Comment on : “Platinum-group element geochemistry and geodynamic evolution of Chilas complex gabbros, Kohistan Island Arc NE Pakistan”

Abstract

An article (Zafar et al., 2020, 372–373, 105,691) recently published in Lithos proposes new petrogenetic interpretations regarding the Chilas Complex (CC) gabbros, and collisional history of the Kohistan Island Arc (KIA). Geochemical modeling based on bulk analysis of a single rock type has led the authors to argue against the previously proposed interpretations about the (1) genesis of CC through diapirism or rift-related magmatism and (2) timing of the collision of the Indian continental plate with KIA. The authors have postulated that the CC gabbroic rocks originated as a result of the northward subduction of the Indian plate beneath the Eurasian plate at ca. 85 Ma; mature arc-type magmatism in the Neo-Tethys Ocean. The irrefutable evidence for the existence of the thousands of km thick Kohistan-Ladakh Island Arc (KLA) system and the Neo-Tethys Ocean between the Indian and Eurasian plates preclude the possibility for such subduction and direct collision in the northern territory of Pakistan. Furthermore, the geochemical signatures do not offer unequivocal evidence for arc-continent collisional setting; instead petrogenetic modeling based on a re-evaluation of Zafar et al. (2020) data favors a back-arc basin (BAB) origin for the CC gabbros and thus endorses the previously proposed BAB tectonic setting for CC. Hence a thorough investigation of the data acquired and rationality of the interpretation by Zafar et al. (2020) is warranted since it contradicts the previously proposed and generally accepted concepts regarding the genesis of CC and collision of KIA with the Indian and Eurasian plates.