Transmission Electron Microscopy of the Magnetic Mineralogy of the Mt. Stuart Batholith: An Attempt to Better Elucidate the Origin of a Controversial Magnetization <p> HR: <span class="hr"> 0830h<br></span> AN: <span class="an"> GP31C-0761 <a href="../absbook/fm03-GP31C.pdf">[PDF]</a><br></span> TI: <span class="ti"> Transmission Electron Microscopy of the Magnetic Mineralogy of the Mt. Stuart Batholith: An Attempt to Better Elucidate the Origin of a Controversial Magnetization <br></span> AU: <span class="au"> * Geissman, J W<br></span> EM: <span class="em"> jgeiss@unm.edu<br></span> AF: <span class="af"> Department of Earth and Planetary Sciences, Northrop Hall, University of New Mexico, Albuquerque, NM 87131 United States<br></span> AU: <span class="au"> Brearley, A J<br></span> EM: <span class="em"> brearley@unm.edu<br></span> AF: <span class="af"> Department of Earth and Planetary Sciences, Northrop Hall, University of New Mexico, Albuquerque, NM 87131 United States<br></span> AU: <span class="au"> Housen, B A<br></span> EM: <span class="em"> bernieh@cc.wwu.edu<br></span> AF: <span class="af"> Geology Department, Western Washington University, Bellingham, WA 98225 United States<br></span> AB: <span class="ab"> The mid-Cretaceous Mt. Stuart batholith, north Cascades of Washington, has been the focus of numerous paleomagnetic studies aimed at understanding the tectonic history of the pluton in the context of potential large-magnitude translation of part of the western borderland of North America. These studies have partly demonstrated the complexity of the magnetic mineralogy of the pluton and, in particular, the spatial distribution of different principal magnetization carriers. For example, pyrrhotite has been suggested as an important carrier of the remanence in the batholith (in the northern part of the pluton, a reverse polarity magnetization may be carried by pyrrhotite, implying magnetization considerably after emplacement). A more recent study reaffirms other early investigations that suggested that the remanence in much of the batholith is carried by single-domain magnetite and is of normal polarity, which is consistent with high temperature cooling of the intrusion at ca. 91 Ma. To better understand the carriers of the magnetization(s) characteristic of the pluton, we have inspected representative samples (from numerous sites), using transmission electron microscopy (JEOL 2010, 200 kV TEM with Oxford ISIS EDS). To date our work has concentrated on identifying and characterizing fine, sub-micron particles of magnetite in feldspars, principally plagioclase, in mineralogically fresh samples from the pluton. The paragenesis of pyrrhotite in the batholith, if indeed present, and the possibility that it is of secondary, low temperature origin, remains to be investigated. <br></span> DE: <span class="de"> 1519 Magnetic mineralogy and petrology<br></span> DE: <span class="de"> 1525 Paleomagnetism applied to tectonics (regional, global)<br></span> DE: <span class="de"> 3625 Descriptive mineralogy<br></span> SC: <span class="sc"> Geomagnetism and Paleomagnetism [GP]<br></span> MN: <span class="mn"> 2003 Fall Meeting<br></span></p></body></html>