<p>The answer is yes, but the differences, if you mean tangible differences in composition and nature of the melt and not just primary melt source, are  minor and technical. This is a complex subject but I will try and give a reasonably accurate general answer.</p>
<p>Melts in arc settings are dominantly produced by flux melting of the mantle wedge overlying a subducting slab, with variable melt inputs from the slab itself and the sediments that slab has carried down with it. We now know, and there is general consensus among igneous petrologists, that the flux for mantle melting is provided by a mixture (supercritical fluid) of melt and fluids derived from the subducting slab and associated sediments, and the ratio of these two components varies from system to system as we would expect in nature. There are, however, rare cases where it appears the majority of a melt was sourced from the subducting oceanic basalt slab (adakites), however in most cases the majority of the melt is primitive mantle derived stuff.</p>
<p>In back-arc/extensional settings the melt is typically (assuming passive rifting here) derived from adiabatically upwelling asthenospheric mantle that is reacting to thinning of the overlying crust. This might at first glance appear to indicate that both arc and extensional magmas are deriving partial melts from essentially the same source (lets not discuss mantle heterogeneity here). However, the addition of that flux component to the arc magma changes the composition of the melt ever so slightly (your feelings about scale here might differ), and this can be observed through isotopic and trace element analysis. Indeed, we know that the slab is affecting our melt for that very reason: we can see it in the chemistry.</p>
<p>In fact, there appears to be a great deal of variation in magma chemistry as you move away from or towards the arc as well as along an individual arc, which reflects the influence of fluids derived from a subducting slab and the thermal structure of the subduction zone and slab. <a href="https://www.frontiersin.org/articles/10.3389/feart.2022.1055255/full" rel="nofollow noreferrer">Here</a> is a recent paper on that.</p>
<p>Further, one setting can effect the other. Depleted asthenospheric mantle from the back-arc extensional setting can be cycled into the sub-arc/mantle wedge melting region and affect the chemistry of melts as well as the volcanism in the arc. See <a href="https://www.sciencedirect.com/science/article/pii/S0012821X19302766" rel="nofollow noreferrer">this paper</a> for some discussion of how this might work.
It has also been shown that fluids from the subduction zone can be incorporated in, and affect, the chemistry of back-arc extension related melts. The proximity of the spreading center/zone of extension to the subduction zone/sub-arc melting region controls how much of an influence the subduction zone has on the magma. See <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JB090iB13p11431?casa_token=P26SrTFGWjUAAAAA:S7ap_CfzELXLateFXuiU6mmT7Oh4jqM2f3SsOrXPxZxXCYvUHcbKtaXXaLUcW4cUUMyBnOVMJ68MDRs" rel="nofollow noreferrer">this paper</a> for a bit on that from a case-study point of view. This is mostly the result of viscous mantle flow, although that is an immense simplification and there is significant room for nuance there.</p>
<p>If you would like specifics on what exactly the chemical differences are between melts in these two settings the sources I've provided are a good place to look. However, I am also happy to provide a more detailed/less simplified response that includes those aspects as well.</p>

CC BY-SA 4.0
2024-02-23T00:30:59.223Z
2024-02-23T00:30:59.223Z
Josiah
<p>There is subduction-related arc magmatism, such as the Andes, Indonesia, New Zealand, and elsewhere. In the same tectonic environment there's post-collisional extension magmatism such as in New Zealand.</p>
<p>What properties differ between these two kinds of magmatism?</p>
<p>For example Taupo Volcanic Zone is a Quaternary back arc spreading zone. A coinciding place with arc magmatism
Here is a paper relating the subject.
Wright, I. C. (1992). Shallow structure and active tectonism of an offshore continental back-arc spreading system: the Taupo Volcanic Zone, New Zealand. Marine geology, 103(1-3), 287-309.</p>

CC BY-SA 4.0
2024-02-07T08:23:43.847Z
do you have any links or sources to add a bit more context to your question.
trond hansen
<subduction><magmatism>
Is there any diferrence between arc magmatism and post-collisional extension magmatism?
Muharrem Yavuz
# Is there any diferrence between arc magmatism and post-collisional extension magmatism?

(Asked by: username_0 on 2024-02-06)

There is subduction-related arc magmatism, such as the Andes, Indonesia, New Zealand, and elsewhere. In the same tectonic environment there's post-collisional extension magmatism such as in New Zealand.

What properties differ between these two kinds of magmatism?

For example Taupo Volcanic Zone is a Quaternary back arc spreading zone. A coinciding place with arc magmatism
Here is a paper relating the subject.
Wright, I. C. (1992). Shallow structure and active tectonism of an offshore continental back-arc spreading system: the Taupo Volcanic Zone, New Zealand. Marine geology, 103(1-3), 287-309.

**Tags:** subduction, magmatism

> **Comments:**
> **username_1**: do you have any links or sources to add a bit more context to your question.  

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## 1 answers

### Answer by username_2 on 2024-02-23. Score: 3 | Accepted answer

The answer is yes, but the differences, if you mean tangible differences in composition and nature of the melt and not just primary melt source, are minor and technical. This is a complex subject but I will try and give a reasonably accurate general answer.

Melts in arc settings are dominantly produced by flux melting of the mantle wedge overlying a subducting slab, with variable melt inputs from the slab itself and the sediments that slab has carried down with it. We now know, and there is general consensus among igneous petrologists, that the flux for mantle melting is provided by a mixture (supercritical fluid) of melt and fluids derived from the subducting slab and associated sediments, and the ratio of these two components varies from system to system as we would expect in nature. There are, however, rare cases where it appears the majority of a melt was sourced from the subducting oceanic basalt slab (adakites), however in most cases the majority of the melt is primitive mantle derived stuff.

In back-arc/extensional settings the melt is typically (assuming passive rifting here) derived from adiabatically upwelling asthenospheric mantle that is reacting to thinning of the overlying crust. This might at first glance appear to indicate that both arc and extensional magmas are deriving partial melts from essentially the same source (lets not discuss mantle heterogeneity here). However, the addition of that flux component to the arc magma changes the composition of the melt ever so slightly (your feelings about scale here might differ), and this can be observed through isotopic and trace element analysis. Indeed, we know that the slab is affecting our melt for that very reason: we can see it in the chemistry.

In fact, there appears to be a great deal of variation in magma chemistry as you move away from or towards the arc as well as along an individual arc, which reflects the influence of fluids derived from a subducting slab and the thermal structure of the subduction zone and slab. [Here](https://www.frontiersin.org/articles/10.3389/feart.2022.1055255/full) is a recent paper on that.

Further, one setting can effect the other. Depleted asthenospheric mantle from the back-arc extensional setting can be cycled into the sub-arc/mantle wedge melting region and affect the chemistry of melts as well as the volcanism in the arc. See [this paper](https://www.sciencedirect.com/science/article/pii/S0012821X19302766) for some discussion of how this might work.
It has also been shown that fluids from the subduction zone can be incorporated in, and affect, the chemistry of back-arc extension related melts. The proximity of the spreading center/zone of extension to the subduction zone/sub-arc melting region controls how much of an influence the subduction zone has on the magma. See [this paper](https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JB090iB13p11431?casa_token=P26SrTFGWjUAAAAA:S7ap_CfzELXLateFXuiU6mmT7Oh4jqM2f3SsOrXPxZxXCYvUHcbKtaXXaLUcW4cUUMyBnOVMJ68MDRs) for a bit on that from a case-study point of view. This is mostly the result of viscous mantle flow, although that is an immense simplification and there is significant room for nuance there.

If you would like specifics on what exactly the chemical differences are between melts in these two settings the sources I've provided are a good place to look. However, I am also happy to provide a more detailed/less simplified response that includes those aspects as well.


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