Geochronology, Geochemistry and Geological Significance of the Early Paleozoic Waizuishan Pluton in the Southern Beishan Orogenic Belt

The Beishan Orogenic Belt, situated in the central segment of the southern margin of the Central Asian Orogenic Belt (CAOB), has undergone prolonged, multi-stage subduction and accretion. It represents a key region for reconstructing the tectonic evolution of the southern CAOB margin and the closure of the Paleo-Asian Ocean. The Early Paleozoic was a significant crustal evolution period for the Beishan Orogenic Belt, characterized by frequent magmatic activity. Previous studies primarily focused on the central-western part of the belt, reporting a magmatic flare-up at 450−420 Ma. This study presents systematic geochronological and geochemical investigations of the Waizuishan pluton, located on the southeastern edge of the Shuangyingshan-Huaniushan tectonic unit within the Beishan Orogenic Belt. The Waizuishan pluton mainly comprises quartz diorite (and granodiorite. Zircon U-Pb dating yielded crystallization ages of (427.1±3.4) Ma and (418.6±2.8) Ma. The rocks belong to the metaluminous series (A/CNK＜1), exhibiting calc-alkaline and magnesian affinities. They possess low total rare earth element (ΣREE) contents, are enriched in light rare earth elements (LREEs), and show weak negative Eu anomalies (δEu=0.72−0.86). Geochemically, they are enriched in large-ion lithophile elements (LILEs: e.g., Rb, Th, U, K, Pb) and depleted in high-field-strength elements (HFSEs: e.g., Nb, Ta, P, Zr, Ti). Zircon εHf(t) values range from −2.0 to 0.6, corresponding to Hf crustal model ages (T_DMC) of 1.53−1.36 Ga. The geochemical signatures indicate that the Waizuishan pluton is an I-type granite formed within a subduction-related continental margin igneous arc. It was derived predominantly from the remelting of Mesoproterozoic crustal material with minor contributions from mantle-derived components. Nearly contemporaneous magmatism occurred within all four tectonic units of the Beishan Orogenic Belt. Zircon Hf model ages from Paleozoic igneous rocks (500−350 Ma) exhibit prominent peaks at 1.5−1.4 Ga and 0.8−1.0 Ga, correlating with Mesoproterozoic (～1.4 Ga) and Neoproterozoic (～0.9 Ga) tectonothermal events. This suggests that the various tectonic units of the Beishan Orogenic Belt likely share a common source region. Comparisons with the Yili Block and Central Tianshan Block indicate that these three terranes show stronger affinities with the Baltica and Laurentia cratons, whereas they lack affinity with the Tarim Craton, as represented by the Dunhuang Block.