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Kinematic deformation model of the south-central subandean zone, Bolivia
Journal of South American Earth Sciences ( IF 1.8 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.jsames.2020.102768
Ángel Sánchez , Ana María Goncalves , Keven Asquith , Kevin Hill

Abstract The Bolivian Subandean region is characterized as a thin-skinned fold-thrust belt with structures persisting for 50–100 km along strike in a broadly North-South direction. The evolution of the Subandean structures is related to shortening and mass transfer. The stratigraphy comprises ∼12 km of Ordovician to Recent sediments, which are dominated by the Paleozoic section including Devonian source and reservoir horizons capped by the Middle Devonian Los Monos regional seal. Detachments occur at top of basement, dipping 2° to the west, within the Silurian and two Devonian levels, including the Los Monos shale. The fold-belt contains the Mega Gas Fields of Bolivia. This study focused on an exploration target in the Iguembe structure, located nearby the Margarita and Incahuasi Gas Fields. In addition to the standard methodology of integrating seismic lines, surface geology and well data, this study also utilized magnetotelluric (MT) analysis to create regional structural sections that were balanced and restored, recording ∼40% shortening between 12Ma and the present. The compression was propagated from west to east along a basal detachment along top basement at ∼12 km depth, creating four different and superimposed structural units. The Ordovician to Middle Devonian section deformed as antiformal stacks at ∼15 km spacing, with the highly ductile Los Monos horizon overlying it and acting as a major detachment and seal. The Upper Devonian to Cretaceous section was buttressed by over 5 km of overlying Neogene sequence; in such a way, that it was forced to propagate to the surface directly above the antiformal imbricates in a sequence of triangle zones above and along the Los Monos detachment. The 5+ km thick Neogene section is preserved as parallel bedded open synclines between the triangle zone culminations. The Middle Devonian source and reservoir may have been buried 6–8 km prior to deformation, which has reduced porosity, but also generated hydrocarbons. It is plausible that during the Siluro-Devonian Cordilleran compressional phase, gentle regional anticlines or inversion structures might have been formed, perhaps with ∼15 km spacing. These may have trapped the early-formed hydrocarbons and preserved porosity. These anticlines would be the nuclei for subsequent contractional deformation in the Neogene, with hydrocarbons re-migration and some hydrocarbons remnants trapped in the original structures.

中文翻译:

玻利维亚中南部亚安迪带运动学变形模型

摘要 玻利维亚 Subandean 地区的特征是一条薄皮褶皱逆冲冲断带,构造沿大方向南北走向持续 50-100 公里。Subandean 结构的演变与缩短和传质有关。地层包括约 12 公里的奥陶纪至近代沉积物,以古生界剖面为主,包括泥盆纪源和被中泥盆纪洛斯莫诺斯区域封盖覆盖的储层层。分离层发生在基底顶部,向西倾斜 2°,位于志留纪和两个泥盆纪层内,包括洛斯莫诺斯页岩。折叠带包含玻利维亚的巨型气田。本研究的重点是位于 Margarita 和 Incahuasi 气田附近的 Iguembe 构造中的勘探目标。除了整合地震测线、地表地质和井数据的标准方法外,本研究还利用大地电磁 (MT) 分析创建了平衡和恢复的区域结构剖面,记录了 12Ma 和现在之间约 40% 的缩短。压缩沿约 12 公里深度的顶部基底沿基底分离自西向东传播,形成四个不同的叠加结构单元。奥陶纪至中泥盆纪剖面变形为约 15 公里间距的反形式叠层,高延展性的 Los Monos 地层覆盖在其上并作为主要的拆离和密封。上泥盆统至白垩统剖面由超过 5 公里的上覆新近系层序支撑;以这样的方式,它被迫传播到正上方的反形式叠瓦上的表面,在洛斯莫诺斯支队上方和沿线的一系列三角形区域中。5+ 公里厚的新近系剖面被保留为三角形带顶点之间的平行层状开放向斜。中泥盆统烃源和储集层在变形前可能已被埋藏 6-8 公里,这降低了孔隙度,但也产生了碳氢化合物。很可能在志鲁-泥盆纪科迪勒拉挤压相期间,可能形成了缓和的区域背斜或反转构造,其间距可能约为 15 公里。这些可能捕获了早期形成的碳氢化合物并保留了孔隙度。这些背斜将成为新近纪后续收缩变形的核心,
更新日期:2020-11-01
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