Continental crustal growth and reworking during plate convergence: Implications from Late Mesozoic magmatism in the Southern Qiangtang Terrane, Tibetan Plateau

The timing, processes, and mechanisms of crustal growth in convergent continental margin terranes remain pivotal yet enigmatic questions in solid Earth science. The Southern Qiangtang terrane in central Tibet underwent significant Mesozoic crustal growth and reworking, driven by the northward subduction of the Bangong-Nujiang Tethyan Ocean. However, the specific processes and mechanisms involved remain debated, primarily between the traditional subduction zone model and the mélange-diapir model. This study presents geochronological, geochemical, and Sr-Nd-Hf isotopic data for intrusive rocks from the Jiacuo area in the western Southern Qiangtang terrane. We propose that the Songxue, Kunchukechu Co, and Liqunshan plutons were generated by partial melting of the lower crust, triggered by the heating from a hydrated mantle wedge-itself hydrated by slab-dehydration-followed by varying degrees of magma mixing. In contrast, the Rehung pluton formed in a slab roll-back setting, where upwelling asthenosphere facilitated the ascent of remelted oceanic plateau materials that subsequently mixed with crustally-derived magmas. For the first time, we utilize the spatiotemporal variations in ε_Hf(t), ε_Nd(t), Sr/Y, and (La/Yb)_N ratios of Late Mesozoic magmatic rocks to divide the crustal evolution of the Southern Qiangtang terrane into three distinct stages: partial melting of ancient lower crust (180-160 Ma), crust-mantle magma mixing (160-140 Ma), and upwelling of remelted oceanic plateau materials (130-100 Ma). These findings provide critical new insights into the Late Mesozoic crustal evolution of the Southern Qiangtang terrane and elucidate the genetic connections between slab dynamics and crustal growth and reworking.