Middle Jurassic Paleolatitude of the Tethyan Himalaya: New Insights Into the Evolution of the Neo‐Tethys Ocean.

The paleogeography of the Tethyan Himalaya (TH) during the Mesozoic is vital to constrain the evolutionary history of the Neo‐Tethys Ocean, but reliable paleomagnetic data from Jurassic rocks in this area are scarce. Here, we report the first high‐quality paleomagnetic results from the Middle Jurassic (∼175–173 Ma) Lanongla Formation limestones in the Nyalam area of the TH. For most specimens, stepwise thermal or hybrid demagnetization reveals two well‐defined magnetization components. A low‐temperature component, which is isolated between natural remanent magnetization and 200–300°C, is consistent with the present geomagnetic field direction. A high‐temperature component, which is isolated between 300–350°C/10–25 mT and 500–580°C/60–120 mT, passes fold tests at the 95% and 99% confidence level, indicating a prefolding primary magnetization. The tilt‐corrected site‐mean direction for 28 paleomagnetic sites is Ds = 331.0° and Is = −49.9° with α95 = 2.7°, which provides a Fisherian site‐mean paleopole at 23.7°N, 292.9°E with A95 = 2.8° and a paleolatitude of 31.7 ± 2.8°S for the Nyalam study area (28.6°N, 86.1°E). A comparison between the reliable Middle Jurassic‐Early Cretaceous poles obtained from the TH and those observed from the Lhasa terrane reveals that the Neo‐Tethys Ocean for the reference point (29.1°N, 86.1°E) had a latitudinal width of 3,500 ± 1,000 km at ∼174 Ma, reached its greatest width of 7,000 ± 1,000 km at ∼137 Ma, and had an average latitudinal spreading rate of ∼10.4 cm/year during ∼174–137 Ma. Plain Language Summary: The Neo‐Tethys Ocean here refers to the prehistoric ocean that existed between the Lhasa terrane to the north and the Indian plate to the south during the much of the Mesozoic and early Cenozoic. Knowledge of the development of the Neo‐Tethys Ocean is crucial to understanding the evolution of the Himalayas and Tibetan Plateau. However, the opening of the Neo‐Tethys Ocean remains controversial. In this work, we report what we consider is the first high‐quality Middle Jurassic age paleopole from the Tethyan Himalaya, which shows that the Nyalam area was located at 31.7 ± 2.8°S at ∼174 Ma and that the Neo‐Tethys Ocean was at least ∼3,500 km wide in a N–S direction at that time. Key Points: The Nyalam area of the Tethyan Himalaya (TH) was located at 31.7 ± 2.8°S at ∼174 MaThe Neo‐Tethys Ocean opened a latitudinal width of ∼3,500 km at ∼174 Ma and reached its greatest width of ∼7,000 km at ∼137 MaThe Neo‐Tethys Ocean had an average latitudinal spreading rate of ∼10.4 cm/year during ∼174–137 Ma [ABSTRACT FROM AUTHOR]