Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aps..aprb17080m&link_type=abstract
American Physical Society, April Meeting, Jointly Sponsored with the High Energy Astrophysics Division (HEAD) of the American As
Astronomy and Astrophysics
Astrophysics
Scientific paper
Our studies of numerous recrystallized fissures in 4 granite plutons of Wasatch Range, i.e., Mount T-W-M^1,6,7 Bonanza Pk.-Midway,^2 Little Cottonwood and Ferguson Canyon plutons, all of which formed magma chambers reaching Earth-atm. interface, estab. that they resulted from high thermal gradients and not passages of earthquake waves.^4 Magma chambers formed, solidified during Permo-Carboniferous Ice Age (roughly 1/3...1/4 billion yr ago), a time interval preceding extrusion of Rocky Mts., 10^8 yr ago, and while fluid, some belched lava flows^5 extending over its reservoir walls to run hundreds of m. We have shown how the magma melts, dilutes and replaces overlying metamorphic rock^7 to reach Earth's surface, so that a pluton containing large amounts of dross (Fe-ores, etc.) had a short fluid lifetime. We also described how offshoots from a long-running main fissure form acute angles with that fissure^3. Recryst. fissures, reaching depths of perhaps 100 m, had initial fractures near time of solidification of top portion of magma chamber, while still hot (<= 1600^oF), a time when max. stresses occur near granite surface due to high thermal gradients, owing to snow coverage, rain water, stream flow over granite surface, partial coverage by ocean, etc., during P-C ice age - when region of Wasatch Range existed at sea level, S. L. Valley being covered entirely by ocean water and region east of Wasatch Boul. rising gently above Pac. Ocean to elev. of possibly 500-1000 ft, say, at a distance of 10-15 mi to e, as implied by Chinese wall of limestone on Grandeur Pk, another in Neff's Canyon running e from n ridge of her 9200 ft saddle-summit, as well as a dozen other ancient calcified stream beds emptying into ocean to w, in S.L. Valley. This existed prior to regional uplift (of similar topog.) of over 4000 ft. Details of how earthquake waves form an epicenter from which propagate 2 stress fields in diam. opp. directions to open up, by a few m, surface granite to form a long running fissure of km lengths, are unknown, e.g., the one 12 ft wide, 50-100 m s of White Pine Lake.^1 Many exs. of thermofissures of 1-2 ft widths are believed known but one of ques. of 6 ft width at epicenter running both n, s for only 50-75 m to term. is located on w spur of Maybird Gulch, and is seen when viewing w from trail leading to 2 upper small lakes. (This abstract corrects that e-mailed and printed in Bul. A.P.S., 45(9), 192, 2000.) raggedright ^1K.L. McDonald, Bul. A.P.S., 32(4), 1124; ^2 35(9), 2132; ^3 33(3),485; ^4 33(9), 1982-3; ^5 36(9),2466; ^6 37(5),1256-7; ^7 38(1),740. Submitted by Dr. Keith L. McDonald, APS Member MC402346
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