Seismic structure of the Balmuccia Peridotite from a high-resolution refraction and reflection survey

IF 2.8 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Damian Pasiecznik, Andrew Greenwood, Florian Bleibinhaus, György Hetényi
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Abstract

Summary In anticipation of a forthcoming scientific deep drilling initiative within the Western Alps near Balmuccia, Italy, a high-resolution seismic survey is performed at the proposed drill site. This site is situated within the Ivrea Verbano Zone (IVZ), characterized by lower-crustal materials and fragments of upper mantle rocks exposed adjacent to the Insubric Line. The 2-km-long seismic survey crosses an isolated km-scale outcrop of peridotite near the town of Balmuccia. Applying P-wave traveltime tomography, a substantial contrast in seismic velocities is identified, with velocities in the range of 1–8 km s−1. The peridotite displays velocities ranging from 6 to 8 km s−1. The higher velocities near 8 km s−1 are consistent with laboratory measurements on small-scale samples, while the low velocity areas within the peridotite body reflect the influence of fractures and faults. The mean velocity derived for the peridotite body is ca. 7 km s−1. The reflection seismic analysis reveals subvertical reflectors positioned at the peridotite boundaries mapped at the surface, converging at a depth of ca. 0.175 km b.s.l. which images a lens-like structure for the peridotite body. However, the area beneath the imaged lens and the deeper Ivrea Geophysical Body (IGB) suggested by earlier studies is not well imaged, which leaves room for other interpretations regarding the relationship of these two bodies. Prior geophysical investigations provide only approximate depth estimates for the top of the IGB, spanning between 1–3 km depth b.s.l. Although the reflection data does not exhibit a series of continuous reflectors beneath the peridotite, a prominent reflection at ca. 1.3 km depth may indicate the top of the IGB.
通过高分辨率折射和反射勘测研究 Balmuccia橄榄岩的地震结构
摘要 为迎接即将在意大利巴尔穆奇亚附近的西阿尔卑斯山开展的深层科学钻探活动,在拟议的钻探地点进行了一次高分辨率地震勘测。该地点位于伊夫雷亚-韦尔巴诺区(Ivrea Verbano Zone,IVZ)内,其特点是下地壳物质和上地幔岩石碎片暴露在 Insubric Line 附近。全长 2 千米的地震勘测穿越了巴尔穆奇亚镇附近一个孤立的千米级橄榄岩露头。应用 P 波行进时间层析成像技术,确定了地震速度的巨大反差,速度范围为 1-8 km s-1。橄榄岩的速度介于 6 至 8 千米/秒之间。8 km s-1 附近的较高速度与实验室对小规模样本的测量结果一致,而橄榄岩体内部的低速区域则反映了断裂和断层的影响。橄榄岩体的平均速度约为 7 km s-1。反射地震分析表明,在地表绘制的橄榄岩边界处有亚垂直反射体,在大约 0.175 千米(海拔)深处汇聚,形成了橄榄岩体的透镜状结构。然而,成像透镜体和早期研究提出的更深的伊夫雷亚地球物理体(IGB)下面的区域并没有得到很好的成像,这就为有关这两个体之间关系的其他解释留下了空间。虽然反射数据没有显示橄榄岩下有一系列连续的反射体,但在大约 1.3 千米深的地方有一个突出的反射体,这可能表明橄榄岩下有一个更深层的 Ivrea 地球物理体。1.3 千米深度处的突出反射可能表明了 IGB 的顶部。
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来源期刊
Geophysical Journal International
Geophysical Journal International 地学-地球化学与地球物理
CiteScore
5.40
自引率
10.70%
发文量
436
审稿时长
3.3 months
期刊介绍: Geophysical Journal International publishes top quality research papers, express letters, invited review papers and book reviews on all aspects of theoretical, computational, applied and observational geophysics.
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