are mainly controlled by NNE-and EW-trending faults. Syenites distributed in the periphery of metasediments and surrounded by gneisses were intruded by Cretaceous granitic rocks in the northeastern part. Syenites of grey or pink color can be classified texturally into porphyritic foliated, porphyritic massive, foliated and massive. Syenite rock samples from prospecting drill cores and outcrops were studied thoroughly in petrography and geochemistry. Major rock-forming minerals are alkali feldspars, plagioclase, amphibole and biotite, which correspond to syenite or quartz syenite in the IUGS classification scheme, and accessories are quartz, sphene, apatite, zircon, opaques and some secondary minerals such as sericite, chlorite, epidote and etc. The Harker's diagrams of major oxide abundances vs SiO2 contents reveal regular variation trends for all syenites, where with increasing of SiO2 contents Al2O3, TiO2, Fe2O3T, MgO, CaO and P2O5 contents decrease systematically but K2O content tend to decrease. Abundances of V, Sc, Ba, Zn, Sr, Ni, Co, Cr and Y display decreasing patterns with the increase of SiO2 content, while those of Rb, Th, U and Pb vary in an increasing trend. Syenite samples show a relatively uniform pattern of weakly negative Eu anomalies and an enrichment pattern of light REE's compared with heavy REE's. Various petrochemical diagrams such as Na2O+K2O vs SiO2, AFM, A/CNK vs A/NK and others for syenites in the study area show that syenites in the Yangyang area are assigned to alkaline to alkaline series and I-type granites. Conclusively the syenites in the Yangyang area can be suggested to be derived from an igneous origin and evolved through alkali feldspar differentiation. Key Words: syenite, petrography, geochemistry

Experimental studies of uranium, palladium, silver, and lead: Partitioning and phase stability

Wheeler, Kevin Thad Columbia University 2007 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

I seek an understanding of current and past planetary processes and events through constraining the chemical composition of the Earth's core. I use experimental techniques to simulate nature in a laboratory setting rather than to analyze natural samples. The range of techniques and equipment varies from one atmosphere furnaces to diamond anvil cells, but this thesis contains results mostly from piston cylinder and multianvil experiments. In chronological order of research conducted, the projects of my graduate work that are detailed in this thesis are (1) Phase stability of PbS with pressure; (2) Partitioning of U between molten sulfide and molten silicate; (3) Partitioning of Ag and Pd between molten sulfide and molten silicate. 1. PbS phase stability. This project was conceived to help resolve a classroom discussion about the Pb paradox; but it ended up a very different project more of interest for phase equilibrium and material science questions than for mantle/core geochemistry. Experimentally, it started as a difficult technical problem because molten PbS reacts with or wets most standard capsule materials, making it very difficult to contain. This technical issue was resolved with grade HP boron nitride capsules which proved to be relatively chemically inert and resistant to wetting. The study employed differential thermal analysis and conductivity measurements to define the phase boundaries of PbS. Liquidus slopes of PbS and other similarly structured and sized compounds correlate well with volume change on melting. However slopes do not correlate with published values of entropy of melting as is required from the Clapeyron equation, calling into question the accuracy of published entropy data. Galena was found to transform from cubic to orthorhombic structure at 26 kbar for all sub-liquidus temperatures. 2. U partitioning. The motivation for this study originated from the need to constrain the quantity of radioactive elements in the core in order to determine their contribution to planetary heat flux and geodynamo generation. K has been shown to partition into iron sulfide under magma ocean relevant conditions. Performing a similar study on U is a natural extension. This study employed piston cylinder and multianvil experiments to investigate the partitioning behavior of U in the liquid metallic sulfide-liquid silicate system. Previously existing analytical problems with measuring low U metal contents were overcome by use of LA-ICP-MS. This study concluded that, although there is variation in DUmetallic sulfide/silicate with S content, the absolute concentration of U in the core is too small to account for a significant amount of heat production or geodynamo power. 3. Pd-Ag partitioning. This study attempts to constrain the amount of 107Ag, the radiogenic daughter product of 107Pd (t1/2 = 6.5 million years), expected in Hawaiian basalts if they contain core a core component. In order to evaluate the feasibility of this finding, it is necessary to constrain how much Pd and Ag would have partitioned into the core during planetary differentiation. This study used experimental techniques from the U study to address partitioning in this system. The experimental Ds for Pd and Ag from this study are in concert with observed mantle observations, eliminating the necessity of processes in excess of a magma ocean to explain them. Applicability this study's experiments to an early Earth magma ocean is limited because of the high trace element concentrations used and the sensitivity of DPd to Pd concentration. However, insight from this study has allowed alternative interpretation of previously published data putting them into concert with mantle observations as well. Furthermore, this study highlights problems in experimentally determining partition coefficients for Pd as well as other elements. Variations in experimental chemical and physical conditions may have large impact on the shape and extent of relevant phase volumes. This can alter the composition of coexisting phases thereby impacting the calculation of D. D in this context is no longer a simple ratio of two static phases. Instead, it is a complexly changing relationship sensitive to changes in chemical and physical conditions.

Constraining subduction zone processes through local, regional, and global chemical systematics

Turner, Stephen Judson Harvard University 2015 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Subduction zones recycle material from Earth's surface into the mantle, and are an important means of continent building. The subduction system serves as a stamp, imprinting the distinct chemical characteristics of our planet's geological reservoirs, and distinguishing it within the solar system. As such, the elemental exchanges mediated by this system are a long-standing focus of geochemical and geophysical research. Advances in geochemical techniques and improved geophysical models of subduction have illuminated the processes which give rise to arc volcanism. Great strides have been made in answering the question of what goes down, and what comes back up, though much remains unknown. Arc volcanoes provide a valuable window into the complex subduction environment, and so a comprehensive understanding of arc magma petrogenesis provides a means to resolve significant outstanding questions. The processes that regulate the compositions of erupted arc magmas are complicated, however. In order to use arc magmas as a tool for constraining elemental fluxes across large-scale geochemical reservoirs, we must trace the path of lavas sampled on Earth's surface back down through the lithosphere. Once we reach the asthenosphere, we require constraints on the conditions from which the magma was generated -- a mantle source, fluxed by some hydrous material originating from the subducting plate. Chapter 1 of this dissertation addresses the question of how magma ascent through the crust can vary on short timescales (∼50 years) at a single location, specifically at Bezymianny Volcano, in Kamchatka, Russia. This project was conducted following two field seasons at Bezymianny. Field experience provided an on-the-ground understanding of this volcano's unique magma system, and fostered multi-disciplinary interactions with geophysicists and seismologists that informed the interpretation of its geochemistry. Bezymianny often erupts multiple times per year. The sample set used in this study was collected by several different volcanologists over five decades, and provides unprecedented temporal resolution of sampling for this time period. Chapters 2 and 3 were motivated by Chapter 4, rather than the other way around. Chapter 4 is a regional investigation of chemical variability along the Chilean Southern Volcanic Zone (SVZ). The SVZ is a classic study area for igneous chemistry, in which the compositions of erupted magmas vary along and across the strike of the volcanic arc. Along with magma chemistry, multiple physical parameters that may influence the subduction system (or simply, "subduction parameters"), also vary along-strike. This ambiguity motivated a re-examination of the relationships between subduction parameters and global magma chemistry. In many ways this project builds upon the study of Plank and Langmuir (1988), but also utilizes the extensive literature database that has been developed in the interim. The new data enable assessment of not only major elemental variation, but also trace elements and isotopes. Chapter 2 presents the systematics of a global dataset, which includes several new observations of global correlations between trace elements and trace element ratios. In Chapter 2, this dataset is used to investigate whether the global trends might arise from intra-crustal processes. This possibility is supported by the correlations between chemical parameters and the thickness of the crust. The main crustal processes considered are high-pressure crystal fractionation and mixing between primary magmas and an enriched crustal component. High-pressure fractionation trends are not found to be more abundant at arcs with thick crust, however, and the composition of the hypothetical global contaminant is unlikely to exist in nature. The global magma variation is therefore most plausibly primary in nature, arising from processes in the slab or mantle, rather than the crust. Chapter 3 investigates whether variable slab fluxes or melting processes are responsible for the global correlations in magma chemistry. The correlations with crustal thickness, if not produced by processes within the crust itself, are suggestive of a melting process. The chemical parameters also correlate, however, with the slab "thermal parameter," implicating processes within the downgoing plate. In addition to the arc front chemical systematics, it is shown that rear-arc volcanic compositions, after filtration to minimize the effects of slab input, have strong correlations between Sr and Nd isotopes. Rear-arc Nd isotopes also correlate well with the Nd isotope values of the arc front. Finally, in Chapter 4, we apply this global modeling framework back to the problem of the SVZ. It is demonstrated that the systematics of the SVZ mimic those of the global system in a remarkable way. The correlations between elements within the global dataset are also present in the SVZ, and these trends overlap. An extensive dataset of rear arc SVZ samples is used to demonstrate control of Nd isotopes and other compositional features by variable mantle heterogeneity, rather than variable slab flux. (Abstract shortened by UMI.).

Hydrologic controls on nitrate-N removal in a riparian system

Angier, Jonathan University of Maryland College Park 2001 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Agricultural nitrate can have a negative environmental impact on surface waters, such as rivers that drain into the Chesapeake Bay. Riparian buffer strips are considered to provide natural remediation for groundwater nitrate, but this function is based on relatively simple models of riparian zone hydrology and stratigraphy. The purpose of this study was to assess the combined influences of hydrology and geochemistry on groundwater nitrate in a riparian zone. The study site, at the USDA-Beltsville Agricultural Research Center, is in the mid-Atlantic coastal plain of Maryland. The site contains a small 1<super> st</super>-order stream that is instrumented with five stations for monitoring stream flow and chemistry, and 170 nested piezometers (mostly in transects) for evaluating groundwater hydrology and geochemistry. The portion of the stream that shows the highest rate of flow increase per area contains discrete zones of enhanced groundwater discharge to the surface. These zones display high vertical hydraulic heads, which relate to the amount of groundwater discharged. One particular area of intense groundwater upwelling supplies approximately 3.5% of the total stream outflow, yet comprises only 0.006% of the riparian zone (or 0.001% of total catchment area). The upwelling zones also supply most of the nitrate to the surface. Dissolved oxygen concentrations are high in the underlying aquifer, and in the overlying soil where hydraulic heads are high. Areas where upwelling groundwater is absent display anaerobic conditions throughout the soil. Oxic conditions, rapid groundwater movement, and limited contact area inhibit nitrate removal in upwelling zones. Chloride, sulfate, and dinitrogen data confirm that the direction of groundwater flow in upwelling areas is vertical. Valley morphology, combined with subsurface stratigraphy and macroporosity, are largely responsible for deviation from more commonly assumed horizontal flow in the subsurface. The geomorphological and stratigraphic setting, where valley fill consists of fine-grained wetland soils over a more hydraulically-conductive aquifer, is typical for the mid-Atlantic coastal plain. Groundwater-fed headwater wetlands are also common in this region, so the results of this research may be applicable to a larger extent, and should be viewed in the context of the wider problem of surface water nitrate loading.