Saucers, Fingers, and Lobes: New Insights on Sill Emplacement From Scaled Laboratory Experiments
Saucers, Fingers, and Lobes: New Insights on Sill Emplacement From Scaled Laboratory Experiments
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碟形、指形和瓣形：规模化实验室实验对窗台安放的新见解
DOI：
10.1029/2022jb024421
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Jonas Köpping
中科院分区：
文献类型：
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作者：
Uchitha N. Arachchige;A. Cruden;Roberto Weinberg;A. Slim;Jonas Köpping
我们研究了碟形底槛在上地壳中形成和分割的条件。我们进行了一系列规模化的实验室实验，使用粘弹性塑性Laponite RD®（LRD）凝胶来模拟上地壳岩石，并使用牛顿石蜡油作为岩浆模拟物。碟形窗台总是在两层地壳的实验中形成。这些实验表明，从内部平坦岩床到外部倾斜岩席的急剧过渡，其特征在于非平面边缘。结果表明：（a）当岩床半径与上覆岩层深度之比在0.5 ~ 2.5之间时，发生从内部平坦岩床到外部倾斜岩席的过渡，（B）外部倾斜岩席倾角在15° ~ 25°之间变化，（c）这种过渡受基质材料层间杨氏模量之比控制;（d）在实验基台的传播尖端处形成不规则的指状和/或叶状段几何形状;以及（e）边缘段及其连接件的演变和几何形状在内部和外部基台内是不同的。结果还表明，形成自然碟形窗台几何形状对高水平应力（>5 MPa）没有严格要求。我们的结论是，岩浆侵位到层状粘弹塑性上地壳类似物的模拟实验再现了天然碟形岩床及其边缘分割的复杂性。实验窗台的行为与侵入尺度下的脆弹性断裂机制兼容，而边缘裂片和指状段最有可能与裂纹尖端尺度下发生的小尺度粘塑性不稳定性有关，这可能得益于宿主材料的低断裂表面能。
We investigate the conditions under which saucer‐shaped sills form and segment in the upper crust. We performed a series of scaled laboratory experiments that employ visco‐elastic‐plastic Laponite RD® (LRD) gels to model upper crustal rocks, and Newtonian paraffin oil as the magma analog. Saucer‐shaped sills always formed in experiments with a two‐layer upper crust. These experiments show sharp transitions from an inner flat sill to outer inclined sheets, which are characterized by non‐planar margins. The results show that: (a) the transition from an inner flat sill to an outer inclined sheet occurs when the sill radius to overburden depth ratio is between 0.5 and 2.5; (b) outer inclined sheets dip angles vary from 15° to 25°; (c) this transition is controlled by the ratio of the Young's modulus between the host material layers; (d) irregular finger‐like and/or lobate segment geometries form at the propagating tip of the experimental sills; and (e) the evolution and geometry of marginal segments and their connectors are different within the inner and outer sill. The results also suggest that there is no strict requirement for high horizontal stresses (>5 MPa) to form natural saucer‐shaped sill geometries. We conclude that analog experiments of magma emplacement into layered visco‐elastic‐plastic upper crustal analogs reproduce the complexity of natural saucer‐shaped sills and their marginal segmentation. The behavior of the experimental sills is compatible with brittle‐elastic fracture mechanisms operating at the intrusion scale, while marginal lobes and finger‐like segments are most likely linked to small‐scale visco‐plastic instabilities occurring at the crack tip scale, possibly aided by the low fracture surface energy of the host material.