Late Paleozoic tectonic switching and metallogenic evolution of the southern Yili arc terrane, NW China

Abstract

Recognition of tectonic switching is of great significance for understanding the formation and evolution of ancient accretionary orogenic belts and can provide insights into metallogenic evolution. The western Tianshan orogenic belt, which lies within the southern Central Asian Orogenic Belt (CAOB), experienced a prolonged tectono-magmatic evolution during the late Paleozoic in response to evolution of the Paleo-Asian Ocean. The aim of this contribution is to constrain the subduction process and timing of tectonic switching from subduction to collision in southern parts of the western Tianshan. To address this, we present the results of an integrated investigation of whole-rock major and trace element and Sr-Nd-Hf isotope data, together with zircon U-Pb ages for late Paleozoic volcanic rocks from the southern Yili arc terrane of the southern western Tianshan. Based on the temporal-spatial distribution of different compositions of volcanic rocks, three distinct episodes of magmatism have been recognized, including: 1) ∼ 380 – ∼340 Ma, this episode of magmatism has high Ce/Y ratios of basalts and Ho/Yb ratios of felsic rocks, and show large variations in εHf(t) (−9.6 to + 15.6) and εNd(t) (−5.2 to + 5.4) values, which is interpreted to be originated from a mantle source with variable input of slab-derived components incorporated in a trench advance setting; 2) ∼ 340 – ∼320 Ma, this episode of magmatism shows low Ce/Y ratios of basalts and Ho/Yb ratios of felsic rocks, and relatively higher εHf(t) (−3.8 to + 14.6) and εNd(t) (−1.5 to + 5) values, reflecting crust-mantle interactions and likely formation in a back-arc basin environment; 3) ∼ 320 – ∼300 Ma, this episode of magmatism has Ce/Y ratios of basalts and Ho/Yb ratios of felsic rocks, and mostly positive εHf(t) (−1.1 to + 14.5) and εNd(t) (+1.6 to + 8.4) values, suggesting continent–continent collision between the northern Tarim Craton and the southern limb of the Kazakhstan composite continent (i.e., Yili and Chinese Central Tianshan Block). Consistently, the two tectonic switching events (ca. 340 Ma and ca. 320 Ma) were temporally associated with skarn Zn-Pb and orogenic Au mineralization in southern Yili arc terrane, respectively. This study presents an example of multiple tectonic switching and metallogenic evolution in hot accretionary orogens.