ROTATING OUT OF RODINIA: PALEOMAGNETIC EVIDENCE FOR A 50 DEGREE CRYOGENIAN-EDIACARAN ROTATION OF THE YUKON STABLE BLOCK RELATIVE TO LAURENTIA

Understanding the breakup of the Proterozoic supercontinent Rodinia is crucial for testing links between tectonics and climate, plumes, and the evolution of life. Rifting on the northern and western margins of Laurentia, at the core of Rodinia, can be distinguished by studying the strata exposed on the Yukon stable block. However, potential movement of the para-authochthonous Yukon block relative to autochthonous Laurentia along the Snake River fault complicate interpretations of breakup geometry and timing. Here we present new paleomagnetic data from the ca. 717 Ma Mount Harper Volcanic Complex, located on the Yukon block, that speaks to its movement. Four paleomagnetic directions were isolated: a low-temperature direction recording the present geomagnetic field, a mid-temperature direction consistent with a Cretaceous overprint, and two high-temperature directions. Of the two high-temperature directions, one likely represents a chemical overprint, while the other direction is interpreted to be primary. This primary pole is distinct from the expected ca. 720 Ma Laurentian pole derived from the Franklin large igneous province (Denyszyn et al. 2009). The two poles can be aligned via an approximately 50 degree counterclockwise rotation of the Yukon stable block relative to Laurentia. As well as resolving this paleomagnetic data, counterclockwise rotation and dextral displacement between the Yukon block and Laurentia along the Snake River fault resolves a set of previously perplexing geological observations. Particularly, the proposed tectonic motion aligns paleo-flow measurements in Paleoproterozoic strata, Neoproterozoic fault orientations, and facies belts of the Yukon block with those of Laurentia. We propose that the rotation was Ediacaran in age, accommodated by the opening of the Richardson trough, and coincided with the initiation of the Selwyn basin and final rifting on the western Laurentian margin. With this rotation, Neoproterozoic Laurentian tectonic events can be divided into three distinct stages: 1) the development of an aulacogen during early Neoproterozoic rifting of the northern margin; 2) formation of narrow basins and localized folding during Cryogenian dextral transtension and transpression; and 3) Ediacaran rifting on the western margin.