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A combined paleomagnetic and geochronological investigation has been performed on Cretaceous rocks in southern Qiangtang terrane (32.5°N, 84.3°E), near Gerze, central Tibetan Plateau. A total of 14 sites of volcanic rocks and 22 sites of red beds have been sampled. Our new U–Pb geochronologic study of zircons dates the volcanic rocks at 103.8 ± 0.46 Ma (Early Cretaceous) while the red beds belong to the Late Cretaceous. Rock magnetic experiments suggest that magnetite and hematite are the main magnetic carriers. After removing a low temperature component of viscous magnetic remanence, stable characteristic remanent magnetization (ChRM) was isolated successfully from all the sites by stepwise thermal demagnetization. The tilt-corrected mean direction from the 14 lava sites is D = 348.0°, I = 47.3°, k = 51.0, α 95 = 5.6°, corresponding to a paleopole at 79.3°N, 339.8°E, A 95 = 5.7° and yielding a paleolatitude of 29.3° ± 5.7°N for the study area. The ChRM directions isolated from the volcanic rocks pass a fold test at 95% confidence, suggesting a primary origin. The volcanic data appear to have effectively averaged out secular variation as indicated by both geological evidence and results from analyzing the virtual geomagnetic pole (VGP) scatter. The mean inclination from the Late Cretaceous red beds, however, is 13.1° shallower than that of the ~ 100 Ma volcanic rocks. After performing an elongation/inclination analysis on 174 samples of the red beds, a mean inclination of 47.9° with 95% confidence limits between 41.9° and 54.3° is obtained, which is consistent with the mean inclination of the volcanic rocks. The site-mean direction of the Late Cretaceous red beds after tilt-correction and inclination shallowing correction is D = 312.6°, I = 47.7°, k = 109.7, α 95 = 3.0°, N = 22 sites, corresponding to a paleopole at 49.2°N, 1.9°E, A 95 = 3.2° (yielding a paleolatitude of 28.7° ± 3.2°N for the study area). The ChRM of the red beds also passes a fold test at 99% confidence, indicating a primary origin. Comparing the paleolatitude of the Qiangtang terrane with the stable Asia, there is no significant difference between our sampling location in the southern Qiangtang terrane and the stable Asia during ~ 100 Ma and Late Cretaceous. Our results together with the high quality data previously published suggest that an ~ 550 km N–S convergence between the Qiangtang and Lhasa terranes happened after ~ 100 Ma. Comparison of the mean directions with expected directions from the stable Asia indicates that the Gerze area had experienced a significant counterclockwise rotation after ~ 100 Ma, which is most likely caused by the India–Asia collision. [ABSTRACT FROM AUTHOR]

To further constrain the India–Asia collisional process, a combined paleomagnetic and geochronologic study has been carried out on the Upper Cretaceous Jingzhushan Formation redbeds and the Lower Cretaceous Dianzhong Formation volcanic rocks dated at ~ 121–117 Ma from the Cuoqin area in the central Lhasa terrane. Stepwise thermal demagnetization successfully isolated reliable characteristic remanent magnetization (ChRM) directions that include dual polarity and pass positive fold tests at 95% and 99% confidence levels, indicating prefolding primary magnetizations. The tilt-corrected site-mean direction for 33 redbed sites is D = 316.8°, I = 30.2° with α 95 = 5.4°, corresponding to a paleopole at 49.0°N, 344.3°E with A 95 = 5.3°, and the other for 12 volcanic sites is D = 350.5°, I = 25.5° with α 95 = 7.7°, corresponding to a paleopole at 70.5°N, 292.9°E with A 95 = 7.4°. Our new paleomagnetic results, together with reliable Cretaceous paleomagnetic data obtained from the Lhasa terrane, demonstrate that the southern margin of Asia was located at ~ 15.1°N during the Cretaceous. Comparison with the apparent polar wander paths (APWP) of India and the Cretaceous–Paleocene paleopoles of the Himalayan terrane suggests that the India–Asia collision was likely a complex process, which consists of the collision of the Lhasa and Himalayan terranes at 54.0 ± 2.1 Ma, the longtime subduction of an intra-oceanic basin between the Himalayan terrane and the Indian craton from ~ 54.0 to ~ 40.4 Ma, and the collision of the Himalayan terrane and the Indian craton at 40.4 ± 4.1 Ma. Comparing with the Late Cretaceous average pole of the East Asia APWP reveals that a latitudinal convergence of 780 ± 240 km has taken place between the Lhasa terrane and East Asia (the Hexi corridor) since the India–Asia collision; the amount of latitudinal shortening deduced from paleomagnetic data is very consistent with the 600–1000 km accommodated by the Cenozoic fold and thrust belts between the Lhasa terrane and Hexi corridor. [ABSTRACT FROM AUTHOR]

During the Albian and Cenomanian, the Earth underwent profound climatic and oceanographic changes that were recorded in sedimentary successions on a global scale. Carbon isotope records spanning this time interval have been established in the western Tethys, eastern Pacific and North Atlantic Oceans, but not yet in the eastern Tethys Ocean. In this paper, we present biostratigraphic, chemostratigraphic and cyclostratigraphic characteristics of the uppermost Albian–lowermost Cenomanian in an eastern Tethyan section (Youxia, southern Tibet). Based on calcareous nannofossil biozones and the bulk rock δ 13 C curve, the Albian-Cenomanian boundary interval (ACBI) was identified and correlated to the western Tethys and Atlantic Oceans. In the Youxia section, δ 13 C values range from approximately 0‰ to +1.3‰ (−0.03‰ to +1.31‰). Four subevents (a, b, c and d) were distinguished in the ACBI carbon isotope curve via correlation with other sections. Based on a spectral analysis of the carbonate content, we recognized Milankovitch short eccentricity (~100 kyr) and precession (22.2 kyr) cycles, suggesting that orbital variations modulated depositional processes. The duration of the ACBI was estimated at ~311 kyr, while OAE 1d lasted for ~233 kyr in the eastern Tethys Ocean, consistent with the duration calculated from Atlantic Ocean records. [ABSTRACT FROM AUTHOR]

The evolution of the Neo-Tethys Ocean had a profound effect on global climate change and the evolution of life. To better constrain the Cretaceous paleogeographic position of the Tethyan Himalaya and evolution of the Neo-Tethys Ocean, combined paleomagnetic and detrital zircon U Pb geochronological research was performed on samples from the Gyabula Formation, constrained at ca. 117.7–94.4 Ma, in the Zhongba area of the northern Tethyan Himalaya. Both positive fold and reversal tests combined with a maximum grouping at 106% unfolding indicate that the high-temperature component directions were acquired before folding and were most likely of primary origin. The tilt-corrected directions yielded a paleopole at 29.2°N, 280.5°E with A 95 = 5.1° and a corresponding paleolatitude of −29.0° ± 5.1°N for the sampled area (29.7°N, 84.0°E). No significant inclination shallowing was identified from the sampled cherts. Comparison of the observed paleolatitude with those expected from the Indian craton indicated that an 840 ± 670 km north-south distance existed between the northern Tethyan Himalaya and the Indian craton for the reference point (29.7°N, 84.0°E). Because of the anticlockwise rotation of the Indian craton, this amounts to a crustal extent of 1130 ± 900 km at ca. 106 Ma, which represents the amount of north-south crustal shortening. Our new results, together with reliable Cretaceous paleomagnetic data obtained from the Tethyan Himalaya, indicate that no wide oceanic basin extended between the Tethyan Himalaya and Indian craton at ca. 106–75 Ma and that there was still a contiguous Indian subcontinent. • The Zhongba area of the northern Tethyan Himalaya (TH) was located at 29.0° ± 5.1°S at ca. 117.7–94.4 Ma • 1130 ± 900 km of north-south shortening occurred between the northern Tethyan Himalaya and the Indian craton • No wide oceanic basin extended between the TH and the Indian craton at ca. 106–75 Ma [ABSTRACT FROM AUTHOR]