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Towards an integrated tectonic model for the interaction between the Bambuí basin and the adjoining orogenic belts: Evidences from the detrital zircon record of syn-orogenic units
Journal of South American Earth Sciences ( IF 1.8 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.jsames.2020.102831
Matheus Kuchenbecker , Antônio Carlos Pedrosa-Soares , Marly Babinski , Humberto Luís Siqueira Reis , Dora Atman , Ricardo Diniz da Costa

Abstract The Sao Francisco craton and its surrounding orogens are some of the most important tectonic elements of South America, and key regions to understanding the assembly of Western Gondwana in the Proterozoic-Palaeozoic transition. During this major tectonic event, diachronic collisions between small continents developed an intricated orogenic system, where several orogens evolved in unique paths through time and space. In such collisional settings, there are some tectonic processes that promote subsidence, thus controlling the formation of orogenic-related sedimentary basins. Furthermore, the tectonic activity in collisional orogens generates dynamic landscapes that usually favor increased erosion and sediment generation to feed these basins, making them key places to seek for clues about the tectonic evolution of their surroundings. On the Sao Francisco craton, the Bambui Group records a complex foreland system, which evolved in response to the lithospheric overload exerted by the uplift of both Brasilia belt and Aracuai orogen. In turn, both Salinas Formation and Ibia Group comprise orogenic deposits resting within the Aracuai orogen and Brasilia belt, respectively, whose tectonic significance is still under debate. Here we present new U–Pb (LA-ICP-MS and SHRIMP) and Lu–Hf isotopic analyses on a great amount of detrital zircon grains extracted from the rocks of the Bambui Group and Salinas Formation, together with a thorough data compilation from the literature. The two units present similar provenance patterns, sharing the major detrital zircon age peaks (550–650 Ma, 950–1050 Ma, 1750–2000 Ma, 2600–2800 Ma) and maximum depositional age in c. 550 Ma. The Ediacaran zircons recovered from the Bambui Group show a wide range of the eHf(t), ranging from c. −17 to +15, which suggest the existence of multiple late Neoproterozoic sources, some of them juvenile and some with a long crustal residence. The variation in detrital zircon age patterns and eHf(t) values from different units within the Bambui Group provided additional clues of provenance changes occurred during the evolution of the basin. The new data obtained for the Salinas Formation constrain its deposition between 548 and 500 Ma, which have an important implication on its tectonic significance. We propose that in both Brasilia belt and Aracuai orogen sides, the early foredeep deposits of the Bambui basin should have been incorporated to the orogenic domains, which could explain the apparent lack of deposits recording the climax of the Brasilia belt uplift (c. 630 Ma) within the cratonic area. In this same direction, we consider that both Salinas Formation and Ibia Group could represent remnants of these early foreland deposits related to the uplift of Brasilia belt and Aracuai orogen, respectively, incorporated to the orogenic wedges due to the advance of the deformational fronts. Therefore, what we know as Bambui Group is in fact the remaining record of an advanced stage of the foreland system, when subsidence was already influenced by the two evolving orogens. Altogether, the analyses of the stratigraphic, structural and geochronological data converge towards an integrated tectonic model for the interaction between the Bambui basin and the surrounding orogens during West Gondwana amalgamation.

中文翻译:

Bambuí 盆地与相邻造山带相互作用的综合构造模型:来自同造山单元碎屑锆石记录的证据

摘要 圣弗朗西斯科克拉通及其周围的造山带是南美洲最重要的构造要素,是了解元古界-古生代过渡时期西冈瓦纳大陆集合的关键区域。在这一重大构造事件中,小大陆之间的历时碰撞形成了一个错综复杂的造山系统,其中几个造山带以独特的时空路径演化。在这种碰撞环境中,有一些构造过程促进了沉降,从而控制了与造山带相关的沉积盆地的形成。此外,碰撞造山带中的构造活动产生了动态景观,通常有利于增加侵蚀和沉积物的生成,为这些盆地提供食物,使它们成为寻找周围环境构造演化线索的关键场所。在圣弗朗西斯科克拉通上,Bambui 群记录了一个复杂的前陆系统,该系统是为了响应巴西利亚带和 Aracuai 造山带隆升所施加的岩石圈超载而演化的。反过来,Salinas 组和 Ibia 组分别包含位于 Aracuai 造山带和巴西利亚带内的造山沉积物,其构造意义仍在争论中。在这里,我们对从 Bambui 组和 Salinas 组的岩石中提取的大量碎屑锆石颗粒进行了新的 U-Pb(LA-ICP-MS 和 SHRIMP)和 Lu-Hf 同位素分析,以及来自文学。两个单元呈现出相似的物源模式,共享主要的碎屑锆石年龄峰值(550-650 Ma、950-1050 Ma、1750-2000 Ma、2600-2800 Ma)和最大沉积年龄c。550 马。从 Bambui 群中回收的埃迪卡拉纪锆石显示出很大的 eHf(t) 范围,从 c. −17 到 +15,表明存在多个晚新元古代源,其中一些源是幼年的,一些具有长地壳居住地。Bambui 群内不同单元的碎屑锆石年龄模式和 eHf(t) 值的变化为盆地演化过程中发生的物源变化提供了额外的线索。Salinas组获得的新数据将其沉积限制在548至500 Ma之间,这对其构造意义具有重要意义。我们认为,在巴西利亚带和阿拉库艾造山带两侧,班布伊盆地的早期前渊沉积物应该已被纳入造山带,这可以解释在克拉通区域内明显缺乏记录巴西利亚带隆起(约 630 Ma)高潮的沉积物。在同一方向上,我们认为 Salinas 组和 Ibia 组都可以代表这些分别与巴西利亚带和 Aracuai 造山带抬升相关的早期前陆沉积物的残余物,由于变形锋的推进而并入造山楔。因此,我们所知的 Bambui Group 实际上是前陆系统高级阶段的剩余记录,当时沉降已经受到两个演化造山带的影响。总之,地层学、构造学和地质年代学数据的分析趋向于在西冈瓦纳河合并期间班布伊盆地与周围造山带之间相互作用的综合构造模型。
更新日期:2020-12-01
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