The Deep Water Cycle

This is going to be a long one that puts the boring back into geology, but I feel science needs to be represented. Ignore it even.

Source Texts:

en.m.wikipedia.org...

www.pnas.org...

courses.lumenlearning.com...

www.geolsoc.org.uk...

geology.com...


To begin, ocean water is introduced into the mantle via subducting plates.

I will just use source text, because it is correct.

Water is not just present as a separate phase in the ground. Seawater percolates into oceanic crust and hydrates igneous rocks such as olivine and pyroxene, transforming them into hydrous minerals such as serpentines, talc and brucite. In this form, water is carried down into the mantle. In the upper mantle, heat and pressure dehydrates these minerals, releasing much of it to the overlying mantle wedge, triggering the melting of rock that rises to form volcanic arcs. However, some of the "nominally anhydrous minerals" that are stable deeper in the mantle can store small concentrations of water in the form of hydroxyl (OH−), and because they occupy large volumes of the Earth, they are capable of storing at least as much as the world's oceans.

The conventional view of the ocean's origin is that it was filled by outgassing from the mantle in the early Archean and the mantle has remained dehydrated ever since. However, subduction carries water down at a rate that would empty the ocean in 1–2 billion years. Despite this, changes in the global sea level over the past 3–4 billion years have only been a few hundred metres, much smaller than the average ocean depth of 4 kilometres. Thus, the fluxes of water into and out of the mantle are expected to be roughly balanced, and the water content of the mantle steady. Water carried into the mantle eventually returns to the surface in eruptions at mid-ocean ridges and hotspots. This circulation of water into the mantle and back is known as the deep water cycle or the geologic water cycle

Good intro, good points made, which will be summed up eventually.

Start with the continental slab subducting.

We know for over a 200 million year period, which is still ongoing, the Juan de Fuca Plate (Farralon) has been subducting under Western North America. It uplifted the Rockies, Basin and Range, and more recently The Sierra Nevada, and youngest of all, The Cascades.

Yet as this slab subducts it introduces ocean water to the upper mantle.

Subduction-zone magmatism is triggered by the addition of H2O-rich slab-derived components: aqueous fluid, hydrous partial melts, or supercritical fluids from the subducting slab. Geochemical analyses of island arc basalts suggest two slab-derived signatures of a melt and a fluid. These two liquids unite to a supercritical fluid under pressure and temperature conditions beyond a critical endpoints.

An upper bound on the amount of water in the mantle can be obtained by considering the amount of water that can be carried by its minerals (their storage capacity). This depends on temperature and pressure. There is a steep temperature gradient in the lithosphere where heat travels by conduction, but in the mantle the rock is stirred by convection and the temperature increases more slowly (see figure).[13] Descending slabs have colder than average temperatures.

But how does the water get to the upper mantle to percolate downwards? Is it even recognized as water anymore?

The further you go down, the more is lost.

As an oceanic plate descends into the upper mantle, its minerals tend to lose water. How much water is lost and when depends on the pressure, temperature and mineralogy. Water is carried by a variety of minerals that combine various proportions of magnesium oxide (MgO), silicon dioxide (SiO2), and water.

You can see the process follows minerals rich in magnesium oxide and silica dioxide. (More of the former) For reference "low silica" magma still has about 45-55 silica.

Felsic = high silica 65%+
Mafic = low silica less than 65%

Mafic magmas are low in silica and contain more dark, magnesium and iron rich mafic minerals, such as olivine and pyroxene. Felsic magmas are higher in silica and contain lighter colored minerals such as quartz and orthoclase feldspar.

Olivine is from Mafic Magma, which is generally around 4% water content, Olivine, a little less than 2%.

Olivine has a very high crystallization temperature compared to other minerals. That makes it one of the first minerals to crystallize from a magma. During the slow cooling of a magma, crystals of olivine may form and then settle to the bottom of the magma chamber because of their relatively high density. This concentrated accumulation of olivine can result in the formation of olivine-rich rocks such as dunite in the lower parts of a magma chamber.

Olivine occurs in both mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica. That magma crystallizes to mafic rocks such as gabbro and basalt. Ultramafic rocks usually contain substantial olivine, and those with an olivine content of over 40% are described as peridotites. Dunite has an olivine content of over 90% and is likely a cumulate formed by olivine crystallizing and settling out of magma or a vein mineral lining magma conduits. Olivine and high pressure structural variants constitute over 50% of the Earth's upper mantle, and olivine is one of the Earth's most common minerals by volume. The metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content also produces Mg-rich olivine, or forsterite.

Olivine is a starting point after magma. Olivine has up to 2% water and has several high-pressure polymorphs that decrease in overall water storage capacity.

The mantle can be divided into the upper mantle (above 410 km depth), transition zone (between 410 km and 660 km), and the lower mantle (below 660 km). Much of the mantle consists of olivine and its high-pressure polymorphs. At the top of the transition zone, it undergoes a phase transition to wadsleyite, and at about 520 km depth, wadsleyite transforms into ringwoodite, which has the spinel structure. At the top of the lower mantle, ringwoodite decomposes into bridgmanite and ferropericlase.

Summary point:

Subducting plates draws magnesium rich mafic magma deeper into upper mantle, where it becomes olivine. All carry "water" in OH bond form. Like a WINO, "Water In Name Only".

The normally anhydrous mantle works like a sponge. Saturation cannot be determined. Storage capacity is the upper bound, and how hydrous or anhydrous it is is unknown.

Estimates are still anywhere from 1/4 to 4 times the amount of water as the oceans. We don't know, because we can only study it with diamond inclusions. (See below)

The final part of this Deep Water Cycle is the return of the water to the oceans via Magma.

Next post..

Continued...

It's not the same water returning.

Repeat this again:

In the upper mantle, heat and pressure dehydrates these minerals, releasing much of it to the overlying mantle wedge, triggering the melting of rock that rises to form volcanic arcs. However, some of the "nominally anhydrous minerals" that are stable deeper in the mantle can store small concentrations of water in the form of hydroxyl (OH−), and because they occupy large volumes of the Earth, they are capable of storing at least as much as the world's oceans.

Then add this:

The huge pressure at these depths (20 to 100 km) squeezes the rock like a sponge, forcing the melted material (magma) to rise toward the surface.

Back to mafic magma. Almost EVERY arc volcano on earth magma/water content is about 2-6%.

Basalts formed at mid-ocean ridges and hotspots originate in the mantle and are used to provide information on the composition of the mantle. Magma rising to the surface may undergo fractional crystallization in which components with higher melting points settle out first, and the resulting melts can have widely varying water contents; but when little separation has occurred, the water content is between about 0.07–0.6 wt%. (By comparison, basalts in back-arc basins around volcanic arcs have between 1 wt% and 2.9 wt% because of the water coming off the subducting plate.)

Further evidence of this is in diamond inclusions.

Another diamond was found with ringwoodite inclusions. Using techniques including infrared spectroscopy, Raman spectroscopy, and x-ray diffraction, scientists found that the water content of the ringwoodite was 1.4 wt% and inferred that the bulk water content of the mantle is about 1 wt%

So there you have it.

The Water cycle. From oceans to magma to olivine to storage capacity to polymorphs. The processes involved in the deep water cycle is multifaceted, involves magma crystalizing, changing, and changing again. And while some collects in hydrous minerals, other hydrated magma rises and returns water in liquid form via ocean vents around spreading ridges and volcanic arcs.

*************************************

The best I can do to hopefully explain this, so there's at least the scientific counter to this companion thread.. While it won't shoot down the faith behind it needs to at least serve as a juxtaposition to what I feel is nonsense.

People want to believe what they will, that's free choice. Anyone can sift through and find the points that fit and assert anything they want. But it gets ludicrous and mocks geoscience at some point. It becomes pseudoscientific assertions based on lack of knowledge how these processes actually work.

Please stop using geology to validate your boat story and young planet. It's annoying, and possibly the worst field of science to use.

Good post. I think I read recently that the ringwoodite is holding more water than the oceans are.

One thing about plate techtonics that has always bothered me are the rockies. They are so far away from the subduction zone compared to other mountain ranges. It almost doesn't make sense to me.

a reply to: dust2023

Thank you..

One thing about plate techtonics that has always bothered me are the rockies. They are so far away from the subduction zone compared to other mountain ranges. It almost doesn't make sense to me.

It goes the subduction pretty much compressed the western North American continental slab to that point. Basin and Range does appear to be a crumpled piece of continent.

The theory holds that a pacific plate (the Farallon plate) was subducted underneath North America at a shallow angle. The shear stress exerted at the base of the lithosphere as the plate traveled eastward was enough to push up the Rocky Mountains.

a reply to: Degradation33

Please stop using geology to validate your boat story and young planet. It's annoying, and possibly the worst field of science to use.

I didn't feel like wading into that other thread, because I don't know much about rocks and oil,

but, it struck me that:

If all that so-called "solid water" came to the surface, that would leave a huge void between the inner core and outer mantle. The cataclysm would have been so much worse when the increased weight of the ocean caused total collapse into that void.

I don't think any boat would have survived such an event.
ETA:
I mean, nothing would have survived; not mountains, not geological record, not biological record; totally pulverized. Reduced to dust (silt mud).

sarcasm/ Then human civilization is older than the mountains; older than the dinosaur bones. T-Rex is younger than Egypt. Surely, there would have been human vs Sauron wars documented in great detail. /sarcasm

a reply to: FullHeathen

Thank you for reading.

That other thread is somewhere between a root canal and a comedy sketch.

But that is a humorous point. Especially how much ringwoodite there is down there. Very expensive transition zone this planet has. Lots of diamonds mixed in too.

Creation of this thread prevented me from pulling my hair out.

Once upon a time I was in a competition with my older sister for "most useless major after college", we tied. Unless I want to earn lab tech pay to work in East Jesus, ND, if that.

a reply to: Degradation33

Great thread, and required reading for some of the creationist Noah's Ark fans bumping their gums in the other.

a reply to: Degradation33

1st paragraph last sentence of your first source quote

... because they occupy large volumes of the Earth, they are capable of storing at least as much as the world's oceans.

I wasn't really able to process anything after, not because I'd put any stock whatsoever in that other thread, but it just sounds like alot, I'm still processing...

Ok let me play devils advocate...

What changes would have to ocurre for Let's say half that water to be released faster than it could refurbish?
what would the consequences be of such an event?

a reply to: Terpene

What changes would have to ocurre for Let's say half that water to be released faster than it could refurbish?

The pressure would need to change significantly for a start.

a reply to: andy06shake

There is violent enough activity in the universe to affect gravity.
Would pressure be affected by the gravitational pull of another celestial body passing a little to close?

a reply to: Degradation33

Thanks for the post. Can't read it tonight, but will in the next few days (Christmas stuff and all).
Glad that someone knows what they're talking about.

Merry Christmas

a reply to: Terpene

What changes would have to ocurre for Let's say half that water to be released faster than it could refurbish?
what would the consequences be of such an event?

Olivine yes, one of its polymorphs, not much of a chance of getting much of it out. If the temperature at the depths most ringwoodite exists isn't enough to melt it, what is?

*Except at the very bottom..

www.bnl.gov...

The water contained within ringwoodite in the transition zone is forced out when it goes deeper (into the lower mantle) and forms a higher-pressure mineral called silicate perovskite, which cannot absorb the water. This causes the rock at the boundary between the transition zone and lower mantle to partially melt.

Not much of it gets that far.

"When a rock with a lot of H2O moves from the transition zone to the lower mantle it needs to get rid of the H2O somehow, so it melts a little bit," Schmandt said. "This is called dehydration melting."

"Once the water is released, much of it may become trapped there in the transition zone," Jacobsen added.

Just a little bit of melt, about one percent, is detectible with the new array of seismometers aimed at this region of the mantle because the melt slows the speed of seismic waves, Schmandt said.

Beneath the transition zone in the lower mantle:

The most common compound is silicate perovskite, made up of magnesium, iron, silicon and oxygen.

So most of the transition zone water is in ringwoodite, but a small portion at around 660 km melts and forms a molten layer on the lower mantle.

But most of the melting happen in the very upper mantle, and Olivine is easier to melt, so go with that. Let's try to get the water out of that first.

The analog I like for extracting water from olivine is like trying extract aluminium oxide from feldspar.

The temperatures at which olivine melts is between 1500 and 2200 K (1200-2000° C) depending on type of olivine.

Forsterite-rich olivine is the most abundant mineral in the mantle above a depth of about 400 km (250 mi); pyroxenes are also important minerals in this upper part of the mantle.

Forsterite's melting temperature is unusually high at atmospheric pressure, almost 1,900 °C (3,450 °F), while fayalite's is much lower – about 1,200 °C (2,190 °F). Melting temperature varies smoothly between the two endmembers, as do other properties.

And the unusually high melting temperature also answers how it can stay in crystaline form until the transition zone. But melts and changes phase at around 400 km of depth.

So to answer your question, the earth would need to become superheated all at once and turn the 150 km of mostly forsterite into an olivine melt, as well as melting the ringwoodite beneath it.

Ummm... The sun going red giant overnight should do it. But then it's all going to be in magma form.. so not much good for a typical flood. Flood volcamism on a level not experienced in billions of years. Like the early earth after the impact of Thea. It would make the event that created The Siberian Traps look like a geyser.

Basically kill everything and everyone and turn the earth into its infant self. An uninhabitable molten ball of lava.

a reply to: Terpene

Enter cataclysm that surrounds the likes of Nibiru/Wormwood/Nemesis i should imagine?

originally posted by: Terpene
a reply to: andy06shake

There is violent enough activity in the universe to affect gravity.
Would pressure be affected by the gravitational pull of another celestial body passing a little to close?

a reply to: Phantom42338

Thank you, but I still messed up...

Reversed storage capacity.

My quote.

Olivine is a starting point after magma. Olivine has up to 2% water and has several high-pressure polymorphs that decrease in overall water storage capacity.

INCREASE in overall storage capacity. Olivine has generally up to a 1% storage capacity, but is MOSTLY ANHYDROUS in the mantle.

Used that 2% several times too. One source did say that when reviewing for these posts in my defense.

Seawater percolates into oceanic crust and hydrates igneous rocks such as olivine and pyroxene, transforming them into hydrous minerals such as serpentines, talc and brucite. In this form, water is carried down into the mantle.In the upper mantle, heat and pressure dehydrates these minerals, releasing much of it to the overlying mantle wedge, triggering the melting of rock that rises to form volcanic arcs.

While mantle Olivine CAN store up to 1%, it's mostly around 20 PPM or 1/50,000 in the "dry" part of the mantle.

Sources are actually split on how much water is in the upper mantle olivine. The concensus essentially states the 'water', or analog thereof, gets pushed back up into the wedge or taken down via olivine polymorphs.

With the transition zone essentially trapping the the water (inside minerals) barring a volcanic resurfacing.

The team conducted experiments at both Lawrence Livermore and at Arizona State on olivine, the predominant mineral in the upper mantle, which reaches to a typical depth of 410 kilometers. Characteristically light green in color, olivine has been found to contain water within its crystalline structure. At higher pressures corresponding to greater depths (down to typically 660 kilometers), olivine transforms to minerals with different crystalline structures known as wadsleyite and ringwoodite, which can hold even greater amounts of water.

Still doesn't change the overall though.

Just thought I should correct myself.

a reply to: Degradation33

What about a change in pressure, like andy suggested... How would that affect it?

What if the gravity lessens and the core sort of expands?

In my mind not only water is affected by moons gravity.

why can't we have magma tides?

If the core was doing strange things could it also melt the water holding materials?

a reply to: andy06shake

As in... a question...

Enter the usual distractions from legit questions... Why?

But if you really need a name to that hypothetical scenario try theia.
before colliding I'd wager that it would pass pretty close a couple of time.

It's pretty safe to say, something big is out there and we dont yet know what, where, and when, but the math doesn't lie...

a reply to: Terpene

Where is the distraction?

Nibiru/Wormwood/Nemesis legends and idologies are indeed linked to cataclysm.

Point of fact they are based on the very premise.

The mathematics does indeed seem to suggest there is some form of a large planetary body that remains undetected in our star system probably somewhere out there most likely in an and orbit about 20 times farther from the Sun on average than Neptune.

There might be quite a few massive objects in the likes of the Kuiper belt.

Still no real proof they come anywhere near the inner planets all the same of the definitive sorts.

a reply to: andy06shake

Where is the distraction?

Nibiru/Wormwood/Nemesis legends and idologies are indeed linked to cataclysm.

They are also linked to coockooo... So instead of adressing the simple scenario described, you jump to the existing coockoo theories we all know, and not adress the scenario and it's effects on pressure. Why, else would you conduct a discussion like that?

Still no real proof they come anywhere near the inner planets all the same of the definitive sorts.

In some popular theories the moon is suggested to be the aftereffects of such an impact. Just knowing a little about orbits suggest that there is only one impact but many fly by. Those could have a great impact on gravity

The asteroid belt is another possible candidate for something rather violent happening in our cosmic neighborhood.

Things like that can happen, and just because we have no memory of it happening doesn't mean it never did or can't.

Try and keep the scenario to which this thread attempts to give scientific counterpart in mind.

I'm just trying to create scenarios that could lead to a massive release of the earth bound water, so you can scientifically discredit them. On my first follow up question you start to argue with pop culture, I know you can do better...

How does gravity affect pressure? Just to think big.

We could also go small and ask. How would a sudden evaporation of all the surface water effect pressure on the areas below?

Is it a rise or a lowering of the pressure that affects the release of the bound water?

I always wondered if Water can be made as a new meterial or if there is a set ammount on the planet a reply to: Degradation33