The Huayra Huasi Volcanic Complex of Miocene age (11.88 ± 0.15 Ma U–Pb zircon) was emplaced in the Northern Puna plateau of Argentina, spatially associated with ignimbrites erupted from Altiplano–Puna Volcanic Complex calderas. The complex comprises biotite-bearing dacites and low-SiO₂ rhyolites in the northern area and high-SiO₂ rhyolites in the south, all with peraluminous compositions (A/CNK > 1.0–1.22). The units have broadly similar initial Sr and Nd isotopic ratios (⁸⁷Sr/⁸⁶Sr ∼ 0.71013–0.71225 and εNd ∼ −5.4 to −7.0) and are composed of plagioclase, quartz, sanidine and biotite as the main phenocryst phases. All units host macroscopic microgranular enclaves and xenoliths of sillimanite–biotite schists, sillimanite- and sillimanite–garnet gneisses, as well as fibrous alumina-rich microxenoliths, the latter being especially abundant in the southern rhyolites. Petrographic, mineral and whole-rock geochemistry, geothermometric and isotopic data indicate that all units of the complex originated by contamination of andesite magmas through assimilation of upper crustal lithologies in early stages of magma evolution. The fibrous alumina-rich microxenoliths are composed almost entirely of refractory minerals (sill + Kfsp ± Pl ± Bt) and interpreted as peritectic or restitic products of partial melting of assimilated metasedimentary rocks similar to the unmodified metamorphic xenoliths in the complex. Geochemical modeling indicates that, after early-stage contamination, each magmatic unit evolved separately. Whereas the northern dacites and low-SiO₂ rhyolites underwent assimilation and fractional crystallization throughout their history, the southern rhyolites mainly evolved via fractional crystallization of felsic phases alone. This study shows that the peraluminous nature of felsic magmas do not necessarily originate by partial melting of crustal material but can be acquired by metaluminous magmas during later evolution. The processes shown here of assimilation and fractional crystallization and pure fractional crystallization has relevance for other igneous bodies of similar compositions in the Puna backarc and worldwide.

中新世 Huayra Huasi 火山杂岩（11.88 ± 0.15 Ma U-Pb 锆石）位于阿根廷北部普纳高原，在空间上与从 Altiplano-Puna 火山杂岩火山口喷发的火山熔岩有关。该复合体由北部含黑云母英安岩和低SiO ₂流纹岩和南部高SiO ₂流纹岩组成，均具有过铝质成分（A/CNK > 1.0-1.22）。这些单元具有大致相似的初始 Sr 和 Nd 同位素比率 ( ⁸⁷ Sr/ ⁸⁶Sr ∼ 0.71013–0.71225 和 εNd ∼ -5.4 到 -7.0)，由斜长石、石英、闪长石和黑云母作为主要斑晶相组成。所有单元都含有宏观微粒飞地和硅线石-黑云母片岩、硅线石-和硅线石-石榴石片麻岩以及富含纤维的氧化铝微捕虏体，后者在南部流纹岩中尤为丰富。岩石学、矿物和全岩地球化学、地热测量和同位素数据表明，该复合体的所有单元都起源于岩浆演化早期上地壳岩性同化作用对安山岩浆的污染。纤维状富含氧化铝的微捕虏体几乎完全由难熔矿物组成（基石 + Kfsp ± Pl ± Bt），被解释为同化变质沉积岩部分熔融的包晶或残质产物，类似于复合物中未改性的变质捕虏体。地球化学模型表明，在早期污染之后，每个岩浆单元分别演化。而北方英安岩和低 SiO₂流纹岩在其历史上经历了同化和分步结晶，南方流纹岩主要通过长英质相分步结晶演化。本研究表明，长英质岩浆的过铝质性质不一定来源于地壳物质的部分熔融，而是可以在后期演化过程中为金属铝质岩浆所获得。这里显示的同化和分步结晶以及纯分步结晶的过程与普纳弧后和世界范围内其他类似成分的火成岩体有关。