Geochemistry of fine-grained clastic rocks in the Mesoproterozoic Kawabulake Group: implications for provenance and the tectonic model of the Eastern Tianshan, Xinjiang, NW China

Abstract

The Mesoproterozoic Kawabulake Group, which is unconformably overlain by the Lower Cambrian Huangshan Formation and conformably overlies the Mesoproterozoic Xingxingxia Group in the Eastern Tianshan area, NW China, is comprised mainly of siltstone, slate, sandstone and phyllite. New geochemical data for the clastic rocks from the Kawabulake Group were investigated to constrain the provenance and weathering history of the source rocks, in order to evaluate the tectonic evolution of the Eastern Tianshan area. Kawabulake Group rocks are compositionally similar to PAAS (average Post-Archean Australian Shale), indicating derivation from a felsic source that is characterized by depletion in some HFSEs such as Nb, Ta and Ti. The Chemical Index of Alteration (CIA) for the sandstone, siltstone and slate samples (CIA = 60 on average) suggests intensely weathered sources. Light REE-enrichment patterns ((La/Yb)CN = 4–20) coupled with negative Eu anomalies (Eu/Eu* between 0.44 and 0.89 with an average of 0.62) are similar to those of PAAS, consistent with cratonic sources. The major and trace element compositions imply a dominantly Precambrian felsic source region with a minor contribution from mafic materials. The Sr–Nd isotopic compositions and the ages of T DM2 (~3.4, 2.5–1.8, 1.2 and 1.0 Ga) are consistent with the evolutionary history of Kuluketage in the northern Tarim, suggesting that the Tarim Craton was the main source area for the Kawabulake Group.