Circular geomorphic features permissive to interpretation as conduits of mantle degassing
Gabelman, John W.
published: Jan 1, 1984
ArtNo. ESP136000203004, Price: 19.00 €
Circular geomorphic features, unless demonstrably surface- or strata-bound, may be surface expressions of near-vertical pipes or disks formed exogenetically by meteorite impact, or endogenetically by karst collapse, diapirism by low-gravity solids, dissolution-digestion by magmas or corrosive fluids, rapid pneumatolytic drilling by magmatic, organic, or mantle gases, or focused rock jointing by the above gases escaping more slowly. Whole-plug pipes defined by ring joint or fracture zones with interior plugs of little fractured or displaced country rock may be formed by slow gas escape, perhaps as a prelude to explosion. Synoptic satellite viewing of unprecedentedly large areas has engendered a flood of discoveries of "circles" too large for recognition at aircraft heights, commonly clustered along lineaments of deep tectonic significance. Many appear to be of the whole-plug variety, not attributable to conventional mechanisms. These may imply slow gas drilling on a grand, if not global, scale that in turn suggests mantle degassing as a possibly continuing phenomenon more prevalent than suspected. To investigate the degassing concept, example circles are being studied by multilevel repeated imagery, image enhancement, fracture analysis, radiometry, emanometry, magnetometry, gravimetry, petrography, and geochemistry. Thus far multilevel imaging illustrates a very wide size range of circles whose recognition depends on observation height. Tonal enhancement suggests geochemical distinction, commonly supported to some extent by soil/rock analysis. A suite of added elements suggestive of the mantle is being defined. Mantle gases would be unavoidably mixed with crustal fluids and gases, and perhaps stored in traps.