Orogenic cyclicity and episodic tectono-magmatic processes in the formation of the Paleozoic northern Yili magmatic arc, Central Asian Orogenic Belt.

To understand the orogenic cyclicity that built the northern Yili magmatic arc in the southern Balhkash-Yili arc of the Central Asian Orogenic Belt, we synthesize its tectono-magmatic processes using new and existing U-Pb geochronological dates (228), Hf-in-zircon (1605 spots), bulk-rock geochemical data (1458), and Sr-Nd isotopic analyses (461) of magmatic rocks. Based on temporal-spatial distribution of magmatic rocks and their geochemical composition, four magmatic episodes (ca. 470-440 Ma, 420-380 Ma, 350-320 Ma, and 300-260 Ma) punctuated by a magmatic gap (ca. 440-420 Ma) and two high-flux magmatic pulses (ca. 380-350 Ma and 320-300 Ma) were recognized. These episodic magmatic processes are proposed to be dynamically associated with changes in configuration of the subducted Junggar oceanic slab, including 470-440 Ma initial subduction, 440-420 Ma flat subduction, 420-380 Ma retreating subduction, 380-350 Ma advancing subduction, and 350-320 Ma retreating subduction, followed by slab break-off in ca. 320-300 Ma and subsequent lithospheric delamination in a postcollisional setting during the Permian (ca. 300-260 Ma). In addition, tectonic transition (ca. 380 Ma and 320 Ma) from extension to compression were suggested to be closely related to the two phases of porphyry Cu mineralization events in the Balkhash-Yili arc. High crustal thickness and more mature arc evolution with prominent crust-mantle interaction may be responsible for the significant porphyry Cu endowment in the northern Balkhash-Yili arc. [ABSTRACT FROM AUTHOR]