The lack of distinction of Middle Chinese initials *dz, *z in Modern Hakka and Gan dialects

In Mandarin (or Guanhua), a northern Chinese dialect, there is a distinction between the Middle Chinese initials *dz and *z, just like what the rhyme book Guangyun stated. However, in the South of China, dialects such as Hakka and Gan do not share this feature completely. Base on the data in the Dialect Survey of Hakka-Gan dialects, most of the dialect points have more than 50% of affricates that corresponds to MC *z, the remainder are mainly fricatives. "The admonitions for the Yan Clan: Phonetics" has provided some phonetic description of the southern variety of Middle Chinese at the time and one of the features was the absence of the contrast between MC *dz and *z. Chinese dialectologists believe that Hakka and Gan dialects formed as a result of the migration from the north to south due to war. In theory, Hakka and Gan dialects should be like Mandarin, which inherits the contrast of MC *dz and *z. But this is not the case. To explain the affricates corresponding to MC *z, I am going to argue that it is due to dialect contact. The formation of both dialects was the result of dialect contact of Northern Middle Chinese and Southern Middle Chinese, with the southern variety as a substrate. This can explain why there is an absence of contrast of MC *dz and *z in so many words. For fricatives that correspond to MC *z, this is due to influence with the northern dialects geographically and socially after Hakka and Gan dialects were formed.