Continents as a chemical boundary layer
Continents as a chemical boundary layer
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大陆作为化学边界层
DOI：
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发表时间：
1981
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通讯作者：
Thomas H. Jordan
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作者：
Thomas H. Jordan
构造圈结构可以用三种基本类型的表面边界层来描述：化学边界层（c.b.l.）、机械边界层（m.b.l.）和热边界层（t.b.l.）。在古老的海洋盆地之下，c.b.l. 的厚度。 （约 40 公里）小于 m.b.l. 的距离。 （约 100 公里）或 t.b.l. （约 150 公里），但旧大陆克拉通下方存在类似结构的假设很难与地震观测相一致。因此，我们研究了另一种模型，该模型假设 c.b.l. 更厚。在克拉通下方，其地幔成分由低密度橄榄岩组成，玄武岩成分已耗尽。根据地震学和岩石学数据，推断这种增强的 c.b.l.延伸至 m.b.l 下方。深度超过 150 公里，并起到稳定厚（> 200 公里）t.b.l. 的作用。防止对流破坏。由于其耐火特性，sub-m.b.l. c.b.l. 的一部分构成了一个稳定的地球化学储层，它显然被从深部地幔或下降板片流出的大离子亲石元素所浸渍。因此，它的产热量很高（约 0.1 μW/m3），并且对表面热通量贡献很大。大陆c.b.l.的演化历史和动态。尚未被很好地理解，特别是双扩散不稳定性的作用，但大陆块融合成“超级大陆”以及由此带来的造山挤压被认为是c.b.l.中的重要过程。形成。
Tectospheric structure can be described in terms of three basic types of surficial boundary layers: chemical (c.b.l.), mechanical (m.b.l.) and thermal (t.b.l.). Beneath old ocean basins the thickness of the c.b.l. (ca. 40 km) is less than that of either the m.b.l. (ca. 100 km) or the t.b.l. (ca. 150 km), but the hypothesis that a similar structure underlies the old continental cratons is difficult to reconcile with seismic observations. We therefore examine an alternate model which postulates a much thicker c.b.l. beneath the cratons whose mantle component consists of a low-density peridotite depleted in its basaltic constituents. On the basis of seismological and petrological data it is inferred that this augmented c.b.l. extends below the m.b.l. to depths exceeding 150 km and acts to stabilize a thick ( > 200 km) t.b.l. against convective disruption. Because of its refractory nature the sub-m.b.l. portion of the c.b.l. constitutes a stable geochemical reservoir which has evidently been impregnated by large-ion lithophile elements fluxing from the deep mantle or from descending slabs. Consequently, its heat production is high (ca. 0.1 μW/m3) and it contributes significantly to the surface heat flux. The evolutionary history and dynamics of the continental c.b.l. are not well understood, especially the role of double-diffusive instabilities, but the fusion of the continental masses into ‘supercontinents’ and the orogenic compression that this entails are thought to be important processes in c.b.l. formation.