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Fig. 10. Contour diagrams of composite fabrics for (A) open microfractures (B) partially open microfractures, and (C) FIP in the middle portion of the damage zone (MDZ). Great circle shows orientation of the Punchbow fault; diamonds show the orientation of the Punchbowl fault b-axis, normal and slip direction. Lower-hemisphere equal-area projections with N at top Density contour interval is one sigma beginning with two sigma. Number o: data indicated.

Figure 10 Contour diagrams of composite fabrics for (A) open microfractures (B) partially open microfractures, and (C) FIP in the middle portion of the damage zone (MDZ). Great circle shows orientation of the Punchbow fault; diamonds show the orientation of the Punchbowl fault b-axis, normal and slip direction. Lower-hemisphere equal-area projections with N at top Density contour interval is one sigma beginning with two sigma. Number o: data indicated.

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Fig. 2. Geologic map of the Punchbowl fault on the northeast side of the San Gabriel Mountains, southern California. The location of the Devil’s Punchbowl Los Angeles County Park is shown. The Punchbowl Formation, on the north side of the fault, likely was deposited in a pull-apart basin during the early The Punchbow!] fault is an inactive, exhumed fault of the San Andreas transform system located near the boundary between the San Gabriel Mountains and Mojave Desert, central Transverse Ranges, southern California (Fig. 2). It is ocated approximately 5 km southwest of and is parallel to the active strand of the San Andreas fault. The Punchbowl fault is truncated to the northwest and to the southeast by the San Andreas and is considered an abandoned strand of the San Andreas system (Dibblee, 1968, 1987; Weldon et al., 993). The fault commonly displays sinuous and paired traces that cut crystalline rock of the San Gabriel basement complex and folded Paleocene and younger sedimentary
Fig. 2. Geologic map of the Punchbowl fault on the northeast side of the San Gabriel Mountains, southern California. The location of the Devil’s Punchbowl Los Angeles County Park is shown. The Punchbowl Formation, on the north side of the fault, likely was deposited in a pull-apart basin during the early The Punchbow!] fault is an inactive, exhumed fault of the San Andreas transform system located near the boundary between the San Gabriel Mountains and Mojave Desert, central Transverse Ranges, southern California (Fig. 2). It is ocated approximately 5 km southwest of and is parallel to the active strand of the San Andreas fault. The Punchbowl fault is truncated to the northwest and to the southeast by the San Andreas and is considered an abandoned strand of the San Andreas system (Dibblee, 1968, 1987; Weldon et al., 993). The fault commonly displays sinuous and paired traces that cut crystalline rock of the San Gabriel basement complex and folded Paleocene and younger sedimentary
Fig. 3. Geologic map of the Devil’s Punchbowl showing the sampling locations along several traverses away from the Punchbowl fault and across axes of folds in the Punchbowl Formation.
Fig. 3. Geologic map of the Devil’s Punchbowl showing the sampling locations along several traverses away from the Punchbowl fault and across axes of folds in the Punchbowl Formation.
Fig. 4. Density of mesoscopic scale fractures and subsidiary faults in the Punchbowl Formation sandstone as a function of distance from the Punchbowl fault along four different traverses. Linear density is determined from the total number of fracture intercepts with two perpendicular line segments at each measurement station. Fracture density decreases with distance from the fault except locally near large subsidiary faults (shown by arrows coded to traverse by shade). Subsidiary faults cutting the Punchbowl Formation and basement complex in the damage zone of the Punchbowl fault display preferred orientations (Fig. 5). Most faults are nearly vertical and display a single preferred orientation of b-axes steeply plunging to the west-northwest. Faults striking northwest are right-lateral, and faults striking
Fig. 4. Density of mesoscopic scale fractures and subsidiary faults in the Punchbowl Formation sandstone as a function of distance from the Punchbowl fault along four different traverses. Linear density is determined from the total number of fracture intercepts with two perpendicular line segments at each measurement station. Fracture density decreases with distance from the fault except locally near large subsidiary faults (shown by arrows coded to traverse by shade). Subsidiary faults cutting the Punchbowl Formation and basement complex in the damage zone of the Punchbowl fault display preferred orientations (Fig. 5). Most faults are nearly vertical and display a single preferred orientation of b-axes steeply plunging to the west-northwest. Faults striking northwest are right-lateral, and faults striking
Fig. 5. Subsidiary fault fabric in the Punchbowl fault zone in the (A) Punchbowl Formation and (B) San Gabriel basement complex. Contoured fabric diagrams show normals to all subsidiary faults, normals to all faults with known right-lateral sense of shear, normals to all faults with known left-lateral sense of shear, and b-axes. Great circles show orientation of the Punchbowl fault and the mean orientation of right-lateral and left-lateral subsidiary faults. Lower-hemisphere equal-area projections with N at top. Number of data indicated. Contoured using Kamb method with two sigma contour interval.
Fig. 5. Subsidiary fault fabric in the Punchbowl fault zone in the (A) Punchbowl Formation and (B) San Gabriel basement complex. Contoured fabric diagrams show normals to all subsidiary faults, normals to all faults with known right-lateral sense of shear, normals to all faults with known left-lateral sense of shear, and b-axes. Great circles show orientation of the Punchbowl fault and the mean orientation of right-lateral and left-lateral subsidiary faults. Lower-hemisphere equal-area projections with N at top. Number of data indicated. Contoured using Kamb method with two sigma contour interval.
Samples of Punchbowl Formation used for fabric analysis “ Distance from the ultracataclasite layer. > IDZ-FC = innermost damage zone and fault core; MDZ = middle portion of damage zone; ODZ = outer damage zone; PS = five samples across Punchbowl Syncline. Table 1
Samples of Punchbowl Formation used for fabric analysis “ Distance from the ultracataclasite layer. > IDZ-FC = innermost damage zone and fault core; MDZ = middle portion of damage zone; ODZ = outer damage zone; PS = five samples across Punchbowl Syncline. Table 1
Fig. 6. Linear microfracture density in the Punchbowl Formation sandstone as a function of distance from the Punchbowl fault. Density determined from the total number of fracture intercepts along ninety (90) randomly oriented line segments from three mutually perpendicular petrographic sections for each sample.
Fig. 6. Linear microfracture density in the Punchbowl Formation sandstone as a function of distance from the Punchbowl fault. Density determined from the total number of fracture intercepts along ninety (90) randomly oriented line segments from three mutually perpendicular petrographic sections for each sample.
Fig. 7. (a) Photomicrograph of open microfractures, sealed microfractures, and FIP in a quartz grain. Open microfractures cut sealed microfractures and sealed microfractures cut FIP. Q = quartz, C = calcite cement, O = open microfracture, F = fluid inclusion planes, and S = sealed microfracture. Plane-polarized light. (b) False color X-ray elemental image of large open transgranular microfracture (O, TR), cutting laumontite-sealed microfractures (L). Q (yellow) = quartz, P (blue) = plagioclase feldspar, K (green) = potassium feldspar, L (red) = laumontite. (c) Transmitted, cross-polarized light and (d) cathodoluminescence image of intragranular microfractures filled with calcite. The calcite in microfractures and pores appears similar in cathodoluminescence intensity. SC = strongly luminescent calcite. (e) Transmitted, cross-polarized and (f) cathodoluminescence image of strongly and weakly luminescent calcite in pores and microfractures. Strongly luminescent calcite cuts weak luminescent calcite. Q = quartz, SC = strongly luminescent calcite, and WC = weakly luminescent calcite.
Fig. 7. (a) Photomicrograph of open microfractures, sealed microfractures, and FIP in a quartz grain. Open microfractures cut sealed microfractures and sealed microfractures cut FIP. Q = quartz, C = calcite cement, O = open microfracture, F = fluid inclusion planes, and S = sealed microfracture. Plane-polarized light. (b) False color X-ray elemental image of large open transgranular microfracture (O, TR), cutting laumontite-sealed microfractures (L). Q (yellow) = quartz, P (blue) = plagioclase feldspar, K (green) = potassium feldspar, L (red) = laumontite. (c) Transmitted, cross-polarized light and (d) cathodoluminescence image of intragranular microfractures filled with calcite. The calcite in microfractures and pores appears similar in cathodoluminescence intensity. SC = strongly luminescent calcite. (e) Transmitted, cross-polarized and (f) cathodoluminescence image of strongly and weakly luminescent calcite in pores and microfractures. Strongly luminescent calcite cuts weak luminescent calcite. Q = quartz, SC = strongly luminescent calcite, and WC = weakly luminescent calcite.
Fig. 8. Fabric of open, sealed, and partially open microfractures, and FIP within individual samples. Great circle shows orientation of the Punchbowl fault: filled circles show the orientation of the Punchbowl fault b-axis, normal and slip direction. Lower-hemisphere equal-area projections with N at top. Density contour interval is one sigma beginning with two sigma. Number of data indicated.
Fig. 8. Fabric of open, sealed, and partially open microfractures, and FIP within individual samples. Great circle shows orientation of the Punchbowl fault: filled circles show the orientation of the Punchbowl fault b-axis, normal and slip direction. Lower-hemisphere equal-area projections with N at top. Density contour interval is one sigma beginning with two sigma. Number of data indicated.
cross-cutting relations between microfractures and cements, between the different types of cement, we infer that the FIP are t and ear. the fau he most ancient microfractures, and thus record the iest fracturing events. It is possible that some FIP are inherited fracture from the parent rock and therefore represent events unrelated to Punchbowl faulting. None- ess, because the density of FIP increases towards the t and to the ot orientations of the FIP are representative of fracturing during t orientations within each spatial domain are similar her fracture types, we conclude that the preferred he growth of and subsequent wear along the Punchbowl fault. The open fractures, in general, cut all other fracture types and are interpreted to record the latest fracturing events. Open microfractures are the most likely fracture type to record post-faulting processes, such as uplift and exhumation (Fig. 9), as well as damage during sample preparation. However, the density, fabric and cross-cutting relations of the open fractures suggest that they were formed during the faulting process, and thus are used as a record of deformation during later stages of faulting. The partially open and sealed microfractures are used as the best record of intermediate-stage fracture events (Fig. 9).
cross-cutting relations between microfractures and cements, between the different types of cement, we infer that the FIP are t and ear. the fau he most ancient microfractures, and thus record the iest fracturing events. It is possible that some FIP are inherited fracture from the parent rock and therefore represent events unrelated to Punchbowl faulting. None- ess, because the density of FIP increases towards the t and to the ot orientations of the FIP are representative of fracturing during t orientations within each spatial domain are similar her fracture types, we conclude that the preferred he growth of and subsequent wear along the Punchbowl fault. The open fractures, in general, cut all other fracture types and are interpreted to record the latest fracturing events. Open microfractures are the most likely fracture type to record post-faulting processes, such as uplift and exhumation (Fig. 9), as well as damage during sample preparation. However, the density, fabric and cross-cutting relations of the open fractures suggest that they were formed during the faulting process, and thus are used as a record of deformation during later stages of faulting. The partially open and sealed microfractures are used as the best record of intermediate-stage fracture events (Fig. 9).
Fig. 9. Relative timing of events related to Punchbowl faulting in the Devil’s Punchbowl area inferred from timing determinations as described in text. The early, intermediate and late relative time periods recorded by the fabrics of FIP, partially open and sealed microfractures, and open microfractures, respectively, are indicated. J.E. Wilson et al. / Journal of Structural Geology 25 (2003) 1855-1873
Fig. 9. Relative timing of events related to Punchbowl faulting in the Devil’s Punchbowl area inferred from timing determinations as described in text. The early, intermediate and late relative time periods recorded by the fabrics of FIP, partially open and sealed microfractures, and open microfractures, respectively, are indicated. J.E. Wilson et al. / Journal of Structural Geology 25 (2003) 1855-1873
Fig. 11. Composite fabric of FIP rotated to the pre-fold orientation for the (A) middle portion of the damage zone (MDZ) and (B) five samples from the limbs of the Punchbowl syncline furthest from the ultracataclasite layer. Compared with the present day fabrics in the MDZ (Fig. 10C) and in the samples from the limbs of the Punchbowl Syncline, the prefolding fabrics are more random (see text). Symbols are the same as in Fig. 10. Lower- hemisphere equal-area projections with N at top. Density contour interval is one sigma beginning with two sigma. Number of data indicated. The orientation of bedding varies 166° in strike and 50° in dip for the five samples taken at distances greater than
Fig. 11. Composite fabric of FIP rotated to the pre-fold orientation for the (A) middle portion of the damage zone (MDZ) and (B) five samples from the limbs of the Punchbowl syncline furthest from the ultracataclasite layer. Compared with the present day fabrics in the MDZ (Fig. 10C) and in the samples from the limbs of the Punchbowl Syncline, the prefolding fabrics are more random (see text). Symbols are the same as in Fig. 10. Lower- hemisphere equal-area projections with N at top. Density contour interval is one sigma beginning with two sigma. Number of data indicated. The orientation of bedding varies 166° in strike and 50° in dip for the five samples taken at distances greater than
Fig. 12. Orientations of microfractures predicted by models of fault growth and wear for the Punchbowl fault. Great circle shows orientation of the Punchbowl! fault; diamonds show the orientation of the Punchbowl fault b- axis, normal and slip direction assuming a N65°W strike, 65°SW dip, and 35° rake to the SE. Lower-hemisphere equal-area projections with N at top.
Fig. 12. Orientations of microfractures predicted by models of fault growth and wear for the Punchbowl fault. Great circle shows orientation of the Punchbowl! fault; diamonds show the orientation of the Punchbowl fault b- axis, normal and slip direction assuming a N65°W strike, 65°SW dip, and 35° rake to the SE. Lower-hemisphere equal-area projections with N at top.
Fig. 13. Comparison of fault model predictions and the composite fabric of all microfracture types in the (A) inner damage zone and fault core (IDZ- FC) domain, and (B) for the middle portion of the damage zone (MDZ) domain. Symbols the same as in Fig. 12. Lower-hemisphere equal-area projections with N at top. Number of data indicated.
Fig. 13. Comparison of fault model predictions and the composite fabric of all microfracture types in the (A) inner damage zone and fault core (IDZ- FC) domain, and (B) for the middle portion of the damage zone (MDZ) domain. Symbols the same as in Fig. 12. Lower-hemisphere equal-area projections with N at top. Number of data indicated.
Fig. 14. Comparison of fault model predictions and the composite fabric of all FIP in the outer portion of the damage zone (ODZ) domain. Symbols the same as in Fig. 12. Lower-hemisphere equal-area projections with N at top. Number of data indicated. : Inspection of the fabric of FIP in samples at d istances from the ultracataclasite ranging between 10 and 480m show evidence of a spatially homogeneous fabric (Fig. 8). On the basis of microfracture intensity traverse d ata, the sample interval between 10 and 480m would cover the outermost damage zone (ODZ) and boundary with the undeformed host rock (Fig. 6). The FIP fabric in t he ODZ displays two sets, as shown by the composite fabric diagram for the six samples (Fig. 14). One set is perpendicular to the
Fig. 14. Comparison of fault model predictions and the composite fabric of all FIP in the outer portion of the damage zone (ODZ) domain. Symbols the same as in Fig. 12. Lower-hemisphere equal-area projections with N at top. Number of data indicated. : Inspection of the fabric of FIP in samples at d istances from the ultracataclasite ranging between 10 and 480m show evidence of a spatially homogeneous fabric (Fig. 8). On the basis of microfracture intensity traverse d ata, the sample interval between 10 and 480m would cover the outermost damage zone (ODZ) and boundary with the undeformed host rock (Fig. 6). The FIP fabric in t he ODZ displays two sets, as shown by the composite fabric diagram for the six samples (Fig. 14). One set is perpendicular to the
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GeologyStructural GeologyFault Damage ZoneFault MechanicsFault growth
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