Petrogenetic investigation of Eoarchean to Neoarchean anorthosite-bearing layered intrusions

虽然太古代含斜长岩的层状侵入体体积很小，但在大多数太古代克拉通中分布广泛。这些层状侵入体通常与绿岩带有关，主要由同构造-后构造花岗岩类侵入。有些侵入体发生在高等级片麻岩地。尽管太古代斜长岩分布广泛，但其成因尚不清楚。几个突出的科学问题仍有待解决，以确定它们的岩石成因及其对早期地球演化的意义。这些问题包括：(1)太古宙斜长岩是如何形成的？(2)高钙（b> An70）巨晶斜长石的成岩意义是什么？(3)巨晶斜长岩为何局限于太古宙岩石记录？(4)它们侵入了什么类型的地壳（洋壳还是陆壳）？(5)从太古代到新太古代，它们是否表现出系统的地球化学变化？(6)产生这些岩石的地球动力学背景是什么？为了解决这些问题，我计划在未来五年内研究西澳大利亚和加拿大的太古宙含斜长岩层状侵入体。研究对象包括西澳大利亚Yilgarn克拉通3.73 Ga的Manfred侵入岩、西澳大利亚东皮尔巴拉克拉通3.47 Ga的East Pilbara侵入岩和加拿大苏必利尔省新太古代（约2.75 Ga）的Shawmere和Pipestone Lake侵入岩。我将系统地对这些侵入体中的每个岩性单元进行采样，并分析其主微量元素和同位素（Sm-Nd, Th-U-Pb, Lu-Hf， O），以提高我们对这些侵入体岩石成因的认识。这些层状侵入体中每种岩石类型的岩石学和地球化学特征有望反映导致这些岩石及其来源的组成和同位素变化的岩石学过程。这些岩石学过程可以与地球早期全球尺度的太古宙地球动力学过程联系起来。这些侵入体的地球化学特征将用于约束10亿年（3.7-2.7 Ga）地幔温度下降对太古宙岩石成因和地球动力学过程的影响。研究结果具有以下重要意义：(1)加强对太古宙含斜长岩层状侵入岩成因的认识；(2)为地球早期地幔热演化与斜长岩形成之间的关系提供地球化学约束；(3)验证和完善太古宙克拉通起源的地球动力学模型；(4)通过培训地质学家，使他们具备勘探太古代斜长岩侵入体所需的专业知识，从而使加拿大资源行业受益，这些侵入体具有很高的铬、钒、铜、镍、钛和铂族元素矿床的潜力。

Although they are volumetrically small, Archean anorthosite-bearing layered intrusions are widespread in most Archean cratons. These layered intrusions are typically associated with greenstone belts, and are intruded mainly by syn- to post-tectonic granitoids. Some of the intrusions occur in high-grade gneissic terrains. Despite their widespread occurrence, the petrogenesis of Archean anorthosites is not well understood. Several outstanding scientific questions remain to be resolved to constrain their petrogenetic origin and significance for the evolution of the early Earth. These questions include: (1) How did Archean anorthosites originate? (2) What is the petrogenetic significance of high-Ca (>An70) megacrystic plagioclase? (3) Why are megacrystic anorthosites restricted to the Archean rock record? (4) What type of crust (oceanic versus continental) did they intrude? (5) Do they display any systematic geochemical changes from Eoarchean to Neoarchean? (6) What was the geodynamic setting(s) that produced these rocks? To address these questions over the next five years, I plan to study Archean anorthosite-bearing layered intrusions in Western Australia and Canada. The intrusions to be studied include the 3.73 Ga Manfred intrusion in the Yilgarn Craton of Western Australia, the 3.47 Ga East Pilbara intrusion in the East Pilbara Craton of Western Australia, and the Neoarchean (ca. 2.75 Ga) Shawmere and Pipestone Lake intrusions in the Superior Province of Canada. I will systematically sample each lithological unit in these intrusions 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 intrusions. The petrographic and geochemical characteristics of each rock type in these layered intrusions are expected to reflect the petrological processes responsible for the compositional and isotopic variations in these rocks and their sources. These petrological processes can then be linked to the global-scale Archean geodynamic processes in the early Earth. The geochemistry of these intrusions will be used to constrain the effects of declining of mantle temperatures over one billion years (3.7-2.7 Ga) on the petrogenetic and geodynamic processes in the Archean. The results of this investigation will have the following significance: (1) enhance our knowledge on the petrogenetic origin of Archean anorthosite-bearing layered intrusions; (2) provide geochemical constraints on the relationship between the thermal evolution of the mantle and anorthosite formation in the early Earth; (3) allow us to test and refine the geodynamic models proposed for the origin of Archean cratons; and (4) benefit the Canadian resource industry by training geologists with the expertise needed to explore for Archean anorthosite-bearing intrusions that have a high potential for chromium, vanadium, copper, nickel, titanium, and platinum group element mineral deposits.