Petrogenesis of the post-orogenic dike complex--Constraints to lithosphere delaminafion.
造山后脉岩组合的岩石成因——对岩石圈拆沉作用的约束

The post-orogenic dike complex is generated after cooling of its host batholiths,and may be a signature of the orogenic stress field transformation in an orogenic belt.Such dikes cropped out broadly in the granitic batholiths of early Mesozoic orogen, Kunlun Mountains,and late Mesozoic orogen,Taihangshan-Yanshan Mountains.These dikes can be subdivided into five groups such as lampropheric,basaltic,dioritic,granodioritic-granitic and silica-rich granitic dikes.Analysis of the major and trace elements suggests that they were produced by consolidation of different primary or parental magmas,respectively.There are not any important evidences to relate among these dikes by fractional crystallization,assimilation and magma mixing.Accordingly,it is to be required that all possible source layers in the lithosphere-asthenosphere system have reached the conditions to partial melt.A synthesized analysis of data from high T-P experiments,regional lithosphere structures and event consequence of geological processes suggests that lithosphere delamination is the best reasonable mechanism to trigger generation of the regional dike complex.A simplest heating modeling imply that the conditions for contemporaneous partial melting of intermediate granulite,basaltic eclogite and mantle peridotite at different depth levels can be satisfied if the top of asthenosphere window reached some depth level (for example,82kin in Kunlun orogenic belt).In this case,there would be 6 to 8 horizontal positions appropriated to magma generation in the lithosphere- asthenosphere system.The welling of hotter asthenosphere up into the window would trigger not only decompressional melting of mantle peridotite,but also transformation of the regional stress field from compression to extension,creating favorable condition for fast emplacement of magmas.The present petrogenesis model could reasonably explain geology and major- and trace-element futures of the post-orogenic dike complexes,also fits their characteristics in isotopic geochemistry.