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

区域性纳交代作用的可能原因和后果：以加拿大安大略省萨德伯里撞击结构为例

• 批准号: 521601478
• 负责人: Professor Dr. Hartwig E. Frimmel
• 金额: --
• 依托单位: Lehrstuhl für Geodynamik und Geomaterialforschung
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/521601478?language=en
• 关键词: Possible; causes; consequences; regional; Na

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.

钠交代作用是一种广泛存在于数百公里区域范围内的地质现象，其原因，特别是在大陆地壳内，至今仍知之甚少。它可能与富NaCl溶液的普遍循环有关，富NaCl溶液来自含钾长石、含岩盐的沉积序列的变质作用，或可能与岩浆衍生的超压流体有关，超压流体具有很高的成矿潜力，如氧化铁-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，甚至导致传统上被认为相对不流动的元素的流动性。在加拿大安大略的1.85 Ga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知之甚少的现象。根据DFG最近在该地区支持的项目中取得的成果，它比以前认识到的更广泛，并与强烈的角砾岩密切相关。它的年龄和地质原因仍然没有解决。钠长石化和角砾岩化可能与萨德伯里撞击有关，但也可能与古元古代造山作用过程中的钠碱性岩浆作用或全盆地流体循环有关。本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，并澄清它是否与撞击事件有关，与撞击无关的碱性岩浆作用，或与其他原因有关。在前一种情况下，它将对我们理解热液系统如何通过对（早期）地球表面的影响而形成产生影响，并对早期生命环境的形成产生影响。然而，如果不是撞击成因，而是岩浆成因，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，如通常在IOCG矿区或碱性岩浆区发现的金属。上述目标将通过地质野外工作、岩相学、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相结合来实现。