Provenance of Middle Triassic sediments in the Southern Youjiang Basin: Insights from detrital zircon geochronology and tourmaline geochemistry

Abstract

The sedimentary provenance and tectonic setting of the Youjiang Basin in southwestern China remain debated, particularly regarding the relative contributions of the Indochina Block and the southeastern margin of the South China Block (SCB) during the Indosinian Orogeny. This study integrates detrital zircon U–Pb geochronology and tourmaline geochemistry from Middle Triassic turbidites of the Baifeng Formation to constrain sediment provenance and tectonic evolution during the Indosinian Orogeny. A total of 189 concordant zircon ages reveal four major age populations at 2100–1500 Ma, 1200–730 Ma, 570–410 Ma and 375–234 Ma, accounting for approximately 85% of the concordant zircon population. The coexistence of abundant Late Palaeozoic–Early Mesozoic zircons with substantial Neoproterozoic and Early Palaeozoic components suggests input from a source region characterised by both Late Palaeozoic–Early Mesozoic arc‐related magmatism and older continental crust. Tourmaline compositions further indicate source contributions from Li‐poor granitoids, pegmatites, alaskites and metasedimentary rocks. Zircon CA–DA characteristics indicate significant input from relatively young magmatic sources, consistent with sediment generation in a convergent continental‐margin setting. Integrated provenance evidence suggests that the Middle Triassic Baifeng Formation sediments were predominantly derived from a Late Palaeozoic–Early Mesozoic continental arc along the southeastern margin of the SCB. These results provide new constraints on sediment dispersal patterns and tectonic evolution of South China during the Indosinian Orogeny and highlight the role of Paleo‐Pacific‐related continental arc processes in basin development.