List of Figures

1. Geologic map showing the location of the Cerro de Costilla complex.
2. Bedding and foliation data in the southern portion of the Cerro de Costilla complex.
3. Minor grain boundary migration in plagioclase.
4. Typical quartz microstructures.
5. Biotite aggregate in the least deformed tonalite with granular titanite grains.
6. Bent, recrystallized biotite grain.
7. Biotite partially replaced by symplectic plagioclase and titanite.
8. Lobes of fine-grained myrmekite (x) replacing K-feldspar.
9. Biotite, plagioclase and quartz forming incipient folium between grains of plagioclase.
10. Subgrains and new grains along grain boundaries and fractures in primary plagioclase.
11. A single plagioclase grain broken into three pieces.
12. Biotite and quartz growing filling fractures in a primary plagioclase grain.
13. Thinning and internal deformation of a biotite grain to form a new folium.
14. Biotite grain bent, deformed and recrystallized into a developing foliation.
15. Hornblende partially replaced by biotite and fragmented into a folium.
16. Continuous foliae of biotite and quartz with small fragments of titanite, epidote and hornblende.
17. Biotite and quartz ‘beards’ on plagioclase
18. Biotite grain cut through by a foliae to which it contributes by recrystallizing into aligned new grains.
19. Development of an S/C-type fabric around plagioclase grains.
20. Blue-green hornblende, biotite and quartz form a ‘beard’ between pulled apart fragments of green-brown hornblende.
21. Hornblende grain necked down, fragmented and partly replaced by biotite.
22. Foliae formed mainly of titanite fragments with some quartz and minor biotite.
23. Biotite cut by a folium containing titanite and disaggregated plagioclase-titanite symplectite.
24. Anastomosing foliae forming an S/C-type fabric around plagioclase grains.
25. Fine-grained biotite, plagioclase, quartz and titanite folium linking biotite foliae.
26. ‘Ribbons’ of recrystallized quartz
27. Plagioclase clast with ‘beard’ of biotite and quartz.
28. Plagioclase clast with ‘beard’ of biotite and quartz.
29. Plagioclase clast with ‘beard’ of biotite and quartz extending into a folium.
30. Shattered plagioclase clast with infilling of quartz.
31. Plagioclase-quartz symplectite (x) replacing plagioclase.
32. Fine-grained, biotite-rich matrix in the most strongly deformed rock.
Table 1.
33. Bulk chemistry from interior to margin of the shear zone.
34. Isocon plot of average interior and marginal bulk compositions across the shear zone.
Table 2.
Table 3.
35. Chemistry of major minerals across the shear zone.
36. Modal mineralogy from the interior to the margin of the shear zone.
37. Backscattered electron image showing symplectic plagioclase, biotite and titanite replacing primary biotite.
Table 4.
Table 5.
38. Two component mixing model for undeformed Cerro de Costilla tonalite and host granitic orthogneiss.
39. Coupling of deformation, reaction and diffusion/advection in the transformation of tonalite to mylonite.
  Index