Reativation of Taxaquara Fault and its morphotectonic influence on the evolution of Jordão River catchment, Paraná, Brasil

ABSTRACT: The Paraná basin is one of the major morphotectures of the South American continent. Although its tectono-sedimentary evolution has been widely studied and fairly well understood, this paper aims to fill a gap in knowledge comprising the tectonic evolution after the end of its last sedimentary cycle, in the Upper Cretaceous. In this context, the Jordan River watershed, situated in the surroundings of Guarapuava municipality, south central region of Paraná State, was selected for structural and morphometric analysis where the Cretaceous volcanic rocks of Serra Geral Formation are exposed. The Jordan River watershed was studied for the influence exerted by Taxaquara Fault Zone on its morphologic evolution, since Taxaquara Fault Zone is associated to the Brazilian cycle and extends eastwards to the Ribeira belt in the state of São Paulo. The morphometric analysis consisted in the interpretation of the Jordan River watershed drainage network and relief elements, considering the distribution of existing knickpoints in the water courses. Structural analysis was based on the calculation of the stress fields responsible for the activation of local fault zones, which were determined by their spatial arrangement and the statistical and mechanical treatments of structural data. During the Oligocene and Miocene, erosional processes developed a planing surface which marks the relief in the central region of the Jordan River watershed and serves as a stratigraphic marker for the associated deformational events. Three events that contributed to the morphological framework of the Jordan River watershed were defined: an oldest one, probably active before the development of the Jordan pediplane in the Paleogene, by a NE-SW maximum horizontal stress (SHmax); and two more recent ones, being one of Plio-Pleistocene age, with a N05W SHmax, and a still active event of transtensive nature showing a N75W SHmax. The paleostress analysis points to a similarity between the Cenozoic evolution of Paraná Basin and the tafrogenic basins of southeast Brazil, revealing the amplitude of the deformation events associated to the studied period and ensuring the importance of further studies on the morphotectonic evolutions of intracratonic regions of the South American plate and their correlation to the Andean tectonic cycle.

摘要：巴拉那盆地（Paraná Basin）是南美大陆主要的地貌构造单元之一。尽管其构造-沉积演化已得到广泛研究且认知较为充分，但本文旨在填补其晚白垩世末次沉积旋回结束后构造演化相关的研究空白。在此背景下，本文选取位于巴拉那州中南部瓜拉普阿瓦市周边的约旦河流域作为研究对象，开展构造与形态计量分析，该区域出露有塞拉热拉尔组（Serra Geral Formation）的白垩纪火山岩。本次研究聚焦塔萨夸拉断裂带（Taxaquara Fault Zone）对约旦河流域地貌演化的影响，该断裂带与巴西构造旋回相关，向东延伸至圣保罗州的里贝拉造山带（Ribeira belt）。形态计量分析环节主要针对约旦河流域的水系网络与地貌单元展开解译，并结合河道内现存的裂点（knickpoint）分布特征开展研究。构造分析则基于对控制局部断裂带活化的应力场开展计算，其依据为断裂带的空间展布特征，以及对构造数据开展的统计与力学处理结果。在渐新世与中新世时期，侵蚀作用塑造了一级剥蚀面，该剥蚀面界定了约旦河流域中部的地貌形态，同时可作为关联变形事件的地层标记。本文明确了三类塑造约旦河流域地貌格局的构造事件：最古老的一期事件可能于古近纪约旦山麓剥蚀面形成前活动，其最大水平主应力（SHmax）方向为北东-南西向；另外两期为较新事件：其一为上新世-更新世时期，最大水平主应力方向为北05西向；还有一期仍处于活动状态，具有走滑拉张（transtensive）性质，最大水平主应力方向为北75西向。古应力分析结果表明，巴拉那盆地的新生代演化与巴西东南部的tafrogenic盆地具有相似性，这揭示了研究期内相关变形事件的影响范围，同时证实了针对南美板块克拉通内区域地貌构造演化及其与安第斯构造旋回相关性开展进一步研究的重要价值。