Review:
1.What is the orientation relationship
between maximum shear stresses and
principal stresses?
2.What are trajectories of principal stresses?
Stress Analysis for the Formation
of En Echelon Veins and
of Vortex Structures
Stress Analysis For The Formation
Of En Echelon Veins
En echelon quartz veins
En echelon slaty cleavages are
perpendicular to the en echelon
quartz veins,
After J.G.Ramsay,1967
Observe the en echelon veins
and examine the relationship
among the en echelon
extensional veins,the slaty
cleavages and the straight
shearing veins
En echelon veins
Considering the equilibrium of an
triangular plate element
Set the coordinate systems as in
the diagram,we have the
equilibrium equations:
?F?=0 and ?FT=0
Stress analysis
?
T
?
?
?
?
135
?1
?1
?2
?2
Formation of the
En echelon veins
(After Wang,W.X,
1984)
Sigmoid en echelon veins
conclusion
? Finite shear and finite rotation are the cause of formation
of the sigmoid and reverse sigmoid veins in an en
echelon structure
? In a ductile-brittle shear zone,en echelon slaty cleavages
are usually perpendicular to en echelon veins
? Significance of the en echelon sigmoid and reverse
sigmoid veins include:
1) indicator of shear sense
2) indicator of ductile-brittle condition
3) helpful to prospecting and mining
Formation of Vortex Fractures
Vortex fractures,Inner Mongolia
Trajectories of compressive
Axes in the Western Alpine
Arc drawn from focal
mechanism
(After Vialon et al.,1989)
Vortex fracture system
from brittle coating
experiment
(Zeng Z.X.et al.,1992)
Vortex fractures
in model
(From Zeng Z.X.,
1992)
Trajectories for vortex fracture system
Summary for procedure of
research on geological structures
? Observe structural features in field
practice
? Construct mechanical models
? Mechanical analysis
? Check result in further field practice
Problems(2):
1) Try to explain one kind of structure studied
in previous lessons
2) Think about the significance of the
trajectories of principal stresses
Problems(1):
Derive equation (1) and equation (2)
Determine the shear sense of different shear
zones with different en echelon veins
1.What is the orientation relationship
between maximum shear stresses and
principal stresses?
2.What are trajectories of principal stresses?
Stress Analysis for the Formation
of En Echelon Veins and
of Vortex Structures
Stress Analysis For The Formation
Of En Echelon Veins
En echelon quartz veins
En echelon slaty cleavages are
perpendicular to the en echelon
quartz veins,
After J.G.Ramsay,1967
Observe the en echelon veins
and examine the relationship
among the en echelon
extensional veins,the slaty
cleavages and the straight
shearing veins
En echelon veins
Considering the equilibrium of an
triangular plate element
Set the coordinate systems as in
the diagram,we have the
equilibrium equations:
?F?=0 and ?FT=0
Stress analysis
?
T
?
?
?
?
135
?1
?1
?2
?2
Formation of the
En echelon veins
(After Wang,W.X,
1984)
Sigmoid en echelon veins
conclusion
? Finite shear and finite rotation are the cause of formation
of the sigmoid and reverse sigmoid veins in an en
echelon structure
? In a ductile-brittle shear zone,en echelon slaty cleavages
are usually perpendicular to en echelon veins
? Significance of the en echelon sigmoid and reverse
sigmoid veins include:
1) indicator of shear sense
2) indicator of ductile-brittle condition
3) helpful to prospecting and mining
Formation of Vortex Fractures
Vortex fractures,Inner Mongolia
Trajectories of compressive
Axes in the Western Alpine
Arc drawn from focal
mechanism
(After Vialon et al.,1989)
Vortex fracture system
from brittle coating
experiment
(Zeng Z.X.et al.,1992)
Vortex fractures
in model
(From Zeng Z.X.,
1992)
Trajectories for vortex fracture system
Summary for procedure of
research on geological structures
? Observe structural features in field
practice
? Construct mechanical models
? Mechanical analysis
? Check result in further field practice
Problems(2):
1) Try to explain one kind of structure studied
in previous lessons
2) Think about the significance of the
trajectories of principal stresses
Problems(1):
Derive equation (1) and equation (2)
Determine the shear sense of different shear
zones with different en echelon veins
