Anderson Don L, Natland James H
Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125; and
Department of Marine Geosciences, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149
Proc Natl Acad Sci U S A. 2014 Oct 14;111(41):E4298-304. doi: 10.1073/pnas.1410229111. Epub 2014 Sep 8.
Convection in an isolated planet is characterized by narrow downwellings and broad updrafts--consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic interior, and a cooling highly conductive but thin boundary layer above the core. Parts of the surface layer sink into the interior, displacing older, colder material, which is entrained by spreading ridges. Magma characteristics of intraplate volcanoes are derived from within the upper boundary layer. Upper mantle features revealed by seismic tomography and that are apparently related to surface volcanoes are intrinsically broad and are not due to unresolved narrow jets. Their morphology, aspect ratio, inferred ascent rate, and temperature show that they are passively responding to downward fluxes, as appropriate for a cooling planet that is losing more heat through its surface than is being provided from its core or from radioactive heating. Response to doward flux is the inverse of the heat-pipe/mantle-plume mode of planetary cooling. Shear-driven melt extraction from the surface boundary layer explains volcanic provinces such as Yellowstone, Hawaii, and Samoa. Passive upwellings from deeper in the upper mantle feed ridges and near-ridge hotspots, and others interact with the sheared and metasomatized surface layer. Normal plate tectonic processes are responsible both for plate boundary and intraplate swells and volcanism.
孤立行星中的对流具有狭窄的下沉流和宽广的上升流特征，这是阿基米德原理、热力学第二定律所要求的冷却以及压缩对物质特性的影响所导致的结果。一个具有传导性低粘度核心的成熟冷却行星会形成一个厚厚的绝缘表面边界层，该边界层具有热最大值、亚绝热内部以及核心上方冷却的高传导性但很薄的边界层。表面层的部分物质沉入内部，取代较老、较冷的物质，这些物质被扩张的洋脊夹带。板块内火山的岩浆特征源自上边界层内部。地震层析成像揭示的、显然与表面火山有关的上地幔特征本质上是宽广的，并非由于未分辨的狭窄喷流所致。它们的形态、纵横比、推断的上升速率和温度表明，它们是对向下通量的被动响应，这与一个通过表面散失的热量比从核心或放射性加热获得的热量更多的冷却行星相适应。对向下通量的响应与行星冷却的热管/地幔柱模式相反。由剪切驱动从表面边界层提取熔体解释了黄石、夏威夷和萨摩亚等火山省的情况。来自上地幔更深层的被动上升流为洋脊和近洋脊热点提供物质，其他上升流则与剪切和交代的表面层相互作用。正常的板块构造过程既导致了板块边界以及板块内的隆升和火山活动。
