Biogenic Carbon in Magmatic Minerals and Implications for the Preservation and Obliteration of Hadean Isotopic Biosignatures

当地球成为宜居行星时，早期地质材料的保存是不稳定的。自冥古宙以来，只有罕见的碎屑锆石晶体逃脱了湮没。这些晶体还含有丰富的包裹体，这证明了它们的形成条件。冥古宙锆石中石墨包裹体的轻碳同位素组成已被解释为表明陆地生命的早期出现。我们的目标是在这一发现的基础上，通过研究冥古宙后花岗岩矿物中的石墨包裹体(1)设计有助于识别包裹体后圈闭扰动的标准；(2)限制火成岩中的石墨与生物碳质物质的关系，以及这些物质如何对岩浆碳预算做出贡献。本研究将首次利用相关显微分析成像和高空间分辨率质谱技术来解决岩浆岩中石墨的来源，特别是作为包裹体的石墨。从北美东北部和中欧的两个s型花岗岩位置获得的见解将改善对锆石中冥古宙石墨包裹体的解释。我们计划开发的方法将在一个国际研究联盟的合作中实施，该联盟目前已经成功地确定了世界上数量最多的冥古宙锆石晶体，以寻找来自冥古宙的额外碳质包裹体。

The preservation of geologic materials from the early period when Earth became a habitable planet is precarious. Only rare examples of detrital zircon crystals have escaped obliteration since the Hadean eon. These crystals also host a rich inclusion assembly which attests to their formation conditions. The presence of light carbon isotopic compositions of graphite inclusions in Hadean zircon has been interpreted to indicate an early emergence of terrestrial life. We aim to follow up on this discovery by investigating graphite inclusions in minerals from post-Hadean granites by (1) devising criteria which can aid in identifying post entrapment disturbance of inclusions, and (2) constraining how graphite in igneous rocks relates to biogenic carbonaceous materials, and how these materials contribute to magmatic carbon budgets. The proposed research will, for the first time, use correlated micro-analytical imaging and high spatial resolution mass-spectrometry techniques to resolve the origins of graphite in magmatic rocks, especially as inclusions. Insights gained from two S-type granite locations in northeastern North America and Central Europe will improve the interpretation of Hadean graphite inclusions in zircon. The methodologies we plan to develop will be implemented in a collaborative search for additional carbonaceous inclusions from the Hadean by an international research consortium, which currently has succeeded in identifying the largest number of Hadean zircon crystals worldwide.