Mapping and structural geology in mineral exploration where theory hits the fan rodney j holcombe principal consultant, hcov global. Unfolding veined fold limbs to deduce a basins prefolding. Planes consider curved line on the hemisphere as a series of points project a line through each point to the zenith, intersecting the plane of projection zenith 8. A lineation may be a primary igneous or sedimentary fabric element, such as an array of elongate kfeldspar. These are two contoured schmidt equalarea stereonet plots for poles to foliation a and poles to bedding b. On my way to a conference in italy, i chose to spend a week in france. The red dot at the top of the stereonet is the pole of the best fit line and represents the fold axis of the anticline. To simplify plotting planes on the stereonet, it is convenient to plot the pole to each plane. Qline hinges offer a great option for quality at a very competitive price. Note also that the pole to this plane parallels the hinge line of the fold as does the main timber in the photo. Workbook 2 stereonets school of earth and environment.
Note that in the 2d view, the great circle meets the circumference at 060 o and 240 o that are two points on a horizontal line across the plane. Its helpful when starting out with stereonets to visualize the plane or line as it. We can now consider how two lines the ones in green plot. Problem 1 a fold tightness is described in terms of the interlimb angle, the internal angle between the. Hinge line article about hinge line by the free dictionary. Where that line passes through the stereonet project. Understanding that the axial hinge is the point of maximum curvature or bending in a fold, it is going to be located at the intersection of the two limbs or great circles in this case. A many geological structures such as fold hinges, mineral lineation, igneous flow. A stereonet should be visualized as the bottom half of a sphere. The b axis corresponds to the fold hinge line, the line that links points of maximum curva ture on a folded surface. What is plotted on the stereonet is a projection of where a given line or plane intersects the lower hemisphere surface. Software for stereographic projection there are several pieces of software that youd like to check out for that purposes.
What is the plunge and trend of the hinge to this fold. Contents scoo o t n nvironent 4 introduction to stereonets a stereonet is a lower hemisphere graph on to which a variety of geological data can be plotted. Introduction to stereonets 4 stereonet terminology 6 setting up a stereonet 7 1. Fold classifications a anticlines, synclines, antiforms. Structural geology, geol 330 spring 2012 folding lab magic eye folds. A stereographic projection, or more simply a stereonet, is a powerful method for displaying and manipulating the 3dimensional geometry of lines and planes davis and reynolds 1996. Determing the trend and plunge of a line from a stereonet in some cases, you will need to read off the trend and plunge of a line from a stereonet. How to interpret fold data on a stereonet by dr jacqui houghton. Small circles angles are slightly distorted and make the circles appear as ellipses. If a plane projects onto the stereonet as a great circle, then a line or lineation on the plane will plot as a point on the same. What is the feature indicated by the heavy black dashed line.
Sasaki 1979 recognized four stages in larval development. The strike line of a bed, fault, or other planar feature, is a line representing the intersection of that feature with a. Stereographic analysis of folds as always, show your work for all problems. If a plane projects onto the stereonet as a great circle, then a line or lineation on the plane will plot as a point on the same great circle. The plunge of the hinge line reverses along a doubly plunging fold. These free and userfriendly programs are outstanding for any geologist. Structures are also subjected to live loads whose position may vary on the structure. Hinge limb angularity 75 layer shape around fold 75 fold symmetry 77 fold vergence 77. The hinge line can easily be perceived in these images of a mussel shell and an ark shell. Dont suppose anybody could help me out with this stereonet. Plot the axial trace of the fold that you measured in the field on a stereonet assume it is a line with zero plunge together with the fold axis. Asymmetric rounded fold with a curvilinear hinge line fig. Jun 15, 2017 folds on stereonets 000 180 270 090 000 180 270 090 best fit girdle profile plane fold axis. Fold geometry and classification free powerpoint templates page 1 folds are wave like structure that results from deformation of bedding, foiliation or other originally planar surface in rocks.
Stereographlc projection of a line the orientation ofany lineargeologic structure such as a mineral lineation. Teaching resources in structural geology leeds university. Mar 20, 2019 equal area stereonet with small circles showing consistent size. A line is drawn from that projection point to the lower hemisphere intersection point light green dashed lines. One thing that has been bugging me lately is how the geoscience community teaches how to manipulate and interrogate spatially oriented data. Trying to interpret such data plotted as raw orientations scatter plots on a stereonet, without further data treatment is difficul. A fold restoration methodology is presented in which fold limbs, and the structures they contain, are rotated back to their depositional horizontal position by removing the tilt of the fold hinge line and the dip of individual fold limbs. Mar 28, 2014 hinge line shown in waltz here, but also danced in slow foxtrot and tango. Mapping and structural geology in metals exploration. No doubt this one of the hardest things to become accustomed to in the world of structural geology. So, just read that point off the stereonet like a lineation. Stereonet analysis of data from arbuckle mountains near. Webbased teaching resources in structural geology in the school of earth sciences of the university of leeds.
The longitudes are planes that intersect in a common line the ns line, and thus appear as great circles in the stereonet. The structure and tectonic history of the scremerston. The limb may thus be redefined as the fold segment between a hinge line and the adjacent inflection line, which is the locus of inflection points. The north end of the strike line is trending 330 azimuth n30w, and the dip line is trending 240 azimuth sw quadrant 90 degrees from strike. Best fit girdle is the equivalent of the profile planes and contains all the poles to bedding. Pitch angles are in the range 090 o, with a pitch of 0 o being a line parallel to the strike, and a pitch of 90 o being a line parallel to the dip line. In addition, i used the programs faultkin version 7. It is frequently seen that the strata forming the earths crust have been not only tilted out of the horizontal but also bent and buckled into folds. Connecting the hinge points on a specific folded surface defines the hinge line fold axis or. Gy403 structural geology lab university of south alabama. Stereographic projection an overview sciencedirect topics. Line rake or pitch on a plane diagrams illustrating strike, dip, trend, plunge.
Further instructions on how to plot and interpret geological fold data. It is frequently seen that the strata forming the earths crust have been not only tilted. Definition, parts and types structural geology geology. Types of folds with photos fold occurs when one or a stack of originally flat and planar surfaces, such as sedimentary strata. Planes intersect the sphere as great circles and lines intersect the sphere as points. The pole forms a 90 angle with the strike line and a 90 angle with the dip line. Structural geology exercises with glaciotectonic examples part ii james s. Limbs of fold regions of lowest curvature on folds h. A chevron fold near calico ca, has one limb oriented 26030 and its other limb is 10060. Gg303 lecture 28 9401 4 stephen martel 284 university of hawaii nomenclature for folds young young young old old young old old syncline anticline. The fold axis and fold hinge line have the same attitude. Prior to folding, the poles to a bedding plane plot as a single point or a concentration of points on a stereonet.
Proyeksi stereonet adalah proyeksi yang didasarkan pada perpotongan bidanggaris bantu suatu permukaan bola. Bitte immer nur genau eine deutschenglischubersetzung eintragen formatierung siehe guidelines, moglichst mit einem guten beleg im kommentarfeld. Stereographic projection of a line, in this case the normal or pole to a plane. A hinge line is an imaginary longitudinal line along the dorsal edge of the shell of a bivalve mollusk where the two valves hinge or articulate. Since the intersection of two planes forms a line, we will plot the hinge as a dot on the stereonet. The projections of the latitudes, which are not planes but cones coaxial with the ns line, are usually referred to as small circles also their projections onto the stereonet. In trying to document the character of structural elements it is not uncommon to have hundreds of orientation readings. Pdf strabospot is a geologic data system that allows researchers to digitally collect, store, and share both field and laboratory data. Trying to interpret such data plotted as raw orientations scatter plots on a stereonet, without further data treatment is difficult and susceptible to. Stereonet of the hinge line of the fold d stereonet of the cleavage, poles to planes with a best fit great circle. Determine from the outcrop pattern whether this fold is cylindrical has a straight hinge line or non. Even when you think you understand the concept entirely, when youre out in the field you may be questioning yourself as to how to exactly measure the. This is part five of a series of videos used on the first year structural geology. The pole is a line running through the center of the projection sphere and perpendicular to the plane fig.
A best fit line was drawn along a great circle through the poles and shows that the foliations were striking in a general east to west direction on both sides of the canyon. Feb 21, 2012 understanding that the axial hinge is the point of maximum curvature or bending in a fold, it is going to be located at the intersection of the two limbs or great circles in this case. Its helpful when starting out with stereonets to visualize the plane or line as it cuts through a 3dimensional bowl props may be helpful. Kemudian tarik garis sepanjang lingkaran besar great circle yang melalui hinge line dan melewati titik b, sehingga membentuk suatu bidang yang merupakan bidang simetri lipatan axial plane. Evenfoldsgetparasites spring,2012 this exercise is meant to mimic a field experience in which you, the student, will measure bedding cleavage relationships and asymmetric folds in order to map a regionalscale structure. The plunge is read by placing the intersection point on the ns line and counting down and the direction is read by marking the on the primative where the line intersects the ns line and rotating the. The orientation of the plane also must be givenin order to uniquely orient the line. Links to basic information on folds and faults and virtual field trips to the alps, lebanon, moine thrust belt in scotland and nanga parbat. Fold geometry nature of folds any bend, warp, or flexure in a geologic surface that we presume to have been originally planar is a fold. The hinge of the fold is the crease in the paper, that is to say, the line along which the curvature of the strata or paper is at a maximum.
The structure and tectonic history of the scremerston region. Structural geology free download as powerpoint presentation. The one line is formed by the intersection of the ns vertical plane and the red plane of interest, and the other by the ew vertical plane and the red plane of. From clipon to soft close, to minihinges and traditional hinges, the qline brand is your onestopshop. Finally, i would like to thank my future wife, nicole volpe, who held my sanity. The fold axis is the most important structural element of a fold because it shows the direction of maximum continuity of this fold. An online stereonet program that allows you to create and view all of your geologic stereonet information in 3d. You are now ready to begin plotting lines, planes, and poles. Eps116 moss beach 2016 mmt university of california. The fault is a line, but has an area of importance as. To derive the parental orientation of these prefolding brittle structures, folds need to unfold.
As you make your hand dip more shallowly, the cyclographic trace ofyour hand approaches the rim of the bowl and starts to look like a circle. The intersection made by the line or plane with the spheres. Visible geology runs in the browser so there is no need to download anything, just click to add lines and double click to add planes. This is a printable 2 degree equal angle wulff stereonet in pdf format. The orientations of lines and planes can be plotted relative to the center of a sphere, called the projection sphere, as shown at the top of fig. They are designed to meet your manufacturing and compatibility requirements.
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