Editorial for Minerals Special Issue “From Diagenesis to Low-Grade metamorphism”

DO CAMPO, MARGARITA; NIETO, FERNANDO

Minerals

MDPI

Lugar: Basilea; Año: 2020 vol. 10

Rocks aected by pressure?temperature conditions in the transitional field between diagenesisand low-grade metamorphism make up large domains of the Earth?s upper continental and oceaniccrust. Due to its borderline character, the conventional approaches of metamorphic petrography orthose of sedimentary petrology are not completely adequate to unravel the physical?chemical geneticconditions of these rocks. In general, the system does not reach equilibrium, or this is limited tothe nanoscale, thus the advance of mineral reactions is controlled by kinetics and results in commondefective mineral phases commonly occur. In this context, the concept of reaction progress has been consolidated as more adequate than that of grade. This explains why the study of theserocks has developed during decades of specific methods of study and consequently has its ownnomenclature. Powerful tools for the study of defective phases, with special emphasis on clayminerals, are electron microscopy and X-ray difraction, which have led to the development of specificcriteria of grade and pressure gradient. In addition to clay minerals, other materials such as organicmatter, index minerals of basic rocks, and fluid inclusions have also been appliedto these diagenetic/metamorphic rocks. Even though initial apparent contradictions arise, furtherstudies have demonstrated the complementariness of the dierent approaches and encourage theirjoint use.