造山后脉岩组合的岩石成因——对岩石圈拆沉作用的约束

造山后脉岩组合是在寄主岩基冷却之后形成的，可能是造山带应力场转换的标志。昆仑造山带早中生代末期以及太行山-燕山造山带晚中生代花岗质岩基中广泛出露这种类型的脉岩，可划分为煌斑岩质，玄武质，闪长质，花岗闪长质．花岗质和富硅花岗质等5组。主元素和痕量元素分析表明它们是不同的原生岩浆固结的产物，相互之间不存在重要的分离结晶，同化混染和岩浆混合作用的关系，因而要求软流圈／岩石圈系统不同圈层的源区岩石同时达到部分熔融的条件。结合已有的高温高压实验，区域岩石圈结构和地质事件序列的分析，认为岩石圈拆沉作用是造山后脉岩组合形成的最合理触发机制。简单热模拟表明，软流圈窗顶界埋深达到一定深度时（例如昆仑造山带为82km），可以满足处于不同深度位置的中性麻粒岩，基性榴辉岩和地幔橄榄岩同时发生部分熔融。这时，岩石圈／软流圈系统可以有6～8个产生岩浆的位置。热的软流圈物质快速涌入软流圈窗，不仅触发地幔岩的减压熔融，也可能导致区域构造应力场由挤压转换为伸展，为岩浆的快速侵位创造了条件。所提供的岩石成因模型可以更合理地解释造山后脉岩组合的地质特征，主元素和痕量元素特征，也可以满足同位素体系变异所要求的条件。

Petrogenesis of the post-orogenic dike complex--Constraints to lithosphere delaminafion.

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.