Is there a Grenvillian orogen in the southwestern Tarim Craton

Abstract The Rodinia Supercontinent assembled through global-scale Grenvillian (1300–900 Ma) orogeny, so identification and correlation of Grenvillian orogens is fundamental to the geological reconstruction of Rodinia. The Tarim Craton, NW China, has been considered as a building block of Rodinia, but its Neoproterozoic tectonic evolution and relationship with Rodinia remain enigmatic. It was proposed that a Grenvillian orogenic event occurred in the southwestern Tarim, possibly related to its amalgamation with northern Australia. Key evidence for this model came from the ~1.0 Ga 40Ar/39Ar ages of the Kalakashi Group in the Tiekelike belt, southwestern Tarim. In this contribution, we report zircon U-Pb ages and Lu-Hf isotopic data, as well as whole-rock geochemical data for the Kalakashi Group from the Buqiong section where a ~1.0 Ga 40Ar/39Ar age was reported. Our field and petrographic observations indicate that the primary rock assemblage of the Kalakashi Group is orthogneiss, garnet-bearing mica schist, marble and minor amphibolite. Zircon U-Pb dating of five orthogneisses and an amphibolite yielded crystallization ages of 900–850 Ma and a thermal/fluid overprinting event at ~420 Ma. Lu-Hf isotopic analyses of the dated zircon grains from two orthogneisses yielded eHf(t) values from −4 to +7, indicating a mixture of mantle- and crust-derived materials. Geochemical data show that the orthogneisses have relatively high FeOT/MgO and 10,000*Ga/Al ratios, elevated contents of high-field-strength elements (HFSE) and negative Ba, Sr and Eu anomalies, characteristic of A1-type granite, indicating that the parental magma erupted in an intra-plate rifting setting. Our results indicate that the Kalakashi Group is a volcanic-sedimentary succession that deposited in the Neoproterozoic, rather than the Paleoproterozoic or Mesoproterozoic as previously thought. We found no evidence for a Grenvillian orogenic event from the Kalakashi Group in the Buqiong section. Instead, the age and geochemistry of the studied orthogneisses are remarkably similar to those of the Sailajiazitage Group, although the latter was affected by weaker metamorphism and deformation. Reliable geochronological data from igneous and metamorphic rocks, as well as detrital zircons from Neoproterozoic strata, indicate that no typical record of Grenvillian orogeny occurred in either the north or the south of the Tarim Craton. Instead, we suggest that the northern Tarim was probably dominated by a long-term subduction-accretion, whereas the southern Tarim was likely in a long-term rifting environment in the early Neoproterozoic.