Nature of the basement of the South Kunlun Block and significance to tectonic evolution of the Tibetan Plateau: Nd-Sr-O isotopic evidence from granitoids

Abstract

The West Kunlun mountain range along the northwestern margin of the Tibet Plateau consists of the North Kunlun and the South Kunlun Blocks welded together during the Paleozoic, and is one of the most poorly-understood orogenic belts in China. A general consensus has been reached that the North Kunlun Block is part of the Tarim Craton, but hot debate exists on the nature and origin of the South Kunlun.

Samples were collected from the 471 Ma Yirba Pluton, the 405 Ma North Kudi Pluton (NKP) and the 214 Ma Arkarz Shan Intrusive Complex (ASIC), representing >60% of the Kudi area, the South Kunlun Block. Their Sr and O isotope compositions exclude significant involvement of mantle-derived magma in the genesis of the granitoids; therefore the granitoids can be used to decipher the nature of lower/mid crust in the area.

All the samples give Mesoproterozoic Nd model ages (1.1 -1.5 Ga), similar to those for the exposed metamorphic complex in the area. This indicates that the South Kunlun Block does not have an Archean basement, therefore this block cannot be a micro-continent once separated from the North Kunlun Block, as previously suggested. Instead, it is likely that the South Kunlun Block is composed of laterally accreted materials along the south margin of the North Kunlun Block, or even an allochthonous terrane accreted to the south margin of the North Kunlun Block/Tarim Craton.