The Outcrop in the Crystal

It's my 20th post!  This blog post is the first of several that will highlight an outcrop that drove my interest in Maine geology.  If you're looking for the outcrop it's on Rte. 115 on the Gray/ Windham border.  Or check it out on the Sphere app.  

The outcrop told the story of Maine.  The white rock, a granite, bubbled up when Africa's coast collided with our own 450 million years ago, sealing Maine into the Pangeaic interior.  The black basalt resulted from one of the volcanoes that once again cleaved the supercontinent in two when Pangea split.  The glittery schist told the tale of a muddy ocean bottom that predated both two igneous rocks.  But how did the green rock get there?

There were obvious clues.  The parallel stripes of white, green, and sometimes even gray told tales of piling layers.  The fact that these layers took turns with schist, a mudstone altered by heat and pressure, as one scanned the outcrop from left to right suggested that it, too, formed in that muddy sea.  Other facts didn't add up.  The tough rock scored glass.  Most of the usual sedimentary suspects wouldn't do that; unmetamorphosed mudstone and limestone were just too soft.  Their metamorphic progeny, schist and marble would have crumbled as well.  Sandstone, and its postbear quartzite, would do the job, but the look wasn't right.  The rock lacked the granularity of sandstone, and the sugariness of quartzite.

The truth became clearer as I began to research Silurian time, a period between 416 and 444 million years ago, in which the green rock formed.  The ocean bottom that it gathered in was flanked on three sides.  To the north lie North America, to the south, a hunk of land that would become Maine's coast. To the east, Western Europe plugged another opening preventing the flow of currents.  The phlegmatic basin, just south of the equator, became poor in oxygen, but rich in life.  Lacking our usual breath of life, the creatures of the sea resorted to extreme measures - consuming sulfur.  

The chemistry of this bounded sea played an important role in the green rock's formation.  As a coral reef, in an aerated ocean, degrades, it forms limestone, which is composed of the elements calcium, carbon and oxygen.  Our sluggish sea would have produced a similar product, with one small difference: the sulfur consumption exchanges some of the sediment's calcium for a new element - magnesium.  The rock it forms goes by a different name: dolomite.

Even dolomite doesn't have the strength to scratch glass.  The rock would require one final transformation.  As plates moved, the basin grew smaller, and then disappeared.  The formation of Pangea spurred an influx of fluids: some large, like the bulb of magma that formed the white granite, some less immense, like the infusion of quartz and water that flowed through the ancient ocean bottom.  This liquid sought out any channel it could access, including spaces in the schist, and the dolomite.  The schist proved passable, but inert.  The dolomite was reactive.  The heat and chemicals in the flowing fluid released carbon and oxygen from the dolomite (as carbon dioxide).  Some of the quartz stuck around, providing the white layers of the rock.  The green crystals, a mineral called diopside, kept the calcium and magnesium of the dolomite and replaced the CO2 with silicon and oxygen from the quartz.  

The outcrop is a testament of Maine's geological history.  It documented the marine roots and the accordion push-pull of continents.  The green diopside crystal, a fractal of that outcrop, records the deoxygenated ocean bottom in its calcium and magnesium.  It further tells the tale of the pushing and pulling continents in its silicon and oxygen.  The green crystal, a mere fragment of the outcrop, tells the outcrop's entire story.

Bickle, M. J. , H. J. Chapman, J. M. Ferry, D. Rumble, and A. E. Fallick. "Fluid Flow and Diffusion in the Waterville Limestone, South—Central Maine: Constraints from Strontium, Oxygen and Carbon Isotope Profiles." Journal of Petrology 38.11 (1997): 1489-1512. Print.

Ferry, J. M.. "A Comparative Geochemical Study Of Pelitic Schists And Metamorphosed Carbonate Rocks From South-central Maine, USA." Contributions to Mineralogy and Petrology 80.1 (1982): 59-72. Print.

Fischer, Dan , Tammy (Yue) Liu, Emily Yip, and Korsen Yu. "The Silurian Period."The Silurian Period. University of California Museum of Paleontology, 5 July 2011. Web. 6 Dec. 2013. <http://www.ucmp.berkeley.edu/silurian/silurian.php>.

Hussey, Arthur M., II, 1996, Bedrock geology of the North Windham 7.5' quadrangle, Maine; Maine Geological Survey (Department of Conservation), Open-File Report 96-16, 6 p.

Helmholtz Centre for Ocean Research Kiel (GEOMAR) (2012, June 7). How does dolomite form?. ScienceDaily. Retrieved December 8, 2013, from http://www.sciencedaily.com/releases/2012/06/120607105815.htm

Wilde, Pat , William Berry, and Mary Quinby-Hunt. "Silurian Oceanography."Marine Sciences Group. University of California, Berkeley, n.d. Web. 8 Dec. 2013. <http://www.marscigrp.org/sil91.html>.

Beyond Pangea: The Chain Lakes' Long History

Every middle schooler hears about Pangea.  You look at the world map and envision the ocean closing and that land before time re-forming.  And that's the end.  You don't think about what happened before because no one ever told you that there was a before.  Well, I am here to set you straight.

Don't get me wrong.  Pangea is old.  When Pangea was THE place to be, dinosaurs had not yet set foot on this Earth.  In fact, the dry center of the giant continent set the stage for water loving amphibians to evolve into drought tolerant reptiles.  Later, these reptiles gave birth to the generations that would become the feared lizards we call dinosaurs.  Here in Maine, however, you will find no trace of dinosaurs, because nearly every rock was formed before the oceans that collapsed to make way for Pangea produced their parting waves.

What's important to realize is that the formation of whole Earth continents, like Pangea, is a cycle.  These so-called supercontinents occur occasionally throughout Earth history.    Six hundred million years ago, the supercontinent of the day, one that we call Pannotia, would have filled much of the space taken up by the modern day western Pacific Ocean, and a large hunk of Antarctica, too.  About 1.3 billion years ago, Rodinia was gathering all the Earth's land masses at the equator.  This is the point at which we will begin our journey back to the future.

The Chain Lakes Massif, an elevated hunk of land just north of Sugarloaf, may be the best perch from which to watch the story unfold.  A supercontinent is formed when an ocean closes.  The weighty seafloor rock descends into the Earth beneath the lighter continental shoreline. The diving rock melts, and then reascends, forming a chain of volcanoes, not unlike the modern Andes.  The larger the colliding continents, the larger the mountain chain - and Rodinia was big!  The billion year old mountain chain is now the core of North America, running the 3000 miles from Newfoundland, Canada to Veracruz, Mexico.  Big mountains fall fast, and as rain and ice dragged sediment from the peaks it dropped it into the closing ocean.  Some scientists think it was this sediment that would become the Massif.  As the ocean closed, the sediment may have changed from mud to stone.

A billion years ago Rodinia was formed, but this, too, must pass.  The mega-continent shattered.  While the 3000 mile backbone, called the Grenville Province, stayed intact, the sedimentary shorelines drifted away.  While the cycle continued, the sedimentary island moved along the Earth's surface, but 400 million years after it started its journey, the Massif came home.  As its ocean closed, and Pannotia gathered, the piece of land that would become the Chain Lakes became nestled in the heart of the new supercontinent.  Nestled may be an understatement, because the crushing force of the continent forming squeezed, buried, and roasted the rock, altering it from a simple sedimentary rock to a banded metamorphic one called gneiss.

Pannotia didn't last long, and when the proto-Pangea split, the Massif hung on to what would become North America.  In fact at that time it would have been coastal property, but that would change as oceans closed one more time.  The Iapetus Ocean (Iapetus was the father of Atlas, and the Iapetus was the predecessor of the Atlantic) closed in stages.  The first impact was a set of Carribean-like islands, the next a small continent called Avalon.  Each collision provided more heat and more pressure, driving the gneissic metamorphism of the once sedimentary rock even further; and making the geologic puzzle harder to solve.

The final crunch came as Africa found its place in the Pangeaic landscape.  The world, different than the one in which we now reside, would at least be familiar to our geographic sensibilities.  South America cuddled up with western Africa, and northern Africa spooned by New England.  Pangea may be the first chapter in our middle school geology texts, but it was one of the last in this corner of Maine.

DiPietro, Joseph A. Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History. Burlington, MA: Elsevier, 2013. Print.

Landing, Ed. "Vestiges of Rodinia: Adirondack and Hudson Highlands." New York State Geological Survey. New York State Museum, n.d. Web. 11 Nov. 2013. <http://www.nysm.nysed.gov/nysgs/nygeology/tectonic/02.html>.

Meert, Joseph . "A History and Preview of Supercontinents through Time." Gondwana Research. N.p., n.d. Web. 11 Nov. 2013. <http://gondwanaresearch.com/hp/supercon.pdf>.

A Piece of Deer Isle: Rapakivi Fingerprints

When I first started learning about rocks I remember being impressed that each rock formation was unique.  The reddish color of a brownstone cobble in Finlayson, Minnesota informed me that the rock had made the 50 mile trip from the iron rich shores of Lake Superior.  I've started to look for fingerprints in rocks, and there is none more common in Maine than the rapakivi crystals of Deer Isle granite.

Deer Isle Stonework in Falmouth, Maine

While the formation has its home on its namesake island downeast, Deer Isle granite is everywhere.  You can hardly take a step in the L.L. Bean flagship store without resting your sole on a slab. I've noted its presence in kitchen counters, cutting boards, and outdoor stonework.  It even secreted itself into the foundation of Yankee Stadium, a long trip for a stone from Red Sox territory.  In any of these locations the rock would be instantly recognizable by its round pink crystals wrapped in a ring of white.

Close up of Deer Isle granite.  Notice the rounded pink crystal
in the center, and the white rim surrounding it.

The ring not only gives up the source location, it tells a story.  The pink mineral, microcline feldspar, is not normally round. When it developed deep under the surface it would have taken the form of a prismatic rod with regular angles. But this was under pressure.  Where the microcline first solidified may have been 10 miles under the surface. That means 10 miles of rock weight are pressing down on our magma stream like the grasp of Superman.  Just like the hero's clutch could turn coal into diamond, the added pressure that comes with this weight turned liquid rock into solid.  But the crystal had formed before its time.

As this slurry of magma and loose crystals rose up toward the surface, the weight pressing on it subsided.  Without the added pressure, the geometric crystals began to melt, leaving only their rounded centers behind. As the ooze ascended, crystal formation conditions changed.  The microcline, more stable in the deeper conditions, would now be replaced by a different mineral, white plagioclase feldspar.  Because the two minerals are very similar, the plagioclase quickly continues the pattern disrupted by the pressure drop.

Conditions must be just so to create this pattern. A cooler magma channel, the white mineral never forms.  The pressure drops too quickly and the pink feldspar melts altogether. Deer Isle granite's unmistakeable fingerprint is a result of its unique story of formation, dissolution, and restoration. This distinctness may be one trait that makes the stone desirable, but it is certainly one that makes it recognizable.

Eklund, O., and A.D. Shebanov. "The origin of rapakivi texture by sub-isothermal decompression." Precambrian Research 95.1-2 (1999): 129-146. Print.

Hooke, Roger Leb.. "A Geologic History of Deer Isle, Maine." College of the Atlantic, Serpentine Ecology Conference. July 2007. Web. 14 Oct. 2013. <www.coacommunity.net/downloads/serpentine08

Nekvasil, Hanna. "Ascent of Felsic Minerals and Formation of Rapakivi." American Mineralogist 76 (1991): 1279-1290. Print.

Prinz, Martin. Rocks and Minerals Simon & Schuster's Guide to Rocks and Minerals.. New York, NY: Simon and Schuster, 1978. Print.

9 Stories from my Stone Pile

1. The Layers

The layers in this rock suggest that it accumulated over time as sediment piled up somewhere. In the case of this rock it most likely occurred at the bottom of an ocean.

2. The Metamorphosis 

The layered rock was exposed to intense heat and pressure. Though not hot enough to melt the rock the heat and pressure were sufficient to cause minerals to migrate through the solid rock toward one another. This migration fused microscopic clay particles into visible shards of mica pictured here.

3. The Mixing

The dark gray rock in the picture above has a composition similar to the rock above. When Africa collided with North America the magma that formed the white rock rose from below the ocean bottom. Hunks of ocean bottom floated in the molten rock like ice cubes as the liquid rock hardened into the light colored rock.

4. The Crystals 

As the light colored magma cooled, similar minerals were drawn toward one another. Because cooling happened deep underground minerals could move freely through the warm liquid. The pockets of quartz (clear), hornblende (black), and feldspar (white) grew larger and larger until they froze into solid crystals.

5. The Big Crystals 

As the mass of crystals from the picture above solidified, they may have shrunk or cracked leaving space for water and more magma to pulse through the spaces. The water allowed the crystals to grow even larger than regular granite, making a rock called pegmatite.

6. The Splitting

As we all know Pangaea was not a permanent fixture. When it split it was not a clean break. Many places in Maine cracked, creating fractures throughout the coastal region. These joints provided space for new rocks, like the black one above to get up close and personal with older rocks.

7. The Black Rock 

Earlier, I mentioned that the light colored magma came when Pangaea formed. Less dense granite tends to form when continents collide, while dark basalt, pictured above is a sign of splitting. As the two hunks of massive continent diverged, magma that formed through this black rock spilled through every crack it could find.  This dark rock is Pangaea's swan song. 

8. The Ice
Bedrock tends to break off at relatively sharp angles.  Streams tend to form rounded rocks.  These stones fall somewhere in the middle.  They have softened edges, but flat faces.  A mile of ice covered this spot several thousand years ago.  The glacier scraped every type of bedrock in Maine, plucking off chunks as it went.  The glacier broke away hard edges, and sanded off flat facets as rocks were dragged across the ground.

9.The Pile 

The glacier grabbed everything it could, from clay to boulders, and everything in between.  Farmers could plough through the small stuff, but these stones got in the way.  As the freeze-thaw cycle of Maine's weather brought stones to the surface, farmers fought back by flinging them to the edges of fields.  Here lie the remains of decades of farm labor and hundreds of millions of years of geologic history.

Unfolding the Camden Hills

Two weeks ago my friend Colin and I climbed Mount Megunticook.  I was bending his ear about a particular rock, or piece of geologic history when he asked me the question: so how did the Camden Hills get here?  The question haunted me.  It's certainly a question I'd pondered.  I just hadn't made any headway.  I'd researched it too; the answers were either non-existent, or just didn't add up. Glaciers? But, ice sheets scoured the whole state.  Why leave peaks here?  Granite? There may be occasional injections of the light colored rock, but no more than other, lower regions of the state.  Over the intervening weeks I revisited both and decided that perhaps the answer lies in the the shattered infrastructure of the region.

I've mentioned in a previous post that this region was ground zero for a major collision between plates, and the impact is still visible on a relief map.  The ridges to the north and west of the Camden Hills look like ripples in a carpet pushed up by slid furniture.  If Africa was a couch, and Maine an area rug, this isn't too far from the truth.  When Pangea formed, Maine's rock needed to take up less space.  Like the carpet, part went up, and the rest stayed down.  The difference is, rock is not so good at bending.  Instead, a wedge of rock cracks off along a fault, and slides up the face of the piece next to it.  This crack-slide scenario occurred twice, with state geologic maps showing thrust faults not far from two ridges: one that includes Levenseller Mountain, Moody Mountain and Philbrick Mountain and another that features Hatchett Mountain and Coggans and Clarry Hills.

If collision shoves rock skyward, extension drops it down.  When Africa moonwalked its way out of Pangea, it stretched Maine behind it.  Certain blocks of Earth dropped down, filling would be holes with wedges of rock.  To the southeast of the Camden Hills, the land quickly plunges to ocean. The state maps once again show a fault and a cross section makes it look as though the fault block  descended with extending crust.

Where does this leave us?  Three hunks of rock stacked up piggy-back and a piece of ocean dropped into a hole left by a departing Africa.  The Camden Hills, with Megunticook the highest mountains on the Atlantic coast south of Acadia, are the top piggy with the drop to the ocean providing stunning views.  Of course, the once neat blocks have been intruded by magma, and worn down by glaciers and time.  But, I believe, these small giants, are more a tribute to the tug of war between continents than the ice and granite.

Bloom, Arthur. Geomorphology: A Systematic Analysis of Late Cenozoic Landforms. Upper Saddle River, New Jersey: Prentice Hall, 1991. Print.

"Facing Hatchet Mountain." Hope Historical Society. Hope Historical Society, n.d. Web. 15 Sept. 2013. <www.hopehist.com/Himages/HD402.html>.

Flanders . "Mount Megunticook : Climbing, Hiking & Mountaineering : SummitPost."Climbing, Hiking, Mountaineering : SummitPost. SummitPost.org, 12 Oct. 2013. Web. 15 Sept. 2006. <http://www.summitpost.org/mount-megunticook/234387>.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000

The Ocean Bottom on the Mountain

Ernest Hemingway is rumored to have won a bet by telling the world's shortest story: "For Sale: Baby shoes, never worn."  As I sat on the side of Dorr Mountain, waxing geologically to my brother-in-law, he pointed out to me that the story I was telling was really much shorter than the words I was using.  Perhaps a shorter telling would have gone something like this: "Ocean bottom found on a mountaintop."

Hemingway's story was all about what it implied.  So what is implied by a four-foot boulder of ocean bottom rock?  Time.  Ignoring that this rock was part of a much larger formation, we can conclude that these four feet must have piled up over time.  One resource suggests that clay, likely once a major component of this chunk of sea floor, gathers at 10mm every thousand years.  This isn't a rock; this is a time lapse of 1.2 million years of arduously slow settling of clay.

So what about the mountain itself? The depths at which granite is formed are measured in miles (kilometers really, but this is America, right?).  That means that the bulb of granite that makes up most of Mount Desert Island once rested deep under the Earth's surface; now Dorr Mountain stands nearly a quarter mile above sea level.  Over the hundreds of millions of years since that deep magma cooled, wind, water and ice have excavated the remains of an ancient collision between North America and the ancient land mass on which MDI rests.

A look at the sea bottom rock implies something more. Several flat faces, on many planes, give evidence of glaciers. The glacier that plucked that rock from its original bed dragged the behemoth across the Earth's surface like cheese across a grater. The chaotic innards of the glacier occasionally flipped the mighty stone, smoothing yet another face.  The glacier, perhaps a mile tall, would have both ripped at Dorr, and been slowed by it. As the ice layed the mountain low, it may have slowed sufficiently to drop some of its load - seafloor included.

Hundreds of thousands of years of piling clay, miles of erosion, and an ice sheet a mile thick, all whispered in the language of rocks.  Scenes like this, like the glacier that came before them, cover Maine. Millions of shorts stories, implying so much more.

Ansley, J. E. 2000. The Teacher-Friendly Guide to the Geology of the Northeastern U.S. Paleontological Research Institution, Ithaca, NY.  

Hardcastle, Tim . "Pelagic clay ." Historical Geology- Wikibooks. Wikibooks, n.d. Web. 1 Sept. 2013. <http://en.wikibooks.org/wiki/Historical_Geology/

Miller, Robert B. , Scott R. Paterson, and Jennifer P. Matzel. "Plutonism at different crustal levels: Insights from the ~5–40 km (paleodepth) North Cascades crustal section, Washington." The Geological Society of America Special Paper 456 (2009)

Petford, N. , A. R. Cruden, K. J. W. McCaffrey, and J.-L. Vigneresse. "Granite magma formation, transport and emplacement in the Earth's crust." Nature408 (2000): 669-673. Print.

"Dorr Mountain : Climbing, Hiking & Mountaineering : SummitPost." Climbing, Hiking, Mountaineering : SummitPost. N.p., n.d. Web. 1 Sept. 2013. <http://www.summitpost.org/dorr-mountain/416282>.

A Piece of Ira: Unwrapping Turbidites

The first mistake many potential geology nerds make is to assume that any given rock doesn't have an interesting story.  If they didn't make that mistake I would be sitting here reading their blogs rather than writing my own.  What makes this error so common is that many of these stories are hidden, or written in languages that we can't read.  My friend Jenn brought me a wonderful story from Ira Mountain in a flat sparkly package.

Aww...Schist.  The sparkly covering on this rock is
ancient ocean bottom heated in a continent colliding oven.

Nothing wraps a rock in sparkles cheaper than mica.  Gold and Silver requires hot magma to transport heavy metals from deep within the Earth, where denser metals tend to reside.  Mica is a working man's sparkle.  It's the mud under your fingernails, or more likely the mud at the bottom of the ocean.  Fine-grained particles, like crushed up mica, drift through water under the power of the slightest current. They settle only when wave power is nearly nil.  In other words the deep dark ocean.  This mud is composed of a few things, but mica contributes heavily to the mix.  Of course, you'd never know it because the particles are so small.  Finishing the shiny package means burying the rock and crushing it between a continent, say North America, and a microcontinent, perhaps a prehistoric piece of land that now makes up shoreline on Maine, Greenland, the United Kingdom and Scandinavia called Avalonia. The heat and pressure caused small particles to migrate toward one another creating the large sparkles we now see.

Quartzite Revealed.  Notice the blockier texture on the
bottom half of the rock.  There is a thin layer of schist
below the quartzite,

Of course, you can't just wrap wrapping paper.  A glance between the layers of gray-green mica reveals a reddish blocky layer with a sugary appearance that has been compared to the texture of a gumdrop. This is where the surprise and the story lie.  Quartzite, unironically, is made out of quartz. Because quartz won't break down into to tiny pieces the way mica does, its grain size tends to bottom out at a 0.0025 inch.  The mass provided by this bulk causes even fast moving water like that on a wavy coastline to drop sand grains like they were hot, much to the enjoyment of southern Maine's beach-goers.  Crush that sand in the vise of continents and you get quartzite.

So what brings the unmoving abyss of the ocean bottom next to the active coast.  One possibility is time.  Sea level has fluctuated throughout geologic time.  To whit, the Hannaford in West Falmouth was built on ocean bottom from the ice age, and taking I-95 north of Gray reveals sandy roadsides that may be beaches of the same time period.  This sort of shift in water level is certainly capable of creating a rock that transitions from mudstone to sandstone and back again, or post crushing, a quartzite sandwich, with schist bread.

But there is another possibility.  The Carrabassett Formation, out of which the north half of Ira Mountain has been cut, is known for its turbidites.  Imagine an underwater ridge.  The top of the ridge, exposed to the movement of waves and the final surges of upland streams, plays host to hefty sediments like the aforementioned sand.  The bottom of the ridge, protected from the rigamarole, cradles the tiny clays. Then something happens.  A stream changes course.  A rogue wave mixes things up.  The ridgetop sediments, perhaps already precariously perched, fall down.  The movement stirs up everything, creating a stew of water, sand and clay.  As time passes the turbid water clears again, first dropping the heavy sand, then setting down the lighter clay.  This process would repeat again and again over the life of the ocean and the ridge until these layered sediments became stone.

Which of these possible histories is true is unclear.  Maybe this detail of the story is unwritten, or maybe I just haven't learned how to read this piece of the language.  It is the hope that we might know more, that there is some unwrapped gift, that keeps me looking and keeps me learning.

Adams, Dennis. "About Beach Sand."Beaufort County Library. Beaufort County Library, Web. 14 Aug. 2013. <http://www.beaufortcountylibrary.org/htdocs-sirsi/beachsan.htm>.

Dorais, Michael J., Robert P. Wintsch, Wendy R. Nelson, and Michael Tubrett. "Insights Into The Acadian Orogeny, New England Appalachians: A Provenance Study Of The Carrabassett And Kittery Formations, Maine." Atlantic Geology 45 (2009): 50-71.

Hanson, Lindley . "The many expressions of a New England formation." Vignettes: Key Concepts in Geomorphology. SERC, Web. 15 Aug. 2013. <http://serc.carleton.edu/vignettes/collection/25133.html>.

Schieber, Jürgen . "Sedimentary Structures." Indiana University. Indiana University, n.d. Web. 15 Aug. 2013. <http://www.indiana.edu/~geol105/images/gaia_chapter_5/sedimentary_structures.htm>.

Weller, Roger . "Schist Photos." Virtual Geology Museum. Cochise College , 24 May 2013. Web. 15 Aug. 2013. <http://skywalker.cochise.edu/wellerr/roc