Petrogenetic investigation of Eoarchean to Neoarchean anorthosite-bearing layered intrusions

尽管它们的体积很小，但太古宙斜长岩层状侵入体在大多数太古宙克拉通中都很普遍。这些层状侵入体通常与绿岩带有关，主要受同构造-后构造花岗岩类侵位。其中一些侵入岩发生在高级片麻岩地体中。尽管太古宙斜长岩广泛存在，但其成因尚不清楚。一些悬而未决的科学问题仍有待解决，以限制它们的岩石成因和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(&gt；An70)巨晶斜长岩的岩石成因意义是什么？(3)为什么巨晶斜长岩仅限于太古宙岩石记录？(4)它们侵入了什么类型的地壳(洋壳和陆壳)？(5)它们是否表现出从太古代到新太古代的系统的地球化学变化？(6)产生这些岩石的地球动力学环境(S)是什么？为了在接下来的五年里解决这些问题，我计划研究西澳大利亚和加拿大的太古宙斜长岩层状侵入岩。将要研究的侵入岩包括西澳大利亚伊尔加恩克拉通的3.73Ga Manfred侵入体，西澳大利亚东皮尔巴拉克拉通的3.47Ga East Pilbara侵入体，以及加拿大苏必利尔省的新太古代(约2.75Ga)肖米尔和Pipestone Lake侵入体。我将对这些侵入岩中的每个岩性单位进行系统的取样，并对其进行主量元素和痕量元素及同位素(Sm-ND、Th-U-Pb、Lu-Hf、O)的分析，以加深对这些侵入岩的岩石成因的认识。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成分和同位素变化的岩石学过程。然后，这些岩石学过程可以与地球早期全球范围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将被用来限制超过10亿年(3.7-2.7Ga)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。这次调查的结果将具有下列重要意义：(1)加强我们对含太古代斜长岩层状侵入岩的岩石成因的认识；(2)为地幔的热演化与地球早期的斜长岩形成之间的关系提供地球化学约束；(3)使我们能够测试和完善所提议的太古宙克拉通起源地球动力学模型；(4)通过培训具有勘探高潜力铬、钒、铜、镍、钛和铂组元素矿床的地质学家所需的专业知识，使加拿大资源行业受益。

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.