Structure of the Wollaston Lake Reflector (Trans-Hudson Orogen, Canada) from reflection AVO analysis: Fractured diabase intrusion, fluids, or silicified shear zone?
Structure of the Wollaston Lake Reflector (Trans-Hudson Orogen, Canada) from reflection AVO analysis: Fractured diabase intrusion, fluids, or silicified shear zone?
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DOI：
10.1016/j.tecto.2007.04.010
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发表时间：
2007-08
期刊：
影响因子：
2.9
通讯作者：
Jinfeng Ma;I. Morozov
中科院分区：
文献类型：
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作者：
Jinfeng Ma;I. Morozov
在加拿大萨斯喀彻温省北部1994年岩探跨哈德逊造山带（THOT）的地震反射剖面S2b中观测到的近160公里长的沃拉斯顿湖反射面（WLR）是晶体地壳中最壮观和记录最完整的特征之一。基于对其正入射反射率的建模，最初将观测到的亮点反射率解释为一系列表状辉绿岩侵入体。为了进一步阐明其结构，我们对S2b线进行了再处理，并分析了带偏移量的幅值变化（AVO）的WLR。与传统的（近似）AVO分析相比，我们使用了精确的Zoeppritz方程，并考虑了薄层（混合正极性和负极性）反射率。研究结果提出了两种可能的解释：1)反射面是由大量基性侵入引起的，在这种情况下，侵入岩石的泊松比异常σ≥0.33;2)WLR代表一个硅化剪切带，只有中等（例如，~ 5-10%）的围岩蚀变，σ≈0.2。虽然这两种模式可能在某种程度上共存于WLR中，但其亮度，清晰度，巨大的横向范围和光滑的形状有利于第二种解释。在这两个模型中，在一个主要的地壳分离中，一个破裂的充满流体的带应该在WLR的形成中发挥了关键作用。反射器与横向和深部运移流体的关联也得到了大地电磁测量结果的支持。在科拉超深钻孔（俄罗斯）的研究中，在相当深度发现了游离流体或变质流体，这也表明流体可能有助于WLR的结构和形成。
A nearly 160-km long Wollaston Lake Reflector (WLR) observed in seismic reflection profile S2b of the 1994 Lithoprobe Trans-Hudson Orogen transect (THOT) in northern Saskatchewan (Canada) is among the most spectacular and well-recorded features imaged within the crystalline crust. Based on modeling of its normal-incidence reflectivity, the observed bright spot reflector was originally interpreted as a series of tabular diabase intrusions. In order to further elucidate its structure, we reprocessed line S2b and analysed the WLR for the Amplitude Variations with Offset (AVO). By contrast to conventional (approximate) AVO analysis, we used the exact Zoeppritz equations and considered a thin-layer (mixed positive and negative polarities) reflectivity. The results suggest two possible interpretations of the WLR: 1) the reflector caused by a massive mafic intrusion as suggested earlier, in which case the intruded rocks should have anomalous Poisson's ratios of σ≥0.33, and 2) the WLR represents a silicified shear zone, with only moderate (e.g., ∼5–10%) alteration of the host rock and σ≈0.2. Although both of these models may to some extent co-exist within the WLR, its brightness, sharpness, great lateral extent and smooth shape favour the second interpretation. In both models, a fractured fluid-filled zone within a major crustal detachment should have played a key role in the formation of the WLR. The association of the reflector with laterally- and depth-migrating fluids is also supported by magneto-telluric measurements of crustal conductivity beneath the WLR. Analogies from the studies of the Kola Superdeep Borehole (Russia), where free or metamorphic fluids were found at comparable depths, also suggest that fluids may contribute to WLR structure and formation.