Geochronological research of the Lincang Batholith is one key scientific problem to discuss the tectonic evolution of the Tethys. Two granitic specimens were selected from the Mengku-Douge area in the Lincang Batholith to perform the LA-ICPMS Zircon U-Pb dating based on thorough review of petrological, geochemical, and geochronological data by the former scientists. Rock-forming age data of biotite granite specimen from Kunsai is about 220 Ma, the Norian age. However, the west sample from Mengku shows 230？Ma, the Carnian age. The later intrusion in Kunsai area located east to the Mengku area shows directly their uneven phenomena in both space and time and may indirectly reflect the space difference of the contraction-extension transformation period of the deep seated faults. Considering the former 40Ar/39Ar data and the outcrop in Mengku, the Lincang Batholith should have experienced one tectonic exhumation and regional subsidence cycle. The regional subsidence cycle has close relations to the expansion of the Meso Tethys. 1. Introduction The Sanjiang-Indochina region is one key area to study the evolution of the Tethys [1–10] (Figure 1). The Changning-Menglian zone was considered as the major faunal break between Gondwanan assemblage to the west and Cathaysian to the east [11, 12]. The subduction-related magmatism occurred along the western edge of the Lanping-Simao-Indochina terrane throughout the Triassic and the closure of Palaeo-Tethys [12, 13]. The Lincang Batholith extends ~370？km from north to south, covering the Chiangrai-Chiang Mai region of Thailand, with an area of more than 10000？km2 (Figure 2). It has been shown by many authors that there is great mineral potential [14]. Figure 1: Map of plate tectonics and ore-forming metals in the southern Sanjiang and Indochina peninsula. (a) Scope of Tethys and zone divisions; (b) research area and distribution of major metals: (1) Changning-Menglian-Chiangmai PaleoTethys Suture (time and space after [ 1, 21, 22]); (2) Ailaoshan-Song Ma Paleo-Tethys Suture (time and space after [ 2, 6, 8]); (3) Bangong Co-Nujiang Meso-Tethys Suture (time and space after [ 5]); (4) Yanlung Tsangpo-Naga-Arakan New-Tethys Suture (time and space after [ 22, 23]); (F1) Nujiang-Saging Fault Zone; (F2) Ranong Fault Zone; (F3) Three Tower Fault Zone; (F4) Tonle Sap Fault Zone; (F5) ？à Lat-Bianhe Fault Zone; (F6) ？iên Biên Phú Fault Zone; (F7) Changshan-Da Nang Fault Zone; (F8) Lanjiang Fault Zone; (F9) Ailaoshan-Red River Fault Zone; (F10) Xianshuihe-Xiaojiang Fault Zone; (F11) Lancang-Jinghong Fault Zone. Figure 2: Regional
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