Abstract The ca. 3.47 Ga Duffer Formation has been considered to carry one of the oldest paleomagnetic records. Yet, the lack of rock magnetic data limits the interpretation of the nature of the remanence. We conducted a rock magnetic and paleomagnetic investigation on columnar dacite of the Duffer Formation. The main magnetic minerals are phenocrysts of titanomagnetite and magnetite, and secondary hematite in groundmass. Detailed thermal demagnetization revealed more complex natural remanence than previously estimated, consisting of four components with typical unblocking temperature of 200–350, 200–500, 590, and 690 °C. Combined with alternating field demagnetization and rock magnetic data, they are attributed to titanomagnetite, coarse-grained magnetite, fine-grained magnetite, and hematite, respectively. The comparison of unblocking temperature and coercivity suggests that the previously proposed secondary component is carried by fine-grained magnetite as well as hematite, while the putative primary component is carried by coarse-grained magnetite and titanomagnetite. Microscopic observations showed that coarse-grained magnetite and titanomagnetite are primary crystals, although this does not necessarily indicate they preserve primary remanence. The remanence directions of all components revealed higher scatter than the previous studies, suggesting the need for caution in interpretation. The low unblocking temperature of titanomagnetite suggests that if their remanence is truly primary, the rocks must have kept below ~ 250 °C for ~3.47 billion years.

中文翻译：

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鉴定约 1 年的古地磁剩磁载体。来自皮尔巴拉克拉通 Duffer 地层的 3.47 Ga 英安岩

摘要约。3.47 Ga Duffer 组被认为是最古老的古地磁记录之一。然而，缺乏岩石磁性数据限制了对剩磁性质的解释。我们对 Duffer 组的柱状英安岩进行了岩石磁性和古地磁研究。主要磁性矿物为钛磁铁矿和磁铁矿斑晶，基质中次生赤铁矿。详细的热退磁揭示了比之前估计的更复杂的自然剩磁，由四个组件组成，典型的解锁温度为 200-350、200-500、590 和 690 °C。结合交变场退磁和岩石磁性数据，它们分别属于钛磁铁矿、粗粒磁铁矿、细粒磁铁矿和赤铁矿。解锁温度和矫顽力的比较表明，先前提出的次要成分由细粒磁铁矿和赤铁矿携带，而推定的主要成分由粗粒磁铁矿和钛磁铁矿携带。显微观察表明粗粒磁铁矿和钛磁铁矿是初级晶体，尽管这并不一定表明它们保留了初级剩磁。所有组件的剩磁方向显示出比以前的研究更高的散射，表明需要谨慎解释。钛磁铁矿的低解阻温度表明，如果它们的剩磁确实是原生的，那么岩石必须在约 34.7 亿年的时间内保持在约 250 °C 以下。