The Early Permian Tarim Large Igneous Province: Main characteristics and a plume incubation model

Abstract

The Early Permian magmatism in Tarim, NW China comprises diamondiferous kimberlites, lamprophyres, flood basalts, Fe–Ti oxide ore-bearing layered mafic–ultramafic intrusions, bi-modal dyke swarms, alkaline igneous complexes (including syenites and A-type granites), rhyolites and pyroclastic rocks. The extent of this intraplate magmatism exceeds 250,000 km 2 , making it comparable to Large Igneous Provinces (LIPs). Screening of available radiometric ages reveals three main magmatic episodes in the Tarim LIP, with the first being marked by ~ 300 Ma small-volume kimberlites, followed by two phases of bimodal magmatism at ~ 290 Ma and at ~ 280 Ma, respectively. This relatively long time interval of the Early Permian magmatism is consistent with a low eruption rate of the Tarim LIP and is supported by the intercalation of volcanic rocks with sediments in outcrops and drill holes. Although the spatial distribution of each magmatic episode in the Tarim LIP is far from assessed, it seems that the ~ 290 Ma flood basalts are widespread across the province, whereas ~ 300 Ma kimberlites and ~ 280 Ma ultramafic–mafic–felsic intrusions and dyke swarms only occur in the Bachu Uplift and around the margins of the Tarim craton. We propose that the ~ 300 Ma kimberlites were derived from deep part of the metasomatized sub-continental lithospheric mantle (SCLM), while the ~ 290 Ma flood basalts were likely formed as a result of mixing of plume-derived melts with SCLM-derived melts (e.g., lamproitic melt) as they rose through the SCLM. In contrast, the ~ 280 Ma magmas were most likely derived from the convecting mantle. A plume incubation model is proposed to account for the temporo-spatial distribution of the Tarim LIP, in which different styles of plume–lithosphere interaction are recognized. In the first two episodes, the mantle plume incubating the base of the craton provides the heat that triggered melting of the enriched components in the SCLM. In contrast, adiabatic decompression melting within the plume produced the ~ 280 Ma magmatic phase. Thermal modeling suggests that lithospheric thinning by thermal erosion might have been associated with the upwelling mantle plume, with the greatest thinning occurring in the Bachu area. Thinned spots and weak zones at the margins of cratons and mobile belts caused preferential channeling of plume flow and subsequent decompression melting. This explains the localized distribution of ~ 280 Ma magmas in the Tarim LIP. • Spatial distribution of igneous rocks in the Tarim large igneous province • Three magmatic episodes possess distinct rock association and geochemistry. • Lithospheric thinning in association with thermal erosion by upwelling mantle • Plume–lithosphere interaction in the formation of the Tarim LIP