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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Control on seafloor spreading geometries by stress- and strain-induced lithospheric weakening
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Control on seafloor spreading geometries by stress- and strain-induced lithospheric weakening

机译：通过应力和应变引起的岩石圈减弱来控制海底扩展几何

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Seafloor spreading typically occurs along ridge segments oriented at right angles to plate motion and offset by orthogonal transform faults. Few regions exhibit different patterns, such as the East Pacific Rise (EPR), which additionally displays overlapping spreading centres (OSCs) and microplates. We introduce a dynamical model using two independent, scalar types of damage in an elastic plate that generates most observed spreading geometries as natural failure modes, suggesting that the dynamics of the underlying mantle have only a minor influence on accretionary plate margins. The elastic modulus that is affected by the damage determines the type of localized deformation. Damage reducing the bulk modulus tends to result in tensile fractures, while a reduction in shear modulus leads to shear fractures. The damage source determines the fracture orientation. Material weakening in tension results in fractures perpendicular to the most tensile principal stress, while shear weakening results in two conjugate fractures at 45° relative to the applied stress. Strain or energy-dependent damage results in propagating, localized fractures. Stress-dependent damage tends to evolve into diffuse regions that may eventually focus into narrow zones. Starting from small perturbations with reduced elastic moduli as nucleation points, all ridge geometries start with ridge propagation caused by tensile energy reducing both elastic moduli by a model of damage caused by tensile energy reducing both moduli. Orthogonal transform faults develop in regions between offset segments if there is an additional reduction in shear modulus due to shear stress. The orthogonality of the transform faults does not derive from the local stress orientation but from the dynamics of damage focusing which causes the fault to converge towards an optimal geometry that concentrates nearly all deformation into damaged zones. OSCs form when the shear damage leading to transform faults is suppressed, while microplate formation requires additional reduction of the shear modulus by tensile energy. Oblique spreading at 45°, recently discovered along ultraslow spreading ridges, occurs when both moduli are weakened by shear energy. A parameter regime exists in which ridge–transform patterns develop at low applied tension, while microplates form at higher stresses. These results indicate that at least three different micromechanical processes operate with different evolution rates. OSCs and oblique spreading require different material properties.
机译：海底扩展通常沿着与板块运动成直角的脊段发生，并因正交变换断层而偏移。很少有区域表现出不同的模式，例如东太平洋上升（EPR），它还显示出重叠的扩散中心（OSC）和微孔板。我们引入了一种动力学模型，该模型在弹性板中使用两种独立的标量类型的损伤，该损伤模型会生成大多数观察到的扩展几何形状作为自然破坏模式，这表明底层地幔的动力学对增生板边缘的影响很小。受损伤影响的弹性模量决定了局部变形的类型。降低体积弹性模量的损伤易于导致拉伸断裂，而剪切模量降低导致剪切断裂。损坏源决定了断裂方向。拉伸中的材料减弱会导致垂直于最大拉伸主应力的断裂，而剪切减弱会导致相对于所施加应力在45°处发生两次共轭断裂。应变或能量相关的损坏会导致局部扩展的裂缝。与应力有关的损害往往会演变成扩散区域，最终可能集中在狭窄区域。从具有减小的弹性模量作为成核点的小扰动开始，所有的脊几何形状都以由拉伸能减小两种弹性模量的破坏模型为基础，由拉伸能减小两种弹性模量引起的脊传播。如果由于剪切应力而导致剪切模量进一步降低，则正交变换断层将在偏移段之间的区域中发育。转换断层的正交性不是由局部应力方向决定的，而是由破坏集中的动力学引起的，这导致断层朝着最佳几何形状收敛，该几何形状几乎将所有变形集中在受损区域。当抑制导致相变断层的剪切损伤时，会形成OSC，而微孔板的形成则需要通过拉伸能进一步降低剪切模量。当两个模量都被剪切能减弱时，就会发生在最近沿超慢扩散脊形成的45°倾斜扩散。存在一个参数范围，其中在较低的施加张力下会形成脊形转换模式，而在较高的应力下会形成微孔板。这些结果表明至少三个不同的微机械过程以不同的演化速率运行。 OSC和倾斜散布需要不同的材料属性。

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