Post-magmatic fracturing, fluid flow, and vein mineralization in supra-subduction zones: a comparative study on vein calcites from the Troodos ophiolite and the Izu–Bonin forearc and rear arc

Based on the published data of pillow lava-hosted mineralized veins, this study compares post-magmatic fracturing, fluid flow, and secondary mineralization processes in the Troodos and Izu–Bonin supra-subduction zone (SSZ) and discusses the crucial factors for the development of distinct vein types. Thin section and cathodoluminescence petrography, Raman spectroscopy, fluid inclusion microthermometry, and trace element and isotope (87Sr/86Sr, δ18O, δ13C, Δ47) geochemistry indicate that most veins consist of calcite that precipitated from pristine to slightly modified seawater at temperatures  15 Myr after subduction initiation. Therefore, high-T mineralization (calcite, quartz, analcime) up to 230 °C is restricted to the Troodos SSZ

Geochemistry of Vein Calcites Hosted in the Troodos Pillow Lavas and Their Implications for the Timing and Physicochemical Environment of Fracturing, Fluid Circulation, and Vein Mineral Growth

Calcite veins hosted in pillow lavas of the Late Cretaceous Troodos suprasubduction zone ophiolite provide insights into the timing and physicochemical environment of postmagmatic fracturing and fluid circulation through oceanic crust. This study presents rare earth element and yttrium (REE+Y) concentrations, δ13C, δ18O, 87Sr/86Sr, and clumped isotopic (Δ47) compositions of vein calcites in order to investigate their fluid sources, formation temperatures, and precipitation ages. These geochemical data are combined with microtextural analyses. Intersections of 87Sr/86Sr ratios of vein calcites with the Sr isotope seawater curve suggest two distinct calcite veining phases. Major calcite veining within an interval of ~10 Myr after crust formation is characterized by microtextures that point to extensional fracturing related to crack and sealing, host rock brecciation, and advective fluid flow. These vein calcites show REE+Y characteristics, 87Sr/86Sr ratios, and clumped isotopic compositions indicative of precipitation from seawater at <50 °C. Extended fluid residence times intensified fluid‐rock interactions and lowered Y/Ho ratios of some blocky vein calcites, whereas crack and sealing resulted in pristine seawater signatures. Low 87Sr/86Sr ratios of localized high‐temperature blocky vein calcites point to the involvement of hydrothermal fluids. These calcites show Mn‐controlled oscillatory growth zonations that probably developed in a closed system out of equilibrium. Later calcite veining (<75 Ma) may have coincided with rotation and/or uplift of the Troodos ophiolite. Microtextures of these vein calcites indicate fluid diffusion and fracture‐independent crystallization pressure‐driven veining. Their variably modified seawater signatures resulted from diffusion‐related fluid interaction with hydrothermal sediments

Tensions in specifying computing curricula for K-12: towards a principled approach for objectives

In this article we examine key issues and tensions for developing and specifying Computing-related elements of curricula design, particularly the role of Computer Science in the curriculum. The article is based on a series of discussions and analyses of curriculum designacross various countries with different approaches and traditions of Computing in the curriculum

Postmagmatic Tectonic Evolution of the Outer Izu‐Bonin Forearc Revealed by Sediment Basin Structure and Vein Microstructure Analysis: Implications for a 15 Ma Hiatus Between Pacific Plate Subduction Initiation and Forearc Extension

International Ocean Discovery Program Expedition 352 recovered sedimentary‐volcaniclastic successions and extensional structures (faults and extensional veins) that allow the reconstruction of the Izu‐Bonin forearc tectonic evolution using a combination of shipboard core data, seismic reflection images, and calcite vein microstructure analysis. The oldest recorded biostratigraphic ages within fault‐bounded sedimentary basins (Late Eocene to Early Oligocene) imply a ~15 Ma hiatus between the formation of the igneous basement (52 to 50 Ma) and the onset of sedimentation. At the upslope sites (U1439 and U1442) extension led to the formation of asymmetric basins reflecting regional stretch of ~16–19% at strain rates of ~1.58 × 10−16 to 4.62 × 10−16 s−1. Downslope Site U1440 (closer to the trench) is characterized by a symmetric graben bounded by conjugate normal faults reflecting regional stretch of ~55% at strain rates of 4.40 × 10−16 to 1.43 × 10−15 s−1. Mean differential stresses are in the range of ~70–90 MPa. We infer that upper plate extension was triggered by incipient Pacific Plate rollback ~15 Ma after subduction initiation. Extension was accommodated by normal faulting with syntectonic sedimentation during Late Eocene to Early Oligocene times. Backarc extension was assisted by magmatism with related Shikoku and Parece‐Vela Basin spreading at ~25 Ma, so that parts of the arc and rear arc, and the West Philippine backarc Basin were dismembered from the forearc. This was followed by slow‐rift to postrift sedimentation during the transition from forearc to arc rifting to spreading within the Shikoku‐Parece‐Vela Basin system

Computer science in the school curriculum:Issues and challenges

This paper is based on analysis and discussion undertaken over several years by researchers, policymakers and practitioners from a range of countries which vary in their approaches to the curriculum for Computer Science. The discussions, undertaken predominantly within the International Federation of Information Processing (IFIP) and EDUsummIT communities were motivated by a need to examine the rationale, issues and challenges following some concerns across the globe about the position and nature of Computer Science in the school curriculum. We summarise our findings and focus specifically on challenges for the computer science education community in communicating, clarifying needs and promoting curriculum change in order to encourage Computer Science in the curriculum both theoretically and practically.No Full Tex