For permission to copy, contact editing@geosociety.org  2003 Geological Society of America 867 GSA Bulletin; July 2003; v. 115; no. 7; p. 867–880; 7 figures. Life and death of the Resurrection plate: Evidence for its existence and subduction in the northeastern Pacific in Paleocene–Eocene time Peter J. Haeussler ² Dwight C. Bradley U.S. Geological Survey, 4200 University Drive, Anchorage, Alaska 99508, USA Ray E. Wells U.S. Geological Survey, 345 Middlefield Drive, Menlo Park, California 95064, USA Marti L. Miller U.S. Geological Survey, 4200 University Drive, Anchorage, Alaska 99508, USA ABSTRACT Onshore evidence suggests that a plate is missing from published reconstructions of the northeastern Pacific Ocean in Paleocene– Eocene time. The Resurrection plate, named for the Resurrection Peninsula ophiolite near Seward, Alaska, was located east of the Kula plate and north of the Far- allon plate. We interpret coeval near-trench magmatism in southern Alaska and the Cascadia margin as evidence for two slab windows associated with trench-ridge- trench (TRT) triple junctions, which formed the western and southern bound- aries of the Resurrection plate. In Alaska, the Sanak-Baranof belt of near-trench in- trusions records a west-to-east migration, from 61 to 50 Ma, of the northern TRT tri- ple junction along a 2100-km-long section of coastline. In Oregon, Washington, and southern Vancouver Island, voluminous ba- saltic volcanism of the Siletz River Volca- nics, Crescent Formation, and Metchosin Volcanics occurred between ca. 66 and 48 Ma. Lack of a clear age progression of magmatism along the Cascadia margin sug- gests that this southern triple junction did not migrate significantly. Synchronous near-trench magmatism from southeastern Alaska to Puget Sound at ca. 50 Ma docu- ments the middle Eocene subduction of a spreading center, the crest of which was sub- parallel to the margin. We interpret this ca. 50 Ma event as recording the subduction- ² E-mail: pheuslr@usgs.gov. zone consumption of the last of the Resur- rection plate. The existence and subsequent subduction of the Resurrection plate explains (1) north- ward terrane transport along the south- eastern Alaska–British Columbia margin between 70 and 50 Ma, synchronous with an eastward-migrating triple junction in southern Alaska; (2) rapid uplift and vo- luminous magmatism in the Coast Moun- tains of British Columbia prior to 50 Ma related to subduction of buoyant, young oceanic crust of the Resurrection plate; (3) cessation of Coast Mountains magmatism at ca. 50 Ma due to cessation of subduction, (4) primitive mafic magmatism in the Coast Mountains and Cascade Range just after 50 Ma, related to slab-window magmatism, (5) birth of the Queen Charlotte transform margin at ca. 50 Ma, (6) extensional exhu- mation of high-grade metamorphic ter- ranes and development of core complexes in British Columbia, Idaho, and Washing- ton, and extensional collapse of the Cordil- leran foreland fold-and-thrust belt in Al- berta, Montana, and Idaho after 50 Ma related to initiation of the transform mar- gin, (7) enigmatic 53–45 Ma magmatism as- sociated with extension from Montana to the Yukon Territory as related to slab breakup and the formation of a slab win- dow, (8) right-lateral margin-parallel strike-slip faulting in southern and western Alaska during Late Cretaceous and Paleo- cene time, which cannot be explained by Farallon convergence vectors, and (9) si- multaneous changes in Pacific-Farallon and Pacific-Kula plate motions concurrent with demise of the Kula-Resurrection Ridge. Keywords: tectonics, Eocene, Kula plate, Farallon plate, North America, magmatism. INTRODUCTION Marine magnetic anomalies in the northern Pacific provide evidence for the existence of three plates and their associated spreading ridges during the early Tertiary: the Kula, Far- allon, and Pacific plates (Atwater, 1970; Grow and Atwater, 1970). However, subduction of a critical part of the anomaly record beneath North America destroyed what would be the most straightforward evidence for (1) the ge- ometry of the Kula-Farallon Ridge; (2) the lo- cation of its intersection with the continental margin, and (3) the possible existence of other ridges and plates in the region. The onshore geologic record is the sole remaining source of evidence for these features. Along the northeast Pacific margin, geolo- gists have long suggested that interactions with the Kula-Farallon Ridge could explain unusual near-trench Paleocene–Eocene mag- matism both in southern Alaska and the Wash- ington and Oregon coastal ranges—regions separated by 4000 km (Figs. 1, 2). In the Cascadia margin of coastal Oregon, Washing- ton, and southern Vancouver Island, geologists proposed that intersection of the Kula-Farallon Ridge with the continental margin (Fig. 1A)