Changes in crustal thickness of Zhongdian block, eastern Tibetan Plateau, and implications for formation and preservation of porphyry ore deposits

The eastern Tibetan Plateau has the highest topographic relief on Earth and is studded with abundant mineral reserves. However, the orogenic evolution and its link to mineral resources are unclear. The Zhongdian block, as the convergent center of several blocks during the final closure of the Paleotethys, is one of the most important regions for exploring the evolution of the eastern Tibetan Plateau. The geochemical parameters of intermediate-composition magmatic rocks can reflect mineral assemblages in the lower crust and can be used to constrain crustal thickness. Here, we show that the whole rock Sr/Y and (La/Yb)(N) and zircon Eu/Eu* values for the Late Triassic and Late Cretaceous intermediate to silicic magmatic rocks reveal two changes in crustal thickness of the Zhongdian block. The crustal thickness of the Zhongdian block increased to >70 km during ca. 230 to 210 Ma, while it decreased from >70 km to similar to 55 km during ca. 90 to 80 Ma. The two changes in crustal thickness could have benefited the formation of Late Triassic subduction-related porphyry copper deposits and Late Cretaceous collision-related porphyry molybdenum deposits. By quantitatively constraining the paleoelevation of the Zhongdian block, we interpret the existence of a paleoplateau (similar to 5500 m in elevation) during the Early Jurassic-Early Cretaceous and a relict peneplain (similar to 3500 m) during the Late Cretaceous to the present day. This is supported by the absence of Jurassic-Cretaceous strata and the decrease in the erosion rate during the Late Cretaceous. The slowing of the erosion rate caused by the decrease in elevation during the Late Cretaceous may be key to the preservation of these Mesozoic porphyry ore deposits. Quantifying crustal thickness is of great significance for understanding how orogenesis impacts elevation, magmatism, and mineralization in the eastern Tibetan Plateau.

Automated summary

This study reveals the changes in crustal thickness in the eastern Tibetan Plateau and their relationship with mineralization by analyzing the geochemical parameters of magmatic rocks in the Zhongdian block. The study also suggests the existence of a paleoplateau during the Early Jurassic to Early Cretaceous and a relict peneplain since the Late Cretaceous. The decrease in erosion rate during the Late Cretaceous is considered crucial for the preservation of Mesozoic porphyry ore deposits.