Xianwei Jiao:Middle Jurassic Paleolatitude of the Tethyan Himalaya: New Insights Into the Evolution of the Neo-Tethys Ocean【JGR,2023】
Sep 4, 2023 Views:398

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.

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