Lower Cretaceous turbidites in the Shiquanhe-Namco Ophiolite Melange Zone, Asa area, Tibet: Constraints on the evolution of the Meso-Tethys Ocean

Turbidites from the Shiquanhe-Namco Ophiolite Melange Zone (SNMZ) record critical information about the tectonic affinity of the SNMZ and the evolutionary history of the Meso-Tethys Ocean in Tibet. This paper reports sedimentologic, sandstone petrographic, zircon U-Pb geochronologic, and clastic rocks geochemical data of newly identified turbidites (Asa Formation) in the Asa Ophiolite Melange. The youngest ages of detrital zircon from the turbiditic sandstone samples, together with similar to 115 Ma U-Pb concordant age from the tuff intercalation within the Asa Formation indicate an Early Cretaceous age. The sandstone mineral modal composition data show that the main component is quartz grains and the minor components are sedimentary and volcanic fragments, suggesting that the turbidites were mainly derived from a recycled orogen provenance with a minor addition of volcanic arc materials. The detrital U-Pb zircon ages of turbiditic sandstones yield main age populations of 170-120 Ma, 300-220 Ma, 600-500 Ma, 1000-700 Ma, 1900-1500 Ma, and similar to 2500 Ma, similar to the ages of the Qiangtang Terrane(age peak of 600-500 Ma, 1000-900 Ma, similar to 1850 Ma and similar to 2500 Ma) and the accretionary complex in the Bangong-Nujiang Ophiolite Zone (BNMZ) rather than the age of the Central Lhasa Terrane (age peak of similar to 300 Ma, similar to 550 Ma and similar to 1150 Ma). The mineral modal compositions, detrital U-Pb zircon ages, and geochemical data of clastic rocks suggest that the Asa Formation is composed of sediments primarily recycled from the Jurassic accretionary complex within the BNMZ with the secondary addition of intermediate-felsic island arc materials from the South Qiangtang Terrane. Based on our new results and previous studies, we infer that the SNMZ represents a part of the Meso-Tethys Suture Zone, rather than a southward tectonic klippe of the BNMZ or an isolated ophiolitic melange zone within the Lhasa Terrane. The Meso-Tethys Suture Zone records the continuous evolutionary history of the northward subduction, accretion, arc-Lhasa collision, and Lhasa-Qiangtang collision of the Meso-Tethys Ocean from the Early Jurassic to the Early Cretaceous. (C) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

Automated summary

Turbidites from the Asa Ophiolite Melange in Tibet provide critical information about the tectonic history and sediment sources of the region. Detrital zircon ages and mineral compositions suggest a mainly recycled orogen provenance with minor volcanic arc material inputs. The study indicates an Early Cretaceous age for the Asa Formation, with main detrital U-Pb zircon age populations ranging from 170 Ma to 2500 Ma.