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首页> 外文期刊>Journal of the Geological Society >Detrital heavy minerals, white mica and zircon geochronology in the Ordovician South Mayo trough, western Ireland: Signatures of the Laurentian basement and the Grampian orogeny
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Detrital heavy minerals, white mica and zircon geochronology in the Ordovician South Mayo trough, western Ireland: Signatures of the Laurentian basement and the Grampian orogeny

机译：西爱尔兰奥陶纪南马约海槽中的碎屑重矿物，白云母和锆石年代学：劳伦式地下室和格兰屏造山运动的特征

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摘要

The Ordovician strata of the South Mayo Trough in western Ireland were deposited as a conformable sequence, first in the forearc of a north-facing oceanic arc, then in a synorogenic basin above the arc-continent collisional Grampian orogen, then in an extensional hanging-wall basin above the exhuming Dalradian metamorphic complex and, finally, in an Andean-type margin successor basin. This depositional history, and its relationship to the Grampian orogeny, to the pre- and post-collision arcs, and to sources in the Laurentian foreland, is recorded in detrital heavy mineral suites, Ar/Ar ages of detrital white micas, and U-Pb ages of detrital zircons. Heavy minerals record the progressive extensional unroofing of an obducted ophiolite complex, then the rapid extensional unroofing of the Grampian Dalradian metamorphic complex. White mica ages give Neoproterozoic, Mesoproterozoic, and Neoarchaean ages in the lower part of the sequence then, at about 466 Ma, synchronously with the appearance of amphibolite-facies metamorphic detritus, a tightly unimodal Grampian metamorphic age. Zircons yield mainly Mesoproterozoic and Neoarchaean ages, indicating a Laurentian source, and a Grampian age of 460-468 Ma. Paralleling the appearance of Grampianage micas, the colour of zircon changes from dominantly purple to dominantly colourless, reflecting the thermal annealing effect of metamorphism. However, the temperature of Grampian metamorphism was not high enough to reset the U-Pb isotopic systematics of detrital zircons.
机译：爱尔兰西部南马约海槽的奥陶纪地层以一致的顺序沉积，首先沉积在朝北的海洋弧的前臂中，然后沉积在弧大陆碰撞格伦比造山带之上的同生盆地中，然后沉积在伸展的悬空中。墙盆地位于发掘的达拉迪安变质综合体之上，最后位于安第斯型边缘继承盆地中。在碎屑重矿物组，碎屑白云母的Ar / Ar年龄，U-Ar年龄中记录了这种沉积历史及其与Grampian造山运动，碰撞前后弧以及Laurentian前陆来源的关系。碎屑锆石的Pb年龄。重矿物记录了被风化的蛇绿岩复合物的渐进伸展开顶，然后是格兰屏达拉迪安变质复合物的快速伸展开顶。白云母年龄在该序列的下部给出了新元古代，中元古代和新古生年龄，然后在约466 Ma时，与闪石相变质碎屑的出现同步，出现了紧密的单峰式Grampian变质时代。锆石主要产生中元古生代和新古生代时代，表明它是劳伦生源，而格兰屏年龄为460-468 Ma。平行于Grampianage云母的外观，锆石的颜色从主要为紫色变为主要为无色，反映了变质的热退火效应。然而，Grampian变质的温度还不足以重置碎屑锆石的U-Pb同位素系统。

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