{"id":8692,"date":"2026-02-24T00:09:06","date_gmt":"2026-02-24T00:09:06","guid":{"rendered":"https:\/\/tomeri.org\/notes\/?p=8692"},"modified":"2026-04-02T19:58:08","modified_gmt":"2026-04-02T19:58:08","slug":"ancient-landscapes-of-western-north-america-blakely-and-hanney","status":"publish","type":"post","link":"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/","title":{"rendered":"Ancient Landscapes of Western North America*, Blakely and Hanney"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">*<em>Ancient Landscapes of Western North America: A Geologic History with Paleogeographic Maps<\/em>, Ronald C. Blakely and Wayne D. Hanney. 2018.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-purple-color\"><em>February 2026<\/em><\/mark><\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_85 counter-hierarchy ez-toc-counter ez-toc-light-blue ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#About_the_Book\" >About the Book<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#The_Book\" >The Book<\/a><ul class='ez-toc-list-level-2' ><li class='ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C1_Introduction\" >C1. Introduction.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C2_Principles\" >C2. Principles<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C3_The_Cordilleras_Foundations_Paleoproterozoic_and_Mesoproterozoic_Periods_Ca_1800-1000_Ma\" >C3. The Cordillera&#8217;s Foundations: Paleoproterozoic and Mesoproterozoic Periods: Ca. 1800-1000 Ma.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C4_The_Cordilleras_Long-Lived_Passive_Margin_Neoproterozoic_to_Middle_Devonian_Periods_Ca_1000_Ma-400_Ma\" >C4. The Cordillera&#8217;s Long-Lived Passive Margin: Neoproterozoic to Middle Devonian Periods: Ca. 1000 Ma-400 Ma<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C5_The_Antler_Orogeny_and_the_First_Suspect_Terrane_Middle_Devonian_to_Late_Pennsylvanian_Ca_400-300_Ma\" >C5. The Antler Orogeny and the First Suspect Terrane: Middle Devonian to Late Pennsylvanian: Ca. 400-300 Ma<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C6_The_Amalgamation_of_Pangaea_and_the_Sonoma_Orogeny_Early_Permian_to_Early_Triassic_%E2%80%93_Ca_300-240_Ma\" >C6. The Amalgamation of Pangaea and the Sonoma Orogeny: Early Permian to Early Triassic &#8211; Ca. 300-240 Ma.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C7_The_Arrival_of_Wrangellia_and_the_Nevadan_Orogeny_Late_Triassic_to_Late_Jurassic_Ca_240-145_Ma\" >C7. The Arrival of Wrangellia and the Nevadan Orogeny: Late Triassic to Late Jurassic: Ca. 240-145 Ma<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C8_The_Continental_Arc_Sevier_Orogeny_Western_Interior_Seaway_and_Flat-Slab_Subduction_Cretaceous_Period_Ca_145-65_Ma\" >C8. The Continental Arc, Sevier Orogeny, Western Interior Seaway and Flat-Slab Subduction: Cretaceous Period: Ca. 145-65 Ma.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C9_Flat-Slab_Subduction_the_Laramide_Orogeny_Uplift_of_the_Colorado_Plateau_and_Rocky_Mountains_Paleocene_and_Eocene_Ca_65-35_Ma\" >C9. Flat-Slab Subduction, the Laramide Orogeny, Uplift of the Colorado Plateau and Rocky Mountains: Paleocene and Eocene: Ca. 65-35 Ma<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C10_Changing_Tectonics_Cooling_Climates_and_the_Dawn_of_Crustal_Extension_Late_Eocene_to_Early_Miocene_ca_35-20_Ma\" >C10. Changing Tectonics, Cooling Climates and the Dawn of Crustal Extension: Late Eocene to Early Miocene (ca. 35-20 Ma)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#Interlude_History_of_the_Farallon_Plate_by_Claude\" >Interlude: History of the Farallon Plate, by Claude<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C11_The_End_of_Cordilleran_Subduction_and_the_Formation_of_the_Basin_and_Range_Early_and_Middle_Miocene_Ca_20-10_Ma\" >C11. The End of Cordilleran Subduction and the Formation of the Basin and Range: Early and Middle Miocene: Ca. 20-10 Ma<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C12_Interior_Basins_Drainage_Integration_and_Deep_Incision_Late_Miocene_to_Pliocene_Ca_10-26_Ma\" >C12. Interior Basins, Drainage Integration and Deep Incision: Late Miocene to Pliocene: Ca. 10-2.6 Ma.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-16\" href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/#C13_The_North_American_Cordillera_Today_Pleistocene_Holocene_and_the_Anthropocene_Ca_26_Ma_to_Present\" >C13. The North American Cordillera Today: Pleistocene, Holocene and the Anthropocene: Ca. 2.6 Ma to Present.<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"About_the_Book\"><\/span>About the Book<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">This book is about the tectonic assembly, and I suspect the geomorphology, of what is now the Western United States. In particular, it will use paleogeographic maps \u2013 in which the first author is an expert \u2013 to describe the sequence of processes. Besides great maps, the book contains a lot of lovely pictures of geologic landscapes.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This book will have some overlap with the book on Canadian geology we read recently \u2013 Four Billion Years and Counting \u2013 and also with John McPhee&#8217;s <em>Assembling California<\/em>, which we read a couple of years ago. We being me and CJS.<\/p>\n\n\n\n<!--more-->\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"The_Book\"><\/span>The Book<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C1_Introduction\"><\/span>C1. Introduction.<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Reviews the aim and scope of the book.<\/li>\n\n\n\n<li>Covers a few fundamentals like the assembly of the North American Craton, and some of its subsequent development especially outside of the regions that will be the focus  of this book.<\/li>\n\n\n\n<li>The book is focused on the Cordillera, basic the region of North American including the western mountain belt, and areas to its west.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Other interesting bits<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>There&#8217;s a nice map of the North American Craton on page 4. It shows three Archean cratons collided about 2Ga, and are stitched together by accretionary orogens to form the earliest version of Laurentia. The next billion years saw the accretion of various terranes to the south and east of Laurentia. <\/li>\n\n\n\n<li>Parts of 2 of the 3 Archean cratons (and a little bit of extra crust) forms the Canadian Shield &#8212; <mark style=\"background-color:#f4ca16\" class=\"has-inline-color has-dark-gray-color\">I&#8217;m not sure what differentiates the Canadian Shield from the stitched together cratons &#8212; maybe it is the area of that region that is uncovered?.<\/mark> <\/li>\n\n\n\n<li>When terranes accrete to a continent the often create compressive pressure that initiate an orogeny.<\/li>\n\n\n\n<li><strong>Thrust\/Reverse faults <\/strong>occur when one block of crust is pushed up over another in response to compressional forces. It is called a  thrust fault if the angle is &lt; 45\u00b0, and reverse fault if \u2265 to 45\u00b0. <\/li>\n\n\n\n<li><strong>Detachment\/Normal faults <\/strong>occur when on block of crust moves down relative to the other because of extensional forces, with detachment being at a  &lt; 45\u00b0, and normal if \u2265 to 45\u00b0.  A detachment fault that flattens with depth is called a <strong>listric fault<\/strong><\/li>\n\n\n\n<li><strong>Autochthon\/Allochthon<\/strong>: The fault block that is thrust up over\/covered up by the other fault block.<\/li>\n\n\n\n<li><strong>The Colorado Plateau<\/strong> has remained fixed on the North American craton except for a slight rotation during the Cenozoic. (<mark style=\"background-color:#f4ca16\" class=\"has-inline-color\">Is it considered part of the craton or is it &#8216;on top&#8217; of it &#8212; how do you tell the difference?<\/mark>)<\/li>\n\n\n\n<li><strong>The Colorado <\/strong><b>Plateau<\/b> has remained fixed on the North American carton, excepting a slight rotation during the Cenozoic.<mark style=\"background-color:#f4ca16\" class=\"has-inline-color\"> Is the CP considered part of the NA craton or is it something that sits &#8216;on top&#8217; of it?<\/mark><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C2_Principles\"><\/span>C2. Principles<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This chapter reviews the basic principles one needs to understand the book. These include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Terranes<\/strong>.<em><mark style=\"background-color:#55c3dc\" class=\"has-inline-color\"> A terrane is a complete block of crust that can be shown to have completely different history, age, and origins than neighboring blocks<\/mark><\/em>. Terranes that are from far away are often referred to as <strong>exotic or suspect terranes.<\/strong> The concept was developed in the 1970&#8217;s. By the 1990&#8217;s hundreds of terranes had been described, and now the focus is more on groups of terranes. Terranes are classified in terms of their suspected origins, examples being continental fragments, volcanic arcs, mid-ocean plateaus, and so on. <\/li>\n\n\n\n<li><strong>Suturing and jumping. <\/strong>When a terrane collides with a continent the subduction zone often  &#8216;jumps&#8217; outward &#8212; i.e. the original terrane sutures to the continent and &#8216;clogs&#8217; the existing trench. <\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Sediment and sedimentary processes.<\/strong> Sedimentary environments are divided into<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>continental environments<\/strong>: rivers, lakes, eolian settings, and alluvial fans &#8212; usually quartz rich sandstone, mudstone, and shale<\/li>\n\n\n\n<li><strong>shoreline environments<\/strong>5: beaches, barrier bars, and tidal flats \u2013 usually sandstone, mudstone, and shale<\/li>\n\n\n\n<li><strong>offshore marine<strong> environments<\/strong>:<\/strong> Sandstone, mudstone and limestone; may show signs of bioturbation. <\/li>\n\n\n\n<li><strong>Deep water marine environments<\/strong>:  slope rise; abyssal plane; submarine canyon and fan; trench. Turbidites and slump deposits.<\/li>\n\n\n\n<li><strong>Carbonate deposits<\/strong> form in marine environments, but most prolifically in the absence of mud and sand<\/li>\n\n\n\n<li><strong>Volcanic sediments<\/strong> &#8212; ash, tephra, flows \u2013 can be found in any of the environments if volcanism is taking place.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Igneous rocks and processes<\/strong>. The Cordillera contains some of the most extensive deposits of igneous rocks on the planet because of the subduction of the Farallon plate (the largest tectonic plate known). <\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Andesite is commonly found in arc complexes. <\/li>\n\n\n\n<li>The granite batholiths of the Sierra Nevada used to have andesite above them, but it has eroded away. <\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Ophiolites<\/strong> are a suite of rocks representing oceanic crust that has been shoved to the surface in a process called obduction. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Metamorphic rocks<\/strong>. <\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Blueschist is produced during high pressure metamorphism of oceanic crust during subduction.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Cordilleran Margins<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">There are active plate boundaries characterized by interaction between oceanic and continental crust. The two types of active boundaries are <strong>subduction boundaries<\/strong> (which may or may not involve accretion) and <strong>transform boundaries<\/strong> &#8212; both are commonly found together. <\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C3_The_Cordilleras_Foundations_Paleoproterozoic_and_Mesoproterozoic_Periods_Ca_1800-1000_Ma\"><\/span>C3. The Cordillera&#8217;s Foundations: Paleoproterozoic and Mesoproterozoic Periods: Ca. 1800-1000 Ma.<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">&#8220;fleeting snapshots in the long cavalcade of time&#8230;&#8221;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The mantel is in motion, at about the same pace as fingernail growth, because of the heat of <strong>radioactive decay near the core-mantle boundary.<\/strong><\/li>\n\n\n\n<li><strong>The Cheyenne Belt<\/strong> is the southern edge of the ancient Archean craton &#8212; it runs roughly along the line demarcated by the Wyoming-Colorado border. The craton, in place by 2.5 Ga, was where further material began to be accreted at about 1.8 Ga. Metamorphic rocks produced during that period of accretion are, among other places, found in the inner gorge of the Grand Canyon. <\/li>\n\n\n\n<li>There are three phases to the accretion of material along the Cheyenne Belt. \n<ul class=\"wp-block-list\">\n<li>1. The Archaean craton in Montana, Wyoming and Northeast Utah<\/li>\n\n\n\n<li>2. Accretion of basement rocks of Colorado, Arizona and the rest of Utah.<\/li>\n\n\n\n<li>3. The western half of the cordillera (Nevada, California, Oregon, Washington, Idaho and British Columbia) was underlain only by ocean plate until various younger pieces of crust are attached piecemeal starting in 325 Ma.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>xxx<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C4_The_Cordilleras_Long-Lived_Passive_Margin_Neoproterozoic_to_Middle_Devonian_Periods_Ca_1000_Ma-400_Ma\"><\/span>C4. The Cordillera&#8217;s Long-Lived Passive Margin: Neoproterozoic to Middle Devonian Periods: Ca. 1000 Ma-400 Ma<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>dropped down basins<\/li>\n\n\n\n<li>passive margins persist for 200 Ma following precambrian &#8212; on the south<\/li>\n\n\n\n<li>Wasatch line: SLC to Las Vegas &#8212; tectonic hinge<\/li>\n\n\n\n<li>1Ga\u20134000 Ma &#8211;600 Ma of passive margins &#8212; on the west?<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C5_The_Antler_Orogeny_and_the_First_Suspect_Terrane_Middle_Devonian_to_Late_Pennsylvanian_Ca_400-300_Ma\"><\/span>C5. The Antler Orogeny and the First Suspect Terrane: Middle Devonian to Late Pennsylvanian: Ca. 400-300 Ma<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>arrival of terrains from west starting at 400 Ma<\/li>\n\n\n\n<li>Antler orogeny<\/li>\n\n\n\n<li>confused about subduction dipping to the west and then the east, page  74<\/li>\n\n\n\n<li>Alamo impact &#8212; 367Ma<\/li>\n\n\n\n<li>Trench rollback &#8212; collapsed mountains; created back arc basins as west of Japan<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C6_The_Amalgamation_of_Pangaea_and_the_Sonoma_Orogeny_Early_Permian_to_Early_Triassic_%E2%80%93_Ca_300-240_Ma\"><\/span>C6. The Amalgamation of Pangaea and the Sonoma Orogeny: Early Permian to Early Triassic &#8211; Ca. 300-240 Ma.<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C7_The_Arrival_of_Wrangellia_and_the_Nevadan_Orogeny_Late_Triassic_to_Late_Jurassic_Ca_240-145_Ma\"><\/span>C7. The Arrival of Wrangellia and the Nevadan Orogeny: Late Triassic to Late Jurassic: Ca. 240-145 Ma<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C8_The_Continental_Arc_Sevier_Orogeny_Western_Interior_Seaway_and_Flat-Slab_Subduction_Cretaceous_Period_Ca_145-65_Ma\"><\/span>C8. The Continental Arc, Sevier Orogeny, Western Interior Seaway and Flat-Slab Subduction: Cretaceous Period: Ca. 145-65 Ma.<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>&nbsp;Pangea-induced overheating leads to rifting and faster motion of the subducting Farallon plate, with various terranes being sutured onto the W coast and arc volcanism occurring in the Cordillera and compression east of that.&nbsp;<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">I found this chapter difficult to follow, and am not sure of the timing and interrelationship of many of the events following the breakup of Pangea. Later: I put the earlier draft of this into Claude, and it assisted in ordering the events covered in mynotes.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Breakup of Pangea (300Ma\u2014~150Ma).&nbsp;<\/strong>The Pangean supercontinent had the effect trapping core\/mantle heat beneath it, leading to rifting and volcanism. As Pangea broke up, new rifts created the central Atlantic, the Gulf of Mexico, The Canadian Basin, and the Indian Ocean. The pent up energy also increased plate motion, and thus subduction (e.g., the Farallon plate beneath the North American plate. More igneous material per unit time may have been created during the Cretaceous than any other period of time in the Phanerozoic.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Wranglia suturing (~175\u2013100 Ma).&nbsp;<\/strong>Wranglia originally formed as an oceanic plateau, the collided with the Alexander terrane (which had also collided with the Peninsular terrane), and then a subduction trench to Wranglia\u2019s west sutured rocks from the Chugatch terrane onto Wranglia.&nbsp;<strong>Coast Plutonic Zone intrusion (~160\u201345 Ma).&nbsp;<\/strong>The Coast Plutonic Complex intruded into the suture zone and produced plutons called \u2018<strong>stitching plutons.<\/strong>\u2019 Once Wrangellia docked, the subduction trench was pushed westward, and&nbsp;<strong>that&#8217;s where the Franciscan Assemblage then began accumulating<\/strong>. So Wrangellia&#8217;s accretion is essentially the precondition for the Franciscan\/forearc\/Sierra Nevada system that dominates the rest of the chapter.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>By 100 Ma (Cretaceous) there are a series of parallel belts running NW-SE:<\/strong><\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Trench \u2014 where Farallon plate subducts; Franciscan Assemblage accumulates here as an accretionary wedge\/m\u00e9lange.<br><strong>The Franciscan Assemblage accumulates in the Cordilleran trench (~150\u201365 Ma)<\/strong>.&nbsp;<ol><li><strong>Accretionary wedge =&gt; melange\/coast range.<\/strong>The accretionary part of the Franciscan melange piled up forming an early iteration of the Pacific coast ranges. It generally takes the form of a&nbsp;<strong>melange\u2014<\/strong>a large-scale brecciated rock in a mud-sand (greywracke) matrix with unsorted fragments of all sizes.&nbsp;&nbsp;&nbsp;The Franciscan assemblage may be up to 16,000 meters thick, though subsequent tectonics make it difficult to be sure.&nbsp;&nbsp;Franciscan material can be found from Santa Barbara to at least Oregon. Later strike-slip faulting moved some of the Franciscan melange north where they are exposed in the Straits of Georgia in British Columbia.&nbsp;<\/li><\/ol>\n<ol class=\"wp-block-list\">\n<li><strong>Blueschist metamorphism.&nbsp;<\/strong>Some of the Franciscan Melanage was subducted undergoing blue schist (high pressure, low temperature) metamorphism. I believe some of the subducted material can be seen in ophiolites on the California Coast 50-100 miles north of the bay area.&nbsp;<\/li>\n<\/ol>\n<\/li>\n\n\n\n<li><strong>Forearc basin.&nbsp;<\/strong>A basin formed to the east of the Coast Range \u2014 it is termed a forearc basin because it sits on the sea-ward side of the magmatic arc (Sierra Nevada) produced by subduction. Some of the best exposures of forearc basin rock is found from La Jolla to Point Loma, California.<\/li>\n\n\n\n<li><strong>Magmatic arc (peak: ~120\u201380 Ma).&nbsp;<\/strong>The ongoing subduction of the Farallon plate during the Cretaceous produced a vast magmatic arc from SE Alaska to Baja California. The produced extrusive felsic rocks on the surface, and granitic rocks below; the surface material has eroded, but the granitic material form the plutons and batholiths that make up the Sierra Nevada and the granitic spine of Baja.&nbsp;<\/li>\n\n\n\n<li><strong>Sevier fold-and-thrust belt (140\u201355 Ma).&nbsp;<\/strong>As various terranes attached to the west coast, compression continued to dominate the central and eastern cordillera. Thin layers of shale and mudstone were deformed and thrust over one another, forming the mountains in eastern Nevada, Western Utah, and in Wyoming and Montanna. The process is called thin-skinned deformation.&nbsp;<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Flat Slab Subduction (circa 85 Ma).<\/strong>&nbsp;An oceanic plateau riding on the Farallon plate subductes giving the subducting plate more buoyancy and decreasing the subduction angle. This event reorganizes the whole system with these consequences:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The magmatic arc&nbsp;<strong>shuts down or migrates eastward<\/strong>&nbsp;(no longer the right depth for melting above the slab)<\/li>\n\n\n\n<li>Compression propagates far inland \u2014 this drives the&nbsp;<strong>Laramide orogeny<\/strong>&nbsp;(block uplifts in Colorado, Wyoming, New Mexico), which is distinct from the Sevier thin-skinned belt<\/li>\n\n\n\n<li>The Western Interior Seaway axis shifts east<\/li>\n\n\n\n<li>The Franciscan Assemblage continues accumulating, but the geometry changes<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C9_Flat-Slab_Subduction_the_Laramide_Orogeny_Uplift_of_the_Colorado_Plateau_and_Rocky_Mountains_Paleocene_and_Eocene_Ca_65-35_Ma\"><\/span>C9. Flat-Slab Subduction, the Laramide Orogeny, Uplift of the Colorado Plateau and Rocky Mountains: Paleocene and Eocene: Ca. 65-35 Ma<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C10_Changing_Tectonics_Cooling_Climates_and_the_Dawn_of_Crustal_Extension_Late_Eocene_to_Early_Miocene_ca_35-20_Ma\"><\/span>C10. Changing Tectonics, Cooling Climates and the Dawn of Crustal Extension: Late Eocene to Early Miocene (ca. 35-20 Ma)<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">As the Farallon plate subducts, the Pacific plate encounters the North American plate and a transform margin is formed with the Pacific Plate moving North relative to the&nbsp;&nbsp;NA plate.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The Transform Margin.&nbsp;<\/strong>The Pacific plate is moving WNW and the North American plate is moving WSW. Over time, the Pacific plate will begin \u2018stealing\u2019 blocks from the NA plate in a process called \u201cPlate Capture.\u201d The northward movement of the Salinia block is one example of this.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The two Triple Junctions and continued subduction.&nbsp;<\/strong>At either end of the (lengthening) transform margin we find triple junctions \u2013MTZ (the Mendocino triple junction) and RTZ (the Rivera triple junction) where remnants of the now broken up Farallon plate (the Gorda plate at the MTZ&nbsp;&nbsp;and the Cocos plate at the RTZ) are still subducting and creating arc volcanism inland. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The Gorda plate.<\/strong> The Gorda plate is relatively young \u2013 it originates at the Gorda Ridge which is only a few hundred kilometers offshore.&nbsp;The plate travels such a short distance before reaching the subduction zone that it simply hasn&#8217;t had time to cool much since forming. At the point of subduction it&#8217;s only a few million years old, compared to oceanic plates elsewhere that may be 50\u2013100+ Ma when they reach a trench. This young, warm oceanic crust is less dense and more buoyant than old, cold crust and it provides less &#8220;slab pull&#8221; (the gravitational force of a dense, sinking slab dragging the plate down&#8211; one of the main drivers of subduction velocity), so subduction is slower. This partly explains why there is no well-defined trench offshore and why large interface earthquakes are infrequent \u2014 though when they do occur, they can be very large. This also explains why the Gorda plate experiences significant intraplate deformation&nbsp;&nbsp;&#8212; folding and buckling &#8212; inside its boundaries due to stresses from its neighboring plates. Some geologists do not consider the Gorda plate to be a true plate.&nbsp;&nbsp;That said, the subducting Gorda plate drives volcanism in northern California&nbsp;<a href=\"https:\/\/en.wikipedia.org\/wiki\/Gorda_plate\" target=\"_blank\" rel=\"noreferrer noopener\">Wikipedia<\/a>&nbsp;\u2014 specifically Mount Shasta and Lassen Peak and the southern Cascades.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The Juan de Fuca plate.<\/strong> To the north of the Gorda plate the Juan de Fuca plate is subducting below the NA plate at the Cascading subduction zone, producing the Cascade Range volcanos &#8212; the Juan de Fuca will be completely subducted in 1 to 2 million years and the margin will likely be a transform fault. The Cascadia subduction zone is gradually shutting down piece by piece, with slabs breaking off while the remaining plate continues to subduct\u2014 so the Juan de Fuca\/Explorer system as a whole is in the process of terminal fragmentation, the same fate the full Farallon plate met earlier.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The Cocos Plate<\/strong>. The Cocos plate was created approximately 23 million years ago (when the Farallon plate broke off two pieces (the other being the Nazca plate) off the coasts of Mexico, Guatemala, El Salvador, Nicaragua, Costa Rica, and Panama, subducting eastward beneath both the North American and Caribbean plates along the Middle America Trench.\u00a0Cocos subduction drives two distinct volcanic arcs. The\u00a0<strong>Trans-Mexican Volcanic Belt<\/strong>\u00a0(TMVB) \u2014 a chain running east-west across central Mexico, including Popocat\u00e9petl \u2014 is fed by Cocos and Rivera subduction beneath the North American plate. Further south, the\u00a0<strong>Central American Volcanic Arc<\/strong>\u00a0(CAVA) runs the length of Guatemala, El Salvador, Nicaragua, and Costa Rica, fed by Cocos subducting beneath the Caribbean plate. Subduction of the Cocos and Rivera plates has produced a series of volcanic arcs in Mexico and Central America. The most geologically interesting feature is that the Cocos plate is undergoing flat-slab subduction beneath central Mexico \u2014 an almost exact modern analogue to the Laramide flat-slab episode\u00a0<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Metamorphic Core Complexes.&nbsp;<\/strong>The pull of the Pacific plate will also cause extension of the NA plate that was previously thickened resulting in the Basin and Range area. Slices of crust (carapace rocks) are being pulled away along low angle detachment faults, and the removal of theses masses allow deeper metamorphic rocks to rise buoyantly, which increases slippage along the detachment faults, in a positive feedback loop. The rising metamorphic rocks create domes \u2013 the metamorphic core complexes. And the carapace rocks sliding away rotate backwards into a low-angled fault plane creating tilted layers.&nbsp;&nbsp;<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Interlude_History_of_the_Farallon_Plate_by_Claude\"><\/span>Interlude: History of the Farallon Plate, by Claude<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><em><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-purple-color\">TDE: Please describe the history of Farallon plate, from its origin to its breakup and subduction under the NA plate. Give approximate times<\/mark><\/strong><\/em><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\">Claude: <br>Here&#8217;s the history in roughly chronological order.<\/mark><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\"><strong>~250 Ma \u2014 Origin in Panthalassa<\/strong><br>Before the Farallon existed as a distinct plate, the proto-Pacific ocean (Panthalassa) was dominated by three plates meeting at a triple junction: the Izanagi, Phoenix, and what would become the Farallon. The Farallon plate formed one of the three main plates of Panthalassa, alongside the Izanagi plate and the Phoenix plate, which were connected by a triple junction.\u00a0<a href=\"https:\/\/en.wikipedia.org\/wiki\/Farallon_Plate\" target=\"_blank\" rel=\"noreferrer noopener\">Wikipedia<\/a>\u00a0The Pacific plate itself formed later at the center of this triple junction.<\/mark><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\"><strong>~200\u2013180 Ma \u2014 Subduction begins<\/strong><br>The Farallon plate began subducting under the west coast of the North American plate \u2014 then located in modern Utah \u2014 as Pangaea broke apart, during the Early Jurassic.\u00a0<a href=\"https:\/\/en.wikipedia.org\/wiki\/Farallon_Plate\" target=\"_blank\" rel=\"noreferrer noopener\">Wikipedia<\/a>\u00a0This is the subduction system that would, over the next 150 million years, build most of western North America. The subduction formed a line of volcanoes stretching all the way from Alaska to Central America.<\/mark><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\"><strong>~200\u201385 Ma \u2014 Terrane accretion and arc building<\/strong><br>Through the Jurassic and Cretaceous, the Farallon plate did two major things simultaneously. First, it acted as a conveyor belt, carrying oceanic plateaus, island arcs, and continental fragments eastward and accreting them onto North America \u2014 Wrangellia, the Alexander terrane, and others. During the subduction of the Farallon plate, it accreted these island arcs and terranes to the North American plate. Much of western North America is composed of these accreted terranes.\u00a0<a href=\"https:\/\/en.wikipedia.org\/wiki\/Farallon_Plate\" target=\"_blank\" rel=\"noreferrer noopener\">Wikipedia<\/a>\u00a0Second, subduction generated the enormous Cretaceous magmatic arc \u2014 the batholiths of the Sierra Nevada, the Peninsular Ranges, and the Coast Ranges of British Columbia.<\/mark><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\"><strong>~90\u201350 Ma \u2014 Flat-slab subduction and the Laramide orogeny<\/strong><br>An oceanic plateau riding on the Farallon plate subducted at roughly 90 Ma, increasing the plate&#8217;s buoyancy and flattening its subduction angle. The Farallon plate developed a flat-slab segment starting at ca. 90 Ma, coinciding with subduction of the Conjugate Shatsky Rise oceanic plateau. From ca. 80 to ca. 55 Ma, the flat slab grew in length to as much as 2,000 km from the plate margin.\u00a0<a href=\"https:\/\/pubs.geoscienceworld.org\/gsa\/geosphere\/article\/18\/2\/476\/611097\/Numerical-models-of-Farallon-plate-subduction\" target=\"_blank\" rel=\"noreferrer noopener\">Geological Society of America<\/a>\u00a0This suppressed arc magmatism along the coast and pushed deformation far inland, producing the Laramide block uplifts in Colorado, Wyoming, and New Mexico \u2014 far east of where you&#8217;d expect subduction effects.<\/mark><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\"><strong>~55\u201330 Ma \u2014 Slab steepening, rollback, and Basin and Range extension<\/strong><br>As the oceanic plateau material eventually eclogitized and became denser, the slab began to steepen and roll back. The flat slab is inferred to have undergone rollback in a plane subparallel to the direction of plate convergence until ca. 30 Ma.\u00a0<a href=\"https:\/\/pubs.geoscienceworld.org\/gsa\/geosphere\/article\/18\/2\/476\/611097\/Numerical-models-of-Farallon-plate-subduction\" target=\"_blank\" rel=\"noreferrer noopener\">Geological Society of America<\/a>\u00a0This rollback stretched and thinned the previously overthickened crust, initiating Basin and Range extension. Meanwhile the Farallon plate as a whole was shrinking rapidly through ongoing subduction.<\/mark><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\"><strong>~30 Ma \u2014 The East Pacific Rise reaches the trench; plate breakup<\/strong><br>This is the pivotal moment. Around 30 million years ago, a dramatic segmentation occurred when the mid-ocean ridge collided with the continent, effectively splitting the ~10,000-km-long plate into two smaller plates. This gave rise to the San Andreas Fault that now connects the northern and southern portions of the former plate, the Juan de Fuca plate off Washington state and the Cocos plate off Central America.\u00a0At this point the Farallon ceases to exist as a coherent entity. The Pacific plate comes into direct contact with the North American plate along what becomes the San Andreas transform system.<\/mark><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\"><strong>~30 Ma\u2013present \u2014 Remnant fragments<\/strong><br>The surviving pieces continue subducting but are themselves fragmenting. The Juan de Fuca broke into the Gorda (south) and Explorer (north) microplates. The Cascadia subduction zone is gradually shutting down piece by piece, with slabs breaking off while the remaining plate continues to subduct.\u00a0<a href=\"https:\/\/www.lsu.edu\/science\/news\/2025\/09\/shuck-sci-adv.php\" target=\"_blank\" rel=\"noreferrer noopener\">Louisiana State University<\/a>\u00a0Buried remnants of the Farallon slab are still detectable today via seismic tomography \u2014 cold, dense slabs sitting in the mantle beneath the western US, some as deep as the lower mantle.<\/mark><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-medium-pink-color\"><strong>The through-line<\/strong>: the Farallon plate&#8217;s ~180-million-year subduction history essentially\u00a0<em>built<\/em>\u00a0western North America \u2014 its terranes, its mountain ranges, its batholiths, its sedimentary basins \u2014 and its death throes are still playing out in the Cascades, the San Andreas, and the Basin and Rang<\/mark><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C11_The_End_of_Cordilleran_Subduction_and_the_Formation_of_the_Basin_and_Range_Early_and_Middle_Miocene_Ca_20-10_Ma\"><\/span>C11. The End of Cordilleran Subduction and the Formation of the Basin and Range: Early and Middle Miocene: Ca. 20-10 Ma<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C12_Interior_Basins_Drainage_Integration_and_Deep_Incision_Late_Miocene_to_Pliocene_Ca_10-26_Ma\"><\/span>C12. Interior Basins, Drainage Integration and Deep Incision: Late Miocene to Pliocene: Ca. 10-2.6 Ma.<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C13_The_North_American_Cordillera_Today_Pleistocene_Holocene_and_the_Anthropocene_Ca_26_Ma_to_Present\"><\/span>C13. The North American Cordillera Today: Pleistocene, Holocene and the Anthropocene: Ca. 2.6 Ma to Present.<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Views: 31<\/p>","protected":false},"excerpt":{"rendered":"<p>*Ancient Landscapes of Western North America: A Geologic History with Paleogeographic Maps, Ronald C. Blakely and Wayne D. Hanney. 2018. February 2026 About the Book This book is about the tectonic assembly, and I suspect the geomorphology, of what is now the Western United States. In particular, it will use paleogeographic maps \u2013 in which &hellip; <a href=\"https:\/\/tomeri.org\/notes\/2026\/02\/24\/ancient-landscapes-of-western-north-america-blakely-and-hanney\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Ancient Landscapes of Western North America*, Blakely and Hanney<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":4,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"federated","footnotes":""},"categories":[1],"tags":[],"class_list":["post-8692","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/posts\/8692","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/comments?post=8692"}],"version-history":[{"count":25,"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/posts\/8692\/revisions"}],"predecessor-version":[{"id":9077,"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/posts\/8692\/revisions\/9077"}],"wp:attachment":[{"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/media?parent=8692"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/categories?post=8692"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tomeri.org\/notes\/wp-json\/wp\/v2\/tags?post=8692"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}