First Fold 2009

The traditional "First Fold" picture - see 2008 and 2007). I just can't get enough of this cool folded bed in the lower Prince Albert Formation.
This class was fun - and every one of them was pretty keen in the field! Also did their chores without nagging! Truly a first on both counts. It was a nice one to go out on - my last trip to Laingsburg, at least as a lecturer at UCT.

It was a big year for transitions - as Dr. John Rogers, our sedimentologist with whom I have taught this part of the field course for the last 4 years, will be retiring at the end of this year.
We were lucky to have the two new guys (our replacements) accompanying us for the trip, in a kind of hand-over. It was great to be in the field with them and see all the energy and interest and excitement they will bring to the department. They both saw a lot of research potential in the area too - I hope some of their plans will turn into future Honours projects for these students!

As you can see, they worked well together in the field. All the groups did. I haven't seen their final maps yet but I have a feeling they will be good.
Every year I change it up a little bit - we usually do a "structure training day" and a "sedimentology training day" before they start mapping on their own. This year it went particularly well. I decided to focus directly on field methods instead of rehashing the structure topics we discussed in the classroom. We practiced sketching from afar and ground-truthing the sketch, and talked a lot about scale and planning where to go. Here's an example of a student with his field sketch of a faulted anticline thrusted over a faulted anticline. That peaky Prince Albert Formation sure does take up a lot of the strain in this part of the fold belt.

Here we are on the last day - the last day, for me, of formal teaching at UCT. Pretty sad about that but also looking forward to the next phase of my life.

The Cake Practical

The theme of this month's Accretionary Wedge blog carnival is "Time to Think Out of the Box", in terms of approaches to teaching. I thought I'd contribute an activity I've been running in my classes which comes directly out of a box - a cake mix box.

We spend a lot of time in my Honours tectonics class (that's equivalent to a senior seminar in Tectonics in the states) talking about the lithosphere.

We discuss and in some cases, calculate:

• the flexural thickness (relatively thin, <10km>
• thermal definitions (thickness varies, but temperature is really a proxy for rheology),
  
• definitions based on a sheared layer (high seismic anisotropy) separating the lithosphere from the asthenosphere,
  
• more abstract definitions based on calculated rheologic transitions (using more complex proxies than just temperature)
  
• discussion expanded this year to include looking at sub-continental lithospheric mantle which has been a stable geochemical reservoir for a very long time.. therefore not likely communicating with the convecting mantle (shout out to my colleague Steve), a distinction which is obviously important and in some places observable but was previously not on my radar.

However, for the students to really grok* this they have to have a good grasp on the concept that the same material can behave both as either an elastic or ductile solid under different conditions of pressure and temperature. There begins the search for an analog material.

The Cake Practical

As it turns out, cake deforms elastically at low stress and non-recoverably (let's call it viscous) at higher stress. This is a cheap tolerable proxy for Maxwell behavior. I bake some thin sheet cakes - from an ordinary cake mix - each pair of students gets about 100cm² piece of 3cm thick cake. The technical staff of the department was kind enough to provide me with a few "core samplers" = pieces of 1" pvc, about 2" long, with a nice bevel cut around one end to sharpen it for cutting into the cake. They also need an ordinary metric ruler and a watch or cell phone with a stopwatch.

The students cut as many sample cores from the cake as they can. This leads to a bit of waste, invariably eaten, thereby increasing the general level of blood sugar excitement in the room.

Fernando shows his glee at performing rheological experiments
on rock analog materials. Photo: William Cheng.

I give a bit of a talk about elastic at low stress, viscous at higher stress rheologic models and remind them that elastic deformation is linearly related to stress by the Young's modulus:

σ = E * e
where σ is stress in Pascals, E is the Young's Modulus in Pascals, and e is the linear strain (change in length / original length).

They are also reminded that viscosity is the relationship between stress and strain rate, not linear strain, by the relation:

σ = η * ε

Where η is the viscosity in Pa*s and ε is the strain rate in s^-1.

We assume a Maxwell rheology wherein:

σ = η ε + E e

and also assume that if we do experiments at very low stress, viscous strain negligible (all strain is elastic) and therefore set η ε = 0 at very low stress. This enables the students to isolate the Young's modulus (E).

Load is applied by placing other food items (of labeled mass, e.g. small cans and jars) on top of the cake cores. The students measure the surface area of contact and calculate applied stress.**

The students are asked to design and execute experiments to determine:

• the Young's Modulus

Cake sample after elastic rebound (there's a bit of a delay there - hysteresis loop?)
Photo: William Cheng

This turns out to be amazingly reproducible. For my cake this year, everybody seemed to get a result between 5-8 kPa. Or, since the concept of significant figures doesn't seem to have taken hold, 6449.33352 Pa.... that's another issue.

• the elastic limit

100g jar of capers produces about 1.2 kPa load on the cake core.
Amazingly, at 50% shortening the cake core still rebounds elastically.
Must be all those eggs I put in.
Photo: William Cheng

This parameter is bracketed by increasing the load on the sample until the sample no longer rebounds elastically to its original height after the load is removed. For the cans and jars I brought, all groups bounded the elastic limit at between 100g capers and 400g organic kidney beans. With our cake core samples this is between about 1-6 kPa. Next time I would get more intermediate weights.

• the viscosity (for deformation above the elastic limit)
  

Under the 400g can o' beans, the cake has gone viscous and very little rebound is
observed. No conch shell or painted stick reported either...
(Photo: William Cheng)

The viscosity is the most unreliable part of this experiment, mostly because the students have to estimate the timescale of deformation and that timescale is very short. Perhaps larger pieces of cake would address this....

Anyway this prac gets good reviews. The discussions of the lithosphere seem to go well afterwards, although I will let you know for sure after the exams in October. I have used the same concept for a more open-ended inquiry and had students investigating the shear modulus by sheathing the cores in plastic wrap and shearing them, investigating the temperature effects by freezing them and microwaving them [don't tell the boss I broke into his lab for a little N₂ (liq)]. Obviously no amount of temperature increase is going to allow dislocation glide in chocolate so the metaphor rapidly breaks down. However - I never have to clean anything up with this lab... except wiping a few crumbs from the table tops.

Hoping someone out there will improve on this or suggest improvements... leave me a comment if you have any ideas!

*I was introduced to the Grok concept by my algebra II teacher in high school who made us chant (daily) the quadratic formula "so that if any of you two reproduce, your children will be born knowing it". Well, Mr. Steiger, x equals the opposite of B plus or minus the square root of B squared minus four-A-C over two-A.

** Yes I'm aware that the labeled weight on the can only refers to the food inside and does not include the weight of the container. Trust me this is not the largest source of error here and anyway, saves time and hassle when the students have only a short time to complete their experiments.

Carrots and brains

I made these! I fought the snails.


My lithops are turning themselves inside out for spring. Absorbing their old leaves and making new ones. Resurfacing like Venus. Looks like brains.


You know what else is cute, but I don't have a picture? My students had a slumber party on the roof of the geology building last night.

Carried away at the Pizza Place

This is what can happen if you mark cross sections and eat pizza and there are crayons on the table. Particularly if you keep thinking about what you wish the cross sections would look like...

It's that Field Mapping time of year again

Hey folks I'm back from Laingsburg again with the 2nd year field trip. Every year it seems to get better and better as the sedimentologist and I iron out the plan and I get to know the field. This year's class seemed particularly keen and that makes it even more fun of course. And since they've let me know they found this blog, I'll say they were also clever and good looking, and don't forget to turn in your course evaluations kids. Anyway.

Here's the now traditional "first fold photo" (see 2007 first fold photo). Always a bit of a step up learning about trend and plunge and remembering strike and dip. This year I had an extra prac during 2nd year structure and we used it to do some mock mapping exercises. Seemed like it helped. We were forced by the weather to do things a bit differently this year because it snowed/sleeted on our first day of instruction. What the hey? this is not why I moved to Africa, to field map under ice. At least, not Quaternary ice...

Anyway I'm going to try to arrange some more inclement weather for next year because that was the only day the students complained about the mapping conditions. Awesome.

I digress for a moment to show you a cute tiny angulate tortoise. What could be cuter?

We return to customary annual photos with the "giant pencil cleavage fencepost" installment for 2008 (see 2007 giant pencil cleavage fencepost). This beauty makes use of the Laingsburg Formation turbidite sands.
Sunrise on the last morning in camp:
Time to rise and shine!
more hard core geology posts to come!

Snowball Earth Strata near Kogelfontein

Some time ago, in the middle of an igneous field trip no less, we were out on the coast of Namaqualand near the Kogelfontein igneous complex. The Kogelfontein rocks are Cretaceous, which to a South African is pretty much Yesterday, or in other words, that piddly small part of the geologic time scale that nobody bothers to learn. Did I mention that my students don't learn the Phanerozoic part of the time scale? And similarly, I never learned the other 80% of the time scale? Remind me to chalk that up on my list of SA-USA translation problems in English. I do feel like I've been accepted to some degree, with all my idosyncracies, because people don't correct me anymore when I say "Al-U-Min-Um"**. But I digress... it is a blog after all.

Anyway we took a detour to see this incredible outcrop of interbedded black turbiditic shales and clean, beautiful white marble. Yes, shales (sedimentary) and marble (metamorphic, or should I just say recrystallized).
This assemblage, Neoproterozoic* in age, is a key assemblage in the Snowball Earth story - a story better told by other outcrops in other places, perhaps, but there's evidence for it here if you accept it as such. The story goes that at 600Ma (give or take), the earth experienced a total glaciation - most of the continental landmass at the time was at high latitudes, close to the poles, and as earth cooled and entered the glacial period the continents were completely covered by ice sheets. If you're familiar with the concept of albedo - the reflectivity of the earth - you will know that rocks will absorb light and heat from the sun and re-emit it all as heat, warming the atmosphere. Ice, on the other hand, will reflect the majority of that energy back to space, and will not do the nice turn-light-into-heat action that bare land can do. The bare land bit is important here, because this is hundreds of millions of years before plants, or fungi, or any of those great heat collectors working for us today emerged onto land. So a planet with its land mass covered in ice is a very cold planet indeed, and has lost its means for warming itself from the sun's heat.

As the story goes, tectonics was still chugging away under all that ice, warming the oceans from mid-ocean ridge volcanoes and supporting tiny islands of bacterial life. The combined effect of the geothermal heat and the CO2 from volcanoes and life was eventually enough to break the cycle of cooling, and the planet warmed again. As land began to see the sun, the warming sped up and the oceans warmed up very quickly.

One of the fascinating things about CaCO3, that is marble, that is the most common mineral form of CO2, is that it is reversely soluble - that is, it dissolves more easily in cold water than in hot. That's the opposite of most everything, sugar, salt, most other minerals... So when the oceans were cold, there was a lot of CO2 dissolved in them. When the oceans warmed up quickly, all that CO2 was no longer stable in the dissolved state and CaCO3 - limestones - precipitated on the seafloor all over the world. We usually associate limestones with warm shallow places - coral reefs, etc. - but in the late-Neoproterozoic warming, limestones were forming everywhere, even in the very deep sea. Enter the outcrop at Kogelfontein.

The black shales here are deep water deposits (again, or so the story goes) that are very rarely found in association with limestones, anywhere in the rock record. Here they are together, repeated at least a couple of times: a shale, a limestone, a shale, a limestone. Or is it?

Here's trusty TA Duane pointing out the reason for the repetition. The reddish rounded lump he's standing on is the long thin hinge of an isoclinal bedding parallel fold - the axial plane of the fold lies in the plane of bedding.
The fold is ultimately doubly-plunging - it rounds off at both ends like a big sausage (that would be wors in local parlance) but there are others along strike. And in between, some beautiful evidence of tectonic interference with the stratal succession: shear foliations in otherwise sugary marbles, and strange little cuspate-lobate structures on ptygmatic folds (not sure what that folded bed is). That ZA 50-center is the size of a US quarter.


Here's a shot down the axis where a quartz-rich bed is desperately trying to maintain its radius of curvature in spite of the drag:


So the moral of the story is: earth warmed up, and here we are. Whether these marine seds actually provide anything more than circumstantial evidence for Snowball Earth and catastrophic warming of the oceans is still under debate. The other moral of the story is: don't measure section in an accretionary complex***.


*Neoproterozoic is about 1Ga -> Cambrian, for those who share my timescale bias problems.
** as opposed to "Al-Yu-Min-E-Um"
***I don't really know if it's an accretionary complex. It's supposed to be an along-strike equivalent to the Malmesbury Group down here in Cape Town. But that's an axe to grind for another post.

Nouswells, Northern Cape

A few weeks ago I went on the third year Igneous field trip to the northern cape and southern Namibia. What an incredible part of the world. We drove north through Springbok, South Africa on the N7 and left the highway in a terrane of rounded granite "koppies" in a sea of red sand. The sun went down on us while the vans got increasingly stuck in this sand.
Here's the first time we got stuck... Turns out flash flooding a few weeks before had washed soft sand across the old sandy tracks in this desolate area of sheep herding. The ground surface was marked by mini-deltas, braided stream channels, and all kinds of tiny miniaturized flood features in the fine sand. We ended up leaving the vehicles in disarray all over the desert and hiked in the last couple of kilometers to the campsite.


In the morning, Chris handed out some aerial photos and we sent the students off into the desert while the instructor team got started on the digging out process.

Due to the mid-day heat, we started them out early in the morning and had them return to camp for lunch/siesta and back out for more mapping in the afternoon. This was the first time for me mapping in an essentially all-intrusive landscape. There was enough diversity in the intrusive suites that it's not too hard to tell them apart in the field. In contrast to mapping bedded rocks however, structures are often obscured and it's almost impossible to predict what you might see at the next outcrop since you have no "initial shape" model to work from. That means you have to actually visit every outcrop you can find. This makes things a bit slower...
Here's an intrusive contact between medium-grained pink granite (top) and porphyritic adamelite (bottom). The adamelite is easy to identify because it has those big squarish feldspar crystals. The intrusive contacts here are "soft" like this - and irregular.


The country rock to all these intrusives is the Orange River Volcanic Suite. These were generally some gritty, blackish-green actinolite metabasalt and some metasediments. Here's a quartz-talcy shear zone with a sheath folded quartz vein!!!! Props to Johann the metamorphic petrologist who found this and showed it to me!!


Here's the class checking out some of the amphibolites in the ORVS:


Duane caught this crazy beetle out of the air. They buzz around slow and lazy making a mini-helicopter sound.

Here's an awesome fault surface in the ORVS. The rock here is a quartz porphyry - maybe - but it might be a metasomatic product. The thin darker pink layer on the surface of the outcrop is a cataclasite layer, and the rounded quartz grains get stretched out into ellipsoids with increasing flattening toward the cataclasite layer - and oh yes, I got a gorgeous big oriented sample.

More on Plagiarism

Yesterday I posted about the issue of students plagiarizing from blogs, which, judging from the response, is clearly a touchstone issue for a lot of us in the business. The comments mostly centered around discussing the criteria for appropriate use of blogs (and similar sources) for students.
Andrew has taken to the next level with his comment:

"Christie, you've probably been plagiarized before. What's different this time is that a colleague informed you--but why did they do so? Did they ask you to change your practices? What do they do at their school? This is a separate discussion from the one you've chosen to feature. What do you expect of your peers? Can teachers be 'bad teachers' "

I should clarify here that the colleague who contacted me did not ask me to take down the material, or to stop blogging about local field trip areas. His words:

"Your blog should include a warning -- "NOT TO BE USED FOR UNDERGRADS ASSIGNMENTS" !"

He's right - and so timely considering the discussions going around - rather than complaining about use/misuse I can take steps to address inadvertent cases by giving some instruction for appropriate use when I post potentially useful information. You'll see from the warning I chose to put up that I didn't follow the letter of his recommendation. I do think undergrads can use this information for assignments, according to principles of appropriate use. I don't know the details of the field assignment at Neighbor U.

In answer to Andrew, you're right, I probably have been plagiarized before. My initial response to hearing about it from a colleague was a bit embarrassed - wondered if I had done something wrong. Glad to have been reading all the recent discussion about blogging because it helped clarify my opinion that the internet really has changed everything about information and intellectual property, as well as propriety - and our societal expectations haven't adapted to address that. Asking my students not to google a topic when they have been assigned to read about it would be even more hopeless than asking them not to download Heroes from a mirror site in Thailand. But I digress.

At my institution we are able to use Turn-It-In, a service which compares submitted text to millions of print and web sources and simply highlights identical strings. I then go through and visually review each string. I did an informal experiment in which I read a paper first and circled suspicious areas. Turn-it-in identified the same trouble spots, but saved me a lot of time by identifying the source. This service has taken a lot of criticism for various reasons - one being the presumption of student guilt. Since professors have been manually comparing sources to check for plagiarism since the dawn of papers, I think the writing and the checking should move into the internet age together. I am not swayed by any of the arguments against using the service.

My undergraduate institution had a very strict honor code. I left with a very polarized view of plagiarism and people who committed it.

In my current position, I realize that plagiarism is probably much more common than I previously thought, and that there are subtleties that can cause students to cross the line without evil intent. For example, I busted a student last year for a "mash-up" essay - basically interleaving complete sentences from two or three sources into semi-coherent paragraphs. When I confronted the student about this, he/she replied that this approach was necessary because he/she didn't understand the material but was trying to patch it together to complete the assignment. He/she was genuinely horrified to be accused of plagiarism and had honestly wanted to do the right thing. The concept of synthesis - of taking information 100% from other sources but phrasing it in such a way as to make it your own - was not there.

In response, I developed a handout on writing - probably too long to be read by many students in full! But I am comforted to know that when a student is in violation, I can at least demonstrate that they were specifically given a definition of the "mash-up" and told that it was not appropriate. At a school which has no liberal arts component, sometimes students are expected to learn this by osmosis but in my opinion, it is much more effective to teach them explicitly how to write scientific papers. Subsequent results have been much better and the students are motivated to follow my guidelines. So in answer to Andrew's "Can teachers be bad teachers?" I think I would hesitate to use the word "bad", but maybe we fail our students when we assume prior knowledge that they don't have. And that includes failing to give them clear instruction on our expectations.

This situation is not really a test case for all these subtleties, because the student who plagiarized was so blatant that there is no way it could have been inadvertent, and the colleague who contacted me made a simple request that I agreed with: to suggest guidelines for appropriate use when publishing information that could be used in many ways.

(c) 2008

*Click here to download my writing handout in Word format. Anyone may use any part or the whole document for any teaching purpose, no attribution is necessary. It is somewhat poorly organized anyway so I will fix that for next year.

Bad Students! No!

I just received word that a 3rd year student at a nearby university turned in significant portions of my Sea Point Contact field trip post for his/her own field trip report to the same locality. Fool! No pity for plagiarizers!

As a new grad student I once googled some suspicious-looking text strings in a student's New Idria field report and discovered that a recently graduated student had posted all of his school projects on his website for some reason. Naturally the student failed and I wrote to the blogger and asked him to take the material down or password-protect it. At the time I felt this was a fair course of action because the material he posted was an exact model of what we were asking students to do.

Now what about geoblogging? Field trip blogging? There's been a lot of buzz lately about whether it is ethical to critique or comment on peer-reviewed papers in the blogosphere, where the public often has access to the critique but not the original paper. In my opinion, anything that's published becomes public information and commentary is free. However, some discretion is advised, because these blogs are often written by people who carry some kind of official authority on the topic and there is a fine line between the "official word of the scientific community" and some casual spouting off by somebody who writes the "official word" as their day job. The discussion made me think about my flip language on this blog and my tacit assumption that if nobody comments, nobody reads it. Not true, eh? I suppose I could check my stats on blogger or something.

Anyway, I would like to think that somebody might be interested in the geologic information I post, as I am interested in others' posts, particularly field experiences, research questions, etc. but I am HORRIFIED that students might misuse this material. Almost worse is the thought that students or anybody else might inadvertently use blogs over more reputable sources. Students:

(I'll spare the rest of you for now, but any students who want to hear it, drop me an email.)

I am not going to stop blogging about field experiences and interesting problems. I can't anticipate every assignment that might be set at every university (although I could have anticipated this particular one, had I thought about it) to avoid writing something that might be utilized by an unscrupulous person. I will however, add a threatening copyright notice.

It's in the sidebar.

What else can be done? Anything?

(c) 2008 C. D. Rowe

What I've seen recently besides my honours students all day every day

Green Point Stadium - under construction for World Cup 2010.Experimenting with lino printing.

Now back to prepping for my practical exercise tomorrow - turns out nobody remembers how to add or multiply vectors, today's prac was a slog.

Rock of the Week #1

When we were out in the field, the third years told me they felt they needed more practice identifying rocks in hand sample. Of course I asked myself, "What would Hilde do? She would find a way to give a prize." Thus was born:
Each week I will put a new and different rock out in the office with 3-pts worth of questions and all the students will try to identify the rock and submit their answers. Winners for each class level are named at the end of the semester. Just for fun, I'll post the RoW here on my blog as well and you kids can play along at home. This is the e-RoW. No handlens, knife, or acid on the monitor.

RoW#1:
1. What is the dominant mineral in this rock (1 pt)
2. How was this rock formed? (2 pt)
Some third years examining RoW#1 in Shirley's office:

Malmesbury Group and the SeaPoint Contact

The Geological Society of South Africa, Western Cape Branch held its end-of-year field trip on Saturday 8 Jan. I have been working on this blog post since then but got distracted writing a shorter (less slangy) summary for the GSSA WCB newsletter. So sorry but here it is finally. It was a walk through the Tygerberg terrane of the Malmesbury Group up to the lit-par-lit contact with the Cape Granite at Sea Point, Cape Town. Now don't give up yet, I'll tell you what all that means in a minute. The leaders were Prof. Alex Kisters (structure) from U. Stellenbosch and my dear friend Dr. John Rogers (sedimentology) from good ol' UCT.

Zircon is a great little mineral that grows during igneous or metamorphic heating in rocks, and it takes in all the Uranium. After the hot period ends, the uranium starts to decay, like a little stopwatch in the rock. This makes it possible to date the igneous or metamorphic heating in a rock. If that rock then erodes, dumping sediment into an ocean basin, the zircon's other special feature comes into play - it's darn hard. It survives all that tossing around and when you collect the sediment millions or billions of years later, it's still intact, tiny stopwatch ticking away. Even if the sed has been through another heating event, it's possible to find some of the little grains which didn't reset their clocks. So you can say, the age of the youngest zircon stopwatch in the sediment (or detritus) is an older boundary on the age of the sedimentary deposit. See? cool.

Anyway, the Malmesbury Group is a huge pile of shale-siltstone-sandstone deposited in the latest preCambrian times. It is therefore not fossiliferous in the least, which makes it somewhat more difficult to determine exactly how old it is. Some people have picked detrital zircons out of it that give 3 age groups: 2 billion years, ~1.5 billion years, and 545 million years. This means the part of the Malmesbury where these data were collected was deposited after 545Ma.

John got us started off with an orientation at Three Anchor Bay. John can be counted on for all kinds of maps, rocks, artifacts, old theses, any type of "visual aid" one could possibly wish for on a field trip!

The sedimentary structures came on fast and furious. You would have to hike miles and miles across Kodiak to find a tenth of the good stuff we saw in less that a mile of strolling. Here is a gorgeous bed that I (and Saranne Cessford, thereby earning me some credibility) interpreted as a rip-up bed: that is, a bed of sandstone, minding its own business on the seafloor, got torn up by a mudflow! which ripped it into blocks, later to settle out in the mud.


Mega version of the same: a true Olistostrome! Here full big sandstone beds have been tumbled and broken in a massive mudflow. This one is only about 4m thick but imagine if it were an order of magnitude thicker - that's where it starts getting really complicated to tell if a melange (or mix of rocks) is made by sedimentary processes or tectonic processes. Ask me later why that even matters, it's a whole nother question.

OK now for the real fun: Name That Structure (NTS). We used to play this game as undergrads, when we were first learning structures... Thinking, no doubt, that this was a rookie pursuit and we would soon run out of structures we couldn't identify. WRONG.

Something weird happening here, not immediately obvious. It has to do with bedding-cleavage intersection, but the bedding is not... normal. is it caused by the cleavage? or is the cleavage wrapping around some weird bedding features? Two pictures and then my theories. First outcrop photo: vertical joint surface normal to bedding strike, cleavage is vertical, bedding dips ~50° to your right. Second photo, cleavage barely right-dipping, bedding is left-dipping, and the big limpet is ~2cm long axis.

Theories (and I should say here that initial impressions split quite neatly between sedimentary and structural geologists):
1. Scallopy bedding - these are ripple marks with sand lags into the troughs. Cleavage later wrapped around them.
2. Structural feature - less well defined but since the wavelength is seriously perfectly regular, as well as the amplitude, and these only occur in the fold hinge - maybe they are some kind of disharmonic folding.
3. Rayleigh-Taylor discontinuities, with top planed off by subsequent turbidity currents, overprinted by pressure solution cleavage which intensifies within R-T "intrusions".

Obviously option 3 is all me and I can't blame anybody else for it. However I'm currently 60% for option 1. Opinions? How come nobody comments on my blog? And is it really true that the Japanese geologists have a petrol-rockblade-skillsaw which would be the perfect sampling solution to this kind of problem?

We get closer and closer to the contact with the granites and little dikes (dykes; ZA) seem to emerge everywhere - dikes which are folded with the pressure solution cleavage - serious compression (ductile!) during the granitic intrusion - leaving NO EVIDENCE whatsoever in the absence of active strain markers. Isn't that beautiful?

Here we have John showing Alex's sketch of the contact. The cross section Alex drew is visible to the naked eye in the profile of Lion's head which we could see from the road. Really nice place to see into the rocks. In the foreground you can see my pal Kirsten from Dresden. She runs the new ICPMS (inductively coupled plasma mass spectrometer) at work, that is, unless Eskom randomly shuts off power to random neighborhoods at random times during the day for 2-2.5 hr intervals. Oh wait that's exactly what's going on! It's called "load sharing". Maybe Ken Lay faked his own death and has found a new liberal state to punish with Enron style rolling blackouts! Or maybe not. but I digress...
Now we come to the best part. As you can see in the hillside of Lion's Head, above, we were walking from the black shales toward the edge of a big granite batholith. The contact runs right through Lion's Head and the 403Ma sandstones unconformably overlie it. As we approached the contact there were more and more little granite dikes, then bigger, then we started seeing evidence of macroscopically ductile flow in the black shales as well as the pinkish granites:
The layering is parallel to the contact, as if the granitic magma squeezed its way up hundreds of tiny parallel cracks into the black shales. There is a bit of a metamorphic aureole but really it's only a few 10's meters wide of spotty hornfels - not too hot and not too big. That's a good piece of evidence to suggest that instead of one big giant bubble of hot magma, which would have really cooked the rock around it, the whole body of granites might have arrived slowly over a long period, through tiny cracks. Kind of like ants in my kitchen... one then 10 then 1000...

The big square crystals you see are feldspars that crystallized in the magma chamber at depth and were carried up with the migrating magma. You can see in this photo that some of them seem not to be in the pink granite, but are actually surrounded with black shales. How is that done? Alex gave an explanation based on Norm Sleep's (Stanford) theory using a really elegant fluid pressure model of one of these tiny cracks. Here's Alex with his explanatory sketch, which didn't photograph, so here's my attempt to recreate it:
Anyway all the parallel dikes create an overall gradational contact where there are thicker and more frequent dikes until one crosses the contact and then it's all granite. This is called lit-par-lit or bed-by-bed.

so the question that remains: did the shale melt? or just deform viscously (but very slowly) under high temperature?



There are some conspicuously NOT FLUID looking blocks in there.