High-pressure partial melting of mafic lithologies in the mantle
High-pressure partial melting of mafic lithologies in the mantle
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DOI：
10.1093/petrology/egh057
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发表时间：
2004-12-01
影响因子：
3.9
通讯作者：
Pertermann, M
中科院分区：
文献类型：
--
作者：
Kogiso, T;Hirschmann, MM;Pertermann, M
我们回顾了与高压下镁铁质岩性（辉石岩）部分熔融相关的实验相平衡，以揭示辉石岩的整体成分与其熔融关系之间的系统关系。辉石矿相平衡的一个重要方面是石榴石-辉石热分流的存在，由 CaO-MgO-Al2O3-SiO2 投影中的顽辉石-Ca-Tschermaks 辉石-透辉石平面定义。在自然系统中，这种划分出现在压力高于 2 GPa 的情况下，其中石榴石和辉石是辉石岩中的主要残余相。位于分水岭两侧的块状成分具有从次固相线到液相线的不同相组合，并产生从强霞石标准成分到石英标准成分的不同类型的部分熔融物。固相线和液相线位置几乎不受天然辉石岩成分相对于热分界的位置的影响，而是主要由散装碱含量和镁值控制。残余矿物相体积的变化也会影响部分熔体成分。如果在部分熔化过程中不存在橄榄石，则与石榴石橄榄岩衍生的部分熔体相比，石榴石相对于单斜辉石的相体积随着压力的增加而膨胀，产生具有高Ca/Al和低MgO的液体。
We review experimental phase equilibria associated with partial melting of mafic lithologies (pyroxenites) at high pressures to reveal systematic relationships between bulk compositions of pyroxenite and their melting relations. An important aspect of pyroxenite phase equilibria is the existence of the garnet-pyroxene thermal divide, defined by the enstatite-Ca-Tschermaks pyroxene-diopside plane in CaO-MgO-Al2O3-SiO2 projections. This divide appears at pressures above similar to2 GPa in the natural system where garnet and pyroxenes are the principal residual phases in pyroxenites. Bulk compositions that reside on either side of the divide have distinct phase assemblages from subsolidus to liquidus and produce distinct types of partial melt ranging from strongly nepheline-normative to quartz-normative compositions. Solidus and liquidus locations are little affected by the location of natural pyroxenite compositions relative to the thermal divide and are instead controlled chiefly by bulk alkali contents and Mg-numbers. Changes in phase volumes of residual minerals also influence partial melt compositions. If olivine is absent during partial melting, expansion of the phase volume of garnet relative to clinopyroxene with increasing pressure produces liquids with high Ca/Al and low MgO compared with garnet peridotite-derived partial melts.