Mesozoic Subduction Accretion History in Central Tibet Constrained From Provenance Analysis of the Mugagangri Subduction Complex in the Bangong‐Nujiang Suture Zone

Abstract

AbstractThe Mugagangri Complex in central Tibet provides a record of the subduction accretion history between the Lhasa and Qiangtang terranes and consists of coherent sedimentary sequences, strongly dismembered formations, and siliciclastic‐matrix block‐in‐matrix mélange. We identified three different groups of sandstone within the Mugagangri Complex. Group 1 is volcaniclastic lithic (Q41F19L40, Lm16Lv77Ls7) and exhibits youngest U‐Pb detrital zircon (YDZ) ages of 177–170 Ma. Group 2 is litho‐quartzose (Q67F6L27, Lm23Lv63Ls13) with YDZ ages of 237–213 Ma. Groups 1 and 2 show provenance affinity with the Qiangtang terrane to the north. Group 3 is similar to Group 2 in detrital mode (Q67F2L31) and U‐Pb detrital zircon age spectra but is distinguished by more sedimentary fragments (Lm17Lv24Ls59), a 1,200–1,100 Ma age peak that is possibly characteristic of the Lhasa terrane to the south and YDZ ages of 284–246 Ma. During (and possibly prior to) Late Triassic time, the recycled orogen‐derived sandstones, including Group 2 and possibly Group 3, were deposited on the ocean floor adjacent to the Qiangtang terrane. During the early Middle Jurassic, the arc‐derived sandstone (Group 1) was deposited and accreted through the northward subduction of Bangong‐Nujiang oceanic lithosphere. During the late Middle to Late Jurassic, Groups 2 and 3 may have been deposited in a trench or trench slope basin, with Group 3 receiving detritus from both the Lhasa and Qiangtang terranes. These three groups of sandstone and ocean plate stratigraphy were mixed in the mélange during the accretion between the Lhasa and Qiangtang terranes.