The significance of Paleoarchean granitoids from the Saglek Block, Labrador, Canada

IF 3.2 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
Tanmay Keluskar , Monika A. Kusiak , Daniel J. Dunkley , Simon A. Wilde , Martin J. Whitehouse , Keewook Yi , Shinae Lee
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引用次数: 0

Abstract

The Saglek Block in the Nain Province of northeast Canada is part of the North Atlantic Craton. It comprises Archean gneisses that record magmatic and metamorphic ages between ca. 3.9 and 2.5 Ga. In this study, a grey banded gneiss from Maidmonts Island records an age of 3.72 Ga, which is equated with Uivak I gneisses reported from across the Saglek Block, and contains 3.8 Ga xenocrysts. These rocks were deformed and metamorphosed prior to the intrusion of augen gneiss protoliths on both Maidmonts and Mentzel islands that record U-Pb zircon ages of 3.33 Ga. These rocks are composed of ferroan calc-alkaline granite and granodiorite and were likely generated by partial melting of pre-existing quartzo-feldspathic crust, as attested by the presence of ca. 3.8 Ga xenocrysts. Such augen gneiss was previously classified as ca. 3.6 Ga ‘Uivak II gneiss’, a term we argue should now be abandoned. The final magmatic events recorded on Maidmonts and Mentzel islands took place in the Neoproterozoic with the emplacement of granitic stocks at ca. 2.72 Ga, and sills and dykes at ca. 2.57 Ga. This sequence of magmatic events from the Eoarchean to Neoarchean is very similar to that recorded in the Itsaq Gneiss Complex of southwest Greenland, where, based on the Hf signature, it has been suggested that a change in tectonic environment resulted from the initiation of subduction at ca. 3.2 Ga. Although Lu-Hf and Sm-Nd isotopic signatures from the ca. 3.33 Ga gneisses have been interpreted in the literature as due to partial melting of Hadean mafic crust, alternatively, they can be generated by partial melting of Eoarchean continental crust in a continental arc setting. We argue this is more consistent with the non-TTG geochemistry of the augen gneisses.

加拿大拉布拉多萨格尔克区块古新世花岗岩的意义
加拿大东北部纳恩省的萨格莱克区块是北大西洋克拉通的一部分。它由阿基坦片麻岩组成,记录的岩浆和变质年龄约在 3.9 至 2.5 Ga 之间。在这项研究中,来自梅德蒙茨岛的灰色带状片麻岩记录的年龄为3.72 Ga,与整个萨格莱克地块报告的Uivak I片麻岩相当,并含有3.8 Ga的异晶。这些岩石在麦德蒙茨岛和门采尔岛的奥长片麻岩原岩侵入之前发生了变形和变质,其锆石U-Pb年龄为3.33 Ga。这些岩石由铁质钙碱性花岗岩和花岗闪长岩组成,很可能是由先前存在的石英-长石地壳部分熔融而成,其中存在的约 3.8 Ga 的异晶石证明了这一点。这种奥长片麻岩以前被归类为约 3.6 Ga 的 "Uivak II 片麻岩",我们认为现在应该放弃这个术语。麦德蒙茨岛和门策尔岛记录的最后岩浆事件发生在新元古代,花岗质岩浆在约 2.72 Ga 处形成,而岩柱和岩堤则在约 2.57 Ga 处形成。从新元古代到新元古代的这一岩浆事件序列与格陵兰岛西南部的Itsaq片麻岩复合体所记录的岩浆事件序列非常相似,根据Hf特征,有人认为大约在3.2 Ga时开始的俯冲导致了构造环境的改变。3.2 Ga.尽管来自约 3.33 Ga 片麻岩的 Lu-Hf 和 Sm-Nd 同位素特征表明,格陵兰岛西南部的构造环境发生了变化。3.33Ga片麻岩的Lu-Hf和Sm-Nd同位素特征在文献中被解释为哈代黑云母地壳的部分熔融所致,但它们也可能是在大陆弧环境中由新元古代大陆地壳的部分熔融产生的。我们认为这更符合奥陶纪片麻岩的非TTG地球化学特征。
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来源期刊
Precambrian Research
Precambrian Research 地学-地球科学综合
CiteScore
7.20
自引率
28.90%
发文量
325
审稿时长
12 months
期刊介绍: Precambrian Research publishes studies on all aspects of the early stages of the composition, structure and evolution of the Earth and its planetary neighbours. With a focus on process-oriented and comparative studies, it covers, but is not restricted to, subjects such as: (1) Chemical, biological, biochemical and cosmochemical evolution; the origin of life; the evolution of the oceans and atmosphere; the early fossil record; palaeobiology; (2) Geochronology and isotope and elemental geochemistry; (3) Precambrian mineral deposits; (4) Geophysical aspects of the early Earth and Precambrian terrains; (5) Nature, formation and evolution of the Precambrian lithosphere and mantle including magmatic, depositional, metamorphic and tectonic processes. In addition, the editors particularly welcome integrated process-oriented studies that involve a combination of the above fields and comparative studies that demonstrate the effect of Precambrian evolution on Phanerozoic earth system processes. Regional and localised studies of Precambrian phenomena are considered appropriate only when the detail and quality allow illustration of a wider process, or when significant gaps in basic knowledge of a particular area can be filled.
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