Apr
18

Eclogitization and Shear Zone Kinematics: Conclusions

It has been a long research process but an incredibly rewarding one. Below are the conclusions I was able to draw from my results and analyses:

The rocks both within SZ2 and adjacent to it derive from the same gabbroic-gabbronoritic host protolith based on a variety of petrologic data and analyses. The rocks are massive outside of the shear zone and are mylonitic within the shear zone, are all metaluminous with prominent Eu-anomalies and are olivine-normative. Mylonites exhibit an amphibolite-facies overprinting of their original mafic mineral assemblage, as well as the massive rocks outside of the NE boundary of the zone. There was essentially no volume change during deformation and densities across the zone remained invariable. Structural data, analyses, and observations show that SZ2 experienced general shear (Wm = 0.9) during shear zone formation and can be classified as a left-lateral, ductile shear zone. 3D strains yield apparent flattening and denote moderate-strong oblate strain. Displacement for the zone was relatively low (D = ~30 m) due to the incorporation of zone normal shortening during shearing and low applied stresses.

The interpretation of these data in conjunction with information from previous works and qualitative observations suggests that as the original plutons were emplaced and subducted during the Caledonian Orogeny, there were seismically-induced cracks that allowed for fluid-mediated strain weakening at eclogite-facies metamorphic conditions. This spurred dynamic recrystallization and shear zone formation. Amphibolite-facies overprinting occurred after this eclogite-facies shear zone formation as the rocks were beginning to exhume. This points towards crustal weakening during this time at both large, orogenic-scales and smaller scales through fluid-injection and resultant, low-displacement shearing.

Further research could be devoted towards further chemical analyses of the sparse pyroxene grains found within SZ2 as well as a vorticity analysis and strain analysis for the remaining shear zones in the Nusfjord area and on other islands in Lofoten. Instances where evidence of deep crustal processes get exhumed for observation and study today (such as eclogite-facies shear zones) are rare and extremely limited. Thus, their study and interpretation are vital to furthering our understanding on the small-scale and tectonic levels.

 

This research would not have been possible without the financial support of the College of William & Mary’s Roy R. Charles Center for Academic Excellence. I would like to thank Dr. Christopher Bailey and Dr. Brent Owens for their unwavering support, expertise, and guidance during this research process. Special thanks should also be given to Cecilia Hurtado and Mark Simonds for their help with various softwares and figure design.

Speak Your Mind

*