Quantitative comparison of structural and alteration genesis relations of Masahim and Bidkhan-volcano calderas: Located in northern strip of Dehej-Sardu'ieh, Kerman, Iran

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The origin of hydrothermal alterations in different facies of calderas can be exogenous or endogenous, depending on the age of volcanism and the kind of structures in an area. Naturally, most alterations have proportion with faults and fractures which facilitate fluid penetration. Comparing different locations of areas with high concentration of fractures in studied volcanic areas of Masahim and Bidkhan calderas and investigating the alterations of central facies within current study suggests that there is the strong relation between argillic alteration (as supergenic and exogenous alteration) and lineaments whereas phylic alterations as more endogenous genesis alteration have less general relation with lineaments. In Masahim caldera, with younger volcanism age, the origin of clay minerals is mostly related with meteoric waters and its major mineral is kaolin. According to XRD experiments, minerals such as pyrophyllite and dickite (as endogenous clays) are not very common in Masahim caldera; most alterations in Masahim volcanic area are argillic with exogenous origin. On the other hand in Bidkhan caldera, as older volcano than Masahim caldera, despite the argillic presence, phylic alterations (with endogenous origin) are significantly observed as well. Conformity matrix of alteration map and upper bound of the lineament-index map in Masahim and Bidkhan areas shows conformity coefficients of 37.8 and 29 percent for argillic and 1.1 and 10.7 for phylic alterations, respectively. Positive relation between argillic alteration and lineament-index, and weaker relation between phylic alteration and the factor of lineaments in center of Masahim and Bidkhan calderas, alongside with closer relation between general alterations regime of Masahim area (mostly exogenous) and lineament-index, indicates and confirms stronger effects of faults in supergenic processes compared with hypogenic processes within these areas. Also, due to older age of volcanism activity in Bidkhan caldera (longer time of erosion action) and younger age of Masahim volcanism (shorter time of erosion action), current surface observable facies are deeper facies in Bidkhan caldera with more endogenous phylic alterations, while in Masahim caldera, more surface facies are mostly argillic exogenous alterations.