STRATIGRAPHIC, STRUCTURAL AND GEOCHRONOLOGICAL CONSTRAINTS ON THE MAKE-UP AND BREAK-UP OF RODINIA (Invited Presentation)

Geological mapping and geochronology of Neoproterozoic successions in NW Canada and California have resulted in revisions to the timing and geometry of the formation and break-up of Rodinia.

In NW Canada, the 1100-850 Ma Pinguicula Gp (PG) is unconformably overlain by the 850-780 Ma Fifteenmile Gp (FG), which is broadly equivalent to the Mackenzie Mountains Sgp (MMSG). Large lateral facies changes in the FG and MMSG are the product of syn-sedimentary NNW-side-down normal faulting. The MMSG is in turn cut by ~780-660 Ma right-lateral structures that locally accommodate the Coates Lake and Rapitan Gps in transtensional grabens, and elsewhere fold the MMSG in structures assigned to the Corn Creek Orogeny. These structures are themselves cut by 660-635 Ma normal faults, which are capped by the basal Ediacaran Ravensthroat Dolostone. An additional unconformity-bound tectonostratigraphic unit and change in sedimentary source is present in upper Ediacaran strata.

In Death Valley, CA, the pre-1100 Ma lower Crystal Spring Fm is unconformably overlain by the 770-740 Ma upper Crystal Spring Fm, followed by the Beck Spring Dolomite, and the basal unit of the Kingston Peak Fm (KP1). These strata are overlain by the Virgin Spring Limestone and the 717-635 Ma portion of the Kingston Peak Fm (KP2-KP4); these also contain multiple angular unconformities of unknown duration. KP2-KP4 are capped by the basal Ediacaran Noonday Fm. An additional sedimentary break of unknown duration is associated with conglomerates at the base of the Johnnie Fm.

We propose a new model for the Neoproterozoic tectonic evolution of western North America. Beginning at 1100-850 Ma, the accretion of S. China provided a source of Grenville-age zircons and grains that fill the 1400-1600 Ma North American magmatic gap. We suggest that the 850-780 Ma extension in NW Laurentia is related to its proximity to the plume that Australia-S. China-Laurentia-Siberia passed over, which manifested itself sequentially in the Gaidner, Gubei, Gunbarrel, and Franklin LIPs. The whole of the western margin became active between 780 and 635 with right-lateral translation, resulting in a series of transtensional basins and transpressional folding. True rifting associated with significant crustal thinning and subsequent thermal subsidence did not occur until the latest Ediacaran.