Low temperature magnetic properties of the Late Archean Boolgeeda iron formation (Hamersley Group, Western Australia): environmental implications

Frontiers in Digital Humanities

Thomazo, Christophe¹  Deldicque, Damien¹  Carlut, Julie³  Philippot, Pascal³  Isambert, Aude³  Buoncristiani, Jean-Franois³  Pecoits, Ernesto³  Bouquerel, Hlne³  Vennin, Emmanuelle⁴  Baton, Frank⁴  Ader, Magali⁶  Muller, Elodie⁶ 

[1] de Bourgogne, Dijon, France;Ecole Normale SupéInstitut de Physique du Globe de Paris, Universite Paris Diderot, Sorbonne Paris Cite, UMR 7154 Centre National de la Recherche Scientifique, Paris, France;UMR, Centre National de la Recherche Scientifique 6282 Biogéologie, UMR8538, Paris, France;osciences, Universitérieure - Gé

关键词: rock magnetism;    Verwey transition;    banded iron formation;    archean;    great oxidation event;    Hamersley Group;    Magnetite;   

DOI  :  10.3389/feart.2015.00018

学科分类：社会科学、人文和艺术（综合）

来源: Frontiers

【 摘 要 】

The origin of the iron oxides in Archean and Paleoproterozoic Banded Iron Formations is still a debated question. We report low and high temperature magnetic properties, susceptibility and saturation magnetization results joined with scanning microscope observations within a 35 meters section of the Late Archean Boolgeeda Iron Formation of the Hamersley Group, Western Australia. With the exception of two volcanoclastic intervals characterized by low susceptibility and magnetization, nearly pure magnetite is identified as the main magnetic carrier in all iron-rich layers including hematite-rich jasper beds. Two populations of magnetically distinct magnetites are reported from a 2 meter-thick interval within the section. Each population shows a specific Verwey transition temperature: one around 120-124 K and the other in the range of 105-110 K. This temperature difference is interpreted to reflect two distinct stoichiometry and likely two episodes of crystallization. The 120-124K transition is attributed to nearly pure stoichiometric magnetite, SEM and microprobe observations suggest that the lower temperature transition is related to chemically impure silician magnetite. Microbial-induced partial substitution of iron by silicon is suggested here. This is supported by an increase in Total Organic Carbon (TOC) in the same interval.

【 授权许可】

CC BY