Structural analysis of Archean rocks in the Negaunee area, Michigan: Constraints on Archean versus early Proterozoic deformation

Abstract

Ol Introduction Ol Regional geology and tectonic framework O3 Archean O3 Early Proterozoic O3 Rock units and lithologies O3 Archean Rocks O4 Kitchi Schist O4 Mona Schist OS Undifferentiated greenstone OS Compeau Creek Gneiss O6 Dead River pluton O6 Reany Creek Formation O6 Early Proterozoic rocks O6 Metamorphism O6 Structural features and their geometries O6 Structural correlation with adjacent areas O6 Structural domains and analyzed features O6 Regional 82 foliation and F2 folding O7 Domain I O7 Domain II O7 Domain III O7 03 north-side-up, dip-slip shear zones O8 Distribution and timing of 03 shearing O8 Carp River Falls shear zone (domain I) Oil Dead River shear zone (domain III) O12 03 shear zones in domain II O12 04 structures O13 D4 crenulations O13 D4 kink bands O13 D4 strike-slip shearing O14 Early Proterozoic folding, domain II O15 Early Proterozoic reactivation of shear zones O16 Finite strain analysis O16 Introduction O16 Kitchi Schist and lower member of the Mona Schist O17 Sheared rhyolite tuff member of the Mona Schist O18 Early Proterozoic metasedimentary rocks O18 Kinematic framework of the deformations O18 Focus of discussion and results O18 Archean deformations O19 D2 deformation O19 D3 deformation O19 D4 deformation O21 Relationship of D4 features to shear zones O21 Stress orientations and kink band development 021 Early Proterozoic deformation O22 Effects of Early Proterozoic deformation on Archean basement rocks O23 Contents III Interpretation of finite strain data O23 Strains in domain I O23 D2 fabrics and finite strains O23 Effects of D3 shearing O24 Strains in domain III O24 Type-a rhyolite O25 Type-b rhyolite O25 Implications for Archean tectonic history O26 Summary and conclusions O27 References cited O27 FIGURES 1. Regional geologic map of Upper Michigan O2 2. Geologic map of the Negaunee study area O4 3. Map outlining structural domains within the study area O8 4. Equal-area projections of D2 fabric elements O9 5. Photomicrograph of F2 crenulations and 82 cleavages O10 6. Photograph of F2 folds in basalt O10 7. Equal-area projections of 83 foliation poles Oil 8. Photograph of 03 en-echelon tension veins O12 9. Photomicrograph of asymmetrical pyrite porphyroclast deformed during 03 O12 10. Photomicrograph of sigma porphyroclasts formed during 03 O13 11. Equal-area projection of D4 crenulation hinge lines O14 12. Photograph of D4 kink bands O14 13. Schematic drawing of conjugate kink bands O15 14. Equal-area projections of D4 kink planes and kink hinges O15 15. Photograph of asymmetrical (D4) fold in a 03 shear zone O16 16. Equal-area projections of Early Proterozoic fabric elements and Early Proterozoic finite strain axes O17 17. Equal-area projection of finite strain axes and Flinn diagram of finite strains from domain I O19 18. Equal-area projections of finite strain axes and D4 stretching lineations, and Flinn diagram of finite strains from domain III O20 19. Equal-area projection of ai orientations estimated from D4 kink bands, and sketch of D4 kink band model O22 20. Schematic mode...