Several aspects of very lowgrade metamorphism were discussed in this article, including ① Küblers creation of “anchizone” and its role in the solution of the boundary between diagenesis and metamorphism, which is an internationallyagreed puzzle in geology; ② contribution and role of “illite crystallinity” in the research of very lowgrade metamorphism of clastic rocks; ③ calibration of instrumental, and a proposed calibration formula between Kübler Index and domain size; ④ diagenetic and metamorphic index minerals; ⑤ new pattern and genetic interpretation for very lowgrade metamorphism of SongpanGarzê and Bayan Har orogens; ⑥ in addition, some scientific regulations were discussed. It is proposed that the boundary between diagenesis and metamorphism can be ascertained by a combination of index minerals with “illite crystallinity”. It is realized that to establish a set of standards of “illite crystallinity” from Himalaya is very important and essential. New interpretation of metamorphic pattern of Triassic flysches in the Tibet plateau could be used for genetic analysis of very lowgrade metamorphism of clastic rocks beyond the only model burial metamorphism.