Previous Paleomagnetic Data Research Articles

Paleolatitude of Mafic Dykes in the Xiugugabu ophiolite: Implications for the intraoceanic Trans-Tethyan subduction zone and multistage India-Eurasia collision

An intraoceanic Trans-Tethyan subduction zone has been identified in both the Kohistan-Ladakh arc and the West Burma Terrane. This has significant implications for the India-Eurasia collision. Concurrently, the dismembered ophiolites within the Yarlung-Tsangpo Suture Zone likely originated from the intraoceanic Trans-Tethyan subduction zone or the Andean-type southern Eurasian continental margin. A paleomagnetic study was conducted on the Lower Cretaceous (∼120–130 Ma) mafic dykes in the Xiugugabu ophiolite to resolve the uncertainty of its origin. The characteristic remanent magnetization (ChRM) obtained through stepwise thermal demagnetization successfully passed consistency/fold and reversal tests. After tilt correction, the overall mean direction of the ChRM was D = 296.9°, I = −25.5°, k = 47.6, α95 = 4.5°, and N = 22, indicating a paleolatitude of 13.4°N/S and a paleopole at 15.0° N, 326.6°E with A95 = 3.8°. Compared with previous paleomagnetic data from the Trans-Tethyan subduction zone, our findings strongly support the involvement of the Xiugugabu ophiolite in the intraoceanic Trans-Tethyan subduction zone. This finding reinforces the hypothesis that there were two distinct subduction zones in the Neotethyan Ocean during the Early Cretaceous. One subduction zone was situated on the southern margin of the Gangdese Arc. The second was the intraoceanic subduction zone, located approximately 3500 km from the southern margin of Eurasia, in the southern hemisphere. Our results also support a multistage India–Eurasia collision process involving continental plates, intraoceanic arcs, and terranes within the Neo-Tethyan Ocean.

Full vector paleomagnetic estimation from the Paraná-Etendeka Large Igneous Province, southern Brazil: Implications on the onset of Cretaceous Normal Superchron

Comprehensive paleomagnetic study from the Paraná-Etendeka Igneous Province (PEIP), Serra Geral Formation, southern Brazil (∼ 135 Ma) adds to the scarce southern hemisphere paleomagnetic database. Twelve paleomagnetic sites from the exposed stratigraphy of the PEIP were recovered from basaltic lava flows in northern Rio Grande do Sul state. These volcanic rocks erupted between 131.5 and 135.6 Ma. The reliability of the rock magnetism data was confirmed before being accepted for paleo-intensity analysis. The Thellier-Coe paleointensity protocol was applied to 109 collected specimens, and 26 individual samples from 9 sites were selected to test for consistency of the paleointensity determinations. The new high-quality mean paleointensity value of 30.6 ± 7.2μT corresponds to a virtual dipole moment (VDM) of 5.75 ± 0.49 × 1022 Am2. These values correspond to approximately 72% of the present-day Earth's magnetic field and suggest that the Earth's magnetic field strength was slightly elevated compared to the long-term average geomagnetic field that prevailed during the Cretaceous Normal Superchron. The calculated paleomagnetic pole (Plong = −27.5° and Plat = −78.6°, A95 = 3.5°) presents an angular difference of 22° with respect to the expected pole declination with an inclination of 5°. This difference may correspond to secular variations considering the confidence cones. Our results, when compared with previous paleomagnetic data, approach the accuracy of recent models for the Cretaceous interval.

Timing the break-up of the Baltica and Laurentia connection in Nuna – Rapid plate motion oscillation and plate tectonics in the Mesoproterozoic

Meso– to Neoproterozoic geological and paleomagnetic data support a direct connection between Baltica and Laurentia in both Nuna and Rodinia supercontinents, however in different relative configurations. Previous paleomagnetic data limit the time of break-up of Nuna core configuration and ca. 90° rotation of Baltica relative to Laurentia between 1.27 Ga and 0.99 Ga. Despite the well documented relative motion of continents, the tectonic mode during the Meso– to Neoproterozoic has been questioned and the operation of single lid tectonics at 1.6–1.0 Ga during the Nuna-Rodinia supercontinent cycles has been proposed.In this study, new paleomagnetic and whole rock 40Ar-39Ar geochronological data from a basic dyke in Stugun central Sweden are combined with coeval data to produce a 1.22 Ga (1.244–1.200 Ga) moderate-quality paleomagnetic pole. This is done to better estimate the break-up time of the core of Nuna and explore the plate tectonics at the Mesoproterozoic. The new pole fills part of the 1.247–1.140 Ga gap in the paleomagnetic record of Baltica. By comparing apparent polar wander paths (APWPs) and calculated drift velocities, a break-up of Baltica and Laurentia at 1.12–1.04 Ga is suggested. Plate velocities calculated for Laurentia, Baltica and Siberia for the time of the Nuna supercycle are similar and low to moderately high corresponding with the present-day tectonic speeds. Furthermore, the obtained velocity peaks may be related with onset of the break-up of the Nuna supercontinent, the break-up of the direct Baltica–Laurentia connection in Nuna and nascent Rodinia. We suggest that the velocity peaks and large oscillating shifts in late Mesoproterozoic pole positions for Laurentia and Baltica result from a combination of relative plate motion and inertial interchange true polar wander (IITPW) events. Both IITPW events and relative plate motions argue for an operation of plate tectonics in the Meso– to Neoproterozoic.

Forced subduction initiation within the Neotethys: An example from the mid-Cretaceous Wuntho-Popa arc in Myanmar

Abstract Despite decades of research, the mechanisms and processes of subduction initiation remain obscure, including the tectonic settings where subduction initiation begins and how magmatism responds. The Cretaceous Mawgyi Volcanics represent the earliest volcanic succession in the Wuntho-Popa arc of western Myanmar. This volcanic unit consists of an exceptionally diverse range of contemporaneously magmatic compositions which are spatially juxtaposed. Our new geochemical data show that the Mawgyi Volcanics comprise massive mid-oceanic ridge basalt (MORB)-like lavas and dikes, and subordinate island arc tholeiite and calc-alkaline lavas. The Mawgyi MORB-like rocks exhibit flat rare earth elements (REEs) patterns and are depleted in REEs, high field strength elements (except for Th) and TiO2 concentrations relative to those of MORBs, resembling the Izu-Bonin-Mariana protoarc basalts. Our geochronological results indicate that the Mawgyi Volcanics formed between 105 and 93 Ma, coincident with formation of many Neotethyan supra-subduction zone ophiolites and intraoceanic arcs along orogenic strike in the eastern Mediterranean, Middle East, Pakistan, and Southeast Asia. Combined with its near-equatorial paleo-latitudes constrained by previous paleomagnetic data, the Wuntho-Popa arc is interpreted as a segment of the north-dipping trans-Neotethyan subduction system during the mid-Cretaceous. Importantly, our restoration with available data provides new evidence supporting the hypothesis of a mid-Cretaceous initiation of this >8000-km-long subduction system formed by inversion of the ∼E-W–trending Neotethyan oceanic spreading ridges, and that this was contemporaneous with the final breakup of Gondwana and an abrupt global plate reorganization.

On the Early Permian shape of Pangea from paleomagnetism at its core

Although central to an understanding of Earth's paleogeography and the myriad processes that it affects, the geometry of Pangea during the early phase of its lifetime has remained a topic of contention since the plate tectonic revolution. Despite decades of analysis and discussion, the crux of this debate still largely hinges on sparse, legacy paleomagnetic data derived from early Permian rocks of the Moroccan Meseta. In this work, we present the results of a study designed to revisit, update and expand on those key data, with the provision of new geochronologic and paleomagnetic results from six Permo-Carboniferous basins in central Morocco. New U-Pb zircon ages from volcanic rocks substantiate and refine existing geochronological data and reveal that volcanism among the studied basins spanned approximately 30 Ma, from at least 305 to 277 Ma, but was possibly punctuated by a more intense pulse in the mid-early Permian (~285 Ma). These new U-Pb data furthermore suggest that the age estimates previously assigned to the key poles from the Moroccan Meseta are probably too young, by some ~10 Ma. New paleomagnetic results from six basins yielded a common, well-defined remanent magnetization from 20 sites that is demonstrated to be pre-middle Permian in age. However, it remains unclear whether this magnetization (which is directionally similar to the previous paleomagnetic data from the same basins) is a primary magnetization acquired at ~285 Ma, or a syn-folding remagnetization that was acquired shortly thereafter, at ~275 Ma. In adopting both interpretations as alternative hypotheses, we examine the corresponding paleogeographic implications of both. Through exhaustive comparisons with reference apparent polar wander paths and the direct reconstruction of Gondwana using these new paleomagnetic results, we demonstrate that in either case (i.e. whether the remanent magnetization is primary or was acquired soon after during folding) the data is compatible with a Pangea A geometry during the early Permian. We close with a topical discussion of some persisting arguments used to defend Pangea B and why we consider them to be flawed.

Volcanic Rocks in the Udyl’ Segment of the Kiselevka–Manoma Accretionary Terrane (Sikhote-Alin): Petrogeochemistry, Formation Conditions, and Tectonic Setting

New petrogeochemical data were used to determine the conditions of the formation and tectonic setting of volcanic rocks of the Lake Udyl’ area. These rocks were compared with similar rocks in the region. The volcanic rocks of the Lake Udyl’ area are subdivided into two genetic types: (1) within-plate oceanic volcanic rocks ascribed to the accretionary volcanogenic–siliceous complex (Tithonian–Valanginian–Hauterivian–Barremian) similar to accretionary complexes in other segments of the Kiselevka–Manoma Terrane, and (2) suprasubduction-zone volcanic rocks from the island-arc volcanogenic-terrigenous complex (Valanginian–Hauterivian–Aptian–Albian–Cenomanian). A synthesis of new geological and petrogeochemical data, as well as previous geochronological and paleomagnetic data indicates the co-occurrence of genetically diverse complexes in the Udyl’ segment.

Paleogeographic and tectonic evolution of the Pampia Terrane in the Cambrian: New paleomagnetic constraints

Paleomagnetic, magnetic fabric and rock magnetic studies were carried out in the late Middle to early Late Cambrian Campanario Formation exposed in NW Argentina. The study also presents preliminary results from the Early Cambrian metasediments of the Puncoviscana Formation and from Mojotoro intrusive. A new paleomagnetic pole, C2, was computed for the Campanario Formation (23.6°N, 346.5°E, A95, 7.0°, N: 11 sites) from the localities of Tilcara (T), Terma de Reyes (R) and El Perchel (EP), including previous data from Santa Victoria Oeste (M), in northernmost Argentina. A positive fold test was obtained for Tilcara locality while a positive regional tilt test was obtained for mean site directions for the four localities. This pole can be considered as the representative pole position for the Pampia terrane for the late Middle to Late Cambrian. Previous paleomagnetic data for the same formation from the Iruya-Matancillas locality show an in situ clockwise rotation of about 30° around a vertical axis when compared with the mean Pampia pole. The same is observed when comparing the early Ordovician pole for the Santa Rosita Formation at those localities with the recently obtained coeval pole of the La Pedrera Formation, indicating that local tectonic rotations, affected that area. These results suggest that previous paleomagnetic interpretations for these Late Cambrian and Early Ordovician rocks in the region as recording displacement of the Pampia terrane in Cambrian times are probably incorrect. Additionally, two virtual geomagnetic poles were computed for the Puncoviscana Formation (TP1: 34.5°N, 52.3°E, A95: 5.0°, n: 22 specimens and TP2: 38.3°N, 33.6°E, A95: 5.7°, n: 14 specimens) and one for the Mojotoro Intrusive (MO: 9.1°N, 345.6°E, A95: 16.4°, n: 11 specimens). These and previous Early Cambrian paleomagnetic data from the Pampia terrane differ from Gondwana coeval reference directions in inclination and/or declination, lacking a simple pattern.

Paleomagnetism of Permo–Triassic volcanic units in northern Patagonia: are we tracking the final stages of collision of Patagonia?

A paleomagnetic and geochronologic study was carried out on Late Permian-to-Early Triassic magmatic units exposed in the North Patagonian Massif, near the locality of Estancia La Esperanza (Rio Negro Province, Argentina), to provide better paleogeographic and tectonic constraints on the evolution of Patagonia and its relations with Gondwana in the Late Paleozoic–Early Mesozoic. The study included the Late Permian (264 ± 2 Ma) Rhyolite Dome, the Collinao Dacite, for which we obtained a U–Pb zircon crystallization age of 253 ± 2 Ma, several basic dikes, that intrude older granite units (255 ± 2 Ma), and a swarm of acidic dikes for which an Early Triassic age had been previously assigned that we confirmed with a U–Pb zircon age of 244 ± 2 Ma. A paleomagnetic pole (C), computed on the basis of seven VGPs, was obtained for the Collinao Dacite and associated units (48.3°S, 349.9°E, N = 7, A95 = 15.1°). A single VGP for the somewhat older Rhyolite Dome falls close to that pole. A second paleomagnetic pole (A) which strongly disagrees with the C position was computed based on 12 VGPs from the same number of acidic dikes (87°S, 51.5°E, N = 12, A95 = 8.1°). The basic dikes, with ages bracketed between the dacitic and the rhyolitic dikes, yielded four VGPs, two of which are consistent with the C pole and the other two are close to the A pole. The C pole falls on a much older position (Late Carboniferous) on different Gondwana/South America reference paths, which is clearly anomalous based on its Late Permian age. The A pole, in turn, is consistent with the 250/240 Ma paleomagnetic poles in most reference paths for Gondwana/South America. Either regional tilting or rotation around a vertical axis to explain the anomalous C pole is unlikely considering the local geological evidence. A working model is presented to explain the discrepancy as due to around 30° CCW rotation of the whole North Patagonian Massif during the latest Permian and earliest Triassic, closing a V-shaped basin that separated it from southern Gondwana, as the final stages of collision of an allochthonous or para-autochthonous Patagonia terrane. This hypothesis is consistent with Late Permian-to-Early Triassic evidence of deformation in the Hesperides Basin as well as in northern Patagonia. Scarce previous paleomagnetic data from this region can be reconciled with this model, considering that they are very loosely constrained in age.

Provenance, age, and tectonic implications of Neoproterozoic strata in the Jiamusi Massif: Evidence from U–Pb ages and Hf isotope compositions of detrital and magmatic zircons

The Jiamusi Massif forms part of the eastern Central Asian Orogenic Belt (CAOB) and the Pacific oceanic tectonic domain, but its tectonic affinity is highly controversial. Here, we present U–Pb ages and Hf isotope compositions of detrital zircons from five metasedimentary rocks and one monzogranite within the Jiamusi Massif, and our aim was to constrain the depositional ages and provenance of the strata, as well as the tectonic affinity of the massif. Two specimens of two-mica schist from the Upper and Lower Kimkanskaya groups (Russian Far East) yielded zircon age populations at 572, 826, 891, 958, and 1776Ma, and 682, 752, 835, and 925Ma, respectively; a sericite schist and muscovite schist from the Majiajie Group (NE China) yielded zircon age populations at 951, 1232, 1419, 1643, and 2687Ma, and 1151, 1276, 1444, 1623, 1805, and 2652Ma, respectively; and a two-mica schist from the Ximashan Formation of the Mashan Group (NE China) yielded zircon age populations at 994, 1281, 1439, 1647, and 1805Ma. Taking into account the general geological relationships in the area, zircon age populations, and Hf isotopic compositions, combined with an age of 492Ma for a monzogranite that intrudes the Ximashan Formation, we conclude that the Lower Kimkanskaya Group formed in the Neoproterozoic and was sourced mainly from a Neoproterozoic terrane, whereas the Majiajie Group and Ximashan Formation formed in the Neoproterozoic but were sourced dominantly from a Mesoproterozoic terrane. Taking into account previous paleomagnetic data, our dating results and comparisons with zircon age populations in Precambrian rocks from northeastern Gondwana and the southern Siberia, North China, and Tarim cratons, suggest that the Jiamusi Massif has an affinity with the Tarim Craton.

PETRO- AND PALEOMAGNETIC STUDIES OF BASALTS OF THE UPPER DEVONIAN APPAINSKAYA SUITE (WESTERN YAKUTIA)

PETRO- AND PALEOMAGNETIC STUDIES OF BASALTS OF THE UPPER DEVONIAN APPAINSKAYA SUITE (WESTERN YAKUTIA)

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.

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.

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.

Further paleomagnetic results for lower Permian basalts of the Baoshan Terrane, southwestern China, and paleogeographic implications

The Baoshan Terrane of southwestern China is considered to have been part of the Cimmerian block during the late Paleozoic; consequently, knowledge of its paleoposition and geological evolution can provide constraints on the Permian breakup of northern East Gondwana. Therefore, we conducted paleomagnetic and rockmagnetic studies on lower Permian basalts from four localities in the Baoshan Terrane. The basalts hold a stable characteristic remanent magnetization (ChRM) at high temperatures (300–680°C) that is carried by magnetite, maghemite, and hematite with both pseudo-single and multiple domains. To test the reliability of data from these volcanic rocks, we analyzed the geomagnetic secular variation (GSV) and reliability of both the present data and previous paleomagnetic data. The results from 23 sites yield a single reversed polarity directed downwards to the southwest, giving a site-mean direction of Dg/Ig=156.7°/56.6° (kg=8.0, α95=11.4°) before tilt correction, and Ds/Is=218.3°/60.1° (ks=14.1, α95=8.4°) after tilt correction. The result passed the fold test, but the GSV was able to be averaged out in only two sections. All available data were examined section-by-section using the angular dispersion (SB) of virtual geomagnetic poles (VGPs) to ensure that the GSV was completely averaged out. Because the dispersion in declinations is likely to have been affectedby subsequent tectonic deformation, the paleosecular variation (PSV) could not be evaluated from all the data amassed from different sections, and the PSV was able to be removed from only four (combined) sections. A small-circle fit of these VGPs gives an averaged paleocolatitude of 51.9°±3.7° (N=31 sites) centered on 24°N, 99°E. The result indicates that the sampled area of the Baoshan Terrane was located at a latitude of 38°S±3.7° during the late early Permian. A comparison of this result with early Permian data from Gondwanan blocks suggests that the Baoshan Terrane was situated near the junction of northern India and northwestern Australia, and that it broke away from western Australia after the early Permian.

Internal crustal deformation in the northern part of Shan-Thai Block: New evidence from paleomagnetic results of Cretaceous and Paleogene redbeds

In order to describe the internal deformation of the northeast part of the Shan-Thai Block resulting from the penetration of the Indian plate into Asia, a paleomagnetic study was carried out on the Cretaceous and Paleogene strata in the southern part of the Simao Terrane. High-temperature magnetic components with unblocking temperatures around 680 °C were isolated and positive fold test shows its primary nature of magnetization. The tilt corrected site-mean directions of the Lower Cretaceous and Upper Cretaceous from the Menglun area are Ds = 46.2°, Is = 45.9°, k = 11.0, α95 = 10.6° and Ds = 33.2°, Is = 30.9°, k = 68.4, α95 = 8.2°, respectively. The site-mean directions of the Upper Cretaceous and Lower Paleogene for the Mengban area are Ds = 50.5°, Is = 31.0°, k = 207.6, α95 = 6.4° and Ds = 43.5°, Is = 23.0°, k = 26.1, a95 = 13.4°, respectively. The results of the Lower Cretaceous and Upper Paleogene from the Mengla area are Ds = 46.9°, Is = 42.2°, k = 27.3, α95 = 7.7° and Ds = 41.8°, Is = 23.8°, k = 38.9°, a95 = 5.8°, respectively. In comparison with previous paleomagnetic data of the Simao Terrane, the rotational deformation can be divided into four stages. The Cretaceous and Paleocene sediments of the Simao Terrane experienced intensive folding before the early Oligocene. During the early Oligocene to early Miocene, the Shan-Thai and Indochina Blocks experienced southeastward extrusion with ~ 20° clockwise rotation relative to the South China Block. During the middle to late Miocene, the Shan-Thai Blocks experienced more 15° clockwise rotation. Since the late Miocene, the activity of strike-slip faults surrounding the Simao Terrane enhanced the internal differential rotations of the Terrane. These deformation processes finally resulted in a complex internal deformation of the Simao Terrane.

Kinematics of the Central Taurides during Neotethys closure and collision, the nappes in the Sultan Mountains, Turkey

In the Central Taurides, the Sultan Mountains comprise in ascending order the Cimendere unit and the Aksehir, Doganhisar, Cay nappes composed of metasedimentary sequences deposited from Cambrian to Tertiary. The overthrust of the Cay nappe on the Lutetian Celeptas formation representing the uppermost stratigraphic position in the Cimendere unit indicates that the latest nappe emplacement occurred during the Middle Eocene. The Oligocene and Miocene rocks are in post-tectonic facies in the west Central Taurides. The kinematic data from these nappes related to closure of the Neotethys reveal a top-NE shear sense in the northwest part and a top-SE shear sense in the southeast part of the Sultan Mountains. The Sultan Mountains are located in the north part of the Isparta Angle which was tectonically assembled by the Lycian, Hoyran–Beysehir–Hadim and Antalya allochthons on the Bey Daglari and Anamas–Akseki autochthons from the Latest Cretaceous to the Late Pliocene. The previous paleomagnetic data showed that the west and east subsections of the Isparta Angle were subjected to post-Eocene 30°–40° anticlockwise and clockwise rotations, respectively. In consideration of these paleomagnetic data, the kinematic data measured in the Sultan Mountains might be restored into approximately E–W-trending linear fabric associated with a top-E shear sense. These new kinematic data from the nappes in the Sultan Mountains disagree with the existing tectonic models that suggest N–S nappe translation over the Central Taurides during the latest Cretaceous–Middle Eocene. The alternative tectonic model for the Antalya nappes in the core of the Isparta Angle related to east–west compression suggests westward and eastward nappe emplacements on the surrounding autochthons. However, the new kinematic data presented here point consistently to a top-E shear sense in all tectonostratigraphic units in the Sultan Mountains currently located in the north part of the Anamas–Akseki autochthon.

New and revisited paleomagnetic data from Permian–Triassic red beds: Two kinematic domains in the west-central Pyrenees

New paleomagnetic results of Permian–Triassic red beds from Bielsa, Aure and Somport-Anayet sectors in the Pyrenean Axial Zone are presented and combined with revisited and reviewed paleomagnetic data from the west-central Pyrenees. The paleomagnetic data from the red beds vary between different sectors that share similar structural position; i.e. whilst all sectors share the existence of a characteristic prefolding component, a Cenozoic postfolding component is found only in one area but not in other areas with similar structural position and kinematics. Previous paleomagnetic data to the west of the studied zone reveal a pre-Turonian remagnetization component, but this secondary component is not found in an area that shares a similar structural position (Aure). This variability suggests that the paleomagnetic behavior is the result of a series of factors related to the particular tectonic history of the region (sedimentation, burial, and deformation during basin inversion) and therefore paleomagnetic data demands careful assessment in order to unravel the kinematics of areas with equivalent structural positions in orogens.However, important kinematic implications that hold in the Pyrenees can be inferred from the restoration of the Permian–Triassic characteristic magnetizations to positions previous to the paleomagnetic rotations recorded by Cretaceous or Cenozoic paleomagnetic data. The restoration reveals on one hand the lack of large rotations in the South Pyrenenan Zone except in the Nogueras area, according to Bates (1989), and on the other hand, the contrasting rotations recorded to the west of the studied zone, in the Paleozoic Basque Massifs (PBM) and the South-Pyrenean Zone, indicating the existence of two different tectonic domains in the west-central sector of the Pyrenees. The strong clockwise rotations postdating the Early Cretaceous remagnetization that are recorded in the PBM and in the North Pyreneean Zone, suggest a late dextral shear deformation affecting areas near the North Pyrenean Fault Zone.

Paleomagnetic results from the Early Cretaceous Zenong Group volcanic rocks, Cuoqin, Tibet, and their paleogeographic implications

A paleomagnetic study has been carried out on the Early Cretaceous Zenong Group volcanic rocks (ca. 110–130Ma) near Cuoqin town in the central Lhasa terrane. Stepwise thermal demagnetization up to 680°C isolated a stable high-temperature component (HTC) including antipodal dual polarities. The HTC directions passed both a fold test at 99% confidence and a reversal test at 95% confidence, suggesting a primary origin. The tilt-corrected average direction for 18 sites is D=327.0°, I=35.7°, κ=59.3°, α95=4.5°, which corresponds to a paleopole at 58.2° N, 341.9° E (A95=4.6°), yielding a paleolatitude of 19.8°±4.6° N for the study area. Our results, combined with previous paleomagnetic data, suggest that southern Tibet was at a mean paleolatitude of 20° N during the Cretaceous and Paleogene. When compared with the apparent polar wander paths of Asia, the difference suggests that only ca. 870km north–south crustal shortening has accumulated between the Lhasa terrane and stable Asia since ca. 110Ma. When comparing the paleolatitudes of the Lhasa terrane and India, the results indicate that the width of the Neotethys was 6720±690km during the Early Cretaceous.

Paleomagnetic constraints on an Archean–Paleoproterozoic Superior–Karelia connection: New evidence from Archean Karelia

Charno–enderbitic granitoids in the Karelia craton of the Fennoscandian shield have been studied paleomagnetically. The characteristic remanence component has a steep negative inclination and is interpreted to record magnetization at a maximum age of 2684±2Ma. Consistently stable results were obtained from 12 sites in the Koitere area, corresponding to regions with high positive magnetic anomalies and high remanence intensities. Petrographic studies, coupled with rock magnetic investigations, indicate that the remanence resides in fine SD/PSD magnetite grains formed during Neoarchean clinopyroxene alteration. Cross-cutting vertical/subvertical Paleoproterozoic dolerite dykes suggest that the Koitere granitoids are in their original orientations and were not affected by Svecofennian deformation at ca. 1.9–1.8Ga.The Koitere granitoids have an opposite polarity compared to the steep positive inclination remanence direction of the previously studied ca. 2.63Ga Varpaisjärvi enderbites and granulites. The data from Koitere and Varpaisjärvi imply that at ca. 2.7–2.6Ga the Karelia craton was located at high latitudes of 80–60°, whereas previous paleomagnetic data from ca. 2.5Ga formations in the Vodlozero terrane in NW Russia indicate a near-equatorial position.Comparison of paleomagnetic data from the Koitere and Varpaisjärvi granulite-grade rocks with rocks of similar age in the Superior craton shows that at ca. 2.7–2.6Ga the Superior and Karelia cratons were located at high latitudes and in close proximity, although the present data cannot demonstrate that the cratons were amalgamated. However, during the Archean–Paleoproterozoic transition at ca. 2.50Ga both cratons experienced significant rotation and drifting to near-equatorial paleolatitudes, suggesting that the Superior and Karelia cratons may have been attached at that time.

Rapid Early Cambrian rotation of Gondwana

Research Article| August 01, 2010 Rapid Early Cambrian rotation of Gondwana Ross N. Mitchell; Ross N. Mitchell Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, Connecticut 06511, USA Search for other works by this author on: GSW Google Scholar David A.D. Evans; David A.D. Evans Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, Connecticut 06511, USA Search for other works by this author on: GSW Google Scholar Taylor M. Kilian Taylor M. Kilian Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, Connecticut 06511, USA Search for other works by this author on: GSW Google Scholar Geology (2010) 38 (8): 755–758. https://doi.org/10.1130/G30910.1 Article history received: 28 Nov 2009 rev-recd: 21 Mar 2010 accepted: 25 Mar 2010 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ross N. Mitchell, David A.D. Evans, Taylor M. Kilian; Rapid Early Cambrian rotation of Gondwana. Geology 2010;; 38 (8): 755–758. doi: https://doi.org/10.1130/G30910.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Based on the history of Mesozoic–Cenozoic plate motions, as well as simple dynamical considerations, a “speed limit” for tectonic plates has been suggested at ∼20 cm/yr. Previous paleomagnetic data from the Early Cambrian of Gondwana are conflicting but generally imply rapid motions approaching that limit. Herein we describe results from a continuous paleomagnetic sampling of Lower to Middle Cambrian strata from the Amadeus Basin, central Australia. We find characteristic remanence directions that show an ∼60° declination shift through the section. Assuming a tectonically assembled Gondwana supercontinent by Early Cambrian time, this large vertical-axis rotation of its Australian sector corresponds to an equally large translation across paleolatitudes for its Brazilian and West African sectors. Analysis of all high-quality paleomagnetic data from Gondwana both confirms and constrains the 60° rotation to have occurred toward the end of Early Cambrian time, at rates exceeding 16 +12/–8 cm/yr. These observations suggest that either nonuniformitarian plate tectonics or an episode of rapid true polar wander occurred during the Cambrian “explosion” of animal life. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.