Paleolatitudes of the Tibetan Himalaya from primary and secondary magnetizations of Jurassic to Lower Cretaceous sedimentary rocks

Abstract

The Tibetan Himalaya represents the northernmost continental unit of the Indian plate that collided with Asia in the Cenozoic. Paleomagnetic studies on the Tibetan Himalaya can help constrain the dimension and paleogeography of ''Greater India,'' the Indian plate lithosphere that subducted and underthrusted below Asia after initial collision. Here we present a paleomagnetic investigation of a Jurassic (limestones) and Lower Cretaceous (volcaniclastic sandstones) section of the Tibetan Himalaya. The limestones yielded positive fold test, showing a prefolding origin of the isolated remanent magnetizations. Detailed paleomagnetic analyses, rock magnetic tests, end-member modeling of acquisition curves of isothermal remanent magnetization, and petrographic investigation reveal that the magnetic carrier of the Jurassic limestones is authigenic magnetite, whereas the dominant magnetic carrier of the Lower Cretaceous volcaniclastic sandstones is detrital magnetite. Our observations lead us to conclude that the Jurassic limestones record a prefolding remagnetization, whereas the Lower Cretaceous volcaniclastic sandstones retain a primary remanence. The volcaniclastic sandstones yield an Early Cretaceous paleolatitude of 55.5 S [52.5 S, 58.6 S] for the Tibetan Himalaya, suggesting it was part of the Indian continent at that time. The size of ''Greater India'' during Jurassic time cannot be estimated from these limestones. Instead, a paleolatitude of the Tibetan Himalaya of 23.8 S [21.8 S, 26.1 S] during the remagnetization process is suggested. It is likely that the remagnetization, caused by the oxidation of early diagenetic pyrite to magnetite, was induced during 103-83 or 77-67 Ma. The inferred paleolatitudes at these two time intervals imply very different tectonic consequences for the Tibetan Himalaya.

Paleomagnetic results from the Early Cretaceous Lakang Formation lavas: Constraints on the paleolatitude of the Tethyan Himalaya and the India–Asia collision

“…For example, Klootwijk and Bingham (1980) reported paleomagnetic data from the Early Cretaceous ThakkholaDzong Formation (Fm) sandstone (TD) in the Thakkhola basin of Nepal. This sandstone paleopole is located at 12.0 • N, 289.0 • E, corresponding to a southern mid-latitude that is very consistent with that expected from the apparent polar wander paths (APWP) of India (e.g., van Hinsbergen et al, 2012;Yang et al, 2014;Huang et al, 2015c). Furthermore, Huang et al (2015c) obtained a farther south latitude of ∼55 • S from the Early Cretaceous Wölong Fm volcaniclastic stones (WL).…”

“…This sandstone paleopole is located at 12.0 • N, 289.0 • E, corresponding to a southern mid-latitude that is very consistent with that expected from the apparent polar wander paths (APWP) of India (e.g., van Hinsbergen et al, 2012;Yang et al, 2014;Huang et al, 2015c). Furthermore, Huang et al (2015c) obtained a farther south latitude of ∼55 • S from the Early Cretaceous Wölong Fm volcaniclastic stones (WL). These results imply that neither a wide intra-ocean nor a large north-south gap existed between the Tethyan Himalaya and India during the earliest Cretaceous.…”

“…Comparing 48.1 • ± 5.7 • S calculated for the southernmost margin of the Tethyan Himalaya with the 50.2 • ± 2.8 • S predicted by the Indian APWP at 130 Ma shows a paleolatitude difference of 2.1 • ± 6.4 • (230 ± 710 km), revealing the same conclusion that the Tethyan Himalaya was part of a contiguous Indian subcontinent at 134-130 Ma and there was no wide ocean separating the Indian craton from the Tethyan Himalaya at 134-130 Ma (e.g., Klootwijk and Bingham, 1980;van Hinsbergen et al, 2012;Yang et al, 2014;Huang et al, 2015c) (Fig. 8).…”

“…8). Significantly, such a Late Cretaceous extension has also been inferred from alkaline volcanic rocks and volcaniclastic strata exposed in a broad belt of the Tethyan Himalaya from northern India to southeastern Tibet (e.g., Gradstein et al, 1991;Gibling et al, 1994;Jadoul et al, 1998;Zhu et al, 2009;Hu et al, 2010). Furthermore, provenance analyses of Lower Cretaceous through Lower Miocene strata in Nepal showed that the Amile Fm (Cretaceous-Early Eocene) detrital zircons exhibit U-Pb ages characteristic of Indian cratonic sources without signs of derivation from Tethyan Himalayan strata, whereas the Bhainskati Fm (Middle-Late Eocene) detrital zircon patterns are typical of Tethyan Himalayan strata (e.g., DeCelles et al, 2004DeCelles et al, , 2014Najman et al, 2005).…”

“…Paleomagnetic data indicate more than 1500 km of separation between the southern edge of the Tethyan Himalaya and cratonic India when it first collided with the southern margin of Asia (e.g., Patzelt et al, 1996;Yi et al, 2011;van Hinsbergen et al, 2012). Notably, although paleomagnetic data have been obtained from the Early Cretaceous Tethyan Himalaya (e.g., Klootwijk and Bingham, 1980;Appel and Li, 1988;Appel et al, 1998;Huang et al, 2015c), they provided quite different paleolatitudes. For example, Klootwijk and Bingham (1980) reported paleomagnetic data from the Early Cretaceous ThakkholaDzong Formation (Fm) sandstone (TD) in the Thakkhola basin of Nepal.…”