Editing Coast Mountains (section)

====Coast Range Arc eruptive period====
{{Main|Coast Range Arc}}
The final event began when the [[Farallon Plate]] continued to subduct under the new continental margin after the Insular Plate and Insular Islands collided with the old continental margin, supporting a new continental volcanic arc called the [[Coast Range Arc]] about 100 million years ago during the [[Late Cretaceous]] period.<ref name="KO">{{cite book | last = Stowell | first = Harold H. |author2=McClelland William C. | title = Tectonics of the Coast Mountains, Southeastern Alaska and British Columbia |publisher = [[Geological Society of America]] |page = 101 |url = https://books.google.com/books?id=5SgAthT0MuAC&q=tectonics+of+the+Coast+Mountains+southeastern+Alaska+and+British+Columbia |isbn = 0-8137-2343-4 |access-date =2008-09-04| date = 2000-01-01 }}</ref> Magma rising from the Farallon Plate under the new continental margin ascended through the newly accreted Insular Belt, injecting huge quantities of granite into older igneous rocks of the Insular Belt.<ref name="AD"/> At the surface, new volcanoes were built along the continental margin.<ref name="AD"/> Named after the Coast Mountains, the basement of this arc was likely Early Cretaceous and [[Late Jurassic]] intrusions from the Insular Islands.<ref name="KO"/>

[[Image:Late Cretaceous Coast Mountains plate tectonics.jpg|thumb|right|Plate tectonics of the Coast Range Arc about 75 million years ago]]
One of the major aspects that changed early during the Coast Range Arc was the status of the northern end of the Farallon Plate, a portion now known as the [[Kula Plate]].<ref name="AD"/> About 85 million years ago, the Kula Plate broke off from the Farallon Plate to form a [[mid-ocean ridge]] known to geoscientists as the [[Kula-Farallon Ridge]].<ref name="AD"/> This change apparently had some important ramifications for regional geologic evolution. When this change was completed, Coast Range Arc volcanism returned and sections of the arc were uplifted considerably in latest Cretaceous time.<ref name="SI">[https://web.archive.org/web/20170420060002/https://books.google.com/books?id=AAZBokqaWj8C&pg=PA66&lpg=PA66&dq=Coast+Mountains+origins&source=web&ots=Gjg_FBlH2R&sig=mHwPx7nmsQV2KxRG-YW7tQ9_e5o&hl=en&sa=X&oi=book_result&resnum=1&ct=result Geology of a Transpressional Orogen Developed During Ridge-Trench ... - Google Books]. Books.google.ca. Retrieved on 2013-07-21.</ref> This started a period of mountain building that affected much of western North America called the [[Laramide orogeny]].<ref name="AV">{{cite web | title = Laramide orogeny | publisher = [[Encyclopædia Britannica, Inc.]] | year = 1998 | url = http://tlacaelel.igeofcu.unam.mx/~GeoD/colision/figs/orogeny/laramide.html | access-date = November 16, 2008 | url-status = dead | archive-url = https://web.archive.org/web/20090526224324/http://tlacaelel.igeofcu.unam.mx/~GeoD/colision/figs/orogeny/laramide.html | archive-date = May 26, 2009 }}</ref> In particular a large area of dextral transpression and southwest-directed thrust faulting was active from 75 to 66 million years ago.<ref name="SI"/> Much of the record of this deformation has been overridden by [[Tertiary]] age structures and the zone of Cretaceous dextral thrust faulting appears to have been widespread.<ref name="SI"/> It was also during this period when massive amounts of molten granite intruded highly deformed ocean rocks and assorted fragments from pre-existing island arcs, largely remnants of the Bridge River Ocean.<ref name="AD"/> This molten granite burned the old oceanic sediments into a glittering medium-grade [[metamorphic rock]] called [[schist]].<ref name="AD"/> The older intrusions of the Coast Range Arc were then deformed under the heat and pressure of later intrusions, turning them into layered metamorphic rock known as [[gneiss]].<ref name="AD"/> In some places, mixtures of 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.<ref name="AD"/>

Volcanism began to decline along the length of the arc about 60 million years ago during the [[Albian]] and [[Aptian]] [[faunal stage]]s of the Cretaceous period.<ref name="KO"/> This resulted from the changing geometry of the Kula Plate, which progressively developed a more northerly movement along the [[Pacific Northwest]].<ref name="AD"/> Instead of subducting beneath the Pacific Northwest, the Kula Plate began subducting underneath southwestern Yukon and Alaska and during the early [[Eocene]] period.<ref name="AD"/> 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.<ref name="AD"/> 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 present Coast Mountains.<ref name="AD"/> During construction of intrusions 70 and 57&nbsp;million years ago, the northern motion of the Kula Plate might have been between {{convert|140|mm|in|0|abbr=on}} and {{convert|110|mm|in|0|abbr=on}} per year.<ref name="KC">{{cite web|publisher=[[University of Arizona]]|url=http://www.geo.arizona.edu/tectonics/Ducea/Batholiths/Tectonics.htm|title=Tectonic overview of the CPC|access-date=2008-09-07}}</ref> However, other geologic studies determined the Kula Plate moved at a rate as fast as {{convert|200|mm|in|0|abbr=on}} per year.<ref name="KC"/>