Plate tectonic theory was developed 50 years ago and underpins most of our understanding of Earth's evolution. The theory explains observations of magnetic lineations on the seafloor, linear volcanic island chains, large transform fault systems, and deep earthquakes near deep sea trenches. These features occur through a system of moving plates at the surface of the Earth, which are the surface expression of mantle convection. The plate consists of the chemically distinct crust and some amount of rigid mantle, which move over a weaker mantle beneath. However, exactly where the transition between stronger and weaker mantle occurs and what determines and defines the plate are still debated. In the classic definition the plate is defined thermally, by the geotherm‐adiabat intersection, where the plate is the conductively cooling part of the mantle convection system. Many observations such as heat flow, seafloor bathymetry, seismic imaging, and magnetotelluric (MT) imaging are consistent with general lithospheric thickening with age, which suggests that temperature is an important factor in determining lithospheric thickness. However, while age averages give a good indication of overall properties, the range of lithospheric thicknesses reported is large for any given tectonic age interval, suggesting greater complexity. A number of observations including sharp discontinuities from teleseismic scattered waves and active source reflections and also strong anomalies from surface and body wave tomography and MT imaging cannot be explained by a purely thermal model. Another property or process is required to explain the anomalies and sharpen the boundary. Many subsolidus models have been proposed, although none can universally explain the variety of independent global observations. Alternatively, a small amount of partial melt can easily satisfy a range of observations. The presence of melt could also weaken the mantle over geologic timescales, and it would therefore define the lithosphere‐asthenosphere boundary (LAB). The location of melt is important to mantle dynamics and the LAB, although exactly where and exactly how much melt exists in the mantle are debated. Asthenospheric melt interpretations include a variety of forms: in small or large melt triangles beneath spreading ridges, in channels, in layers, along a permeability boundary leading to the ridge, at a depth of neutral buoyancy, punctuated, or pervasively over broad areas and either sharply or gradually falling off with depth. This variability in melt character or geometry may explain the previously described variability in LAB depths. The LAB is likely highly variable laterally as are the locations, forms, and amounts of melt, and the LAB is likely dynamic, dictated by small‐scale convection and the dynamics of melt generation and migration. A melt‐defined, dynamic LAB and a weak asthenosphere have broad implications for our understanding of Earth systems and planetary habitability. A weak asthenosphere caused by volatiles or melt could enable plate tectonic style convection, allow multiple scales of convection, and dictate the driving forces of the system. A better understanding of plate tectonics has broad implications for life on Earth. These include mitigating natural disasters caused by plate motions including volcanoes, earthquakes, and tsunamis. In addition, uplift and subsidence of the tectonic plates affects the sea level, impacting the level of the paleo‐oceans and potentially affecting climate change estimates through geologic time. Finally, plate tectonic processes shape the surface morphology of the planet, making continents that enable our existence on land and the ocean basins that hold our free‐surface water. Remarkably, despite large amounts of material transfer into and out of the mantle, and multiple scales of convection, plate tectonics has maintained a hydrosphere over billions of years that is favorable for life.

中文翻译：

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岩石圈-软流圈边界的性质

板块构造理论是50年前发展起来的，它巩固了我们对地球演化的大多数理解。该理论解释了对海底，线性火山岛链，大型转换断层系统以及深海海沟附近的深层地震的磁力线观测。这些特征是通过地球表面移动板块的系统而发生的，这是地幔对流的表面表现。板块由化学上独特的外壳和一定数量的刚性地幔组成，这些地幔在下方较弱的地幔之上移动。但是，究竟是在更强的地幔还是在较弱的地幔之间发生了过渡，以及确定和定义板块的原因仍然存在争议。在经典定义中，板块是通过地热-绝热线相交来定义的，其中板是地幔对流系统的传导冷却部分。热流，海底测深法，地震成像和大地电磁（MT）成像等许多观察结果与岩石圈的总体厚度随年龄增长而一致，这表明温度是确定岩石圈厚度的重要因素。然而，尽管平均年龄很好地表明了总体性质，但对于任何给定的构造年龄间隔，所报告的岩石圈厚度范围都很大，这表明复杂性更高。纯粹的热模型无法解释许多观测结果，包括远震散射波和活动源反射的剧烈不连续性，以及表面波和体波层析成像和MT成像的强烈异常。需要另一个属性或过程来解释异常并锐化边界。已经提出了许多次固相模型，尽管没有一个模型能够普遍解释各种独立的全球观测结果。可替代地，少量的部分熔融可以容易地满足一系列观察。熔体的存在还可能在地质时标上削弱地幔，因此将定义岩石圈-软流圈边界（LAB）。熔体的位置对地幔动力学和LAB很重要，尽管人们一直在争论到底在地幔中的确切位置和数量。软流圈的熔体解释包括多种形式：在扩散脊下方的小或大熔体三角形，在通道中，在层中，沿着通向脊的渗透边界，在中性浮力深度处的点状，分层，或遍及广阔区域，并随着深度急剧或逐渐下降。熔体特征或几何形状的这种可变性可以解释先前描述的LAB深度的可变性。LAB可能在横向上高度变化，熔体的位置，形式和数量也很可能变化，并且LAB可能是动态的，这取决于小规模对流以及熔体生成和迁移的动力学。熔体定义的动态LAB和软弱的软流圈对我们对地球系统和行星的可居住性的理解具有广泛的意义。由挥发物或熔体引起的软弱的软流层可以使板块构造对流，允许多种尺度的对流，并决定系统的驱动力。对板块构造的更好理解对地球生命具有广泛的意义。这些措施包括减轻由板块运动（包括火山，地震和海啸）引起的自然灾害。此外，构造板块的隆升和沉降会影响海平面，影响古海洋的水平，并可能通过地质时间影响气候变化的估计。最后，板块构造过程塑造了行星的表面形态，形成了使我们能够存在于拥有自由表面水的陆地和海洋盆地上的大陆。值得注意的是，尽管有大量的物质进出地幔，并且对流尺度多种多样，但板块构造仍在数十亿年的时间里维持着对生命有利的水圈。构造板块的隆升和沉陷影响海平面，影响古海洋的水平，并可能通过地质时间影响气候变化的估计。最后，板块构造过程塑造了行星的表面形态，形成了使我们能够存在于拥有自由表面水的陆地和海洋盆地上的大陆。值得注意的是，尽管有大量的物质进出地幔，并且对流尺度多种多样，但板块构造仍在数十亿年的时间里维持着对生命有利的水圈。构造板块的隆升和沉陷影响海平面，影响古海洋的水平，并可能通过地质时间影响气候变化的估计。最后，板块构造过程塑造了行星的表面形态，形成了使我们能够存在于拥有自由表面水的陆地和海洋盆地上的大陆。值得注意的是，尽管有大量的物质进出地幔，并且对流尺度多种多样，但板块构造仍在数十亿年的时间里维持着对生命有利的水圈。使大陆能够在陆地和拥有我们自由表面水的海洋盆地中生存。值得注意的是，尽管有大量的物质进出地幔，并且对流尺度多种多样，但板块构造仍在数十亿年的时间里维持着对生命有利的水圈。使大陆能够在陆地和拥有我们自由表面水的海洋盆地中生存。值得注意的是，尽管有大量的物质进出地幔，并且对流尺度多种多样，但板块构造仍在数十亿年的时间里维持着对生命有利的水圈。