Petrogenesis and tectonic significance of mafic--ultramafic rocks from Southwest Yunnan, China.

This study focuses on the mafic--ultramafic lavas of the Early Carboniferous outcrop in Mangxin, southwestern Yunnan, China. Picrites with 26-32 wt% MgO and a quenched texture are the most significant components of this rock association. This article divides the Mangxin picrites into two types. The mantle potential temperature (Tp) of these picrites is higher than the Tp range of mid-ocean ridges and reaches that of mantle plumes. According to the geochemical characteristics, the Type-1 picrites probably formed from the melting of the mantle plume head and were contaminated by ambient depleted mantle, whereas the Type-2 picrites formed from themelting of mantle plume tails. These plume-related mafic--ultramafic rocks in Mangxin and the ocean island basalt (OIB)-carbonate rock associations in many areas of the Changning--Menglian belt provide significant evidence for the improvement of previous models of the Palaeotethyan oceanic plateau. [ABSTRACT FROM AUTHOR]