Postdoctor SU Benxun and his teacher QIN Kezhang present a detailed description of the petrological and mineralogical features of the Xiadong mafic-ultramafic complex in the Middle Tianshan Massif, Central Asian Orogenic Belt.

Primary and secondary Hbls show wide compositional variations. These petrological and mineralogical features as well as mineral chemistry are comparable to typical Alaskan-type complexes worldwide, which are widely considered to have formed above subduction zones. The chemistry of clinopyroxene and chromite supports an arc plate-tectonic origin for the Xiadong complex. Its confirmation as an Alaskan-type complex implies that the MTM, with Precambrian basement, was probably a continental arc during oceanic plate underflow and further supports the hypothesis of southward subduction of the Palaeozoic Junggar Ocean.

Figure 1. (A) Location map of the study area in the Central Asian Orogenic Belt and partly in the Tarim Craton. (B) Regional geological map of the Eastern Tianshan and Beishan Rift showing the distribution of Palaeozoic mafic–ultramafic complexes. (Image by SU)

Figure 3. Field and outcrop photographs of the Xiadong mafic–ultramafic complex. (Image by SU)

Su et al. Occurrence of an Alaskan-type complex in the Middle Tianshan Massif, Central Asian Orogenic Belt: inferences from petrological and mineralogical studies. International Geology Review. 2012, 54( 3): 249-269 (Download Here)