Quaternary Basin Evolution and Basaltic Volcanism of Crater Flat, Nevada, From Detailed Ground Magnetic Surveys of the Little Cones

Ground magnetic surveys of the Quaternary (0.77‐0.98 Ma) Little Cones and surrounding areas of southern Crater Flat, Nevada, reveal detailed images of buried basaltic lava flows not evident from surface exposures. Magnetic maps derived from these surveys show an apron of buried lava extending radially up to 300 m from the center of the two cones. Modeling of the anomalies indicates burial of the lava apron by up to 15 m of alluvium on top of approximately 10 m thick lava flows. From these results, we estimate a volume \u3e0.01 km3 of volcanic material for the Little Cones, comparable to the more completely exposed and similarly aged Red and Black Cones of central Crater Flat. Partial burial of the Little Cones by alluvium, in contrast to the exposed flows associated with Red and Black Cone, suggests differential subsidence of the southern part of the basin in the Quaternary. This pattern of subsidence is consistent with recent structural studies that show increased slip toward the south on major normal faults within and adjacent to the eastern and western margins of the basin. The depth of burial indicates sediment accumulation rates of approximately 0.03 mm/yr, similar to rates since the Miocene (Tortonian) based on the thickness of alluvium above 10.0 to 11.5 Ma basalts in the USW VH‐2 drill hole. These comparatively rapid sedimentation rates suggest that other Quaternary and Pliocene volcanic centers may be buried in southern Crater Flat without surface expression