Some isostatic and thermal consequences of the vertical strain geometry in convergent orogens
Some isostatic and thermal consequences of the vertical strain geometry in convergent orogens
复制标题
会聚造山带垂直应变几何结构的一些等静压和热后果
DOI：
10.1016/0012-821x(90)90056-4
复制
发表时间：
1990
影响因子：
5.3
通讯作者：
R. Powell
中科院分区：
文献类型：
--
作者：
M. Sandiford;R. Powell
大陆变形，特别是地表抬升、水平浮力和地壳的变质作用，在很大程度上取决于地壳和地幔岩石圈之间应变分布的方式。由于这些垂直应变可能通过对流减薄或下热边界层[2]的分离等过程被强烈地“解耦”，而这种“解耦”的程度在造山带[3]中随时间和空间的变化而变化，因此分别在地壳ƒc和岩石圈ƒ1的尺度上参数化垂直应变是有用的。我们通过考虑在热稳定岩石圈收敛变形期间可能发展的数字ofƒc−ƒ1paths的热和均衡后果来说明这种参数化。根据地壳和地幔岩石圈垂直应变的“解耦”程度，定性地区分了造山带中的三个distinctƒc−ƒ1paths。1型路径不涉及解耦，因此岩石圈的垂直应变是均匀的。对于givenƒc， 1型路径导致相对较低的地表海拔和低-中变质温度，适合于蓝闪片岩和巴罗维变质组合的发育。第2型路径是由于地幔岩石圈在造山期尺度上的对流减薄等过程导致的浅解耦，但只有在岩石圈初始增厚相当大之后才会发生。2型路径导致相对较高的地表海拔，如givenƒc，只有在地幔岩石圈变薄后才会产生中到高的变质温度。与地幔岩石圈变薄相关的势能增加（导致浮力增加多达1013Nm−1）将迅速终止会聚变形，其结果是变质加热将延迟增厚变形，并可能引起造山带的伸展塌陷。第3类路径涉及随着地壳增厚，地幔岩石圈有效变薄，其结果是，特别是在地壳活跃增厚期间，可能出现相对较高的变质温度。对于给定的驱动力，沿3型路径的收敛变形将在相对smallƒcproviding处终止，这是高-低变质岩组合发育的合适位置。
The thermal and isostatic consequences of continental deformation, particularly surface elevation, horizontal buoyancy forces and metamorphism in the crust, depend to a considerable extent on the way in which strain is distributed between the crust and the mantle lithosphere [1]. Since these vertical strains may be strongly “decoupled” by processes such as convective thinning or detachment of the lower thermal boundary layer [2], with the extent of this “decoupling” varying in space and time in an orogen [3], it is useful to parameterise the vertical strain on the scale of the crust,ƒc, and lithosphere,ƒ1, respectively. We illustrate this parameterisation by considering the thermal and isostatic consequences of a number ofƒc−ƒ1paths which may develop during the convergent deformation of a thermally-stabilised lithosphere. Three qualitatively distinctƒc−ƒ1paths in orogens are distinguished on the extent of “decoupling” between vertical strains in the crust and mantle lithosphere.Type 1 pathsinvolve no decoupling, so the vertical strain in the lithosphere is homogeneous. For a givenƒc, Type 1 paths result in relatively low surface elevation and low-intermediate metamorphic temperatures appropriate for the development of glaucophane-schist and Barrovian metamorphic assemblages.Type 2 pathsallow decoupling due to processes such as convective thinning of the mantle lithosphere on the orogenic timescale but only after considerable initial lithospheric thickening. Type 2 paths lead to relatively high surface elevations, for a givenƒc, and intermediate to high metamorphic temperatures only after the mantle lithosphere is thinned. The increase in potential energy associated with mantle lithospheric thinning (resulting in an increase in buoyancy forces by as much as 1013Nm−1) will quickly terminate convergent deformation, with the result that metamorphic heating will postdate the thickening deformation, and may induce extensional collapse of the orogen.Type 3 pathsinvolve efficient mantle lithosphere thinning as the crust thickens with a consequence being, particularly, the possibility of relatively high metamorphic temperatures during active crustal thickening. For a given driving force, convergent deformation along a Type 3 path will be terminated at relatively smallƒcproviding an appropriate setting for the development of highT—lowPmetamorphic assemblages.