MAGNETIC FABRICS OF ASH-FLOW TUFFS: AN ANISOTROPY OF MAGNETIC SUSCEPTIBILITY AND ANISOTROPY OF REMANENCE EXAMINATION OF THE CA. 2.13-2.11 HUCKLEBERRY RIDGE TUFF, YELLOWSTONE PLATEAU VOLCANIC FIELD

The Yellowstone Plateau volcanic field, commonly associated with the term “super-eruption”, has been associated with three major, large-volume caldera forming events over the past ca. 2.1 Ma. Understanding the modern setting and recent evolution of this volcanic field, in particular its geophysical and geodynamic expression, has been the nearly career-long endeavor of this year’s Woollard Award recipient. The three members of the ca. 2.13 to 2.11 Ma Huckleberry Ridge Tuff constitute the largest and most widespread of these eruptions, at ~2,500 km³. The Huckleberry Ridge Tuff has been the subject of several paleomagnetic studies, including one involving our Woollard Award recipient, to investigate the magnitude of post ca. 2.1 Ma west side down tilting of the footwall and hanging wall of the Teton normal fault system. Anisotropy of magnetic susceptibility (AMS) and anisotropy of remanence data are being acquired from the three members of the Huckleberry Ridge Tuff in order to better understand the patterns of emplacement of these widespread pyroclastic deposits and important time stratigraphic markers. Sites in all three members of the tuff typically yield well-developed AMS fabrics, with an imbrication plane, normal to a typically well-grouped minimum principal susceptibility axis (k3), that often dips in the direction of the inferred caldera sources for the three members. The considerable variation in the magnetic properties of each member of the tuff, as a function of the degree of welding and subsequent devitrification/vapor phase alteration, offers opportunities for detailed comparisons between AMS and anisotropy of remanence (anhysteretic remanent and isothermal remanent magnetization, acquired at different field ) data. Comparative studies are being conducted on samples of tuff Member B from distal, outflow facies sites in Swan Valley, the northeast flank of the Snake Range, and the southern end of the Tetons.