Petrogenesis of the Niagara Icefalls Ultramafic-mafic Complex, Northern Victoria Land, Antarctica

• Main Author: Arias Austin Tanner
• Other Authors: 박정우, 아리아스 오스틴, 자연과학대학 지구환경과학부
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 서울대학교 대학원 2021
• Subjects: Antarctica; Niagara Icefalls; Northern Victoria Land; Boninite; Ultramafic; 550; Bowers; Victoria Land; Antarc*
• Online Access: https://hdl.handle.net/10371/176059; https://dcollection.snu.ac.kr/common/orgView/000000166061

학위논문 (석사) -- 서울대학교 대학원 : 자연과학대학 지구환경과학부, 2021. 2. 박정우. The Niagara Icefalls ultramafic-mafic complex is located within the Wilson terrane, near to the tectonic border between the Bowers and Wilson terranes, within Northern Victoria Land, Antarctica. Previous studies indicate this complex was emplaced ~514 Ma during a period of extension within Northern Victoria Land (Tribuzio et al., 2008; Rocchi et al., 2011) based on U-Pb zircon ages and its boninite-like geochemical affinity (Tribuzio et al., 2008). In this study, the petrogenetic model of the Niagara Icefalls ultramafic-mafic complex was revisited using whole-rock and mineral major and trace element data from a more extensive sample set, with new SHRIMP zircon U-Pb geochronology and LA-MC-ICP-MS Lu-Hf isotope data. The results reveal a more complex petrogenetic model than previously described. The mineral and whole-rock data exhibit boninitic characteristics with low whole-rock TiO2 content (<0.07%) and depleted HREEs and HFSEs while showing a relative enrichment in LREEs and fluid-mobile elements. However, differences in mineral chemistry between wehrlite and pegmatitic gabbronorite in the North and a sequence of dunite, orthopyroxenite, and gabbronorite in the South, suggest these rocks were produced from different parental melts. Furthermore, zircons from pegmatitic gabbronorite, which cross-cut wehrlites, have a mean age of 513.7 ± 2.6 Ma, whereas the mean age of zircons in gabbronorite associated with dunite and orthopyroxenite is 500.3 ± 4.2 Ma. These temporal and chemical disparities among similar boninite-like plutonic rocks suggest they were formed at two stages. These two stages are contemporary with metamorphic and igneous ages of ultramafic-mafic rocks found along the Lanterman suture, suggesting two subduction stages occurred with ~15 Ma gap in this region. The first stage ~514 Ma produced a sediment-influenced high-Ca boninite-like melt. Subsequently, ~500 Ma the second instance of boninitic magmatism occurred, producing a more-depleted ...