Eurasian Apparent Polar Wander Path Research Articles

Magnetostratigraphy of the Tuotuohe Formation in the Tuotuohe Basin, Central-Northern Tibetan Plateau: Paleolatitude and Paleoenvironmental Implications

Paleolatitude evolution could provide a general paleo-location framework for explaining the paleoclimate change and tectonic deformation in geological time. Strengthening the paleolatitude study of the Tuotuohe Basin is important for understanding the history and mechanism of the tectonic uplift process in the north-central Tibetan Plateau. In this study, we introduced the magnetostratigraphy for the Tuotuohe-D (TTH-D) section in the Tuotuohe Basin, central-northern Tibetan Plateau, in order to constrain the chronology and to reconstruct the paleolatitude of the basin during the deposition of the Tuotuohe Formation. The results indicated that the Tuotuohe Formation in the TTH-D section was deposited between 38.5 and ~36.7 Ma. Combining this age with the results from the Tuotuohe section indicates that the age of the Tuotuohe Formation spans the interval from >38.5 Ma to ~33 Ma. Additionally, other paleomagnetic data of the Tuotuohe Formation from the Tuotuohe section, combined with the data from this study, indicate that the paleolatitude of the Tuotuohe Basin during the late Eocene was 25.9 ± 4.2°. That means that the Tuotuohe Basin was located in a subtropical anticyclonic zone and that the paleoenvironment during the late Eocene might be controlled by subtropical high pressure. Additionally, paleomagnetic results from the Qiangtang terrane and the bordering regions are combined with the results of our study, which suggest that the paleolatitude of the Tuotuohe Basin at ~26 Ma coincides well with the Eurasian apparent polar wander path for that interval, and that the N-S India–Asia convergence was reduced or ceased at ~26 Ma in the Tuotuohe Basin.

53–43 Ma Deformation of Eastern Tibet Revealed by Three Stages of Tectonic Rotation in the Gongjue Basin

AbstractThe 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.

Paleomagnetism of the Late Cretaceous volcanic rocks of the Shimaoshan Group in Yongtai County, Fujian Province

It has been debated whether there was southward movement of the South China Block (SCB) during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks (~88 Ma) of the Shimaoshan Group in Yongtai County, Fujian Province. Rock magnetic experiments showed that magnetite in pseudo-single-domain and multi-domain grain and hematite were predominant magnetic phases. Stepwise thermal demagnetization successfully isolated characteristic directional components at high-temperature interval (> 500°C) from 383 specimens in 19 sites, which yielded a paleomagnetic pole for the studied section at 83.1°N, 152.6°E (N = 19, A95 = 3.9°), and the scatter SB = 9.0. The Fisher distribution of virtual geomagnetic poles (VGPs) and the consistence of SB with the expected value at the 95% confidence level indicate that the yielded paleomagnetic pole is free of paleomagnetic secular variation influence. The new pole, which is well consistent with that from the Eurasian apparent polar wander path (APWP) curve, suggests no obvious southward movement of the sampling site during the Cretaceous. South China Block, Late Cretaceous, volcanic rock, paleomagnetic secular variation, paleomagnetic pole

A new paleogeographic configuration of the Eurasian landmass resolves a paleomagnetic paradox of the Tarim Basin (China)

New paleomagnetic data from Permian red beds and Middle Jurassic limestones from the Tarim Basin pose a paradox. Their declinations are similar to Upper Carboniferous to Neogene rocks collected from the same sections, and their inclinations parallel present values. When assuming that lower than expected inclinations in continental sedimentary rocks arise from inclination shallowing effects, then the paleolatitudes of all Upper Carboniferous to Present rocks from Tarim are indistinguishable. Local vertical axis block rotations occurring in the last 20 million years explain why declinations vary at different localities in the basin. Our Middle Jurassic data positions Tarim 23.6 ± 8.4° farther south than that predicted from the coeval reference pole for Eurasia; however, no geologic argument exists to support the closure of a large ocean basin between Tarim and Siberia since the Middle Jurassic. Thus the paradox: are the rocks from Tarim totally overprinted, or is the middle Mesozoic part of the reference Eurasian apparent polar wander path erroneous? Several lines of evidence suggest the Tarim rocks are not remagnetized. We conclude that Tarim has experienced little or no apparent polar wander since the Carboniferous. Moreover, our Middle Mesozoic reconstruction of Eurasia using the new Middle Jurassic pole from Tarim results in a more geologically compatible solution for the eastern Asian blocks over previous reconstructions.

Evidence for coeval Late Triassic terrestrial impacts from the Rochechouart (France) meteorite crater

High temperature impact melt breccias from the Rochechouart (France) meteorite crater record a magnetization component with antipodal, normal and reverse polarities. The corresponding paleomagnetic pole for this component lies between the 220 Ma and 210 Ma reference poles on the Eurasian apparent polar wander path, consistent with the 214 ± 8 Ma 40Ar/39Ar age of the crater. Late Triassic tectonic reconstructions of the Eurasian and North American plates place this pole within 95% confidence limits of the paleomagnetic pole from the Manicouagan (Canada) meteorite impact crater, which is dated at 214 ± 1 Ma. Together, these observations reinforce the hypothesis of a Late Triassic, multiple meteorite impact event on Earth.

Paleomagnetism of Upper Jurassic to Lower Cretaceous volcanic and sedimentary rocks from the western Tarim Basin and implications for inclination shallowing and absolute dating of the M-0 (ISEA?) chron

Stepwise demagnetization isolates a stable magnetic component in 13 sites of basalt flows and baked sediments dated at 113.3±1.6 Ma from the Tuoyun section, western Xinjiang Province, China. Except for one flow from the base of the ∼300 m thick section, the rest have exclusively reversed polarity. The sequence correlates with chron M-0 in some geomagnetic polarity time scales, which potentially places the section just before the start of the Cretaceous Long Normal polarity superchron. Five of 11 sites of Early Cretaceous red beds that underlie the basalts possess coherent directions that pass both fold and reversals tests. Six sites of Upper Jurassic red beds have a magnetic component that was likely acquired after folding in the Tertiary. The mean paleolatitude of the Lower Cretaceous red beds is 11° lower than that of the Lower Cretaceous basalts suggesting the red beds underestimate the true field inclination. We further test this result by calculating the paleolatitudes to a common point of the available Early Cretaceous to Present paleomagnetic poles from red beds and volcanic rocks from central Asian localities north of the Tibetan Plateau. We find that paleolatitudes of volcanic rocks roughly equal the paleolatitudes calculated from the reference Eurasian apparent polar wander path (APWP) and that paleolatitudes of red beds are generally 10–20° lower than the paleolatitudes of volcanic rocks and those predicted from the reference curve. Our study suggests that central Asian red beds poorly record the Earth’s field inclination, which leads to lower than expected paleolatitudes. Good agreement in paleolatitudes from volcanic rocks and the Eurasian APWP argues against proposed canted and non-dipole field models.

Resolving the problem of shallow magnetizations of Tertiary age in Asia: insights from paleomagnetic data from the Qiangtang, Kunlun, and Qaidam blocks (Tibet, China), and a new hypothesis

We present new paleomagnetic results obtained at 39 sampling sites from five sections of Tertiary red bed formations: two Eocene formations from the Qiangtang block of Tibet (Xialaxiu locality; 32.8°N, 96.6°E) and the Xining basin of Qaidam (Xining locality; 36.5°N, 102.0°E) and three Neogene formations from the Xining basin (Jungong locality; 34.7°N, 100.7°E) and the Kunlun block (Tuoluo lake and West Yushu localities; 35.3°N, 98.6°E and 33.2°N, 96.7°E, respectively). Thermal demagnetization of the rocks isolated a high‐temperature component that we interpret as the primary magnetization in four localities. The paleopoles lie at 52.6°N/352°E (dp/dm = 6.0°/10.7°) for Xialaxiu, 61.6°N/211.3°E (dp/dm = 9.7°/16.1°) for Xining, 66.0°N/228.6°E (dp/dm = 3.6°/6.9°) for Jungong, and 53.9°N/205.4°E (dp/dm = 5.6°/10.0°) for West Yushu. As in previous studies of Tertiary formations from Asia, the inclinations we obtained are shallower (by 18° to 26°) than the magnetic field computed from the Eurasian apparent polar wander path (APWP) at 10 and 20 Ma for Neogene rocks and at 40 and 60 Ma for Eocene rocks. On the basis of a compilation of Eocene data from the South China Block, Tibet, central Asia and Kyrgyzstan, we conclude that this inclination anomaly reflects erroneous predictions of positions of the Siberian craton when based on the APWP of Eurasia. The main reason for this discrepancy might be nonrigid behavior of the Eurasian plate in the Tertiary. Combination of this with intracontinental shortening of Asia under the penetration of India provides a full explanation for the anomaly. Verification of this new interpretation of the “inclination anomaly” will require new geologic and paleomagnetic data from the northern parts of these remote regions in Mongolia and Siberia.

Timing of the North‐South China collision from new middle to late Mesozoic paleomagnetic data from the North China Block

We collected paleomagnetic samples from 43 sites of Middle and Upper Jurassic and Cretaceous rocks along a 250 km wide east‐west trending belt located north of the suture between the North and South China Blocks. In each case, laboratory treatment isolates dual polarity, antipodal magnetizations that are demonstrably pre‐folding. The paleomagnetic poles show very good coherence with coeval poles from other localities from the North China Block (NCB), suggesting the apparent polar wander path (APWP) from the NCB is not distorted by post‐Middle Jurassic local vertical axis block rotations. A comparison of the NCB APWP with that from the South China Block suggests that collision continued after the Early Jurassic and ended no later than the Late Jurassic. A cusp in the NCB APWP coincides with a marked angular unconformity that separates Middle Jurassic from Upper Jurassic and younger sediments. Together, these observations indicate that the scissor‐like collision and associated deformation ceased at the Middle to Late Jurassic boundary (∼159 Ma). The time of rapid (1°/Ma) relative angular velocity between the two plates (225 to 190 Ma) coincides with a peak in U‐Pb and Ar‐Ar dates obtained from metamorphic rocks in the suture. The combined Late Jurassic and Cretaceous paleomagnetic data from both blocks suggest that the united China plate traveled 2000 km north relative to Eurasia during the Late Jurassic before docking in the Cretaceous. This younger collision event is also marked by a cusp on the Cretaceous part of the Eurasian APWP.

Paleomagnetism and tectonics of the Southern Tarim Basin, northwestern China

We report Late Carboniferous, Permian, and early Tertiary paleomagnetic data from the southern Tarim basin. Prefolding magnetizations were isolated in each case. The Late Carboniferous–Permian and early Tertiary poles lie at 64.6°N, 166.5°E, A95 = 6.3° and 58.1°N, 202.0°E, A95 = 12.7°, respectively. The Late Jurassic to early Tertiary (J3–E1) paleolatitudes of Tarim and several basins throughout central Asia are similar, yet significantly (10° to 20°) shallower than those predicted by the Eurasian apparent polar wander path. Resolving this discrepancy remains a major problem in Asian paleomagnetism. Discordance of the late Paleozoic poles from Tarim and Siberia suggest that Tarim has rotated about 30° counterclockwise with respect to Siberia since the Permian. Where paleomagnetic samples of both Late Carboniferous to Early Triassic (C3–T1) and J3–E1 ages were collected from the same area of Tarim, a great circle passes through the means of the poles and the sampling locality. This suggests that (1) only a difference in inclination (and not declination) distinguishes the two data sets, and (2) vertical axis block rotations of the C3–E1 strata occurred after E1. Although based on data of lesser quality, the mean Early to Middle Jurassic (J1–2) pole from Tarim differs significantly from the Eurasian reference pole, requiring radical tectonic solutions to resolve them. The Tarim J1–2 pole is indistinguishable from both the mean J3–E1 and C3–T1 poles. The similarity of all the poles and the analogous tectonic setting of present‐day central Asia to that of the late Paleozoic in eastern North America raises the question whether all the data from Tarim are overprinted.

Paleomagnetic results from Cretaceous and Jurassic rocks of South and Southwest Yunnan: evidence for large clockwise rotations in the Indochina and Shan-Thai-Malay terranes

Cretaceous and Jurassic redbeds have been sampled from South and Southwest Yunnan, China, for paleomagnetic study. The paleomagnetic directions resolved from the Cretaceous rocks indicate that the Xiaguan area, which is located on the Red River fault, has not been rotated with respect to stable Eurasia since at least Late Cretaceous times and that the Jinggu-Mengla area 200–400 km farther south has been rotated by 46–65° clockwise. The Jurassic results reveal the same rotation pattern. At face value, the differences between the observed Cretaceous paleolatitudes and those predicted from the Eurasian apparent polar wander path (APWP) indicate a southward extrusion of the region, but the amount of extrusion is not large enough to be resolved by paleomagnetic methods. Comparison with Mesozoic paleomagnetic data from central Yunnan, northern Thailand and northwestern Borneo suggests that the Red River fault is not a demarcation between unrotated and significantly rotated regions, and that Sundaland did not respond to the India-Asia collision as a single coherent unit. The existing paleomagnetic data from East Asia appear to indicate that the crust in central Tibet and Tien Shan north of Tarim directly in front of the Indian indentor has been substantially shortened and thickened whereas the crust in the syntaxial areas has probably been largely squeezed out. To further evaluate the relative importance of crustal thickening and extrusion in the tectonic evolution of the Tibetan plateau, paleomagnetic investigation should be intensified in the bounding zones to the Indian indentor and be expanded into the Cenozoic sedimentary rocks in Tibet and surrounding regions.

New paleomagnetic data from the Huanan Block, China, and Cretaceous tectonics in Eastern China

A total of 72 grey-green fine-grained sandstone and siltstone core samples (from 10 sites) were collected from the Early Cretaceous Jieshan and Hekou Formations at Yongan, in the Huanan Block of southeastern China (Fujian Province). After removal of an erratic soft magnetic component in fields of 10–20 mT, stable magnetizations were retrieved from both rock units which are carried mainly by single-domain/pseudo-single-domain (SD/PSD) magnetite or titanomagnetite, as suggested by isothermal remanent magnetization, coercivity measurements and microscopic observations. The Hekou Formation yields a tilt-corrected pole at 66.9°N, 221.4°E ( n=5 sites, K=203.3, A 95=5.4°). A fold test on this result suggests that the magnetization was acquired before tilting which occurred shortly after deposition (between Early and Late Cretaceous). This magnetization is related to a primary sedimentary fabric, as indicated by the low-field anisotropy of magnetic susceptibility (AMS) measurements. The positive fold test and occurrence of a primary sedimentary fabric suggest a depositional origin for the stable magnetization. The Jieshan Formation gives a pole at 70.8°N, 228.7°E ( n=5 sites, K=47.7, A 95=11.2°) in geographic coordinates, which is statistically indistinguishable from the tilted pole for the Hekou Formation. The associated stable magnetization corresponds to a secondary fabric. These features indicate that the Jieshan Formation has been remagnetized during Cretaceous time. The predominance of SD/PSD magnetite or titanomagnetite and igneous activities in eastern Fujian during the Cretaceous suggest a viscous thermal remanent magnetization origin for the secondary magnetization. The Early Cretaceous pole from the Hekou Formation is similar to those for the Yangzi Block, suggesting that the Huanan Block has been accreted to the Yangzi Block at least since Early Cretaceous time. A high consistency of Cretaceous poles from the Sino-Korean, Yangzi and Huanan Blocks as well as Hainan Island indicates that eastern China has been a coherent tectonic unit since Cretaceous time, although there might have been a small amount of northward displacement of the sampling area with respect to the Yangzi Block during the Early-Late Cretaceous period as a result of the overthrust of the Huanan Block onto the Yangzi carbonate platform. Comparison of Cretaceous poles for eastern China with the Eurasian apparent polar wander path (APWP) suggests that no paleomagnetically detectable relative motion has taken place since the Cretaceous. The Cretaceous poles of eastern China, however, display a paleomagnetically significant westward motion (about 9° in angular distance), which is not observed in the Eurasian APWP. This difference may be indicative of a younger age corresponding to the Cretaceous-Tertiary boundary for all Late Cretaceous poles from eastern China, or more probably may imply a minor error in the definition of the Eurasian APWP.

Paleomagnetism of Cretaceous to lower Tertiary rocks from southwestern Sichuan: a revisit

A re-study has been carried out on the Cretaceous to lower Tertiary rocks from southwestern Sichuan province on the South China Block. The characteristics remanent magnetization (ChRM) resolved from the Paleocene-Eocene Leidashu Formation is of dual polarity and very shallow inclination. The anomalouslylow paleolatitude (6.9 ± 6.3°N) indicated by the inclination is not supported by geological evidence from this region and is probably due to inclination error related to depositional and/or post-depositional processes. A positive fold test, as well as the prevalence of normal polarity, suggests that the ChRM of the Mid-Upper Cretaceous Xiaoba Formation might be acquired during the Cretaceous Long Normal Superchron (CLNS). The tilt-corrected mean direction of the Xiaoba Formation (D/I = 8.1°/38.8°, α95 = 6.6°, N = 18 sites) is not significantly different from a preliminary result (D/I = 357.6°/31.6°, α95 = 8.6°, N = 12 samples) we reported earlier for the collective Xiaoba and Leidashu formations. The resultant paleopole (81.5°N/220.9°E, A95 = 7.1°) is coincident with other Cretaceous poles for the Chinese blocks. Comparison with the Eurasian apparent polar wander path (APWP) indicates neither significant rotation nor latitudinal translation of the study area relative to Eurasia. The newly obtained mean direction for the Xiaoba Formation is believed to be more reliable than our earlier result since it is based on a larger sample size and is apparently free from effects of the shallow inclination observed in the Leidashu Formation, and should supercede our previous preliminary result. The paleopole derived from sevenentes of the Lower Cretaceous Feitianshan Formation (69.0°N/204.6°E, A95 = 4.3°) deviates from the track from the Late Jurassic to Late Cretaceous poles; the deviation might be reduced by further sampling.

A Cretaceous pole from south China, and the Mesozoic hairpin turn of the Eurasian apparent polar wander path

To contribute to the apparent polar wander path (APWP) of the South China Block and Eurasia in general, we collected paleomagnetic samples from Mesozoic red beds around the city of Ya' an (30°N, 103°E) in the western tip of the Sichuan Basin. In this paper we present the results from 373 oriented cores taken from one section representing 3 km of sedimentary rocks. The section is dated with continental ostracods and with a magnetostratigraphic correlation between a densely sampled 272‐m sequence and the polarity time scale, giving an upper Jurassic to Upper Cretaceous or Lower Tertiary age. The remanent direction is remarkably stable throughout the section (D=2.0°, I=34.2°, k=63.1,α95=3.6°, N=26/28 sites). While this fact might suggest that the section has been remagnetized, paleomagnetic and rock magnetic tests indicate that the remanence is primary. The pole position (78.6°N, 273.4°E, dp=2.4°, dm=4.1°) corresponds to a rather low paleolatitude (λ=18.8°±2.4°) but is consistent with other Cretaceous poles from China. If one accepts the Eurasian APWP of Irving and Irving (1982), this result would imply that more than 1000 km of shortening took place between South China and Eurasia, following the acquisition of the remanence. However, there is no geological evidence for this large shortening. We propose that the remanence was acquired within the time corresponding to the tip of the hairpin turn (∼150–50 Ma) in the revised APWP of Besse and Courtillot (this issue). The local geology suggests that the syncline from which the samples were taken has been rotated by 15°±5° counterclockwise, which is reflected in a similar discrepancy between the measured paleodeclination and that predicted by the Besse and Courtillot (this issue) Eurasian APWP. After correcting for this rotation, the pole position is 70.9°N, 225.2°E (dp=2.4°, dm=6.5°). We conclude that Eurasia was fully assembled by the end of the Jurassic and that the Mesozoic Eurasian hairpin turn is a real feature.

Paleomagnetic study of Mesozoic continental sediments along the northern Tien Shan (China) and heterogeneous strain in central Asia

A paleomagnetic study of rocks from the northern foot of the Tien Shan and the southern border of the Dzungar Basin, east of Urumqi (44.2°N, 86.0°E), spanning ages from middle Jurassic to early Tertiary was carried out to constrain the tectonic evolution in central Asia since Mesozoic time. Five middle Jurassic sites reveal a remagnetized direction close to the present Earth field in geographic coordinates: D = 6.6°, I = 72.6° (α95 = 7.4°). Thirteen out of 17 upper Jurassic and lower Cretaceous sites yield a characteristic direction (stratigraphic coordinates) of D = 12.7°, I = 48.6° (α95 = 5.5°). Nine of 16 upper Cretaceous and lower Tertiary sites provide a characteristic direction of D = 12.5°, I = 51.3° (α95 = 6.9°). The latter two directions pass fold and reversal tests. The pole positions are close to each other and to the Besse and Courtillot [1989, 1990] Eurasian apparent polar wander path, for ages ranging from 130 to 70 Ma. However, the difference in paleolatitudes amounts to about 5.9°±3.7°, which could indicate significant continental shortening in the Altai Mountains and perhaps further north, subsequent to India‐Asia collision. The pole positions from the Dzungar Basin are close to those found for the Tarim [Li et al., 1988a], leading to an insignificant paleolatitude difference (3.0°±6.9°), but showing a larger difference in declination (8.6°±8.7°). These paleomagnetic results are compatible with a model of heterogeneous deformation in the western part of the collision zone between India and Siberia. A significant shortening in the Altai, a slight counterclockwise rotation of the Dzungar block, the westward‐increasing shortening in the Tien Shan with attendant clockwise rotation of the Tarim block are all consistent with this model, in which Tibet, the Tien Shan and the Altai undergo differential strain along strike in a relay fashion, with the total India‐Siberia convergence remaining approximately constant.

Paleomagnetism of basalts from Alborz: Iran part of Asia in the Cretaceous

Paleomagnetic results are reported from 20 sites within three units of volcanic rocks of Cretaceous age from the Central Alborz Mountains, Iran. After application of progressive demagnetization either with alternating magnetic fields or with heating, the mean characteristic remanence direction is found to be D = 33.3°, I = 47.5° ( α 95 = 7.2°). Both the paleomagnetic analyses and the inspection of polished thin sections of the lavas point to magnetite as the main carrier of remanence. The paleomagnetic pole is located at 61°N, 147.5°E. This is quite near to the positions of the poles of Cretaceous age on the Eurasian apparent polar wander path. It is suggested that in Cretaceous times northern Iran was at its present position with respect to Eurasia.