The Late Triassic–Early Jurassic Subduction System in the North Qiangtang: Insights Into the Closure Timing of the Jinsha Paleo‐Tethys Ocean and Continental Growth of the Central Tibetan Plateau

Abstract

As a significant branch of the eastern Tethys Ocean, the Jinsha Paleo‐Tethys Ocean has attracted widespread attention in the past decades. However, the closure timing of the Jinsha Ocean and the dominant mechanism of continental growth remain subjects of intense debate. This study presents new evidence of ridge subduction during 237–197 Ma, including high‐Mg rocks, adakites, Nb‐enriched basalts and normal arc rocks from the North Qiangtang terrane (NQT), central Tibetan Plateau. The identified high‐temperature, high‐oxygen fugacity magmatic belt, evidenced by the ribbon pattern of magnetic anomalies, reveals the blowtorch effect of a slab window obliquely crossing the NQT. Hf isotope data indicate that the Late Triassic–Early Jurassic ridge subduction promoted both the addition of depleted mantle and the recycling of enriched continental crust. In contrast, εHf(t) values of the Late Triassic igneous rocks display a continuous increase with time in the northern NQT but a decrease in the southern NQT, reflecting distinct slab geodynamics across the region. These observations, together with published regional data, suggest the Jinsha Ocean had not closed until the Early Jurassic (ca. 196 Ma). Meanwhile, the Late Triassic–Early Jurassic subduction system in the NQT was shaped by slab rollback and ridge subduction of the Jinsha Ocean to the north, and by subduction and closure of the Longmuco‐Shuanghu Ocean to the south. Our study highlights that crustal growth is dominated by accretionary orogenesis rather than collisional orogenesis, with ridge subduction and slab rollback being effective mechanisms of continental growth.