Metamorphism and partial melting of high-pressure pelitic granulites from the Qianlishan Complex: Constraints on the tectonic evolution of the Khondalite Belt in the North China Craton

High-pressure pelitic granulites with a peak assemblage of garnet+kyanite+K-feldspar+plagioclase+biotite+quartz have been found from the Qianlishan Complex in the westernmost part of the Khondalite Belt, an east-west-trending Paleoproterozoic orogen between the Ordos and Yinshan Blocks in the North China Craton. Petrographic evidence indicates that high-pressure pelitic granulites underwent the prograde, peak and post-peak decompression stages. The early prograde metamorphic stage (M-1) is represented by an inclusion-type mineral assemblage of quartz + plagioclase + muscovite + biotite + sillimanite, which occurs within the core of garnet porphyroblasts. The peak metamorphic stage (M-2) is marked by the mantle growth of garnet porphyroblasts and matrix minerals kyanite, K-feldspar, biotite, plagioclase and quartz. The decompression stage (M-3) is indicated by sillimanite replacing kyanite, the formation of the cordierite + sillimanite symplectite in the matrix (M3-1), and the cordierite corona replacing garnet (M3-2). These mineral assemblages and their P-T estimates based on the assemblage stability fields of P-T pseudosection constructed in NCKFMASHTO define a clockwise P-T path involving near-isothermal decompression. Combined with available metamorphic age data, the clockwise P-T paths reconstructed for high-pressure pelitic granulites from the.Qianlishan Complex and medium-pressure pelitic granulites from other complexes in the Khondalite Belt are in accord with collision between the Yinshan and Ordos Blocks to form the Western Block at similar to 1.95 Ga, followed by the exhumation and associated decompressional partial melting at similar to 1.88 Ga. (C) 2014 Elsevier B.V. All rights reserved.