exploring geological processes - mines
TRANSCRIPT
Exploring Geological Processes
Santanu BoseDepartment of Geology
Experimental Tectonics Laboratory University of Calcutta
Kolkata - 700019
Structural Analysis
• Descriptive Analysis– Recognize and describe structures and measure their
locations, geometries and orientations
• Scale, Structural Elements
• Kinematic Analysis– Focus on motion of materials
• Dynamic Analysis– Interpret motions in terms of applied forces
Simulate earth processes in a controlled experiment
Build intuition versus actual prediction
Identify controlling processes or conditions
Physical Models
Cross sections in Mountain Belts
Experimental Set up
Coulomb wedge
Critical taper (a+b)=(b+mb)[(1-sin∅c/1+sin∅c)]
∅c
Critical taper of a Coulomb wedge (after Dahlen, 1990) as a function
of the co-efficient of basal friction (μb) and the angle of internal
friction (∅c). α and b are the surface and basal slopes respectively.
Development of thrust wedges in sandbox
Low basal friction High Basal Friction
Journal of Structural Geology, 2009
The ramp location consistently shifts away from the backstop.
(a) Localization of ramp
initiation close to the model front
with basal slope = 5°.
(b) Overall sliding of sand wedge
on frictional base with basal slope =
7°. No ramp initiation in the
model.
Progressive development of
monovergent wedges with horizontal
base. The wedge growth is associated
with progression of sequential thrust in
the foreland direction (right to left).
Maximum elevation located close to the
backstop.
Bivergent thrust wedge with a basal
slope (b= 3°). Location (vertical
arrow) of ramp initiation far away
from the backstop. Wedge growth
involves progression of a set of back
thrusts from the point of ramp
initiation.
• Schematic models of mono
and bi-vergent wedges.
• In case of bi-vergent wedge
the zone of maximum elevation
(Axial Zone) occurs away from
the backstop.
Simplified cross section across
central Nepal Himalaya
showing the topography of the
Himalayan wedge (after
Avouac, 2007). Main
Himalayan Thrust (MHT) acts
as the basal decollement.
Geomorphic and Tectonic units of the Himalayan Mountain Belt
Geol. Soc. London, 2015
Vs=8 cm/yr
Vs=6 cm/yr
Vs=4 cm/yr
Flow Types
Strike-wise Variations in Topography
Tail geometry around porphyroclasts
Rotation of porphyroclast
Varying Tail geometry
Summary
•Models are useful to think about processes that happen
too slowly.
•Models are useful to educate our power of observations
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