Geochemical variation among small eruptive centers in the central SVZ of the Andes: An evaluation of subduction, mantle and crustal influences

Subduction zone magmatism is an important and extensively studied topic in igneous geochemistry. Recent studies focus on from where arc magmas are generated, how subduction components (fluids or melts) are fluxed into the source of the magmas, and whether or how the subduction components affect partial melting processes beneath volcanic arcs at convergent boundaries. ^ At 39.5°S in the Central Southern Volcanic Zone of the Andes, Volcano Villarrica is surrounded by a suite of Small Eruptive Centers (SEC). The SECs are located mostly to the east and northeast of the stratovolcano and aligned along the Liquine-Ofqui Fault Zone, the major fracture system in this area. Former studies observed the geochemical patterns of the SECs differ distinctively from those of V. Villarrica and suggested there may be a relationship between the compositions of the volcanic units and their edifice sizes. This work is a comprehensive geochemical study on the SECs near V. Villarrica, using a variety of geochemical tracers and tools including major, trace and REE elements, Li-Be-B elements, Sr-Nd-Pb isotopes and short-lived isotopes such as U-series and 10Be. In this work, systematic differences between the elemental and isotopic compositions of the SECs and those of V. Villarrica are revealed and more importantly, modeled in terms of magmatic processes occurring at continental arc margins. Detailed modeling calculations in this work reconstruct chemical compositions of the primary magmas, source compositions, compositions and percentages of different subduction endmembers mixed into the source, degrees of partial melting and different time scales of the SECs and V. Villarrica, respectively. Geochemical characteristics and possible origins of the two special SECs—andesitic Llizan, with crustal signatures, and Rucapillan, to the northwest toward the trench, are also discussed in this work. ^

China's Relations with Brazil and Argentina and Implications for U.S. Security Concerns [Student's Paper Series]

This study on China’s relations with Brazil and Argentina, as well as its implications for U.S. concerns examines two main questions: Why China’s increasing influence on Brazil and Argentina may be considered a cause for U.S. security concerns? And if this is the case, how do China’s strategic alliances with the two countries has impacted U.S. leadership? In an effort to look at China’s influence from multidimensional angles and beyond China’s visible economic influence in these two countries, this paper argues that China’s interest in the Latin American region, with a focus on brazil and Argentina, responds to a more crafted, pragmatic and tailored vision with long-term strategic and political goals. The results of this study reveal that China – avoiding intra-regional competition through a strategic diversification of sectors – has been able to secure critical resources for its population as well as promote enduring alliances in the region that could represent a plausible cause of concern for U.S. interests. In this regard, China’s avoidance of a direct challenge to traditional partners’ influence has responded to the gaps left by a gradual, but steady lack of U.S. involvement.

Two Decades Out of the Whirlpool: Past (and Possible Future) United States Interventions in Latin America [Student's Paper Series]

This paper examines the history of U.S. interventions in Latin America and attempts to explain their frequency by highlighting two factors – besides security and economic interests – that have made American interventions in Latin America so common. First, immense differences in size and influence between the United States and the States of Latin America have made interventions appear to be a low risk solution to crises that threaten American interests in the region. Second, when U.S government concerns and aspirations for Latin America converge with the general fears and aspirations of American foreign policy, interventions become much more likely. Such a convergence pushes Latin American issues high up the U.S. foreign policy agenda because of the region’s proximity to the United States and the perception that costs of intervening are low. The leads proponents of intervention to begin asking questions like “if we cannot stop communism/revolutions/drug-trafficking in Latin America, where can we stop it?” This article traces how these factors influenced the decision to intervene in Latin America during the era of Dollar Diplomacy and during the Cold War. It concludes with three possible scenarios that could lead to a reemergence of an American interventionist policy in Latin America. It makes the argument that even though the United Sates has not intervened in Latin America during the twenty-two years, it is far from clear that American interventions in Latin America will be consigned to the past.

The Effect of Mobile Technology as an Active Student Response System on the Acquisition of U.S. History Content of Secondary Students with Specific Learning Disabilities

Students with specific learning disabilities (SLD) typically learn less history content than their peers without disabilities and show fewer learning gains. Even when they are provided with the same instructional strategies, many students with SLD struggle to grasp complex historical concepts and content area vocabulary. Many strategies involving technology have been used in the past to enhance learning for students with SLD in history classrooms. However, very few studies have explored the effectiveness of emerging mobile technology in K-12 history classrooms. This study investigated the effects of mobile devices (iPads) as an active student response (ASR) system on the acquisition of U.S. history content of middle school students with SLD. An alternating treatments single subject design was used to compare the effects of two interventions. There were two conditions and a series of pretest probesin this study. The conditions were: (a) direct instruction and studying from handwritten notes using the interactive notebook strategy and (b) direct instruction and studying using the Quizlet App on the iPad. There were three dependent variables in this study: (a) percent correct on tests, (b) rate of correct responses per minute, and (c) rate of errors per minute. A comparative analysis suggested that both interventions (studying from interactive notes and studying using Quizlet on the iPad) had varying degrees of effectiveness in increasing the learning gains of students with SLD. In most cases, both interventions were equally effective. During both interventions, all of the participants increased their percentage correct and increased their rate of correct responses. Most of the participants decreased their rate of errors. The results of this study suggest that teachers of students with SLD should consider a post lesson review in the form of mobile devices as an ASR system or studying from handwritten notes paired with existing evidence-based practices to facilitate students’ knowledge in U.S. history. Future research should focus on the use of other interactive applications on various mobile operating platforms, on other social studies subjects, and should explore various testing formats such as oral question-answer and multiple choice.

The effect of mobile technology as an active student response system on the acquisition of U.S. history content of secondary students with specific learning disabilities

Students with specific learning disabilities (SLD) typically learn less history content than their peers without disabilities and show fewer learning gains. Even when they are provided with the same instructional strategies, many students with SLD struggle to grasp complex historical concepts and content area vocabulary. Many strategies involving technology have been used in the past to enhance learning for students with SLD in history classrooms. However, very few studies have explored the effectiveness of emerging mobile technology in K-12 history classrooms. ^ This study investigated the effects of mobile devices (iPads) as an active student response (ASR) system on the acquisition of U.S. history content of middle school students with SLD. An alternating treatments single subject design was used to compare the effects of two interventions. There were two conditions and a series of pretest probesin this study. The conditions were: (a) direct instruction and studying from handwritten notes using the interactive notebook strategy and (b) direct instruction and studying using the Quizlet App on the iPad. There were three dependent variables in this study: (a) percent correct on tests, (b) rate of correct responses per minute, and (c) rate of errors per minute. ^ A comparative analysis suggested that both interventions (studying from interactive notes and studying using Quizlet on the iPad) had varying degrees of effectiveness in increasing the learning gains of students with SLD. In most cases, both interventions were equally effective. During both interventions, all of the participants increased their percentage correct and increased their rate of correct responses. Most of the participants decreased their rate of errors. ^ The results of this study suggest that teachers of students with SLD should consider a post lesson review in the form of mobile devices as an ASR system or studying from handwritten notes paired with existing evidence-based practices to facilitate students’ knowledge in U.S. history. Future research should focus on the use of other interactive applications on various mobile operating platforms, on other social studies subjects, and should explore various testing formats such as oral question-answer and multiple choice. ^