U-series disequilibria in Guatemalan lavas, crustal contamination, and implications for magma genesis along the Central American subduction zone

作者：Walker James A^*; Mickelson J Erik; Thomas Rebecca B; Patino Lina C; Cameron Barry; Carr Michael J; Feigenson Mark D; Edwards R Lawrence

来源：Journal of Geophysical Research, 2007, 112(B6): B06205.

DOI：10.1029/2006JB004589

New U-series results indicate that Guatemalan volcanic rocks display both U-238 and Th-230 excesses. Th-230 excess is restricted to volcanoes in central Guatemala, both along and behind the front. Th-230 excess correlates with a number of incompatible element ratios, such as Th/Nb and Ba/Th. It also shows a negative correlation with MgO. Guatemalan volcanic rocks have (Th-230/Th-232) ratios that overlap those of Costa Rican volcanics and are therefore considerably lower than the unusually high ratios characterizing volcanic rocks from Nicaragua. Along-arc variations in (Th-230/Th-232) therefore mirror those of a number of diagnostic geochemical parameters, such as Ba/La, which are symmetrical about a peak in west central Nicaragua. The one siliceous lava analyzed, from the Cerro Quemado dome complex, has a recognizable crustal imprint, distinguished, for instance, by high Th/Nb and low Ba/Th. In mafic samples, U-238 excess is attributed to addition of a U-enriched fluid component from the subducting Cocos plate. Our preferred explanation for Th-230 excess in Guatemalan mafic samples, on the other hand, is crustal contamination, consistent with the relatively high Th/Nb and low Ba/Th ratios in these samples. We suspect, however, that crustal contamination only exerts a sizable control over the U-series disequilibrium of mafic magmas in Guatemala, and not elsewhere along the Central American volcanic front. This agrees with previously published trace element and isotopic evidence that throughout Central America, with the exception of Guatemala, mafic magmas are largely uncontaminated by crustal material.

• 出版日期2007-6-19
• 单位国家自然科学基金委员会