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首页> 外文期刊>Geochimica et Cosmochimica Acta: Journal of the Geochemical Society and the Meteoritical Society >Late Archean mantle composition and crustal growth in the Western Superior Province of Canada: Neodymium and lead isotopic evidence from the Wawa, Quetico, and Wabigoon subprovinces
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Late Archean mantle composition and crustal growth in the Western Superior Province of Canada: Neodymium and lead isotopic evidence from the Wawa, Quetico, and Wabigoon subprovinces

机译：加拿大西部优势省的太古宙晚期地幔成分和地壳生长：Wawa，Quetico和Wabigoon次省的钕和铅同位素证据

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摘要

Neodymium and lead isotopes are presented for late Archean rocks from the Wawa, Quetico, and Wabigoon subprovinces (Sp) in the Western Superior Province (Ontario, Canada). The isotopic compositions were determined on greenstone volcanic sequences, pre-tectonic (2.73-2.69 Ga) trcndhjemite-tonalite-granodiorite (TTG) suites, metasedimentary rocks, and post-tectonic (2.69-2.67 Ga) dioritic to granitic plutons in order to characterize the mantle and crustal reservoirs involved in the evolution of the southern part of the Western Superior Province. Although derived from a depleted mantle, almost all the greenstone volcanism and pre-tectonic TTG suites record contamination by crustal material as old as 3.2 Ga. Neodymium and lead isotopic compositions of the pre-tectonic TTG can be modeled as products of the melting of amphibolitic crust (e.g., subducted basalts) contaminated by 1-10% of subducted sediments. Moreover, lead isotopes of TTG suites provide evidence that the isotopic compositions of these subducted sediments varied as a result of the addition of new ca. 2.7 Ga juvenile material, in agreement with neodymium isotopic differences recorded by sedimentary units of the Quetico Sp (50:50 mix of young:old crusts) and Wawa Sp (75:25 young:old). Neodymium and lead isotopes of the post-tectonic REE-enriched Archean sanukitoid suites define an isotopic trend which is distinct from that of the TTG suites and which is interpreted to reflect the importance of crustal assimilation in the evolution of these suites. Furthemore, such plutons found in the Wawa Sp have more juvenile neodymium and lead isotopic compositions and higher Nd contents than those intruded into the Quetico and Wabigoon Sp which have more crustal isotopic signatures and lower Nd concentrations. This geographical difference could be due either to differences in Nd contents of initial Archean sanukitoid magmas, lesser assimilation in the Wawa Sp or, more probably, because the Wawa crust is on average more juvenile than the Quetico and Wabigoon crusts in agreement with the fact that the geographical difference mirrors that recorded by metasedimentary rocks deposited in Quetico and Wawa Sp.
机译：呈现了上西区（加拿大安大略省）Wawa，Quetico和Wabigoon副省（Sp）的太古宙晚期岩石的钕和铅同位素。在绿岩火山岩序列，构造前（2.73-2.69 Ga）长晶硬质岩-tonalite-granodiorite（TTG）套件，准沉积岩和构造后（2.69-2.67 Ga）对花岗岩的闪长岩中确定同位素组成地幔和地壳储层参与了西部优越省南部的演化。尽管源自枯竭的地幔，但几乎所有的绿岩火山岩和构造前TTG套件都记录了早于3.2 Ga的地壳物质的污染。构造前TTG的钕和铅同位素组成可被模拟为两性岩溶融化的产物被俯冲沉积物污染1-10％的地壳（例如俯冲玄武岩）。此外，TTG套件中的铅同位素提供了证据，表明这些俯冲沉积物的同位素组成由于添加了新的ca而变化。 2.7 Ga幼体，与Quetico Sp（年轻：旧地壳的50:50混合比）和Wawa Sp（75:25年轻：旧）的沉积单位记录的钕同位素差异一致。后构造富含稀土元素的太古宙类uki甲套件的钕和铅同位素定义了与TTG套件不同的同位素趋势，并被解释为反映了地壳同化在这些套件演变中的重要性。此外，与侵入Quetico和Wabigoon Sp的那些具有更多地壳同位素特征和较低Nd浓度的那些相比，在Wawa Sp中发现的这类lut具有更多的钕和铅同位素组成，以及更高的Nd含量。这种地理上的差异可能是由于原始太古宙的浅浮雕岩浆的Nd含量不同，Wawa Sp中的同化作用较小，或者更可能是因为Wawa地壳的平均年龄比Quetico和Wabigoon地壳年轻，这与以下事实一致：地理差异反映了Quetico和Wawa Sp中沉积的准沉积岩所记录的差异。

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