Geochemistry and geochronology of the Rathjen Gneiss: Implications for the early tectonic evolution of the Delamerian Orogen
Geochemistry and geochronology of the Rathjen Gneiss: Implications for the early tectonic evolution of the Delamerian Orogen
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DOI：
10.1046/j.1440-0952.1999.00712.x
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发表时间：
1999-06
影响因子：
1.2
通讯作者：
J. Foden;M. Sandiford;J. Dougherty-Page;I. Williams
中科院分区：
文献类型：
--
作者：
J. Foden;M. Sandiford;J. Dougherty-Page;I. Williams
拉特金片麻岩是阿德莱德褶皱冲断带南部最古老、结构最复杂的花岗质侵入岩，因此对德拉梅造山带的形成时间提供了重要的限制。Rathjen片麻岩中的锆石显示出复杂的生长历史，反映了继承、岩浆结晶和变质作用。这两个单一的锆石蒸发（“Kober”技术）和SHRIMP分析产量最好的估计514 - 6 - 5 Ma的火成岩结晶，大大超过其他已知的长英质侵入年龄在南部阿德莱德褶皱冲断带。这个年龄对德拉姆变质作用的开始有一个较早的限制，并且与已知的地层限制相一致，这表明早寒武世Kanmantoo群在不到2000万年的时间内沉积，埋藏和加热。在随后的变质作用中形成了锆石上的高U增生，并获得了503 - 6 - 7 Ma的206 Pb/238 U年龄。德拉梅利亚造山运动持续不超过3500万年。Rathjen片麻岩的侵位作为一个前或早期同构造花岗岩强调其地球化学特征，这表明与板内或非造山花岗岩的联系。相比之下，年轻的同构造花岗岩在南部阿德莱德褶皱冲断带的地球化学特征更典型的花岗岩在会聚造山带。早奥陶世后构造花岗岩标志着非造山成分的回归。花岗岩化学对构造过程变化的敏感性是显著的，并清楚地反映了壳幔源贡献的变化。
The Rathjen Gneiss is the oldest and structurally most complex of the granitic intrusives in the southern Adelaide Fold-Thrust Belt and therefore provides an important constraint on the timing of the Delamerian Orogen. Zircons in the Rathjen Gneiss show a complex growth history, reflecting inheritance, magmatic crystallisation and metamorphism. Both single zircon evaporation (‘Kober’ technique) and SHRIMP analysis yield best estimates of igneous crystallisation of 514 6 5 Ma, substantially older than other known felsic intrusive ages in the southern Adelaide Fold-Thrust Belt. This age places an older limit on the start of the Delamerian metamorphism and is compatible with known stratigraphic constraints suggesting the Early Cambrian Kanmantoo Group was deposited, buried and heated in less than 20 million years. High-U overgrowths on zircons were formed during subsequent metamorphism and yield a 206Pb/238U age of 503 6 7 Ma. The Delamerian Orogeny lasted no more than 35 million years. The emplacement of the Rathjen Gneiss as a pre- or early syntectonic granite is emphasised by its geochemical characteristics, which show affiliations with within-plate or anorogenic granites. In contrast, younger syntectonic granites in the southern Adelaide Fold-Thrust Belt have geochemical characteristics more typical of granites in convergent orogens. The Early Ordovician post-tectonic granites then mark a return to anorogenic compositions. The sensitivity of granite chemistry to changes in tectonic processes is remarkable and clearly reflects changes in the contribution of crust and mantle sources.