The association of mafic–ultramafic intrusions and A-type magmatism in the Tian Shan and Altay orogens, NW China: Implications for geodynamic evolution and potential for the discovery of new ore deposits

Abstract

The NW China region is characterised by tectonic and lithostratigraphic domains, such as the Tian Shan and Altay orogens, the Tarim, Junggar and Turpan Basins. The Tian Shan and Altay orogens are part of the Central Asian Orogenic Belt. The NW China region was affected by a series of thermal events that occurred between the Silurian and the Triassic, which resulted in the emplacement of numerous granitic plutons and mafic–ultramafic intrusions. A number of these granitic plutons are of A-type affiliation, which on the basis of the positive εNd values are likely to have been derived from mantle sources. In addition, at least two large igneous provinces (LIPs) can be recognised in NW China, namely the 345–325 Ma Tian Shan LIP and the ca. 270–280 Ma Tarim LIP. Age and field data suggest a spatial and temporal relationship between the mafic–ultramafic intrusions and A-type granites within the LIPs. In this paper we discuss mafic–ultramafic intrusions that host magmatic Ni–Cu sulphide deposits (Kalatongke in the Altay, Huangshan and Poyi–Poshi) in the eastern Tian Shan. These intrusions are typically zoned, characterised by an envelope of early gabbroic rocks that enclose later ultramafic units. These zoned mafic–ultramafic intrusions have some features that are comparable with Alaskan-type complexes. Taking into consideration the spatial–temporal relationship of the mafic, mafic–ultramafic rocks and A-type granites, we suggest that these magmatic events occurred during an extensional regime, possibly related to a mantle superplume event that affected much of central Asia during the Permian, of which the Siberian Traps and the Emeishan continental flood basalts of SW China are part. If the A-type felsic magmatism took place during a superplume event, we also suggest that these rocks may be conducive to host iron–oxide–copper–gold (IOCG) style mineralisation. We conclude with a model that attempts to explain the relationship between the zoned mafic–ultramafic intrusions and mantle plume activity in NW China during the Permian.