4.13变质岩
Section outline
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What is the history of this rock?
::这块岩石的历史是什么?The in this photo is a banded gneiss. The bands are made of different . The light bands are more felsic , and the dark bands are more mafic . The minerals separated due to heat and pressure. The waviness of the bands also shows how the rock was hot enough to alter. It was not hot enough to melt all the way.
::照片中是一个带带状的格奈斯。 乐队是由不同的乐队组成的。 光带更像felsic, 暗带也更粗糙。 矿物质因热和压力而分离。 乐队的摇晃也显示了岩石是如何热到可以改变的。 光带不够热,不能完全融化 。Metamorphism
::变形主义Metamorphic rocks start off as some kind of rock. The starting rock can be igneous, sedimentary, or even another metamorphic rock . Heat and/or pressure then change the rock into a metamorphic rock. The change can be physical, chemical, or both.
::变形岩石开始时是某种岩石。 始发岩石可以是皮质的、沉积的,甚至是另一种变形岩石。 热和(或)压力会将岩石变成变形岩石。 变化可以是物理的、化学的,也可以是两者兼而有之。During metamorphism , a rock may change chemically. Ions move in or out of a mineral. This creates a different mineral. The new minerals that form during metamorphism are more stable in the new environment. Extreme pressure may lead to physical changes. If pressure is exerted on the rock from one direction, the rock forms layers. This is foliation . If pressure is exerted from all directions, the rock usually does not show foliation.
::在变形过程中, 岩石可能会发生化学变化 。 恒星会进出矿物质 。 这会产生不同的矿物质 。 在变形过程中形成的新矿物在新环境中比较稳定 。 极端压力可能导致物理变化 。 如果从一个方向对岩石施压, 岩石会形成层 。 这是叶子 。 如果从各个方向施压, 岩石通常不会显示变形 。There are two main types of metamorphism: contact and regional.
::变化主要有两种类型:联系和区域。Contact Metamorphism
::接触变形Contact metamorphism occurs when magma contacts a rock. Even if the rock does not get hot enough to melt, The magma's extreme heat changes the rock. ( Figure ).
::当岩浆接触岩石时,就会发生接触变形。即使岩石的热量不足以熔化,岩浆的极端热量也会改变岩石。 (图 )(A) Hornfels is a rock that is created by contact metamorphism. (B) Hornfels is so hard that it can create peaks like the Matterhorn in the Alps. Regional Metamorphism
::区域变形主义Regional metamorphism occurs over a wide area. Great masses of rock are exposed to pressure from rock and sediment layers on top of it. The rock may also be compressed by other geological processes, such as tectonic plate motions. If the rock is buried deeply, it may also experience high temperatures.
::区域变形在广大地区发生,大块岩石受到岩石和沉积物层的压力,岩石还可能受到地质过程的压缩,例如构造板块运动。如果岩石被深埋,它也可能经历高温。(A) Regional metamorphic rocks often display layering called foliation. (B) Regional metamorphism with high pressures and low temperatures can result in blueschist. Metamorphism does not cause a rock to melt completely. It only causes the minerals to change by heat or pressure. If the rock melts completely, it will cool to become an igneous rock .
::变形主义不会导致岩石完全融化,而只会通过热或压力改变矿物质。 如果岩石完全融化,它会变得冷却,成为不光彩的岩石。Hornfels is a rock with alternating bands of dark and light crystals. Hornfels is a good example of how minerals rearrange themselves during metamorphism ( Figure ). The minerals in hornfels separate by density. The result is that the rock becomes banded. Gneiss forms by regional metamorphism from extremely high and pressure.
::Hornfels是一块由深晶体和光晶体交替带组成的岩石。 Hornfels是一个很好的例子,说明矿物在变形过程中是如何重新排列的(图 ) 。 黄蜂中的矿物因密度而分离。 其结果是岩石被捆绑在一起。 从极高的压力和压力来看,Gneiss是由区域变形形成的。Summary
::摘要- Any type of rock—igneous, sedimentary, or metamorphic—can become a metamorphic rock.
::任何类型的岩石——有色石、沉积石或变形石——都能成为变形石。
- Contact metamorphism occurs when a rock is altered by heat from nearby magma.
::当岩石被附近岩浆的热量改变时,就会发生接触变形。
- Regional metamorphism occurs over a large area when a rock is buried or compressed.
::当岩石被掩埋或压缩时,大片地区出现区域变形。
Review
::回顾- Compare and contrast the two types of metamorphism.
::比较和对比这两类变形。
- Under what conditions does a rock become foliated?
::岩石在什么条件下会变成叶状的?
- Describe how and why rocks are altered by regional metamorphism.
::描述岩石如何和为什么因区域变形而改变。
- Any type of rock—igneous, sedimentary, or metamorphic—can become a metamorphic rock.
