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Regional control structures of kimberlite emplacement in the southern São Francisco Craton basement: A multidisciplinary approach including a representative example from Junco diatreme (Divinópolis, MG, Brazil)
Journal of South American Earth Sciences ( IF 1.8 ) Pub Date : 2022-09-15 , DOI: 10.1016/j.jsames.2022.104027
Francisco José da Silva, Renato de Assis Barros, George William Clemence Junior, Diego Guilherme da Costa Gomes, Luiz Carlos Bertolino, Eduardo Duarte Marques

In the southernmost São Francisco Craton, the well-exposed Archean to Paleoproterozoic basement shows kimberlite bodies that represent the last southeastern clusters associated with the Azimuth 125° structure. The absence of Mesozoic to Cenozoic overlying cover rocks in the region allows in-depth aeromagnetic geophysical interpretation of the structural controls responsible for the emplacement of kimberlites. The main controlling structures are depicted by the crosscut NW-SE dyke swarms of Paraopeba, Pará de Minas, and Transminas with the E-W lineaments, characterized by quartz veins and hydrothermalites in the area. The Junco kimberlite intrusion occurs in the region, and reproduces some regional controls at a local scale: the ascent mechanism along a mafic dyke (Pará de Minas swarm) and the placement in the intersection of the mafic dyke with E-W structures. Geological mapping confirmed the remote interpretation and defined the intrusion as oval-shaped, with the magnetic model indicating a bulky diatreme body up to 500 m depth. The goal of this research is to show the importance of the regional controls, their relation to the Junco intrusion, and combine aerogeophysical analysis, geological mapping, mineral chemistry, and lithosphere information to unravel potentially linking processes operating at variable scales. In this context, regolith material overlying the intrusion was sampled, and the indicator minerals pyrope garnet, clinopyroxene, ilmenite, and chromite were selected and analyzed for mineral compositions using electron probe microanalysis. Pyrope garnet and chromite do not show a relation to diamond's potential fields. Ilmenite analyzes indicate relatively high level of oxidation, a characteristic that differentiates the Junco diatreme from kimberlites occurring in the Alto Paranaíba Igneous Province within the southern Brasília Fold Belt. Single-clinopyroxene thermobarometry calculations provided pressure-temperature array values ranging from 745 °C to 832 °C and 31.3 kbar to 38.9 kbar, respectively. A geotherm model was fitted resulting in an estimated surface heat flow of 49.0 mW/m2 and a lithospheric thickness of 202 km. The average equilibration depth of the clinopyroxene at 99.6 km points to pressure-temperature conditions consistent with the stability field of graphite.



中文翻译:

南圣弗朗西斯科克拉通地下室金伯利岩就位的区域控制结构:一种多学科方法,包括 Junco diatreme 的代表性示例(Divinópolis,MG,巴西)

在最南端的圣弗朗西斯科克拉通,暴露良好的太古宙至古元古代基底显示了金伯利岩体,它们代表了与方位角 125° 结构相关的最后东南部集群。该地区没有中生代至新生代覆盖岩,因此可以对导致金伯利岩就位的结构控制进行深入的航空磁地球物理解释。主要控制构造由 Paraopeba、Pará de Minas 和 Transminas 的横切 NW-SE 岩脉群描绘,具有 EW脉络,以石英脉为特征和该地区的热液矿。Junco金伯利岩侵入发生在该地区,并在局部范围内再现了一些区域控制:沿着镁铁质岩脉(Pará de Minas swarm)的上升机制以及在镁铁质岩脉与EW结构的交汇处的放置。地质测绘证实了远程解释,并将侵入体定义为椭圆形,磁性模型表明深度达 500 m 的巨大直径体。这项研究的目的是展示区域控制的重要性,它们与 Junco 入侵的关系,并结合航空地球物理分析、地质填图、矿物化学和岩石圈信息,以揭示在可变尺度上运行的潜在联系过程。在这种情况下,风化层对覆盖侵入体的材料进行取样,选择指示矿物镁铝榴、单斜辉石、钛铁矿和铬铁矿,并使用电子探针显微分析法分析矿物成分。黄铁榴石和铬铁矿与钻石的势场无关。钛铁矿分析表明氧化程度相对较高,这是 Junco diatreme 与发生在 Alto Paranaíba火成岩省在巴西利亚南部褶皱带内。单斜辉石热气压计计算提供的压力-温度阵列值分别为 745 °C 至 832 °C 和 31.3 kbar 至 38.9 kbar。拟合了地热模型,估计地表热流为 49.0 mW/m 2,岩石圈厚度为 202 km。单斜辉石在99.6 km处的平均平衡深度指向与石墨稳定场一致的压力-温度条件。

更新日期:2022-09-15
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