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Shallow seismic investigations of the accretionary complex offshore Central Chile
Marine Geology ( IF 2.9 ) Pub Date : 2021-02-05 , DOI: 10.1016/j.margeo.2021.106437
Sebastián Obando-Orrego , Eduardo Contreras-Reyes , Anne M. Tréhu , Joerg Bialas

Thrust ridges are accretionary structures often associated with local uplift along splay faults and cold seep activity. We study the influence of a NS-trending thrust ridge system on the transition between the accretionary prism and the continental framework (shelf break) offshore the Maule Region (central Chile at 35°–36°S) by examining its 2-D and 3-D seismic velocity structure. The experiment comprises five densely spaced seismic refraction lines running subparallel to the trench and recorded at nine OBH/S (ocean bottom hydrophone/seismometers) deployed along the central line. Results show a narrow margin-parallel volume (approximately 6 × 50 × 5 km3) whose velocity distribution is consistent with sedimentary rocks. The shallow sedimentary unit is characterized by the presence of very low velocity hydrate-bearing sediments (<1.7 km/s), which are interpreted as highly porous sedimentary rocks (>50% porosity) within the Gas Hydrate Stability Zone (GHSZ) suggesting low hydrate content. These zones spatially correlate with fluid activity in the vicinity of the NS trending thrust ridges based on local high heat flow values (>40 mWm−2) and seepage mapping. On the other hand, the splay faults that crop out on the flanks of the thrust ridge structures might be responsible for tectonically induced vertical fluid migration.



中文翻译:

智利中部增生复合地带的浅层地震调查

推力脊是增生性构造,通常与沿扇形断裂和冷渗流活动引起的局部隆升有关。我们通过研究二维区域和二维区域3来研究莫尔地区(智利中部35°–36°S)附近增生棱柱逆冲脊脊系统对增生棱镜和大陆架(搁板断裂)之间过渡的影响。 -D地震速度结构。该实验包括5条密集间隔的地震折射线,这些折射折射线平行于沟槽延伸,并记录在沿中心线展开的9个OBH / S(海底水听器/地震仪)上。结果显示窄的边距-平行体积(大约6×50×5 km 3),其速度分布与沉积岩一致。浅层沉积单元的特征是存在极低速的含水合物沉积物(<1.7 km / s),这被解释为天然气水合物稳定区(GHSZ)内的高孔隙度沉积岩(孔隙度> 50%),表明沉积速率低水合物含量。这些区域基于局部高热流值(> 40 mWm -- 2)和渗流映射,与NS趋势推力脊附近的流体活动在空间上相关。另一方面,在逆冲脊构造侧面产生的张开断层可能是构造诱发垂直流体运移的原因。

更新日期:2021-02-15
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