科研之友
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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.
- 出版日期2015-12
