Chemical Characteristics of Zircon and Apatite Minerals of Two Types of Rhyodacites in Xiangshan,Jiangxi Province and Their Geological Significance
To ascertain the diagenetic ages,physicochemical conditions,rock types,and genetic models of rhyo-dacite and rhyodacite porphyry in the western Xiangshan area,zircon LA-ICP-MS dating and mineral chemical an-alyses of zircon and apatite were conducted.The findings reveal that the diagenetic ages of rhyodacite and rhyoda-cite porphyry are(138.6±1.1)Ma and(137.6±1.5)Ma,respectively,with diagenetic temperatures ranging from 706～843 ℃ and 683～788 ℃.The apatite saturation temperatures for the two rock types are 943～978℃ and 943～966℃,respectively.Additionally,the relative oxygen fugacity of zircons are from-2.09 to+0.06 and from-2.05 to-0.37,while those of apatites are from+0.30 to+1.49 and from+0.05 to+1.25,re-spectively.Both rhyodacite types are confirmed to be products of the same magmatic event,characterized by high temperatures,low oxygen fugacity,and low water content.Their parental magma originated from the crust,exhib-iting no overt signs of crust-mantle mixing,and the rocks are classified as A-type granites.The formation of these rhyodacites can be attributed to the subduction of the Pacific plate in the SW direction,with the upwelling and sustained heat supply from the asthenosphere triggering partial melting of diorite residual phases.
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