Mid-Neoproterozoic tectonic switch from orogeny to intraplate extension in NW Tarim Craton: New evidence from a composite dike of the Aksu Group

It is widely acknowledged that the Tarim Craton plays a crucial role in the supercontinent Rodinia. However, the timing and regime of the Neoproterozoic orogeny, as well as the subsequent tectonic evolution along the northern margin of the Tarim Craton, remain contentious. Recent research has revealed a composite dike in the Aksu blueschist terrane located in the NW Tarim, which sheds new light on the pivotal Neoproterozoic tectonic transition. This dike comprises deformed granites and undeformed diabases, resulting from two-episode igneous events shortly after the orogenic metamorphism. The granites exhibit S-type affinities, with high silica, calcicalkalic, and peraluminous compositions. Enriched isotopic signatures and diagnostic inherited zircons suggest that they derived from the metasedimentary rocks of the accretionary complex. Conversely, the following diabase dike displays tholeiitic affinity, right-sloping REE patterns, enriched LILEs, and a pronounced depletion of high-field-strength elements. Moderately enriched Sr-Nd isotopes and chondrite-akin Hf isotopes of these di abases imply that they were likely derived from partial melting of the metasomatized subcontinental lithospheric mantle. Zircon U-Pb chronological results reveal that the crystallization of these granites occurred at around 780 Ma. When combined with the maximum depositional age of protolith of the Aksu Group metapsammite obtained by detrital zircon dating, the metamorphic age of the Aksu blueschist terrane is limited to a short duration of 800-780 Ma, which is similar to the syn-orogenic metamorphism and crustal melting in the NE Tarim margin constrained to 830-790 Ma. Structural and petrological analysis suggests that the granites underwent deformation and dynamic recrystallization, while the diabases did not. This likely reflects the post-orogenic processes followed by the extrusion of mafic dike swarm associated with lithospheric stretching. The composite dike highlights a rapid tectonic shift from orogeny to intraplate extension during the mid-Neoproterozoic (780-760 Ma). Widespread late Neoproterozoic intraplate mafic and A-type granitic magmatism occurred in the Tarim and its adjacent blocks (Central Tianshan, Yili, and Kazakhstan) along the southwestern Central Asian Orogenic Belt, indicating that these blocks shared a similar geodynamic evolution related to the breakup of Rodinia.