Sub-volcanic breccias: combining ore deposit, volcanology and geophysical perspectives

斑岩矿床的勘探和开采有大量证据表明，大型（> 100米）管道、岩墙和不规则角砾岩体形成于千米深，在空间和时间上与含水弧岩浆系统有关。该项目将汇集经济地质学、火山学和地球物理学领域的知识，从物理上理解贫瘠和矿化角砾岩是如何形成的，并改进我们对今天记录的火山动荡信号的解释。Sillitoe（1985）关于“火山深成弧中与矿石有关的角砾岩”的经典论文汇编了关于角砾岩体的大小和几何形状、岩性、形状、组成碎片的大小和垂直位移。地下角砾岩体的性质差异很大（例如，碎片没有垂直位移，位移> 1公里），因此其形成必须有多种机制。该项目将侧重于与次火山岩浆和热液过程有关的角砾岩，这些过程是由岩浆释放热液或由储层岩浆碎裂和喷发形成的。物理建模将考虑随着挥发性饱和岩浆的侵位和结晶，进一步释放挥发性物质，侵入体和周围岩石中不断变化的应力，以及火山爆发和圆顶/扇形坍塌引起的岩石深处的应力（例如蒙特塞拉特; Druitt等人，2002年）。所有的模型以及由此得出的假设都将受到地质学证据的约束和检验。第二组研究将评估与经济地质学家发现的角砾岩形成有关的预期监测信号（地震活动、地面变形、气体排放）。另一方面，将审查现代火山爆发和非爆发危机的动荡信号（例如，Werner等人，2011年），并考虑是否有任何可能与相当于地质记录中的深层角砾岩事件的过程有关。

There is abundant evidence from exploration and mining of porphyry ore deposits that large (>100s of meters) pipes, dikes and irregular bodies of breccia form at kilometers depth, spatially and temporally associated with hydrous arc magmatic systems. This project will bring together the fields of economic geology, volcanology and geophysics, both to physically understand how the barren and mineralized breccias form, as well as to improve our interpretations of volcanic unrest signals recorded today.The classic paper on "Ore-related breccias in volcanoplutonic arcs" by Sillitoe (1985) compiles information on the size and geometry of breccia bodies, and lithologies, shape, size and vertical displacements of the constituent fragments. The properties of the sub-surface breccia bodies vary considerably (e.g. no vertical displacement of fragments to >1km displacement) and so there must be multiple mechanisms for their formation. The project will concentrate on breccias associated with sub-volcanic magmatic and hydrothermal processes that form by either release of hydrothermal fluids from magmas or from fragmentation and eruption of magmas from reservoirs. The physical modelling will consider evolving stresses in intrusions and surrounding rocks as volatile-saturated magmas are emplaced and crystallize, exsolving further volatiles, as well as stresses in rocks at depth induced by eruptions and dome/sector collapse (e.g. Montserrat; Druitt et al., 2002). All models, and hypotheses derived from them, will be constrained and tested by evidence from geology. A second strand of research will assess the expected monitoring signals (seismicity, ground deformation, gas emissions) that would be associated with the formation of breccias like those that have been uncovered by economic geologists. The flip side will be to review unrest signals from modern eruptive and noneruptive crises at volcanoes (e.g. Werner et al., 2011) and consider whether any might be related to processes equivalent to the deep brecciation events in the geological record.