2-2-2-2-2-2-2-2-2-2-2-2-2 From: James Jackson <jackson.js@xxxxxxxxxxx> Initiation and Evolution of Arc-Forearc systems in Cascadia and Beyond Session Number T7 Session Type:Oral Questions? contact mdarin@xxxxxxx Endorser(s):GSA Structural Geology and Tectonics Division; GSA Sedimentary Geology Division; GSA Geophysics and Geodynamics Division This session explores the tectonic, magmatic, sedimentary, and paleogeographic evolution of the Cascadia arc and forearc system from the early Eocene through the Miocene. Examples from analogous modern or ancient subduction margins are also encouraged. Decades of work along the Cascadia margin (USA) have provided valuable insights into the geologic evolution of the Pacific Northwest, as well as essential operative processes at ocean-continent convergent margins such as arc magmatism, forearc basin development, and accretionary wedge dynamics. Despite its reputation as a classic example of a well-behaved subduction margin, the evolution of Cascadia has been complicated by a profound tectonic reorganization since the early Eocene involving spreading ridge and plate reconfigurations, subduction initiation, rapid sedimentation and basin formation, shifting depositional systems, complex faulting, folding and vertical-axis rotations, and interactions between arc- and plume- related magmatism. Fundamental aspects of the tectonic evolution of this iconic subduction zone are not well understood. For instance: When did the Ancestral Cascade arc initiate, and how did it affect sedimentary depositional systems and paleogeography? How did basin subsidence, sedimentation, deformation and surface uplift vary along strike of the margin during and after subduction initiation? How did plate boundary reorganization, the Yellowstone plume, and other geodynamic mechanisms modulate topography and base level, and what effects did they have on depositional systems? What is the nature and origin of Siletzia, and is it an autochthonous or allochthonous terrane? A multi-disciplinary session integrating studies from along the Cascadia margin that examine the interplay between tectonics, magmatism, sedimentation, and geodynamics would be an important step forward in unravelingthe complex geologic history of this world- class subduction margin. We welcome contributions that summarize stratigraphic, structural, paleontologic, geochronologic, geophysical and other data sets that provide new insights into the tectonic and paleogeographic evolution of Cascadia. We particularly seek submissions that examine the age, correlation, and tectonostratigraphic evolution of pre-arc and forearc basin depositional systems (e.g., Umpqua, Chuckanut, Clarno, Tyee, Coaledo, etc.), and the space-time evolution of arc (e.g., Challis, Ancestral Cascades), transitional (Clarno), and hotspot (Yellowstone) magmatism. Examples from analogous modern or ancient convergent margins and numerical modelling studies are also invited, especially those focused on intrinsic geodynamic processes that influence upper-plate deformation, sedimentation, and magmatism in continental arc settings. 2-2-2-2-2-2-2-2-2-2-2-2-2 ------------------------------
