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The Amdo microcontinent which separates the Qiangtang terrane to the north and the Lhasa terrane to the south is a key terrane for reconstructing the tectonic evolution of Central Tibet. We report the new finding of retrograde eclogites within the Amdo microcontinent in this study. The eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, rutile and quartz and underwent a four‐stage metamorphic evolution, including a peak eclogite facies stage (M1) at ~20–24 kbar and 580–620°C, followed by an HP granulite facies decompression stage (M2) at ~13–15 kbar and 750–780°C, a subsequent MP‐UHT granulite facies heating stage (M3) at 8–10 kbar and >840°C and a final amphibolite facies retrogression (M4) at 5.3–6.0 kbar and 560–580°C. The eclogites exhibit rare earth element distribution patterns and trace element abundances similar to those of N‐MORB and arc‐related volcanics, with depleted whole‐rock εNd(t) values of 3.4 to 4.2, and are inferred to have formed in a back‐arc basin tectonic setting. Zircon and rutile U–Pb dating yields a protolith age of 226 ± 5 Ma, a peak eclogite facies metamorphic age of 190 ± 1 Ma, an HP granulite facies metamorphic age of 179 ± 1 Ma and an amphibolite facies retrograde age of 172 ± 1 Ma. The clockwise P–T–t paths and the oceanic protolith signature of retrograde eclogites suggest that part of the back arc basin was subducted to depths of ~80 km. Tectonic erosion associated with the subduction of the Amdo microcontinent beneath the Tethys Ocean accounts for the deep subduction of the back‐arc basin and the absence of arc magmatic rocks in the northern Amdo microcontinent. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau is located in the eastern part of the Tethys-Himalayan megatectonic domain and consists of a series of microplates that successively accreted to the southern edge of the Eurasian Continent. These microplates have undergone complex evolutionary processes during rifting, drift and collision. The gravity and magnetic anomalies show that the anomaly characteristics on the Tibetan Plateau is significantly different in the north-south direction, from the Qaidam Microplate to the Lhasa Microplate. In this paper, we apply an improved Logistic Filter method, combined with the upward continuation of gravity anomalies, to identify multi-scale tectonic boundaries in the Tibetan Plateau region. The results show that the edge detection results correspond well in space with fracture zones and suture/ophiolite zones. Also, there are clear discontinuities along both sides of the middle and western sections of the Bangong-Nujiang Suture Zone and the eastern section of the Jinshajiang-Ailaoshan Suture Zone. We refined the boundaries of five microplates, including the South and North Qiangtang and the South, Central and North Lhasa, in the southern Tibetan Plateau. Then, we analyzed the evolutionary processes of these microplates and the transformation of the types to which the microplates belonged during different historical periods by combining relevant evidences from other geological records and plate reconstruction. These microplates are strongly related to the evolutionary history of the Tethys Ocean. The closure of the Neo-Tethys Ocean triggered a large-scale orogeny between the Indo-Asian continents, and these microplates were eventually accreted in the orogenic belt. We analyze the formation patterns and boundary types of microplates in the evolutionary process and then divide into three stages, i.e., rifting-derived, accretion-derived, and subduction-derived stages. The transformation patterns of microplate types at different stages provide a new perspective for the study of the evolution of mega-orogenic belts. • Tectonic interpretation and microplate division of the Tibetan Plateau with gravity and magnetic data. • Multi-scale edge detection at different depths on the Tibetan Plateau by the improved Logistic Filter method. • A transformation pattern of microplate types during the evolution of Qiangtang and Lhasa microplates. [ABSTRACT FROM AUTHOR]