Geological Survey Bulletin Volume 1516

Geological Survey Bulletin Volume 1516

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. Excerpt: ...symbols and units. which the high occurs (fig. 24). Laboratory measurements on the five samples collected also tend to indicate that some of the metavolcanic rocks are significantly more magnetic than the quartz monzonite of Lee Vining Canyon (table 10). Depending on the size and shape of the magnetic mass, a minimum magnetization of about 5X10"4 emu/cm3 is required for a rock mass to cause even a small aeromagnetic anomaly, say, 507, at 1,000 ft (300 m) or more above ground. Rock units listed in table 10 with total magnetizations less than 5X10"4 emu/cm3--such as the Triassic granitic rocks, most of the metasedimentary rocks, and some of the metavolcanic rocks--are not magnetic enough to cause significant aeromagnetic anomalies, and they produce local variations of less than 1007 at ground level (fig. 25). Ground magnetic data were also obtained from M' southeast along the Sierran crest and Wilderness boundary toward the center of the aeromagnetic anomaly as far as M" (fig. 24). The total magnetic intensities at ground level show little variation along M'-M" ( 1007) and do not correlate with the rise of about 1507 at the 13,500-ft (4,100 m) level indicated by the aeromagnetic map. Thus, these ground data cast some doubt on the validity of the interpolation between flight lines. The aeromagnetic flightline that crosses the Wilderness area to the south of the interpolated center of the Mount Gibbs anomaly (H322, fig. 24) also rises from a background level of about-20Oy and reaches a maximum value of about+1007 nearly 1 mi km) east of the Sierran crest (fig. 24). The original analog data for this profile have been traced, the IGRF removed manually (Leaton and Barraclough, 1971), and the data registered to the topographic profile more

Product details

  • Paperback | 40 pages
  • 189 x 246 x 2mm | 91g
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236638743
  • 9781236638748