Paleomagnetic and Chronologic Data Bearing on the Permian/Triassic Boundary Position of Qamdo in the Eastern Qiantang Terrane: Implications for the Closure of the Paleo‐Tethys.

The tectonic evolution of the eastern Paleo‐Tethys in the Three‐Rivers headwater region remains uncertain, especially because of the lack of quality paleomagnetic data from the east Eastern Qiangtang Terrane (EQT). Here, we present an integrated paleomagnetic and zircon U‐Pb geochronologic study of the Gadikao Formation (Fm.) volcanic rocks in the EQT. This previously assumed Carboniferous or Permian rock unit is now zircon U‐Pb dated to ∼254–248 Ma. Our new high quality (29 sites and 257 samples) inferred primary paleomagnetic results yield a robust Permo‐Triassic boundary paleopole of 59.7°N and 228.2°E (A95 = 3.3°), with a paleolatitude of 10.0 ± 3.3°N for the study area. Integrated with other reliable Permo‐Triassic paleomagnetic data of the EQT and the Tarim Block and other lines of geologic evidence, we propose that the EQT drifted continuously northward during 300–200 Ma and the Paleo‐Tethys Ocean probably closed at ∼232–220 Ma around the Qamdo region, most likely at 230 Ma. Plain Language Summary: The drift history of the Qiangtang Terrane is the key to understand the evolution of the "Proto‐Tibet" and the Paleo‐/Meso‐Tethys Oceans, which is still under debate. In this work, we provide U‐Pb zircon data to constrain (254–248 Ma) a high quality paleomagnetic pole (59.7°N, and 228.2°E, with A95 = 3.3°) for the EQT, which was located at ∼10.0°N during ∼254–248 Ma. Integrated with other available lines of evidence, we propose that the EQT drifted continuously northward during the Permian and Triassic and collided with the Songpan‐Ganzi/Tarim Terrane, resulting in the closure of the Paleo‐Tethys Ocean around the Qamdo region during ∼232–220 Ma, most likely at about 230 Ma. Key Points: The previous upper Paleozoic Gadikao Formation yields high precision Zircon U‐Pb dates from ∼254 to 248 MaThe volcanic rocks yield a robust Permo‐Triassic boundary paleopole of 59.7°N and 228.2°E (A95 = 3.3°)The closure of the Paleo‐Tethys Ocean around Qamdo is best estimated at ∼232–220 Ma, mostly likely at ∼230 Ma [ABSTRACT FROM AUTHOR]