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Structural Analysis and Synthesis A Laboratory Course in Structural Geology Third Edition SOLUTIONS MANUAL Stephen M. Rowland University of Nevada, Las Vegas Ernest M. Duebendorfer Northern Arizona University Ilsa M. Schiefelbein ExxonMobil Corporation, Houston, Texas Separate maps are available on request from artworkcd@bos.blackwellpublishing.com ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 1 9.1.2007 3:11pm Compositor Name: SJoearun Chapter 1 Note to instructors You may wish to accept errors of !1–28 on orthographic projection problems. Our experience is that the careful student can always come within !18 of the attitudes determined below. Answers Worked solutions are presented below. Problem 1.1 a) N128E 0128 f) N378W 3238 b) 2988 N628E g) 2338 N538E c) N868W 2748 h) 2708 N908W d) N558E 0558 i) 0838 N838E e) 1268 N548W j) N38W 3578 Problem 1.2 a) 3148, 498NW Impossible f) 3338, 158SE Impossible b) 0868, 438W Possible g) 0898, 438N Possible c) N158W, 878NW Impossible h) 0658, 368SW Impossible d) 3458, 628NE Possible i) N658W, 548SE Impossible e) 0628, 328S Possible Attitudes a, c, f, h, and i are impossible because the strike and dip cannot be in the same direction. Problem 1.3 Lineation Feasible? Explanation Type of fault a) Due north, 348 Yes Lies within fault plane; plunge less than dip Oblique-slip b) 1408, 08 Yes Lies within fault plane; plunge ¼ 0 Strike-slip c) N668W, 338 No Lineation does not lie within fault plane d) 0508, 478 Yes Lies within fault plane; plunge ¼ dip Dip-slip e) Due north, 758 No Plunge steeper than dip ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 2 9.1.2007 3:11pm Compositor Name: SJoearun Problem 1.4 258NW Problem 1.5 338SE Problem 1.6 N248E, 33.58NW Problem 1.7 a1 ¼ 39#S a2 ¼ 19:5#E Problem 1.8 25.18NW Problem 1.9 32.58SE Problem 1.10 Any direction between N308E and S308E Problem 1.11 N618E, 118S Problem 1.12 (a) 258NW (b) 328SE ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 3 9.1.2007 3:11pm Compositor Name: SJoearun 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Structural Analysis and Synthesis ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 3 Solutions Problem 1.4 Problem 1.5 True dip (δ) = 2.58NW Apparent dip (α) =338SE Problem 1.6 Problem 1.7 Stirke = 0248, dip = 338NW α1 = 39!S α2 = 19.5!E E-W cross section N -S cross section Problem 1.8 tan d ¼ ( tana=sinb) a ¼ 20# b ¼ 51# tan d ¼ tan 20#=sin 51# ¼ 0:468 d ¼ 25:1#NW Problem 1.9 tan d ¼ ( tana=sinb) d ¼ 48# b ¼ 35# tana ¼ ( tan 48#)( sin 35#) ¼ 0:637 a ¼ 32:5#SE ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 4 9.1.2007 3:11pm Compositor Name: SJoearun 4 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Analysis and Synthesis 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Problem 1.10 tan d ¼ ( tana= sinb) d ¼ 2# a ¼ 1# sinb ¼ tan 1#= tan 2# ¼ 0:4998 b ¼ 30# All directions between N308E and S308E Problem 1.11 u1 ¼ 220#; a1 ¼ 4# u2 ¼ 100#; a2 ¼ 7# tan (angle between u1 and true dip direction) ¼ csc(u1 $ u2) [( cota1)( tana2) $ cos (u1 $ u2)] ¼ csc 120# [(cot4#)( tan 7#)$ cos 120#] ¼ 1:155 [(14:301)(0:1228) $ ($0:5)] tan 69# ¼ 2:606 true dip direction ¼ 220# $ 69# ¼ 151# strike ¼ N618E tan d ¼ ( tana=sinb) tan d ¼ tan 4#=sin 21# d ¼ 11#SE ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 5 9.1.2007 3:11pm Compositor Name: SJoearun 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Analysis and Synthesis ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 5 Chapter 2 Note to instructors Problem 2.2. Note that these are elevations above sea level (not depths below surface) to the top of the Bree conglomerate. Students should be encouraged to use geological judgment where no data are present – specifically, structure contours in the northwest corner of the map should be drawn to define a north-plunging anticline by analogy with the major structure (north-plunging syncline) in the center of the map. You may wish to ask students to place appropriate fold symbols on the structure contour map (see below). As a supplement, students could determine absolute strike and the dip of surface at specified localities. These of course will vary somewhat in dip magnitude because of slight variability in the placement of individual structure contours from student to student. Students should color the Bree Creek quadrangle map before Chapter 3. You may wish to specify a uniform color scheme for map units to facilitate grading and assisting students in the lab. Problem 2.3. Note that values given are depths below a flat surface. Answers and solutions Problem 2.1 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 6 9.1.2007 3:11pm Compositor Name: SJoearun Problem 2.2 Student maps will differ in detail from the solution provided here. Problem 2.3 Dip ¼ tan d ¼ D elevation=map distance ¼ 6600=12500 $ 27:5# Depth to D ¼ (map dist:)( tan d) ¼ (15600)( tan 37:5) ¼ 8110 54850 $ 8110 ¼ 46740 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 7 9.1.2007 3:11pm Compositor Name: SJoearun ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Structural Analysis and Synthesis -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 7 Problem 2.4 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 8 9.1.2007 3:11pm Compositor Name: SJoearun 8 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Structural Analysis and Synthesis ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Chapter 3 Note to instructors Problem 3.1. The strike of Thd on Gandalf’s knob can be determined easily, but the dip cannot. However, by using information from exposures farther south within the western fault block, it can be shown that the dip is 38NE on Gandalf’s Knob as it is to the south. The 4000’ structure contour representing the base of Thd at Gandalf’s Knob occurs at the correct position relative to the 4800’ and 5200’ structure contours to the south. Problem 3.2. We specify localities to determine thickness for sake of uniformity (and for consistency with thicknesses that appear in subsequent cross sections (Problem 4.4)). Thicknesses could be determined from other localities on the map; however, variable outcrop widths lead to thickness determinations that may vary by a factor of two or more. This variation is, of course, typical of ‘‘real world’’ situations, but it will be easier on the grader if all students measure thicknesses at the same locality.Measured thicknesses at the specified localities should vary by no more than 5–10% between students, and can therefore be evaluated. Problem 3.3. In some instances, it will not be possible for students to construct two parallel strike lines at both the top and bottom of a unit. They may have to rely on spot elevations, or in some cases, interpolate elevations between contours. Because this exercise deals with some of the thinnest and most gently dipping units on the map, calculated thicknesses will vary considerably. Problem 3.4. We find that students devise all sorts of improbable solutions to these maps. To circumvent this problem, students should be required to ‘‘defend’’ their cross sections. Alternatively, the instructor could limit possibilities by imposing some constraints. For example, the instructor could state that the contact in exercise (a) dips 758 to the west. In this case, the only viable solutions are a fault or intrusive contact – a nonconformity is virtually ruled out. As a second example, in exercise (b), the instructor could specify that formation Y is younger than formation X and that the contact dips west. This would restrict viable interpretations to either an angular unconformity or normal fault. Answers and solutions Problem 3.1 Thd Tr Tg Northeastern fault block Northern exposures N628W, 58NE N168W, 118NE N168W, 118NE Southern exposures N168W, 118NE N168W, 118NE Central fault block Northern area N248W, 98NE N248W, 98NE Galadriel’s Ridge N248W, 98NE N248W, 98NE Southwestern area N228W, 98NE N228W, 98NE Western fault block Gandalf’s Knob N788W, 38NE Southern exposures N788W, 38NE ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 9 9.1.2007 3:11pm Compositor Name: SJoearun Problem 3.2 Tmm 410’ Tm 450’ Tts 2540’ Tb 630’ Te 4430’ Problem 3.4 Problem 3.5 Stratigraphic column not provided here, but should be straightforward. Problem 3.3 Thd Tr Tg Gollum Ridge 120’ Gandalf’s Knob 600’ Galadriel’s Ridge >400’ 100’ Mirkwood Creek about 100’ N. of Edoras Creek >400’ ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 10 9.1.2007 3:11pm Compositor Name: SJoearun 10 ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Structural Analysis and Synthesis ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Chapter 4 Solutions Problem 4.1 Problem 4.2 Problem 4.3 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 11 9.1.2007 3:11pm Compositor Name: SJoearun Problem 4.4 Structure sections A–A’ and B–B’. Note that the structure sections shown on the following pages were constructed using the Bree Creek Quadrangle map from the second edition because the final draft of the map for the third edition was not available to us before the publisher’s deadline for this solutions manual. Although the map has not changed in content, it is possible that minor differences in final production of the map for the third edition may have occurred (contacts shifted slightly, etc.) and, therefore, there may be minor deviations between the solutions presented below and cross sections that are constructed from the final third edition map. We believe, however, that the solutions presented below are fundamentally correct. Of course there will be variations from student to student due to different interpretations regarding fold shape, etc. The critical issues are keeping bedding thicknesses constant and maintaining consistent displacement on the faults (i.e., all beds cut by a fault should be displaced equal amounts). ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 12 9.1.2007 3:11pm Compositor Name: SJoearun 12 ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Structural Analysis and Synthesis ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- R O W L A N D / Stru ctu ral A n alysis an d Syn th esis x x x x x x x x x x _4 _0 1-0 9 F in al P ro o f p age 1 3 9 .1 .2 0 0 7 3 :1 1 p m C o m p o sito r N am e: SJo earu n R O W L A N D / Stru ctu ral A n alysis an d Syn th esis x x x x x x x x x x _4 _0 1 -0 9 F in al P ro o f p age 1 4 9 .1 .2 0 0 7 3 :1 1 p m C o m p o sito r N am e: SJo earu n Chapter 5 Note to instructors This is a rather long chapter; you may wish to assign only selected exercises. It is our experience that the careful student can usually obtain answers within a degree or two from those listed below. Answers Problem 5.1 258NW Problem 5.2 N658W, 308SW Problem 5.3 (1) Plunge ¼ 138; trend ¼ S58E (1758) (2) Pitch ¼ 148 (3) Pitch ¼ 338 Problem 5.4 Plunge ¼ 208; trend ¼ S428W (2228) Problem 5.5 Bearings: N828E and S588W Problem 5.6 N308E, 758SE Problem 5.7 (1) Plunge ¼ 188; trend ¼ S758W (2558) (2) N158W, 728E (3) 1248 (4) N488W, 228SW (5) Plunge ¼ 118; trend ¼ S208E (1608) (6) Downhill ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 15 9.1.2007 3:11pm Compositor Name: SJoearun Problem 5.8 N538W (or 1278/3078), 538SW Problem 5.9 Plunge ¼ 708; trend ¼ N508E (0508) Problem 5.10 228 toward 3498 Problem 5.11 Using Thd ¼ N628W, 58NE and Tr ¼ N168W, 118NE (from Problem 3.1): Attitude ¼ N88E, 88E; direction of tilt ¼ 88 in direction of S808E (1008) Problem 5.12 N468E, 328NW ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 16 9.1.2007 3:11pm Compositor Name: SJoearun 16 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Solutions Problem 5.1 Problem 5.2 Problem 5.3 Problem 5.4 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 17 9.1.2007 3:11pm Compositor Name: SJoearun 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Structural Analysis and Synthesis -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 17 Problem 5.5 Problem 5.6 Problem 5.7 Problem 5.8 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 18 9.1.2007 3:11pm Compositor Name: SJoearun 18 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5.9 Problem 5.10 Problem 5.11 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 19 9.1.2007 3:11pm Compositor Name: SJoearun 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Structural Analysis and Synthesis ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 19 Problem 5.12 ROWLAND / Structural 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Chapter 6 Answers Problem 6.1 Fold description should contain the following descriptive elements: the block depicts cylindrical, symmetric, open folds with interlimb angles of 90–1058 that plunge 308 northeast and whose axial surfaces strike N208E and dip 608 west. Problem 6.2 Layer 1: class 2. Layer 2: class 1B (possibly class 1C). Layer 3: class 3. See solution on p. 23 for sketch. Problem 6.3 Class designation may vary slightly – sample size is small and it is difficult to locate isogons precisely: (a) Class 3 (using dark band in center of specimen). (b) Class 2. (c) Class 1B or 1C depending on where measured. (d) Class 1B. Problem 6.4 Students may have to be reminded about the rules for determining orientation of fold axes in overturned beds. Note that, by strict definition, a noncylindrical fold has no fold axis. Sketches are on p. 24. (a) Trend ¼ 2508; plunge ¼ 268. (b) Trend ¼ 1358; plunge ¼ 688. (c) Noncylindrical folds; no fold axis (variable hinge line orientations). (d) Trend ¼ 0008; plunge ¼ 08. (e) Trend ¼ 1808; plunge ¼ 458. Problem 6.5 (1) Sketches will vary – folds are high amplitude. (2) Axial surfaces are approximately 3458, 508SW. (3) Approximate fold axis: trend 2008 (S208W); plunge 458. ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 21 9.1.2007 3:12pm Compositor Name: SJoearun Solutions Problem 6.1 Instructors may wish to allow some leeway with regard to position of axial surfaces and crest/trough lines. Because these folds are open, hinge lines (and thus trace of the axial surface) cannot be located with great precision. ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 22 9.1.2007 3:12pm Compositor Name: SJoearun 22 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6.2 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 23 9.1.2007 3:12pm Compositor Name: SJoearun 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Synthesis xxxxxxxxxx_4_01-09 Final Proof page 24 9.1.2007 3:12pm Compositor Name: SJoearun 24 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Chapter 7 Note to instructors On fold profiles (Problem 7.1, question 2; and Problem 7.2, question 2) the attitudes that students obtain for axial surfaces will vary due to imprecision inherent in construction and choice of ‘‘best fit’’ axial surface (hinge points are not perfectly aligned). In particular, in the case of gently plunging fold axes that trend within a few degrees of the strike of the axial surface, slight variations in inferred strike of the axial surface can result in large differences in estimated dip. This should be taken into account when grading students’ lab exercises (especially axial surfaces for the western and central blocks). In Problem 7.2, question 2, the profile of the folds in the central block must be drawn from southern exposures. In this region, the axial surface dips very steeply to the west. In the northern exposures, the axial surfaces dips more moderately west- ward (about 508). The axial surface determined by the profile technique will thus differ from that determined by p maxima on the contour diagram (which reflects data from both northern and southern parts of block). Students should note the difference in orientation in their fold descriptions. Answers Problem 7.1 (1) Trend ¼ 2718; plunge ¼ 358 (see sketch on next page). (2) Strike of axial plane ¼ 0168 (see sketch on next page). (3) See sketch on next page. (4) Folds are symmetrical and close (with interlimb angle 50–608). Axial surface strikes 0168anddips368W.Fold axis trends2718andplunges358; a reclined fold. Problem 7.2 (1) See sketches on p. 27. (2) See sketches on p. 28. West block: hinge trend¼ 148, plunge¼ 128. Axial surface strike¼N128E, dip 838E. Central block: hinge trend ¼ 128, plunge ¼ 108. Axial surface strike ¼ N138E, dip ¼ 858E. Northeast block: hinge trend ¼ 158, plunge ¼ 248. Axial surface strike ¼ N128E, dip ¼ 848E. (3) West block: class 1B. Central block: class 2. Northeast block: class 3 (slightly convergent; some students may get class 2). (4) West block: these are class 1B, symmetrical, open folds (interlimb angle of 1208). Axial surfaces strike N128E, dip 838E, and p axis trends N148E and plunges 128. Crosscutting relationships indicate that these folds formed between the Eocene and Miocene. Central block: these are class 2, symmetrical, close folds (interlimb angle of 458). Axial surfaces strike N138E, dip 58E, and p axis trends N128E and plunges 108. Crosscutting relationships indicate that these folds formed between the Eocene and Miocene. Northeast block: these are class 3, symmetrical, open folds (interlimb angle of 90–1008). Axial surfaces strike N128E, dip 848E, and p axis trends N158E and plunges 248. Crosscutting relationships indicate that these folds formed between the Eocene and Miocene. (5) See plots for Problem 7.2, question 1 (p. 27). ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 25 9.1.2007 3:12pm Compositor Name: SJoearun Solutions Problem 7.1 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 26 9.1.2007 3:12pm Compositor Name: SJoearun 26 ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Structural Analysis and Synthesis ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Problem 7.2 7.2 (1) Solutions will vary depending upon contour interval used. Overall patterns should be similar to those shown. ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 27 9.1.2007 3:12pm Compositor Name: SJoearun ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Structural Analysis and Synthesis ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 27 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 28 9.1.2007 3:12pm Compositor Name: SJoearun 28 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Structural Analysis and Synthesis ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Chapter 8 Note to instructors For Problems 8.1 and 8.3, the strike and dip of bedding shown on the maps do not correspond to a single bed but rather to random bedding attitudes measured in the field. This is a common situation in strongly cleaved rocks where specific marker beds cannot be identified. Students should merely use form lines to define the shapes of folds. Students will have a difficult time completing this exercise if they treat each attitude as if it were measured on a single bedding surface. Solutions Problem 8.1 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 29 9.1.2007 3:12pm Compositor Name: SJoearun Problem 8.2 Problem 8.3 Actual positions of axial surfaces will vary with student; there is some leeway. The number and sequence of folds must be as shown. 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8.4 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 31 9.1.2007 3:13pm Compositor Name: SJoearun 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Structural Analysis and Synthesis ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 31 Problem 8.5 ROWLAND / Structural 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F o r st ru ct u re se ct io n s C – C ’a n d D – D ’s tu d en ts sh o u ld d ra w si m il ar fo ld s. T h ey w il l b e u n ab le to k ee p b ed d in g th ic k n es se s co n st an t an d st il l h o n o r th e m ap co n st ra in ts . B ed d in g th ic k n es s ch an ge s ar e n o t ex tr em e, h o w ev er . 8 .5 .2 . St ru ct u re se ct io n C – C ’ ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 33 9.1.2007 3:13pm Compositor Name: SJoearun 8 .5 .2 . St ru ct u re se ct io n D – D ’ 8 .5 .3 . F 1 fo ld ax es p lu n ge ge n tl y to th e w es t– so u th w es t an d n o rt h –n o rt h ea st ; ax ia l su rf ac es ar e in cl in ed to su b h o ri zo n ta l (r ec u m b en t fo ld s) . In te rl im b an gl es ra n ge fr o m n ea r ze ro to ab o u t 1 5 8. F o ld s ar e sy m m et ri c (w h en ef fe ct s o f la te r fo ld in g ar e ta k en o u t) . F o ld cl as s is ty p e 2 (s im il ar ). F o ld in g is p o st -M is si ss ip p ia n b u t p re -C re ta ce o u s. T h e D ar k T o w er G ra n o d io ri te cu ts th e fo ld s. F 2 fo ld ax es p lu n ge ge n tl y to th e so u th ; ax ia l su rf ac es ar e m o d er at el y in cl in ed to th e w es t. In te rl im b an gl es ar e b et w ee n ab o u t 2 0 8 an d 5 0 8. F o ld s ar e as ym m et ri c. F o ld cl as s is ty p e 1 B (p ar al le l) . F o ld in g is p o st -E o ce n e b u t p re -M io ce n e. ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 34 9.1.2007 3:13pm Compositor Name: SJoearun Chapter 9 Answers Problem 9.1 Slip ¼ 320 m (see solution on p. 38). Problem 9.2 Slip ¼ 260 m (see solution on p. 38). Problem 9.3 (1) Yes, attitude 3338, 678NE could be the result of rotation (see solution on p. 39). (2) 358 rotation. Problem 9.4 Post-Rohan Tuff/pre-Helm’s Deep Sandstone tilting Post-Helm’s Deep Sandstone tilting Northeastern fault block 88 toward 1048 58 toward 238 Central fault block 78 toward 628 38 toward 128 Western fault block 38 toward 128 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 35 9.1.2007 3:13pm Compositor Name: SJoearun Problem 9.5 (1) Fault A: normal fault; post-Lower Miocene, pre-Middle Miocene. Fault B: left-slip tear fault; post-Triassic, pre-Middle Miocene (by inference that tear fault is related to the thrust fault, Fault C). Fault C: thrust fault; post-Triassic, pre-Middle Miocene. Fault D: left-slip fault; post-Middle Miocene, pre-Miocene (upper, Tm). Fault E: thrust fault; post-Silurian (may wishto accept post-Triassic if the two thrusts are considered related), pre-Jurassic. (2) Contact ‘‘a’’: nonconformity. Contact ‘‘b’’: intrusive. Contact ‘‘c’’: angular unconformity. Contact ‘‘d’’: disconformity. Structure at ‘‘e’’: trough of northeast-plunging syncline. Structure at ‘‘f’’: fenster. Structure at ‘‘g’’: klippe. Structure at ‘‘h’’: axial region of northeast-trending overturned anticline. (3) Overturned dips: the 778W dip in the Ordovician just west of fault E; the 478W dip in the Silurian just east of fault E; the 728W dip in the Pennsylvanian- Permian just east of fault C. (4) Tm must be younger than other Miocene units because it overlaps fault D that cuts the middle Miocene unit (5) 20 km based on presence of klippe. (6) 1. Deposition of Cambrian through Devonian rocks; unconformity; deposition of Pennsylvanian through Triassic rocks. 2. Folding and associated thrusting of these rocks along faults C and E; tear fault B forms during this time. 3. Intrusion of Jurassic plutons. 4. Uplift and erosion. 5. Deposition of Eocene through lower Miocene rocks. 6. Normal faulting (fault A) and associated tilting of Eocene–lower Miocene rocks. 7. Post-faulting erosion. 8. Deposition of middle Miocene rocks. 9. Southwest tilting of middle Miocene rocks. 10. Left-slip faulting along fault D. 11. Erosion (probable). 12. Deposition of Tm unit. 13. Erosion to present. ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 36 9.1.2007 3:13pm Compositor Name: SJoearun 36 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Structural Analysis and Synthesis ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Pr ob le m 9. 6 M irk w oo d fa ul t Br ee C re ek fa ul t G ol lu m Ri dg e fa ul t N or th Br ee C re ek fa ul t 1. Ty pe N or th : no rm al So ut h: re ve rs e (p ro ba bl y re ve rs e fa ul t w ith m in or no rm al re ac tiv at io n po st -T r) N or m al se pa ra tio n; pr ob ab ly no rm al sl ip . Pr es er va tio n of Te rt ia ry st ra ta in ha ng in g w al l su gg es ts at le as t a si gn ifi ca nt co m po ne nt of no rm al sl ip N or m al se pa ra tio n; pr ob ab ly tr ue no rm al sl ip be ca us e ha ng in g w al lr oc ks ar e co ns is te nt ly yo un ge r N or m al se pa ra tio n; pr ob ab ly tr ue no rm al sl ip be ca us e en tir e Te rt ia ry se ct io n pr es er ve d in ha ng in g w al lr oc ks 2. A tt itu de N -S to N 20 8E ; 35 8W N 58 W to N 58 E; 75 8W N 58 W to N 58 E; 75 8W N 21 8E to N 45 8E ; 80 8N W 3. St rik e se pa ra tio n D ip se pa ra tio n (c he ck fo r co ns is te nc y w ith st ud en t cr os s se ct io ns ) In de te rm in at e Po or ly co ns tr ai ne d 41 00 m m ea su re d fro m Tt s- Tb co nt ac t (p ro je ct ed to fa ul t) M in im um 58 00 m ba se d on se pa ra tio n of K dt un it 4. A ge Po st -M io ce ne , pr e- Pl io ce ne Po st -C re ta ce ou s is on ly co ns tr ai nt Po st -M io ce ne Po st -M io ce ne ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 37 9.1.2007 3:13pm Compositor Name: SJoearun Solutions Problems 9.1 and 9.2 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 38 9.1.2007 3:13pm Compositor Name: SJoearun 38 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Structural Analysis and Synthesis -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Problem 9.3 ROWLAND / Structural Analysis and Synthesis xxxxxxxxxx_4_01-09 Final Proof page 39 9.1.2007 3:13pm Compositor Name: SJoearun ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Structural Analysis and Synthesis -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 39
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