Patterns of Typical Cleavage Traces Analysed by the Chart Digitizer. A
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• • Fig. 21: Patterns of typical cleavage traces analysed by the chart digitizer. A - Specimen 1, B - Specimen B, C - Specimen 7, D - Specimen 8, E - Specimen 2-12, F - Specimen 2-13, G - Specimen 2-14. All magnifications x 1. 34. electronic chart digitizer at the Division of Mineral Physics, CSIRO, North Ryde, and results calculated by program GOLLUM (see Appendix II). Initially two specimens were digitised (Specimen A, Plate 5A, and Specimen B, Fig.21B) and results for lengths and spacings are shown in Figure 22. On graphs of length versus orientation from the dominant cleavage plane (Figs. 23A and B) the pattern as predicted by the model in Chapter 1 (p.25-29) was not observed. Instead, a distribution to both sides of the dominant cleavage plane occurred. The real distributions exhibit a close similarity to the theoretical curves, indicating that the cleavage planes are diverging on both sides away from the dominant cleavage plane. Because of the unusual pattern encountered it was decided to examine more specimens, particularly of "fracture" cleavage to see if similar patterns could be recognised. Specimen B for slaty cleavage has an almost parallel orientation with only two cleavage planes out of a total of 66 diverging more than 8° from the dominant cleavage plane. Subsequently the lengths and orientations of cleavage planes in fourteen specimens and photographs were determined using the electronic digitizer. Specimens were collected from four main localities within the Block and can be grouped into five divisions with respect to the orientation of the bedding and mesoscopic folds: (a) the plane of the specimen is parallel to the ac-plane, and bedding and the dominent cleavage are subvertical (e.g. Specimen 1, Figs. 21A and 24A); (b) similar to (a) except that the bedding is subhorizontal (e.g. Specimen 2-13, Figs. 21F and 26C); (c) similar to (a) except that the bedding has an approximate east-west strike and dips moderately to the north (e.g. Specimen 2, Plate 6B and Fig. 25A); (d) similar to (c) except the bedding dips moderately to the south (e.g. Specimen 2-12, Figs. 2-12 and 26C); and (e) the plane of the specimen is subhorizontal and hence not in the ac-plane (e.g. Specimen 3A, Plate 6A and Fig. 26A). A summary of results is presented in Table 3 and Figs. 23-26. For most specimens there is a symmetrical distribution of points on both sides of the dominant cleavage plane, and this cannot be explained by the 60 SlECI,MEN A SPECIMEN A N - W6 N = 421 24 Mean = 8.12 mm Mean = 1.63 mm 20 S.D. = 6.32 mm S.D. = 0.74 mm Minimum = 0.13 mm Minimum = 0.01 mm % 16 Maximum = 44.66 mm Maximum = 7.70 mm 12 0 2 6 10 14 18 22 26 30 34 38 42 46 4 6 10 LENGTH (mm) SPACING (mm) SPECIMEN B SPECIMEN B 28 N = 66 N = 370 24 - Mean = 10.13 mm Mean = 0.92 S.D. = 6.87 mm S.D. = 0.50 mm 20 Minimum = 2.60 mm Minimum = 0.15 mm Maximum = 33.96 mm Maximum = 3.95 mm % 16 . 12 4 12 16 20 2• 28 32 36 2 3 LENGTH (mm) SPACING (mm) 32 SPECIMEN 1 SPECIMEN 3A 28 N = 248 N = 84 Mean = 7.32 mm Mean = 6.73 mm 24 S.D. = 5.43 mm S.D. = 5.70 mm Minimum = 1.48 mm Minimum = 1.94 mm Maximum = 30.09 mm Maximum = 37.47 mm 16 12 0 4 8 12 16 20 24 28 32 36 0 4 8 12 lb 20 24 28 32 36 40 LENGTH (mm) LENGTH (mm) Fig. 22: Results for lengths and spacings of cleavage planes in specimens analysed by an electronic chart digitizer. Table 3: Summary of results for cleavage patterns from the Coffs Harbour Block, and comparison with theoretical curves Orientation Pattern of sample on 1 v. 8 graph Sample Orientation Location of dominant Orientation of sample and comparison with theoretical Number of bedding cleavage model for 1 = sin 0 A Unit D, Coramba Beds unknown unknown unknown symmetrical distribution about dominant Woolgoolga cleavage plane, for S = 1.63 mm 53.6% of GR 6330 2695 data occur beneath the theoretical curve B Brooklana Beds, not observed 134/N/89 perpendicular to small variation in orientation about the GR 5768 2792 cleavage dominant cleavage plane. For S = 0.92 mm 89.4% of data are beneath the curve 1 Unit D, Coramba Beds 072/N/86 076/S/82 166/E/82, in ac-plane symmetrical distribution. For S = 2 mm Arrawarra on limb of monocline 83.9% of data occur beneath the theoretical GR 6324 2756 curve 6 Unit A, Coramba Beds 074/S/70 100/S/83 strike approximately symmetrical distribution. Using S = 3 mm Mutton Bird Island N-S, subvertical dip 84.2% of data fall under the theoretical GR 6262 2458 curve 7 Same location as 074/S/70 100/S/83 strike approximately symmetrical distribution. 88.3% of points Specimen 6 N-S, dip about 3O°W, fall beneath the curve for S = 2 mm in ac-plane 8 Brooklana Beds, 134/N/80 127/N/86 normal to cleavage in symmetrical distribution with 86.6% of Coffs Harbour the vertical plane data occurring under the theoretical curve GR 6262 2450 for S = 2 mm 2 same as Specimen 1 087/N/32 075/N/78 000/E/70 in ac-plane symmetrical distribution. For S = 2 mm 79.0% of data are under the curve 3B same as Specimen 1 similar to Specimen 2 ac-plane (subvertical) one-sided distribution similar to the theoretical model, 75.4% of data occur beneath the theoretical curve of S = 3 mm Table 3: (continued) rientationOrientation Sample Pattern of sample on 1 v. 0 graph Location of dominant Orientation of sample and comparison with theoretical Number of bedding cleavage model for 1 = sin 0 1-30A, same as Specimen 1 062/N/40 S 081/N/82 in ac-plane A - symmetrical, S = 3 mm, 86.3% of data ia 1-30B fall beneath curve S 087/S/85 lb B - one sided distribution but reverse pattern to the predicted one, for S = 3.5 mm, 70.5% of points are under the curve 4 same as Specimen A 027/W/38 102/S/80 010/E/62, in ac- symmetrical distribution. For S •. 2 mm (hinge of plane 74,3% is under the curve fold) 5 same as Specimen A unknown 100/S/80 horizontal symmetrical with 81.0% of data beneath curve of S = 2 mm 3A same as Specimen 3B same as specimen 3B horizontal curve fits model. For S = 4.5 mm 91.7% of data fall beneath curve 2-12, same location as 12 E-W strike strike is all specimens in all show a symmetrical distribution, with 2-13, specimen A. Collected dip to south E-W with ac-plane a greater scatter in 12 and 14 than in 13 2-14 from limbs and hinge 13-horizontal subvertical from the hinge area. For 12 S = 3 mm and of an anticline 14-dip to dip 85.3% is beneath curve. Using 5 mm for north 13 gives 88.2% beneath curve. For 14 with S = 3 mm, 79.7% of data fall under the curve 1 SPECIMEN B N . 66 A SPECIMEN A N • 506 40 ao. E 0 -M 60 M 2,0 60 C SPECIMEN 4 N 218 10 sa - 90 60 30 0 30 60 90 • 4o- • SPECIMEN 5 D N 232 30- 20- 20• 10- 10 , 910 • - 00 60 30 30 60 90 • -•0 60 30 30 60 ORIENTATION Idew•e61 °Rif NTATION ∎ d•lleey1 Fig. 23: Graphs of length of cleavage plane versus orientation from the dominant cleavage plane for specimens from the Coffs Harbour Sequence. A SPECIMEN 1 30- N • 248 111 SPECIMEN 7 C N • 111 30• I z . • N . to . 1V E TT ■1 .. -4 GI 3.4 . 34 II N 1I- SPECIMEN 6 i• N=146 I • ' 1 '' ' 40 30 4 40 SPECIMEN 8 N r 172 IS- 40 21 . - I - 44 U 3I I 30 SO 44 • -40 30 0 40. ORIE NIA I iON tto cmit NTAYION- Fig. 24: Graphs of length of cleavage plane versus orientation from the dominant cleavage plane for specimens from the Coffs Harbour Sequence. SPECIMEN 30 N=130 SPECIMEN 2 N= 233 14 . ' r • • • % -Is Is 3s • is N N 2 CIS r SPECIMEN 1-300 N = 268 .:p I. 3: t l 3s so 0 C SPECIMEN 1-30A N =219 E 40 30 0 z 2I 21 11. ,,, 31 0 N N -00 N N is es so. -so C)Htl NIAT ION ORIF NTATION- Fig. 25: Graphs of length of cleavage plane versus orientation from the dominant cleavage plane for specimens from the Coffs Harbour Sequence. SPECIMEN 2-13 60 Na21"3 SPECIMEN SA N.84 30. 30 • II 35 SPECIMEN 2-14 N • 266 • Ir •• 30 i 3r• SPECIMEN 2-12 N ■ 266 SO 40- JS- = z 20- 10, • 4. 10 13. • • • • • • .• • • .2.• .• • ••• 00 00 31 I 30 GO 00 II 30 • 30 60 N E N T A .4 • Fig. 26: Graphs of length of cleavage plane versus orientation from the dominant cleavage plane for specimens from the Coffs Harbour Sequence. 35. theoretical model. In three cases (Specimen 3A, Fig. 26A; Specimen 3B, Fig. 25B; Specimen 1-30B, Fig. 25D) the data fit the theoretical model.