<p>I figure you're looking for more exotic examples, and some geologists may well have some offhand, but I want to say "yes" because of the example of carbonatite rocks described in this <a href="http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html" rel="nofollow noreferrer">geology page from San Diego State University</a>:</p>

<blockquote>
  <p>Carbonatites are perhaps the most unusual of all lavas. They are
  defined, when crystalline, by having more than 50% carbonate
  (CO3-bearing) minerals, and typically they are composed of less than
  10% SiO2.</p>
</blockquote>

<p>Which would rely on the carbon cycle and the deposition of atmospheric CO2 onto the seafloor by biological processes.</p>

<p>However:</p>

<blockquote>
  <p>Some scientists believe that the Ca-carbonatites are generated by
  fractional melting of crustal carbonate rocks. However, others believe
  that the Ca-carbonatites are not primary magmas at all, but rather
  derived from the alteration of Na-rich natrocarbonatite lavas.</p>
</blockquote>

<p>There is an interesting paper in GeoScienceWorld titled <a href="http://geology.geoscienceworld.org/content/45/4/379" rel="nofollow noreferrer">Atmospheric K-feldspar as a potential climate modulating agent through geologic time</a> that addresses your topic as the author tries to estimate K-feldspar (Kfs) flux through geologic time -- which addresses your question from the other direction: assessing atmospheric content (in some cases simple dust deposition) over billions of years by evaluating its traces in the geological record.</p>

CC BY-SA 3.0
2017-07-13T10:00:18.477Z
Carbonatites are my favourite rock! And the topic of my PhD research...
Gimelist
CC BY-SA 3.0
2017-07-13T15:25:56.660Z
@Michael Knowing things is like cheating! 

Any suggestions to improve, withdraw, or replace my answer are welcome.
jeffronicus
CC BY-SA 3.0
2017-07-13T23:06:29.030Z
That's the problem - there are so many things we don't know about carbonatites :)
Gimelist
CC BY-SA 3.0
2017-07-10T14:52:12.507Z
2017-07-10T14:52:12.507Z
jeffronicus
<p>Recently I was reading <a href="http://press.princeton.edu/titles/9691.html" rel="nofollow noreferrer">'How to build a habitable planet'</a> by Langmuir and Broecker and in chapter 15 they speak about how Life has led to a difference in oxidation potential in the atmosphere, essentially leading to the earth becoming a fuel cell. They also spoke about how this led to certain ions being oxidized - ie uraninite to uranyl oxide, iron to hematite.</p>

<p>I was wondering if this could mean that as atmospheric composition would affect the sea floor, when this subducted it would affect the melt of the mantle - as far as I'm aware, it is the dehydration of the subducting slab which allows for the hydration, and therefore melt, of the mantle in regions such as Japan. If the subducting slab's composition is affected by the atmosphere, could this have any effect on the composition of the igneous rocks formed? Would this be detectable?</p>

<p>Thank you.</p>

CC BY-SA 3.0
2017-07-13T09:50:06.517Z
Related: [What, if any, paleoclimate data can be derived from igneous rocks?](https://earthscience.stackexchange.com/q/2914/725)
Gimelist
CC BY-SA 3.0
2017-07-13T09:59:53.240Z
Also, the answer is yes. Carbonatites are rare igneous rocks formed by melting of carbonated mantle. That carbon can be introduced by subduction of marine sediments. Oxidation state is another thing. Magmas formed by melting of oxidised rocks tend to be more oxidised, and this affects the composition and fractionation trends of minerals like magnetite, ilmenite and other mafic minerals.
Gimelist
CC BY-SA 3.0
2017-07-13T10:14:13.993Z
Thanks! With regard to the oxidation state, could something like the Fe/S ratio also be affected? While Fe and S would both get oxidised in the mantle, their precipitation out of the ocean depends on the oxygen present - would this have a notable effect?
user1150512
CC BY-SA 3.0
2017-07-13T10:34:16.190Z
you're opening a can of worms here - the oxidation state of Fe in the mantle is still a highly debated topic (mostly Fe2+ though, Fe3+ is minor). Sulfur is usually reduced as sulfide, and not sulfate. This is much more complicated and long than can be written down in a comment here.
Gimelist
CC BY-SA 3.0
2017-07-13T14:20:40.627Z
Thank you! Do you know of any relevant papers I could look through? Cheers.
user1150512
<atmosphere><igneous>
Can the atmosphere affect the composition of igneous rocks?
user1150512
# Can the atmosphere affect the composition of igneous rocks?

(Asked by: username_0 on 2017-07-09)

Recently I was reading ['How to build a habitable planet'](http://press.princeton.edu/titles/9691.html) by Langmuir and Broecker and in chapter 15 they speak about how Life has led to a difference in oxidation potential in the atmosphere, essentially leading to the earth becoming a fuel cell. They also spoke about how this led to certain ions being oxidized - ie uraninite to uranyl oxide, iron to hematite.

I was wondering if this could mean that as atmospheric composition would affect the sea floor, when this subducted it would affect the melt of the mantle - as far as I'm aware, it is the dehydration of the subducting slab which allows for the hydration, and therefore melt, of the mantle in regions such as Japan. If the subducting slab's composition is affected by the atmosphere, could this have any effect on the composition of the igneous rocks formed? Would this be detectable?

Thank you.

**Tags:** atmosphere, igneous

> **Comments:**
> **username_1**: Related: [What, if any, paleoclimate data can be derived from igneous rocks?](https://earthscience.stackexchange.com/q/2914/725)  
> **username_1**: Also, the answer is yes. Carbonatites are rare igneous rocks formed by melting of carbonated mantle. That carbon can be introduced by subduction of marine sediments. Oxidation state is another thing. Magmas formed by melting of oxidised rocks tend to be more oxidised, and this affects the composition and fractionation trends of minerals like magnetite, ilmenite and other mafic minerals.  
> **username_0**: Thanks! With regard to the oxidation state, could something like the Fe/S ratio also be affected? While Fe and S would both get oxidised in the mantle, their precipitation out of the ocean depends on the oxygen present - would this have a notable effect?  
> **username_1**: you're opening a can of worms here - the oxidation state of Fe in the mantle is still a highly debated topic (mostly Fe2+ though, Fe3+ is minor). Sulfur is usually reduced as sulfide, and not sulfate. This is much more complicated and long than can be written down in a comment here.  
> **username_0**: Thank you! Do you know of any relevant papers I could look through? Cheers.  

---

## 1 answers

### Answer by username_2 on 2017-07-10. Score: 1

I figure you're looking for more exotic examples, and some geologists may well have some offhand, but I want to say "yes" because of the example of carbonatite rocks described in this [geology page from San Diego State University](http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html):

> Carbonatites are perhaps the most unusual of all lavas. They are
> defined, when crystalline, by having more than 50% carbonate
> (CO3-bearing) minerals, and typically they are composed of less than
> 10% SiO2.

Which would rely on the carbon cycle and the deposition of atmospheric CO2 onto the seafloor by biological processes.

However:

> Some scientists believe that the Ca-carbonatites are generated by
> fractional melting of crustal carbonate rocks. However, others believe
> that the Ca-carbonatites are not primary magmas at all, but rather
> derived from the alteration of Na-rich natrocarbonatite lavas.

There is an interesting paper in GeoScienceWorld titled [Atmospheric K-feldspar as a potential climate modulating agent through geologic time](http://geology.geoscienceworld.org/content/45/4/379) that addresses your topic as the author tries to estimate K-feldspar (Kfs) flux through geologic time -- which addresses your question from the other direction: assessing atmospheric content (in some cases simple dust deposition) over billions of years by evaluating its traces in the geological record.

> **Comments:**
> **username_1**: Carbonatites are my favourite rock! And the topic of my PhD research...  
> **username_2**: @Michael Knowing things is like cheating!   Any suggestions to improve, withdraw, or replace my answer are welcome.  
> **username_1**: That's the problem - there are so many things we don't know about carbonatites :)  

---

