Structural and metamorphic evolution of the Robertson River metamorphics with pressure-temperature-deformation-time (P-T-D-t) path
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(2) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. THIS IMAGE HAS BEEN REMOVED DUE TO COPYRIGHT RESTRICTIONS. Figure 1. Location map showing major regional geological features and the area in which detailed work was done outlined by a box (Compiled from Withnall 1985).. D1.
(3) THIS IMAGE HAS BEEN REMOVED DUE TO COPYRIGHT RESTRICTIONS.
(4) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. a). c) b). 070. o. 080. 90. Figure 3. a) Sketches of the oriented rock sample marked and cut into a horizontal slab, from which b) multiple-vertical thin sections are cut from a horizontal rock slab. The FIA (foliation intersection/inflection axis preserved within porphyroblasts) is determined where the asymmetry of the inclusion trails changes c) when viewed from one direction.. D3.
(5) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 4. Photomicrographs showing the structural features and their interpretations, observed in the matrix and within porphyroblasts; a) garnet (Grt) porphyroblast with sigmoidal type inclusion trails representing pre-S 1, wrapped by andalusite (And) overgrowing S 1, that continues through to main foliation S1/2, and sillimanite (Sill) plus biotite (Bt) overprinting early phases; b) staurolite (St) porphyroblast replaced by andalusite in the matrix with S 1 preserved as a crenulation hinge within the staurolite and S 1/2 as the predominant foliation; c) andalusite replacing an older staurolite generation that overgrew S1, and younger staurolite generation overgrew S 1/2 . S3 and S 4 represent a crenulated foliation and steep cleavage respectively; d) garnet porphyroblast containing staircase inclusion trails, truncated by the matrix foliations. S2 is preserved in the strain shadow of the garnet and away from the porphyroblast it decrenulates and rotate towards S 1/2 that is overprinted by S 3; e) staurolite porphyroblast overgrew S 1/2, S 2 preserved within the porphyroblast as the steep crenulation cleavage was destroyed in the matrix because of the reactivation; f) textural relationship showing the replacement of staurolite by prograde muscovite and the overprinting of garnet and andalusite by sillimanite plus biotite. The plates at left lower corners of photos show the sample number and vertical thin section directions around compass..
(6) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. mc135. 140º. mc152. 160º. mc137. 000º. mc135. 000º. M. CIHAN. D4.
(7) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 5. a) Rose diagrams showing the orientations of total FIAs, b) FIA1 (ENE-WSW), FIA2 (E-W) and FIA3 (N-S) in garnet porphyroblasts, and c) FIA2 (E-W), FIA3 (N-S) and FIA4 (NE-SW) in staurolite porphyroblasts across the study area. See Table 1 for the FIA data.. D6.
(8) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. a). M. CIHAN. 0.95. 0.13 0.12. 0.90. 0.11. 0.10. 0.85. 0.09. XCa XMg XMn. 0.08. Fe/(Fe+Mg )XFe 0.80. 0.07. 0.06. 0.75. 0.05 0.04. 0.70 1. b). 3. 5. 7. 9. 11. 13. 15. 17. 19. 1. 0.135. 3. 5. 7. 9. 1 1. 1 3. 15 1 7. 19. 0.95. 0.125. 0.90. 0.115 0.85. 0.105 XCa XMg XMn. 0.095 0.085. Fe/(Fe+Mg) XFe. 0.80. 0.75. 0.075 0.70. 0.065 0.055. 0.65. 1. 3. 5. 7. 9. 11 13 15 17 19 21 23 25 27 29 31. 1. 3. 5. 7. 9 11 13 15 17 19 21 23 25 27 29 31. Figure 6. Compositional zoning profiles (X Mn, XCa , XMg, XFe and XFe/(Fe+Mg)) of garnet porphyroblasts in sample mc135 (a) and mc 137 (b). In mc135 the garnet shows a lack of zoning as indicated by a flattened XMn profile, whereas in mc137 the garnet preserves growth zoning.. D8.
(9) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 7. Pseudosection (a) displaying the mineral stability fields, with respect to the bulk composition of mc137 (core-gr1 in (c)). The isopleths of XMn, XCa and X Fe (b) derived from the probe analysis of the core and median of a garnet are calculated and then plotted based on the compositions (c) estimated using the fractionation method of Evans (2004)..
(10) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. a). 9. ctd chl g. ky chl st g pl. chl ctd g zo. 8. ctd chl zo. ky st g pl bi. bi st g pl. ctd chl pl g zo. X Fe X Ca. X Mn. ctd chl pl zo X Mn. 6. ky g pl bi. chl ctd pl g. 7. ctd chl pl. sill st g pl bi. X Fe. sill g pl bi. chl st g pl bi. 5. X Ca. ctd chl st pl. bi st pl. sill st pl bi. chl st pl. 4. M. CIHAN. bi sill pl bi st chl pl. 3. and st chl pl chl pl. MnNCKFMASH-mc137. chl pl and. and pl bi chl. Otz + Ms + H2O in excess. bi and pl. 2. 52. 510. 530. b). 550. 570. 590. 610. 630. 650. 670. XFe. 2 sigma. XCa. 2 sigma. XMn. 2 sigma. Core (gr1). 0.6875. 0.0247. 0.0901. 0.0079. 0.1314. 0.0107. Median (gr20). 0.7238. 0.0249. 0.1051. 0.0077. 0.0779. 0.0095. Bulk Rock Compositions (mol proportions; SiO2 free). c) Al2O3 FeO MnO MgO CaO Na2O K2O SUM. Core (gr1). Median(gr20). 47.66 21.24 0.40 14.53 2.94 4.91 8.33 100.00. 48.16 20.51 0.24 14.71 2.85 5.01 8.51 100.00. D9.
(11) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 8. Backscatter images show the monazite grains and also their locations (a-e) from sample mc152. The numbered circular spots represent the locations of analyses presented in Table 4..
(12) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. a). b). 152m1. M. CIHAN. Mean = 1606 ± 23 [1.5%] 95% conf. Wtd by data-pt errs only, 0 of 5 rej. MSWD = 0.90, probability = 0.46. 152m2. Mean = 1584 ± 16 [1.0%] 95% conf. Wtd by data-pt errs only, 0 of 5 rej. MSWD = 0.64, probability = 0.63. Mean = 1589 ± 17 [1.1%] 95% conf. Wtd by data-pt errs only, 0 of 7 rej. MSWD = 2.4, probability = 0.024. c). 152-1. d). Mean = 1512 ± 15 [0.97%] 95% conf. Wtd by data-pt errs only, 0 of 6 rej. MSWD = 0.44, probability = 0.82. 152-6. D15.
(13) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 9. a) Weighted average plot of 9 individual monazite ages with 95% confidence level for rock sample mc152 ; b) Probability density curve suggests three distinct age populations..
(14) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. data-point error symbols are 2σ. a). 1640 1620 1600 1580 1560 1540 1520 1500. Mean = 1551 ± 27 [1.7%] 95% conf. Wtd by data-pt errs only, 0 of 9 rej. MSWD = 23, probability = 0.000. 1480. b). 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 1480. 1500. 1520. 1540. 1560. 1580. 1600. 1620. 1640. Age (Ma) Age 1508.5 1559.5 1589.8 relative. ±2 σ fraction 8.3 0.22 7.9 0.33 9.5 0.45 misfit = 0.318. ±2 σ 0.31 0.39 ---. D16.
(15) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 10. Backscatter images show the monazite grains and also their locations (a-b) from sample mc135. The numbered circular spots represent the locations of analyses presented in Table 4..
(16) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. 135g. a). Mean = 1592 ± 24 [1.5%] 95% conf. Wtd by data-pt errs only, 0 of 9 rej. MSWD = 2.9, probability = 0.004. Mean = 1601 ± 31 [1.9%] 95% conf. Wtd by data-pt errs only, 0 of 6 rej. MSWD = 2.0, probability = 0.078. b). 135m4. Mean = 1596 ± 13 [0.83%] 95% conf. Wtd by data-pt errs only, 0 of 9 rej. MSWD = 0.54, probability = 0.82. 135m3. D17.
(17) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 11. a) Weighted average plot of 6 individual monazite ages with 95% confidence level for rock sample mc135; b) Probability density curve suggests two distinct age populations..
(18) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. a). M. CIHAN. data-point error symbols are 2 σ. 1650. 1630. 1610. 1590. 1570. 1550. Mean = 1573 ± 23 [1.5%] 95% conf. Wtd by data-pt errs only, 0 of 6 rej. MSWD = 7.0, probability = 0.000. 1530. 1510. b). 0.14. 0.12. 0.10. 0.08. 0.06. 0.04. 0.02. 0.00 1500. 1520. 1540. 1560. 1580. 1600. 1620. 1640. Age (Ma) Age ±2 σ fraction 1557.2 9.2 0.51 1595.8 11 0.49 relative misfit = 0.693. ±2 σ 0.58 ---. D18.
(19) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 12. Backscatter electron images show the monazite grains and also their locations (a-d) from sample mc137. The numbered circular spots represent the locations of analyses presented in Table 4..
(20) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. a). Mean = 1586 ± 22 [1.4%] 2 σ Wtd by data-pt errs only, 0 of 5 rej. MSWD = 1.6, probability = 0.16. Mean = 1564 ± 20 [1.3%] σ Wtd 2 by data-pt errs only, 0 of 6 rej. MSWD = 1.7, probability = 0.14. 137stm3. Mean = 1561 ± 19 [1.2%] 2 σ Wtd by data-pt errs only, 0 of 7 rej. MSWD = 0.63, probability = 0.71. b). 137stm1. 137stm2. c). M. CIHAN. d). 137m-2. Mean = 1599 ± 17 [1.1%] 2 σ Wtd by data-pt errs only, 0 of 9 MSWD = 1.5, probability = rej. 0.15. D19.
(21) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 13. a) Weighted average plot of 7 individual monazite ages with 95% confidence level for rock sample mc137; b) Probability density curve suggests a single age group..
(22) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. data-point error symbols are 2σ. a). 1650. 1630. 1610. 1590. 1570. 1550. 1530. Mean = 1574 ± 16 [0.99%] 95% conf. Wtd by data-pt errs only, 0 of 7 rej. MSWD = 1.5, probability = 0.16. 1510. b). 0.16 0.14. 0.12 0.10 0.08. 0.06 0.04. 0.02 0.00 1500. 1550. 1600. 1650. Age (Ma) Age ±2 σ fraction 1567.8 13 0.70 1596 26 0.30 relative misfit = 0.976. ±2 σ 0.69 ---. D20.
(23) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 14. Backscatter images show the monazite grains and also their locations (a-b) from sample mc133. The numbered circular spots represent the locations of analyses presented in Table 4..
(24) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. a). M. CIHAN. Mean = 1524 ± 27 [1.8%] 95% conf. Wtd by data-pt errs only, 0 of 6 rej. MSWD = 3.3, probability = 0.006. 133-st1. b). Mean = 1526 ± 14 [0.92%] 95% conf. Wtd by data-pt errs only, 0 of 12 rej. MSWD = 1.4, probability = 0.15. 133-m3. D21.
(25) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 15. a) Weighted average plot of 5 individual monazite ages with 95% confidence level for rock sample mc133; b) Probability density curve suggests normal distribution of a single age population..
(26) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. a). M. CIHAN. data-point error symbols are 2σ. 1560. 1550. 1540. 1530. 1520. 1510. Mean = 1524.1 ± 6.3 [0.42%] 95% conf. Wtd by data-pt errs only, 0 of 5 rej. MSWD = 1.18, probability = 0.32. 1500. 1490. b). 0.20 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 1480. 1500. 1520. 1540. 1560. 1580. Age (Ma) Age ±2 σ fraction 1520.8 10 0.53 1529.7 14 0.47 relative misfit = 0.991. ±2 σ 0.86 ---. D22.
(27) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Figure 16. a) Weighted average plot of 27 individual monazite ages with 95% confidence level from all rock samples; b) Probability density curve suggests three distinct age populations..
(28) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. data-point error symbols are 2σ. a). 1660 1640 1620 1600 1580 1560 1540 1520. Mean = 1551 ± 12 [0.80%] 95% conf. Wtd by data-pt errs only, 0 of 27 rej. MSWD = 14, probability = 0.000. 1500 1480. b). 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 1470. 1490. 1510. 1530. 1550. 1570. 1590. 1610. 1630. 1650. 1670. Age (Ma) Age 1518 1559.3 1592.2 relative. ±2 σ fraction 5.6 0.25 6.3 0.37 6.9 0.38 misfit = 0.468. ±2 σ 0.20 0.25 ---. D23.
(29) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. Reactivation-antithetic shearing along compositional layering and S1. S1/2 No reactivation-synthetic shearing along S2. S1 Progressive shearing S2 Progressive shortening. Figure 17. Sketch showing decrenulation of early-formed differentiated crenulation cleavage. Progressive synthetic shearing parallel to S 2 switches to progressive antithetic shearing along S1 -S1/2 across a boundary between reactivated and non-reactivated zones; thereby early deformation partitioning domains (progressive shearing and progressive shortening) are locally destroyed.. D24.
(30) ABSOLUTE TIME CONSTRAINTS ON DEFORMATION AND METAMORPHISM. M. CIHAN. 10. 9. 8. 7. 1559 Ma. O1-O3. 6. 5. ? 1500 Ma. 1655 Ma. 4. ?. 3. O4 1550 Ma. 2. 1. 0 450. 470. 490. 510. 530. 550. 570. 590. 610. 630. 650. 670. 690. Temperature (ºC). Figure 18. P-T-D-t diagram that shows clockwise loop overprinted by gently sloping path with increasing pressure and temperature. O 1 -O4 stands for deformation periods characterized by NNW-SSE, N-S, E-W and NW-SE, respectively. M 1 represents early medium pressure-temperature metamorphism, followed by retrogressive metamorphism, M 2, which are overprinted by low pressure-high temperature metamorphism, M 3.. D25.
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