Generation of komatiite magma and gravitational differentiation in the deep upper mantle
Generation of komatiite magma and gravitational differentiation in the deep upper mantle
复制标题
DOI：
10.1016/0012-821x(84)90121-3
复制
发表时间：
1984-02
影响因子：
5.3
通讯作者：
E. Ohtani
中科院分区：
文献类型：
--
作者：
E. Ohtani
硅酸盐液体的密度与基本的，苦味酸，和超基性的组成已估计从矿物在高压下的熔化曲线。在高于70 kbar的压力下，由上地幔部分熔融产生的硅酸盐液体比橄榄石和辉石更致密，并且石榴石是唯一在70 kbar至至少170 kbar的压力下比液体更致密的相。在此压力范围内，石榴石和部分液体从上升的部分熔融底辟中分离出来。因此，具有高Ca/OAl 2 O3比值的贫铝科马提岩可能来自于上地幔深部的底辟构造，其压力范围为70 ~ 140 kbar（200-400 km深度），在那里，高温石榴石的选择性分离作用得以有效地进行。另一方面，未贫化铝的科马提岩可能来自较浅深度（< 200 km）的底辟。通过从上升底辟中选择性分离石榴石，预计在200公里以上的深度会富集火成石榴石。地震波速度剖面中的200公里不连续性可以用深度大于200公里的火成石榴石的相对高浓度来解释。
The densities of silicate liquids with basic, picritic, and ultrabasic compositions have been estimated from the melting curves of minerals at high pressures. Silicate liquids generated by partial melting of the upper mantle are denser than olivine and pyroxenes at pressures higher than 70 kbar, and garnet is the only phase which is denser than the liquid at pressures from 70 kbar to at least 170 kbar. In this pressure range, garnet and some fraction of liquid separate from ascending partially molten diapirs. It is therefore suggested that aluminium-depleted komatiite with a highCa/OAl2O3ratio may be derived from diapirs which originated in the deep upper mantle at pressures from 70 kbar to at least 140 kbar (200–400 km in depth), where selective separation of pyropic garnet occurs effectively. On the other hand, aluminium-undepleted komatiite is probably derived from diapirs originating at shallower depths (< 200 km). Enrichment of pyropic garnet is expected at depths greater than 200 km by selective separation of garnet from ascending diapirs. The 200-km discontinuity in the seismic wave velocity profile may be explained by a relatively high concentration of pyropic garnet at depths greater than 200 km.