Microtextures of titanite (CaTiSiO₅) in exceptionally preserved Archean pillow lavas have been proposed as the earliest examples of microbial ichnofossils. An origin from microbial tunneling of seafloor volcanic glass that is subsequently chloritized and the tunnels infilled by titanite has been argued to record the activities of subseafloor microbes. We investigate the evidence in pillow lavas of the 3.35 Ga Euro Basalt from the Pilbara Craton, Western Australia, to evaluate the biogenicity of the microtextures. We employ a combination of light microscopy and chlorite mineral chemical analysis by EPMA (electron probe micro‐analysis) to document the environment of formation and analyze their ultrastructure using FIB‐TEM (focussed ion beam combined with transmission electron microscopy) to investigate their mode of growth. Petrographic study of the original and re‐collected material identified an expanded range of titanite morphotypes along with early anatase growth forming chains and aggregates of coalesced crystallites in a sub‐greenschist facies assemblage. High‐sensitivity mapping of FIB lamellae cut across the microtextures confirm that they are discontinuous chains of coalesced crystallites that are highly variable in cross section and contain abundant chlorite inclusions, excluding an origin from the mineralization of previously hollow microtunnels. Comparison of chlorite mineral compositions to DSDP/IODP data reveals that the Euro Basalt chlorites are similar to recent seafloor chlorites. We advance an abiotic origin for the Euro Basalt microtextures formed by spontaneous nucleation and growth of titanite and/anatase during seafloor‐hydrothermal metamorphism. Our findings reveal that the Euro Basalt microtextures are not comparable to microbial ichnofossils from the recent oceanic crust, and we question the evidence for life in these Archean lavas. The metamorphic reactions that give rise to the growth of the Euro Basalt microtextures could be commonplace in Archean pillow lavas and need to be excluded when seeking traces of life in the subseafloor on the early Earth.

中文翻译：

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从西澳大利亚州的皮尔巴拉克拉顿（Pilbara Craton）解构地球上最古老的鱼类化石记录：对于在太古宙海底寻找生命的启示。

钛矿（CaTiSiO ₅）在保存完好的太古宙枕头熔岩中，有人提出将其作为微生物鱼龙化石的最早例子。有人认为，海底火山玻璃的微生物隧穿起源于随后的氯化作用，并在隧道中填充钛铁矿，从而记录了海底微生物的活动。我们调查了来自西澳大利亚州Pilbara Craton的3.35 Ga Euro玄武岩枕形熔岩中的证据，以评估微纹理的生物成因。我们结合使用光学显微镜和通过EPMA（电子探针显微分析）进行的亚氯酸盐矿物化学分析来记录形成环境，并使用FIB-TEM（聚焦离子束结合透射电子显微镜）分析其超微结构，以研究其模式。增长。对原始和重新收集的材料进行的岩相学研究确定了亚青绿岩相组合中钛铁矿形态类型的扩展范围，以及早期的锐钛矿生长形成链和聚结的晶体的聚集体。跨微结构切割的FIB薄片的高灵敏度图谱证实，它们是聚结的微晶的不连续链，这些微晶的横截面高度可变，并且包含丰富的亚氯酸盐包裹体，不包括先前空心微隧道矿化的起源。将亚氯酸盐矿物成分与DSDP / IODP数据进行比较后发现，欧洲玄武岩亚氯酸盐与最近的海底亚氯酸盐相似。我们推进了欧洲玄武岩微结构的非生物起源，该结构是由海底热液变质过程中钛酸盐和/或锐钛矿的自发成核和生长形成的。我们的发现表明，欧元玄武岩微结构与近期海洋壳中的微生物鱼鳞石不具有可比性，因此我们质疑这些太古代熔岩的生命证据。导致欧洲玄武岩微结构生长的变质反应在太古代的枕形熔岩中很常见，当寻找早期地球下海底生物的踪迹时，需要将其排除。