Editing Geology (section)

===Structural geology===
{{Main|Structural geology}}
[[File:Orogenic wedge.jpg|thumb|upright=1.8|A diagram of an orogenic wedge. The wedge grows through faulting in the interior and along the main basal fault, called the [[Decollement|décollement]]. It builds its shape into a [[critical taper]], in which the angles within the wedge remain the same as failures inside the material balance failures along the décollement. It is analogous to a bulldozer pushing a pile of dirt, where the bulldozer is the overriding plate.]]

Structural geologists use microscopic analysis of oriented thin sections of geological samples to observe the [[fabric (geology)|fabric]] within the rocks, which gives information about strain within the crystalline structure of the rocks. They also plot and combine measurements of geological structures to better understand the orientations of faults and folds to reconstruct the history of rock deformation in the area. In addition, they perform [[analogue modelling (geology)|analog]] and numerical experiments of rock deformation in large and small settings.

The analysis of structures is often accomplished by plotting the orientations of various features onto [[stereographic projection|stereonets]]. A stereonet is a stereographic projection of a sphere onto a plane, in which planes are projected as lines and lines are projected as points. These can be used to find the locations of fold axes, relationships between faults, and relationships between other geological structures.

Among the most well-known experiments in structural geology are those involving [[Accretionary wedge|orogenic wedges]], which are zones in which [[mountain]]s are built along [[convergent boundary|convergent]] tectonic plate boundaries.<ref>{{Cite journal |author=Dahlen |first=F. A. |year=1990 |title=Critical Taper Model of Fold-and-Thrust Belts and Accretionary Wedges |journal=Annual Review of Earth and Planetary Sciences |volume=18 |pages=55–99 |bibcode=1990AREPS..18...55D |doi=10.1146/annurev.ea.18.050190.000415}}</ref> In the analog versions of these experiments, horizontal layers of sand are pulled along a lower surface into a back stop, which results in realistic-looking patterns of faulting and the growth of a [[critical taper|critically tapered]] (all angles remain the same) orogenic wedge.<ref>{{Cite journal |doi= 10.1016/S0191-8141(97)00096-5 |title= Material transfer in accretionary wedges from analysis of a systematic series of analog experiments |year= 1998 |author= Gutscher, M |journal= Journal of Structural Geology |volume= 20 |pages= 407–416 |issue= 4|bibcode = 1998JSG....20..407G |last2= Kukowski |first2= Nina |last3= Malavieille |first3= Jacques |last4= Lallemand |first4= Serge }}</ref> Numerical models work in the same way as these analog models, though they are often more sophisticated and can include patterns of erosion and uplift in the mountain belt.<ref>{{Cite journal |author=Koons |first=P. O. |year=1995 |title=Modeling the Topographic Evolution of Collisional Belts |journal=Annual Review of Earth and Planetary Sciences |volume=23 |pages=375–408 |bibcode=1995AREPS..23..375K |doi=10.1146/annurev.ea.23.050195.002111}}</ref> This helps to show the relationship between erosion and the shape of a mountain range. These studies can also give useful information about pathways for metamorphism through pressure, temperature, space, and time.<ref>{{cite journal |last1=Dahlen |first1=F. A. |last2=Suppe |first2=J. |last3=Davis |first3=D. |year=1984 |title=Mechanics of Fold-and-Thrust Belts and Accretionary Wedges: Cohesive Coulomb Theory |journal=[[Journal of Geophysical Research]] |volume=89 |issue=B12 |pages=10087–10101 |bibcode=1984JGR....8910087D |doi=10.1029/JB089iB12p10087}}</ref>