Abstract:

Plagioclases with special zonal structure were seen occasionally in diorite intrusion in Pingshun, southern Taihang Mountains. The plagioclases is characterized by high Ca-riched basic plagioclases (An>63) in the core and Na-riched in the rim, and a corrosion zone formed between the core and the rim that composed epidote and sericite. In addition there are distinctive compositional differences between core and rim of the plagioclase xenocrysts. Based on the evidences from the components and textures of the plagioclause, the following scenario about the magma evolution is tentatively suggested. Mantle magma originating from the EMI underplated to lower crust and crystallized Ca-riched basic plagioclases under high temperature. Crustal source magma originated by melting of lower crust with the help of heat-carrying mantle magma. Mantle magma and crustal magma ascended quickly along Taihang deep fault, intruded into shallow crust, and mixed. Meanwhile, early-formed basic plagioclases dissoluted because of sudden reduced pressure and formed corrosion zone with irregular shape. The crust-mantle magma crystallized Na-riched plagioclases on the basis of Ca-riched basic plagioclases and formed plagioclases with special zonal structure, providing the most direct evidence to magma mixing in the study area.

Key words: Pingshun diorite, xenocryst, zonal structure of plagioclase, crust-mantle magma mixing