不完美岩浆过程中的微量元素效应

本文综述了国外近年来在不完美岩浆过程中微量元素效应研究方面的进展。在完美平衡过程（平衡部分熔融或者平衡部分结晶）中和在完美分离过程（分离熔融或者分离结晶）中，熔融或者结晶对于高度不相容元素和高度相容元素相对浓度变化的差异悬殊的影响效应是众所周知的。完美分离过程需要满足以下３个条件：（１）每一批次被分离的熔体或者晶体的量趋向于无穷小；（２）晶体与熔体的彻底分离；（３）体系相对于源区物质和残留物质是完

TRACE ELEMENT GEOCHEMICAL EFFECTS OF IMPERFECT MAGMATIC PROCESSES

Progresses in the research or trace element geochemical effocts in imperfect magmaticprocesses are reviewed and synthesized in this paper. The strongly contrasted effocts ofmelting or crystallization under perfect equilibrium conditions, under perfect fractionalpartial melting, and under perfcct fractional crystallization upon the relative concentra-hons of the highly incompatible and highly compatible elements are well known and aresurveyed at the start. For the perfect fractional processes to be operative three conditionsmust be met, inc1udirrgf (i) infinitesimal size of the batches of liquid or crystals removed,(ii) perfect separation of the crystal and liquid phases, and (iii) perfect closure of the sys-tem to fluxes of the source material and the residue. The consequences of departures fromthe above three conditions are explored. These departures can very substantially reduce thediffercnces between the trace element concentrations generated in the products and thoseexpected in a perfect equilibrium process. The RXCT model fits the situation where thevolcanic eruption taps the more differentiated magma before the mixing stage. An alterna-hve ideal model, i.e. the RXTC model, is applicable to the more common process of hy-brid magma eruption. In mid-ocean ridge basalts, the RXTC model may explain whylarge variations in incompatible elements coexist with moderate depletion of compatible el-ements.