Carolina Chang

B.Sc. (Honours) Thesis

LOW TEMPERATURE THERMAL HISTORY OF MAINLAND NOVA SCOTIA USING APATITE AND ZIRCON (U-TH)/HE THERMOCHRONOLOGY

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Passive margins are the transition between continental and oceanic crust. Their formation begins with continental rifting, sedimentation in the syn-rift basins, may include magmatic sequences, and seafloor spreading at which point the faults are no longer active and the margin is considered passive. During the supercontinent configuration of Pangaea, Nova Scotia was sutured to Morocco and began to rift apart in the late Triassic and separated by the early-mid Jurassic, when the margin became passive and the Atlantic Ocean began to open.'BR.'BR. Recently, investigation of structural relationships and low temperature thermochronology in passive margins has revealed that there are in fact reactivated faults at multiple localities on the Atlantic margins; of interest for this project is the Nova Scotian and US margin where km-scale post-rift vertical movements are observed. In comparison to the US, the Scotian margin has a largely subdued topography and represents the transition from volcanic margin to the south and non-volcanic to the north. Cooling ages in the New England White Mountains obtained using apatite fission track analysis yield Cretaceous ages that researchers propose may be a result of small scale asthenospheric convection or changing orientation of seafloor spreading. In Nova Scotia, cooling ages are Triassic and Jurassic. Differences between the two proximal margins raise the question of what processes are responsible for their respective ages and whether those processes take place in both the US and Scotian margin. The US margin can be used as a valuable comparison since it has been more extensively investigated compared to the Canadian extension.'BR.'BR. The objective of this project is to constrain the thermal history of southern mainland Nova Scotia using apatite and zircon (U-Th)/He analysis, which yields the age at which a sample cooled beyond ~70 ˚C and 185 ˚C, respectively. Five bedrock samples collected revealed cooling beyond 185 ˚C occurred at 220 Ma and beyond 70 ˚C at 188.4 Ma. Cooling rates are one order of magnitude greater during cooling from 185 – 70 ˚C than 70 ˚C to mean surface temperature, suggesting Nova Scotia’s low temperature thermal history is dominated by post-rift erosion unlike the US passive margin.

Keywords: Thermochronology, Nova Scotia, passive margin, (U-Th)/He analysis
Pages: 72
Supervisor: Isabelle Coutand