Now showing items 11299-11318 of 20330

    • Machine Learning, Optimization, and Anti-Training with Sacrificial Data

      Rozenbilt, Jerzy W.; Head, Kenneth L.; Valenzuela, Michael Lawrence; Rozenbilt, Jerzy W.; Head, Kenneth L.; Lysecky, Roman L.; Marcellin, Michael W. (The University of Arizona., 2016)
      Traditionally the machine learning community has viewed the No Free Lunch (NFL) theorems for search and optimization as a limitation. I review, analyze, and unify the NFL theorem with the many frameworks to arrive at necessary conditions for improving black-box optimization, model selection, and machine learning in general. I review meta-learning literature to determine when and how meta-learning can benefit machine learning. We generalize meta-learning, in context of the NFL theorems, to arrive at a novel technique called Anti-Training with Sacrificial Data (ATSD). My technique applies at the meta level to arrive at domain specific algorithms and models. I also show how to generate sacrificial data. An extensive case study is presented along with simulated annealing results to demonstrate the efficacy of the ATSD method.
    • Machine Learning-based Author Identification for Social Media Forensics

      Hariri, Salim; Shao, Sicong; Ditzler, Gregory; Akoglu, Ali (The University of Arizona., 2021)
      Social media have gained extreme popularity due to the explosive growth of cyberinfrastructures, mobile devices, Internet technologies, and services. However, they also provide potential anonymity, which in turn harbors hacker forums, carding shops, underground marketplace, dark websites, and so on. As a result, social media have become the playground of cyber threat actors who conduct various malicious operations such as selling stolen cards, disseminating misinformation, propagating hacking tools, spreading malware samples, planning cyberattacks, and organizing trolling campaigns. Therefore, it is urgent to study effective methods that can identify the authors behind the digital text in order to enable forensic analysis, enhance security, and reduce social media misuse. In recent years, machine learning-based author identification has become a promising solution to identify the author of text. However, it is still an underexplored research field in social media forensics. This thesis investigates machine learning-based author identification subfields, including author attribution, author verification, author clustering, and their applications to social media forensics. Internet Relay Chat (IRC) has traditionally been used for legitimate purposes. Yet, cyber threat actors extensively abuse it to generate a wide range of illegal content and perform malicious behaviors due to its potential anonymity and popularity among hackers. Unfortunately, author identification research in IRC remains a largely underexplored area. In this thesis, we first present our automatic social media monitoring and threat detection method that can effectively collect data for author identification tasks and then present a novel author attribution framework and its application to IRC. It consists of a holistic feature extraction model and an ensemble of ensembles for multi-class classification. We then bring a novel author verification framework under the principle of one-class learning to effectively verify the authorship of IRC texts. This research also examines author clustering for social media forensics. Most author identification studies focus on author attribution and author verification, while the author clustering research is largely ignored. Meanwhile, cyber threat actors widely make use of Twitter to create alias accounts for numerous malicious purposes, especially in trolling campaigns and misinformation propagations. Thus, developing an effective author clustering method for Twitter is urgent. In this research, we developed a novel unsupervised learning-based author clustering framework and its application to Twitter. We delivered the capability to identify the group among many Twitter aliases even without prior knowledge of the number of authors. We address the effectiveness and demonstrate the feasibility of our author identification frameworks through diverse experiments. Our author attribution approach can achieve more than 90% attribution accuracy given hundreds of candidates in the author attribution experiments. In the author verification experiments, over 70% of author cases, our author verification approach can achieve more than 99% AUC. In the author clustering experiments given more than one hundred unlabeled text samples, our author clustering approach attains an average accuracy of 81.93% when knowing the number of authors and an average accuracy of 74.78% without prior knowledge of the number of authors.
    • Machine Reading for Scientific Discovery

      Fong, Sandiway; Surdeanu, Mihai; Hahn-Powell, Gus; Fong, Sandiway; Surdeanu, Mihai; Morrison, Clayton (The University of Arizona., 2018)
      The aim of this work is to accelerate scientific discovery by advancing machine reading approaches designed to extract claims and assertions made in the literature, assemble these statements into cohesive models, and generate novel hypotheses that synthesize findings from isolated research communities. Over 1 million new publications are added to the biomedical literature each year. This poses a serious challenge to researchers needing to understand the state of the field. It is effectively impossible for an individual to summarize the larger body of work or even remain abreast of research findings directly relevant to a subtopic. As the boundaries between disciplines continue to blur, the question of what to read grows more complicated. Researchers must inevitably turn to machine reading techniques to summarize findings, detect contradictions, and illuminate the inner workings of complex systems. Machine reading is a research program in artificial intelligence centered on teaching computers to read and comprehend natural language text. Through large-scale machine reading of the scientific literature, we can greatly advance our understanding of the natural world. Despite remarkable progress (Gunning et al., 2010; Berant et al., 2014; Cohen, 2015a), current machine reading systems face two major obstacles which impede wider adoption: <i>Assembly</i> The majority of machine reading systems extract disconnected findings from the literature (Berant et al., 2014). In areas of study such as biology, which involve large mechanistic systems with many interdependent components, it is essential that the insights scattered across the literature be contextualized and carefully integrated. The single greatest challenge facing machine reading is in learning to piece together this intricate puzzle to form coherent models and mitigate information overload. In this work, I will demonstrate how disparate biomolecular statements mined from text can be causally ordered into chains of reactions (Hahn-Powell et al., 2016b) that extend our understanding of mechanistic biology. Then, moving beyond a single domain, we will see how machine-read fragments (influence relations) drawn from a multitude of disciplines can be assembled into models of children’s heath. <i>Hypothesis generation and “undiscovered public knowledge”</i> (Swanson, 1986a) Without a notion of research communities and their interaction, machine reading systems struggle to identify knowledge gaps and key ideas capable of bridging disciplines and fostering the kind of collaboration that accelerates scientific progress. With this aim in mind, I introduce a procedure for detecting research communities using a large citation network and derive semantic representations that encode a measure of the flow of information between these groups. Finally, I leverage these representations to uncover influence relation pathways which connect otherwise isolated communities.
    • Macro- and Micro-Scale Geoarchaeology of Ucagizli Caves I and II, Hatay, Turkey

      Stiner, Mary C.; Holliday, Vance T.; Mentzer, Susan Marie; Goldberg, Paul; Kuhn, Steven L.; Quade, Jay; Stiner, Mary C.; Holliday, Vance T. (The University of Arizona., 2011)
      This project documents the multi-scalar formation processes of two northern Levantine coastal Paleolithic cave sites using field geology, archaeological micromorphology and sediment geochemistry. Located in within several hundred meters of each other, the sequences from Üçağızlı I and II present an opportunity to compare late Middle and early Upper Paleolithic hominin adaptations to a similar coastal environment. The morphologies of the sites and the suite of coastal geomorphic features available to the area's Paleolithic occupants were impacted by fluctuations in sea level as well as tectonic events. The sites share similar formation histories that include active karstic processes, marine inundation, occupation by hominins, partial collapse of the cave vaults, and erosion of the uppermost archaeological deposits. Mousterian occupation of Üçağızlı II began after the formation of a series of stable sea level features that date to Marine Isotope Stage (MIS) 5a. Hominin utilization of the highly eroded portions of the cave continued at least through the middle of MIS 3, although the cultural attribution of the youngest materials is presently unknown. Üçağızlı I contains a sequence of Initial Upper Paleolithic, Ahmarian and Epipaleolithic materials dating to MIS 3 and 2. Micromorphology of the archaeological sediments reveals strong anthropogenic contributions to the infilling of both caves, in particular the deposition of abundant, well-preserved wood ashes. In both sequences, post-depositional insect bioturbation has negatively impacted the combustion features, resulting in alteration of the original sedimentary fabrics and loss of information regarding hominin activities such as sweeping, rake-out and dumping of ashes. In Üçağızlı II, the dominant mode of sedimentation is anthropogenic; a series of intact and cemented combustion features located beneath the highest point of the cave ceiling is surrounded by sediment exhibiting evidence of both rodent and insect bioturbation. In Üçağızlı I, phases of human activity alternated with periods of natural sedimentation. Combustion features in the site include isolated hearths, stacks of hearths, rake-out or sweeping deposits, ash dumps, and mixed burned materials that have been impacted by colluvial reworking and bioturbation. In sum, the two sites contain similar types of anthropogenic sediments despite differing cultural affiliation.
    • MACRO-ECONOMIC DECISION-MAKING: THE 1964 AND 1968 REVENUE ACTS

      Simpson, Phillip Michael, 1943- (The University of Arizona., 1971)
    • Macroecology: Going from patterns to processes, a theory and its test

      Rosenzweig, Michael L.; McGill, Brian James (The University of Arizona., 2003)
      This dissertation focuses on two patterns in macroecology. The first describes the distribution of abundances between species (SAD) within a single community. The second describes the structure of abundance across a species range (SAASR). The central result is that the SAASR, combined with some other assumptions, can be shown both theoretically and empirically to explain the SAD (as well as several other patterns such as the species area relationship or SPAR). Given the increased importance of the SAASR pattern, I then provide an extensive analysis of empirical data to test for the existence and exact nature of the SAASR as well as developing the first quantitative assessments of proposed mechanisms underlying the SAASR. I also clarify a current point of confusion about SADs: whether they are truly log left-skewed. I next present a philosophy of science paper on how best to test macroecological theories. Finally, I apply this approach to a well-known macroecological theory that is generally considered to be strongly tested and show that the existing tests are, in fact, weak.
    • MACROMOLECULAR SYNTHESIS IN LEUCOSPORIDIUM STOKESII DURING HEAT INJURY AND RECOVERY

      Spencer, John W. (John William), 1940- (The University of Arizona., 1972)
    • Macrophage response to polymeric vascular grafts

      Williams, Stuart K.; Salzmann, Dennis Lee, 1970- (The University of Arizona., 1997)
      The use of materials for replacement or repair of biological tissue and organs has been attempted for thousands of years. Regardless of material used or site of implantation all biomedical materials elicit a foreign body response by the host characterized by the presence of macrophages and foreign body giant cells with the polymer for the duration of the implant. This inflammatory response is believed to be responsible for the lack of biocompatibility of implanted materials. Furthermore, each type of biomedical device suffers from specific problems that may lead to the ultimate failure of the implant. Synthetic polymeric vascular grafts fail primarily due to the inherent thrombogenecity of the material and anastomotic neointimal thickening. In an attempt to create a non-thrombogenic lining on the blood contacting surface of vascular implants, the promotion of an endothelial lining on the luminal surface of vascular grafts has been investigated. This can be accomplished by both artificial and natural mechanisms. Regardless, it is believed that the inflammatory response elicited by the implant influences the angiogenic mechanisms and neointimal thickening associated with the implant. The relationship between inflammation and angiogenesis associated with biomedical implants remains to be delineated. Studies in this dissertation attempt to determine this relationship by examining the inflammatory response and inflammatory cytokines released by cells associated with polymeric implants and how these bioactive molecules influence the angiogenic response. Furthermore, an advancing technology in vascular repair, endovascular grafts, was tested in two vascular models to assess the general healing characteristics, inflammatory response and the formation of blood vessels associated with the device. The results from these studies suggest that the inflammatory response plays a fundamental role in the formation of blood vessels around polymeric implants and neointimal thickening on the luminal surface of vascular implants. From these experiments a greater understanding of the healing response associated with vascular grafts has resulted.
    • Macroscopic lattice dynamics.

      Miller, Peter David. (The University of Arizona., 1994)
      The modulational behavior of exact oscillatory solutions to a family of non-linear systems of coupled differential equations is studied both numerically and analytically. The family of lattice systems investigated has applications ranging from theoretical biology to numerical methods. The goal is to obtain a description, given by a system of partial differential equations valid on long spatial and temporal scales, of the microscopic vibrations in the lattice. A theory of simple harmonic plane wave modulation is given for the entire family of microscopic systems, and the structure of the corresponding modulation equations is analyzed; particular utility is gained by casting the modulation equations in Riemann invariant form. Although difficulties are encountered in extending this theory to more complicated oscillatory modes in general, the special case of the integrable Ablowitz-Ladik system allows the program of describing more complicated modulated oscillations to be carried out virtually to completion. An infinite hierarchy of multiphase wavetrain solutions to these equations is obtained exactly using methods of algebraic geometry, and the complete set of equations describing the modulational behavior of each kind of multiphase wavetrain is written down using the same machinery. The distinguishing features of modulation theory in the presence of resonance are described, and an unusual set of modulation equations is derived in this case. The results of this dissertation can be interpreted in the context of nonequilibrium thermodynamics of regular oscillations in nonlinear lattices; instabilities in the modulation equations correspond to predictable phase transitions.
    • Mad Mark Twain: Rage and Rhetoric in the Life and Works of Samuel L. Clemens

      Jenkins, Jennifer L.; Fredericks, Sarah Elizabeth; Hurh, Paul; Abraham, Matthew (The University of Arizona., 2020)
      Interweaving literary biography, rhetoric, and emotion studies, this dissertation argues that anger was fundamental to Mark Twain’s social and literary epistemologies. Although scholars have largely dismissed his temper as anecdotal, Twain considered anger vital to maintaining social order and strategically employed angry rhetoric in his personal and professional writings. Neither irrational nor haphazard, Twain’s vitriol demonstrates remarkable rhetorical awareness and literary artistry. Whether haranguing his publishers about dwindling profits or eviscerating his private secretary Isabel Lyon in the little-known Ashcroft-Lyon Manuscript, Twain weaponized his emotions utilizing classical Aristotelian theories of persuasion. Moreover, many defining literary tropes of Twain’s most celebrated works originated in these angry texts, further cementing their importance to his literary development. Through close reading of his newspaper articles, letters, and autobiographical texts, this study traces evolving rhetorical patterns in Twain’s vituperation and demonstrates how his anger script impacted his participation in nineteenth-century literary culture.
    • MADAME BOVARY: THE DIALECTICS OF COLOR AND LIGHT

      Knapp, Judith Poole (The University of Arizona., 1980)
      Color and light, consistent with most visual phenomena in Madame Bovary, are more than mere descriptive tools: they actually serve as vehicles for Flaubert's characteristic use of symbolism. When taken cumulatively throughout the novel, the meanings ascribed to certain color and lighting effects often symbolize specific situations or a character's psychology, while at the same time reflecting a particular point of view. This dissertation initially examines the questions of point of view, major themes and Emma's psychology. Though most of the novel is recounted by an omniscient third-person narrator, he frequently takes a back seat so that Emma's point of view, for one, becomes the dominant manner of presentation. By shifting from one point of view to another, the narrator presents us with much conflicting symbolism--are we witnessing a scene and its color and light through Emma's dreamy gaze or perhaps in a more objective light shed by the narrator? An additional source of conflict is to be found in Emma's psychology and the major themes of Madame Bovary, as they both center around the heroine's inability to distinguish dreams from reality, with reality eventually gaining the upper hand and crushing Emma's dream world. Color and light symbolism naturally mirror all of these conflicts, with positive symbols often overshadowed by negative ones. There are three basic types of illumination present in the novel--(1) dim light reflecting Emma's romantic nature; (2) harsh, revealing brightness which, in the present, sheds light on an all-too pervasive reality; and (3) a lack of illumination emphasizing Emma's depression and leading ultimately to the utter darkness of death. Seven individual colors are explored for their symbolic aspects: blue, white, yellow, black, red, pale, and green. Blue symbolizes Emma's dreams and aspirations, her desire to attain an always nebulous higher state of being, which of course she will never reach. White can at times be interpreted along classical lines as representing innocence, naivete, and potential, or conversely emptiness and ennui, as in the case of this same potential remaining unfulfilled. Yellow signifies reality which is always ready to engulf Emma and her dreams and is seen as yellowing the whiteness of her potential. Black takes on several symbolic connotations, usually dependent upon the point of view of the person lending it symbolic value. It can be seen as a reflection of the Church, of mystery, or, for Emma, of the perfect romantic hero who must dress in black. As the narrator is aware, however, and communicates to the reader, all meanings of black in the novel merely culminate in its traditional connotation, that of death, in this case, Emma's of course. Red is another shade which can be divided into positive and negative aspects, with the positive signifying sensuality, voluptuousness, and by extension a certain erotic vision of love. On the negative side, we find many characteristics of red that Emma herself would consider disagreeable: a peasant origin, outlook or attitude, and a lack of sophistication sometimes coupled with crudeness or insensitivity. One or more of three basic meanings can be ascribed to pale in any given context; it can represent a dull uninteresting existence, a romantic ideal--for Emma--, or merely a pallor caused by illness or indisposition. Green, the final hue treated, is a secondary color on the artist's palette combining the blue of dreams and the yellow of reality, thus crating a feeling of malediction for Emma and a fatal mixture, since one cannot survive in the face of the other. In the end, Emma is forced to recognize the reality which had been so clearly illuminated throughout the novel by the narrator and, unable to face the light, she ironically turns instead to the total darkness of death.
    • Made in Mexico: Souvenirs, artisans, shoppers and the meanings of other "border-type-things"

      Parezo, Nancy J.; Alvarez, Maribel (The University of Arizona., 2003)
      In spite of their ubiquitous presence, the artisans who make serialized souvenirs for the tourist markets in the US-Mexico border and the people who buy these objects are invisible to the academic communities on both sides of the national divide. Simultaneously ignored by the Mexican folk arts canon; borderlands studies; Mexican historiography; and the anthropological literature interested in signs and symbolism, these allegedly low-grade and marginalized objects and people are nonetheless integral to the development of capitalism in Mexico. This work is an ethnography of the system of objects known as "Mexican curios" from the point of view of those who make the objects and those who consume them. It focuses specifically on one family of artisans that makes plaster figurines in Nogales, Sonora and shoppers at a Flea Market in Tucson, Arizona. The ethnography seeks to answer the questions: "Why is the most visible invisible?" and "How does invisibility become socially-installed and contested?" The study argues that instead of considering Mexican curios as the degenerate rear-guard to standards of good taste, or, as affronts to state-sanctioned ideas about folk art, these objects and the meanings attributed to them by makers and consumers must be read "in reverse." That is, as subtexts of fragmented projects of nationalism and social distinction. Curios distort by negation and playful inter-cultural negotiations dominant intellectual ideas about national patrimony and "worthiness." Plaster curio artisans and shoppers invent their own narratives to counter perceptions about their value as human beings and citizens. They appropriate, exppropriate, transform, and invent discourses about aesthetics, work, class, gender, and historical memory to invest meaning into their practices and their identities. The study stresses the importance of vernacular social histories as a mean through which subordinated people can regain a sense of empowerment when they interact with structures of power over which they have no control. In addition, the ethnography attempts to open a dialogue about the limits and the opportunities afforded by the disciplines of Folklore and Anthropology when they are wielded by research participants for their own goals.
    • Madera 1965: Obsessive Simplicity, the Agrarian Dream, and Che

      Beezley, William H.; Henson, Elizabeth; Womack, John R., Jr.; Gosner, Kevin; Lanza, Fabio; Beezley, William H. (The University of Arizona., 2015)
      On September 23, 1965, a small group of campesinos, teachers, and students attacked the army base in Madera, Chihuahua. In Mexico, this attack is widely considered to be the first of the socialist armed movements of the late 1960s and‘70s, inspiring the 23rd of September League and others. Nearly all the existing literature focuses on the group’s turn to armed struggle - but is this what we should remember them for? The attack was preceded by five years of public mobilizations in support of the agrarian struggle and broader demands, involving vast numbers throughout the state, in a movement that transcended political parties and engaged in direct action. It was this broad social movement that nourished and gave birth to the armed movement; it was as innovative as Arturo Gámiz’s application of Che’s Guerra de Guerrillas to the sierra. I further argue that the armed struggle itself, which developed in the remote backlands, derived as much from a long tradition of armed self-defense endemic to the region as it did to the Cuban example. I also look at the participation of women, both voluntary and involuntary, in these events and the uses to which the assault on the base has been put in recent times.
    • Madrid como Espacio de Narrativa Cinematográfica

      Compitello, Malcolm A.; Pereira Jimenez, Maria de los Angeles; Nantell, Judith; da Costa Bezerra, Katia (The University of Arizona., 2018)
      Madrid, es la imagen icónica del cine español. La ciudad, como figuración emblemática, se va construyendo a partir de sus múltiples representaciones cinematográficas. Las circunstancias socioculturales, políticas y los cambios estéticos que se advierten en el cine español en las décadas del 80 y 90 determinan otra forma de apropiación de la ciudad, haciéndola trascender de espacio real a espacio narrativo. Esta tesis quiere demostrar la incorporación del espacio urbano como parte integrante de la imagen cinematográfica y elemento esencial de la narración fílmica en activa interacción con el contexto sociocultural de la película; fundamentos estos que sitúan al espacio citadino como una categoría estética y un componente más del lenguaje cinematográfico. PALABRAS CLAVE: espacio urbano, lenguaje cinematográfico, espacio-tiempo-contexto.
    • Madrid Modernista: Espacios Urbanos Madrilenos en la Literatura Bohemia del Modernismo Espanol

      Compitello, Malcolm A.; Vizoso, Pedro Jose; Compitello, Malcolm A.; Gilabert, Joan; Nantell, Judith (The University of Arizona., 2010)
      This study offers an analysis of the interaction between urban spaces and bohemian literature in Madrid around 1900. I argue that bohemianism and bohemian literature are actually part of a very well structured cultural discourse--a discourse of social resistance--and must be studied as such. At the same time, the obvious urban nature of this phenomenon is a deciding aspect of it. In order to know how the bohemian discourse evolved in Madrid from 1850s to 1920s--from Realism to Modernismo--we have to study the core and reciprocal relationship between bohemianism and the city. This issue has not yet been explored within Hispanism, in spite of the fact that it provides a very useful perspective for considering the period as a synthesis of intellectual and artistic matters.In my dissertation I engage the essential aspects of bohemianism in the turn of the twentieth century Spanish literature. I focus on the characterization and use of space in the bohemian discourse of Peninsular Modernismo. My starting point is the description and characterization of such a discourse as it has been constructed, analyzing how it takes form in a variety of different kind of texts. I study the construction and evolution of its "cartographic imaginary" (David Harvey), an image of the city that bohemian literature uses to resist the bourgeois order imposed on Madrid's urban spaces and the capitalistic process that supports it. I argue that bohemianism was taken by the peninsular version of Hispanic Modernismo as its central aesthetic discourse. Consequently, and because of the subaltern and marginal nature of it, Modernismo could never position itself at the central stage of the 1900s Spanish culture.
    • Magmatic and hydrothermal evolution of the Cripple Creek gold deposit, Colorado, and comparisons with regional and global magmatic-hydrothermal systems associated with alkaline magmatism

      Barton, Mark D.; Jensen, Eric Paul (The University of Arizona., 2003)
      The Cripple Creek district, Colorado is renowned for its epithermal gold telluride veins which have produced over 21 million ounces of gold from an intensely altered alkaline diatreme complex (total production + economic resources of >900 tons Au, geologic resource >>1000 tons). Gold mineralization principally occurs as telluride minerals hosted by swarms of narrow veins composed of quartz ± fluorite, carbonate, adularia, pyrite > barite/celestite and accessory base metal sulfides. Mineralized hydrothermal breccias are also found in the district, along with low-grade, bulk tonnage resources that are targets of current mining activities. Newly recognized is a complex history of hydrothermal alteration and magmatism that led up to, and continued past the development of gold mineralization. These include the development of large volumes of low-temperature, alkali feldspar-rich styles of alteration, and more restricted volumes of high temperature, pyroxene and biotite-rich types. Gold mineralization is associated with voluminous K-feldspar + pyrite ± carbonate alteration that largely postdates igneous activity, and these are widely developed in the upper ∼1000 m of the volcanic complex. These follow a complex magmatic history characterized by at least three cycles of recharge. Although voluminous sulfate (anhydrite) and sulfide-rich styles of mineralization were also developed in the latest stages of hydrothermal activity, a remarkable aspect of Cripple Creek is the distinct underdevelopment of acid styles of alteration; feldspar and carbonate-rich styles of alteration predominate at all levels of exposure. The link between alkaline magmatism and gold deposits has been long recognized, but relatively recent discoveries of large, high grade deposits (Ladolam, Philippines, Porgera, Papua New Guinea), along with continued production from districts like Cripple Creek, encourages continued exploration. Salient characteristics shared by these deposits include telluride-rich mineralization accompanied by extensive carbonation, and voluminous K-metasomatism. Likewise, hydrolytic (acid) alteration tends to be poorly developed in many alkaline systems. This has important environmental implications, as the high acid buffering potential makes these deposits environmentally favorable to mine. The potential in alkaline systems for large and high grade deposits, coupled with the common lack of recognition of their distinctive styles of alteration and mineralization, makes these a compelling exploration target.
    • The Magmatic and Hydrothermal Evolution of the Ertsberg Intrusion in the Gunung Bijih (Ertsberg) Mining District, West Papua, Indonesia

      Titley, Spencer; Gibbins, Stacie Lynn; Titley, Spencer; Titley, Spencer; Barton, Mark D.; Seedorff, Eric; Patchett, Jonathon; Ducea, Mihai (The University of Arizona., 2006)
      The Ertsberg Intrusion (EI) is located approximately 1.5 km southeast of the Grasberg super-porphyry Cu-Au deposit (GIC), in the Gunung Bijih (Ertsberg) Mining District, West Papua, Indonesia. Intrusion- and carbonate-hosted mineralization is associated with the 3.28-2.97±0.54 Ma multi-phase intrusive complex. The orientation of the intrusion-hosted mineralized zone is parallel to the direction of porphyry dike emplacement in the intrusive complex and to regional structures. Potassic, phyllic, propylitic and endoskarn alteration types are recognized in the EI, distributed over 7 vein types. Three vein stages initiate pre-porphyry dike emplacement, and mineralization occurs pre- and post-dike emplacement. Cu-Au mineralization is associated with pre-dike biotite-bornite-anhydrite veinlets (Stage III), and post-dike quartz-anhydrite-bornite+chalcopyrite//green sericite veins (Stage V), and quartz-anhydrite-chalcopyrite-pyrite//white sericite veins (Stage VI). Sulfides associated with each alteration type in the EI have d³⁴S values that range between -3.0 to 3.6‰. Sulfate d³⁴S between alteration types are variable: potassic (9.6- 11.1‰) and hydrolytic (10.2-16.6 ‰). The bulk isotopic sulfur (d³⁴S(SS)) composition for fluid in equilibrium Stage III veins is 7.5‰, which is higher than would expected for an oxidized calc-alkaline fluid, thus I invoke the addition of heavy sulfur from the sedimentary anhydrite nodules in adjacent carbonate host rocks. There is an overall decrease in bulk isotopic sulfur (d³⁴S(SS)) composition for hydrothermal fluid throughout the span of hydrothermal activity. A degassing mafic magma chamber at depth, and/or the leaching of previously deposited sulfides are likely responsible for this decrease. Sulfide-sulfate equilibrium temperatures for potassic alteration in the EI average 574°C, approximately 125°C cooler than sulfide-sulfate equilibrium temperatures in the GIC. Calculated oxygen isotopic compositions for water in equilibrium with anhydrite from early potassic veins in both the Ertsberg Stockwork Zone and GIC suggest this component was derived from a non-magmatic source; the sedimentary anhydrite nodules are a probable source. The calculated oxygen and hydrogen isotopic compositions for water in equilibrium sericite from intermediate veins in the ESZ and GIC show the fluid was derived from a magmatic water and/or magmatic vapor; however, the water responsible for late hydrolytic alteration in both intrusive centers provides evidence for mixing of magmatic water (vapor) with meteoric water. Mass balance calculations using the EI volume estimate, and the known mineralization associated with the EI show that the EI has an insufficient volume of H₂O to account for the known volume of hydrothermal alteration and mineralization. Coupled with sulfur, oxygen and hydrogen isotope data, and Re-Os isotope source data, this suggests additional input of hydrothermal fluids from deeper magmatic and sedimentary sources, with moderate addition of meteoric water into the hydrothermal system during Stage VI vein formation.
    • Magmatic and structural controls on mineralization in the Paleocene magmatic arc between 22°40' and 23°45' south latitude, Antofagasta, II region, Chile

      Guilbert, John; Williams, William Conard; Guilbert, John; Titley, S. R.; Damon, Paul E.; Ruiz, Joaquin (The University of Arizona., 1992)
      Geochemical and structural data from the Paleocene magmatic arc in a part of northern Chile constrain magmatism and metallogenesis in the Sierra Gorda, Sierra del Buitre, Lomas Bayas, and San Crist6bal districts. The Paleocene magmas were primarily derived from the mantle which was enriched prior to and/or during ascent by crustal materials. The Nd and Sr isotopes have ranges of 1.06 to 3.34 and 0.703888 to 0.707142, respectively. La/Sm ratios increase and Eu/Eu* ratios decrease from the mafic to felsic phases but these ratios do not correlate with Si0₂ content within the districts. The subtle isotopic heterogeneity and lack of REE systematic behavior within the districts indicate that multiple sources and/or petrogenetic processes generated this rock suite. The geochemical data do not predict metal type among the districts; the spatial relationship, however, of a quartz-eye porphyry with gold mineralization implies consanguinity. Tne petrogenesis of the quartz-eye porphyry is distinct from that of the other Paleocene rocks. The investigated area is characterized by epithermal mineralization that is constrained to two discrete episodes: 1) 65-60 Ma when polymetallic veins, silver rich in the Sierra Gorda and Sierra del Buitre districts, and copper-rich veins in the Lomas Bayas district were emplaced during normal convergence, and 2) 60-55 Ma when shear veins, copper-rich in the Sierra Gorda district and gold-rich in the San Cristóbal district, formed during oblique convergence. Copper mineralization occurred in the Sierra Gorda district during the transition between these episodes. The structural geology of the Chilean continental crust preserves a record of plate interactions along a consuming margin and provides constraints for convergence angle of the oceanic plate. A comparison with other Paleocene-Eocene deposits in northern Chile and southern Peru as well as with Jurassic copper deposits to the west and Oligocene porphyry copper deposits to the east shows that the emplacement of large, magmatism-related ore deposits is principally controlled by change in plate motion. Optimum conditions occur when a change to oblique convergence allows the development of trench-linked strike-slip faults. The paucity of known large ore deposits in the investigated area is due to the lack of extensive margin-parallel strike-slip faults that did not develop because of short-lived oblique convergence as well as the relative magmatic inactivity during changes in plate motion.
    • Magmatic History and Crustal Genesis of South America: Constraints from U-Pb Ages and Hf Isotopes of Detrital Zircons in Modern Rivers

      Gehrels, George E.; Pepper, Martin Bailey; Reiners, Peter; Kapp, Paul; Zandt, George (The University of Arizona., 2014)
      South America provides an outstanding laboratory for studies of magmatism and crustal evolution because it contains older Archean-Paleoproterozoic cratons that amalgamated during Mesoproterozoic and Neoproterozoic supercontinent assembly, as well as a long history of Andean magmatism that records crustal growth and reworking in an accretionary orogen. We have attempted to reconstruct the growth and evolution of South America through U-Pb geochronology and Hf isotope analyses of detrital zircons from 59 samples of sand from modern rivers and shorelines. Results from 5,524 new U-Pb ages and 1,199 new Hf isotope determinations are reported. We have also integrated our data into a compilation of all previously published zircon geochronologic and Hf isotopic information, yielding a record that includes>42,000 ages and>1,600 Hf isotope analyses. These data yield five main conclusions: (1) South America has an age distribution that is similar to most other continents, presumably reflecting the supercontinent cycle, with maxima at 2.2-1.8 Ga, 1.6-0.9 Ga, 700-400 Ma, and 360-200 Ma; (2)<200 Ma magmatism along the western margin of South America has age maxima at 183 Ma (191-175 Ma), 151 Ma (159-143 Ma), 126 Ma (131-121 Ma), 109 Ma (114-105 Ma), 87 Ma (95-79 Ma), 62 Ma (71-53 Ma), 39 Ma (43-35 Ma), 19 Ma (23-15 Ma), and 6 Ma (10-2 Ma); (3) for the past 200 Ma, there appears to be a positive correlation between magmatism and the velocity of convergence between central South America and Pacific oceanic plates; (4) Hf isotopes record reworking of older crustal materials during most time periods, with incorporation of juvenile crustal materials at ~1.6-1.0 Ga, 500-400 Ma and ~200-100 Ma; and (5) the Hf isotopic signature of<200 Ma magmatism is apparently controlled by the generation of juvenile magmas during extensional tectonism and reworking of juvenile versus evolved crustal materials during crustal thickening and arc migration.
    • Magmatic intrusions and hydrothermal systems: Implications for the formation of Martian fluvial valleys.

      Gulick, Virginia Claire.; Baker, Victor R.; Strom, Robert G.; Evans, Daniel D.; Bull, William B. (The University of Arizona., 1993)
      This dissertation investigates the possible role of hydrothermally driven groundwater outflow in the formation of fluvial valleys on Mars. Although these landforms have often been cited as evidence for a past wanner climate and denser atmosphere, recent theoretical modeling precludes such climatic conditions on early Mars when most fluvial valleys formed. Because fluvial valleys continued to form throughout Mars' geological history and the most earth-like stream valleys on Mars formed well after the decline of the early putative earth-like climate, it may be unnecessary to invoke drastically different climatic conditions for the formation of the earliest stream valleys. The morphology of most Martian fluvial valleys indicates formation by ground-water sapping which is consistent with a subsurface origin. Additionally, many Martian fluvial valleys formed on volcanoes, impact craters, near fractures, or adjacent to terrains interpreted as igneous intrusions; all are possible locales of vigorous, geologically long-lived hydrothermal circulation. Comparison of Martian valley morphology to similar features on Earth constrains valley genesis scenarios. Volumes of measured Martian fluvial valleys range from 10¹⁰ to 10¹³ m³. Based on terrestrial analogs, total water volumes required to erode these valleys range from -10¹⁰ to 10¹⁵ m³. The clustered distribution of Martian valleys within a given terrain type, the sapping dominated morphology, and the general lack of associated runoff valleys all indicate the importance of localized ground-water outflow in the formation of these fluvial systems. An analytic model of a conductively cooling cylindrical intrusion is coupled with the U.S. Geological Survey's numerical ground-water computer code SUTRA to evaluate the magnitude of ground-water outflow expected from magmatically-driven hydrothermal systems on Mars. Results indicate that magmatic intrusions of several 10² km³ or larger can provide sufficient ground-water outflow over periods (several 10⁵ years) required to form Martian fluvial Valleys. Therefore, a vastly different climate on early Mars may not be necessary to explain the formation of the observed Valleys. Martian hydrothermal systems would have also produced long-lived sources of near-surface water; these localized regions may have provided oases for any microbial life that may have evolved on the planet.