Origin and pre-eruptive conditions of felsic volcanic rocks from the Pinturas River, Patagonia: representatives of the last volcanic episodes of the Jurassic Chon Aike SLIP

The Chon Aike Silicic Large Igneous Province (SLIP), formed during the Jurassic break-up of Gondwana, is one of Earth’s major silicic provinces. This study presents new whole-rock, mineral chemistry, and Nd isotopic data from phenorhyolitic to phenodacitic volcanic and pyroclastic rocks of the Chon Aike Formation in the Pinturas River area, western Deseado Massif, southern Argentina. These high-potassium, calc-alkaline, peraluminous ignimbrites and lavas contain oligoclase-andesine, sanidine, and magnetite-ulvöspinel, with pre-eruptive temperatures ranging from 760°C (magnetite-ulvöspinel) to ~950°C (feldspars), under high oxygen fugacity (−10 to −13). Estimated water contents (0.1–3%) are consistent with explosive volcanism. Isotopic data recalculated to 155 Ma indicate εNdi values between −2.26 and −0.03, pointing to a mixed crustal-mantle source with Mesoproterozoic (Grenvillian) derivation ages (TDM 0.98–1.16 Ga). When integrated with ~600 existing analyses from the Chon Aike SLIP, results support that geochemical differences are more spatial than temporal, shaped by tectonic setting and crustal architecture. While most domains exhibit strong crustal signatures, εNdi values near 0 in the Central domain suggest greater influence of metabasaltic components, consistent with petrogenetic models involving varying melting degrees and minor mantle input. These findings refine understanding of magmatic evolution in the Chon Aike SLIP. The Pinturas River rocks are calc-alkaline, peraluminous, high-potassium rhyolites.The Pinturas River rocks are derived from a mixed Mesoproterozoic crustal and mantle source.The rocks of the Pinturas River are moderately water-rich.Biotites have compositions similar to those of calc-alkaline to alkaline magmas.Younger rocks in the Chon Aike SLIP show fewer crustal traits than the older ones. The Pinturas River rocks are calc-alkaline, peraluminous, high-potassium rhyolites. The Pinturas River rocks are derived from a mixed Mesoproterozoic crustal and mantle source. The rocks of the Pinturas River are moderately water-rich. Biotites have compositions similar to those of calc-alkaline to alkaline magmas. Younger rocks in the Chon Aike SLIP show fewer crustal traits than the older ones.丘艾克硅质大火成岩省（Chon Aike Silicic Large Igneous Province，SLIP）形成于侏罗纪冈瓦纳大陆裂解时期，是地球主要的硅质大火成岩省之一。本研究报道了阿根廷南部德塞阿多地块西部品图拉斯河地区丘艾克组斑状流纹岩-斑状英安质火山岩及火山碎屑岩的全新全岩、矿物化学与Nd同位素数据。这套高钾、钙碱性、过铝质熔结凝灰岩与熔岩赋存更长石-中长石、透长石以及磁铁矿-钛铁尖晶石，喷发前温度介于760℃（磁铁矿-钛铁尖晶石测温）至约950℃（长石测温）之间，氧逸度处于-10至-13区间。估算得到的含水量（0.1%~3%）与爆发式火山作用特征相符。经155 Ma年龄校正的同位素数据显示，εNd(i)值介于-2.26至-0.03之间，指示其源区为混合地壳-幔源，且具有中元古代（格林威尔期）的亏损地幔模式年龄（TDM 0.98~1.16 Ga）。结合丘艾克硅质大火成岩省已有的约600组分析数据，研究结果支持该省的地球化学差异以空间差异为主而非时间差异，其受控于构造背景与地壳结构。尽管多数区域表现出显著的地壳源区特征，但中部区域εNd(i)值接近0，指示变玄武质组分的影响更强，这与涉及不同熔融程度与少量幔源贡献的岩石成因模型相一致。本研究结果深化了对丘艾克硅质大火成岩省岩浆演化过程的认知。品图拉斯河地区的岩石属于钙碱性、过铝质高钾流纹岩，其源区为混合的中元古代地壳与幔源物质，含水量中等，黑云母的成分与钙碱性至碱性岩浆中的黑云母相似；丘艾克硅质大火成岩省中较年轻的岩石相较于古老岩石，其地壳源区特征更弱。