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

发布时间:2021-09-15 放大 缩小

 Abstract The 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 siliciclasticmatrix blockinmatrix mélange. We identified three different groups of sandstone within the Mugagangri Complex. Group 1 is volcaniclastic lithic (Q41F19L40, Lm16Lv77Ls7) and exhibits youngest UPb detrital zircon (YDZ) ages of 177170 Ma. Group 2 is lithoquartzose (Q67F6L27, Lm23Lv63Ls13) with YDZ ages of 237213 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 UPb 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 284246 Ma. During (and possibly prior to) Late Triassic time, the recycled orogenderived 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 arcderived sandstone (Group 1) was deposited and accreted through the northward subduction of BangongNujiang 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.
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