Controls of variable crustal thicknesses on Late Triassic mineralization in the Yidun Arc, Eastern Tibet

Abstract Modern arc-related granitic magmas have variable Sr/Y ratios and metal contents, depending on the thickness of the arc crust on the global scale. However, whether this is true of ancient arcs on a regional scale is still unclear. The Yidun Arc is a Triassic continental arc in Eastern Tibet that has magmatic and mineralization characteristics varying between the northern and southern Yidun Arcs during the Triassic. Several models have been proposed to explain these differences, however, these models are still controversial. To this end, we investigated the petrogenesis of the Late Triassic Xiuwacu intrusion, which is located between the northern and southern Yidun Arcs. The zircon U-Pb dating and Sr-Nd-Hf-O isotopes indicate that the Late Triassic Xiuwacu intrusion was emplaced at 215.6 ± 2.2 Ma and was predominately derived from partial melting of an enriched metastasized mantle combined with amphibole dominated fractionation and a small amount of crustal assimilation. Comparing the Late Triassic Xiuwacu intrusion with other volcanic rocks and intrusions in the Yidun Arc indicates that the Late Triassic Xiuwacu intrusion has a source similar to that of igneous rocks in the southern Yidun Arc. In addition, volcanic rocks and porphyries in the southern Yidun Arc have high Dy/Yb (1.8–2.6, mostly > 2.0) and Sr/Y (24-120) ratios, lack or have slightly negative Eu anomalies, and exhibit calc-alkaline trends, indicating that garnet, amphibole, and magnetite crystalized from their magma source under high pressure. The volcanic rocks in the northern Yidun Arc have low Dy/Yb (1.3–2.2, mostly