Extensional Structures in the Queen Elizabeth Islands and their Implications for Evolution of the Amerasia Basin

Carol Evenchick

Evolution of the Amerasia Basin is controversial owing to the paucity of data to constrain the details of timing and geometry of rifting and seafloor spreading. Although rotational opening of the basin is accepted by some workers, a number of questions remain owing to the lack of well defined magnetic stripes, and the large magnetic anomaly associated with the High Arctic Large Igneous Province. The latter effectively obscures older features that may have constrained orientations and ages of spreading in the northern Amerasia Basin. Data and interpretations from onshore regions bounding the Amerasia Basin have the potential to contribute insight into its geodynamic evolution by providing ages of specific events. For example, dykes and faults of known age can be used to interpret the regional stress at that specific time. Where those features are spatially associated with aeromagnetic anomalies, the anomalies can be interpreted with more confidence. In this paper we describe and interpret the relationships between igneous rocks, extensional structures, and aeromagnetic anomalies on Ellef Ringnes Island, in the Queen Elizabeth Islands, CA. New field data reveal the significance of a suite of faults that are interpreted to be extensional. They are parallel with, and occur in the same area as, mafic dykes and sills, and linear magnetic anomalies. We consider these features to be cogenetic. The intrusions are part of the Cretaceous Queen Elizabeth Islands dyke swarm, one element of the High Arctic Large Igneous Province. Their intrusion may have been coeval with gabbro (ca. 126 Ma) in evaporite domes on the island, or one of the newly recognized stratigraphic horizons of volcanic rock on the island. The volcanic rocks occur in the lower Isachsen Fm, middle and top of the Christopher Fm, and base of Hassel Fm. To better understand the significance of the intrusions and faults, we examine the regional distribution of extensional features along the eastern margin of the Amerasia Basin. Dykes of the Queen Elizabeth Islands swarm, and magnetic anomalies associated with them, have been suggested to define a giant radiating dyke swarm originating at or near the Alpha Ridge. Some workers suggest that the radiating dyke swarm is a direct result of breakup and initiation of the Amerasia Basin. The Ellef Ringnes extensional features are subparallel with one arm of a radiating swarm, but they are also part of a belt of parallel (not radiating) extensional features that overlaps >1000 km of the eastern margin of the Amerasia Basin. Thus an alternate interpretation for the extensional structures from Ellef Ringnes to Melville Island is that they were geodynamically related to spreading in the Amerasia Basin. A challenge for either interpretation is that parts of the Queen Elizabeth Islands swarm do not fit the orientations of either a radiating or parallel pattern; some fan in the opposite direction to a swarm radiating from the Alpha Ridge.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013