Porphyroids of the Irtysh zone of compression

TLDR: Sokoloff et al. as discussed by the authors found that the porphyroid bodies are the same as those of the regionally predominant fracture zones and that their interbedding with rocks of varying composition and age, their contact alterations, metasomatic phenocrysts, and other geological and petrographic evidence, supplemented by chemical analyses, suggest an imrusive character of these rocks, rather than a sedimentary, pyroclastic, effusive origin, though this was believed by some of the earlier investigators.

Abstract: Orientations of the porphyroid bodies are found to be the same as those of the regionally predominant fracture zones. Their “interbedding” with rocks of varying composition and age, their xenoliths, contact alterations, metasomatic phenocrysts (in carbonaceous-sericitic shales near their contacts with the porphyroids), and other geological and petrographic evidence, supplemented by chemical analyses, suggest an imrusive character of these rocks, rather than a sedimentary, pyroclastic, effusive origin, though this was believed by some of the earlier investigators. – V. P. Sokoloff.