DI020-0003
Mesoarchean deposition age for diamond-bearing metasediment of the northwestern Slave craton, Nunavut Territory (Canada)
Abstract:
Here we provide a maximum depositional age for this metasediment using LASS measurements of U–Pb/Hf isotopes on zircon from the metasediment. Cathodoluminescence imaging reveals that most grains have dull internal micro-structures, while back-scattered imaging indicates an abundance of fractures. U–Pb isotopes on the least altered zircon domains of 119 analyses indicate a maximum deposition age of 2964 ± 9 Ma. Older zircon cores show crystallization dates up to ca. 3.5 Ga. Complementary Hf isotope analyses, from the same zircon domains used for U–Pb isotope measurements, indicate a chondritic to slightly sub-chondritic Hf isotopes signature.
The restricted age range of the zircon grains (clustering near 2.96 Ga) suggests that the detritus was derived from a catchment that was likely characterized by small size and little variability in age structure – features broadly consistent with a first-stage erosion cycle from a newly exposed continent. Restricted provenance, and the near-chondritic Hf isotope composition of detrital zircon, together indicates that the diamonds, and gold now found in the region, were likely sourced nearby from one of the Mesoarchean building blocks to the Slave craton. This finding supports the idea that, by ~ 2.95 Ga, a thick, diamond-bearing lithospheric mantle was present beneath a part of the Slave craton [1] that was likely sampled by deeply derived mantle magma. Future work will be required to evaluate the relationship between continental exposure, the origin of detrital gold and the ages of the diamond-bearing lithospheric root, with implications for the timing and mechanisms of craton evolution.
[1] Helmstaedt and Pehrsson, (2012) Geological Association of Canada, Special Paper 49.