Petrogenetic and geodynamic investigation of Archean anorthosite-bearing layered intrusion and greenstone belt associations: implications for the early evolution of the Earth

太古代含斜长岩层状侵入体和绿岩带组合的岩石成因和地球动力学研究：对地球早期演化的影响

• 批准号: RGPIN-2014-04906
• 负责人: Polat, Ali
• 金额: $ 2.7万
• 依托单位: University of Windsor
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=566822
• 关键词: Petrogenetic; geodynamic; investigation; Archean; anorthosite

The geological models proposed to explain the origin of Archean anorthosite-bearing layered complex and greenstone associations in the Superior Province of Canada require re-evaluation within the context of new high-precision geochemical data. Over the next five years, I plan to study the field, petrographic and geochemical characteristics of Archean anorthosite-bearing layered complex and greenstone associations in the Superior Province, to constrain their petrogenesis, geodynamic setting and geological significance. The anorthosite-bearing layered complex and greenstone associations to be studied include the Neoarchean Bad Vermilion Lake (Ontario) and Doré Lake (Quebec) complexes. I will systematically sample each lithological unit in these associations and analyze them for major and trace elements and isotopes (Sm-Nd, Th-U-Pb, Lu-Hf, O), to improve our understanding the petrogenetic origin of these rocks. The geochemical characteristics of each rock type in the layered complexes and spatially associated volcanic rocks are expected to reflect petrological processes responsible for the compositional and isotopic variations in these rocks and their sources. Trace elements and Nd, Pb, Hf and O isotopes are sensitive to petrogenetic processes and thus can be used to distinguish different processes. These petrological processes can then be linked to the regional scale Neoarchean geodynamic processes in the Superior Province, and the geochemistry of these rocks can be used to understand their significance for Archean Earth evolution. Zircon grains from anorthosites, gabbros and felsic volcanic rocks will be dated using U-Pb isotopes, and these grains will also be analyzed for Hf isotopes. Three hypotheses will be tested: (1) anorthosite-bearing layered intrusions and greenstone belts are genetically related and represent relict Archean oceanic crust formed at either divergent or convergent plate margins; (2) they are genetically related and represent fragments of an oceanic plateau derived from a mantle plume; and (3) anorthosite-bearing layered intrusions are unique to the Archean and originated through non-uniformitarian geologic processes. The results of this project will have the following significance: (1) enhance our knowledge on the petrogenetic origin of Archean layered anorthosites and associated mafic to ultramafic intrusive rocks; and (2) the Canadian resource industry will benefit from this research program given that anorthosites and associated ultramafic rocks have high potential for chromite, vanadium, copper, nickel, and PGE (Platinum Group Elements) mineral deposits.

为解释加拿大上级省太古代含斜长岩层状杂岩和绿岩组合的起源而提出的地质模型需要在新的高精度地球化学数据的范围内重新评价。在未来的五年里，我计划在上级省研究太古代含斜长岩层状杂岩和绿岩组合的野外、岩相学和地球化学特征，以约束它们的岩石成因、地球动力学背景和地质意义。待研究的含斜长岩层状杂岩和绿岩组合包括新太古代巴德朱红湖（安大略）和多雷湖（魁北克）杂岩。我将系统地对这些组合中的每个岩性单元进行取样，并分析它们的主量和微量元素以及同位素（Sm-Nd，Th-U-Pb，Lu-Hf，O），以提高我们对这些岩石成因的理解。在层状复合体和空间相关的火山岩中的每种岩石类型的地球化学特征，预计将反映岩石学过程负责这些岩石及其来源的成分和同位素的变化。微量元素和Nd、Pb、Hf、O同位素对成岩作用敏感，可用于区分不同的成岩作用。这些岩石学过程，然后可以联系到区域尺度的新太古代地球动力学过程中的上级省，这些岩石的地球化学可以用来了解他们的太古代地球演化的意义。斜长岩、辉长岩和长英质火山岩中的锆石颗粒将用U-Pb同位素定年，这些颗粒也将进行Hf同位素分析。将检验三个假说：（1）斜长岩层状侵入体和绿岩带在成因上是相关的，代表太古代残留洋壳，形成于扩张或会聚的板块边缘;（2）它们在成因上是相关的，代表地幔柱形成的洋坪碎片;含斜长岩的层状侵入体是太古代特有的，其形成经历了非均变的地质过程。本课题的研究成果具有以下意义：（1）加深了对太古代层状斜长岩及相关镁铁质-超镁铁质侵入岩成因的认识;以及（2）鉴于斜长岩和相关的超镁铁岩具有很高的铬铁矿、钒、铜、镍，和铂族元素矿床。