Petrogenetic investigation of Eoarchean to Neoarchean anorthosite-bearing layered intrusions

虽然它们体积很小，但太古代斜长岩层状侵入体在大多数太古代花岗岩中广泛存在。这些层状侵入体通常与绿岩带有关，并且主要由同构造至构造后的花岗岩类侵入。一些侵入体出现在高级片麻状地形中。尽管它们广泛存在，但太古代斜长岩的成因还不清楚。一些悬而未决的科学问题仍有待解决，以限制其岩石成因的起源和早期地球演化的意义。这些问题包括：（1）太古代斜长岩是如何形成的？(2)高钙（> An 70）巨晶斜长石的岩石成因意义是什么？(3)为什么巨晶斜长岩仅限于太古代岩石记录？(4)它们侵入的是什么类型的地壳（海洋地壳还是大陆地壳）？(5)它们是否显示了从始新世到新太古代的任何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？为了解决这些问题在未来五年内，我计划研究太古代斜长岩轴承层状侵入体在西澳大利亚州和加拿大。待研究的侵入体包括西澳大利亚州Yilgarn地区3.73 Ga的Manfred侵入体、西澳大利亚州东皮尔巴拉地区3.47 Ga的东皮尔巴拉侵入体和新太古代（约100年）的新太古代侵入体。2.75 Ga）肖米尔和管道石湖侵入体。我将系统地对这些侵入体中的每个岩性单元进行取样，并分析它们的主要和微量元素和同位素（Sm-Nd，Th-U-Pb，Lu-Hf，O），以提高我们对这些侵入体的岩石成因的理解。这些层状侵入体中每种岩石类型的岩相学和地球化学特征预计将反映这些岩石及其来源中成分和同位素变化的岩石学过程。这些岩石学过程，然后可以连接到全球规模的太古代地球动力学过程在早期地球。这些侵入体的地球化学将被用来约束的影响，地幔温度下降超过10亿年（3.7-2.7 Ga）的岩石成因和地球动力学过程中的太古代。这一研究结果将具有以下意义：（1）加深对太古代含斜长岩层状侵入体成因的认识;（2）为早期地球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）检验和完善太古代斜长岩成因的地球动力学模型;以及（4）通过培训具有勘探太古代斜长岩侵入体所需专业知识的地质学家，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.