I recently met some Earth Scientists from the Etch A Sketch Skool of Geology and we strolled across to their local diner so we could talk over food.
However, to my horror, I discovered my favourite food was no longer on the menu.
Fold mountains are mountains that form mainly by the effects of folding on layers within the upper part of the Earth’s crust.
Before either plate tectonic theory developed, or the internal architecture of thrust belts became well understood, the term was used for most mountain belts, such as the Himalayas.
The term is still fairly common in physical geography literature but has otherwise generally fallen out of use except as described below.
The forces responsible for formation of fold mountains are called orogenic movements. The term orogenic has derived from a Greek word meaning mountain building.
These forces act at tangent to the surface of the earth and are primarily a result of plate tectonics.
The Earth Scientists came to my rescue and suggested I try some gooey gunk called Orogeny.
Orogeny refers to forces and events leading to a large structural deformation of the Earth’s lithosphere (crust and uppermost mantle) due to the interaction between tectonic plates.
Orogens or orogenic belts develop when a continental plate is crumpled and is pushed upwards to form mountain ranges, and involve a great range of geological processes collectively called orogenesis.
The menu description of Orogeny was particularly unappealing.
Apparently Orogeny is something that is “severely deformed” after being pressure cooked [at somewhere between 200° and 850° degrees centigrade] in “chemically active fluids” deep underground.
The processes of orogeny can take tens of millions of years and build mountains from plains or the ocean floor.
The topographic height of orogenic mountains is related to the principle of isostasy, that is, a balance of the downward gravitational force upon an upthrust mountain range (composed of light, continental crust material) and the buoyant upward forces exerted by the dense underlying mantle.
Frequently, rock formations that undergo orogeny are severely deformed and undergo metamorphism.
Metamorphism is the change of minerals or geologic texture (distinct arrangement of minerals) in pre-existing rocks (protoliths), without the protolith melting into liquid magma (a solid-state change).
The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids.
The chemical components and crystal structures of the minerals making up the rock may change even though the rock remains a solid.
Changes at or just beneath Earth’s surface due to weathering and/or diagenesis are not classified as metamorphism.
Metamorphism typically occurs between diagenesis 200°C, and melting 850°C.
This floppy Orogeny stuff is so distasteful and disgusting that even the Wikipedia hasn’t got the stomach to include a diagram explaining how this gooey gunk is forced through a a right-angled turn deep underground before powering its way to the surface where [the Earth Scientists assured me] it stacks up neatly into mountains of folds.
I called the waitress over and asked what she would recommend from the menu.
She suggested the house speciality: Everest Fossil Fish on a bed of Orogeny.
This is quite a dish.
First they locate a fish fossil deep in the seafloor limestone off the coast of India.
Mount Everest, also known in Nepal as Sagarmāthā and in Tibet as Chomolungma, is Earth’s highest mountain. It is located in the Mahalangur mountain range in Nepal and Tibet.
Its peak is 8,848 metres (29,029 ft) above sea level.
The Himalayas and Mount Everest are young geologically speaking. They began forming over 65 million years ago when two of the earth’s great crustal plates-the Eurasian plate and the Indo-Australian plate-collided.
At the tops of the highest peaks, like Mount Everest, it is possible to find 400-million-year-old fossils of sea creatures and shells that were deposited at the bottoms of shallow tropical seas that are now over 25,000 feet above sea level.
“The Summit of Mt. Everest is Marine Limestone”
The great nature writer John McPhee wrote about Mount Everest in his book Basin and Range: “When the climbers in 1953 planted their flags on the highest mountain, they set them in snow over the skeletons of creatures that had lived in the warm clear ocean that India, moving north, blanked out.
Possibly as much as twenty thousand feet below the seafloor, the skeletal remains had turned into rock. This one fact is a treatise in itself on the movements of the surface of the earth. If by some fiat I had to restrict all this writing to one sentence, this is the one I would choose: The summit of Mt. Everest is marine limestone.”
About.com – Geology of Mount Everest – Stewart Green
The top of Mount Everest is composed of fossil-bearing marine limestone (Mount Qomolangma Formation, the ancient seafloor of the Paleozoic Tethys Ocean) that is believed to be lower to middle Ordovician in age based on a very limited number of “summit grab-samples” from climbers over the years.
2012 Everest Education Expedition: 50th Anniversary of the First American Ascent
Montana State University
Then they wait for the up welling gooey gunk called Orogeny [which is especially cooked at depths between 15 to 20 kilometres] to raise up the limestone seafloor [that contains the fish fossil] to the top of Mount Everest.
During the collision of India with Asia, these rocks were thrust downward and to the north as they were overridden by other strata; heated, metamorphosed, and partially melted at depths of over 15 to 20 kilometres (9.3 to 12.4 mi) below sea level; and then forced upward to surface by thrusting towards the south between two major detachments.
Of interest was the fossil-bearing limestone that crowns Mount Everest, the nature and impact of ice in the region (such as the icefall), and the overall stratigraphy (including limestone, metamorphic rocks, pelites, and quartzites).
The waitress explained the Everest Fossil Fish is quite a delicacy because usually the fish fossils just get deep fried embedded in the Orogeny.
I declined the offer by pointing out that if they couldn’t be bothered to provide an illustration of how Orogeny is processed deep underground before being extruded into neatly folded mountains then I couldn’t be bothered to swallow it hook, line and sinker.
The waitress wandered away muttering something about “pompous kant”.
Before the development of geologic concepts during the 19th century, the presence of marine fossils in mountains was explained in Christian contexts as a result of the Biblical Deluge.
This was an extension of Neoplatonic thought, which influenced early Christian writers.
The 13th-century Dominican scholar Albert the Great posited that, as erosion was known to occur, there must be some process whereby new mountains and other land-forms were thrust up, or else there would eventually be no land; he suggested that marine fossils in mountainsides must once have been at the sea-floor.
Well I think it began with a “k”.