The Khairkhan dunite-troctolite-gabbro massif (Lake Zone of the Western Mongolia) - Example of syncollision Middle Cambrian mafic intrusion

Abstract

Geological, mineralogical, petrochemical and geochronological data are considered for the Khairkhan dunite-troctolite-gabbro massif in the Lake zone of Western Mongolia. The massif intrude the Lower Cambrian molasse stratum and intruded by the Middle Cambrian diorite-plagiogranite bodies (507 Ma). Mineralogical, petrographic and geochemical data show typical suprasubduction characteristics: high An component of plagioclases with increased iron content of olivines, high whole-rock alumina content, low contents of titanium and alkalis, Ta, Nb, Zr and Hf minima. The layered series is characterized by a layers of orbicular gabbros, which can be considered as gabbro-gabbro mingling. At the same time, high-temperature viscous-plastic deformations are characteristic of the layered series, which cover the entire volume of the intrusion. These observations, together with geological and geochronological data related to the melting of the suprasubduction mantle in the Cambrian-Ordovician time, allow treating the Khairkhan massif as an example of syncollisional stratified gabbroids.