BASEMENT CONFIGURATION OF THE NORTHWESTERN SOUTH AMERICA - CARIBBEAN MARGIN FROM RECENT GEOPHYSICAL DATA

IF 0.5 4区 工程技术 Q4 ENERGY & FUELS Ct&f-Ciencia Tecnologia Y Futuro Pub Date : 2007-12-01 DOI:10.29047/01225383.474
J. Cerón, J. Kellogg, G. Ojeda
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引用次数: 28

Abstract

The oceanic nature of the crust in northern Colombia (underlying the Lower Magdalena Basins) has been postulated by different authors as a northern extension of the Cretaceous, mafic and ultramafic rocks accreted to the western margin of northwest Colombia (in the Western Cordillera and Baudo range). Localized, small outcrops of oceanic affinity rocks seem to support this hypothesis. However, geophysical data do not support this northern extension, but clearly mark the boundary between the collisional Panamá terrane with northern South America and the over thrusting of the latter on top of the obliquely convergent Caribbean plate.  We produced maps to basement and Moho topography by integrated modeling of gravity, magnetics, seismic reflection surveys and well data from northwest Colombia and the southwestern Caribbean. In areas with good seismic coverage, the basement under the Lower Magdalena Basins (LMB) is represented by a clear reflector. In areas where seismic data shows poor imaging or is absent, we use a back stripping methodology to model first the sedimentary section, with known densities, composition and geometry controlled by oil wells and high quality seismic data, and then the deeper section. 2,5D gravity and magnetics modeling results in an initial Moho that can be extended to the entire region based on the control of available seismic refraction points. This controlled Moho provides the basis for basement modeling for the whole area and this sequence is iterated for several sections across the region.  Our results indicate that the crust under northern Colombia is continental to thinned continental (transitional) in nature, with densities between 2,6 and 2,7 g/cm3. Our model also requires a dense wedge of sediments (density 2,5 g/cm3) at the base of the modern fold belt, which may represent a fossil sedimentary wedge attached to the continental margin. This wedge may have served as a backstop for the modern fold belt. The gravity modeling does not require oceanic crust to form the basement in the Sinú and San Jacinto fold belts as previously suggested. Discrete layers and thin slivers of oceanic sediments and basement could have been scrapped off the incoming plate and thrusted into an accretionary mélange, and eventually exposed at the surface, as seen in the Mulatos, Chalan and Cansona locations.  The shape of the continental wedge / oceanic crust boundary resembles that of a very low angle/flat subduction zone (ß angle between 2º to 3º), and is interpreted here as a low angle over thrusting of northern South America riding in a highly oblique direction over the underlying Caribbean plate. The map to basement depth obtained during this study forms the basis for basin analysis, oil maturation and evolutionary studies of the region. As an example, we apply our map to a flexural analysis of the LMB. 
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从最近的地球物理资料看南美洲-加勒比边缘西北部的基底构造
哥伦比亚北部(位于下马格达莱纳盆地之下)地壳的海洋性质被不同的作者假设为白垩纪的北延伸,基性和超基性岩石积聚到哥伦比亚西北部的西部边缘(在西科迪勒拉和Baudo山脉)。局部的、小型的海洋亲和岩的露头似乎支持这一假设。然而,地球物理资料并不支持这种向北伸展,而是清楚地标记出巴拿马地体与南美洲北部碰撞的边界,以及后者在斜辐合的加勒比板块顶部的过度逆冲。通过对哥伦比亚西北部和加勒比海西南部的重力、磁力、地震反射调查和井数据进行综合建模,我们绘制了基底和莫霍地形图。在地震覆盖较好的地区,下马格达莱纳盆地(LMB)下的基底有一个清晰的反射体。在地震数据显示成像效果差或没有地震数据的地区,我们首先使用反剥离方法对沉积剖面进行建模,该剖面具有已知的密度、成分和几何形状,由油井和高质量的地震数据控制,然后对更深的剖面进行建模。2.55 d重力和磁力建模得到的初始莫霍曲线,可以基于对可用地震折射点的控制扩展到整个区域。这种可控的莫霍曲线为整个地区的基底建模提供了基础,该序列在整个地区的几个剖面上进行了迭代。结果表明,哥伦比亚北部地壳为大陆-薄大陆(过渡性)地壳,密度在2.6 ~ 2.7 g/cm3之间。我们的模型还要求在现代褶皱带的底部有一个致密的楔形沉积物(密度为2.5 g/cm3),这可能代表了一个附着在大陆边缘的沉积楔形化石。这个楔形物可以作为现代褶皱带的支撑物。重力模拟并不需要海洋地壳在Sinú和圣哈辛托褶皱带形成基底。离散的层和薄的海洋沉积物和基底可能从进入的板块上脱落,并被推入一个增生的区域,最终暴露在地表,就像在穆拉托斯、查兰和坎索纳地区所看到的那样。大陆楔/洋壳边界的形状类似于一个非常低角度/平坦的俯冲带(角在2º到3º之间),在这里被解释为南美洲北部以一个高度倾斜的方向在加勒比海板块上的低角度逆冲。研究获得的基底深度图为该地区的盆地分析、石油成熟和演化研究提供了基础。作为一个例子,我们将我们的地图应用于LMB的弯曲分析。
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来源期刊
Ct&f-Ciencia Tecnologia Y Futuro
Ct&f-Ciencia Tecnologia Y Futuro Energy-General Energy
CiteScore
1.50
自引率
0.00%
发文量
7
审稿时长
>12 weeks
期刊介绍: The objective of CT&F is to publish the achievements of scientific research and technological developments of Ecopetrol S.A. and the research of other institutions in the field of oil, gas and alternative energy sources. CT&F welcomes original, novel and high-impact contributions from all the fields in the oil and gas industry like: Acquisition and Exploration technologies, Basins characterization and modeling, Petroleum geology, Reservoir modeling, Enhanced Oil Recovery Technologies, Unconventional resources, Petroleum refining, Petrochemistry, Upgrading technologies, Technologies for fuels quality, Process modeling, and optimization, Supply chain optimization, Biofuels, Renewable energies.
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