Seismic crustal structure and evolution of the Coast Mountains Batholith

不列颠哥伦比亚省海岸山基(CMB)是北美科迪勒拉地区最大的山基。岩基是地下深处以前大量熔融的岩石，它们向上流动并凝固。CMB是解决地球科学中一个悬而未决的问题的理想自然实验室。大陆地壳的平均成分由安山岩[介于硅质(硅氧化物)和镁铁质(铁/镁氧化物)之间的火山岩]代表。然而，在所有构造体系中，来自地幔的熔体都是玄武岩[一种镁铁质成分的火山岩]。这种差异给地球科学提出了一个基本问题：玄武岩是如何形成安山质地壳的？我们预计，较轻的硅质组分裂解并上升，在上地幔中留下较重的超镁铁质残留物。残留物可能密度太大，下沉到地幔深处，也可能“隐藏”在地壳-地幔边界之下，形成密集的树根。浴石项目主要由美国资金来源(5年内460万美元)资助，通过对CMB的综合地质和地球物理研究来调查这一问题。地震研究是确定地壳和地幔深层岩石类型的最有效技术之一。NSERC将在3年内提供286,500美元的资金，加拿大科学家将作为正式合作伙伴参与整个CMB的重大地壳折射/广角反射(R/WAR)地震计划。这笔捐款将带来几乎是我们所要求的两倍的美国资金来开展这项实验，将使我们能够接触到美国庞大的地震仪池(2500台仪器)，并将使我们能够与来自许多地球科学学科的美国和加拿大科学家进行互动。我们将分享即将取得的重大发现，并促进本科生和研究生的培养，他们将成为工业界、政府和学术界的地球科学家。

The Coast Mountain Batholith (CMB) of British Columbia is the largest batholith in the North American Cordillera. A batholith is a very large volume of previously molten rock in the deep subsurface that worked its way upward and solidified. The CMB is an ideal natural laboratory in which to address an outstanding problem in Earth Sciences. The average composition of the continental crust is represented by andesite [a volcanic rock intermediate between silicic (silicon oxides) and mafic (iron/magnesium oxides)]. However, melts derived from the mantle in all tectonic regimes are basaltic [a volcanic rock of mafic composition]. This discrepancy poses a fundamental problem for Earth Sciences: What processes generate an andesitic crust from basaltic rocks? We expect that the lighter silicic components fractionate and rise up, leaving a heavier ultramafic residue in the upper mantle. The residue may be so dense that it sank deeper into the mantle, or it may lay "hidden" below the crust-mantle boundary as a dense root. The BATHOLITHS project, primarily funded from U.S. sources ($4.6M over 5 years), investigates this problem through an integrated geological and geophysical study of the CMB. Seismic studies are among the most effective techniques for determining rock types in the deep crust and mantle. With NSERC funds of $286,500 over 3 years, Canadian scientists will participate as full partners in a major crustal-scale refraction / wide-angle-reflection (R/WAR) seismic program across the CMB. This contribution will bring nearly double our requested amount in U.S. funds to run the experiment, will provide access to the huge U.S. pool of seismometers (>2500 instruments), and will allow us to interact with U.S. and Canadian scientists from many Earth Science disciplines. We will share the significant discoveries to be made and promote the training of undergrad and graduate students who will become Earth scientists in industry, government and academia.