Graphite and carbonates in the 3.8 Ga old Isua Supracrustal Belt, southern West Greenland

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• 作者：van Zuilen ; Mark A. ; Lepland ; Aivo ; Teranes ; Jane ; Finarelli ; John ; Wahlen ; Martin ; Arrhenius ; Gustaf
• 关键词：Archean ; Isua ; Graphite ; Carbon isotope ratio ; Biomarker ; Metacarbonate
• 刊名：Precambrian Research
• 出版年：2003
• 出版时间：October 10, 2003
• 年：2003
• 卷：126
• 期：3-4
• 页码：331-348
• 全文大小：914 K

文摘

We present a systematic study of abundance, isotopic composition and petrographic associations of graphite in rocks from the ca. 3.8Ga Isua Supracrustal Belt (ISB) in southern West Greenland. Most of the graphite in the ISB occurs in carbonate-rich metasomatic rocks (metacarbonates) while sedimentary units, including banded iron formations (BIFs) and metacherts, have exceedingly low graphite concentrations. Regardless of isotopic composition of graphite in metacarbonate rocks, their secondary origin disqualifies them from providing evidence for traces of life stemming from 3.8Ga. Recognition of the secondary origin of Isua metacarbonates thus calls for reevaluation of earlier interpretations that suggested the occurrence of 3.8Ga biogenic graphite in these rocks. Thermal decomposition of siderite; 6FeCO₃