Carboniferous and Cretaceous mafic–ultramafic massifs in Inner Mongolia (China): A SHRIMP zircon and geochemical study of the previously presumed integral “Hegenshan ophiolite”

Abstract We present SHRIMP zircon ages and whole-rock geochemical data to identify mafic–ultramafic massifs of early Carboniferous and early Cretaceous ages from northern Inner Mongolia, China. The early Carboniferous massifs (Chongenshan–Xiaobaliang–Wusnihei) comprise predominantly lherzolite and minor gabbroic rocks. Zircons from a microgabbro (e Nd (t)  = 9.8) and a plagiogranite (e Nd (t)  = 9) yielded weighted mean 206 Pb/ 238 U ages of 354 ± 7 Ma and 333 ± 4 Ma, that we interpret as reflecting the time of zircon (and magma) crystallization. A volcanic breccia resting unconformably on the ultramafic rocks (serpentinites) has an eruption age of 300 ± 2 Ma and provides a younger minimum …