This question is very general. If you start with an undeformed and unfractured block of rock and put it under stress you will initially get some deformation (at first elastic, then plastic) without formation of a fracture, i. e. folding may occur before fracturing and faulting.

If you start with an already fractured/ faulted block of rock and put it under stress the deformation you get may mostly be accumulated in the fractures/ faults and only along the edges of the fault some folding occurs (fault-bend fold), i. e. faulting may occur from the beginning of your deformation process.

You may find some more information if you browse for plasticity, deformation theory, Mohr-Coulomb criterion, fracture envelope, fault-bend fold, fault-propagation fold, ductility.

Thank you Mr. Michael. your explanation is very helpful :)

This question indeed is very general, but crucially dependent upon the way stress and deformation are modeled. In the theory of differential grade-2 materials the folds (spatial harmonic solutions of the governing PDE) form at lower energy levels. Cheers, RP

It has no simple and straight forward answer. It depends mainly on whether the deformation is in ductile deformation regime or in brittle deformation regime. In ductile deformation regime usually the fold is the structure rather than fault while in brittle deformation regime fault is formed rather than fold, however, in some instances fold and fault both form together (e.g. fault propagation fold).

This is not difficult to determine. Folds which occured before faulting will be affected. Example limbs of folds are likely to be faulted while open folds become tighter.......Faults that occured before folding will show deformation of textures associated with the fault.

surely limbs of folds are likely to be faulted while open folds become tighter...... but not always and not everywhere the fault-related structures are folded by later folding events... strain partitioning can occur along the shear zone boundary planes... in general, in thin-skinned tectonics, one can assume that in a layered sequence contractional deformation firstly generate folds and then, if stress is maintained, shear reactivation of fold limbs and displacement of hinge zones occur..

Mr Abdul Martin 's explanation is acceptable to me. Type of deformation depends upon the material characteristics.

The question requires a review of both strength of materials, and the direction

and speed of the applied forces.

If the direction of the applied compressive forces is essentially horizontal, then

a wave form appears. The sequence in cross section across the wave would

consist of at least five parts that are symmetrical like a wave you would observe on

an oscilloscope. A Hill, a shallow basin, a Fold Mountain Range, a basin, a hill.

The Mountain Range is the primary " Fold " with lateral shortening of originally

horizontal stratographic layers The Lateral shortening in the Horizontal direction,

is offset by the vertical increase in elevation in the Mountain portion and the two

hills on the opposite side of the basin. The Mountain and the two hills are

vertically " unconstrained " because the planets atmosphere can not hold down

the hills and Mountain as they deform. This is not true of the two basins. The basins are vertically " Constrained " by the layers of material underneath them, so the

basins are rather shallow.

In this senario, the direction of the applied forces is horizontal, and the

speed of application is slow so that plastic deformation can occur in the

rock layer without leading to rupture ( fracture ).

if any combination of differential vertical and differential horizontal forces are

applied, and / or the rate of force application is too fast, the rock will rupture

producing a combination of folding and faulting.

In strength of materials this is a shear failure

Many of these structures can be modeled by sheets of paper where the sheets are

laid flat on a smooth surface and lateral applied forces create the primary wave form.

A Magazine can be used to create a combination of vertical and horizontal

forces to see other types of folding.

Both can form simultaneously but of course at different depth level. In deeper level if the environment is favorable enough for ductile environment then one may expect folds there, in contrast at shallower level it is likely to be brittle.........may be some faults

Both can form simultaneously, even in the same place. There is an entire class of (geometric) models of fault-related folds. Fold bend folding and fault propagation folding are best known. Apart from models, there is also field evidence from high-level (shallower than 10 km) thrust belts which exhibit both early stage, "embryonic" folds and thrust faults, implying that both nucleated together.

Interesting points... I think Micheal's explanaton is spot on...

Folds formed due to compressional regime....BUT faults are formed due to compressional, tensional and shearing. stresses. In case of compressional stress ...folds formed first followed by reverse or thrust faults..Tensional and shear-related folds usually overprint folding as they formed in a brittel environment.

To be short and effecient, fructures alway devolops before folding. I dose not mean that they are not reworked after or while folding. But never folds begins before fracturing. c.f. (Ahmodahi& al., 2008, Tavani & al. 2011, Tavani & al., 2012, Beaudoin & al., 2012, my PhD work, paper in preparation...).

Hi everyone,

There is no basic ansver to this question, as everybody can easily see above. In my opinion, tectonic environment (brittle or ductile) and geotectonic environment (spreading center-rift valleys, subducting or obducting oceanic slab, internal basin, etc.) will guide the deformation direction and the range, wether folding or faulting procedures start at first phase, and then how direction the deformation prograding until the changing the tectonic regime.

Jonas Clay is basically correct! Actually there isn't such a thing as a "structural geology theory". And there isn't a cookin' recipe nor a short and efficient answer either. What we do in geology is to see the facts an try to creat a model based on solid scientific knowledge. Lyke the astronomers! Not like astrologists!. Nature is unchangeable, only our interpretation is sometimes elusive. Dear Ryandi, if you have a concrete case you will have to solve it, but that does not mean that your next one will be identical. It will depend on the local characteristics and geologic environment.

The strength of rocks is lower for tensional and higher for compressive stresses. Disttribution of strain in folds is also heterogeneous that means you may have stretching and shortening simultaneously. That simple reasoning illustrates the complexity of the problem and any simplified answer is just meaningless.

First fold then fault

First would be lateral compressive forces.

A fold is a wave form created in more ductile materials undergoing

a slow application of increasing lateral pressure.

A fault is a fracture that propagates at an angle through brittle materials.

Fold and or Fault would be due to both the direction and rate of applied force,

and the other properties of the materials. The weaker the materials, the

more likely it will fold. The stronger the materials, the more likely it is to

fracture creating a fault.

I came to the conclusion a long time ago, that to understand something,

you need to able to create a model that a child would understand.

A ream of Paper can be used to model a fold.

Twisting a piece of chalk, or just breaking it in half can model a fault.

Both ways, in perfect association!!!! First fold and then fault, or viceversa. Or even simultaneously!!!!! Also at the same time, but not physically connected but related to a single ongoing stress tensor......

Based on the geomechanics depends on the medium: Elastic or plastic domain

Based on the geology, the main parameter is the velocity of the deformation e.g. earthquake generates faults no folds then if the time (in term of duration) is a parameter the timing (in term of chronology) is not relevant

There are three different types of fault- fold relationships based on relative time of appearance. and also on kinematics and kinetics and dynamics------1) fault bend folding (first fault then fold) 2) fault propagation folding (when both are contemporaneous) 3) detachment folding (folding then faulting). Kinetically, it depends on when the stress trajectory for a given rock strata touches the bending instability envelop relative to faulting instability envelop (irrespective of regime). If both on the same time fault propagation fold, if bending envelop first then detachment fold, if faulting instability first then fault bend fold.

Geodynamics and matreial properties ( ductile/ brittle) are the main factors for generating fold or fault.

The question - "which is first" appears to be wrong because these processes (folding and faulting) are either interrelated or independent. Hence it will not be fair to decide the sequence of their formation.

Folding may not follow by faulting for plastic media, as well as no folding will appear during crush of brittle one. It resembles the question "What first hen or egg?" But this is alredy solved, a hen, becouse the egg predated birds thaks to grovel.

Independent, fault-then-fold, fold-then-fault or simultaneous. All possible.

Depends on rock strength (RS), strain rate (SR) and temperature gradient (TG). Folds tend to form at lower RS, at lower SR and at higher TG. Boundaries are not sharp, though. Since RS, SR and TG vary in space (vertical and horizontal) and time, is the space-time path of the rock what determines the formation scenario.

If we forget strain rate, temperature gradient and rock lateral variations, and focus *only* in the strength vs. depth diagram, we would have formation of faults and/or folds:

(a) Independently, when out of the brittle-ductile transition zone (BDTZ)

(b) Sequentially, when moving in or out of the BDTZ

(c) Simultaneously (in geological terms), when within the BDTZ

One should not think of what comes first without paying attention to the time-space relationship David mentioned above. If the rock is residing in an area where ductile deformation prevails one cannot expect faulting, instead a rock will continue to fold again and again if the stresses continue for a considerable time. If the same stresses push the rocks to a shallower level of the crust where brittle conditions prevail, faulting will post-date the folding. Similarly, a rock residing at a shallower level of the crust where it behaves in a brittle fashion, when subjected to stresses, will fault first if its strength has been exceeded. It may not fault if it can withstand the stresses. If the stresses push the rock to a deeper level where it will now behave in a ductile fashion, the rock will undergo folding irrespective of whether it has been faulted or not while at shallower levels. As very correctly stated by David rock's strength, strain rate and temperature will combine in different ways to determine whether the rock is going to behave in a brittle or ductile fashion. The thicknesses of the rock layers will also play a role in determining their strengths.

Clark, Blanco, Perera and other researchers have already explained the thing nicely. Few more things to add. Instead of searching for "which one came first?" if the things are analysed as processes then 'egg-hen-egg' or 'hen-egg-hen' becomes equivalent, different phases of a process. Now, for divergent plate boundaries, if the faults are more visible in the fault-fold mechanism; for convergent plate boundaries fold-fault mechanisms are more pronounced. Moreover, for growth faults where the same fault plane can be activated at different types, as we go up and analyse the effects of reactivated faults on recent sediments, rate of damping seems to be increasing and the recent sediments seem as if to be undergoing mild folds in seismic facies (due to resolution limit etc.). Similar effects can be observed in the cases of blind faults and their surface manifestation. Fault-fold relationships in the sedimentary environment and in the hard-rocks are definitely going to generate diverse patterns. If the forcings are known and the fault-fold pattern that emerges is visible, it is possible to predict what lies inside the black-box.

J'ai réalisé des levés de cartographie géologiques détaillées qui m'ont permis de constater que dans les chaînes plissées en Tunisie, on a tout d'abord des phases tectoniques transtensives qui permettent la subsidence et l'accumulation des dépôts sédimentaires. Ces tectoniques transtensives font rejouer ou font naître des décrochements et des failles listriques jouant avec on composantes normales plus ou moins importantes. Certains de ces failles sont réactivées au cours des phases tectoniques compressives et des plis se forment en même temps. Mais d'autres failles restent scellées et ne sont pas réactivées.