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首页> 外文期刊>Contributions to Mineralogy and Petrology >An 40Ar–39Ar investigation of high-pressure metamorphism and the retrogressive history of mafic eclogites from the Lanterman Range (Antarctica): evidence against a simple temperature control on argon transport in amphibole
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An 40Ar–39Ar investigation of high-pressure metamorphism and the retrogressive history of mafic eclogites from the Lanterman Range (Antarctica): evidence against a simple temperature control on argon transport in amphibole

机译：40 Ar–39 Ar研究高压变质作用和兰特曼山脉（南极洲）的镁铁质榴辉岩的倒退历史：反对简单控制温度来控制闪石中氩气的证据

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摘要

Mafic eclogites sampled from a restricted area in the Lanterman Range (Antarctica) retrogressed variably under amphibolite facies metamorphism. Assemblages range from well-preserved eclogite, with minor growth of Na–Ca amphibole, to strongly retrogressed ones with extensive development of Ca amphibole. 40Ar–39Ar furnace step-heating experiments on the different amphiboles yield results varying from plateau ages of ~498 Ma to a near-plateau age of ~490 Ma, and the greater the amphibolite retrogression, the younger the age. 40Ar–39Ar infrared laser-probe analyses on rock chips from a well-preserved eclogite and a slightly retrogressed one reveal the presence of an excess argon component. Whereas excess argon is invariably present in garnet and clinopyroxene developed under high-pressure metamorphism, it is heterogeneously distributed in amphibole on a millimetre scale. Results indicate that excess argon was incorporated during high-pressure metamorphism; this component was then lost during retrogression, while a change in composition of ambient argon to atmospheric argon occurred. New 40Ar–39Ar data and previously published Sm–Nd garnet and U–Pb rutile ages obtained from the same well-preserved eclogite sample suggest that the oldest Na–Ca amphibole age is reliable and not an artefact due to the incorporation of excess argon. The variably retrogressed eclogites are thought to derive from different parts of the enclosing metasedimentary rocks that were variably invaded by fluids during amphibolite facies metamorphism. Thus the circulation of fluids promoting (re)crystallisation, and not temperature, was the main process controlling the rate of argon transport in the studied eclogites. The different 40Ar–39Ar ages are interpreted to record diachronous amphibole growth at different crustal levels during exhumation. Data indicate that there was about a 10-Ma interval between the eclogite facies stage (at ≥1.5 GPa) and the Ca amphibole-hydration forming reaction (at 0.3–0.5 GPa); this translates into an average exhumation rate of 3–4 km/Ma.
机译：在角闪石相变质作用下，从Lanterman山脉（南极洲）有限区域取样的镁铁质榴辉岩呈不同程度的倒退。组合物范围从保存完好的榴辉岩（Na-Ca闪石的少量生长）到强烈逆向的钙闪石的广泛发展。 40 Ar–39 Ar炉在不同闪石上的分步加热实验结果，其结果从高原年龄约498 Ma到近高原年龄约490 Ma不等，而角闪石的回退越大，年龄越小。对保存完好的榴辉岩和稍有倒塌的岩屑进行的40 Ar–39 Ar红外激光探针分析表明，存在过量的氩气成分。石榴石和在高压变质作用下生成的亚基吡咯烷总是存在过量的氩，而在角闪石中则以毫米为单位异质分布。结果表明，高压变质过程中引入了过量的氩。然后该成分在回归过程中丢失，同时发生了环境氩气向大气氩气成分的变化。从相同的保存完好的榴辉岩样品中获得的新的40 Ar–39 Ar数据以及先前发表的Sm–Nd石榴石和U–Pb金红石年龄表明，最古老的Na–Ca闪石年龄是可靠的，而不是由于掺入了过量的氩而造成的伪影。人们认为变质的榴辉岩是来自围岩的沉积物的不同部分，而这些沉积物在闪石相变质过程中受到流体的侵入。因此，促进（重新）结晶而不是温度的流体循环是控制榴辉岩中氩气传输速率的主要过程。解释了不同的40 Ar–39 Ar年龄记录了在掘尸期间不同地壳水平上的闪石闪时生长。数据表明，榴辉岩相阶段（≥1.5GPa）与闪石钙水合形成反应（0.3-0.5 GPa）之间存在约10-Ma的间隔；这意味着平均出土率为3–4 km / Ma。

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  • 来源
    《Contributions to Mineralogy and Petrology》 |2001年第1期|15-35|共21页
  • 作者

    Gianfranco Di Vincenzo; Rosaria Palmeri;

  • 作者单位

    Istituto di Geocronologia e Geochimica Isotopica – CNR Area della Ricerca via Alfieri 1 Ghezzano 56010 Pisa Italy;

    Museo Nazionale dell'Antartide – Sezione di Scienze della Terra Università di Siena via Laterina 8 53100 Siena Italy;

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