Orogenic plateau magmatism

造山高原岩浆作用

• 批准号: NE/H021620/1
• 负责人: Mark Allen
• 金额: $ 49.87万
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2011
• 资助国家: 英国
• 起止时间: 2011 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH021620%2F1
• 关键词: Orogenic; plateau; magmatism

This study will show why some of the highest regions on Earth contain young and active volcanoes. Our particular study area is the high plateau of Iran, which has a unique combination of young volcanic rocks, known tectonic plate thickness and variation in plate thickness, in a region where the plates are actively colliding. Combined with background information on the rock types and thicknesses of the tectonic plates in this region, it will tell us which part of the deep Earth generates the magma, why it is melting, and what controls the ascent to the surface. Volcanoes and mountain ranges show how Earth is active: forces and processes arising from deep within the planet shape the landscapes on which we live. Risks from eruptions, earthquakes and landslides threaten millions of people, but at the same time control the distribution of land, nutrients and water on which we all depend. There are many ways to generate volcanoes and chains of mountains, some of which are entirely separate. But there are certain tectonic settings where they come together, where the moving plates collide continents to create vast regions of deformation known as collision zones. Many of these have occurred through geological time and are now inactive. The mountains of Scotland are the eroded roots of such chains, and the volcanoes once within their midst. But in SW Asia the processes continue at the present day, as the Arabian plate moves northward, pushing in to Eurasia. The rate of motion is roughly 20 mm/yr, but over geological timescales this translates to a considerable amount of deformation: ~700 km of convergence has occurred since initial plate collision ~35 million years ago. Volcanism was common before the collision, in a setting similar to the modern Andes. It reduced in intensity after the initial collision, because one of the main triggers for magmatism ended at this time - downgoing of oceanic plate beneath the Eurasian continent. Later, sporadic magmatism probably represented the tail-off from this process. But in the last few million years there has been an upsurge of volcanic activity across the collision zone, for reasons not entirely understood, but possibly related to a general re-organization of deformation of the Eurasian plate. The volcanic centres are not randomly distributed. We can determine patterns in their locations that give us clues about why the deep Earth is melting. First, they are concentrated in a region within the collision zone that is no longer shortening, known as the Turkish-Iranian plateau. As its name implies, this is a vast, high area with subdued relief, that no longer undergoes the kind of mountain building that once deformed the Earth in this area. That mountain building carries on at the margins of the broad zone that is the site of collision between the Arabian and Eurasian plates. Second, the volcanoes are almost always in the original Eurasian plate, which once lay above a slab of an oceanic plate that has now passed underneath it ('subducted' in the jargon). This slab is a source of water and other volatile compounds that could have been responsible for melting the deep Earth and causing the volcanoes. But it is unclear why water would be present tens of millions of years after the ocean plate stopped moving under Eurasia. Third, many of the volcanoes are located in regions which are still faulting, even if the mountains are not building up. This suggests a link between the faulting and either the generation of the magmatism, or at least its ascent to the surface. Again, the details are not understood and form part of this study. Whereas we generally understand the generation of volcanoes in settings like the Andes, Hawaii and Iceland, the high plateaux of the Earth like Iran and Tibet represent a frontier for science, and an opportunity to comprehend how the end result of plate tectonics can be volcanoes within the highest places on Earth.

这项研究将揭示为什么地球上一些最高的地区含有年轻的活火山。我们特别研究的地区是伊朗高原，在板块碰撞活跃的地区，有着年轻火山岩、已知构造板块厚度和板块厚度变化的独特组合。结合该地区岩石类型和构造板块厚度的背景信息，它将告诉我们地球深处的哪个部分产生岩浆，为什么它正在融化，以及是什么控制了上升到地表。火山和山脉显示了地球是如何活跃的：从地球深处产生的力量和过程塑造了我们生活的景观。火山喷发、地震和山体滑坡的风险威胁着数百万人，但同时也控制着我们所依赖的土地、养分和水的分布。有很多方法可以产生火山和山脉，其中一些是完全独立的。但在某些构造环境中，它们会聚集在一起，移动的板块碰撞大陆，产生巨大的变形区域，称为碰撞区。其中许多都发生在地质时代，现在已经不活跃了。苏格兰的山脉是这些链条的侵蚀根源，火山曾经在它们中间。但在亚洲西南部，随着阿拉伯板块向北移动，挤压欧亚大陆，这一过程至今仍在继续。运动速率约为20毫米/年，但在地质时间尺度上，这转化为相当大的变形量：自约3500万年前的初始板块碰撞以来，已经发生了约700公里的收敛。在碰撞之前，火山活动很常见，其环境与现代的安第斯山脉相似。在最初的碰撞之后，它的强度降低了，因为岩浆活动的主要触发因素之一在这个时候结束了-欧亚大陆下面的海洋板块下沉。后来，零星的岩浆活动可能代表了这一过程的结束。但在过去的几百万年里，整个碰撞带的火山活动激增，原因尚不完全清楚，但可能与欧亚板块变形的总体重组有关。火山中心不是随机分布的。我们可以确定它们位置的模式，这给了我们关于为什么地球深处正在融化的线索。首先，它们集中在碰撞区内一个不再缩短的地区，即土耳其-伊朗高原。正如它的名字所暗示的那样，这是一个广阔的，高的地区，地势平缓，不再经历曾经使该地区的地球变形的那种造山运动。这种造山运动在阿拉伯板块和欧亚板块碰撞的广阔地带的边缘进行。第二，火山几乎总是在最初的欧亚板块上，欧亚板块曾经位于一个大洋板块的板块之上，而大洋板块现在已经从它下面经过（用行话来说就是“俯冲”）。这块板块是水和其他挥发性化合物的来源，这些化合物可能是融化地球深处并引发火山的原因。但目前还不清楚为什么在海洋板块停止在欧亚大陆下移动后的数千万年里会有水存在。第三，许多火山位于断层活动仍在继续的地区，即使山脉没有形成。这表明断层作用与岩浆活动的产生或至少与其上升到地表之间存在联系。同样，细节不被理解，构成本研究的一部分。虽然我们通常理解火山在安第斯山脉，夏威夷和冰岛等环境中的生成，但地球上的高原，如伊朗和西藏，代表了科学的前沿，并有机会了解板块构造的最终结果如何在地球最高的地方形成火山。

项目成果

Distinct sources for high-K and adakitic magmatism in SE Iran

• DOI: 10.1016/j.jseaes.2020.104355
• 发表时间: 2020-07
• 期刊: Journal of Asian Earth Sciences
• 影响因子: 3
• 作者: M. Kheirkhah;I. Neill;M. Allen;M. Emami;Ali Shahraki Ghadimi

Generation of Arc and Within-plate Chemical Signatures in Collision Zone Magmatism: Quaternary Lavas from Kurdistan Province, Iran

碰撞区岩浆作用中电弧和板内化学特征的生成：伊朗库尔德斯坦省第四纪熔岩

• DOI: 10.1093/petrology/egs090
• 发表时间: 2013
• 期刊: Journal of Petrology
• 影响因子: 3.9
• 作者: Allen M

Small-volume melts of lithospheric mantle during continental collision: Late Cenozoic lavas of Mahabad, NW Iran

大陆碰撞期间岩石圈地幔的小体积熔化：伊朗西北部马哈巴德的晚新生代熔岩

• DOI: 10.1016/j.jseaes.2013.06.002
• 发表时间: 2013
• 期刊: Journal of Asian Earth Sciences
• 影响因子: 3
• 作者: Kheirkhah M

Insight into collision zone dynamics from topography: numerical modelling results and observations

• DOI: 10.5194/se-3-387-2012
• 发表时间: 2012-11
• 期刊: Solid Earth
• 影响因子: 3.4
• 作者: A. Bottrill;J. Hunen;M. Allen