Exotic Terranes of the Pacific Northwest

[Music] so how come we don't have a bunch of dinosaur bones here in the pacific northwest is that dawned on anybody we don't have a bunch of big dinosaur excavations and people chiseling into the bedrock and they they got their little paint brushes out and they're little they're little dental tools looking for the skeleton or the or the skull of this dinosaur that's just not a thing we have regularly here in the pacific northwest in fact where do they do have these dinosaur digs they don't have them in washington they've got them in places like that's right so montana colorado utah wyoming alberta those are the places to go in north america for the dinosaur digs thank you [Laughter] audience participation early okay so i think there's a couple reasons that we don't have a bunch of dinosaurs here in the pacific northwest and one of them is to have dinosaurs a good dinosaur dig you need the right kind of rock sedimentary bedrock and you need the rock to be from the age of the dinosaurs the mesozoic era so i've got a cute little geologic time scale here and between 251 and 66 million years ago is the mesozoic era that's the age of the dinosaurs and those states i just mentioned have mesozoic bedrock right at the surface and they have the right kind of rocks they have sandstones and shales and silt stones you're just ready to go to find these dinosaur skeletons so here in the pacific northwest one of the reasons we don't have a bunch of dinosaur bones and dinosaur skeletons is because our mesozoic bedrock our age of the dinosaurs bedrock is not at the surface it's buried in general by about two miles worth of lava rock so you've heard this pacific northwest is an active place it's disneyland for geologists right and part of that is the volcanoes that we've had up here in the cenozoic we've had cascade volcanoes erupting for 40 million years we've had flood basalts burying much of this material so the first major point tonight is we only have a few key spots in the pacific northwest to get a look at our mesozoic basement rock otherwise we're not a great place to study the mesozoic now this is not a lecture on dinosaurs because i don't know much about dinosaurs but it is a lecture on the exotic terrains of the pacific northwest and we need to go to the mesozoic to tell that story so even though we just have a few portals to get direct observations of the mesozoic bedrock that's what we're going to do tonight and those mesozoic bedrock areas in pacific northwest country are these things called exotic terrains it is spelled this way to rain i didn't misspell and an exotic terrain is a piece of crust that formed elsewhere and was added to our continent you've heard of exotic terrains perhaps did you know that there are exotic terrains on both margins of north america this is north america laying on its back here's spokane washington and for to spokane washington to ocean shores we have an incredible collection of exotic terrain scraps of land that were added to north america in the last 200 million years but also if you go to the eastern part of north america if you go east of the appalachians essentially and if you go to knoxville tennessee and go east of knoxville tennessee there are exotic terrains that were added to the east coast of north america older than 300 million years ago so both edges of our continent and in fact edges of all continents have these things called exotic terrains the topic of tonight is looking at these exotic terrains that have been added to the west coast of north america in the last 200 million years and particularly the pacific northwest now a few of you are thoroughly wide awake and you're like well wait a minute you just said that there aren't any dinosaurs in the pacific northwest but didn't they just find a dinosaur bone in washington state a few of you remember this there was a little article on this a little news report 2012 spring of 2012 just a few years ago san juan islands some folks from the burke museum associated with the university of washington were going to succia island one of the northernmost san juan islands and they went to that island because it has what mesozoic sedimentary rock and they weren't looking for dinosaurs they were looking for ammonites a different kind of fossil and they were in these sedimentary rock layers called the nanaimo group and they found some ammonites but they also happened to stumble on a fragment of a left thigh bone of a tyrannosaurus rex san juan islands t-rex the first dinosaur bone ever found in washington and it made big news so there are some places where we can see the mesozoic rock at the surface my first intriguing question for you tonight and i don't expect an answer did that t-rex live and die in washington 80 million years ago or did that t-rex live and die 80 million years ago in mexico people are answering and i think i know why you're answering because i wouldn't ask the question if i wasn't going to make a case for this mexico story so this sounds crazy right up front i got to tell you this sounds crazy but i'm going to try to show you overwhelming evidence tonight i should say it differently i'm going to show you new evidence that is going to bolster an idea that's not accepted by everybody yet in geology that half of the state of washington was originally mexican crust and was moved almost 2 000 miles to the north people are inserting their own jokes at the moment great go for it there wasn't a border i'm saying that was a that was a mexican dinosaur that now is up here and you're like i'm confused like the dinosaur walked up here or what are you saying no i'm saying that that dinosaur died in mexico its remains went into some siltstone 80 million years ago and that whole portion of mexico's crust got shifted north up to us and by the way i'm not just talking about that island in san juan islands i'm talking about many of your beloved spots the upper tiana way ingles lake mount stewart chelan wenatchee i'm saying all of that stuff was originally in mexico and you should be like i don't think i believe you man so it's a wild idea i hope you can strap in and get ready for all this evidence i'm going to show you based on some new scientific work that's been done okay so the fact that most of our terrains have an oceanic story and not really part of this dinosaur story means that i've got to do some drawing for you and actually before i do the drawing let me show you specifically where these portals are where these specific spots are that we can look directly to the mexico in other words where is the mesozoic basement rock not buried by all this lava we can go to the klamath mountains in southwestern oregon we can go to the green horns we can go to the walawas we can go to the bottom of hell's canyon what am i doing i'm seeing where we can go directly to mesozoic basement rock and what i'm really saying is each of these circles have mesozoic exotic terrain locations that we can study they're not all circles because these lavas are burying everything else okanagan highlands and i'm going to draw a big circle for the north cascades including mount sai franklin falls chelan wenatchee all your favorite spots north of ellensburg all the way to canada border and that's it except for a little rimrock inlier so down west of yakima there's some of that rock as well that's it and for many years i was puzzled by the exotic terrain story because all i was doing was looking at this map and i realized i needed to look broader i needed to go up to british columbia and alaska and down to mexico and look at the geology there to see this broad story because especially in the province of british columbia those terrains are not buried they're all up there nice and easy to see so we're going to cross the border with those stories and get them down into washington okay great so let's quickly erase and let's go ahead and try to draw an oceanic generic scene that's going to show a variety of bedrock that we can use here so let me do this very quickly drawing time on the ocean we've got an oceanic island out in the middle of nowhere we've got people living on it if we want no don't do that this is the mesozoic okay great so we'll put a boat in here and this is a tectonic collision between two pieces of ocean floor this is a completely submarine ocean floor collision and can i do this i think i can i'm going to put on the ocean floor we have a bunch of sediment a bunch of silica layers and that eventually is going to be a rock called chert and if we can somehow get to the subflooring of the ocean crust and look at that that's a suite of rocks called an ophiolite and if we get to the other plate where we have taken a bunch of this crust and subducted it and scraped it off of the oceanic plate and added it to this mound of material here this is called a subduction complex or an accretionary wedge or a melange all those words mean the same thing but the point is we have some very specific rocks that form in those locations one of them is a rock you've heard of serpentonite a little bit deeper in the subduction complex again we're under water we're at the edge of an ocean under water a little deeper we're going to get schist specifically green shifts and a little bit deeper yet in the upper plate and a little bit in the lower plate a metamorphic rock called nice i'm not done i'm going to make some more rocks just in this generic oceanic scene you can visualize this being the marianas trench and the marianas islands if you like so this is the volcano made out of lavas that we can call andersite lavas and if we cool off the magma chamber down below we can call that diorite and if we're within 30 degrees north or south of the equator we can have some coral reefs some of you have snorkeled in the corals and that eventually becomes limestone so let's pause and soak in what we've done here we've made one oceanic scene somewhere out in the middle of the pacific let's say and we have one two three four five six seven eight different kinds of rock different kinds of rocks some of them igneous sedimentary and metamorphic all coming from this oceanic scene i'm going to show you tons of beautiful images or at least images you can decide if they're beautiful but there's beautiful spot i said it again you can decide if those places are beautiful these spots have these different kinds of rocks for instance fidalgo island in the san juans has an ophiolite sequence and some beautiful ribbon shirt the ingalls uh lake area is serpentonite the clamuses are pentanite the green horn is from bentonite the bottom of hell's canyon has coral reef limestones we'll show video clips of that so the point is these things were out in the pacific someplace they left the pacific they got added to the edge of north america remember in the last 200 million years that diagram is gone i'm pointing to a diagram that's gone and by the time we're done with adding those exotic terrains we have built the basement of north america okay we're going to keep it moving and now we can talk about timing we're eventually going to get back to that mexico story but we're not ready to go back to that quite yet thank you for your interest your energy is outstanding here all right so you might say well how are these things coming in off of the ocean like what is the mechanism for doing that they're not going to like doggy paddle through the ocean somehow so how are you going to take stuff that's in the ocean floor lift it out of the ocean cram it onto the edge of the continent and in fact some places lift it thousands of feet above sea level well at least the stuff getting to us the model we have which is generally accepted is that there was a large oceanic plate that you haven't heard of it's called the ferralon plate it's a tectonic plate ocean floor that was moving east and subducting beneath north america you know what yeah that's fine so the ferralon plate had terrain blocks riding on them so that's taking our ocean crust and getting them added to the edge of north america but instead of doing dozens and dozens of terrains and having them come in one after another we don't have time for all that and thankfully the timing of this works quite well instead of each terrain coming in by itself there's good evidence now that a bunch of terrains got together out in the ocean they had a party they got together and got connected in a big quilt and then that what we call a super terrain was added as one big hunk so the first big super terrain we're just going to call super terrain roman numeral one if you know the literature this is called the inter montane super terrain it's best exposed up in canada but it makes up the okanagan it also makes up these other areas so everything that i've just outlined this belt here is from this first major super terrain that came in number one and i'm going to put the number 150 because that's the rough date as when this intramontane super terrain came in and got added to the edge of north america so we suddenly went from spokane at our west coast to omak at our west coast when this super terrain one came in okay we can even do that omak spokane we gained a bunch of real estate in the deal good deal for us uh i'm gonna do this quickly uh you can think of that big super terrain as a big battleship and here's another big battleship that's about to come in and dock and we'll call that super terrain number two and before i finish drawing we're going to have that big battleship come in but the issue that i want to convey is that between the two battleships we've got a bunch of cute little boats some sailboats some tugboats in other words some smaller terrain some little scraps of this and that and even some pieces of the ocean floor that aren't going to get caught up in this major collision between these two battleships and so what i'd like to do now is flash forward to a hundred million years ago when we have the next major super terrain the next battleship coming in and adding but i want to add that there's an important zone between those two super terrains and i put a bunch of squiggles and other complicated lines in here because that's all of our little tug boats and sailboats hopefully everybody got out of there and we're going to squish all those things together we're just going to crunch that whole collection of small vessels and i'd like to call that with your permission a batholith complex and that's an important label for us so complex meaning it's like a subduction complex it's got the fragments of serpentinite and green schist and and nice that i was talking about before but some of you know the word batholith it's a large collection of granite it's a big blob of magma that hardened into rock so this tugboat mangled area also has a bunch of these big blobs of granite some of you are a few steps ahead of me i can already hear you and that's great this is mount stewart this is the serpentine out of the upper tiana way this is the crazy rock of the san juans and basically most of the north cascades is this batholith complex that got caught between these two super terrain battleships you with me i think most of you are that's wonderful there's one more terrain to bring in it's called celezia but we're going to ignore it i talked about it a couple winters ago with the liberty gold yellowstone hot spot store so i really want to focus on these two guys now before i lose this sketch and again i've got all these beautiful images and interviews and other things uh before i lose this sketch i want to make it clear not everything here is mexico origin because remember we're just doing this and most of us i think are just assuming oh yeah he's bring stuff in off of the ocean at our latitude remember now there's a mexico story here and so before we quit tonight we want to sever this picture and get that stuff that i just x'ed out that's the stuff that's going to go north towards mexico excuse me it was originally in mexico that's going to be north coming towards us i was already stuff ahead of myself in my mind so not everything let's not go crazy but we're going to be almost crazy by saying everything in the super terrain 2 and half of the bathwood complex is going to be sent to the north okay i need to deal with these crazy swings with this story because we not only have number uh one but number two battleship number two which was a big old super terrain barely shows up on this map in the pacific northwest it's really only vancouver island that's super terrain too so why is that why don't we have more of super terrain too and what's all this stuff in between you tell me what's all this stuff in between the batholith complex very good you pass excellent so what's with this crazy swing that's an important comment to make well since the terrains came in what are our dates 150 this came in 100 million this came in and we've built most of washington by this point since those terrains were added we had some important activity the state of nevada in the last 20 million years after the terrains came in uh doubled in width the state of nevada something called the basin and range extension so we're just going to open up this section of north america and that's going to cause our belt of super terrains to get pushed to the west do you see at the same time some of you know about this thing called a clockwise rotation in the pacific northwest crust that we've talked about a number of times in this lecture series that's also related to this extension and a third thing the san andreas fault in california has been taking a piece of california and shifting it north that's all stuff that has happened since the terrains came in and it's an important point because if we want to go back to talking about taking pieces of mexico and sending them north an idea by the way called baja bc part of baja mexico is now up in british columbia it's an old idea it's been around for 50 years if we want to do that we need to restore these belts i'm going to say this again because this is important these belts look weird today they weren't weird when were just after terrains came in why because we've had extension like an accordion clockwise rotation and shifting along the san andreas fault that has screwed up our terrain pattern so i am very quickly and i don't mean uh kind of quickly i mean very quickly going to be drawing a map of the this is like a bet bar bet now see if i can do this i'm better at drawing the pacific northwest and i am drawing everything else washington oregon california nevada utah idaho et cetera okay so if we restore everything if we get things back to the way they were before all that action our super terrain 1 is going to be here that's super terrain 1. our super terrain two we're in mexico our super terrain two is here and therefore our squashed batholith complex our tugboats that got screwed up are caught in between these two battleships down here so what i'm saying with a straight face is mount stewart and the san juan islands are right down here they're down by cabo san lucas mexico that's the location today and i'm saying that that material is on the trailing edge of this huge block of crust that is going to work its way almost 2 000 miles to the north and that's just talking about the trailing edge where's the leading edge it's up in british columbia and some of it is up in alaska i know it sounds like i'm making this stuff up there's good evidence that's coming to support these ideas and you might have a problem at the moment i'm anticipating your problems perhaps but you might say well wait a minute i thought you said you had this ferralon plate bringing stuff in from the west so how are you physically going to be moving stuff to the north when that's happening that's an excellent question the answer is there is overwhelming evidence that during this time of baja bc when we're moving stuff north we didn't have the farallon plate coming in we had a different tectonic plate and you haven't heard of this one either because it's also vanished it's also gone but there's good evidence that that plate existed and was moving essentially north so this is the magic carpet ride for this baja bc block when the cooler plate was in existence and let me give you some dates that's our magic window magic carpet ride magic window between 75 million years ago and 45 million years ago we had a very discreet time in our history when we had a northward moving oceanic plate the cooler plate and during the cooler plates existence we had this motion so by 45 million years ago everything's up here and it doesn't continue to move north nothing's gone further north with this block at this time okay so you're like i guess i don't know it sounds pretty wild to me i better show me some evidence that's what i want to do now i'm going to show you the evidence very quickly on the chalkboard just make a little list and then we're going to go to all these images and i'll show you what it looks like in living color okay is that a deal great thank you so baja bc one two three four so the first lecture i ever gave downtown here was uh in 2010 and it was called mount stewart a closer look it still exists on youtube and the evidence i had i was talking about baja bc back then but i wasn't totally sure that i liked the idea and partly because the only evidence i had to talk about back then was paleomagnetic evidence and this is going back to the 1970s now this baja bc thing started in the 1970s and the only evidence for it was taking a big granite block like mount stewart measuring the alignment of the magnetic minerals deducing the old latitude where that granite used to be and you're like that sounds i don't know and most of us in geology said now that sounds i don't know because we didn't know how paleomagnetism worked there were only a few guys actually doing it and so this really didn't become a thing among geology 101 textbooks and everything else because the only evidence we had was looking at these old magnetic grains in granite which was kind of an obscure way to go about things so there was just a small group of geologists peddling this idea in the last 15 years or so this is the new information that has at least gotten me excited and a number of other geologists as well that this baja beastly thing is real and i got to tell you before i forget there's still a bunch of geologists that think this is a bunch of baloney they do but there's a growing number especially who take the time to read these scientific papers as i've done recently to put this together so what else can we put on the list we can look at fossils not dinosaur fossils but we can look at plant fossils and look at the shapes of the plants and say something about the old latitude of the rock we can look at ammonite fossils and look for a match if we find some ammonites in the north and some ammonites in the south we can find bedrock matches and this is the one that i think i'm most excited to share with you can we find some bedrock up here in the northwest and some bedrock down south and find a way to match them up to say they used to be together and now they've been separated in other words some of it stayed down there and some of it came up here and finally there's a mineral called zircon which is a teeny tiny mineral that's very durable and there's been work with the zircon minerals to try to put this story together let me give you just a quick verbal description and then we'll go to the images the zircons are so durable that they don't break down they don't crumble away and so if you have a very old zircon a pre-cambrian aid zircon a billion years old it won't go away even if it gets eroded out of pre-cambrian bedrock and gets carried by a river the zircon will remain it will get deposited in another place in our particular discussion pre-cambrian rivers traveling from the old part of north america and carrying these very old pre-cambrian zircons these little grains of salt essentially are being carried by the rivers and deposited like frosting on top of these terrains then if you move the terrain you've got these little salt grains that say hey i came from somewhere can you figure out where i came from and the people who have studied the pre-cambrian zircons in the nanaimo group and the other places where we have sedimentary rocks on these terrains in the northwest are convinced that we've got to get that block all the way back down to mexico to make it work with the original source okay okay so brace yourself i got lots for you but it includes some video clips and some maps and some photographs i won't call them beautiful we're going to start on a terrible morning down in san francisco in 1906. huge earthquake three days of fires wiped out most of downtown and here's some guys the day after that terrible earthquake homeless in downtown san francisco better dress than you and i put together i might add and of course the culprit was the san andreas fault a type of a fault that we need don't we we need a fault that's going to shift ground laterally especially one side of the fault and in 1906 a rather impressive segment of that fault ruptured and what does that mean in the case of the san andreas fault well the sandra's fault is a strike slip fault which means that the ground shifts cleanly there's no uplift there's no down drop there's no big superman crack that opens up it's just one side of this fault shifts north compared to the other shifts north that's what we want right so look at this famous photograph right after the earthquake that was a fence that was across the san andreas fault and it broke cleanly by 10 feet so the san andreas fault comes right through here you can't even see it so that's the kind of shifting we have now please note that that was a big earthquake big earthquake and 10 feet not thousands of miles but 10 feet of sudden motion during the earthquake now scott cronk a friend of mine has gotten up in a drone and flown over the san andreas fault so we're looking north north america plate on one side the pacific plate on the other and the san andreas fault is obviously still active obviously because it's there's a still a beautiful gully right if this thing was dead we wouldn't see that active gully so these earthquakes continue of course in the san andreas fault please note i'm not saying the san andreas fault sent this rock up from mexico because it's too young this is a fault that's only been only been around for 30 million years and we have a total of 200 miles of offset on that fault let me show you how we know that so here's a map of southern california los angeles and santa cruz and san francisco the other side and this sliver everything in california on this side of the fault is moving a different direction than the rest of north america and so if we're patient and wait a few tens of millions of years here's baja mexico and that's the liver of california that's going to be offshore so this is a different baja bc this is actually baja off the shore of british columbia that's not what we were talking about earlier but that's a projection tens of millions of years in the future here's how we know that there's been a total of 200 miles of offset over the last 30 million years on the san andreas fault you take mesozoic bedrock in the southern part of the sierra nevada mountains of california it suddenly stops at the san andreas fault and you find it again up here in the bay area so we can put those things back together and realize that a total of 200 miles have happened now you again you hear what i'm saying there wasn't a big earthquake that made 200 miles of motion right uh 10 feet at a time but if you have thousands and thousands of earthquakes you can get 200 miles of offset so here's a cleaned up map from jennifer hackett and monash dash mapping to show that offset now let's get back to where we belong up here in washington and beautiful mount stewart which is just a few miles from this facility the hell home center and uh this is close to hell homes and i have an iphone that i'm not afraid to use this is a metamorphic rock called green schist you can see why it's a beautiful green rock and there's exposures of this in kittitas county up above lake cleelum on this cold windy rainy slash snowy morning on november 1st how far do we have to look to find the next exposure of this green shift in washington let's try to answer that the answer is burlington hill i'm at burlington washington along interstate 5 where state route 20 crosses i-5 i'm almost to bellingham i'm three hours away from home and look at beneath the moss beneath the different botany is our old friend the green schist so those two locations cleolum and burlington used to be suburbs of each other before something called the straight creek fault was active so did you know that washington has a san andreas fault like fault and you're like oh god i've never heard of this thing something else i've got to worry about with earthquakes i got good news in this case the straight creek fault has been dead for 35 million years it hasn't done any shifting of the crust it hasn't made any earthquakes in 35 million years but these two locations that are separated today were once right next door to each other and we know that by doing the same thing we just did in california by taking mesozoic bedrock and restoring the mesozoic bedrock patterns on geologic maps so this was washington 50 million years ago before the 100 miles of shifting north of western washington again this fault isn't going to help us with baja bc either we're still too young we're at 50 million years and younger but my point is these kinds of faults exist why can't we have faults like this back in baja bc time doesn't have to be one major fault it could be a bunch of smaller faults like this a hundred miles of total offset on this straight creek fault now my wife and i have three boys and two of them went to school in western washington university and it took us three hours to visit them up in bellingham if they only had gone to school there 50 million years ago to get to seattle would have been a drive to the southwest okay straight creek fault too young for our baja bc story but an active fault a total of 100 miles 10 feet at a time wonderful let's look at some bedrock that proves that that hundred miles of offset is a real thing this is the city you live in it's a beautiful town we all feel very lucky to live here and if we go north we can get to this landmark called mount stewart but there's a low ridge right before mount stewart that you have to cross we're up on earl peak we could be long's pass we could be ingalls pass and it's kind of a crappy looking ridge i suppose and if you look carefully at that crappy looking ridge and look carefully at the rock it's mesozoic rock it's exotic terrain material and it's serpentonite now if you have a good memory from just a few uh moments ago we know where sepentanite forms right where it forms in a subduction complex it forms in the ocean that green serpentinite forms here where we scrape off the sediment off a downgoing oceanic slab and we add it to the edge of another plate so that rock is distinct most of us know it by hiking up in the tiana way etc not many places have green rock like this and i want you to visualize the ocean the next time you see that serpentinite if you didn't know that already some of you know the serpentinite is famous for not supporting plant material the chemistry is wrong with that rock so these orange areas as really green rock that has weathered to orange and has a noticeable lack in plant cover serpentinite at ingles lake with mount stewart granite which is coming in a bit artsy shot of the serpentinite in the upper tiana way now let's leave the tiana way river valley and cross the strait creek fault we were just talking about we got to go 100 miles north don't we to find stuff that used to be together we can go to a place called mount shuksan so bellingham is over here here's mount baker which is an active volcano but the next mountain over to the east is mount shuksan it's not a volcano it's a huge pile of green schist and before the start of this lecture you'd be like okay whatever but now we know the significance of green shift we know that it's an ocean story and these rocks are green because they're part of that subduction complex deeper down so these folks are hiking up to the top of shucks and do they know it's oceanic rock probably not does it matter does it take away their enjoyment probably not but we know that this is an exotic terrain from the age of the dinosaurs that was lifted out of the ocean somehow and this gal is at the top of shucks in 9127 feet above sea level now you tell me how that happens how do you take that rock and get it out of the ocean and get it up to a place like that the details and the physics of that i suppose is a lecture for another time but we want to emphasize the fact that half of the basement rock of washington the basement rock of western washington is this oceanic rain material much of it green colored mount psy franklin falls take your pick remember we're not even talking about mexico yet that's a whole other wrinkle to this this is kind of a one-two punch so we've been preoccupied with the subduction complex so far let's keep it moving there's a modern version of a subduction complex today this is the olympic peninsula seattle's here here's the subducting juan de fuca plate subducting during our short time on the planet you can see how complicated the rock is here sir pentanite green schist etc it's all right there now here are windows into the past we've got to be clever as to where we go to visit more of these exotic terrains let's leave the tiana way and go down to oregon to the greenhorn mountains for years geologists working in the baker terrain could not explain how these rocks form they are highly altered and mixed up like no other rocks in the region the mystery was solved when ellen bishop was doing research at the scripps institution of oceanography my colleagues at scripps were dredging the marianas trench looking at ocean island systems in the pacific and they kept coming home with the same kinds of rocks that i was finding except i didn't have to use a ship and a dredge to find these things i just had to walk through the greenhorn mountains and i came up with the same mysterious assemblage that they were finding in the south pacific so let's go down to san francisco and keep this going is there serpentine at any other place besides the pacific northwest well if we go to san francisco and we look at the kind of bedrock that the golden gate bridge is anchored in there we go there's more surpent tonight so this is a western north america story of taking stuff from the ocean and scrapping it on adding to the edge of of north america and this is from the archives this is your speaker at age 10 back we grew up in wisconsin and my parents took us on family trips out here this is my first time out west and they're sad that i'm out here now but they it's like hey you blew it you took us on these trips out to the west i wouldn't have known about how great it is out here without those trips so thanks so this the the franciscan complex is is just more of this uh serpentinite story and even down in baja mexico we still have the green oceanic rock that was scraped off so really we need to leave the pacific northwest at least for this topic and look at the entire alaska down to mexico scene to really put this story into proper perspective and since we're thinking big let's go to pangaea with the super continent that dominated our planet there was one continent and one ocean and noticed that the west coast of north america at pangaea time was spokane so there was no washington we haven't added any of these terrains yet but we now have good maps that show north america splitting away from pangaea and notice here's our scraps of material super terrain one ready to come in the inter montane et cetera and we can just blow through these maps these are all carefully created using all sorts of evidence collected over the last hundred years they're not guesses here's back to the norse west briefly and we can see the old shoreline of that old north american continent and then everything here are the terrains that came in since that time continuing with some more detailed maps of north america splitting away from africa and again please note all these oceanic islands and other scraps the battleships and the tugboats that we were talking about that were going to be coming in in pulses and eventually building north america as we know so these terrain maps are complicated not so much in the northwest because they're buried but if we get up to british columbia or how about this one look at this here's seattle all the way up to the north slope of alaska and every color is a different scrap of terrain material coming in off of the ocean so you can see why this is a daunting task to try to kind of assimilate all this scientific literature and make sense of it and i must admit this guy robert hildebrand has come up with some very creative new ideas based on these pieces of evidence that kind of take tonight's lecture and make it obsolete and i might give a lecture down the road using his brand new ideas involving the terrain story this is one of the earliest geologic maps of north america we're on the east coast and you can see the different colors for the different terrains that were added to the east coast of north america as pangaea was being assembled but back to the northwest thanks for being willing to skip around i guess you don't have any choice but thanks anyway let's go to the bottom of hell's canyon and look at evidence of that first super terrain that came in the inter montane super terrain at that time the west coast was located far inland from today's coast ocean waves broke on beaches in western idaho the blue mountains island arc was one of many island groups offshore plate tectonics gradually close the gap about 115 million years ago the blue mountains arc docked with the continent [Music] the collision occurred along a zone that passes close to riggins idaho near hell's canyon just east of riggins just uh three or four miles you come to what's called the suture zone and you can think of it as a zipper or something like that where the continent's been zippered together with these oceanic islands so this is a classic old vhs tape that somebody put on youtube and i'm grateful to them because i used to show this in class all the time so here's our different combinations of oceanic things that we've been bringing in and the next thing we'll look at is evidence for an old coral reef on an old ocean island that used to be on the far side of the pacific now in oregon as well as the environment where they lived it was soon discovered that some of the fossils from hell's canyon were part of an ancient tropical coral reef [Music] this startling discovery added another twist to the geologic story of hell's canyon coral reefs only grow near the equator in warm ocean water yet here were parts of a fossil reef over 3 000 miles north of the equator and thousands of feet above sea level stanley's work confirmed that the ancient rocks of hell's canyon formed in the ocean and they could have formed thousands of miles away in a tropical setting that bears no resemblance to hell's canyon today so it's an amazing story just in the wallawas in the bottom of hell's canyon here's one more clip from george stanley from university of montana fossil discoveries in the wallawa mountains hinted that the blue mountains island ark was once an entire ocean away i'm standing at the ichthyosaur site and ichthyosaurs are swimming marine reptiles that live during the age of the dinosaurs this particular ichthyosaur fossil was a skull discovered by a high school student very inadvertently who stumbled upon it here in these shales ichthyosaurs like this are swimming reptiles but this particular one is known from only one place in the world and that's in china and that supports the idea that these rocks might have originated very far out in the pacific far away from north america a fossil find in hell's canyon proved that the ancient islands migrated far north from their tropical setting geologist sydney ash a professor at weber state university found the remains of an ancient forest on the banks of the snake river so if you're keeping score we still haven't gotten to the mexico evidence yet if you're losing patience please don't leave it's coming i promise we're still just at super terrain one we're still the thing that came in that didn't move thousands of miles to the north but we're almost there i promise so here's inter montane belt super terrain one the first battleship to come in the insular belt including vancouver island super terrain 2 the next battleship to come in and then all this stuff that got squeezed in between our batholith complex in between the two of them we're going to skip this one and we're going to go right to a couple of maps from bc showing added 150 added 100 we've got that story now but remember they're not talking about mexico they're just ignoring it they're just talking about the most simple story about just bringing the things in out of the ocean and adding them to western canada and the north cascades what we want to do now for the rest of our time is talk about evidence that this stuff and this stuff was added down in mexico and got shifted north so that it now is next to super terrain one do you see all right so let's do that intermontain super terrain one here comes two we're still doing the traditional non-conversion non-traditional version of the story we're going to skip back the oh i got a couple of slides from san juan islands in case you love those places so we go to high twine 20 to anacortes we take the ferry out to friday harbor et cetera and if we get up there we can see that those san juan islands are also exotic terrain blocks the geology is difficult to do there there's too much growth in the way but if you're persistent you can find green shift and serpentonite among all these wonderful trees and ferns and everything else and if we get down to the deception pass area many of you love that area i'm reminding you of where this is now this is on a bridge between fidalgo island and the north part of whidbey island if we explore the bedrock on both sides of deception island we'll see good evidence of mesozoic exotic terrains ribbon chert you know what to do with that remember chert deep ocean floor we're on the ocean floor out in the pacific that ribbon shirt is now just south of deception paths iphone this is the exotic bedrock of the san juan islands it's all from the age of the dinosaurs and was added to the edge of north america before 80 million years ago this stuff's from out in the pacific someplace nobody knows exactly where but look there's a big old block of granite that doesn't belong here this glacial erotic was brought in from canada canada tropical pacific home sweet home all right so that was evidence we had a piece of the ocean floor the subfloor and the floor itself now in the san juans keep in mind we're trying to piece this story together outside of our lava areas and a few oil people have drilled all the way through the lavas to get to the rock beneath and they've found some of the exotic terrains below the lavas but we only have a few holes to work with so it's very difficult to restore that skip that skip this this is talking about celezia the kind of afterthought terrain that we're not focusing on tonight but that chocolate gumdrop came in 50 million years ago after the whole mexico shift happened so finally to the mexico evidence this is all inspired this lecture tonight is inspired from a recent national geology meeting downtown san francisco the geological society of america and i attended a very exciting session that had all these workers who had done work on this baja bc thing in the last few years and i was blown away at the evidence that they shared and since that time i've been reading all their papers and emailing them and trying to put this story together for you so cows glacial ridge mexico does that bother you saying that i hope not so what's the evidence let's start with the paleomagnetic stuff the paleomagnetic evidence so if you take a magma it's liquid underneath the volcano if you cool the magma off there are minerals that are going to start to grow and crystallize and get frozen into place if you have magnetic minerals a mineral called magnetite in that cooling liquid the magnetic mineral magnetite will align itself with the earth's magnetic field and if you are a paleomagnetic specialist you can take the orientation of those magnetite grains and reconstruct where on the earth latitude and wise that granite crystallized that was the original message from this guy up at western the pioneer of this paleomagnetic study a lot of evidence has accrued over the years that major chunks of the western edge of north america didn't form as part of north america they formed out in the pacific someplace and were transported by plate tectonics generally from the south to the north and then they were plastered onto the continent and then sheared up mount stewart was part of an exotic terrain that attached itself to the western edge of north america but where did it come from geologists at western washington university believed the rocks in mount stewart were formed far from here i drove over to western to visit merle back in bernie housing in their paleomagnetic laboratory merle in particular has spent more than 40 years on this topic collecting samples from mount stewart itself and analyzing that rock for a paleomagnetic signature i got in pretty early i'm not a founding father of paleomagnetism but i'm close you know i'm an elderly nephew sort of thing i got an nsf grant and i worked on rocks in the cascades and there it was mount stewart so we went up there and we drilled in about a little more and half a dozen places these granodiorite samples are part of their collection it triggered the whole controversy and it's such a beautiful rock paleomagnetically as well as aesthetically it gives you the nicest directions you've ever seen but those directions came as a shock to the scientific world if their initial results were to be believed the rock and mount stewart originated more than a thousand miles south of where it is today everybody said this guy's nuts and and the problem was mainly that they didn't understand how paleomagnetism worked so it's been a lonely life for merle he's been publishing these papers for much of his career and like some of the interesting minds in science has not had a lot of allies but that is starting to change so maps like this were showing up in beck's time where we took this block of mexico shifted it north and in the most simple maps you've got one major san andreas fault-like structure and the op the opponents to this say well where's this fault if this is happening where's this fault and there's two ways to answer that in my opinion one is remember we're going to open nevada like an accordion we're going to do clockwise rotation after all of this happens and so if we do have a major fault it's probably either offshore or underneath all of our flood basalts but if it's not a major fault and it's a bunch of smaller faults like the straight creek or the san andreas so far then we can piece that together as well and have a hard time looking so this is over christmas time my hand drawn diagrams here's mount stewart down in mexico here the san juans and mexico and we're going to get those guys between 75 and 45 million years ago up to their current position in the pacific northwest we need the cooler plate to do this remember the magic carpet ride that existed during that time window and the cooler plate was a piece of the farallon plate that broke off mysteriously nobody really knows why and the cooler plate no longer exists more evidence that i promised you i've got one slide for plant fossils because i know hardly anything about plants but if you study leaves and the shapes of leaves in other words leaf margins and you go to some fossil leaves up by winthrop washington and the leaves are 100 million years old and they're 100 million year old bedrock you can do an analysis of those leaf shapes and deduce an old climate and therefore an old latitude and the conclusion from this paper about 10 years ago is that from the paleo botany near winthrop that crust was 1300 miles further south which gets us down towards mexico the bedrock matches maybe the most visceral and satisfying way to convince you that this long distance transport happened involves bedrock that you've all seen most of us have been to wenatchee most have driven north to chelan on the west side of the columbia up 97 a right and this is what the drive looks like and most of you all i probably are not looking at these rocks maybe some of you are i wouldn't say they're super photogenic rocks but they're nices and shists that have a particular foliation and some very distinctive minerals and some isotopic signatures so the swat cane nice is exposed just north of wenatchee washington are you ready we have found through scientific work and by we i mean reading all these papers a bedrock match where is there more of that particular metamorphic rock palm springs california the same rock a slightly different metamorphic grade but uh hapmium and other specific details chemically make that work so let me go back the rock north of wenatchee and the rock near palm springs are identical and you're like well that's not mexico that's california man but remember if we restore everything san andreas fault and other things both this rock near palm springs and the rock near wenatchee were together done in mexico this stuff crossed the border to california the other stuff crossed the border to wenatchee so you know what you and i need to do we need to get in our car tonight and go down and fix this sign [Applause] squawking nice so in a brand new paper that came out bedrock in the north cascades bedrock in the mojave desert identical and there's controversy yet about the details of how those metamorphic rocks formed in the subduction zone you want more let's give you more evidence joshua tree national park all that pink on that geologic map is granite beautiful granite yes there's cool looking trees but we're interested in the granite the climbers love the granite of joshua tree are you ahead of me the details of this granite both the chemistry of the granite and the paleomagnetic signature of this granite puts this granite originally a thousand miles south of palm springs down in mexico who else was connected to this joshua tree granite mount stewart identical paleomagnetic signature identical pearl luminous chemistry we can hook those guys back together i told you this was going to be wild tonight did you bring your heart pills you better pop a couple more all these are individual blobs of granite that formed in the subduction zone but there's more evidence we're still with the big granites that are active when the subduction was happening and are no longer active when we have everything solidify all of these pink blotches from baja to central california to the idaho bath lift to the coast range of british columbia they're all these batholiths from subduction and it's a regional story all we have to do then is break off the mexico block with not only super terrain 2 but half of the batholith complex and we can send it north these are the maps that came out 20 years ago from the university of washington taking our block of super terrain 2 and half of the baffle of complex and sending it up to us and remember most of it's in british columbia just the trailing edge of it is what we call the north cascades you want more evidence peter ward from the university of washington has written a series of general science books he is a big fan of ammonites this is what an ammonite fossil looks like collected in some of the sedimentary rock on top of super terrain two this is what the ammonites looked like when they were alive in the mesozoic oceans the ammonites have been found in many of these mesozoic sedimentary layers in western washington a specific site that peter likes is a place called denman island it's part of vancouver island north of the city of nanaimo on vancouver island there are particular ammonites that he can identify that put it at a very narrow age range 77 million years old the only other place he's been able to find those exact same ammonites and those same kind of rocks is down in baja california we're south of tijuana we're south of ensenada he's got another site with the exact same fossils and the same kind of rock he wants to put them together before we do our mexican transport do you want more evidence you see there's a whole bunch of different kinds of evidence leading in this way am i sure this is right i'm not 100 sure right but there's momentum now with this idea and i think if that momentum continues and continues to have more new workers working with new techniques this will be solidified in the geological community let's go to the last piece of evidence the detrital zircons i tried to explain it quickly in the chalkboard let's try it again these are zircons they're little teeny tiny very durable minerals do you remember the little grains of salt they literally are a millimeter across like about the size of a grain of kosher salt so that's what these little zircons are here's how you get the zircons out of a rock we then start by washing it and then we crush it to chip size and a crusher that's much like those used in a mine and then we pulverize it to a powder which is sort of the consistency of baking flour then we pan that powder on a panning table so they've literally crushed a rock sedimentary rock down to flower and they're now separating out these individual zircon grains and with using jeweler's tweezers to select individual crystals and we pick say 40 or 50 of those to process further we want to see the inside structure of the mineral to see if there's any older nuclei on which the later zircon crystallized or is it entirely a homogeneous single generation crystal so we take some crystals and we mount them in epoxy and we polish them down to the center so that's the newest way to get information the newest technique you're down to these grains of salt and you're studying the chemistry of the grains of salt the zircon minerals and also the ages of them and remember the point if they're detrital zircons and you have a bunch of precambrian zircons you can try to find the source of those zircons in other words they were carried by a river and the river came from where did the river come from further east at this latitude then there's no story but if those zircons came down a river down in the mojave desert or further south in mexico then you've got more evidence that mexico got sent up here so the ongoing debate currently currently in 2018 is there's a group of zircon specialists that say the zircons that are in these north cascades rocks including vancouver island are from idaho and there's another group that says those zircons those precambrian zircons are from this part of old north america down in the mojave and there's arguments back and forth between those two groups but with the newest chemistry it looks like there's a better match from the stuff that i've read for this southern option to get these old zircons from the old part of north america and the rivers carrying those zircons in mexico versus idaho lake chelan will visit very briefly i used to think it was an exotic terrain story coming in off of the ocean i now understand instead those complicated rocks of mount stewart are at the deep part of a coastal volcano so instead of a block coming in off of the ocean we're at the edge of mexico creating these rocks you're about to see in this very short clip chris mattenson a geology professor from my school central washington university has had a long-lasting relationship with chelan's bedrock based on the composition of garnet and other minerals that occur in these rocks we know that they originally formed about 30 kilometers below the surface so these rocks record the processes that go on at deep levels underneath the volcanic system and this is one of the few places in the world where we can actually observe these rocks and study them some geologists say the volcanoes were further west and then drifted in and docked here others think the rocks are local and an incredible 15 miles worth of uplift brought this beautiful bedrock up the geologic elevator to the surface mexico mexico mexico mexico mexico mexico mexico mexico baja b.c originally mexico now mostly in british columbia let's finish where we started talking about dinosaurs the discovery of the dinosaur the t-rex bone it was on this tiny sutia island sedimentary rock of the mesozoic many of the other san juan islands are not sedimentary they're more these oceanic rocks we were talking about but it was a t-rex and here's a photo of the collecting site these guys were looking for ammonites and this guy happened to have an eye for a fragment of a left thigh bone of a tyrannosaurus rex this is what was found in the san juan islands this is a full sorry that's still what was found this is a full t-rex thigh bone for comparison this is what was found 80 million years old in a silt stone on suchia island part of a theropod part of the t-rex group the burke museum is about to get leveled and a new burke museum right next door being brought up but as you walk in the front doors of the burke this is the first thing you see right where they after they collect your money that's the first thing you're able to take care of and they still have a dinosaur exhibit but it's really just that one bone we've only found one bone so far in washington in 2012. all of these red dots are the active or the places we have found dinosaur uh bones in north america and so you're like well what's with all this then man you know i've been in eastern washington this is down at granger and then there's uh granger again where dinosaurs roam i'm confused like what is up like was there really a dinosaur bone found well no we can't confuse mammoths can we with dinosaurs we can't do that this is ice age this is the last two million years and dinosaurs are older than 66 but unfortunately that confusion persists even as you drive to ginkgo park and i get questions all the time about where are the dinosaur bones so i'm getting agitated as i speak so let's move on so i'm hoping that you're able to look at mount your beloved mount stewart with a new set of eyes and at least contemplate at least contemplate the possibility that much of the north cascades came from farther to the south so we've really got some work to do to continue this thanks for attending everybody i do appreciate it thank you very much you

Channel: Nick Zentner

Views: 7,143

Rating: 4.98773 out of 5

Keywords: Nick Zentner, Exotic Terranes

Id: r-_zEXWDPz0

Length: 69min 23sec (4163 seconds)

Published: Wed Dec 23 2020