Unnatural Histories: The Lonely Mountain - Part 6

If you've missed the other bits, be sure to check the rest of the series:
Part 1: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain.html
Part 2: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_16.html
Part 3: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_9632.html
Part 4: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_1042.html
Part 5: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_5911.html

Okay, so far I've proposed that the Lonely Mountain is the eroded remnant of the intrusive igneous and hydrothermal component of an ancient arc-volcanic system. Going back to the earlier part about the Misty Mountains, we can now look at this mountain system with a slightly different view. The Misty Mountains is our currently active collisional tectonic feature. The Ered Mithrin could be made of reactivated sutures (from various accreted terranes as Forodwaith and Rhovanion converged on each other) plus erosional highs of more resistant rocks formed through earlier tectonic activities.

What I like about this model is that it doesn't require plate tectonics to be "active" everywhere all at once. Not every feature we see on earth is a result of currently active tectonic processes. Many features are the remnants of past activity. Think of them as a kind of of tectonic "fossil" that has survived simply by not being completely eroded away.

So that has me wondering: do Dwarves or Dragons use a tectonic model of economic geology to decide where they want to live?

Unnatural Histories: The Lonely Mountain, Part 5 - Iron and Tectonics

Okay, the story so far: we've got this "paleo-continent" of Rhovanion with features like the Lonely Mountain and the Iron Hills. Looking at the formation of gold deposits, the most common places on earth include late-stage igneous melts and hydrothermal systems. Something more easily found deep in the bowels of a volcanic system rather than at the surface. Let's take a few moments to look at the Iron Hills - a few leagues to the East. If our volcanic system was once an island arc, could we get iron somewhere from this system too?

Iron ore minerals. Left to right: Taconite pellets, massive hematite, banded iron formation (BIF). Taconite pellets are processed silica-rich iron ore that has been pelletized for easier transport by rail and boat.

Again, let us look to some real-world examples. Most of the iron mined in the world today comes out of "banded iron formations" found in places like Northern Minnesota, Wisconsin, and the Upper Peninsula of Michigan. Other places around the world include the Pilbara region of Western Australia. Many of these deposits are old - like 1-3 billion years old - old. Most of these deposits are associated with deeper marine waters, such as continental shelves or abyssal plains in the open ocean. Conveniently, this deep-water setting is something that could also form in proximity to an island arc. And just for the sake of completeness, an island arc can also be home to carbonate reefs. And carbonate rocks at the surface can yield karst (caves & sinkholes) topography - including caves vast enough to house the elven Woodland Realm palace of King Thranduil. Fun times!

An unexpected tectonic journey: a subducting island arc and associated back-arc basin. The raw materials for our Rhovanion paleo-continent.

Just for fun, let's think about this subducting island a little more. A "Back-Arc Basin" is a feature associated with subduction systems that is counter-intuitive and seems almost magical at first glance. But looking at the dynamics of the situation makes perfect sense. The subducting ocean crust causes the crust on the other side to "roll" over a little bit. Kind of like bending a block of wood creates tension on the top of the bend. This tension can translate into crustal thinning - and produce a small extensional basin adjacent to the compressional subduction zone. Wacky, but then again we're talking about huge slabs of rock that behave differently than we're used to at these immense spatial and temporal scales. And this back-arc basin would have its own associated hydrothermal/igneous system as a result of the decompression melting - hello volcanic-metal-sulfides!

So what do we have? We've got some future Lonely Mountain as an ancient volcanic island arc, rapidly being approached from the rest of the Rhovanion continent acting as the hammer, with the continent of Forodwaith to the north waiting to act as the anvil:

Tolkien-tonics: a hypothesis for the origin of the Lonely Mountain as volcanic island arc. The entire system is collisional in that Rhovanion will eventually collide with Forodwaith, sandwiching the other bits in-between

In the end, we get a bunch of crumply bits along the border of the Forodwaith continent, which may remain as erosional highs (like the Appalachians are today). Then a relatively flat central Rhovanion "craton" and millions of years of erosion exposes the frozen heart of that ancient island arc volcanic system, leaving it as an area of higher, more resistant rock. And chock full of hydrothermal/igneous gold-bearing goodness. Oh, and all those deep marine iron-bearing sediments laid down in that ocean in between Forodwaith and Rhovanion are now pinched up and exposed in the Iron Hills.

Rhovanion/Forodwaith cross-section during the Third Age of Middle Earth

Whew! That is a lot of geologizing. My sixth and last installment will bring us back to the "current" tectonic setting for The Hobbit.

For a complete overview of this series:
Part 1: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain.html
Part 2: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_16.html
Part 3: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_9632.html
Part 4: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_1042.html
Part 5: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_5911.html

Part 6: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_8985.html

Unnatural Histories: The Lonely Mountain, Part 3

When we left, we had established the possible tectonic system responsible for the two large mountain ranges related to events in The Hobbit. The Misty Mountains to the West, and the Ered Mithrin to the North. Side note: Ered Mithrin means "Grey Mountains," and Gandalf was called "Mithrander" or "Grey Pilgrim" by the elves… Any guesses as to what "Mithril" means? Tolkien was an Oxford Professor of Linguistics after all.

In order to untangle the Misty Mountains and Ered Mithrin, I suggested we take a closer look at earlier tectonic clues. In this case, the clues found within the crust that makes up the region called "Rhovanion." Tolkien describes the area west of the Misty Mountains as "Eriador" and north of Ered Mithrin as "Forodwaith." Since geologists often use regional names as a convenient way of tracking old chunks of crust, we'll look at the paleo-continent of Rhovanion.

Geologically speaking we have a few landscape features that are probably important. First, there are several large rivers - the Anduin (The "Great River" down which Frodo and his eight companions paddled south out of Lorien). The southern-most tributary of the Anduin on this map marks the spot where Isildur was waylaid and killed by Orcs on his march back to Eriador. The One Ring he was wearing slipped off his finger and fell to the bottom of the river, to be picked up years later by a hobbit/hobbit relative named Smeagol whereupon he took it deep into the Misty Mountains, only to lose the ring and have it picked up by Bilbo on his way to the Lonely Mountain… Goodness, it's like Tolkien spent years of his life piecing together all sorts of history for this Children's book he wrote (which he did, of course). Where was I? Oh yes, rivers.

Along with the Anduin is the Forest River and the River Running - both of which flow South and East. Interesting to note the headwaters of both the Anduin and Forest rivers start in the foothills of the Ered Mithrin. While the Anduin continues straight south along the edge of the Misty Mountains, the Forest river veers off to the East towards the Sea of Rhune. Something, then is creating a drainage divide between these rivers - some topographic high in the northwest corner of Mirkwood. The River Running also skirts past and away from other topographic highs such as the Mountains of Mirkwood, the Woodland Realm of Sylvan Elves (from whence Legolas the Dreamy would come to join the Fellowship of the Ring), and the Lonely Mountain. Another river that flows into the Sea of Rhune comes south of the Iron Hills.

Thus the rivers help us locate topographic "lows" and the area between rivers helps define topographic highs. Along with the features important to the Middle Earth narrative, we get a better picture of the paleo-continent of Rhovanion.

But how do we get at it's tectonic history, now that all the easily-identified features have long been stripped away by erosion or editorial expedience? The key lies with economic geology. Namely iron and gold - the topics of my next post.


For a complete overview of this series:
Part 1: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain.html
Part 2: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_16.html
Part 3: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_9632.html
Part 4: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_1042.html
Part 5: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_5911.html

Part 6: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_8985.html

Unnatural Histories: The Lonely Mountain, Part 2

I hope you've had a chance to look at a map of Middle Earth. There is a lot going on - the landscape was formed by the need of Tolkien's narrative. Tolkien was a linguist, not a geologist. But he based his descriptions on the places he knew. So his landscape draws on the same geologic history that formed our own world.

In the map above, we see three main features. On the western edge of the map is the long range of the Misty Mountains (they extend further north and south beyond this sketch). To the North lies the Ered Mithrin, or the Grey Mountains. East of the Misty Mountains lies Mirkwood - a large expanse of oak and beech forest. Incidentally, much of the plot for the Hobbit movies comes from the appendices of The Lord of the Rings and the Silmarillion. Although the plot for the movies doesn't really "follow" these sources as it uses them for general plot-directions for Peter Jackson's story. If you watch Peter Jackson's films with this in mind, you'll be much happier. But I digress...

Physiographically the Misty Mountains and the Ered Mithrin form long, linear topographic highs. These kinds of features are often indicative of tectonic stresses distributed over a large area. On earth, "active" tectonic boundaries tend to have these features. The stresses caused by one plate interacting with another deform the rocks along those boundaries. It's not unreasonable to think that the Misty Mountains indicate such a feature.

We can use the shape and orientation of the mountains to infer plate boundaries and the orientation of the stress. If you hold a phone book and push in with both hands, the book will bend. But the orientation of the bend is perpendicular to the direction you push with your hands - like so:

Deformation either from pushing on the phone book, or that caused by colliding tectonic plates, tends to be oriented away from the direction the stress is coming from. Since stress is coming from the left and the right, the least amount of stress is acting forward and backward (with regards to the above picture). So the deformation occurs in that direction.

Since the Misty Mountains are oriented North-South, we can reasonably assume the stress is coming from East-West. And since we have uplift (mountains), we probably are seeing the crust thickening at this boundary, such as happens when two plates converge on each other like India and Asia. If they were pulling away, we would see thinning of the crust - and perhaps a rift valley or three like we see in East Africa and the Arabian Peninsula.

So, we would probably make the same assumption for the Ered Mithrin. But would we be correct? It's not an unreasonable thought, since these are also a long linear uplift feature. But these are oriented perpendicular to the Misty Mountains, which we've already established as forming because the tectonic stress of two plates is oriented East-West. We need to adjust our thoughts if the Ered Mithrin is also forming due to converging plates. If, perhaps there were several plates - the plate below Mirkwood moving Northwest, into a plate on the other side of the Misty Mountains, and another North of the Ered Mithrin. This isn't easy to do all at once, so perhaps the collision forming Ered Mithrin happened first and the Misty Mountains formed later?

Perhaps - this could work, but maybe we should look earlier in time. It might be that an answer lies not with the most immediate pattern, but one formed earlier. Like the way you have a knotted ball of yarn and you can't undo the second-to-last knot until after you've undone some earlier, deeper knots.

For a complete overview of this series:
Part 1: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain.html
Part 2: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_16.html
Part 3: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_9632.html
Part 4: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_1042.html
Part 5: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_5911.html

Part 6: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_8985.html

Unnatural Histories: The Lonely Mountain, Part 1

Like many of you, I saw The Hobbit: The Desolation of Smaug last weekend. Like many of you, I've read "The Hobbit" several times (and had it read to me many times before that). But how many of you have wondered what kind of mountain the Lonely Mountain really was?

Tolkein's description and drawings of the lonely mountain bring to mind an inactive volcano. With its narrow peak and symmetrical slopes. But here's my thought - the Lonely Mountain works much better as a part of a much older and much larger tectonic history of Middle Earth. Let me explain with a little background information, first.

We're told that the Lonely Mountain was a solitary peak perhaps 2,500 - 3,000 meters or so above sea level (since there was some snow on the peak year-round). Assuming the latitude/climate was similar to that of the northern Alps. We also get some backstory on the great Dwarven kingdom of Erebor, which was famous for its deposits of gold and precious gems. Mithril, Tolkien's "unobtanium," was found only in Moria - several hundred miles to the Southwest. To the east lay the Iron Hills. To get to the Lonely Mountain, Bilbo and the Dwarves had to cross the Misty Mountains - a long north-south trending line of imposing peaks.




The photo above is Mt. Baker - A Composite Volcano that I photographed from the (relative) comfort of my economy airplane seat, about 30,000 feet above sea level. The summit reaches a height of about 10,780 feet above sea level. Note the relatively low-lying topography around the summit and the lovely symmetry of the mountain itself.



Here's another grand mountain peak, Grand Teton (summit is 13,775 feet above sea level) from the Garnet Trail, Grand Teton National Park Wyoming.


And here is a wider view of the Teton Range, Wyoming. Relatively young, these mountains are the direct result of extensional tectonic stresses, causing the block of crust I'm standing on (along with the barn) to drop downwards relative to the uplifted mountains in the background. But this tectonic stress is spread out along a north-south trending fault line - made of not one, but many mountain peaks worn sharp by glacial ice and not yet brought down by millions of years of erosion.



This is what gold mining in the western United States used to look like - a long narrow shaft to dig into the gold-rich ore (north-central Nevada). You can see how the mine follows the "vein" of high quality ore along a linear path into the hillside. But there aren't any big mountains nearby...



Longs Peak at sunrise on the Chasm Lake Trail, Rocky Mountain National Park (Colorado). Another lovely mountain peak. By comparison to other areas in Colorado, the rocks in Rocky Mountain National Park are relatively poor in economically valuable minerals like gold and silver. Fortunate for us, because it was easier to set the area aside as a National Park.


Abandoned Iron Mine in Ely, Minnesota. One doesn't need giant mountains to produce economically viable deposits. The iron found in northern Minnesota, Wisconsin, and the Upper Peninsula of Michigan comes from ancient sea-floor deposits over one billion years old.

So we're faced with a few questions. First, if the Lonely Mountain was once a volcano, why is it extinct? What kinds of patterns left by geologic processes here on Earth similar to those described by Tolkien? How do we get gold deposits in such abundance (aside from the "because, magic" clause)? Why did I include a picture of an iron mine?

For this first part, I'm going to leave you with a quick sketch map (drafted in "ArtRage" on my iPad). Look over the topography - where are there areas of likely active tectonics?

Next, I'll go over some of the features and discuss what might lie below the surface as a product of things that happen over what we geologists like to call "deep time."

For a complete overview of this series:
Part 1: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain.html
Part 2: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_16.html
Part 3: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_9632.html
Part 4: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_1042.html
Part 5: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_5911.html

Part 6: http://pascals-puppy.blogspot.com/2013/12/unnatural-histories-lonely-mountain_8985.html

Syntectonic Deposition

One of the major aspects of the "flood-geology model" is that the Paleozoic and Mesozoic sediments were laid down by this giant flood. The major structural features like the faults of the Rocky Mountains, Great Basin, and recent Orogenic (mountain building) events occurred immediately after the deposition of all this material. Some young-Earthers lump the Cenozoic (all the way to the Pleistocene) units into these flood deposits. However, Whitmore and some others recognize that many of these Cenozoic sediments lie atop these major structural features - thus they have to be younger. While I think their base assumptions about the amount of time is ridiculous, I can't disagree that many Cenozoic sediments post-date most of the major structural features in the Rocky Mountains.

If their numeric time frame is correct, then we have large piles of unlithified sediment being tossed about by these large structural features. How you achieve brittle deformation (faults) in unlithified sediment is a subject for later. But, for the sake of argument, let's assume we have major structural features forming in this stuff. One of the great places to see examples of Syntectonic sedimentation (deposits of sediments occurring at the same time as structural deformation) is in Echo Canyon, Utah.



Notice how the beds in the left-most bluff are nearly horizontal, and increase in the magnitude in dip as you go towards the bluffs on the right. Here we see deposition off of an uplifting block of crust - as the crust is thrust upward, the angle changes (this is somewhat oversimplified, but the facts are illustrated here: the angle changes, and can be traced back to tectonic uplift). The material being uplifted are some of these younger blocks of sediment. The materials making up these rock cliffs are sands, silts, and even large, rounded cobbles:



How do you form big, round cobbles from unlithified material? It's not a solid, coherent material: therefore forming well-rounded pieces is virtually impossible (I say "virtually" since there are rare examples). There is no evidence that these thousands of feet of rock were unlithified during faulting. None. And yet the YEFPs try to force their limited observations into a rather dogmatic model. All of the evidence points to a rather straightforward explanation, yet they demand an alternative, non-functional model. This is not, nor will it ever be, science.