Abstract Argon geochronology of white mica has a good potential of recording recurrent dynamic recrystallization in shear zones in the transition from ductile to brittle deformation, as temperature ranges for mineral crystallization and isotopic closure of different grain-size fractions overlap between ca. 275–425 °C. This study presents over 40 K-Ar ages of coarse-grained muscovite and multiple clay-sized white mica fractions extracted from mylonites and fault gouges in southernmost Brazil, complemented by detailed structural and XRD characterization. The widespread obtained ages are best explained in the context of recurrent deformation under retrograde conditions during progressive strain localization and transition from low-grade ductile deformation into brittle faulting. The onset of the Ibare Shear Zone is constrained in the Tonian, followed by reactivation during the Ediacaran evolution of the adjacent Dom Feliciano Belt, which records a remarkable long-term history of recurrent deformation for over 100 Myr. New data extends the geochronological constraints of the Dorsal do Cangucu Shear Zone into low-temperature conditions, estimating the onset of brittle activity at 525-470 Ma by dating early fault gouges formed shortly after final syn-kinematic white mica crystallization in the hosting mylonites. Dating of recurrent faulting events during the Paleo-Mesozoic complement the regional sedimentary and thermochronological record.

中文翻译：

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确定反复剪切带活动的年代和从韧性变形到脆性变形的转变：应用于巴西南部新元古代 Dom Feliciano 带的白云母年代学

摘要 白云母的氩年代学具有记录从韧性变形到脆性变形转变过程中剪切带中循环动态再结晶的良好潜力，因为矿物结晶和不同粒度级分的同位素闭合的温度范围在约 275–425 °C。这项研究展示了从巴西最南端的糜棱岩和断层泥中提取的粗粒白云母和多种粘土大小的白色云母碎片的 40 多个 K-Ar 年龄，并辅以详细的结构和 XRD 表征。在渐进应变局部化和从低等级韧性变形到脆性断层的转变过程中，在逆行条件下的反复变形的背景下，可以最好地解释广泛获得的年龄。Ibare 剪切带的开始被限制在 Tonian，随后在相邻的 Dom Feliciano 带的埃迪卡拉纪演化期间重新激活，该带记录了超过 100 Myr 的反复变形的显着长期历史。新数据将 Dorsal do Cangucu 剪切带的地质年代学限制扩展到低温条件，通过对在承载糜棱岩中最终同运动白色云母结晶后不久形成的早期断层泥进行年代测定，估计脆性活动在 525-470 Ma 开始。古中生代周期性断层事件的测年补充了区域沉积和热年代学记录。新数据将 Dorsal do Cangucu 剪切带的地质年代学限制扩展到低温条件，通过对在承载糜棱岩中最终同运动白色云母结晶后不久形成的早期断层泥进行年代测定，估计脆性活动在 525-470 Ma 开始。古中生代周期性断层事件的测年补充了区域沉积和热年代学记录。新数据将 Dorsal do Cangucu 剪切带的地质年代学限制扩展到低温条件，通过对在承载糜棱岩中最终同运动白色云母结晶后不久形成的早期断层泥进行年代测定，估计脆性活动在 525-470 Ma 开始。古中生代周期性断层事件的测年补充了区域沉积和热年代学记录。