Jeff Tepper: More Geochemistry

[@Siletzia]

Geochemistry was one of my favorite subjects back in the day. The conversations with Professor Tepper are a gift of extraordinary knowledge and presented in a way most observers can fully grasp.

[@PlayNowWorkLater]

Jeff Tepper for the WIN!! Omg! That was fantastic. Learned so much in this video. And Nick, thanks for keeping this engine rolling. Love all the content, and accessibility for us non-trained but interested in the wonderful world of geology. Great stuff!

[@cyndikarp3368]

Jeff explanations brings a more complex picture of geochemistry easier to understand. Thanks for helping this project.

[@reginebellefontaine4936]

This is immensely helpful ! Thank you so much professor Tepper for this lesson. I will come back to this video I am sure, and never be as lost, as afraid as I was when confronted to geochemistry in papers that are way above my league.

[@Ltngstrike]

A huge thank you to Jeff for so graciously giving his time to this project! Merry Christmas to you both and your families!

[@SteinsReality]

THANK YOU NICK AND JEFF!!!!! Nick from one educator to another, you are phenomenal at taking difficult to understand concepts and breaking them into bites of information, and feeding us in a way you don’t have to be a subject matter expert to understand. You also do it without putting us to sleep! I have fewer higher compliments to give! Thank you!!!!

[@_Michiel_]

Thank you Jeff! You're clearly a great teacher by wanting to make sure we understand these diagrams. And thanks to the A student Nick for asking the right questions so more details of the diagrams become clear to us!

[@mbvoelker8448]

Thank you so much, Jeff. Third time was a charm -- I get it now. :D I really appreciate your patience with those of us who struggle with the geochem. The structural and plate tectonics stuff comes easily to me, but the threat of looming geochem was one of the reasons I ended up getting my major in biology instead of geology back in the early 80's.

[@randallfarmer2340]

As someone who last took an igneous petrology course ~1980, this both a great refresher on the techniques I've forgotten as well as a wonderful introduction to what's been developed since then. Bravo!

[@eidrith493]

The posters from Tepper's students really explain it to me. Visuals say many words. Imagine the impact on the evolution of plant and animal life in the area. Siletzia would have brought in its own life forms, including coastal water preferring fish and invertebrates and the parts of Siletzia above water would have hosted some plant life and birds. It would be like in Australia collided with some of the Indonesian islands.

[@Engineer1980]

Wow, this might have been the most informative episode that Nick has provided over the last several years! Professor Tepper‘s ability to explain difficult topics in a way that is clear and relatively easy to understand is nothing short of phenomenal! I could not be more impressed with him and his skill as a teacher and as a scientist. Nick, love how you are linking the break off/rollback story with the history of the Cascade volcanic arc. The big picture view that you take and developing the regional or national geologic story is really helpful for us non-geologists to understand what has happened and how we ended up with the landscape we see today. This community is so grateful to you for what you do for all of us! Thank you, thank you, thank you.

[@thevirtualcockpit5001]

I live on the moraine in the shadow of the Sierra Nevada Batholith, so this series is absolutely fascinating to me. When I go on hikes and see the exposed geology of the Long Valley Caldera intersecting with the glacial carving, all of this makes complete sense. Much appreciated Professor Zentner...and contributors.

[@davidchapin3149]

That was really helpful!! Thanks so much Jeff and Nick. Really a nice explanation of subduction versus slab break-off magmas. The essay on BADR vs BR was also really good.

[@sharonseal9150]

THANK YOU!!! I am not able to watch this entire video until after my Christmas Eve party but I already know that his is going to be a video that I will watch several times so I can grasp the basics. Thanks Nick and Jeff for broadening our knowledge base. This was a genuine early Christmas present.

[@xwiick]

Thanks for all the hard work on these videos!

[@erickolb5108]

Well this is pretty cool! What a great reference for folks not able to access a college classroom. Lots of fun!

[@robmagee100]

Fascinating! I’m so grateful to Nick and Jeff for the time and effort to share their hard-earned knowledge! Learning is Fun! Truth makes for better decision-making! It makes me wish I was a lot younger, with a chance to explore and contribute to the field of geology! I feel a bit like a cobble on the hard, dry ground in the parable of the farmer sowing seeds, in that I am a musician, not a geologist, so I feel a bit selfish in enjoying and soaking up these concepts just for my own learning pleasure…

[@SingersMom-rx8wt]

Thanks Dr Jeff! I got to organic biochemistry working on my education degree but that was 1976! Still interesting. Got to Nick trying to learn about the geology of Utah but had also recently been across Washington. Love how this gives substance to visual observation.

[@kassy6373]

I love these detailed explanations of the science.

[@rayschoch5882]

Retired history teacher - not a geologist or geology student - but I'm enjoying watching/hearing this process, even though I don't really understand all of it.

[@diblust53]

Another great lesson from Dr Tepper! Thank you!

[@gregmoore2386]

Christmas morning keeps giving, thanks Jeff and Nick. Merry Christmas from New Zealand.

[@donnparis137]

Got it; love it: keep this stuff coming!

[@Kevin-Tice]

Thanks to Jeff and Nick-I so appreciate your commitment to learning!

[@willbradley7450]

I just got a great lesson or was it a course in igneous petrology. Wow, thanks Jeff and Nick. Nice foreshadowing too. You have got me like a salmon on the line, keep pulling me in. Geology is fundamentally FUN~!

[@danwelliver7643]

Thank you Jeff and Nick. What a great and informative discussion!

[@inqwit1]

Love it. Was headed out to people watch at a mall, and this takes precedence.

[@Elizabeth-uz1mn]

Thank you Jeff Tepper! What an excellent tutorial.

[@timroar9188]

A very good mini class. It makes it much easier to understand the spider graphs.

[@fez3606]

Excellent presentation! Many thanks Jeff Tepper for your tutelage. I will be referring to this in the future, no doubt!

[@treborg777]

This was a great idea & clarification. Thanks, Dr Jeff!

[@richarddavies7419]

Geochemistry- bring it on!

[@wildwolfwind6557]

Nice of Jeff to spend time doing this and well done❣ Nice to have the more in depth understanding of the various lines on the spidergram. The Nd & Sr diagram seems somewhat similar to the Hafnium. If the Hafnium values were available for the same Cascade volcanoes (including breakoff), the ones in the upper left would/should have low or negative Hafnium values and the ones in the lower right with more crust signature would/should have higher Hafnium values... right? 🤤 🎄☃

[@jefftepper6724]

Hf and Nd isotopes correlate closely, so samples with negative ENd would also have negative Hf values.

[@wildwolfwind6557]

@@jefftepper6724

[@BudKnocka]

Wait a minute,the wedge of Siletzia was on top of the slab that subducted…plugged the subduction…so we got OIB for Siletzia…plus ocean slab…subducting any melting of Siletzia would be OIB and asthenospere…after the slab burn through…would you get any melting it seems. Would Siletzia crashing into the crust…full stop of Siletzia and the subducting plate…into the Craton…so the craton bits would get pushed down into the mix…to get melted by the asthenosphere…so you’d have a series of four melts 1. subducting plate, 2. OIB Siletzia, 3.Spreading ridge Siletzia again, and 4. Craton Crust or craton sediments. Craton melts will be drier.

[@patmurphey5118]

Thankful for the deeper geochem!

[@alanrobbo6980]

Happy Christmas, and a Very Marry New Year, to Everyone from Nicks followers from the U.K.

[@Siletzia]

Yes, and Merry Christmas and a very Happy New Year to you and every one of Nick's followers in the UK from the US.

[@anaritamartinho1340]

Thanks to teaching, this is cool to learn🎉

[@hiker1658]

Answers my questions perfectly! 👍

[@timbyrne914]

Very helpful. Thanks! I was headed down a rabbit hole I didn't need to go down.

[@mikegerbman8141]

Enjoyed Jeff's GeoChem lesson.

[@stevenrey56]

Thanks gentlemen, that was very instructive.

[@kenmunozatmmrrailroad6853]

THIS AMAZING Nick! 'Bringing understanding to geologic theory which from the outside could be deduced as assumption.

[@pmgn8444]

Thanks Jeff and Nick. Very understandable discussion of the geochemistry. (full disclosure, I'm a retired chemical engineer, so I may not be the best person to ask if this was understandable or not! 😅)

[@jerrylitzza8842]

Thank You Jeff !!!!

[@dancooper8551]

This was so helpful! Thanks Jeff.

[@sandythixton4611]

That was fantastic and so helpful!

[@cybernescens]

These Deep Dives with Dr. Tepper are so engaging and informative, such a gift. A question for Dr. Tepper: is there an [affordable] text on this subject you could recommend?

[@Siletzia]

Most geochemistry textbooks are $200 or more. I have a couple of good books that are more affordable and recommended, at least by me, an avid amateur. The first is Geochemistry 2E, 2nd ed. (2020) by William White. I got my paperback edition on Amazon on sale for less than $75. Chapter 7 is "Trace Elements in Igneous Processes," which is applicable to this conversation. It was written for both undergraduate and graduate geology students. The second is Introduction to Geochemistry: Principles and Applications, 1st ed. (2012) by Kula Misra (that has got to be one of the coolest first names for a geologist, ever). This one is more of an introductory course in geochemistry for undergraduate students, but I think would be of value to graduate students, as well. Chapter 6 is "Geothermometry and Geobarometry" and Chapter 12 is "The Core-Mantle-Crust System." Ch 12 goes into the behavior of trace elements during partial melting of source rocks and magmatic crystallization, both of which are highly relevant to this topic and extremely interesting. That book also includes chemical variation diagrams. I think I paid less than $50 for this one on sale. Hope that helps.

[@jefftepper6724]

The problem is that geochem is a very broad field. Textbooks that seek to cover it all tend (in my opinion) to be dry because there is not enough context - geochem is a tool and needs a context. For geochem related to igneous processes I relied on chapters from Winter (Principles of Igneous and Metamorphic Petrology) but most of that book is about petrology. For environmental geochem I used the text by Eby.

[@cybernescens]

​@jefftepper6724 Thank you, Dr. Tepper. I think you mentioned 200 level geochem and so I suppose I meant a typical text you would use in such a class, if you use one. I will check out these recommendations as well. Thank you!

[@KirkHeuer]

Love the cross sections Jeff is doing. Planning on using them soon, more things to come, Do the plutons that do not make it so close to the surface get invaded by warmer and larger plutons later as time passes. does the cooling and crystallization of the magma cause lightening of the pluton causing the buoyancy to increase and make a uplift pattern happen to the batholith? Thanks for sharing this knowledge to us all.....

[@jefftepper6724]

It is common for plutons to intrude one another, repeated pulses of magma that can assemble into a batholith. Later plutons are not necessarily warmer, but they all tend to be low density rocks (rich in qtz and feldspar) that would contribute to crustal uplift and ultimately erosion and exposure of the plutonic rocks at the surface.

[@charlesward8196]

Geochemistry may seem too much like “Inside Baseball” stuff, but it is really what Paul Harvey used to call, “The Rest of the Story.” Every rock tells a story, but without the geochemistry, all you are getting is the CLIF Notes. Thanks for the video!

[@jefftepper6724]

A famous geochemist - I don't remember which one - once said that geochem is what converts idle speculation into testable hypotheses (or something along those lines). I'm sure he was biased, but I've always liked that quote.

[@charlesflorian1758]

Even more video, good going. Explained well. _ Thanks from really wet Prosser. Have great holidays.

[@GeologyDude]

That’s a very helpful summary. Thx!

[@danacwillis]

Would you recommend a commercial lab for the whole rock and trace element analysis. As you mentioned earlier a lot of older analysis did not include the trace elements, and that’s the case for my work, done in the 1980’s. I’d like to see where my Clarno Formation samples fit in terms of source geochemistry.

[@Siletzia]

I hope you get a response to this question, as I have been looking for a lab. I have Siletz River Volcanics samples from Myrtle Point (west of Roseburg) and Marys Peak, OR that I'd like to have analyzed.

[@jefftepper6724]

Hi Dana! Long time since Unocal! We send our samples to ALS Labs in N. Vancouver, B.C. I didn't know you worked on the Clarno ...

[@jamesjohnston3643]

Not that it's terribly an issue, but you might note that the vertical scale is log, linear. Have people tried to sort these using the distance between different sources of rock vs. mean? Obviously vs. normalized (i.e. 1 neutral, not absolute PPM) plots? I don't know how many sets of this information are available, but knowing something about the variation seems interesting to me. (by distance I mean per point on the vector sum (test)^2 -1 (1 being the mean))

[@jefftepper6724]

Yes, log scale is used to compress things on y-axis and make small differences between elements easier to spot. Plots are normalized to an average (MORB in this case) and I think you are suggesting it would be interesting to see standard deviation in that average used? As far as I know that's not been done.

[@jamesjohnston3643]

@@jefftepper6724 Not SD. Treating the vector deviation from 1 1 1 1 1 would, I think, help to classify things. Also, doing the cross-correlation, perhaps? Sorry if that's unclear. I do this kind of stuff on spectra all the time. Now, this isn't a spectra, but the ability of being able to normalize with MORB is a real blessing that I don't have in my audio work. :)

[@wildwolfwind6557]

🤔 How much faster would the rate of rollback need to be (relative to westward movement of NA) to have the age progression / sweep of the Challis magmas in northeast WA? 😻

[@jefftepper6724]

Great question! N. America is moving SW at 4-5 cm/year and rollback was sweeping across NE WA at about 5 cm/year, so I believe that implies that - relative to the deeper mantle - the slab was rolling back at about 10 cm/yr.

[@yukigatlin9358]

😃✨💞I love this, Nick!🩷This is exactly what I needed to be explained!! Jeff, thank you so much for your time!!😘💞 Could you please give us your slides in PDF, I would very much appreciate it ✨

[@jefftepper6724]

I will send the pdf to Nick tomorrow. Thanks for the suggestion, Yuki.

[@Kyle-b5x2k]

One question I still have - what does a hot spot spidergram look like? I really am glad to get a description of this geochem stuff - always something I didn't quite 'get'.

[@jefftepper6724]

A hot spot spidergram is the same as an OIB or mantle plume one (all names for same thing) - it would tend to have a hump at the left end (Sr-K-Ba-Rb-Th) but with no Ta-Nb depletion.

[@amacuro]

When you thiink you couldn't love Jeff any more haha

[@kellyhorton1462]

Hi Prof Z. Merry Christmas

[@kban77]

What kind of signature do the columbia flood basalts have? Isn’t there slab and slab break off issues there?

[@Steviepinhead]

Would expect some strong OIB/mantle plume signatures if the CRB are indeed associated with the YHS, right? ...And now someone who actually knows can chime in and confirm, or not. 😅

[@Siletzia]

The geochemistry of the CRBG basalts is complicated due to differences in regional stratigraphy, as well as for the regions you mentioned. Unlike Siletzia and Yakutat, which likely formed as a result of mantle plume-ocean ridge interaction of the Yellowstone hotspot, the CRBG formed hundreds of kilometers inland and thus its magmas have been subjected to mixing with continental rock material through partial melting episodes in different source regions that were variably enriched or depleted in incompatible elements. It is known that basaltic magmas can travel hundreds of kilometers subaerially and within dike and sill complexes, which can result in variations within a single major eruptive episode. As basaltic magmas traverse the crust, the melts are altered through differentiation and contamination processes which can modify the geochemical "fingerprints" of the eruptive products.

[@jefftepper6724]

Many CRB lavas have an arc signature, probably because they were contaminated by lower crust (which is all old arc terranes). But I believe that same signature could be acquired if the mantle plume interacted with the subducting slab (as it must have done!).

[@Dragrath1]

Ah so that is why Teper is being more cautious on the origin of the Grays river volcanics. Are there any elements/isotopes which can distinguish plume material from asthenosphere melts in general? I remember reading a par which talked about Titanium isotope ratios to gauge the degree of mixing of the upper and lower mantle but why does that occur? It seems to be something related to felsic crust but how does that work?

[@jmflournoy386]

Is Richards 2003 on the Cascades web page?

[@williamwood9948]

A second cup called for in the Coulton tonight... 🤔 ... Perhaps a slight taste of Sr , Rb ? Lol... Got stuck in the "weeds" (with Nick?), and some guy named Jeff came along with a winch... Isotopic!!!

[@Kevin-Tice]

The rutile is the “unfrozen saltwater”?

[@jefftepper6724]

Sort of ... in the salt water analogy we were talking about crystallizing (and what is left in the liquid - incompatible elements) whereas with rutile we are talking about melting (and what is left behind in that case will be compatible elements that are "happier" being in the left behind minerals than in the melt that forms (and ultimately comes to the surface).

[@donnaminar4689]

If Nick is an exemplarily student, maybe we should start to call him "Doctor Zentmer."

[@hughdanaher2758]

Why call it a “Spider Graph?” 😊

[@timbyrne914]

These sorts of diagrams are often drawn radially, like a bike wheel where the spokes representing each category, and the distance from the center representing the value. When you connect the dots drawing it that way it sort of looks like a spider web.

[@hughdanaher2758]

@ Spiders and spider webs I understand when I see them. The triangular charts are more like spider webs; they describe the push and pull of the chemicals in rock types from a central point. The two axis chart just doesn’t say arachnid to me.

[@mr.morelock]

@@timbyrne914 And here's me thinking it was named after a Student named something like "Randy 'Spiderman' Wilson". Ah well. Your explanation makes sense, too. I guess. ;)

[@hughdanaher2758]

@@mr.morelock I’m just a simple Eloi and didn’t realize such a logical solution.

[@jefftepper6724]

I think because someone thought they looked like spiderwebs ?? Lots of tangles lines.

[@ronaldderooij1774]

Poor Nick, he is clearly out of his depth and on top of that he is being told that this geochemistry stuff is kind of in everybody's toolbox...... 😂😂

[@jefftepper6724]

Only in the toolboxes of hard core igneous petrology aficionados ...

[@jmflournoy386]

Is there a TK layer in Selitzia?

[@jefftepper6724]

It's too young ... oldest rocks less than 60 Ma I believe. K-T was at 65 Ma