Paleomagnetic and Geochronologic Results of Latest Cretaceous Lava Flows From the Lhasa Terrane and Their Tectonic Implications

To position the Asian southern margin before the India-Asia collision, paleomagnetic and geochronologic studies were performed on the Dianzhong Formation lava flows from the Shiquanhe area of the westernmost Lhasa terrane (LT). Zircon U-Pb analyses dated the lava flows to 69.52.5Ma. The characteristic remanent magnetization directions contain antipodal polarities and pass fold tests, implying that they are primary magnetizations; this interpretation is supported by rock-magnetic analyses and petrographic observations. Forty-four site-mean directions were divided into 17 statistically independent direction groups. The group-mean direction after tilt correction is Ds=43.3 degrees, Is=30.3 degrees, k=28.0, (95)=6.9 degrees. The corresponding paleopole at 47.8 degrees N, 181.4 degrees E (A(95)=6.4 degrees) yields a paleolatitude of 16.6 degrees 6.4 degrees N for the Shiquanhe area of westernmost Tibet (32.34 degrees N, 80.12 degrees E). Consistent paleolatitudes for the southern margin of the LT calculated from the western and central part of the LT indicate that the leading edge of the LT was aligned relatively W-E. When compared with the reference pole at 70Ma for Eurasia, this new paleopole suggests that crustal shortening between the Shiquanhe area and stable Asia was 1,500800km. This is supported by the crustal shortening (600-1,000km) absorbed by Cenozoic thrust and fold belts within this area, indicating that the magnitude of crustal shortening within Asia north of the India-Asia suture zone was similar in the central and western part of the plateau

Paleomagnetic and Geochronological Results From the Zhela and Weimei Formations Lava Flows of the Eastern Tethyan Himalaya: New Insights Into the Breakup of Eastern Gondwana

The breakup of eastern Gondwana is among the hottest topics in the Earth sciences because of its effect on global climate during the Jurassic-Cretaceous, its influence on the evolution of life, and its importance to paleogeographic reconstruction. To better constrain the Jurassic and Cretaceous paleogeographic position of the Tethyan Himalaya and the breakup of eastern Gondwana, a combined paleomagnetic and geochronological study was performed on the Zhela and Weimei Formations lava flows, dated at similar to 138-135Ma, in the Luozha area of the eastern Tethyan Himalaya. Both positive fold and reversal tests together with a maximum grouping at 100% unfolding indicate that the characteristic remanent magnetization directions are primary magnetizations acquired before folding. The tilt-corrected directions yielded a paleopole at 0.9 degrees N, 293.4 degrees E with A(95)=7.0 degrees and a corresponding paleolatitude of 53.5 degrees S7.0 degrees S for the Luozha sampling area (28.9 degrees N, 91.3 degrees E), validating that the original erupted position of the Zhela and Weimei Formations lava flows was located in the center of the Kerguelen mantle plume. Our new results, together with the published paleomagnetic, geochronological, and geochemical results, demonstrate that the Comei-Bunbury large igneous province originated from the Kerguelen mantle plume. The temporal and spatial relationships between the Comei-Bunbury large igneous province and the Kerguelen mantle plume indicate that eastern Gondwana initially rifted at similar to 147Ma and that the Indian Plate fully separated from the Australian-Antarctic Plate before similar to 124Ma

Paleomagnetic Constraints on the Origin and Drift History of the North Qiangtang Terrane in the Late Paleozoic

To better constrain the origin and drift history of the North Qiangtang terrane (NQT), we report a well-dated paleomagnetic pole from the Late Permian volcanics of the NQT that appears to average out secular variation. Our new results yield a paleolatitude of -7.6 +/- 5.6 degrees N at -259 Ma for our sampling area, which confirms the NQT drifted northward during the Permian and Triassic periods. The equatorial paleolatitude of the NQT is similar to that of the coeval South China block, demonstrating that they were in close proximity. Combined with palaeontological and magmatic evidence, paleomagnetic constraints on the drift of the NQT in the Permian indicate that the NQT moved northward together with the South China block at this time. The paleolatitude evolution of the NQT implies that the NQT rifted from the northern margin of the Gondwana in the Devonian, which is earlier than the departure time of the South Qiangtang terrane. Plain Language Summary The Tibetan Plateau is composed of several different blocks that accreted to the southern margin of Asia. There are still several unanswered questions, such as the following: Where did these blocks originate? How did these blocks accrete to Asia? How did the oceanic basin evolve? In this work, we provide robust evidence to show that the Northern Qiangtang was located at equatorial latitude (-7.6 +/- 5.6 degrees N) during the Late Permian (similar to 259 Ma). The northward drift history together with features of the Northern Qiangtang and South China block indicates that they moved northward together during the Permian and that the Northern Qiangtang rifted from the northern margin of the Greater India margin of Gondwana during the Devonian