Jurassic Paleomagnetism of the Lhasa Terrane-Implications for Tethys Evolution and True Polar Wander

The drift history of the Lhasa terrane from Gondwana to Asia plays a crucial role in understanding the Tethys evolution and true polar wander (TPW). However, few reliable paleomagnetic results from Jurassic strata are currently available for reconstructing its northward journey. We performed a combined paleomagnetic and geochronological study on Bima Formation strata in the Xigaze area. Combined with previous results from the Sangri area, our results reveal a paleolatitude of 8 +/- 4 degrees S at similar to 180 Ma for the reference point (29.3 degrees N, 90.3 degrees E). Along with other paleomagnetic results from the Triassic to Cretaceous, our new results suggest that the Lhasa terrane motion accelerated from similar to 2 cm/yr during similar to 220-180 Ma to similar to 17 cm/yr during similar to 180-170 Ma. Paleolatitude information of the North Qiangtang terrane and Tethyan Himalaya is calculated from paleopoles that meet five criteria, which include (a) structural control, (b) well-determined rock age, (c) stepwise demagnetizations, (d) a minimum of 25 specimens or 8 sites are contained, and (e) robust field or reversal tests are provided. Both terranes also show significant acceleration during their northward motion, which may be related to oceanic slab subduction. Thus, all Gondwana-derived microcontinents seem to share a significant acceleration during their northward motion. In addition, recent paleomagnetic results from volcanic rocks dated at similar to 155 Ma subdivide the overall northward motion during similar to 170-130 Ma into two stages, which include a southward drift during similar to 170-155 Ma followed by northward motion during similar to 155-130 Ma. These results support the fast Late Jurassic TPW during a similar to 10 Myr time span. Plain Language Summary The Tibetan Plateau is composed of the Qiangtang, Lhasa, and Himalaya terranes that originate from Gondwana, which was an ancient supercontinent located mainly in the southern hemisphere. How these terranes moved northward from Gondwana to Asia remains unclear due to poor paleolatitude constraints. We provide paleomagnetic evidence to show that the Lhasa terrane was located at similar to 8 degrees S at similar to 180 million years ago (Ma). Together with reliable paleomagnetic data from Late Triassic (similar to 237-201 Ma) limestones and Middle Jurassic (similar to 174-163 Ma) sandstones, our results suggest a significant acceleration during Lhasa's northward motion at similar to 220-170 Ma. Reliable paleolatitude data show significant accelerations of the Lhasa, North Qiangtang, and Tethyan Himalaya terranes during their northward journey, which may be related to oceanic slab subduction. These significant accelerations may be a common feature of these Gondwana-derived microcontinents. The drift history of the Lhasa terrane during similar to 170-130 Ma can be subdivided into a southward drift during similar to 170-155 Ma and a subsequent northward drift during similar to 155-130 Ma. The yoyo-like drift motion of the Lhasa terrane near the equator before and after similar to 155 Ma supports a fast Late Jurassic pole motion event (named true polar wander) during a similar to 10 Myr time span.

Automated summary

The drift history of the Lhasa terrane from Gondwana to Asia is crucial for understanding the Tethys evolution and true polar wander. This study provides new paleomagnetic evidence that the Lhasa terrane was located at around 8 degrees S around 180 Ma and suggests a significant acceleration in its northward motion from 220-170 Ma.