ANALYSIS OF GRAVITY SLIDING AND OROGENIC TRANSLATION

GRAVITY SLIDING, MAJOR THRUSTING, AND THE DISPLACEMENT OF LARGE CRUSTAL PLATES ARE ACCOMPLISHED BECAUSE STRATA WITH THE LOWEST VISCOSITY IN A ROCK SEQUENCE READILY DEFORM BY SIMPLE (RECTILINEAR) SHEAR FLOW WHEN SUBJECTED TO LOADING. THESE DEFORMING STRATA ARE CALLED DECOLLEMENT ZONES. STRATA ABOVE THESE ZONES ARE TRANSPORTED WITHOUT BEING DEFORMED, PROVIDED THEIR VISCOSITY IS ONE OR MORE ORDER OF MAGNITUDES LARGER THAN THAT OF THE DECOLLEMENT ZONE. EXISTING THEORIES ARE REVIEWED ON THE MECHANICS OF GRAVITY SLIDING AND OROGENIC TRANSLATION. THE FOLLOWING ASSUMPTIONS ARE MADE IN THE ANALYSIS: (1) ROCK CREEP IS THE PREDOMINANT MECHANICAL PROCESS, (2) THIS CREEP IS ACCURATELY MODELED AS FLUID FLOW, PROVIDED AN ADEQUATE FLUID FLOW MODEL IS EMPLOYED, AND (3) ROCK LAYERS IN THE STRATIFIED BODY ARE PERFECTLY UNIFORM LAYERS OF EITHER IDEALLY VISCOUS INCOMPRESSIBLE FLUIDS OR NON-LINEARLY VISCOUS INCOMPRESSIBLE FLUIDS THAT EXHIBIT POWER-LAW BEHAVIOR. THE STUDIED SEQUENCES ARE STYLIZED SO AS TO CONTAIN A FEW THICK, DISTANTLY DIFFERENT ROCK UNITS. THE DEFORMATION OF A 3- LAYER ROCK SEQUENCE CONTAINING A LOW VISCOSITY LAYER IS STUDIED FIRST. THEORETICALLY PREDICTED VELOCITY PROFILES FOR GRAVITY SLIDING OF THIS SEQUENCE SHOWS THAT DECOLLEMENT OCCURS BECAUSE OF LARGE VISCOSITY CONTRASTS BETWEEN ROCK LAYERS. A TWO-STEP METHOD IS USED TO CONSTRUCT VELOCITY PROFILES. THIS METHOD IS DISCUSSED IN THE APPENDIX. SLIDING VELOCITY DECREASES WITH INCREASING VISCOSITY OF A DECOLLEMENT ZONE. DECOLLEMENT OCCURS ABOVE BASEMENT BECAUSE CRYSTAL AND ROCK VISCOSITIES EXCEED TYPICAL SEDIMENT VISCOSITIES BY ORDERS OF MAGNITUDE. IN THE PROCESSES STUDIED, BASEMENT APPEARS RIGID IN COMPARISON TO SEDIMENTS. IT IS CONCLUDED THAT SEVERAL DECOLLEMENT ZONES COULD BE ACTIVE SIMULTANEOUSLY. STRESSES ASSOCIATED WITH OROGENIC THRUSTING ARE REVIEWED USING THE DECOLLEMENT ZONE MODEL WHICH REQUIRES REMARKABLY LOW STRESSES TO SUSTAIN THRUSTING RATES COMPARABLE TO REPORTED RATES OR SEA-FLOOR SPREADING. IF DECOLLEMENT TAKES PLACE ACCORDING TO THE MODEL SUGGESTED, STRUCTURES ASSOCIATED WITH MAJOR CRUSTAL TRANSLATION SHOULD BE RECONCILABLE WITH THE OPERATIVE DEFORMATION MECHANISMS. COMPETENT ROCKS ARE LITTLE AFFECTED BY THE SAME BOUNDARY CONDITIONS THAT RESULT IN THE SEVERE DEFORMATION OF ROCKS WITHIN A DECOLLEMENT ZONE.

  • Supplemental Notes:
    • Vol 81, No 6, PP 1641-1663, 16 FIG, 63 REF, 1 APP
  • Authors:
    • Kehle, R O
  • Publication Date: 1970-6

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  • Accession Number: 00235744
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Aug 26 1970 12:00AM