Missing adakitic granite and syn-subduction mafic dikes within Permian volcanic belts of the southern margin of the CAOB? Comment on “Permian oceanic slab subduction in the southernmost Central Asian Orogenic Belt: Evidence from adakite and high-Mg diorite in the southern Beishan”

Abstract

The petrogenesis of adakite and adakitic rocks and their tectonic settings are debated. Adakites may be derived by many processes which include: partial melting of subducted oceanic slab or lower crustal material; fractional crystallization of basaltic magma; magma mixing processes associated with arc-related and non-arc tectonic settings. It may be inaccurate to assume that adakitic rocks are solely derived from subducted oceanic slabs. The development of accretionary orogens, as it relates to adakite formation, is a topic of significant interest. Geochemical data coupled with field observations are vitally important to address the interplay between tectonics and magma genesis. In this comment, we discuss the petrogenetic processes and possible tectonic setting of the “adakite” in the southern Beishan region of the Central Asian Orogenic Belt (CAOB), to provide insight on the use of geochemical data to discriminate the tectonic setting of their formation. Based on our field observations, we disagree with the model presented by Zheng et al. (2020) as it pertains to the existence of an “ophiolitic mélange” and the evidence of a Permian arc system but rather, advocate that the adakitic rocks at Beishan are generated at an extensional setting.