The tectonic significance of the Cabo Frio Tectonic Domain in the SE Brazilian margin: a Paleoproterozoic through Cretaceous saga of a reworked continental margin

ABSTRACT: The Cabo Frio Tectonic Domain is composed of a Paleoproterozoic basement tectonically interleaved with Neoproterozoic supracrustal rocks (Buzios-Palmital successions). It is in contact with the Neoproterozoic-Cambrian Ribeira Orogen along the SE Brazilian coast. The basement was part of at least three continental margins: (a) 1.97 Ga; (b) 0.59 - 0.53 Ga; (c) 0.14 Ga to today. It consists of continental magmatic arc rocks of 1.99 to 1.94 Ga. Zircon cores show a 2.5 - 2.6 Ga inheritance from the ancient margin of the Congo Craton. During the Ediacaran, this domain was thinned and intruded by tholeiitic mafic dykes during the development of an oceanic basin at ca. 0.59 Ma. After the tectonic inversion, these basin deposits reached high P-T metamorphic conditions, by subduction of the oceanic lithosphere, and were later exhumed as nappes over the basement. The Cabo Frio Tectonic Domain collided with the arc domain of the Ribeira Orogen at ca. 0.54 Ga. It is not an exotic block, but the eastern transition between this orogen and the Congo Craton. Almost 400 m.y. later, the South Atlantic rift zone followed roughly this suture, not coincidently. It shows how the Cabo Frio Tectonic Domain was reactivated as a continental margin in successive extensional and convergent events through geological time.

摘要：卡布弗里乌构造域（Cabo Frio Tectonic Domain）由与新元古代表壳岩（Neoproterozoic supracrustal rocks）构造叠置的古元古代基底（Paleoproterozoic basement）组成，沿巴西东南海岸与新元古代-寒武纪里贝拉造山带（Neoproterozoic-Cambrian Ribeira Orogen）接触。该基底至少曾隶属于三个大陆边缘：(a) 19.7亿年；(b) 5.9亿~5.3亿年；(c) 1.4亿年至今。其岩性主体为19.9亿~19.4亿年的大陆岩浆弧岩石（continental magmatic arc rocks）。锆石核（Zircon cores）显示其继承了刚果克拉通（Congo Craton）古陆缘25亿~26亿年的地壳物质。埃迪卡拉纪（Ediacaran）时期，该构造域发生拉伸减薄，并在约0.59百万年的洋盆发育过程中被拉斑玄武质镁铁质岩脉（tholeiitic mafic dykes）侵入。构造反转之后，这些洋盆沉积因大洋岩石圈（oceanic lithosphere）俯冲作用达到高压力-温度变质条件（high P-T metamorphic conditions），随后以推覆体的形式被抬升剥露于基底之上。卡布弗里乌构造域于约5.4亿年与里贝拉造山带的弧域发生碰撞。它并非外来地体，而是该造山带与刚果克拉通之间的东部过渡带。近4亿年后，南大西洋裂谷带（South Atlantic rift zone）大致沿该缝合带展布，这并非巧合。该构造域展示了其在地质历史中如何在多期伸展与汇聚事件中被反复活化，成为大陆边缘的完整过程。