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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >It started with a plume - early Archaean basaltic proto-continental crust
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It started with a plume - early Archaean basaltic proto-continental crust

机译：它始于羽状流-早期的太古宙玄武质原大陆地壳

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摘要

The lower part of the Pilbara Supergroup records 300 million years of voluminous basaltic magmatism from ca. 3.515 to 3.24 Ga. The basalts are divided into two compositionally distinct but contemporaneous and interbedded types. Compared to low-Ti basalts, high-Ti basalts (TiO2>0.8 wt.%) have relatively high concentrations of HFSE and REE, are generally more Fe-rich, have very low Al2O3/TiO2 (18.7-8.9) and high Gd/Yb ratios (1.12-2.23). The composition of the high-Ti basalts, and their source, did not change significantly throughout the 300 m.y. period of basalt eruption. In contrast, low-Ti basalts show distinct secular trends to lower concentrations of incompatible trace elements and to lower ratios of La/Sm, La/Gd, La/Yb and Gd/Yb that reflect a source progressively more depleted than N-MORB source. Gd/Yb ratios in the younger low-Ti basalts are as low as 0.67, well below estimates for modem depleted mantle (0.98). These values reflect a strongly depleted Source, and possibly also a contribution from a low Gd/Yb source component representing the garnet-bearing residue of previous high-pressure melting events. The source for the low-Ti basalts comprised the accumulated residues of plumes that produced the earliest high-Ti basalts and Of Plumes that produced subsequent high-Ti basalts, and was periodically modified through melt extraction. It remained isolated from the convecting asthenosphere throughout the 300 m.y. period of basaltic magmatism, but parts of it remelted each time one of a series of plumes impinged on the lithospheric mantle. It progressively formed the thick, depleted, and buoyant sub-continental lithospheric mantle (SCLM) that is complimentary to the thick pile of interbedded high- and low-Ti basalt that comprises the bulk of the Pilbara Supergroup. These interpretations support models for Palaeoarchaean protocrust formation through extensive mantle Plume magmatic events, and models that suggest that the Archaean SCLM formed at the same time as early voluminous mafic magmatism. (c) 2005 Elsevier B.V All rights reserved.
机译：皮尔巴拉（Pilbara）超级集团的下部记录了约3亿年的大量玄武岩浆岩。 3.515至3.24 Ga。玄武岩分为两种成分不同但同时代和互层的类型。与低钛玄武岩相比，高钛玄武岩（TiO2> 0.8 wt。％）具有相对较高的HFSE和REE浓度，通常富含铁，具有非常低的Al2O3 / TiO2（18.7-8.9）和高的Gd / Yb比率（1.12-2.23）。在整个300 y y内，高钛玄武岩的组成及其来源均未发生明显变化。玄武岩喷发期。相反，低钛玄武岩显示出明显的长期趋势，即较低浓度的不相容痕量元素和较低的La / Sm，La / Gd，La / Yb和Gd / Yb比，反映出源比N-MORB源逐渐消耗。年轻的低钛玄武岩中的Gd / Yb比低至0.67，远低于现代贫化地幔的估计值（0.98）。这些值反映了强烈耗尽的来源，可能还反映了低Gd / Yb来源成分的贡献，该成分代表以前的高压熔融事件的石榴石残渣。低钛玄武岩的来源包括产生最早的高钛玄武岩的羽状残余物和随后生成高钛玄武岩的羽状残余物，并通过熔体萃取进行定期改性。在整个300 m的时间里，它一直与对流的软流圈保持隔离。玄武岩浆期，但是每次撞击到岩石圈地幔上的一系列羽流中的一个时，它的一部分都会重熔。它逐渐形成了厚的，枯竭的和浮力的亚大陆岩石圈地幔（SCLM），这与包括Pilbara超群大部分的层状高，低钛玄武岩互为补充。这些解释支持通过广泛的地幔柱羽状岩浆事件形成的古古宙原壳模型，并且这些模型表明古生界的SCLM与大量的早期铁镁质岩浆作用同时形成。 （c）2005 Elsevier B.V保留所有权利。

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