older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat, weight and stress to create unusual swirled patterns known as migmatite, appearing to have been nearly melted in the procedure. Volcanism began to decline along the length of the arc about 60 million years ago during the Albian and Aptian faunal stages of the Cretaceous period. This resulted from the changing geometry of the Kula Plate, which progressively developed a more northerly movement along the mainland of Western Canada. Instead of subducting beneath Western Canada, the Kula Plate began subducting underneath southwestern Yukon and Alaska during the early Eocene period. Volcanism along the entire length of the Coast Range Arc shut down about 50 million years ago and many of the volcanoes have disappeared from erosion. What remains of the Coast Range Arc to this day are outcrops of granite when magma intruded and cooled at depth beneath the volcanoes, forming the Coast Mountains. During construction of intrusions 70 and 57 million years ago, the northern motion of the Kula Plate might have been between and per year. However, other geologic studies determined the Kula Plate moved at a rate as fast as per year. Cascadia subduction zone complexes As the last of the Kula Plate decayed and the Farallon Plate advanced back into this area from the south, it once again started to subduct under the continental margin of Western Canada 37 million years ago, supporting a chain of volcanoes called the Cascade Volcanic Arc. At least four volcanic formations along the British Columbia Coast are associated with Cascadia subduction zone volcanism. The oldest is the eroded 18-million-year-old Pemberton Volcanic Belt which extends west-northwest from south-central British Columbia to Haida Gwaii in the northeast where it lies west of mainland British Columbia. In the south it is defined by a group of epizonal intrusions and a few erosional remnants of eruptive rock. Farther north in the large Ha-Iltzuk and Waddington icefields, it includes two large dissected calderas called Silverthrone Caldera and Franklin Glacier Complex while Haida Gwaii to the northeast contains a volcanic formation ranging in age from Miocene to Pliocene called the Masset Formation. Although widely separated from each other, all Pemberton Belt rocks are of similar age and have similar magma compositions. Therefore, these magmatic rocks are believed to be products of arc volcanism related to subduction of the Farallon Plate.