Possible causes and consequences of regional Na-metasomatism: the case of the Sudbury Impact Structure, Ontario, Canada

钠交代作用是一种在数百公里范围内广泛存在的区域范围内的地质现象，其原因，特别是在大陆地壳内，迄今知之甚少。这可能与富氯化钠溶液的普遍循环有关，这些溶液来自蒸散型、含盐岩沉积序列的变质作用，或者可能与岩浆成因的超压流体有关，这些流体具有很高的成矿潜力，如铁氧化物-铜-金(IOCG)矿床。钠交代作用最明显的矿物学表现之一是钠长石化，这是一种极端的交代过程，即使是传统上被认为相对流动不大的元素也会产生流动性。在加拿大安大略省1.85Ga萨德伯里撞击构造(世界上最大的撞击构造之一)周围地区，古元古代岩石的区域钠长石化是一个众所周知但鲜为人知的现象。根据DFG最近在该地区支持的项目取得的成果，它比以前认识到的更广泛，并与强烈的角砾岩密切相关。其年龄和地质原因仍未解决。钠长石化和角砾化作用可能与萨德伯里碰撞有关，也可能与苏打碱岩浆作用或古元古代造山过程中的全盆流体循环有关。这一研究项目的目的是描述萨德伯里周围地区钠交代作用的类型和程度，并澄清它是与撞击事件有关，还是与撞击无关的碱性岩浆作用有关，还是与其他原因有关。在前一种情况下，它将影响我们对水热系统如何通过对(早期)地球表面的影响而形成的理解，并对早期生命环境的形成产生影响。然而，在非撞击成因但岩浆成因的情况下，这将对该区域一系列商品的前景产生深远影响，包括关键金属，这些商品通常见于IOCG矿区或碱性岩浆省。上述目标将通过地质野外工作、岩石学、矿物学、矿物化学、地球化学和同位素研究以及地质年代学分析来实现。

Sodium metasomatism is a widespread geological phenomenon on a regional scale over distances of hundreds of kilometers, the causes of which, especially within the continental crust, are poorly understood so far. It can be related to pervasive circulation of NaCl-rich solutions derived from metamorphism of evaporitic, halite-bearing sedimentary sequences, or to possibly magma-derived overpressured fluids that can have a high mineralizing potential as exemplified by iron oxide-copper-gold (IOCG) deposits. One of the most obvious mineralogical expressions of Na-metasomatism is albitization, an extreme metasomatic process that results in the mobility even of elements traditionally considered relatively fluid-immobile. Regional albitization of Palaeoproterozoic rocks is a well-known but poorly understood phenomenon in the area around the 1.85 Ga Sudbury impact structure (one of the biggest of its kind in the world) in Ontario (Canada). Based on results achieved in a recent DFG-supported project in the area, it is more widespread than previously recognized and intimately associated with intense brecciation. Its age and geological cause remain unresolved. Albitization and brecciation could be related to the Sudbury impact but also to sodic alkali magmatism or basin-wide fluid circulation in the course of Palaeoproterozoic orogenies. The aim of this research project is the characterization of the type and extent of Na-metasomatism in the area around Sudbury and to clarify whether it is related to the impact event, to alkaline magmatism unrelated to the impact or to some other cause altogether. In the former case, it would have consequences on our understanding of how hydrothermal systems could be formed by impacts on the (early) Earth surface with implications on the formation of early life environments. In the case of a non-impactogenic but magmatogenic origin, however, it would have profound implications for the prospectivity of the region for a range of commodities, including critical metals, as typically found in IOCG ore districts or alkaline magmatic provinces. The said aim will be achieved through a combination of geological field work, petrography, mineralogical, mineral-chemical, geochemical and isotopic studies as well as geochronological analyses.