The rhyolitic lava is the Asana Formation asociated with the PCD Quellaveco at southern Peru
Negative Eu ao0malies in evolved rocks are generally a consequence of the fractionation of feldspar, the retention of feldspar in a residuum after partial melting, or both.
Thanks for your answer. Agree with that. The case is that this rocks are assumed like related with mineralization and, fertile rocks, for example adakitic-like rocks, must have weak or no negative Eu anomaly because they are hydrated
Please see whether the rhyolite is associated with relatively more basic rocks like dacite or andesite containing more plagioclase into which much of Eu entered, leaving much less in rhyolite. R. Dhana Raju
The rhyolite is over a welded tuff denominated Paralaque Formation, composed by quartz and plagioclase,with 56% SiO2. But my question is in the way to how to correlate rocks with strong negative Eu anomaly with a fertile rock, because for example adakitic-like rocks, must have weak or no negative Eu anomaly because they are hydrated
The reason it is thought that that rocks termed "adakitic" have no Eu anomaly is because they form at high pressure where plagioclase is not stable. Garnet is typically stable in the zone of melting/differentiation instead and this can sometime be sen in the as HREE depletion. It doesn't really have anything to do with hydration. Plagioclase crystallizaton may also be supressed in water-rich melts, but these are usually strongly peraluminous, dacitic/tonalitic, and quite rare
The REE patterns for this formation suggests fraccionation of amphibole and this formation is related with the porphyry copper deposit Quellaveco but also have the strong negative Eu anomaly. Basically that is my interrogant, if in some way the Eu anomaly can fit with fraccionation of amphibole, because I had read that an hydrous system supress plagioclase crystallization as you say and I can't undestand how can be strong negative Eu anomaly in an hydrous system like this.This magmatism is meta aluminous and calcalkaline of subduction, in southern Peru, related with many PCD like Cuajone, Quellaveco, Toquepala.
I have a similar problem concerning negative Eu, however, not in ryolite but in a more complicated rock. This is still in progress, but here are my thoughts. I have a sericitized and mylonitized ocean floor melange. The REE diagrams show beautiful basalt.type spiders, however, with marked negative Eu. I think that the sericitized plagioclases caused the loss of Eu, which may have otherwise been positive. Can your problem have to do with secondary removal of Eu?
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