Using Photogrammetry to Analyze Structures in a Tectonic Sliver … · 2019-02-22 · Figure 5E- Stereonets for Package 4 structural data. Figure 5F- Stereonets for Package 5 structural

Using Photogrammetry to Analyze Structures in a Tectonic Sliver in the Foot Wall of the Champlain Thrust, Shelburne, Vermont IIChirigos, Michael1; Kim, Jonathan2; Klepeis, Keith1, and Van Hoesen, John3

1Dept. of Geology, University of Vermont, Burlington, VT 05405, [email protected]; 2Vermont Geological Survey, 1 National Life Drive, Montpelier, VT 05620; 3Green Mountain College, One College Circle, Poultney, VT 05764

SP4B

Figure 4A- Western 3D Outcrop Mosaic. Figure 4D- Eastern 3D Outcrop Mosaic (east side).

Figure 6D - Evolution of S1 Pressure-Solution Cleavage from West to East.

S1 pressure-solution cleavage (green) in SP2 below Fault B. Note bedding(S0) (blue) in the microlithons that makes a pronounced intesection lineation (L1) on S1.

S1 pressure-solution cleavage on the western side of SP5 that was deformedby open F2 folds. Note bedding(S0) in the microlithons.

S1 pressure-solution cleavage on the eastern side of SP5 that was deformedby tight F2 folds. Note bedding(S0) in the S1 microlithons and the S2 fracturecleavage that is axial planar to the F2 folds and fortuitously parallel to S0.

S1 pressure-solution cleavage on the central part of SP5 that was deformedby very tight F2 folds. Note that bedding(S0) in the S1 microlithons (parallelto pen) is now subvertical.

Calcite slickensides along Fault B surface. Note pen for scale. Calcite slickensides along Fault C plane. Note hammer for scale

Figure 4H-Slickensides.

EAST

In the Champlain Valley Belt of west-central Vermont, the Champlain Thrust juxtaposed ferruginous quartzites and dolostones of the Lower Cambrian Monkton Fm (hanging wall) with calcareous shales of the Late Ordovician Stony Point Fm (foot wall = Parautochthon), during the Ordovician Taconian Orogeny. Internal to the Parautochthon in this area, a tectonic sliver of dark gray limestone is found that likely correlates with the Cumberland Head Fm.

Structural analysis of a ~100 m long outcrop was accomplished through a combination of photogrammetric techniques and field measurements. We used photogrammetry software to construct photo mosaics of 1) the entire outcrop, 2) each structural package, and 3) across the tectonic boundaries between structural packages. A preliminary structural synthesis is described below. It is important to point out that structures with the same relative age, determined using cross cutting relationships, may have developed diachronously across the outcrop.

The “sliver” of Cumberland Head Fm consists of 5 structural packages that are bounded by 4 faults. The oldest planar structure in each package is bedding (S0), which appears as a millimeter-scale, dark and light, compositional banding. Superposed on S0 at high angles, is a penetrative spaced pressure-solution cleavage S1 that, where associated folds are absent, is thrust-related. Southeast-trending slickensides formed on fault-parallel zones of calcite veins in each of the 4 faults.

In packages 1-3 (numbered from west to east), S1 is truncated by, and/or rotated into parallelism with, the overriding east-dipping thrust faults. These faults (A+B) are deformed by open folds (F2) with a local axial planar spaced cleavage (S2). The fault C boundary between packages 3 and 4 truncates S2. Although the S1 cleavage is openly folded (F3) and fans on the west side of package 4, it shears out on the east side to form a ~vertical fault contact with package 5. Within package 5, S1 is deformed by tight reclined F3 folds, with gently south-plunging axes.

This poster shows photo mosaics of different scales that are integrated with field data to document the structural history of the Shelburne outcrop. Our approach illustrates the utility of using photogrammetric techniques in the structural analysis of complexly deformed outcrops.

Abstract

Figure 1- Lithotectonic Base Map.

General study area and lithotectonic belts on bedrock geologic map (modified from Ratcliffe et al. (2011).

STUDYAREA

Figure 2- Bedrock Geology.

Inset from Figure 1 showing the bedrock geology of the study area (modified from Ratcliffe et al. (2011)). The study area is the yellow polygon.

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Poles to So Poles to S1 Poles to S2 and S2.5 All F2 Fold Data

n = 155n = 26 S2 n = 24S2.5 n = 2

Calculated F2 fold axes n = 27Measured So/S1 intersection lineations n = 8Calculated So/S1 intersection lineations n = 19Measured S1/S2 intersection lineations n = 5Calculated S1/S2 intersection lineations n = 25

Shelburne Farms Lake Outcrop Summary Data

Package 1:Package 2:Package 3:Package 4: Package 5:

So: BlueS1: Light GreenS2: YellowS2.5: MagentaCalculated F2 fold Axes: Black

Measured So/S1 intersection lineations: Dark GreenCalculated So/S1 intersection lineations: Light BlueMeasured S1/S2 intersection lineations: PinkCalculated S1/S2 intersection lineations: Brown

Key:

WEST

Fault C

Faul

t D

SP4A

SP4B

Fault C

’

SP5Fault A

SP2

SP1SP2

SP3Fault B

Fault B Fault C

SP3 SP4A

Fault C

’

Fault CSP4A

SP3

Figure 4B- Central 3D Outcrop Mosaic. Figure 4C- Eastern 3D Outcrop Mosaic (west side).

EAST

Figure 4B- Annotated photo mosaic of the Fault B boundary between SP2 and SP3. Figure 4C- Annotated photo mosaic of SP3 before truncation by Fault C.

WESTSP2

SP1

Fault A

SP2

Fault B

SP3 SP4A

Station 112015-3L

SP3Fault C

SP3

SP4A

Fault C

Faul

t D

SP4B

SP5

Fault C

’

SP5

SP5

Faul

t D

Figure 4A- Annotated photo mosaic of the Fault A boundary between SP1 and SP2. Figure 4D- Annotated photo mosaic spanning from SP3 to SP5, with SP4 between Faults C and D. Figure 4E- Annotated photo mosaic of the western half of SP5. Figure 4F- Annotated photo mosaic of the eastern half of SP5.

SP1

SP2

SP3 SP4SP5

51

3720

73

Figure 3- Detailed Base Map for the Study Area.Airphoto base for the study area that shows the outcrop extent (red), the extent of each of the five Structural Packages (SP)(yellow), the locations of bounding faults (yellow pins), and the attitudesof the faults (blue symbols). The magenta arrows delineate the limits of the 3D outcrop mosaics directly below.

FaultS 2.5 cleavageS 2 cleavageS1 pressure solution cleavageS0 bedding

Legend for Planar Structures

Major fracture

Figure 4G- Annotated photo mosaic of Fault C between SP3 and SP4A.

Package 1 Structural DataPoles to S1 and Calculated F2 fold Axes

S1 n = 22Calculated F2 fold Axes n = 6

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Key:

Package 2 Structural Data

So n = 8S1 n = 84S2 n = 3

Calculated F2 fold Axes n = 21Measured So/S1 intersection lineations n = 2Calculated So/S1 intersection lineations n = 7Calculated S1/S2 intersection lineations n = 9

Poles to So, S1, and S2 F2 Fold DataN

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27090270

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Key:


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Measured S1/S2 intersection lineations n = 4Calculated S1/S2 intersection lineations n = 10

So n = 1S1 n = 13S2 n = 12

Poles to So, S1, and S2 F2 Fold Data




Key:


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So n = 6S1 n = 12S2 n = 12

Measured So/S1 intersection lineations n = 4Calculated So/S1 intersection lineations n = 4Calculated S1/S2 intersection lineations n = 1

Poles to So, S1, and S2 F2 Fold Data




Key:


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90180

270So n = 11S1 n = 20S2 n = 8S2.5 n = 2

Measured So/S1 intersection lineations n = 2Calculated So/S1 intersection lineations n = 8Measured S1/S2 intersection lineations n = 1Calculated S1/S2 intersection lineations n = 5

Poles to So, S1, S2, and S2.5 F2 Fold Data




Key:

Station 112015-3L

Key:S1:S2:Measured S1/S2 intersection lineaions:Calculated F2 fold axes:Fault C Planes:Fault C Slickenlines:

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S1 Planes n = 2S2 planes n = 2Measured S1/S2intersection lineationsn = 1Calculated F2 fold axesn = 1Fault Planes n = 3Slickenlines n =3

Shelburne Farms Outcrop Fault DataFault A Planes

Fault planes n = 5N

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Fault C Planes and SlickenlinesFault C Planes and Slickenlines

Fault Planes n = 3Slickenlines n = 3

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Fault D Planes and Slickenlines


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Fault B Planes and Slickenlines


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Key:Fault Plane:Slickenlines:

Figure 5A- Stereonet of Package 1 Structural data. Figure 5B- Stereonets for Package 2 Structural data. Figure 5C- Stereonets for Package 3 structural data. Figure 5D- Station 112015-3Lstereonet.

Figure 5E- Stereonets for Package 4 structural data. Figure 5F- Stereonets for Package 5 structural data.

Figure 6B- Summary data for all structural packages in the study area.

Figure 6C- Summary data of faults in the study area.Figure 6A- 3D block diagram of the study area.

North

West East

A

A

B

B

C

C

C’

D

Inferred DecollementStage 1

Stage 2

Stage 3

Stage 1: Development of Faults A and BStage 2: Formation of Fault C followed by Faults C’ and DStage 3: Onset of Back folding and the inferred decollement

Hinterland Propagation in Three Stages

So

So

S1S1

S2

S2

++

++

Clockwise rotation of fold axialplanes provides both timing andsense of shear on decollement.

S2.5

F2

F2

Shelburne Farms Lake Outcrop 3D Block Diagram

Fault: Inferred Fault:Slickenlines:Slip/FaultMotionIndicator:Second generationMotion indicator:

++Indicates perspectiveinto outcrop:

So:S1:S2:S2.5:F2 Fold Axes:OverturnedAnticline:

Key:SP1

SP2SP3

SP4A SP4B

SP5

References:Allmendinger, Rick. (2016). Stereonet 9 (Version 9.5.3) [Software].Available from http://www.geo.cornell.edu/geology/faculty/RWA/programs/stereonet.html.Photosynth. Microsoft, 2015; software available at https://photosynth.net.Ratcliffe, N.M., Stanley, R.S, Gale, M.H., Thompson, P.J., and Walsh, G.J., 2011, Bedrock Geologic Map of Vermont: U.S. Geological Survey Scientific Investigations Map 3184, 3 sheets, scale 1:100,000.

Vermont Geological Survey Technical Report VGTR16-2

Citation:Chirigos, M., Kim, J., Klepeis, K., and Van Hoesen, J., 2016, Using Photogrammetry to Analyze Structuresin a Tectonic Sliver in the Foot Wall of the Champlain Thrust, Shelburne, Vermont II: Vermont GeologicalSurvey Technical Report VGTR16-2, 1 plate.

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Using Photogrammetry to Analyze Structures in a Tectonic Sliver … · 2019-02-22 · Figure 5E- Stereonets for Package 4 structural data. Figure 5F- Stereonets for Package 5 structural