Development of abnormal fluid pressures beneath a ramping thrust sheet: Where's the evidence

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5880170

Wiltschko, D V; Smith, R E ^[1]

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1. Texas A and M Univ., College Station, TX (United States). Dept. of Geology and Center for Tectonophysics

Many models for the mechanics of fold and thrust belts hold that fluid pressure is locally, or even everywhere, abnormal, thus aiding both internal deformation and motion along the base. Recent support comes from studies of accretionary prisms where drill-stem measurements of both fluid flow in fault zones and formation pressure are pointed to as evidence for a hydrodynamic system characterized by wide-spread excess fluid pressure. However, despite the general acceptance of high fluid pressure (Pf) as a potentially important controlling mechanism for thrust motion, and despite nearly 30 years of looking, direct evidence for abnormal fluid pressure in ancient continental thrust belts is either rare or ambiguous. The authors have developed a two-dimensional model for the evolution of fluid pressure within and beneath a ramping thrust sheet. In the model, the fluid and heat flow equations are solved and applied at each time step. The model accounts for porosity compaction, thermal pressuring, and fluid flow. Results of this model show, first, that high fluid pressure can be developed during deposition, before thrust motion. The authors used typical rates of deposition, duration of deposition, and a simplified three-layer stratigraphy for North American thrust belts. Second, the models show that high Pf can be maintained and/or further enhanced during thrusting depending upon the permeabilities assigned to the model hydrostratigraphic section. Of the rock properties studied in detail, modes are most sensitive to permeability. Nevertheless, the models show that for best guesses of the relevant rock properties it should be possible to find evidence for high fluid pressure in, (1) the crests of ramp anticlines and, (2) the toe region, especially in the lower plate.

• OSTI ID: 5880170
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
DEPOSITION
ENERGY TRANSFER
FLUID FLOW
FLUIDS
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GEOLOGY
HEAT TRANSFER
PERMEABILITY
RESERVOIR FLUIDS
RESERVOIR PRESSURE
RESERVOIR ROCK
STRATIGRAPHY
TECTONICS
TWO-DIMENSIONAL CALCULATIONS
WESTERN US OVERTHRUST BELT