Fern Beetle-Moorcroft July 14, 2013
Bryn Mawr Summer Science Abstract
Advisor: Arlo Weil
The Baha British Columbia Hypothesis: Fact or Fiction?
The Baha British Columbia (B.C.) hypothesis states that much of present-day B.C. was situated alongside Southern California and Northern Mexico in the middle Cretaceous and was displaced northward during the Late Cretaceous/Paleocene by the north-oblique convergence of the Kula plate with North America. The terranes that now makeup B.C. arrived at their present-day location by the early Eocene (Housen and Beck, 1999). This hypothesis derives primarily from the observed incongruous paleomagnetic directions of the Insular and Intermontane terranes, which have been interpreted to signify post-mid-Cretaceous northward transport of up to 4000 km. More recently, however, it has been concluded that the observed paleomagnetic directions in plutonic rocks found near Prince Rupert B.C. were primarily the result of local deformation as opposed to northward transport along the margin of North America. This new hypothesis is further supported by paleomagnetic data from Cretaceous rocks in Alaska (Duke Island and MacColl Ridge), which signify smaller estimates of latitudinal motion than previously suggested by the Baha B.C. hypothesis (Butler and Gehrels, 2001).
Currently, there are not enough data to concretely determine whether the Baha B.C. hypothesis is fact or fiction. To further test the Baja-B.C. hypothesis, I will sample the volcanic rocks from exotic terranes that are now preserved in Princeton and Vancouver Island, British Columbia. In Princeton, located in the interior of B.C., we will sample Triassic/Jurassic age volcanics and volcano-clastic rocks. Back in the lab we will conduct fold and conglomerate tests to determine the relative age of magnetization acquisition, and if a primary magnetization is determined we will be able to determine the relative paleo-latitude of the terrane with respect to stable North America. On Vancouver Island, we will sample the Bonanza volcanics, which are Jurassic in age and make-up part of the Bonanza Arc assemblage. Sampling at these two localities will allow us to further test models of terrane translation during the latest Cretaceous and early Tertiary, and to ultimately better constrain the tectonic evolution of the western Cordillera.