A new view of the thermal structure of continental mountain ranges: the importance of igneous heat transport

当大陆构造板块碰撞并形成山脉时，山脉内部的岩石变得足够热而融化。这些熔融的岩石穿过地壳上升，在较浅的深度结晶或在火山喷发。然而，我们不知道这些熔岩在地壳中移动时携带了多少热量。这种不确定性很重要，因为这是我们不了解的主要事情之一，关于是什么控制了地球内部的温度分布。我们关心温度的原因是它控制着岩石的强度，以及地球内部矿物质的分布。这些主题具有广泛的重要性，从它们在控制山脉的大小，形状和演变中所起的作用，到经济矿物的分布，我们拟议的研究将通过测试熔融岩石在山脉内部移动多少热量来解决目前的不确定性。这一目标将通过结合三个研究主题来实现：1。当岩石融化时，它们会在一定的温度范围内逐渐融化，由此产生的岩浆的成分取决于岩石变得有多热。因此，观察岩浆冷却时产生的岩石中的矿物质类型可以告诉我们熔融区的温度。当熔融的岩石在地壳的上部就位时，它们会加热周围的环境，导致新的矿物生长，我们可以用它来估计这些周围岩石的温度。我们将把这种方法应用于四个有熔融岩侵位的地区，这样我们就可以计算出不同地点之间的差异有多大。我们可以使用计算机模型将主题（1）中的观测结果转化为对熔岩体就位所需时间的估计，以及发生这种情况时它们的温度。本提案中描述的新计算表明，侵入体周围生长的新矿物的分布足以对这些数量进行严格的估计。这一目标是通过对地壳性质如何随温度变化的新测量而实现的，现代计算机的强大意味着我们能够运行所有必要的计算。通过结合主题（1）和（2）的结果，我们可以建立新的山脉温度的计算机模型。这些模型将包括岩石熔化的影响，以及那些岩石携带的热量，我们已经能够在目标（2）中估计。因此，我们将能够创造一个新的和更准确的了解山区的温度结构。通过将这些信息与我们对岩石强度随温度变化的认识相结合，我们将能够解决一个长期存在的争议，即在山脉带的深处发生了什么，因此它们如何随着时间的推移而演变（例如，岩石是否能够在地壳中的“通道”中流动，就像牙膏从管子中挤出一样）。我们研究的最后一部分将是研究我们的结果对地球科学其他领域的影响。目前的争论是，熔岩的侵入是作为一个单一的大天体发生，还是作为一系列在不同时间到达的较小天体发生。我们对侵入体出现和加热周围岩石的时间的研究结果将使我们能够在我们研究的地区回答这个问题。最后，我们将能够利用我们的结果来更新我们的知识，即我们预计哪些岩石会在地球内的哪些位置产生，因为这取决于温度。这一主题的更广泛的重要性在于，它使我们能够利用当今岩石的分布来推断地质历史中发生了什么，也有助于我们了解具有重要经济意义的矿物的分布。

When continental tectonic plates collide and build mountain ranges, the rocks in the interior of these ranges get hot enough to melt. This molten rock rises through the crust, and crystallises at shallower depths or is erupted at volcanoes. However, we don't know how much heat these molten rocks transport with them as they move through the crust. This uncertainly is important, because it is one of the main things we don't understand about what controls the distribution of temperature within the Earth. The reason we care about temperature is that it controls the strength of rocks, and the distribution of minerals within the Earth. These topics have wide-ranging importance, from the role they play in controlling the sizes, shapes, and evolution through time of mountain ranges, to the distribution of economic minerals.Our proposed research will resolve the current uncertainty by testing how much heat is moved through the interiors of mountain ranges by molten rocks. This aim will be achieved by combining three research themes:1. When rocks melt, they do so gradually over a range of temperatures, and the composition of the resulting magma depends on how hot the rocks became. Looking at the types of minerals in the rocks produced when the magma cools therefore tells us the temperature in the melting zone. As molten rocks are emplaced in the upper part of the crust, they heat up the surroundings, causing new minerals to grow, which we can use to estimate how hot these surrounding rocks became. We will apply this approach in four regions where molten rocks have been emplaced, so that we can work out how much variability there is between different locations.2. We can use computer models to turn the observations in theme (1) into estimates of how long it took to emplace the bodies of molten rock, and how hot they were when this happened. New calculations described in this proposal demonstrate that the distribution of new minerals grown around intrusions is sufficient to make well-constrained estimates of these quantities. This objective is made possible by new measurements of how the properties of the crust vary as a function of temperature, and by the power of modern computers that means we are able to run all of the necessary calculations.3. By combining the results of themes (1) and (2) we can make new computer models of the temperature within mountain ranges. These models will include the effects of the melting of rocks, and those rocks transporting with them the amount of heat that we have been able to estimate in objective (2). We will therefore be able to create a new and more accurate understanding of the temperature structure of mountain belts. By combining this information with our knowledge of the temperature-dependent strength of rocks, we will be able to address a long-running controversy over what happens in the deep interiors of mountain belts, and therefore how they evolve through time (for example whether the rocks are able to flow in 'channels' through the crust, much like toothpaste being squeezed from a tube). The final part of our proposed research will be to examine the implications of our results for other areas of Earth Science. It is currently debated whether intrusions of molten rock occur as a single large body, or as a series of smaller bodies arriving at different times. Our results for how long the intrusions were appearing and heating the surrounding rocks will allow us to answer this question in the regions we study. Finally, we will be able to use our results to update our knowledge of which rocks we would expect to be produced in which locations within the Earth, as this depends on the temperature. The wider importance of this topic is that it allows us to use the distribution of rocks at the present day to infer what happened in the geological past, and also aids our efforts to understand the distribution of economically important minerals.