The alkaline basalts in southern hunan are suggested to have formed by small degrees of decompression melting of the asthenosphere mantle during the initial extension . the transitional ( the chebu gabbro ) and tholeiitic basaltic magmas were generated by relatively larger degrees of partial melting of the mantle 在裂谷初期,软流圈地幔的小比例部分熔融形成碱性玄武岩(湘南) ,在裂谷拉张作用比较强、地幔部分熔融比例比较大时形成赣南和湘南的过渡型(车步辉长岩)及拉斑质玄武岩。