为什么长英质的比镁铁质材料熔点较低?- 江南体育网页版- - - - -地球科学堆江南电子竞技平台栈交换 最近30从www.hoelymoley.com 2023 - 07 - 07 - t14:45:43z //www.hoelymoley.com/feeds/question/174 https://creativecommons.org/licenses/by-sa/4.0/rdf //www.hoelymoley.com/q/174 33 为什么长英质的比镁铁质材料熔点较低? foobarbecue //www.hoelymoley.com/users/63 2014 - 04 - 16 - t18:05:38z 2018 - 11 - 06 - t22:12:45z < p >从博文系列的反应很明显,更多的长英质的矿物熔点低于镁铁质矿物。据我所知,淬火的眼镜也是如此。< / p >

Felsics have a higher degree of SiO2 polymerization in the solid phase, which I would have thought was energetically favorable, and therefore I would have expected a felsic glass to require more energy to melt than a corresponding basaltic glass and therefore have a higher melting temperature. However, the opposite is true. Why is this the case?

//www.hoelymoley.com/questions/174/-/186 # 186 18 由布莱恩·奈特回答为什么长英质的比镁铁质材料熔点较低? 布莱恩骑士 //www.hoelymoley.com/users/112 2014 - 04 - 16 - t19:11:09z 2014 - 04 - 16 - t19:59:22z < p >好问题!如你所知,鲍文的反应级数描述了硅酸盐矿物的结晶顺序在一个冷却的岩浆。< / p > < p >的复杂阴离子硅酸盐四面体的四个氧原子周围一个硅原子,具有较强的共价键连接。每个四面体可以从彼此孤立或他们可能是共价结合在一起通过共享氧原子之间相邻四面体。这样他们可能形成单一链(辉石),双链(角闪石),表(黑云母)和联锁四面体(石英)的三维网络。< / p >

Each of these covalently bonded structural groups (except 3D networks) is bonded to its neighboring structural group (e.g. single chain to single chain) by ionic bonds with intervening cations (K+, Na+, Ca2+, Mg2+, Fe2+, etc.).

Relatively speaking, covalent bonds have lower melting points than ionic bonds. Source

In Bowen's reaction series, the minerals that form at the cooler end of the discontinuous series are richer in silicon and oxygen and poorer in metal cations. Therefore, the minerals at the cooler end are also more dominated by covalent bonds over ionic bonds. This prevalence is the reason why felsic minerals melt at lower temperatures than mafic ones.

Your logic is correct when looking at mineral stability in the face of chemical weathering. At the Earth's surface, those covalent bonds are much more stable and minerals like quartz tend to be much more resistant to weathering than olivine or pyroxene. This is described in the Goldich stability series, which I like to think of as Bowen's reaction series stood on its head.

//www.hoelymoley.com/questions/174/-/2742 # 2742 18 由Gimelist回答为什么长英质的比镁铁质材料熔点较低? Gimelist //www.hoelymoley.com/users/725 2014 - 11 - 06 - t11:46:30z 2017 - 06 - 17 t03:14:20z < p >我想添加到布莱恩的答案,同时也指出一些错误。< / p >

First of all, it is not true that felsic minerals have lower melting temperatures than mafic minerals. Here are some melting temperatures of common minerals, sorted from high to low:

  • Forsterite (mafic): 1890 °C
  • Quartz (felsic): 1713 °C
  • Anorthite (felsic): 1553 °C
  • Diopside (mafic): 1391 °C
  • Fayalite (mafic): 1205 °C
  • Sanidine (felsic): 1150 °C
  • Albite (felsic): 1118 °C

Note that this order differs from the order in Bowen's series. There is no problem with that, because Bowen's series describes the order of crystallisation in common magmas (as Brian correctly identified) and not the crystallisation or melting temperature of the minerals. Although these two are closely related, they are not identical.

So what dictates the order of the minerals in Bowen's series? This is where it gets complicated. The melting temperatures given above only apply to pure minerals in atmospheric pressures. Cooling magmas are never in the exact composition of a pure mineral, and are rarely in atmospheric pressure. Mixing of components (i.e. minerals) in a single magma will depress the crystallisation temperatures of all components, and thus the melting temperatures. Think ice on a road: you can melt it either by heating it, or by adding salt. By adding a second component ($\mathrm{NaCl}$) to the pure component ($\mathrm{H_2O}$) you are making it possible for the ice to melt at temperatures lower than 0 °C.

How does it relate to crystallisation and melting temperatures? Take a look at these two diagrams:

An-Di-FoAn-Fo-Qz (source)

These diagrams describe the order of crystallisation of minerals in a magma whose composition can be defined in terms of the three end members (Anorthite, Diopside, Forsterite, and Anorthite, Forsterite, Quartz). A line of descent is a line that tracks the evolution of the crystallising minerals from a magma. Take for example a magma with equal amounts of Di and Fo and slightly less An than the rest. This magma would first crystallise only forsterite, then it will crystallise forsterite and diopside together and eventually it will crystallise all three minerals together, until there is no more liquid. This is despite the higher melting temperature of anorthite over diopside. Melting this rock would result at first in melting of all three minerals together at 1270 °C, even though their melting temperatures in isolation vary by around 500 °C.

The second diagram shows a more complex situation, where a rock with a Fo rich composition might first crystallise Fo which will then be consumed to form enstatite. A similar magma with slighly less Fo component might not even crystallise forsterite at all, but rather crystallise quartz, even though the overall composition is still Fo-rich.

This subject of magma crystallisation and melting is fascinating and a short introduction is available (with many visual aids) is available here: Teaching Phase Equilibria.

//www.hoelymoley.com/questions/174/-/7689 # 7689 4 答案由Zbynek Burival为什么长英质的材料熔点低于镁铁质吗? Zbynek Burival //www.hoelymoley.com/users/5639 2016 - 03 - 16 - t21:16:24z 2016 - 03 - 16 - t21:16:24z < p >一个技巧——长英质的岩浆基本上是分级衍生的其他岩石。在岩石循环,最不稳定的组件更倾向于长英质的岩石。通常水和通量降低熔点。和长英质的岩石通常有碱金属与镁铁质岩石中Fe / Mg相比。碱金属和动荡的反应更大。< / p > < p >如果你部分镁铁质岩石融化,最活泼多变的组件在第一融化。如果它被删除从源,你得到更多的分级和长英质的融化。重复很多次得到极其分馏融化与最低镁铁质组件和挥发物含量高、高活性元素如碱金属或氟。< / p > < p >通量像水一样,硼、磷、氟等可以强烈降低熔点。如干haplogranite几乎融化在700摄氏度,而一些极端的伟晶岩融化水和挥发物内容可以明显存在波形500摄氏度。干非造山期的花岗岩或ryolites更高的熔点湿年代花岗岩。

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