Precambrian Research 103 (2000) 175 – 189 Crustal-contaminated komatiitic basalts in Southern China: products of a Proterozoic mantle plume beneath the Yangtze Block Mei-Fu Zhou *, Tai-Ping Zhao 1 , John Malpas, Min Sun Department of Earth Sciences, Uniersity of Hong Kong, Pokfulam Road, Hong Kong Received 21 October 1999; accepted 24 March 2000 Abstract Abundant mafic and ultramafic rocks including basalts, komatiitic basalts, and peridotites occur in the Proterozoic Sibao Group, northern Guangxi Province, China. Whereas the basalts are generally pillow lavas, the komatiitic basalts are typically spinifex-textured and, in a few cases, show pyroxene accumulation associated with NiCu(PGE) sulfide deposits. The peridotites occur in the lower portions of differentiated sills, which contain gabbro and diorite in their upper parts. The sills are believed to be co-magmatic with the komatiitic basalts. The spinifex rocks of the Jiepai and Hejia Flows have MgO ranging from 8.9 to 14.3 wt%. The Zhongkui Flow is highly fractionated to form a spinifex zone with lower MgO (5.3–5.9 wt%) and a cumulate zone with higher MgO (17.3–17.9 wt%). Overall the rocks have TiO 2 =0.44–0.74 wt%. Relative to primitive mantle, they are enriched in Th and LREE, but exhibit negative Ti-, Nb-, and P-anomalies. These features are consistent with their formation from a crustally-contaminated komatiitic magma. During this process of crustal contamination, the magmas assimilated sulfur from sediments, which caused sulfide-segregation resulting in the formation of NiCu(PGE) sulfide deposits. The occurrence of the komatiitic basalts in the Sibao Group can be explained by the ascent of a mantle plume beneath a continental rift environment, and implies that the Yangtze Block may have had an Archean basement through which the Sibao komatiitic basalts erupted. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Crustal contamination; Komatiitic basalt; Proterozoic; Southern China www.elsevier.com/locate/precamres 1. Introduction Many Proterozoic terrains, including the Cape Smith Belt, Canada (Hynes and Francis, 1982) and the Baltic Shield (Park et al., 1984; Puchtel et al., 1997) contain komatiitic rocks that are inter- preted to represent products of high-Mg magmas derived by partial melting of the upper mantle. * Corresponding author. Tel.: +852-28578251; fax: +852- 25176912. E-mail address: mfzhou@hkucc.hku.hk (M.-F. Zhou). 1 Present address: Henan Institute of Geology, Zhengzhou, Henan, PR China. 0301-9268/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0301-9268(00)00077-2