冰岛的形成——地球科学堆栈交换江南电子竞技平台江南体育网页版 最近30从www.hoelymoley.com 2023 - 07 - 10 - t12:30:03z //www.hoelymoley.com/feeds/question/18575 https://creativecommons.org/licenses/by-sa/4.0/rdf //www.hoelymoley.com/q/18575 3 冰岛的形成 哈维RAWAT //www.hoelymoley.com/users/18396 2019 - 11 - 26 - t13:52:56z 2019 - 12 - 13 - t15:42:43z < p >冰岛坐落在一个发散洋洋边界。但没有许多岛屿,形成沿不同的边界。为什么如此?为什么不是大洋中脊经常超越海面形成岛屿?为什么沿汇聚板块边界岛屿更常见,他们经常形成群岛吗?< / p > //www.hoelymoley.com/questions/18575/-/18579 # 18579 0 答案由Michael Walsby冰岛的形成 迈克尔Walsby //www.hoelymoley.com/users/17166 2019 - 11 - 26 - t19:21:38z 2019 - 11 - 26 - t19:21:38z < p >岛屿之所以没有形成离散板块边界,这些边界是大海的底部,并且通常相当深。虽然海洋中部山脊其实都是火山,岩浆不有机会堆积,达到表面,因为盘子不是静态的。他们慢慢蔓延开来,岩浆需要它们之间形成新的大洋地壳。逻辑的海底扩张是大海的底部。我只知道一个地方,这发生在陆地上,在埃塞俄比亚阿法尔地区。< / p >

Islands are common on convergent plate boundaries because volcanism is common on convergent plate boundaries. This is where oceanic crust is subducted. Volcanoes and other phenomena connected with subduction tend to form islands. The Pacific 'ring of fire' is an example of this.

//www.hoelymoley.com/questions/18575/-/18600 # 18600 1 答案由user18411冰岛的形成 user18411 //www.hoelymoley.com/users/0 2019 - 11 - 30 - t23:41:49z 2019 - 12 - 01 - t10:57:47z < p >冰岛不仅仅是坐落在一个不同的边界(这本身可以上升到浅深度因为更高的静态和动态升力顺便说一句。)但也(假设)非常根深蒂固的地幔柱岩浆可能产生足够的上升到接近地面的高度。< / p > < p >编辑:喷发的岩浆海洋山脊是“焊接”(“片状的堤坝”)。根据实际的理解,它是俯冲板块的拉力(*)在聚合边界驱动海洋传播,因此“拉伸”的东西而不是导致它们堆积起来。在岭岩浆产生的利率太低完全弥补。< / p >

Islands, if not forming an arc and situated intra-plate, frequently have a plume under them or are fed from fingers of a plume from the side. In the case of Iceland it is (probably) the plume (in co-operation with "viscous fingering") that produces enough material for a subaerial edifice.

(*) ... before somebody objects: not necessarly the plate connected to that ridge, but another one elsewhere, and the earth as a whole can't shrink or grow and also isn't exactly hollow ;-)

//www.hoelymoley.com/questions/18575/-/18680 # 18680 2 答案由jimmcwibb冰岛的形成 jimmcwibb //www.hoelymoley.com/users/18470 2019 - 12 - 12 - t23:33:46z 2019 - 12 - 12 - t23:33:46z < p >迄今为止广泛是正确的答案。冰岛已形成一个巧合的建设性的板块边缘和地幔柱,或“热点”。但要真正了解为什么冰岛有我们需要看一个正常的建设性的板块边界。< / p >

A normal mid-ocean ridge is formed where two plates spread apart so that the mantle, which is at a certain temperature, rises upwards and experiences a decrease in pressure. The lower pressure together with the temperature of the mantle allows some (not all) of the mantle to melt - a process called partial melting. Only a small proportion of the mantle actually melts. This melt rises up through the overlying crust in a series of magma bodies, dykes, and lavas, to form the crust. Crucially, the thickness of the crust that is formed depends on the amount of melt that is created, referred to as the melt thickness.

A normal mid-ocean ridge creates a very thin crust - usually about 7 km. That's just 7 km between the ocean and the mantle. But Iceland is not normal. It sits above a mantle plume, which is a region of anomalously warm mantle. So what happens when we depressurise an area of mantle at a higher temperature than normal? We create a much greater melt thickness. This means the crust that is produced above the plume is greater - as much as 30 km. Since the icelandic crust is so much thicker than normal oceanic crust, the upper part of it is able to rise above the level of the sea. And thus Iceland exists.

To answer your followup questions:

Why do not mid ocean ridges often rise above the sea surface to form islands?

Because it's very rare for a hot spot to coincide with a mid-ocean ridge.

Why are islands more common along convergent plate boundaries where they often form archipelagos?

Because these islands form through very different processes. Convergent plate margins introduce water and other volatiles into the mantle, and these have the effect of reducing the melting temperature of the mantle. This produces melt, which rises up and forms volcanoes and islands. This process occurs at virtually every single destructive plate boundary because the subducting oceanic crust contains water which is liberated during subduction.

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