Exotic C - Craton vs Terranes

hello everybody how's it going this afternoon the local time is 1 43 in the afternoon and we will begin our program session c craton versus terrains at the top of the hour at two o'clock pacific time thanks for joining us how are we doing are we functional a little bit of a delay in the comments but mono make sure we're doing okay with the audio especially you've heard this one before five by five so the audio is coming through just fine huh solid blue light that's good to see the volume's a little low that's because i haven't ramped myself up yet i'm going to be talking like this i'm going to be excited today i hope i'm excited every time but i'm going to be like this still five by five if i'm this high if i'm this loud okay wonderful let's say hi to some folks here make sure we're doing okay ten by ten that's even better than five by five i think where's everybody from here devin uk hello elise kathy's in australia dw in tacoma the superior from boston mass boston mass boise idaho alabama carlton oregon deer park washington marysville washington notre dame indiana missed a few there new zealand hello wales terrific ashley's in portland taking beautiful photos every day ashley i enjoy those goldendale washington chicago red river gorge i like that area in kentucky the mouth of the columbia silver lake oregon kenosha wisconsin birmingham uk beautiful south eugene tasmania that's wonderful uh yep yep yep more uk that's great to see i'm glad what time is it in the uk i should have looked that up i'm sorry scotland what time is it for you guys is it midnight ottawa ontario texas no buffering yet 10 p.m okay good little nightcap for you guys botswana is are you serious sweden hello i saw an a person from namibia i can't even say it namibia that was exciting uh continues to be exciting to see everybody botswana hey cookie naguacco it's great to have you with us if you haven't been with us before welcome uh oh we got terrain names in nova scotia good lord okay let me check the laptop one more time i've got some thank yous uh today 9 47 p.m in boston uk i didn't know there was a boston uk yeah we still have some haze but we're doing better than we were earlier in the week and many are still dealing with major smoke issues with the wire wildfires here in the west but we're hanging in there the best we can and looks like things will be clearing out in the next by sunday morning when i see you next time but at this point we don't want to get our hopes up to be disappointed so that's great okay so looks like we're not buffering looks like we're five by five i assume we're we're functional uh i do have some thank you so let's get to those let me wet my whistle here quick so things are looking up with air quality at least here in the pacific northwest two very handsome coffee mugs for liz and i no water no coffee and these cups are these mugs are from dave and mary kay in seattle dave was in charge of the drinking water division water quality and supply for seattle public utilities for the last 20 years of his career and mary kay just retired after a 30-year career as a small animal veterinarian so thanks to you guys i appreciate it we will get a lot of use out of these thank you more from seattle this time lindsay on queen anne hill and lindsay knew that we were scheduled liz and i had had planned on doing a rafting trip down the grand canyon i've never been down the grand canyon in a raft before and that was supposed to happen this month so we've been pushed back to next september so lindsay sent some beautiful grand canyon books because she has experience in the grand canyon so lindsay thank you for that and a wonderful card thank you also lindsey set a flashlight uh to see scorpions at night this is next september when liz and i will be hopefully going down the colorado in the bottom of the grand canyon so lindsay thank you and lindsay saw session b and wanted to make sure we were not out of ketchup after session b last sunday so some fancy ketchup from lindsay in seattle thank you lindsay deborah sent a uh some help for uh purchasing uh vinman's day old she knows i like to go in at 5 p.m down in there to jeff's at jeff's at vinman's and get the stuff that hasn't sold i'm a cheap guy so she helped out with that deborah debra some masks some his and her masks to add to our collection we've got a lot but i always lose mine so uh that's helpful uh deborah says uh this is uh to nick zentner aka ned zinger and you're like why this this is a music group called utopia mostly featuring one of my favorite artists todd rundgren and on this vinyl album i wasn't sure deborah i had to check first of all i haven't looked at a vinyl album with the liner notes in a long time so this was fun but uh love is the answer one of my favorite songs ever and uh i shared that much to youtube's dismay with copyright stuff i said shared that last spring so and a six pack of uh german chocolate cake ale from the icicle brewery in leavenworth washington there's only one left we've already been enjoying them so thank you deborah very much and finally for the thank yous we have some birthday greetings patrick happy birthday patrick patrick patrick happy birthday tom foster this would have been tom foster's 61st birthday today so happy birthday tom and a box that arrived from pat in tacoma beautiful card by pat and her artwork on this card it's pat's birthday as well happy birthday pat and pat had these two very special coffee mugs for liz and i roses in liz's garden sunflowers in liz's garden thank you pat you are a talented artist and a generous person so thank you and happy birthday we actually have a slight breeze for the first time and seems like forever so i think everything's anchored down in case things get uh kerfuffled up what but we still have a few minutes let's make sure we're okay audio visual wise let's do that and then we'll say hi to a few more folks oh that breeze oh my god this is so exciting five by five five by five what the hell throw in where you're from too sorry patrick five by five and sprinkling in with a few more locations i'm not sure what kerfuffle is sometimes these words just come out of nowhere i can't say yeah i'm i'm pleased we're not buffering yet uh all good in connecticut the san juan islands lower queen anne well there's lindsay thank you lindsay marlborough massachusetts vancouver bc england lake county illinois nova scotia hey daniel geologically speaking aka todd always great to see you here nancy in missoula lk logan germany warren maine the netherlands the night owl garrett merrill stone island uh loving the breeze loving the breeze douglas arizona calgary alberta jim's in chico california somebody's in craters of the moon i don't know if i believe that or not fine in denmark pennsylvania red deer alberta you are so regular there red deer alberta nice to have you with us etc go badgers north woods 3d okay i um i think i'll save the scheduling information until we get started for real in a few minutes bavaria hello why all the smoke there have been a lot of forest fires uh for the last couple of months it seems like and so we've we've had our challenges all across the west and you know bleeding into the midwest at this point i mean but uh we're we're patiently waiting for a a change perhaps some kind of front will sweep through the backyard tomorrow so we'll see and we'll save our toasts to all the wonderful people who've been working hard on those issues among many other issues my god there's hard to keep track of all the issues that is for sure okay uh this wireless microphone system is so new that i can turn it off as i walk around and clear my head some of you had that suggestion last time when i was kind of off camera but still on mic and kind of coughing and whatever but you know this technology does not come easily to me and i don't want to turn this thing off and turn it back on just in case we're not working again so i'll be on my best behavior i won't do my hacking and my spitting and my whatever but i do need to walk around and just focus i actually have an outline in my pocket i should look at it one more time for today's session c terrains versus craton okay two minutes according to my watch thanks for joining us hey what the hell here's to you for joining us and finding us on a friday afternoon at 2 p.m i'm so glad that you're with us how many do we have over 500 okay good first buffer i'll pretend i didn't see that okay i'll see you in two minutes uh uh you well good afternoon thank you for joining us my name is nick zettner i teach geology at the university and towns called central washington university and we continue with these live streams from my backyard even though campus is open even though i'm teaching now face to face in the morning i had a good session this morning by the way with my students everybody wearing masks blah blah blah even though that's the case i continue with these live streams here in the backyard and i'm so glad that you're with us today and i hope that you can join us for all 26 of these live streams that we've had thus far we've had two i don't know if you've seen them session a talking about a magic window of time that we want to readdress quickly before we get rolling seriously today session b session b talking about glimpses of basement rock here in the american west that have exotic terrains on display and i think i'm now decided that i'm going to go two sessions at a time i'm going to plan two sessions at two sessions at a time and so c and d are friday now at 2 p.m and then sunday morning at 9 00 a.m pacific and here they are so i've decided we will stick with the original plan i had this title originally called craton versus terrain and i'll get into it mainly focusing on north america's craton today and i think that's important and you'll see why in just a bit i have changed the title for sunday morning the new title is passive margin and before we're done here this afternoon i'll make sure you see how these two things kind of work together and how it's almost to be continued uh from today to sunday morning at nine o'clock so exotic c exotic d thank you for being with us this is the topic today old north america the craton of old north america and you're like why aren't we going to be talking about these terrains why don't you get started why don't you get up to mount stewart already what are you waiting for why don't you go down to california why don't you go up to alaska we're doing that we're visiting all these exotic terrains and trying to take an inventory of bedrock and ages and fossils and paleomagnetic indicators etc but as a teacher i hope you can understand that i feel like we need to go there when we're ready and i really honestly don't know how many sessions we will do you and i before we actually get to the details of the terrains but i think this context is crucial if we just jump in and start going from terrain to terrain to terrain i don't think it's going to work it may not work anyway but we are in the setting the table stage yet again here today and i want to not only talk about what we know and don't know about the old north american craton i'd like to talk more about this line this boundary between old north america which we decided last time was older in other words this craton was assembled was built piece by piece i might add so we're getting into some new content right away everything is older than 200 million years ago in this craton going from spokane washington to new york city and one of the biggest messages from today i'll get right off my chest right now it's difficult to find this basement as well the main message from session b is that there's plenty of basement here in the pacific northwest but we only get a few glimpses because of all the younger stuff that's happened on the surface in other words most of this terrain basement is concealed that's also true for most of this old north america craton sometimes called laurentia don't worry about it it's old north america so we have a significant age difference everything here basement wise is younger than 200 million years old everything here basement wise is older than 200 million years old but we do have these incredible layers of sedimentary rock collectively called the platform of north america and in most places the old north america's craton is concealed it's buried under paleozoic and mesozoic sedimentary layers on sunday morning our next session we will be looking very carefully right here at something called a passive margin and we'll see that this boundary is even buried by some sediments but the main message is and i've made this way too thick but i wanted to show you that we know if we're on the old north american craton if we can kind of keep track of these sedimentary layers that cover them think of them like persian rugs the persian rugs are quite continuous in many places depending on how far back east you go they're just as simple as they look on this sketch when you get into the rocky mountains of course these layers are no longer flat they've been faulted they've been folded but as a recent interview with ralph hagar indicated he said even there you can kind of get things back to their original flat position you can't do that when you get into exotic terrain country so if you're looking to kind of keep score whether it's mentally or i don't know if you're really into it you're writing stuff out keep track of all the ways we're sure that we're an old craton basement or quote-unquote new terrain basement okay that was my introduction now on the chalkboard is pretty much what we had last time but i want to use it differently today and you might notice that this white line which truly is the boundary between old craton basement and new terrain basement is a drawn a little bit more carefully here today and this portion of this white line is the best place to study this white line and so we'll go to the western idaho sheer zone a little bit today a little bit next time and we'll continue to visit this area in western idaho okay um [Music] one of the lingering things from last time was why terrain t-e-r-r-a-n-e versus terrain t-e-r-r-a-i-n somebody sent this incredible book on i didn't get your name your name wasn't anywhere i don't think so this book by barry lopez home ground language for an american landscape so i'm like goody goody let me let me it's alphabetical to all these terms let me go to t uh nothing okay so that book was i'll use but was not helpful here i got lots of emails lots of comments et cetera i'll just run through this very quickly lorraine reports terrain t-e-r-r-a-n-e was coined in the early 19th century and comes from popular latin terrainum t-e-r-r-a-n-u-m uh jonathan says it might be i like this jonathan it might be helpful another email it might be helpful to remember the difference between terrain and terrain if you consider them as exotic words from another language they both started in old latin and then migrated into english but terrain ain took a detour through france baja to bc with words kinda i like that and william particularly helpful many of you were helpful but i don't want to spend a whole session on this uh williams says i looked up terrain a-i-n excuse me terrain a and e in the oxford english dictionary uh connected series of groups rocks systems of rocks or formation stratigraphical subdivision but most helpful to me is the recent history of the word terrain with an a-n-e all famous geology names here famous science names humboldt in 1823 first proposed terrain a e dana famous mineralogist terrain is used for any single rock or continuous series of rocks 1889 gk gilbert another famous geologist proposed to be used for a stratigraphical subdivision 1895 it's actually used in the literature and has been since that time so my main point and i think most of you know this a-n-e is a geologic term with each of these blocks of crush that have a coherent story and are bounded by faults terrain a i n is kind of a landscape oh my god i'm huffing and puffing this terrain is too much for me it's too steep that's a i n steep terrain gentle terrain beautiful terrain okay all right recall from last time please that we had glimpses in oregon the blue mountains we had glimpses of the basement in the klamaths of southern oregon and the siskiyous northern california we had glimpses in the north cascades where we're spending a lot of time but that's glimpses of the terrain basement not our discussion today i'd like to share with you a scientific paper that introduced me to terrain's a e in 1986 i was a brand new graduate student in pocatello idaho idaho state university didn't know anybody and our incoming group of grad students were forced to take advanced general geology and every week we had a different professor in the department come in but the theme for the fall was suspect terrains and this paper we kept coming back to now the date on this paper is 1980 by coney jones and monger and we dissected this paper then we looked at paleontology we came back to this paper etc and this was really my first introduction to the concept of exotic terrains or suspect terrain the map i want to share with you looks like this uh and i think i made a better copy of it yes right here i'm having flashbacks this is like 35 years ago i'm having flashbacks of seeing this craton stippling here alaska of course british columbia this is 1980 now the history of studying these terrains and how simple this craton is and how complicated this mosaic of exotic terrains are now we've made a lot of progress in the last 40 years but this concept of hopping from a quote-unquote simple craton to a quote-unquote complicated terrain basement is still a major message and that's part of the setting the table here this afternoon our magic window is between 250 200 to 50 million years ago and that's when we will be doing our terrain basement accumulation over the next few weeks to months but if we go back over here to the early days of the north american craton we're suddenly all the way down here into the pre-cambrian and that's where we will be for a majority of today we will be in the pre-cambrian we're going back thousands of millions of years ago so let's get to an actual map looking at the details of what we think we know about old north america's craton even though most of it is buried perfectly calm right now [Applause] have you seen a map that looks like this i'm going to give you a little bit of time to absorb it this is looking at old north america's craton and i want you to notice 1.8 billion years that's the same as 1 800 million years right so this is the size of north america 1800 million years ago 1 800 million same as 1.8 billion there's no washington there's no oregon there's no many of these states they don't exist yet at 1.8 billion years ago but of course the main takeaway and that's my coloring with my little colored pencils is making progress in realizing that our old craton if we're looking at this right now is a composite and these are all ages in billions of years so yes we're back in the precambrian but there's a complicated history back in the precambrian the course is difficult to piece together because we're so far back in time but this is just a tip of the cap to the fact that we haven't had we have not had this old north american craton since day one this old north american craton also has kind of a terrain story if you want to think of it that way so i've got one more of these maps are you ready i'm going to flash to it now this is as recently as 1.8 billion years ago and here's the coastline of this old north american craton which by the way pretty damn similar to today isn't it so this this boundary is so important to us because as recently as 1800 million years ago this is the edge of north america this is the edge of north america now i think this is from keith meldahl's book i can't remember which one but i really like the cartoons here more coloring so now in brown is what i just showed you that quilt that now is a cohesive unit 1.8 billion years ago and now am i close enough for you to see we've got other generations of material being added so again we're bringing stuff in do you want to think of these as micro continents you can do that i don't know if people use that term much anymore but that was the lingo 35 years ago micro-continents but the point is we added to the size of north america old north america's craton we add more material to old north america's craton now we're up to a billion years ago the next batch we bring in with the appellation story 400 to 250 million years ago and then of course in green is really our topic this fall so i hope this isn't two steps backwards before we go forward in the sense that oh my god we got more terrains we have to learn no we're not going to learn all these terrains i don't know that story anyway and i don't have much interest in learning it to be honest it doesn't have any bearing on our story here with the topic i'm looking at the old complicated history of building old north america's craton but you can and there have been plate tectonic models to talk about building old north america's craton in chunks and if you want to think of these micro continents being out there in the water then by all means if you want to bring that micro continent in and add it to old north america's craton and therefore gain a bunch of real estate by all means but we're not going to do a lot of this modeling for quite some time this fall because i want to make sure we have our facts straight before we come up with potential ideas on how this all works so one more time the old north american craton has distinct age areas within it i'll come in real close for you now but much of it is buried much of it is unavailable to us at the surface and when we do get a rare chance to see some of this old north american craton we jump on it where is the clo one of the closest places to ellensburg to see some of this very old north american craton and you might go well i guess john stockton's house maybe i don't know and the answer is no as we'll see on sunday most of the craton here is completely concealed by stuff we'll talk about on sunday we got to go all the way back into montana and wyoming to get a rare chance to see some of this old north american craton that has been pushed through the overlying platform we've actually activated part parts of the craton and lifted it and therefore eroded the platform overhead would you like to see a map of where we can find a couple places where the craton is exposed i'm hoping the answer is yes we doing okay by the way i'm gonna hang on for just a second we're doing okay five by five audio visual i'm sorry to pause but i'm just gun shy i just wanna make sure we're okay good so i've already made the point that this is the sweet spot for us this fall this level of detail to me these authors are finding the right level of detail but also keeping broad storytelling and broad kind of figures so this is what we're gunning for if you only want to buy one book and use it as essentially a textbook for our fall live streams i think this is it am i really plugging this book i guess i am i was surprised with our first session how so many of you wanted to get a book and like read ahead and all that well i think i'm now pretty clear that we're going to be using different pages out of this book this is the second edition of roadside geology of washington by miller and cowan we'll be referring to this almost every time so if you don't have this and you want to be thoroughly prepared and maybe even have the thing oh have the thing open while we're live streaming i guess i guess this would be the book to purchase but i mentioned last time that this roadside series goes back more than uh almost 50 years now and i found in my file cabinet the first a copy of the first roadside geology pretty sure this is the first in 1972 by the two guys at the university of montana that started this series look at the price 1972. and this is from the collection of don ring who passed away a couple of years ago i worked with don for many years don i miss you so in this first roadside geology book from the first printing it's kind of a collector's item really kind of stained oh oh god i think that was loose ahead of time here's there's little fold out maps that's how old this is so from the roadside geology of the northern rockies let's go to one of their first maps and can you see the explanation of the colors oh they're just writing it i see so this is yellowstone this is this is yellowstone park right here but the orange areas maybe you know the beartooth mountains just outside of yellowstone that's one place that comes to mind but there's others here i don't know the geography very well but the orange areas are where we truly have old north american craton lifted to the surface and exposed now this is quite a ways from washington for us to get our hands on some of the old north american craton that's been lifted to the surface and have the platform removed but there's plenty of places in the rockies where there's orange whereas there's old precambrian metamorphic and granites that are from the original material you might be confused right now you said i thought i thought there was i thought there was a bunch of craton in in washington you're saying there isn't i'm saying there isn't at the surface you got to tune in sunday to see the distinction between craton basement and we're kind of where old north america is but it's concealed by younger material so thank you to alton hinman for starting this all back in 1972. now from this vintage uh i was sent something similar which i've never seen before maybe you've seen what i'm about to show you so i got another thank you from this vintage in the 1970s ben in los angeles thank you for finding this somehow i think these are out of print ben's an animator in los angeles and he thought he would create this for us great job ben thank you okay so we've looked at old north america's craton and we're back down at this time now maybe the head is really starting to roll here a little bit i mean that in a good way i hope that i hope to mean that in a good way you're like what else do i know about stuff going on with north america more than one billion years ago or at least more than older than 500 million years ago maybe you know about this topic he goes to the white board so i did a lecture on this i don't know a year and a half ago kind of put it together at the last minute was kind of pleased with it this much of this was new for me but i got some help from a number of geologists who sent some very productive emails look at these dates and realize that this story globally of supercontinents it's just like it sounds if you're brand new to the concept where you truly are taking all the continental scraps of planet earth and gluing them together to make one supercontinent and therefore one big ocean we know for sure pangaea was a supercontinent between 300 and 200 million years ago but there's more and more evidence now for rodinya supercontinent between these dates and supercontinent columbia between these dates now if you're thoroughly wide awake you remember a significant date with those pencil-colored maps from keith there it is 1.8 billion years ago so we'll do a little bit more visualizing of the impact of especially rodinia the super continent on sunday the passive margin meeting we're going to have on sunday morning is going to be directly tied to this rodinia story but in general i'd like you to think at least a little bit today about supercontinents and the fact that it's not an accident i'll show it to you again can i find it uh oh can't find it can't find it i showed you two of those composites of the old craton of north america and one of them that was here's the craton here's the craton at one at eighteen hundred million years ago which is coincident with building supercontinent columbia and then there was some stuff younger than that so that's a key message to us so if you're looking for a really key message here we go this boundary in cross-section and on the map has existed for hundreds of millions of years we'll follow up with this on sunday but this boundary was truly the coast of north america i'm not necessarily saying west coast because we have all sorts of moving blocks north south this is up north is up south is down whatever but this is a long lasting edge until when until we start bringing these exotic terrains in 200 million years ago so we'll keep revisiting that but i can't emphasize that enough right now this is not just a tuesday that this boundary is here it is significant okay let's say you're skeptical for some reason it's healthy to be skeptical to a certain degree i mean you can go overboard i guess but maybe we can ask ourselves this question are we sure things are so different on both sides are we sure that the old craton stops right here are we sure it's not down here beneath all these other scraps of things on the surface yes we're sure and here's the laundry list of reasons for that okay one is that our beautiful continuous platform layers abruptly stop here and we cannot continue a regional set of sedimentary layers across these states can't do it so that's just one piece of evidence let me give you some more now we're into geophysics now which i know almost nothing about but at least i've found some images that i think might be helpful this is some imagery showing the thickness of north america's lithosphere and these are kilometers so the numbers on the right are how many kilometers thick the lithosphere is and the blue is the thicker lithosphere over 200 kilometers thick and the red is the thinner lithosphere and all i'd like you to notice is can you find some states first of all here's washington idaho etc and this boundary is not precisely what i've got here but we can agree can't we that using geophysics using seismic waves going through this material and tomography studies again i know very little the difference between the blue and the red is a sizable difference in lithospheric thickness and this is the first of many attempts to try to look into tomography to look down into the guts of the earth by looking at things indirectly and it'll be a struggle for me but one hope is to show you that there truly is a fundamental difference in lithospheric thickness between the old craton of north america and this scrap heap this quilt this fruit cake this parquet floor this side porch that's been built onto the main foundation of the house in the last 200 million years did that not work for you then let's try something else in the last 15 years a seismic line a seismic profile a geophysical study i'll put a line on here why not i don't have the map oh yeah i do hang on hang on hang on hang on patrick breeze is picking up now i'll show you the map first so there wasn't a trench physically dug uh going from this portion of idaho to this port this portion of oregon to this portion of idaho there wasn't a physical trench but you can think of it as a trench in the sense that some geophysical studies underneath this line tried to image what it looks like under the surface at a certain amount of depth and that location was chosen primarily because we're going from this to this very very different ultimately in the hope of studying this portion of the boundary my fingers on it right now this is called the western idaho sheer zone i've already mentioned it once the wiz and we'll refer to the wiz a fair amount throughout the next couple of weeks i think so here's a map basil tickoff at the university of wisconsin go badgers is has been part of this team i'm sure there are many others that i don't know by name but what you're looking at are these seismic stations i'm almost going to stop talking because i don't really know what i'm talking about but this is the terrain basement area in oregon here's old north america craton down below there's the whiz you can really put your finger right on this white line not in washington because it's concealed that's sunday's topic but in western idaho you really can it's to the east of hell's canyon towns like grainsville or white bird or riggins are nearby so this is the map showing where they put this study i should have the name of the study i don't think i have it but are you ready for what they actually found what it looks like in the subsurface going from terrain basement to old north america basement i assume you're saying yes here it is so first of all we're going from oregon to idaho we're going from crush that originated in the oceans versus continents and this is the moho this boundary between purple and pink is the moho which is the boundary between the crust and the mantle and i just want you to notice there's a significant break a significant change in the depth of the crust as we go across the whiz so my only point here because mostly i don't understand most of what i'm looking at and if you do good on you my main message is it's more than just a bedrock story about changing there's also a geophysical story where we change from one side of the white line to the next is that it is that the only reason we know there's a difference no there's one more and this is one of those topics that i don't know every few years i go i'm going to read on that and figure it out i've never understood it i'm finally going to sit down and figure it out and that was monday of this week of this past week and by monday night i'm like nope i gave it another try i don't know isotope chemistry at all and i can't follow what they're talking about have you heard of an element called strontium strontium i don't i can't even spell it strontium and there's different isotopes of strontium the concept is this first of all this white line on our map which is an important boundary between terrain basement and old north america's craton is regularly called the strontium 706 line and now we're back to 1986 and we're in that grad student session and everybody's kind of posturing and trying to act like they know more than they do that was never a problem for me for some reason i would just say i don't know i wasn't embarrassed i don't know why why don't i get embarrassed why don't i have shame i don't know but i i was perfectly happy at that stage to not bs and just say i don't get it i remember specifically saying raising my hand kind of meekly and saying what is this 706 thing i don't i've never even heard of that and the professors at the time kind of gave me an answer but it didn't really register even but that's almost 40 years ago and we are still using the strontium 706 line as a significant way to geochemically say where the boundary is between old north american craton and exotic terrain basement the concept is this all i can give you is the concept if you're an igneous geochemist and you study magmas and you study magmas that came from depth invaded from below through old craton and if you look at the chemistry the isotopic chemistry these very rare isotopes in that magma that came up through the old craton you will get a certain strontium value or ratio i don't even know like initial ratio i don't know what that means but my message to most of us who don't know anything about strontium either is that there is a significantly different strontium signature in magmas that came up through terrain basement so this is a very sharp line and it's been a sharp line on maps for 50 years i'll say it one more time by studying magmas that are invading this crust versus this crust there's enough of a strontium difference i can't give you more there's enough of a strontium difference that we draw this very sharp line separating those two pieces of crust or cratons or basements if you want to think of it that way so in washington so here's the western idaho sheer zone happens to be right at the strontium 706 line and then here's this thing coming into washington and then doing a big jog and then going up through bc almost clips alberta and then gets up to yukon and here's the 706 line the strontium 706 doing this whoopty whoopty all down through the sierras and into baja now this is how i've chosen to draw this and i'll just grab a couple of maps real quick and show you that there's still a little bit of difference on how people draw this strontium 706 line but it's a significant point for us because if you are in the green you're going to have terrains to talk about and if you're in the white you're not this line this line is my red line on this map so why is there a difference of a great if this is such a smoking gun this strontium business in the magmas why is this even a problem can you guess it's buried in a bunch of places we don't have magmas coming up through the craton and through the terrain basement and visible in many cases why the german chocolate cake ale the columbia river basalts so i'll give you a second to look at this here's the western idaho shear zone it really is a nice simple story there and this dashed line i don't know is it labeled oh yeah here it is the 706 line but people don't know what to do with the strontium 706 line when we swing into washington because there's too much flood basalt covering things up and you're like well can't you at least find it up here can't you once we get out of the basalts can't we find the strontium 706 line in northern washington well i guess but there's difference of opinion there as well so this is one attempt to swing it through now did i take their lead on this well here's another one this is from outside of the xerox room in my building edge of the craton for us today strontium 706 line they swing it kind of the same a little bit different but kind of the same very controversial where this exact boundary swings through washington and obviously that's an issue for us which we'll address a little bit as time goes on i got one more map to show you another option that is even more kind of perplexing to me but i feel like i want to show it to you anyway and it's the first time you'll hear the name robert hildebrand now robert hildebrand we will discuss a fair amount later this fall when we're ready he's got interesting ideas but he has these beautiful maps which we will look at i showed these a little bit in the spring i mean can you get let's not even care about the details but this is basically alaska down to mexico nicaragua to gnome hildebrand's done it less than 10 years ago but what i want to try to show you is he put in the strontium 706 line in a couple of places how can i do this hang on hang on hang on hang on patrick so this is the western idaho shear zone so here's exotic terrains in oregon just a little glimpse right look at all this pale yellow that he's using this is all covered this is all stuff that's getting in our way this is all ketchup thank you lindsay but that's why the western idaho hashir zone is important to us he's got this dashed line saying that's the strontium 706 line where else does he have it not many places if we jump down to eastern california he has the strontium 706 line which is what are you losing it it's this it's our major boundary between old north america basement and terrain basement he's got that boundary in california where to go through the sierra nevada batholith i don't know how controversial that is or not where else does he have this strontium 706 line he's got it running through the north cascades i think that's what that dash line is he doesn't have it labeled as strontium 706 but he's got it running right up through i don't even know what that is like if he really you know what maybe he just means the straight creek fault oh he's got one more place uh backtrack on that sorry you're catching this live man but he does have the seven oh so i didn't even notice this till right now he's got it in nevada as well which is kind of what we've said so did i waste your time there maybe i did maybe this is premature to show you this complicated map but even with all this complication i think my my main takeaway for you is that he's got the strontium 706 line on a complicated map like this indicating that's an important part of our discussion now just another loose end from last time almost done here last time we were talking about how we have so few basement glimpses of the terrain material because of so much activity in oregon for instance it's almost all buried in younger stuff younger than 50 million years old in southern washington it's almost all buried by the columbia river basalt lavas and we have to get up into the okanagan highlands or the north cascades to truly see some of this exotic terrain basement and somebody asked last time and i liked the question so much i went looking for an answer has anybody drilled through the ketchup or the german chocolate cake has anybody drilled through the columbia river basalt lavas and found a terrain and the answer is yes in one place shell oil was in here especially back in the 1980s looking for oil and natural gas and they drilled in a number of places to try to get beneath the basalts to try to find some sandstones and shales that would have some oil and natural gas they found a fair amount of natural gas by the way but it was so much effort and expense to drill through all this lava that they left those drill cores were revealed in different stages depending on who you knew that sort of thing but there was a well is a well i guess still called the darcel well i'm not even sure where it is i forgot to look that up before coming out here but it's a 7 000 foot well a hole drilled 7 000 feet down they got through all the basalts and they found some quartz shift to nice that's roughly 90 million years old which almost certainly has to be an exotic terrain now which one we're not ready we don't we don't know what our terrains look like we don't know what our terrains look like yet on the surface let alone trying to figure out what they are underneath all this lava but this 706 line business also is is is drawn kind of based on the very rare chances to see what's at the bottom of one of these uh holes drilled by shell oil so actually have pictures of the cores does that look like some nice to you it should metamorphic shifts to nice i can guess what terrain that is but i don't want to do it yet or am i giving away company information now am i some sort of whatever [Applause] so they got through the basalts they got through eocene graben sediments and they got into some exotic terrain material at the dar cell well in central washington okay it's ten minutes to three let me check my notes and see if there's anything else we pretty much have a crayton edge just a little sneak peek to sunday's live stream at 9 00 a.m pacific time called passive margin this is clearly an open coastline and an open ocean between 750 million years ago and 200 million years ago so these are gone and this is a bunch of fishes swimming around in the ocean off of this whiz off of this strontium 706 line for sure in ocean between 750 million years ago and 200 million years ago there it is you want it in print there it is and we need to discuss on sunday morning what evidence we have that there wasn't a terrain there that there wasn't a continent parked there and why am i saying 750 what wasn't it open ocean going back to the beginning of the earth the answer is no yeah now i'm trying to trying to get you to come back on sunday no i think that's it for today let's pause and see if there's anything else that i wanted to show you just one other thing we're pretty much leaving the earliest part of the pre-cambrian today and on sunday morning with our passive margin meeting we will begin in the late pre-cambrian and get into the paleozoic and talk about material at spokane that is burying our important boundary oh feels good i'm going to get the laptop i'm going to get the water out and what do you think i should put in it's friday it's friday now if you haven't done live q a with us it'd be nice if you could use the caps lock will i get everyone's question no will i try to of course i will i'm going to pop the live chat out like a boss right between the eyes look for some uppercase questions that you might have about the craton oh that's nice pat miller your piece is proudly on my bookshelf in my office pat is step to butte craton material no i thought it was until recently that will factor in nicely to sunday morning session a bunch of people asking about step two butte step two butte is old rock but not the crate time we're talking about today i'll make sure you see the difference uh in a bit uh nick the first page from my book went flying okay i'll look for it in the garden thank you has that boundary in the old north american wyoming craton block moved at all or has it remained kind of in the same place while stuff gloms onto it thank you device nine i of course it's within the north american plate so the whole thing's drifting with the plate i would think of it as being kind of in the same place and stuff glomming onto it i don't really know how else to think of it but i i i haven't thought much about those old rocks in the craton and maybe somebody maybe a few people who really know um pre-cambrian craton of north america or other continents by the way all seven continents have one of these old cratons and then terrains added on to the edge maybe somebody can add something down below that has meaning it'd be nice if you added a comment that you you were confident what you were saying that you actually had information that was helpful to everyone do you think there are isotopic lines like this on the moon i don't know i don't think so are there fun gems to find and can we do a field trip i love gems just like you do i don't know how to find gems in well i i assume you're asking about the topic today the craton and all i can think of are the rockies or eastern canada actually now that i think about it the canadian shield is a place where all the platform has been stripped away and the craton is right there at the surface in ontario and northern wisconsin and yeah but i just don't know that geology at all nick i thought we were working between 50 and 200 million years ago we are we are but as discussed at the beginning we're setting the table it's the ter it's the terrain story that's in the window we're talking about north america before the terrains arrived i hope that's clear thanks for the questions where on our modern day globe would pangea be situated uh i'll i'll include that on we're gonna go to the cozy fort for the first time on sunday and i have some global animations from christopher scottis i've talked about his youtube channel before it is excellent and um we will place north america at different latitudes and longitudes using christopher's work then what was west of the whiz before 750 million years ago thank you suzanne that's sunday i don't want to give it away the crayton cross section was great does it show where the inland sea area was in north america before the uplift of the rockies that's really what this is about mount sil sylvania these platform sedimentary layers are recording inland seas these are sandstones and shales and limestones that regress transgressions and regressions that's what i was taught when i was an undergraduate in wisconsin we would look at the saint peter sandstone and the some dolomite i can't remember the name right now and you can follow those platform layers so yes if you're familiar with the inland seaway and the age of the dinosaurs and the uplift of the rockies that's all here covering the craton and that will not be a discussion item for us does the strontium 706 line follow the rocky mountain trench or vice versa there's a chance i can find this hang on just a second maybe not i'm sorry i can't we're going to look a lot at the terrain maps that i have for british columbia and yukon and alaska and i have noticed that that strontium 706 line at least that this white line does follow the rocky mountain trench ish and i don't know anything about the rocky mountain trench i mean it's interesting to me that this white line is about where the columbia river is coming out of bc and going into washington is that a coincidence these are things that i've kind of noticed and are curious about and i don't know if i can find anything meaningful um but i'm willing to to to try my hardest stupid way to say that i'll look into that the best i can automatic scroll to the bottom let me come back we'll do a few more here it's not even three o'clock yet great questions thank you for them all is there an exposed layer where one can see the strontium 706 line i guess the western idaho shear zone is the best but remember now this is this is strontium information coming from magma blobs that are on both sides of the white line if that's what you're asking but if you're really just asking can you put one foot on old north america and one foot on terrain the western idaho shear zone is about as close as you can get to that at least in the pacific northwest but you'll see on sunday there's a few problems with that even i like the spirit of your question though will glacier national park and its geology be making an appearance in the near future a little bit sunday but that's it eric the uh the sedimentary layers from glacier park going all the way back to spokane is the topic for sunday and that's pretty much it well it might not be because i've already gotten a bunch of questions from many of you saying you don't really talk about the rockies you're talking to me now you don't really talk about the rockies at all the laramitorogini and there must be some story with these terrains coming in and a connection to the rockies and i've always taught something about the rockies that i don't think is right i've been teaching stuff and i've admitted to my students i don't think it's right and i don't know how seriously i want to carve out time for the rockies but we might uh we might try because i i need you know our biggest mountain range and i i i don't really teach much about them because i don't see i feel like there's some problems a few more guy does the difference in thickness at the boundary affect earthquake period periodicity on the western side i don't know about a thickness difference at the boundary here influencing seismicity there's decent earthquakes that are happening on this map that are far away from the subduction zone that are pretty mysterious to most when will geologists deem the terrain belts of the north american courtier and be considered part of the craton so we were looking at i think i get your question eric i didn't show you this so here's a picture of north america 1600 1680 million years ago in other words almost 1.7 billion years ago and if i come in close can you see the outlines of so here's montana right there i really i don't know which way north is on this but i think eric's question is is saying you know we look at this now as just homogeneous craton even though it's made out of these individual microcontinents or terrains at what point will we kind of color everything just craton i don't know i guess if people are studying north american geology 50 million years from now i guess i don't know it's just a convenience for us to emphasize how unique these terrains are that's my best answer there i think i got your question pritchard formation coming on sunday do exotic terrains become part of the oh you're asking the same thing gene so yes these cree cratons have evolved over time but the expanse of time is so wild remember now we're making these cratons these old cratons over the course of thousands of million years whereas our magic window is just 150 million years of bringing stuff in so these maps i'm showing you from this time look kind of like a quilt just like this looked like a quilt but please remember that the the time scale is so much different that we really can't focus too much i don't think on the micro continent accumulation history of the craton patrick age seven how does it feel is the border between the crate and the terrains mostly vertical or is there a craton under the terrains great question patrick as always this is about as before we had this seismic profile 10 years ago we didn't really have anything like this so this is the white line this is the boundary patrick and i don't know this looks kind of continuous doesn't it and yet there is this break in the base of the crust and i think we should think of the wiz as vertical until we have data to suggest otherwise but we have no evidence patrick to suggest that this old craton continues over here and that's really i think the big point of the whole meeting here today there's no evidence that this continues over here a few more and we're done alan if you if you have an ocean to the west of the craton there should be ocean crush joining the craton question mark you bet that's coming are there serpentine rocks in the craton there may be uh i don't want to belabor this too much because i don't know the accuracy of this or how involved this is but we will use this concept in general throughout this fall if you have something out in the ocean and you've got the rest of the continent nearby and you're eventually going to take that thing out in the ocean and add it you've got to get rid of a bunch of ocean floor and does all the ocean floor definitely go down the tubes much of it does much of it goes down a subduction zone but plenty of it gets caught in the suture zone itself i don't want to do more with that because we're ahead of ourselves lethal leaf says emerald creek recreation area garnets i have no idea if that's part of our story today or not does the different strontium levels in the magma represent the age or the character of the rock definitely the character of the rock that was the whole point of talking about the strontium signature and i'm being loose because i again i still don't know what they're truly measuring it's some kind of ratio there's even another strontium line called the strontium 708 line i don't i don't get that but it the point is magmas coming up through a certain material are going to affect the chemistry of that magma even after the magma solidifies it's going to have an isotopic signature that basically talks about what the magma ate through and if we have magma coming up through significantly different material there'll be a different strontium signature of those magmas okay ed why does the junk writing on top of the subducting plate get smeared onto the uh we're not ready for that ed we don't even know what subduction is yet people asking about floods okay we're off topic uh i'm trying to pronounce your name geniba siddibe how old is the north american craton compared to the oldest rocks we can find on earth so what are the oldest parts of the north american craton and how does that compare to let's say the oldest rocks in the craton of australia which is quite famously where some of the oldest rocks or maybe the oldest rocks on the planet have been found i have to go to my notes one last look at this map from mel doll pretty sure it's from meldow m-e-l-d-a-h-l do you know him he's an excellent author so the this portion of the old craton slave i'm just looking for big numbers and there are definitely older rocks sir or madam from other cratons so i think they're i know there are older rocks in australia from an old portion of their craton compared to ours and if you want to know why i don't know why okay a toast to you here's to your health on a friday afternoon here's the health of all your family members near and far about all your friends whether you check in with your friends by phone or text or email or actually are lucky enough to see your friends from across a fence or with masks friends are important and of course here's to all the exceptional people men and women around the world who have been dealing with all of our crises in 2020 and that list is long we've had a lot of crises but we have a lot of good people with expertise who are helping us thanks for joining us on this friday afternoon i'm going to stick with this i assume we didn't have major buffering problems and pretty quiet liz is still at school she's happy with me doing this before she gets home muffler boys i don't know in school i don't know it's just been damn pleasant out here so it works for me i didn't i realized it doesn't work for any all of you uh some are working at this hour i get it but uh maybe because these are in installments session a b c and so on maybe these will be viewed and enjoyed much more in replay than live i'm not really sure but since many of you are not able to watch us live i'm sorry but i'm sticking with this i think and the next time i'll see you will be sunday morning 9 a.m pacific which is a normal time for us here in the backyard where am i ellensburg washington you are i ellensburg washington usa tgif and thanks to you for watching i'm coming into the white acts right now with my index finger thank you i love you happy birthday goodbye you

Channel: Nick Zentner

Views: 21,861

Keywords: Nick Zentner, craton, terranes

Id: XiMeA2c8JNs

Length: 89min 11sec (5351 seconds)

Published: Fri Sep 18 2020