Escape of magma flow along the southern Central Asian Orogenic Belt prolonged the lifetime of the Tarim mantle plume

When an ascending mantle plume arrives beneath a small craton and encounters ambient orogenic extension, what is likely to happen? We explored this scenario through considering the case of the Tarim mantle plume and the mafic-ultramafic intrusions in the southern Central Asian Orogenic Belt (CAOB). This mantle plume, which arrived beneath the Tarim craton, one of the smaller cratons on Earth, lasted from 300 Ma to 270 Ma with peaks at 290 Ma and 278 Ma. Synchronously, the CAOB was at the late orogenic extension stage with an eastward-propagating, scissor-like closure of the Paleo-Asian Ocean. Ni-Cu sulfide deposits hosted in mafic-ultramafic intrusions are typically associated with mantle plume events. However, an increasing number of Ni-Cu sulfide deposits are recognized as being emplaced in an associated orogenic setting, such as those associated with the southern CAOB. We observed that the number of mafic-ultramafic intrusions decreases with increasing distance from the Tarim craton (from the Tarim plume), and these intrusions show a 7−8-m.y. time lag in their emplacement ages (295−255 Ma, with peaks at 293 Ma, 282 Ma, and 271 Ma) with respect to the timing of Tarim large igneous province magmatism (300−270 Ma) within the Tarim craton. These unusual geochronological and tectonic links suggest that the plume materials were escaping to the northeast along an extensional belt in the southern CAOB, which is perpendicular to the inferred circular boundary of the plume, resulting in the formation of orogenic-style Ni-Cu sulfide deposits and a continuous magma supply from the deep mantle, prolonging the lifetime of the Tarim plume.