Abstract The sedimentology, petrography, and U–Pb dating of two Eocene volcaniclastic horizons of the Punta Torcida and Leticia formations, Austral basin, Tierra del Fuego, Argentina are interpreted and documented. The volcaniclastic deposits, pumicite breccia and tuffaceous sandstones, are formed by glass shards, plagioclase crystals, and pumiceous and lithic andesitic fragments. Originally deposited as tephra fallout, they have been subsequently reworked and redeposited in marine settings. The final deposits, however, are interpreted essentially as syn-eruptive. U–Pb dating of detrital zircons gave a 46.3 ± 0.4 Ma (early Lutetian) age for the top of the Punta Torcida Formation and 41.9 ± 0.71 (late Lutetian) to 39.6 ± 0.82 (Bartonian) ages for the Leticia Formation. Paleogene volcanic rocks are unknown in the Southern Patagonian-Fuegian Andes; hence the studied volcanic deposits with minimal reworking are important to evaluate the time lag between eruption and true depositional ages in detrital zircons. The resulting dates allow evaluating the timing of the important, basin-wide, intra-Eocene unconformity known from Tierra del Fuego to Lago Argentino, Santa Cruz, Argentina. The documented eruptive phases are related to Andean magmatism, probably located in the outcrop area of the Seno Ano Nuevo suite in the Chilean Archipelago.

中文翻译：

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Fuegian Andes 始新世火山活动：来自海相火山碎屑砂岩中的岩石学和碎屑锆石的证据

摘要 解释和记录了阿根廷火地岛南部盆地 Punta Torcida 和 Leticia 地层的两个始新世火山碎屑层的沉积学、岩石学和 U-Pb 测年。火山碎屑沉积物、火山碎屑角砾岩和凝灰质砂岩由玻璃碎片、斜长石晶体以及浮石和岩屑安山岩碎片形成。它们最初作为火山灰沉积物沉积，随后被重新加工并重新沉积在海洋环境中。然而，最终的沉积物基本上被解释为协同喷发。碎屑锆石的 U-Pb 定年给出了 Punta Torcida 组顶部的 46.3 ± 0.4 Ma（早期 Lutetian）年龄和 Leticia 组顶部的 41.9 ± 0.71（晚期 Lutetian）至 39.6 ± 0.82（Bartonian）年龄。南巴塔哥尼亚-菲吉安安第斯山脉的古近系火山岩是未知的；因此，所研究的火山沉积物经过最少的改造对于评估碎屑锆石中喷发和真实沉积年龄之间的时间滞后很重要。由此产生的日期可以评估从火地岛到阿根廷圣克鲁斯的阿根廷湖的重要的、盆地范围内的始新世内不整合的时间。记录的喷发阶段与安第斯岩浆活动有关，可能位于智利群岛 Seno Ano Nuevo 套房的露头区域。