Quantifying the Stability of Continents Using Advances in (U/Th)/He, 4He/3He and U/Pb Apatite Thermochronometry

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At active plate margins, high denudation rates (up to 1 cm/yr) and rapid topographic evolution have been documented. In contrast, billions of years have passed since major tectonic activity perturbed some continental interiors. However, it is now clear that even these apparently stable cratonic cores undergo low amplitude episodes of burial and unroofing, linked to distant tectonic processes and changing patterns of interplate coupling and mantle flow. In this project, recent advances in (U-Th)/He and 4He/3He apatite thermochronometry are being used to investigate thermochronological and geological evidence for Phanerozoic burial and unroofing in portions of the western Canadian shield (Churchill province and Slave craton), which is currently devoid of Phanerozoic cover. Recent recognition of radiation damage control on (U-Th)/He apatite dates holds the promise of deciphering additional portions of the thermal history by investigating apatites with a range of closure temperatures (current data suggests approximately 50-115 degrees C) from the same crustal level. The 4He/3He apatite thermochronometer is sensitive to temperatures lower (down to 30-40 degrees C) than those accessible by other methods, and thus can detect the more subtle changes in thermal regimes that may be preserved within continental interiors. This integrated approach will be used to: 1) carry out a targeted study in the western Churchill province to follow up on provocative preliminary thermochronological evidence for Phanerozoic reburial and unroofing, and 2) commence a reconnaissance investigation of the Slave craton to evaluate the thermochronologic signature of Phanerozoic reburial known to have occurred by recognition of xenoliths of Phanerozoic cover entrained in kimberlite pipes.The results of this project will provide fresh insight into links between surface and lithospheric histories in continental interiors that have not been traditionally investigated using (U-Th)/He techniques. Burial and erosional episodes at the surface may correlate with the intrusion of kimberlite pipes from great depths that are the source of the world's diamonds, depending on the geodynamic driver for enigmatic kimberlite genesis. Understanding the causes of burial and unroofing in continental interiors also may provide basic information about the occurrence of Phanerozoic basinal sequences within cratonic North America that are an important source of fossil fuels.