No abstract

No abstract

No abstract

The Gongjue basin from the eastern Qiangtang terrane is located in the transition region where the regional structural lineation curves from east‐west‐oriented in Tibet to north‐south‐oriented in Yunnan. In this study, we sampled the red beds in the basin from the lower Gongjue to upper Ranmugou formations for the first time covering the entire stratigraphic profile. The stratigraphic ages are bracketed within 53–43 Ma by new detrital zircon U‐Pb ages constraining the maximum deposition age to 52.5 ± 1.5 Ma. Rock magnetic and petrographic studies indicate that detrital magnetite and hematite are the magnetic carriers. Positive reversals and fold tests demonstrate that the characteristic remanent magnetization has a primary origin. The Gongjue and Ranmugou formations yield mean characteristic remanent magnetization directions of Ds/Is = 31.0°/21.3° and Ds/Is = 15.9°/22.0°, respectively. The magnetic inclination of these characteristic remanent magnetizations is significantly shallowed compared to the expected inclination for the locality. However, the elongation/inclination correction method does not provide a meaningful correction, likely because of syn‐depositional rotation. Rotations relative to the Eurasian apparent polar wander path occurred in three stages: Stage I, 33.3 ± 3.4° clockwise rotation during the deposition of the Gongjue and lower Ranmugou formations; Stage II, 26.9 ± 3.7° counterclockwise rotation during deposition of the lower and middle Ranmugou formation; and Stage III, 17.7 ± 3.3° clockwise rotation after 43 Ma. The complex rotation history recorded in the basin is possibly linked to sinistral shear along the Qiangtang block during India indentation into Asia and the early stage of the extrusion of the northwestern Indochina blocks away from eastern Tibet.

We carried out a paleomagnetic investigation on Permian volcanic rocks from central eastern Inner Mongolia, NE China, in order to identify the paleoposition of the North China and Songliao‐Xilinhot blocks during Permo‐Carboniferous times and thereby define the spatial‐temporal history of the eastern Paleo‐Asian Ocean (PAO). Two prefolding magnetization components were isolated from the Sanmianjing and Elitu Formations (~283–266 Ma) along the northern margin of North China block (NMNCB) and the Dashizhai Formation (~280 Ma) in the Songliao‐Xilinhot block (SXB). These two results suggest paleolatitudes of ~4.9°N for the SXB and ~22.3°N for the NMNCB. Previously published results are classified according to recently proposed models and evaluated for the influence of inclination shallowing. Combined with earlier multidisciplinary studies, we propose a tentative paleogeographic reconstruction model for the eastern Central Asian Orogenic Belt (CAOB) during the Late Carboniferous to Early Triassic times. Siberia was situated at middle‐high paleolatitudes (~45°–65°N), and the Central Mongolia‐Erguna and South Mongolia‐Xing'an blocks had a middle latitude (~30°–45°N) from the Late Carboniferous to Early Permian. By the Late Permian to Early Triassic (~250 Ma), there was no significant latitudinal difference between the eastern CAOB blocks. Final closure of the eastern PAO along both the Hegenshan‐Heihe and Solonker sutures took place followed by the formation of Cinamuria.

No abstract

The tectonic blocks that comprise present-day East Asia were amalgamated with Laurussia following the final closure of the Paleo-Asian and Paleo-Tethys oceans in late Paleozoic and Mesozoic times. These events allowed Pangea to reach its maximum packing at 220 Ma prior to supercontinent breakup . Quantifying the movement history of blocks surrounding the Paleo-Asian Ocean (PAO) can provide better understanding on the spatial-temporal evolution of the PAO and shed light on the paleogeography of East Asian blocks during the formation of Pangea.The timing of the PAO's final closure is contentious. Models based primarily on geological evidence (sedimentology, structural geology, metamorphism, provenance analyses, paleobiogeography, petrogeochemistry of igneous rocks, and ophiolites) can be broadly categorized into two end-member groups: (a) Middle-Late Devonian closure mainly supported by two middle Paleozoic orogenic belts recognized near the Solonker and Hegenshan sutures as well as overlying Late Devonian unconformities (e.g.,

The paleomagnetism of the loess unit L8 in Xifeng section of the Chinese Loess Plateau has been studied to determine the behavior of the Matuyama-Brunhes transitional field. Three primary results have been obtained. (1) The M-B transition is located in the low part of L8 and the time duration of this transition defined by directional changes is estimated to be about 3,600 yrs, whereas the intensity changes last about 8,000 yrs, both of the estimations being based on the SPECMAP 5180 time scale (IMBRIE et al., 1984). (2) The morphology of the M-B transition field is characterized not by a single reversal course, but at least by three reversals and one aborted reversal course. The VGP paths obtained are not consistent with a non-dipole axisymmetric field. (3) The geomagnetic fields during this transition seem to have the configurations that dipole field component is at least comparable to the non-dipole ones in magnitude, which does not support the commonly-accepted viewpoint.