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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 >Ar-39/Ar-40 dating of high-pressure rocks from the Ligurian Alps: Evidence for a continuous subduction-exhumation cycle
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Ar-39/Ar-40 dating of high-pressure rocks from the Ligurian Alps: Evidence for a continuous subduction-exhumation cycle

机译：利古里亚阿尔卑斯山高压岩石的Ar-39 / Ar-40年代：连续俯冲-掘出循环的证据

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摘要

We present Ar-39-Ar-40 dating of phengite, muscovite and paragonite from a set of mafic and metasedimentary rocks sampled from the high-pressure (HP) metaophiolites of the Voltri Group (Western Alps) and from clasts in the basal layer conglomerates from the Tertiary molasse which overlie the high-pressure basement. The white mica-bearing rocks display peak eclogitic and blueschist-facies parageneses, locally showing complex greenschist-facies replacement textures. The internal discordance of age spectra is proportional to the chemical complexity of the micas. High-Si phengites from eclogite clasts record a Ar-39-Ar-40 age of ca. 49 Ma for the eclogite stage and ca. 43 Ma for the blueschist retrogression; phengites from a blueschist basement sample yield an age of ca. 40 Ma; low-Si muscovite from a metasediment dates the formation of the greenschist paragenesis at ca. 33 Ma. Our data indicate that the analyzed samples reached high-pressure conditions at different times over a time-span of c.a. 10 Ma. Subduction was continuing during exhumation and blueschist retrograde re-equilibration of higher-pressure, eclogite-facies rocks. This process kept the isotherms depressed, allowing the older HP-rocks to escape thermal re-equilibration. Our results, added to literature data, fit a tectonic model of a subduction-exhumation cycle, with different tectonic slices subducted at different times from Early Eocene until the Eocene-Oligocene boundary. (C) 2005 Elsevier B.V. All rights reserved.
机译：我们从沃尔特里集团（西阿尔卑斯山）的高压（HP）亚闪闪石和基底层砾岩中的碎屑中取样的一组镁铁质和变质沉积岩，介绍了变质岩，白云母和方石的Ar-39-Ar-40定年来自位于高压地下室的第三纪糖蜜。含白云母的岩石显示出尖峰的片状和蓝片岩相共生，局部显示出复杂的绿片岩相置换纹理。年龄谱的内部不一致与云母的化学复杂性成正比。榴辉岩碎屑中的高Si锂镁铁矿记录的Ar-39-Ar-40年龄大约为。榴辉岩阶段为49 Ma，布鲁斯主义的倒退是43 Ma;来自blueschist地下室样品中的锂铁矿的年龄大约为1。 40毫安;沉积物中的低硅白云母可追溯到约格林河绿岩共生的形成。 33马。我们的数据表明，经过分析的样品在c.a的时间跨度内在不同的时间达到了高压条件。 10马在高压，榴辉岩相岩石的发掘和blueschist逆行重新平衡期间，俯冲作用一直在继续。此过程使等温线保持压低状态，从而使较旧的HP岩石逃脱了热重新平衡。我们的结果加到文献数据中，符合俯冲-发掘循环的构造模型，从始新世到始新世-渐新世边界，在不同的时间俯冲了不同的构造薄片。 （C）2005 Elsevier B.V.保留所有权利。

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