Positive Fold Test Research Articles

Early Cretaceous paleomagnetic and geochronologic results from the Tethyan Himalaya: Insights into the Neotethyan paleogeography and the India-Asia collision.

To better understand the Neotethyan paleogeography, a paleomagnetic and geochronological study has been performed on the Early Cretaceous Sangxiu Formation lava flows, which were dated from ~135.1 Ma to ~124.4 Ma, in the Tethyan Himalaya. The tilt-corrected site-mean characteristic remanent magnetization (ChRM) direction for 26 sites is Ds = 296.1°, Is = −65.7°, ks = 51.7, α95 = 4.0°, corresponding to a paleopole at 5.9°S, 308.0°E with A95 = 6.1°. Positive fold and reversal tests prove that the ChRM directions are prefolding primary magnetizations. These results, together with reliable Cretaceous-Paleocene paleomagnetic data observed from the Tethyan Himalaya and the Lhasa terrane, as well as the paleolatitude evolution indicated by the apparent polar wander paths (APWPs) of India, reveal that the Tethyan Himalaya was a part of Greater India during the Early Cretaceous (135.1–124.4 Ma) when the Neotethyan Ocean was up to ~6900 km, it rifted from India sometime after ~130 Ma, and that the India-Asia collision should be a dual-collision process including the first Tethyan Himalaya-Lhasa terrane collision at ~54.9 Ma and the final India-Tethyan Himalaya collision at ~36.7 Ma.

New Late Cretaceous paleomagnetic data from volcanic rocks and red beds from the Lhasa terrane and its implications for the paleolatitude of the southern margin of Asia prior to the collision with India

In order to improve estimation of the paleolatitude of the southern margin of Asia during the Late Cretaceous, as well as the constraints on the intracontinental convergence within Asia due to the India–Asia collision, we performed a combined geochronological and paleomagnetic investigation of Late Cretaceous red bed sequences and intercalated volcanic rocks from the Linzhou Basin in the Lhasa terrane (29.9°N/91.1°E). The results of potassium–argon (K–Ar) dating indicated that the basalt sequences are of Late Cretaceous age (68–75Ma). Stepwise thermal demagnetization successfully isolated high unblocking-temperature characteristic directions from 10 red bed sites and 11 lava flow sites. Positive fold and reversal tests indicate a primary origin for the characteristic remanence of the red beds and basalt sites. The consistent inclination recorded in the red beds and basalt lava flows indicates that no significant compaction-related inclination shallowing has occurred in the red beds from the studied section. The tilt-corrected mean direction is D/I=0.5°/20.2° with α95=6.4° and N=21 sites, corresponding to a paleopole at 70.5°N, 269.6°E with A95=4.9°. The paleomagnetic results yield a paleolatitude of 10.4±4.9°N for the southern margin of Asia in the Late Cretaceous. Compared with expected paleomagnetic directions from the Tethyan Himalaya and Asia, significant crustal shortening of 17.7±5.5° (1960±610km) and 9.4±4.7° (1040±520km), respectively, may have occurred between the southern margin of Asia and the Tethyan Himalaya, and within Asia, since the Late Cretaceous. Based on previous Cretaceous and Paleocene data from the Lhasa terrane, the latitude of the southern margin of Asia was located at a stable paleolatitudinal position (10°–15°N) during the Cretaceous and Paleocene.

Using palaeomagnetism to determine late Mesoproterozoic palaeogeographic history and tectonic relations of the Sinclair terrane, Namaqua orogen, Namibia

Abstract The Sinclair terrane is an important part of the Namaqua orogenic province in southern Namibia containing well-preserved Mesoproterozoic volcano-sedimentary successions suitable for palaeomagnetic and geochronological studies. The Guperas Formation in the upper part of the Sinclair stratigraphic assemblage contains both volcanic and sedimentary rocks cut by a bimodal dyke swarm with felsic members dated herein by U–Pb on zircon at c. 1105 Ma. Guperas igneous rocks yield a pre-fold direction and palaeomagnetic pole similar to that previously reported. Guperas sedimentary rocks yield positive conglomerate and fold tests, with a maximum concentration of characteristic remanence directions at 100% untilting. The combined Guperas data generate a palaeomagnetic pole of 69.8° N, 004.1° E ( A 95 =7.4°, N= 9). The 1105 Ma post-Guperas dykes yield stable remanence directions with positive baked-contact tests and a palaeomagnetic pole at 62.3° N, 031.9° E ( A 95 =6.9°, N= 26), which is coincident with that of the Kalahari-wide Umkondo large igneous province, demonstrating tectonic coherence of the Sinclair terrane with the Kalahari craton at the time of dyke emplacement. These results show that palaeomagnetic and geochronological studies of the Sinclair terrane can provide kinematic constraints on the tectonic evolution of the Namaqua–Natal–Maud orogenic belt and its role in the formation of the Rodinia supercontinent.

Paleomagnetism of Upper Cretaceous red-beds from the eastern Qiangtang Block: Clockwise rotations and latitudinal translation during the India–Asia collision

High-temperature magnetization component was isolated between 600°C and 680°C from Upper Cretaceous red-beds in the Mangkang area, in the eastern end of the Qiangtang Block, Tibetan Plateau. The tilt-corrected site-mean direction is Ds/Is=51.3°/56.1°, with k=31.0 and α95=6.5°, corresponding to a paleolatitude of 36.7±6.7°N. Positive fold and reversal tests indicate a primary magnetization. Inclination shallowing tests show that inclination bias is not present in the Upper Cretaceous red-beds of the Qiangtang Block that might induce through depositional and/or compaction process. However, previous paleomagnetic data obtained from Cretaceous and Paleocene–Eocene volcanic rocks show that the paleolatitudes of the Lhasa Block were 17.1±3.3°N and 22.3±4.4°N, respectively, and 28.7±3.7°N for the central Qiangtang Block yielded from Eocene volcanic rocks. These results show that there was a ∼10° latitudinal discrepancy between the Lhasa Block and Qiangtang relative to Eurasia. However, the Mangkang area of the southeastern Qiangtang Block experienced ∼3.2±7.8° to 7.3±5.2° southward extrusion and ∼40° clockwise rotational movement relative to Eurasia since the Cretaceous, which coincided with the Early Cenozoic rotational extrusion of the Indochina and Shan-Thai Blocks. The crustal deformation in the eastern Qiangtang Block should have been caused by the Indian Plate penetrating into Eurasia in the eastern end of Tibetan Plateau and the formation of the Eastern Himalaya Syntaxis since the Oligocene/Miocene.

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

To better constrain the Early Cretaceous paleogeographic position of the Tethyan Himalaya and the India–Asia collision process, a paleomagnetic study was performed on the Lakang Formation lava flows in the Cuona area in the southeastern Tethyan Himalaya. Stepwise thermal and alternating field demagnetizations successfully isolated reliable characteristic remanent magnetization (ChRM) directions that include antipodal dual polarities and pass positive fold tests at the 99% confidence level and reversal tests at 95% confidence level, indicating prefolding primary magnetizations. The distribution patterns of ChRM directions from the Lakang Formation lava flows are consistent with young lava flows at similar latitudes, suggesting that secular variation has likely been averaged out. The tilt-corrected site-mean direction for 31 sites is D=261.6°, I=−68.5° with α95=3.6°, which provides a paleopole at 26.8°S, 315.2°E (A95=5.7°), corresponding to a paleolatitude of 52.2°±5.7°S for the study area. Comparison of the paleolatitude observed from the Lakang Formation lava flows with that expected from the apparent polar wander paths of India at 130 Ma show a paleolatitude difference of ∼2.1° (∼230 km), indicating that neither a great north-south continental crustal shortening occurred between the Indian craton and the Tethyan Himalaya after 130 Ma, nor that a wide ocean separated them at that time. Comparison with reliable Cretaceous–Paleocene paleomagnetic results observed from the Tethyan Himalaya and the Lhasa terrane indicates that the latitudinal width of the Neo-Tethyan Ocean could have been up to ∼7000 km at 134–130 Ma and an extension should have existed between the Indian craton and the Tethyan Himalaya during the Late Cretaceous and Paleocene. Furthermore, reliable paleomagnetic results suggest that the India–Asia collision was a dual-collision process, consisting of a first collision of the Tethyan Himalaya with the Lhasa terrane (Asia) at 54.9±2.3 Ma and a final continent–continent collision of the Indian craton with the Tethyan Himalaya at 40.0±3.3 Ma.

The Cenozoic rotational extrusion of the Chuan Dian Fragment: New paleomagnetic results from Paleogene red-beds on the southeastern edge of the Tibetan Plateau

Paleomagnetic studies were conducted on the Eocene and Oligocene strata at the western part of the Chuan Dian Fragment in order to describe the crustal deformation induced by continuous penetration of the Indian plate into Eurasia during the late Cenozoic. High-temperature magnetic components with unblocking temperatures of ~680°C were isolated, and positive fold and/or reversal tests reveal the primary nature of the magnetization. The tilt-corrected site-mean directions obtained from the Oligocene and middle-early Eocene strata are, respectively, Ds=200.9°, Is=−31.3°, k=52.8, α95=7.7° and Ds=29.7°, Is=32.0°, k=44.9, α95=5.6°. Comparison of these results with previous paleomagnetic data from the Chuan Dian Fragment shows that the western and central parts of the Chuan Dian Fragment experienced ~20° integral clockwise rotation relative to East Asia since the middle Miocene. However, the eastern part of the Chuan Dian Fragment has experienced different rotational deformation relative to East Asia since the Pliocene, because of the intense regional crustal deformation and activity on fault systems. The eastern boundary of the Chuan Dian Fragment was bounded by the Yuanmou-Luezhijiang left lateral strike-slip fault prior to the Pliocene, and then substituted by the Xiaojiang left lateral strike-slip fault since the Pliocene, due to the eastwards spreading of the clockwise rotational movement of the Chuan Dian Fragment. The evolutionary characteristics of the Ailaoshan-Red River and Xianshuihe-Xiaojiang strike-slip faults were controlled by the difference between the clockwise rotational extrusion velocities of the Chuan Dian Fragment and the Indochina Block.

Paleomagnetic constraints on the paleolatitude of the Lhasa block during the Early Cretaceous: Implications for the onset of India–Asia collision and latitudinal shortening estimates across Tibet and stable Asia

Interbedded volcano-sedimentary sequences are well exposed in the northern part of the Lhasa block in southern Tibet. Zircon U–Pb dating results from two samples indicate that the emplacement age of the Duoni Formation volcanic flows is 120.2±0.5Ma. Paleomagnetic results from 235 progressively demagnetized volcanic rock samples (25 sites) and 41 sandstone samples (5 sites) indicate that the dominant remanence carriers are Ti-poor titanomagnetite and Ti-poor titanohematite in the volcanic samples and Ti-rich titanomagnetite in the sandstone samples. Rock magnetic investigations, systematic demagnetization behavior, positive fold test results, and direct petrographic identifications all indicate that the paleodirections recorded by the chemically stable magnetic particles are primary thermal remanent magnetization in the volcanic flows and primary detrital remanent magnetization in the sandstones. The tilt-corrected ChRM mean direction is D/I=356.4°/16.4° with α95=6.3° (N=19), corresponding to a paleopole position of λp=66.9°N, φp=281.2°E with A95=6.1°. Combined with previously published results, the geochronological dating and paleomagnetic analysis indicate a paleolatitude of 13.1±2.7°N for the southern margin of the Lhasa block during the Early Cretaceous. Therefore, the southernmost margin of the Eurasian continent likely remained at the low-middle paleolatitude of 13.1±2.7°N between the Early Cretaceous and the Paleocene. Based on comparisons to results from the Tethyan–Himalayan block and the reference poles from stable India and Eurasia, the low-middle paleoposition of the Lhasa block during the Early Cretaceous through Early Paleocene suggests that the initial contact between India and Asia occurred at ca. 59.3Ma. Under the assumption of a rigid Eurasian plate, this timing implies that a total collision-related latitudinal convergence of 1450±400km (13.1±3.7°N) has been accommodated by folding, thrust faulting, normal faulting, crustal thickening, intracontinental subduction in Tibet and central Asia and southeastward continental extrusion of the Indo-China block from the eastern syntaxis between the Lhasa block and stable Asia.

New paleomagnetic studies of Cretaceous and Miocene rocks from Jinggu, western Yunnan, China: Evidence for internal deformation of the Lanping–Simao Terrane

Cretaceous, Paleogene, and Miocene sandstones were sampled in the Jinggu area to constrain the internal deformation of the Lanping–Simao Terrane of the Indochina Block. The tilt-corrected overall site-mean direction of the middle Cretaceous strata recorded in the Jinggu area is Ds/Is=77.0°/43.0°, with α95=2.9° (N=47), with a positive fold test indicating a primary remanence acquisition. The site-mean direction recorded for the high-temperature component of the Miocene strata is Ds/Is=13.7°/36.0°, with α95=3.3° (n=38). The best-fit linear regressions between regional tectonic lines and rotation degree from each sampled area in the Lanping–Simao Terrane indicate a direct relationship between tectonic rotation and formation of the sinusoidal shape of the Lanping–Simao arcuate structural zone. The large clockwise rotation in the Jinggu area can be subdivided into three periods. During the formation of the sinusoidal shape of the Lanping–Simao Arc, the Jinggu area and the Indochina Block experienced approximately 20° of clockwise rotation. An additional ∼40° of clockwise rotation in the Jinggu area was caused by bending of the Chongshan–Lancang–Chiang Mai belt between 27 and 20Ma. After the early Miocene, a significant small-scale internal rotation (8.2±3.2°) adjustment occurred in the Jinggu area. Quantitative comparison between the paleomagnetically determined clockwise rotation and tectonic–metamorphic events suggests that the Lanping–Simao Arc was formed by the west-to-east compression and southeastward extrusion of the Shan–Thai Terrane since 36Ma in southeast Tibet.

Did the Kyrenia Range of northern Cyprus rotate with the Troodos–Hatay microplate during the tectonic evolution of the eastern Mediterranean?

Previous palaeomagnetic studies have allowed the recognition of a distinctive area of Neotethyan oceanic rocks, including the Troodos ophiolite in Cyprus and the Hatay ophiolite to the east in southern Turkey, that underwent 90° of anticlockwise rotation between Late Cretaceous (Campanian) and Early Eocene time. The southern and western boundaries of this rotated Troodos–Hatay microplate have been inferred to lie within, or adjacent to, zones of deformed oceanic and continental margin rocks that are now exposed in southern and western Cyprus; however, the northern boundary of the microplate remains undefined. Relevant to this problem, palaeomagnetic data are presented here from basaltic lavas exposed along the Kyrenia Range, mostly from Late Cretaceous (Maastrichtian) sites and one Eocene site. A positive inclination-only fold test demonstrates that remanences are pre-deformational in age, and positive conglomerate tests show that magnetic remanences were acquired before Late Eocene–Early Oligocene time, together suggesting that primary magnetizations are preserved. Data from the eastern Kyrenia Range and the Karpas Peninsula (the easternmost extension of the Kyrenia Range) document significant relative tectonic rotation between these localities, with no rotation in the eastern range versus 30° of anticlockwise rotation of the Karpas Peninsula. Unfortunately, palaeomagnetic sites from the western Kyrenia Range did not yield tectonically interpretable magnetization directions, probably due to complex poly-phase thrusting and folding, and the central range also yielded no interpretable data. However, the available palaeomagnetic data are sufficient to demonstrate that the Kyrenia terrane underwent a separate rotation history to the Troodos–Hatay microplate and also implies that the northern boundary of the Troodos–Hatay microplate was located between the Troodos ophiolite and the Kyrenia Range. The former microplate margin has since been overridden and concealed by two phases of southwards thrusting and folding of the Kyrenia Range units (Mid-Eocene; latest Miocene–earliest Pliocene). The likely cause of the anticlockwise rotation affecting the Karpas Peninsula, and by implication the curvature of the Kyrenia Range as a whole, relates to regional late-stage subduction and diachronous continental collision. The Southern Neotethys sutured in SE Turkey during the Early Miocene, whereas a relict ocean basin remained further west in the easternmost Mediterranean, allowing a remnant N-dipping subduction zone to retreat southwards and so induce the present-day arcuate shape of the Kyrenia Range.

Paleomagnetic study of Plio-Pleistocene sediments in the concentrated deformation zone along the eastern margin of the Japan Sea

Paleomagnetic results are presented for a concentrated deformation zone (CDZ) in a convergent plate boundary region along the eastern Eurasian margin. We sampled late Pliocene–early Pleistocene tuffs and clastic sediments of the Sasaoka Formation (∼750 m thick) in northeastern Honshu, Japan, to test whether the late Pliocene–Quaternary crustal deformation within the CDZ along the eastern margin of the Japan Sea was accompanied by rotation about a vertical axis. Rock magnetic experiments suggest that the principal magnetic carrier is magnetite in the fine tuffs, and magnetic iron sulfide in the fine sandstones. Pre-folding characteristic remanent magnetization was confirmed using a positive bootstrap fold test. We obtained 21 acceptable site-mean characteristic directions that include our preliminary published results, and which cover an interval from ca. 2.7 to 1.7 Ma on the basis of magnetostratigraphic correlations. An updated age–depth model is given, and this allowed us to make numerical age estimates for key interbedded tuff beds (tephras). A positive fold test also suggests that the Gojome syncline began to develop after 1.7 Ma, which means the folding began long after the initiation of late Pliocene crustal shortening in northeastern Honshu. After 100% unfolding, the overall mean direction (D = 359.7°, I = 54.9°, α95 = 6.7°) is indistinguishable from the geocentric axial dipole field direction, indicating that the Gojome syncline, the most prominent structural element in the study area, developed without vertical-axis rotation. A comparison of our results with Plio-Pleistocene directions reported from other areas reveals no paleomagnetically detectable rotation in or adjacent to the CDZ, except for local rotation near strike-slip faults in central Honshu.

Paleomagnetism of the Late Cretaceous ignimbrite from the Okhotsk-Chukotka Volcanic Belt, Kolyma-Omolon Composite Terrane: Tectonic implications

New Late Cretaceous paleomagnetic results from the Okhotsk-Chukotka Volcanic Belt in the Kolyma-Omolon Composite Terrane yield stable and consistent remanent directions. The Late Cretaceous (86–81Ma) ignimbrites from the Kholchan and Ola suites were sampled at 19 sites in the Magadan area (60.4°N, 151.0°E). We isolated the characteristic paleomagnetic directions from 16 sampled sites using an alternating field demagnetization procedure. The primary nature of these directions is ascertained by dual polarities and positive fold tests. A tilt-corrected mean direction (D=42.8°, I=84.7°, k=46.0, α95=10.0°) yields a paleomagnetic pole of 66.7°N, 168.5°E (A95=18.8°) which appears almost identical to the 90–67Ma pole reported from the Lake El’gygytgyn area of the Okhotsk-Chukotka Volcanic Belt (Chukotka Terrane). This consistency suggests that the Kolyma-Omolon Composite Terrane and Chukotka Terrane has acted as a single tectonic unit since 80Ma without any significant internal deformation. Accordingly, we calculate a combined 80Ma characteristic paleomagnetic pole (Long.=164.7°E, Lat.=68.0°, A95=10.9°, N=12) for the Kolyma-Omolon-Chukotka Block which falls 16.5–17.5° south of the same age poles from Europe and East Asia. We ascribe this discrepancy in pole positions to tectonic activity in the area and infer a southward displacement of 1640±1380km for the Kolyma-Omolon-Chukotka Block with respect to the North American and Eurasian blocks since 80Ma; more than 260km of it is attributed to tectonic displacement in the Arctic Ocean due to the opening of the Canadian Basin.

Low paleolatitude for the late Cryogenian interglacial succession, South Australia: paleomagnetism of the Angepena Formation, Adelaide Geosyncline

New paleomagnetic data for red beds (dolomitic siltstone and fine-grained sandstone) from the Angepena Formation of the late Cryogenian interglacial succession between deposits of the Sturt glaciation (ca 660 Ma) and Elatina glaciation (ca 635 Ma) in the Adelaide Geosyncline, South Australia, together with previous paleomagnetic data, indicate that the region lay in low paleolatitudes during the ca 25 Ma-long interglacial interval. Thermal demagnetisation of samples from the Angepena Formation at Depot Flat in the western Flinders Ranges and Nepouie Creek and Balcanoona Creek in the northeastern Flinders Ranges revealed a high-temperature component that decayed to the origin at ∼680°C, consistent with hematite being the only magnetic mineral present. Restoring the strata to the paleohorizontal yielded a positive fold test at the 99% confidence level. The concordance of results for widely separated sites and the positive fold test argue for the early acquisition of remanence before folding of the strata during the Cambrian Delamerian Orogeny. The mean direction after unfolding (n = 71 specimens) is declination D = 25.3°, inclination I = 8.7° (α95 = 4.0°), indicating a pole position at latitude λp = 46.7°S, longitude ϕp = 357.3°E (A95 = 3.2°) and a paleolatitude λ = 4.4 ± 2.0°. Correction for possible inclination shallowing with compaction could increase the inclination to between 12° and 20° depending on the flattening factor used, which would increase the paleolatitude to 6.1–10.3°. A reversal test was rated B, as the critical angle for the normal and reverse distributions is 8.6°, i.e. between 5° and 10°. The new data, and previous paleomagnetic data for Neoproterozoic strata from the Adelaide Geosyncline and the Officer Basin in Western Australia, together indicate that southern Australia remained in low paleolatitudes throughout the Cryogenian.

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

AbstractThe 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.

Paleo-position of the North China craton within the supercontinent Columbia: Constraints from new paleomagnetic results

Several new paleomagnetic and geological studies focused on the reconstruction of the North China Craton (NCC) within the Paleo-Mesoproterozoic Columbia supercontinent. In spite of these new data, there are still widely divergent opinions regarding supercontinental reconstructions. In addition to qualitative correlations of orogenic belts, rift basin ages, stratigraphy and distribution of igneous provinces, paleomagnetic data can provide key constraints on the positioning of individual cratons on the globe. In this paper, we report a detailed paleomagnetic study on the coeval ∼1780Ma mafic dyke swarm and Xiong’er volcanic province, which extended for more than one thousand kilometers in the central NCC. Rock magnetic studies, including thermomagnetic curves, hysteresis loops and the progressive acquisition of isothermal remanence conducted in selected samples, indicate that the dominant magnetic carriers are PSD magnetite. Stepwise thermal demagnetization isolated higher-temperature components directed to NNE/SSW with shallow inclinations from 37 sampling sites (16 sites in Yinshan area, 13 sites in Taihang area and 8 sites in Xiaoshan area). A baked contact test conducted on two Yinshan dykes intruded by a younger dyke demonstrates the magnetization in the Yinshan dykes pre-dates 1320Ma. The existence of dual-polarity magnetizations in both Taihang and Xiong’er areas support our contention that the ChRM was acquired during the cooling of the magma. The primary origin of the ChRM is also supported by a positive fold test on the Xiong’er data, and a coherent regional test between the results from the Taihang and Xiong’er areas. Two different site-mean directions were compiled from these new results along with previous publications. The first direction, from the Taihang and Xiong’er areas, yields Declination (D)/Inclination (I)=12.4°/−3.7° (κ=20.5, α95=4.3°, N=57 sites). The second, from the Yinshan area is at (D) 36.7°/(I)−12.4° (κ=86.8, α95=2.7°, N=32 sites). We argue that the difference is due to Mesozoic and/or Cenozoic vertical-axis rotation of the Taihang and Xiong’er areas with respect to the fixed Yinshan-Ordos basin. The corresponding paleopoles for the Yinshan dykes falls at 245.2°E/35.5°N (A95=2.4°). A comparison between the NCC, Laurentia, Siberia and Baltica is consistent with possible links between these four blocks in a perhaps, even larger, continent. The proximity of Australia and India to the NCC is also evaluated.

New insights into the India–Asia collision process from Cretaceous paleomagnetic and geochronologic results in the Lhasa terrane

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 ~121–117Ma 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 α95=5.4°, corresponding to a paleopole at 49.0°N, 344.3°E with A95=5.3°, and the other for 12 volcanic sites is D=350.5°, I=25.5° with α95=7.7°, corresponding to a paleopole at 70.5°N, 292.9°E with A95=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±2.1Ma, the longtime subduction of an intra-oceanic basin between the Himalayan terrane and the Indian craton from ~54.0 to ~40.4Ma, and the collision of the Himalayan terrane and the Indian craton at 40.4±4.1Ma. Comparing with the Late Cretaceous average pole of the East Asia APWP reveals that a latitudinal convergence of 780±240km 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 600–1000km accommodated by the Cenozoic fold and thrust belts between the Lhasa terrane and Hexi corridor.

Tectonic evaluation of the Indochina Block during Jurassic-Cretaceous from palaeomagnetic results of Mesozoic redbeds in central and southern Lao PDR

Rock magnetic and palaeomagnetic studies were performed on Mesozoic redbeds collected from the central and southern Laos, the northeastern and the eastern parts of the Khorat Plateau on the Indochina Block. Totally 606 samples from 56 sites were sampled and standard palaeomagnetic experiments were made on them. Positive fold tests are demonstrated for redbeds of Lower and Upper Cretaceous, while insignificant fold test is resulted for Lower Jurassic redbeds. The remanence carrying minerals defined from thermomagnetic measurement, AF and Thermal demagnetizations and back-field IRM measurements are both magnetite and hematite. The positive fold test argues that the remanent magnetization of magnetite or titanomagnetite and hematite in the redbeds is the primary and occurred before folding. The mean palaeomagnetic poles for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous are defined at Plat./Plon.=56.0°N/178.5°E (A95=2.6°), 63. 3°N/170.2°E (A95=6.9°), and 67.0°N/180.8°E (A95=4.9°), respectively. Our palaeomagnetic results indicate a latitudinal translations (clockwise rotations) of the Indochina Block with respect to the South China Block of −10.8±8.8° (16.4±9.0°); −11.1±6.2° (17.8±6.8°); and −5.3±4.7° (13.3±5.0°), for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, respectively. These results indicate a latitudinal movement of the Indochina Block of about 5–11° (translation of about 750–1700km in the southeastward direction along the Red River Fault) and clockwise rotation of 13–18° with respect to the South China Block. The estimated palaeoposition of the Khorat Plateau at ca. 21–26°N during Jurassic to Cretaceous argues for a close relation to the Sichuan Basin in the southwest of South China Block. These results confirm that the central part of the Indochina Block has acted like a rigid plate since Jurassic time and the results also support an earlier extrusion model for Indochina.

Cenozoic magnetostratigraphy and magnetic properties of the southern Issyk-Kul basin, Kyrgyzstan

We present paleomagnetic data from the northern flank of the Tianshan range, southeast of Lake Issyk-Kul (Kyrgyzstan). 613 cores were collected in two parallel sections with a total thickness of 960m (Chon Kyzylsuu, CK) and 990m (Jeti Oguz, JO), as well as 48 cores at six sites in a nearby anticline. Rock magnetic analyses identify both magnetite and hematite in the fluvial–lacustrine sediments. The concentration of both minerals, the magnetite:hematite ratio, and the average magnetite grain size increase upward in both sections. Anisotropy of anhysteretic remanent magnetization defines a tectonic fabric with sub-horizontal maximum axes that parallel the strike direction together with intermediate and minimum axes that streak out about a great circle orthogonal to the maximum axes suggestive of a tectonic fabric emplaced during folding. Stepwise thermal demagnetization isolates interpretable magnetization components in 284 samples that define 26 polarity chrons in CK and 19 in JO. A positive fold test, dual polarities and systematic changes in rock-magnetic parameters with depth suggest that the high temperature magnetization component was acquired coevally with deposition. An age model based on a visual magnetostratigraphic correlation of both sections with the geomagnetic polarity time scale defines absolute ages from 26.0 to 13.3Ma, with a fairly constant sedimentation rate of 9–10cm/ka. A correlation based on a numerical algorithm arrives at a slightly different conclusion, with deposition ages from 25.2 to 11.0Ma and sedimentation rates from 5 to 8cm/ka. In comparison with sedimentation rates found at other magnetostratigraphic sections in the Tianshan realm, we infer that the sedimentary record in this part of the Issyk-Kul Basin precedes the more rapid phase of uplift of the Kyrgyz Tianshan. The onset of deposition and concomitant erosion of the adjacent Terskey Range is in good agreement with independent assessments of the exhumation history of this mountain range, with erosion increasing at 25–20Ma and accelerating after 11–13Ma.

Eastern segment of the Kiselevka-Manoma terrane (Northern Sikhote Alin): Paleomagnetism and geodynamic implications

The comprehensive geological-geophysical study of the lower Cretaceous volcanosedimentary rocks of the Kiselevka block of the Kiselevka-Manoma lithotectonic terrane made it possible to reach the following conclusions: (1) The composition of the volcanogenic rocks and the lithology of the sediments of the Kiselevka block indicate their formation in a within-plate oceanic setting; the petro- and geochemical characteristics of the studied volcanic rocks are similar to those of the Hawaiian hot spot. (2) The distinguished characteristic component of the natural remanent magnetization of the volcanosedimentary rock complex of the Kiselevka block yields a positive fold test and age similar to that of the rocks. According to the orientation of this characteristic component, the paleolatitudes of the rock formation (18° ± 5° N) and the coordinates of the paleomagnetic pole (Plat = 18.6°, Plong = 222.4°, dp = 5.2, dm = 9.1°) of the Kiselevka Block were determined. (3) The kinematic reconstructions based on the obtained and published data indicate that, (1) in the Valanginian-Albian, the Kiselevka Block migrated northwestward with the Izanaga Plate at a velocity of 15–20 cm/yr, passing over 5 thou. km up to the Eurasian margin (the Korean Peninsula); (2) in the Albian-Campanian, the block, as a fragment of the Kiselevka-Manoma accretionary wedge, moved along the Eurasian transform margin with a velocity of 4–5 cm/yr to its present-day position, where it was integrated into the continental plate.

Improved Moscovian part of the Gondwana APWP for paleocontinental reconstructions, obtained from a first paleomagnetic pole, age-constrained by a fold test, from In Ezzane area in the Murzuq basin (Algeria, stable Africa)

To improve paleocontinental reconstructions, paleomagnetic reference curves (Apparent Polar Wander Path: APWP) feature for large continents have to be continuously refined by adding up new high-quality data. For stable Africa, the Moscovian period was favorable for such aim, with well-dated and widespread geological formations. A new study has been conducted in the Upper “Dembaba” geological formation of Lower Moscovian age outcropping in the western part of the “Murzuq” basin (Saharan platform). Well-defined ChRMs, combined with remagnetization circles data, both constrained in age by a positive fold test, yield a new significant paleomagnetic pole (λ=25.2°S, ϕ=59.9°E, K=55, A95=5.4°). When joined with previous African data of the same age, it gives an improved reference pole for Africa (λ=28.9°S, ϕ=54.5°E, K=106, A95=3.6°). The Mean Moscovian paleomagnetic pole determined from an updated Gondwana Paleozoic APWP (λ=29.4°S, ϕ=51.5°E, K=11, A95=1.8°), associated with the corresponding Laurussia pole (Domeier et al., 2012), yields a more constrained paleocontinental reconstruction for 310Ma.

Paleomagnetism of Paleozoic sedimentary rocks from the Karatau Range, Southern Kazakhstan: Multiple remagnetization events correlate with phases of deformation

The paleogeography of the Altaids and its kinematic and tectonic evolution during the final collision and amalgamation of Eurasia is still poorly known. Addressing this problem, a paleomagnetic study has been undertaken on Paleozoic sedimentary rocks from the Karatau, Southern Kazakhstan. Stepwise thermal demagnetization reveals the presence of a high‐temperature component of magnetization in most samples. Fold tests indicate a syn‐folding age of magnetic remanence acquisition at three of the five areas studied. Directional data of Devonian and Permian rocks yield a positive fold test, implying a primary magnetization. Resulting prefolding paleolatitudes for Permian and Devonian rocks show the proximity of the Karatau to Baltica during those times. Syn‐ and post‐folding magnetizations result in paleolatitudes for Karatau, which intersect the paleolatitude curve based on the Baltica apparent polar wander path (APWP), at times, which can be correlated to major deformational events at ~280 Ma, ~260 Ma, and ~230 Ma, respectively. We interpret this with complicated pattern of remagnetization events accompanying deformation, which can include syn‐folding remagnetization events and areas of primary magnetic signals. Additionally, the differences between reference declinations based on the APWP for Baltica and observed declinations suggest successive counterclockwise rotational reorganization of the Karatau during the late Paleozoic to Early Mesozoic, with maximal rotation values of ~65° with respect to Baltica. The remagnetization events are correlated with latest intracontinental stages of orogenic evolution in the Ural mountains and thus the Paleozoic amalgamation of the Eurasian continent and suggest synchronous and coherent tectonic evolution in the Urals and Karatau mountains.