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首页> 外文期刊>Geochemistry, geophysics, geosystems >Magmatic consequences of the transition from orthogonal to oblique subduction in Panama
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Magmatic consequences of the transition from orthogonal to oblique subduction in Panama

机译：巴拿马从正交俯冲过渡到倾斜俯冲的岩浆后果

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摘要

The closure of the Central American Seaway is linked with tectonic and magmatic processes that have controlled the evolution of the Isthmus of Panama. We focus on the terminal stages of arc activity in the Central Panama region, and present new geochemical data from approximate to 9 Ma explosive silicic volcanism preserved in three syngenetic tuff beds from the Gatun. The magmatic evolution of the Gatun Formation is controlled by a series of magma mushes where pyroxene is the dominant early forming mafic mineral, with amphibole appearing only relatively late in the fractionation sequence. Our data show Gatun lavas exhibit a strong subduction signature, consistent with plate reconstruction models showing arc-normal subduction from Costa Rica to Panama pre-8.5 Ma. However, large ion lithophile elements are depleted in the Gatun Formation in comparison to other regional suites, indicative of a lower flux of subduction fluid to the Gatun Formation mantle source, which is explained by a shift toward magma generation by decompression following the collision of the arc with South America. Oblique subduction commencing approximate to 8.5 Ma resulted in the shutdown of normal arc activity throughout Panama. We interpret subsequent regional Quaternary adakitic volcanism as a response to this oblique subduction. The now more refractory mantle wedge required greater fluid flux in order to melt. The resultant volatile-rich melts were more prone to deep fractionation of amphibole and garnet cumulates forming adakites. Deep fractionation was potentially enhanced by changing stress regimes on the upper plate caused by oblique subduction.
机译：中美洲航道的关闭与控制巴拿马地峡演变的构造和岩浆作用有关。我们着重研究巴拿马中部地区弧活动的末期，并提出了来自加图的三个同生凝灰岩层中保存的大约9 Ma爆炸性硅质火山岩的新地球化学数据。加通组的岩浆演化受一系列岩浆麝香的控制，其中辉石是主要的早期形成的镁铁质矿物，闪石在分馏序列中仅出现在相对较晚的时期。我们的数据表明，加敦熔岩表现出强烈的俯冲特征，与板块重建模型一致，该模型显示了从哥斯达黎加到8.5 Ma以前的巴拿马的弧线正常俯冲。然而，与其他区域组相比，Gatun组中的大型离子亲石元素被消耗掉了，这表明俯冲流体向Gatun组地幔源的通量降低，这可以解释为，随着碰撞的发生，岩浆通过减压向岩浆生成转变。弧与南美。从大约8.5 Ma的倾斜俯冲开始，导致整个巴拿马正常的弧活动关闭。我们将随后的第四纪第四纪火山活动解释为对这种倾斜俯冲的反应。现在更难熔的地幔楔需要更大的流体通量才能融化。所得的富含挥发物的熔体更易于对角闪石和石榴石堆积物进行深度分级，形成ad石。通过改变斜向俯冲作用而改变上板上的应力状态，有可能增强深层分离作用。

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