The Altaids is the largest orogenic belt in Central Asia occupying some ~9 million km 2 . It is a Turkic-type orogeny assembled between ~750 and ~ 150 Ma around the western and southern margins of the Siberian Craton . All available data published so far, geological, geophysical, and geochemical—mostly high-resolution U Pb ages—document the growth of only three arc systems in Central and Northwest Asia during this time period, an interval throughout which there were no major arc or continental collisions in the area. While the Altaids were being constructed as a Turkic-type orogen, continental crust grew in them by 1/3 of the global average. The Altaids thus added some 3 million km 2 to the continental crust over a period of 0.6 billion years, typical of Phanerozoic crustal growth rates. The methods of reconstruction employed in elucidating the history of the Altaids are shown to be useful also in late Precambrian orogens built by ordinary plate tectonic processes, but contain no index fossils to erect a biostratigraphy . They also show that without a detailed knowledge of the strain histories of orogenic belts soldering different continental entities, no reconstruction can be even approximatley correct.

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. (c) 2020 The Authors. Published by Elsevier B.V. on behalf of International Association for Gondwana Research. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Undeformed and unmetamorphosed diabase dykes up to 5 m wide occur in an area of ∼100 km2 about 50 km northwest of Montreal near the village of Sainte-Sophie. The dykes are subvertical and oriented east–west. The most common phenocryst phase is plagioclase (1–2 mm, exceptionally 10 mm), followed by olivine, and in one dyke, pyroxene. Most dykes have vesicles 0.1–10 mm in diameter and fine-grained margins. Alteration is extensive: plagioclase is partly sericitized, olivine is serpentinized, and zeolites and carbonate are developed in the vesicles and matrix. Ar–Ar dating was challenging, but the weighted mean of two plateau ages indicates intrusion and cooling at 591.6 ± 2.5 Ma. The overall characteristics of these dykes suggest that they may be a facies of the much larger Grenville dyke swarm to the west. However, there are distinct chemical differences that suggest they were fed from a different, generally more enriched mantle source. This zone may be related to the one that produced the alkaline Monteregian intrusions some 470 million years later in the same region. If the Sainte-Sophie dykes are part of the Grenville dyke event, then the use of chemical fingerprints to identify components of this swarm must be used with caution. Another difference between the Sainte-Sophie and main Grenville dykes is the presence of vesicles and zeolites in the former, which suggests the dykes were emplaced close to the surface; hence, this crustal block has seen little erosion during the last 600 million years.

The largest mountain belt in Central Asia (∼9 million km2) is called the Altaids. It was assembled between ∼750 and ∼130 Ma ago around the western and southern margins of the Siberian Craton, partly on an older collisional system (the “Urbaykalides”). Geological, geophysical, and geochemical data—mostly high-resolution U-Pb ages—document the growth of only three arc systems in Central and Northwest Asia during this time period, an interval throughout which there were no major arc or continental collisions in the area. While the Altaids were being constructed as a Turkic-type orogen, continental crust grew in them by 1/3 of the global total. The Altaids thus added some 3 million km2 to the continental crust over a period of 0.6 billion years, typical of Phanerozoic crustal growth rates.

Local-scale folds within the Mississippian Madison Group of the frontal Montana Rockies preserve pre- and synfolding remagnetization data. Paleomagnetic results display inclinations of ∼70°, in contrast to the expected shallower directions for North American Mississippian rocks. The magnetization is chemical in origin, preserved in superparamagnetic to single-domain magnetite grains from fluid activity. Magnetic intensity results in the study area suggest that mineralization was more prevalent in the interior of the fold-and-thrust belt and diminished toward the east, resulting in lower intensities from less magnetite growth in the very frontal portions of the belt into the foreland. Fold test results of individual folds show syn- and prefolding remagnetizations as a function of location across the belt, with synfolding results in more westerly locations and prefolding results in the most frontal folds of the belt. By comparing our synfolding results with previously determined deformation ages for the Rocky Mountains, an Eocene (53.6 Ma) age for the remagnetization can be assigned. Based on the relative timing of remagnetization, a spatial pattern of folding in the study area is revealed. Major folding commenced (i.e., synfolding magnetization) during an Eocene remagnetization event, while the most frontal portion remained undeformed (i.e., prefolding magnetization) and was subsequently folded after regional remagnetization.

Carbonate formations from many locations reveal magnetizations that are secondary. Attaching a numerical age to these remagnetizations would provide information on orogenic processes. To contribute to the effort of assigning an age to remagnetization events, Lower Cretaceous formations from the Monterrey Salient in northeast Mexico were sampled. Individual fold tests reveal eight site-pair synfolding remagnetizations (set A) of Eocene age. The remanence is a chemical remanent magnetization (CRM) carried by magnetite. The magnetization of set B is possibly due to an early carbonate alteration that produced a remanence significantly older than folding. A complexity of set B is that the site pairs reveal k-versus-unfolding percentage diagrams with maximum unfolding peaks at 100 to 125%. An explanation of multiple deformation phases with an earlier horizontal folding phase around a non-plunging horizontal axis and a later vertical axis rotation is suggested for the past 100% peaks of the B sites. The latter deformation, rotation about a vertical axes, is revealed by a declination-strike test in set A sites and site means of the full collection that deviate counterclockwise from the reference declination. By combining synfolding results with published 40Ar/39Ar illite ages of folding (Fitz-Diaz et al., 2016), remagnetization ages in set A sites of 48–52 Ma are obtained. The magnetization in set B sites is likely older, though not well constrained. Interestingly, prior results from the central Sierra Madre Oriental, to the south, show two remagnetization events, Late Cretaceous and Early Eocene in age, in a succession from W to E (Nemkin et al., 2015). The age of folding and remagnetization acquisition in set A sites along the Monterrey Salient are concurrent with the frontal, remagnetized folds in the central Sierra Madre Oriental. Thus, the timing of major remagnetization in the Monterrey Salient occurred in the Eocene.

The Kisii Series lavas of western Kenya were the target of a paleomagnetic study. The Kisii Series is a volcano-sedimentary sequence dated to 2531±3Ma (U–Pb) that rests unconformably over the Mesoarchean–Neoarchean Nyanzian and Kavirondian Series. The paleomagnetic study reported in this paper expands on an earlier study by Brock et al. (1972) using modern demagnetization and analysis techniques. In spite of the advanced methods, the results of both our new study and the previous study are statistically indistinguishable. We therefore combine the results of both investigations to arrive at a grand mean pole at 7°S, 166°E (A95=8°). Due to the relatively minor tilt-corrections, a fold test is inconclusive; however, the dual-polarity magnetization passes a reversal test. We argue for a primary remanence on the basis of a comparison to other paleomagnetic data in Kenya and Tanzania and geological information. We examine the relationships between age-equivalent paleomagnetic poles from the Tanzanian, Zimbabwe and Kaapvaal cratons. Based on this limited dataset, we cannot conclude whether or not the observed apparent polar wander was due to true polar wander or modern-style plate tectonics, such as would be implied by the (variable) apparent polar wander path segments. We favor the latter explanation based on the disparate lengths of the Zimbabwe versus Tanzanian apparent polar wander paths during the 2700–2500Ma interval. The Protopangea model is not consistent with paleomagnetic data from these three cratons.

Paleomagnetic results on thick lava series are among the most important sources of information on the characteristics of ancient geomagnetic fields. Most paleo-secular variation data from lavas (PSVL) are of late Cenozoic age. There are far fewer results from lavas older than 5 Ma. The Central Asia Orogenic Belt that occupies several million square kilometers in Asia is probably the world's largest area of Paleozoic volcanism and is thus an attractive target for PSVL studies. We studied a ca. 1700 m thick lava pile in eastern Kazakhstan of Early Permian age. Magmatic zircons, successfully separated from an acid flow in this predominantly basaltic sequence, yielded an Early Permian age of 286.3 ± 3.5 Ma. Oriented samples were collected from 125 flows, resulting in 88 acceptable quality flow-means (n ⩾ 4 samples, radius of confidence circle α95 ⩽ 15°) of the high-temperature magnetization component. The uniformly reversed component is pre-tilting and arguably of a primary origin. The overall mean direction has a declination = 242.0° and an inclination = −56.2° (k = 71.5, α95 = 1.8°; N = 88 sites; pole at 44.1°N, 160.6°E, A95 = 2.2°). Our pole agrees well with the Early Permian reference data for Baltica, in accord with the radiometric age of the lava pile and geological views on evolution of the western part of the Central Asia Orogenic Belt. The new Early Permian result indicates a comparatively low level of secular variation especially when compared to PSVL data from intervals with frequent reversals. Still, the overall scatter of dispersion estimates that are used as proxies for SV magnitudes, elongation values and elongation orientations for PSVL data is high and cannot be fitted into any particular field model with fixed parameters. Both observed values and numerical simulations indicate that the main cause for the scatter of form parameters (elongation values and elongation orientations) is the too small size of collections. Dispersion estimates (concentration parameter and standard angular deviation) are more robust, and their scatter stems from other sources, which may include non-stochastic features of datasets like clusters, loops etc., or non-stationary behavior of secular variation magnitude over time intervals of many million years.

Description of precipitation patterns and changes in the hydrological cycle during periods of past global change is crucial for providing an understanding of terrestrial climate systems and for predicting impacts of future climate change such as shifting water availability. While a number of proxies and climofunctions exist for reconstructing paleoprecipitation using paleosols, all of the available tools for reconstructing paleoprecipitation are either limited to certain precipitation ranges (effective only for low-precipitation regimes; e.g., depth to Bk, chemical index of alteration [CIA-K]), or are relevant only to a limited range of paleosols (single-pedotype relationships; e.g., calcium-magnesium index [CALMAG]). Here, we measure the acquisition of isothermal remanent magnetization in B horizons of modern soils to quantify the ratio of pedogenic magnetic minerals goethite and hematite, and we use the relationship between these soil magnetic properties and measured climatic variables at each soil site to derive a new quantitative proxy for precipitation. By compiling both literature-derived and measured goethite-hematite (G/H) ratios and mean annual precipitation estimates for a global suite of modern soils (n = 70), we describe a strong linear relationship (R-2 = 0.96) between the G/H ratios of soil B horizons and mean annual precipitation that can be used to estimate paleoprecipitation values for a wide range of climatic regimes (100-3300 mm yr(-1)) and soil types (Inceptisols, Alfisols, Ultisols, Oxisols, Mollisols, Aridisols, Spodosols). We tested the new climofunction using paleosols from the early Eocene of Wyoming, which show that estimates based on G/H ratios compare favorably to and expand upon previously published estimates based on paleosol data.

The Mongol-Okhotsk Ocean closed when the Amuria block, normally considered to have been part of the North China block since the early Mesozoic, and the southern margin of Siberia collided in Late Jurassic to Early Cretaceous times. The resulting suture runs WSW-ENE and is reasonably well defined to the east of longitude 100 degrees E. Because no evidence exists for any westward prolongation of the Mongol-Okhotsk Ocean suture toward the Tarim block, the cryptic termination of the suture is an enigma, compounded by the fact that a tomographically identified slab in the lower 1000 km of the mantle, interpreted as a remnant of Mongol-Okhotsk oceanic lithosphere, has a clear N-S trend, at almost right angles to the surface suture. No sensible explanation can be constructed for a rotation of some 90 degrees of this slab. There is a solution, however, to both these enigmas if we consider that the Triassic Mongol-Okhotsk Ocean existed east of an initially meridian-parallel, but later progressively more sinuous, late Paleozoic Pangea margin. This margin consisted of Siberia, Amuria, and the China continental elements. The Mongol-Okhotsk Ocean was subducting westward during the early Mesozoic and likely older times underneath this margin. This would readily explain the tomographic N-S slab orientation at depths of 2000 km and greater. Paleomagnetic inclination differences between the global apparent polar wander path in Siberian coordinates and results from the North China block show a gradually diminishing trend with time, as these cratons approached each other during the Jurassic. During this time, the paleomagnetic data of the North China block show that it underwent a slight northward motion, but with a considerable counterclockwise rotation of similar to 90 degrees. At the same time, the Mongol-Okhotsk Ocean-bordering margin of Eurasia (between Siberia and Tarim) moved southward by similar to 30 degrees and rotated 45 degrees clockwise. These continental scissoring movements caused doubly vergent subduction of the Mongol-Okhotsk Ocean. Paleomagnetic data suggest final closure of the Mongol-Okhotsk Ocean in latest Jurassic-earliest Cretaceous time. Arc-related rocks above the subduction zone follow the outline around the core of the Tuva-Mongol belt in the eastern Altaids between Amuria and Siberia, and they form a tightening, westward-convex Tuva-Mongol orocline. This large-scale oroclinal bending of the crust above a disappearing ocean is reminiscent of similarly tightening oroclines in Kazakhstan and Variscan Europe, which closed earlier by subduction in the late Paleozoic.

Growth of magnetite has been variably linked to fluid-bearing events or clay diagenesis, and the development of a chemical remagnetization as a result of such events. In this study we examine remagnetized carbonate rocks from the central Sierra Madre Oriental (the Mexican fold-thrust belt) in order to develop a method for dating synfolding remagnetizations. By combining Ar-40/Ar-39 deformation ages with new paleomagnetic results, we present a quantitative method for absolute dating of synfolding remagnetization. We find that the history of the central Sierra Madre Oriental involved two separate remagnetization events in our study area; synfolding remanence acquisition ca. 77 Ma (Late Cretaceous) in the Zimapan Basin and a younger synfolding remagnetization event ca. 44 Ma (mid-Eocene) in the Tampico-Misantla Basin. The growth of magnetite leading to chemical remagnetization detected in these limestones is interpreted as the result of rock interactions with an Fe-bearing fluid.

Paleomagnetic studies of thick lava series are one of the most reliable sources of data on the ancient geomagnetic field. However, most of such data are younger than 5 Ma, with much fewer results on the rest of the Cenozoic and the Mesozoic. Two wholesome results are available for the Precambrian but none for the Paleozoic. Late Permian basalts and rhyolites from northeastern Kazakhstan were studied to obtain first estimates of the geomagnetic-field characteristics during that period. We present preliminary results on part of the collection (66 flows (sites)) from a section ~1600 m thick. The characteristic component of reversed polarity was isolated by stepwise demagnetization at all the sites with a slight error. This component is of prefolding age and, most likely, primary. No abnormal magnetization direction is observed in the data, and the average directions of the characteristic component at the sites are tightly clustered (D = 243.3°; I = −57.0°; k = 79.1; α95 = 2.0°; 65 sites). As compared with the published data on Cenozoic and Mesozoic thick lava series, secular variation was much weaker in the Late Permian than in the Mesozoic or Cenozoic, and the geomagnetic field was less disturbed. Secular-variation models based on the Late Cenozoic data show even more dramatic differences.

Significance Since the Pangea supercontinent formed about 320 million years ago, plumes that sourced large igneous provinces and kimberlites have been derived from the edges of two stable thermochemical reservoirs at the core–mantle boundary. We test whether it is possible to maintain this remarkable surface-to-deep Earth correlation before Pangea through the development of a new plate reconstruction method and find that our reconstructions for the past 540 million years comply with known geological and tectonic constraints (opening and closure of oceans, mountain building, and more). These results have important implications for Earth history, including the style of mantle convection in the deep past and the long-term stability of mantle reservoirs.

The Altaids are one of the largest superorogenic complexes in the world in which two genetically closely related orogenic complexes ended up generating much of northern Asia during the Palaeozoic and the early and medial Mesozoic. This immense superorogenic complex evolved as a consequence of the development of two large island arc systems called the Kipchak and the Tuva-Mongol arcs and that were similar in size to the present-day Southwest Pacific arc chains. They both have rifted from the then combined (or close) Siberian and Russian cratons during the latest Neoproterozoic/earliest Cambrian following the Baykalide/Preuralide orogeny. As a consequence of this rifting, the Khanty-Mansi Ocean opened behind them and they faced the Turkestan and the Khangai-Khantey Oceans, respectively. It is at the expense of these oceans that these two arc systems generated large subduction-accretion complexes. The Kipchak Arc was completely detached from the Siberian craton during the Neoproterozoic and it was reconnected with it along its trend by means of ensimatic arc systems that formed along its strike during the medial to late Cambrian. These ensimatic arcs also accumulated large volumes of subduction-accretion complexes in front of them during their migratory development throughout the Palaeozoic and, in Mongolia and in the Russian Far East, into the medial Mesozoic. As the accretionary complexes grew, magmatic fronts of their arcs migrated into them, turning them into arc massifs by magmatism and HT/LP metamorphism in arc cores. Especially near the Siberian Craton and in the Khangai-Khantey Ocean, the subduction-accretion complexes were fed by turbidites shed from old continental crustal pieces. Where arc magmatic axes migrated into such accretionary complexes, the material of which is of ancient continental provenance, they in places exhibit Proterozoic zircon ages and isotopic signatures inherited from their ancient source terrains leading to the mistaken conclusion of the presence of ancient continental crust under such arcs. It seems imperative to have proper field geological data together with the isotopic work to derive any reliable conclusions concerning crustal growth rates. We have compiled 1090 new, mostly zircon ages of magmatic and some metamorphic rocks from the literature for the whole of the Altaid supeororogenic complex. These ages show continuous arc activity from the Ediacaran into the early Cretaceous in the Altaids, although arc magmatism turned off already in the Triassic in the western Altaids. Much of the succeeding alkalic magmatism in the western moiety of the superorogenic complex was related to strike-slip activity opening the West Siberian basins such as the Nurol and Nadym and the large pull-apart basins of Alakol, Junggar and Turfan. There are numerous other smaller areas of extension related to the late Altaid strike-slip activity and they too have alkalic magmatism associated with them. Some of the alkalic granites not related to the late strike-slip activity may have been related to slab fall-off after terminal collisions, although this is now difficult to document with any confidence. It is noteworthy that no Tibet-type collisional plateaux were ever produced as a consequence of Altaid collisions. We have been able to find no evidence anywhere in the Altaids for independent trans-oceanic migrations of numerous 'terranes' tied to individual subduction zones. Only two major subduction zones were responsible for the entire Altaid evolution from the beginning to the end and this is consistent not only with the present tectonics of the earth, where major subduction zones display great spatial continuity and temporal persistence, but also with the tomographic observations on well-imaged former subduction zones such as those associated with the Tethyan and the North American Cordilleran chains. The entire Altaid collage now occupies some 8,745,000 km(2). At least half of this area represents juvenile addition to the continental crust during the Ediacaran to the earliest Cretaceous interval. That is more than 10% of the entire land area of the Asian continent. Similar events are now going on in the Nipponides in eastern Asia, in the Oceanian arc systems in the southwestern Pacific Ocean and in places around the Caribbea and the southern Antilles. Altaids were one of the main factories-if not the main factory-for the generation of the continental crustal during the earlier half of the Phanerozoic on our earth. This was not because the growth rate of the crust was unusual, but because so much of it was produced in such a huge area and in an interval of some half a billion years.

This study of 118 discrete volcanic flows from the Columbia River Basalt Group is aimed to determine their distribution of geomagnetic field directions and virtual geomagnetic poles (VGPs) and to compare the inherent secular variation parameters with those from other studies. The magnetic signature of these rocks is uniformly carried by primary titanomagnetite, indicating that magnetic changes are due to variations in the magnetic field. Although most flows are flat lying, those that are tilted pass the Tauxe and Watson tilt test. Sequential flows with statistically similar site means were grouped, and directions that were considered outliers were evaluated and removed using the Vandamme cut-off method. Three normal-polarity (N-polarity) and three reversed-polarity (R-polarity) intervals are revealed by the stratigraphically ordered flows and have mean directions of N polarity (dec/inc = 6.6A degrees/+61.2A degrees, k = 29.3, alpha(95) = 4.2A degrees), and R polarity (dec/inc = 178.2A degrees/-59.2A degrees, k = 16, alpha(95) = 5.5A degrees). Regression analysis indicates that the secular variation analysis has not been affected by regional rotation, and that apparent polar wander is negligible. The VGP distribution is almost perfectly circular and supports the preference of VGP positions for the dispersion analysis. Dispersion parameters with corrections for within-site scatter (S-b) show a range of 14.3A degrees aEuro"25.5A degrees, including error limits, and were consistently higher for R-polarity results than for those of N polarity. Published dispersion parameters for extrusives < 5 Ma show S-b values slightly lower than ours, yielding values of 16A degrees aEuro"19A degrees, although the difference is not statistically significant. In contrast, published dispersion parameters from high quality data from the Cretaceous Normal Superchron are lower than those for the Neogene, which suggests that the noisiness of the magnetic field correlates with the frequency of reversals. Our new results allow us to extend the Plio-Pleistocene palaeosecular variation database to the bottom of the middle Miocene. Many Miocene formations on a variety of continents are suitable targets for future analysis. Furthermore, the significant difference between the reversed and N-polarity dispersion parameters is intriguing and needs substantiation.

The Altaids, an Ediacaran to early Cretaceous superorogenic complex in central and northwestern Asia, is bounded on the west by the Urals, on the south by the 'Intermediate Units' consisting of the Alay Microcontinent, the Tarim Block and south China carrying also the Manchuride Orogenic Belt and on the northeast by the Siberian Craton. Within this frame the superorogenic system evolved along two major arc systems, both in part rifted from the Siberian Craton. Throughout the evolution of the system there were no continental or arc collisions until the system was sealed by its final collision with the intermediate units in the late Palaeozoic and the closure of the Khangai-Khantey Ocean during the early Cretaceous. Available reliable palaeomagnetic data are consistent with the operation of only two major arc systems throughout the evolution of the superorogenic complex. During this evolution the Altaids seem to have generated some 3 million km(2) new continental crust which comes to some 0.5 km(3) annually. This is about one-third of the average rate of growth of the continental crust. The global eustatic sea-level seems to have been dominated by the Altaid evolution only during the latest Carboniferous and the early Permian.

The Altaid edifice is the largest superorogenic complex in Asia, which formed between the Ediacaran to the early Cretaceous interval around the western and southern margins of the Siberian Craton occupying some 8,745,000 km2. They grew in part on the ruins of an older, collisional orogenic system, the Urbaykalides. Conflating the two, as is sometimes done in the recent literature, would be like claiming that the Hercynides and the Alpides are the same orogenic belt. Using appellations than other Altaids for the orogenic system described in this paper would not only violate Eduard Suess' priority, but also be wholly inconsistent with their unity of structure and evolution, and would confuse researchers. Available geological and geophysical data are compatible with the development of only two arc systems throughout the evolution of the Altaids in Central and Northwestern Asia from the latest Neoproterozoic to the early Cretaceous. During this entire time interval there was no record of any major collision. ...