Mesoproterozoic paleogeography: Supercontinent and beyond

A set of global paleogeographic reconstructions for the 1770–1270 Ma time interval is presented here through a compilation of reliable paleomagnetic data (at the 2009 Nordic Paleomagnetic Workshop in Luleå, Sweden) and geological constraints. Although currently available paleomagnetic results do not rule out the possibility of the formation of a supercontinent as early as ca. 1750 Ma, our synthesis suggests that the supercontinent Nuna/Columbia was assembled by at least ca. 1650–1580 Ma through joining at least two stable continental landmasses formed by ca. 1.7 Ga: West Nuna (Laurentia, Baltica and possibly India) and East Nuna (North, West and South Australia, Mawson craton of Antarctica and North China). It is possible, but not convincingly proven, that Siberia and Congo/São Francisco were combined as a third rigid continental entity and collided with Nuna at ca.1500 Ma. Nuna is suggested to have broken up at ca. 1450–1380 Ma. West Nuna, Siberia and possibly Congo/São Francisco were rigidly connected until after 1270 Ma. East Nuna was deformed during the breakup, and North China separated from it. There is currently no strong evidence indicating that Amazonia, West Africa and Kalahari were parts of Nuna

Worldwide database for magnetostratigraphy available

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95549/1/eost11864.pd

Archean geodynamics : Ephemeral supercontinents or long-lived supercratons

Many Archean cratons exhibit Paleoproterozoic rifted margins, implying they were pieces of some ancestral landmass(es). The idea that such an ancient continental assembly represents an Archean supercontinent has been proposed but remains to be justified. Starkly contrasting geological records between different clans of cratons have inspired an alternative hypothesis where cratons were clustered in multiple, separate "supercratons." A new ca. 2.62 Ga paleomagnetic pole from the Yilgarn craton of Australia is compatible with either two successive but ephemeral supercontinents or two long-lived supercratons across the Archean-Proterozoic transition. Neither interpretation supports the existence of a single, long-lived supercontinent, suggesting that Archean geodynamics were fundamentally different from subsequent times (Proterozoic to present), which were influenced largely by supercontinent cycles.Peer reviewe

Paleomagnetism of Cryogenian Kitoi mafic dykes in South Siberia: Implications for Neoproterozoic paleogeography

We present a new paleomagnetic pole of 1.1°N, 22.4°E, A95 = 7.4° from the 760 Ma gabbro-dolerite Kitoi dykes located in the southern part of the Siberian Craton. The pole is supported by contact tests and suggests closer position of Siberia relative to Laurentia at 760 Ma than in Mesoproterozoic. We propose that this closer configuration was achieved by dextral transpressive motion of Siberia relative to Laurentia between 780 and 760 Ma. This motion was probably initiated at the first stage of the Rodinia breakup and is coeval with the 780 Ma Gunbarrel magmatic event of the western Canadian shield

Mesoproterozoic intraplate magmatic ‘barcode’ record of the Angola portion of the Congo Craton: Newly dated magmatic events at 1505 and 1110 Ma and implications for Nuna (Columbia) supercontinent reconstructions

In the Angola portion of the Congo Craton, the only Proterozoic large igneous province (LIP) dated prior to this study was the 1380–1370 Ma (Kunene Intrusive Complex and related units). U–Pb TIMS ages on baddeleyite from dolerite sills and gabbro-noritic dykes, has revealed two additional Mesoproterozoic intraplate events: at ca. 1505 and ca. 1110 Ma, that are each proposed to be part of the plumbing system for LIPs. The identification of these three Mesoproterozoic magmatic events (ca. 1505, 1380, and 1110 Ma) represent an initial magmatic ‘barcode’ for this portion of Congo Craton (and formerly connected São Francisco Craton), which can be compared with the magmatic ‘barcode’ record of other blocks to identify former nearest neighbors in the Precambrian supercontinent Nuna (also known as Columbia).Specifically, a 1502 ± 5 Ma U–Pb TIMS baddeleyite age has been obtained for the prominent Humpata dolerite sill which is part of a wider sill province in SW Angola portion of the Congo Craton. The combined presence of both 1505 Ma and 1380 Ma magmatism in the Congo–São Francisco reconstructed craton is a match with similar ages published for two intraplate magmatic provinces in northern Siberia and suggests a nearest-neighbor relationship in the supercontinent Nuna in which northern Siberia is juxtaposed adjacent to the western São Francisco portion of the reconstructed São Francisco–Congo Craton.In addition, a precise U–Pb TIMS baddeleyite age of 1110 ± 2.5 Ma was obtained for a prominent NNW–NNE trending gabbro-noritic (GN) dyke swarm in southeastern Angola, but this age is currently unknown in Siberia suggesting that the breakup of Congo–São Francisco Craton from Siberia happened earlier, perhaps in association with the 1380 Ma event. This 1110 Ma age is however, a precise match with that of the Umkondo large igneous province (LIP) of the Kalahari Craton, and also with mafic intraplate magmatism on other blocks such as the Bundelkhand Craton (India) and the Amazonian Craton. We provisionally consider these three cratons to have been nearest neighbors to the Congo–São Francisco Craton at this time and to have shared this 1110 Ma magmatic event as a LIP node. There is also an age match with the early part of the Keweenawan event (in the interior of the Laurentia); however, on previously discussed paleomagnetic grounds the Keweenawan event is likely to have been distant and unrelated (and on the other side of the Grenville orogen)

The 1.24–1.21 Ga Licheng large igneous province in the North China Craton: Implications for paleogeographic reconstruction

Detailed geochronological, geochemical, and paleomagnetic studies of mafic dyke swarms, often associated with mantle plumes, can provide unique constraints on paleogeographic reconstructions. Mafic dykes with baddeleyite U-Pb ages of 1,233 27 Ma (SIMS), 1,206.7 1.7 Ma (TIMS), 1,214.0 4.9 Ma (TIMS), and 1,236.3 5.4 Ma (TIMS) have been identified in the eastern North China Craton. Geochemical data indicate subalkaline to alkaline basalt compositions with OIB-like trace element signatures and an intraplate tectonic setting. In addition to these geochemical signatures, the radiating geometry of these dykes also suggests a 1.24-1.21 Ga large igneous province caused by a mantle plume event. A new similar to 1.24 Ga paleomagnetic pole at 2.0 degrees N, 165.1 degrees E, A(95) = 11.0 degrees, N = 9 and an similar to 1.21 Ga VGP at -23.0 degrees N, 92.5 degrees E, dp/dm = 4.7 degrees/7.8 degrees have been obtained from these dykes, with the 1.24 Ga pole supported by positive baked contact test. Our paleomagnetic analyses suggest that the North China Craton and the proto-Australian continent could have been separated by 1.24-1.21 Ga from an established Nuna connection at ca. 1.32 Ga. By comparison with Laurentia paleopoles, we present the paleogeography of dispersing North China, proto-Australian, and Laurentia cratons in the late Mesoproterozoic during the breakup of the supercontinent Nuna.Peer reviewe

Palaeomagnetic, geochronological and geochemical study of Mesoproterozoic Lakhna Dykes in the Bastar Craton, India: Implications for the Mesoproterozoic supercontinent

Palaeomagnetic analysis of the Lakhna Dykes (Bastar Craton, India) yields a palaeopole at 36.6°N, 132.8°E, dp=12.4°, dm=15.9°, and the U--Pb zircon age obtained from one of the rhyolitic dykes is 1466.4±2.6 Ma (MSWD=0.21, concordia age based on two analyses with identical Pb--U ages), similar to previously published U\Pb ages. Major and trace element analyses of the Lakhna Dykes show shoshonitic and high-K calc-alkaline affinities consistent with a subduction related characteristics suggesting an active continental margin setting. This is in keeping with the Palaeo- to Mesoproterozoic tectonic environments in the eastern Indian margin. The new 1460 Ma Indian palaeopole was used to test possible palaeopositions of India within the Mesoproterozoic supercontinent Columbia. Of the four palaeomagnetically permissible reconstructions, juxtaposing western India against south-west Baltica is geologically the most reliably constrained and best fitting model. Our preferred reconstruction implies a long Palaeo- to Mesoproterozoic accretionary orogen stretching from south-eastern Laurentia through south-western Baltica to south-eastern India. Breakup of India and Baltica probably occurred in the Late Mesoproterozoic, but additional constraints are needed

Linking collisional and accretionary orogens during Rodinia assembly and breakup: Implications for models of supercontinent cycles

Periodic assembly and dispersal of continental fragments has been a characteristic of the solid Earth for much of its history. Geodynamic drivers of this cyclic activity are inferred to be either top-down processes related to near surface lithospheric stresses at plate boundaries or bottom-up processes related to mantle convection and, in particular, mantle plumes, or some combination of the two. Analysis of the geological history of Rodinian crustal blocks suggests that internal rifting and breakup of the supercontinent were linked to the initiation of subduction and development of accretionary orogens around its periphery. Thus, breakup was a top-down instigated process. The locus of convergence was initially around north-eastern and northern Laurentia in the early Neoproterozoic before extending to outboard of Amazonia and Africa, including Avalonia–Cadomia, and arcs outboard of Siberia and eastern to northern Baltica in the mid-Neoproterozoic (~760 Ma). The duration of subduction around the periphery of Rodinia coincides with the interval of lithospheric extension within the supercontinent, including the opening of the proto-Pacific at ca. 760 Ma and the commencement of rifting in east Laurentia. Final development of passive margin successions around Laurentia, Baltica and Siberia was not completed until the late Neoproterozoic to early Paleozoic (ca. 570–530 Ma), which corresponds with the termination of convergent plate interactions that gave rise to Gondwana and the consequent relocation of subduction zones to the periphery of this supercontinent. The temporal link between external subduction and internal extension suggests that breakup was initiated by a top-down process driven by accretionary tectonics along the periphery of the supercontinent. Plume-related magmatism may be present at specific times and in specific places during breakup but is not the prime driving force. Comparison of the Rodinia record of continental assembly and dispersal with that for Nuna, Gondwana and Pangea suggests grouping into two supercycles in which Nuna and Gondwana underwent only partial or no break-up phase prior to their incorporation into Rodinia and Pangea respectively. It was only after this final phase of assembly that the supercontinents then underwent full dispersal

The magnificent seven : A proposal for modest revision of the Van der Voo (1990) quality index

Thirty years ago, Rob Van der Voo proposed an elegant and simple system for evaluating the quality of paleomagnetic data. As a second-year Ph.D. student, the lead author remembers Rob waxing philosophical about the need to have an appropriate, but not overly rigid evaluation system. The end result was a 7-point system that assigned a (1) or (0) for any paleomagnetic result based on objective criteria. The goal was never to reject or blindly accept any particular result, but merely to indicate the degree of quality for any paleomagnetic pole. At the time, the global paleomagnetic database was burgeoning and it was deemed useful to rank older paleo magnetic results with the newer data being developed in modern laboratories. Van der Voo's, 1990 paper launched a silent revolution in paleomagnetism. Researchers began to evaluate their data against those seven criteria with the anticipation that reviewers would be similarly critical. Today, paleomagnetism is a mature science. Our methods, analyses, and results are more sophisticated than they were 30 years ago. Therefore, we feel it is appropriate to revisit the Van der Voo (1990) criteria in light of those developments. We hope to honor the intention of the original paper by keeping the criteria simple and easy to evaluate while also acknowledging the advances in science. This paper aims to update the criteria and modernize the process. We base our changes on advances in paleomagnetism and geochronology with a faithful adherence to the simplicity of the original publication. We offer the "Reliability" or "R" index as the next generation of the Van der Voo "Quality" or "Q" index. The new R-criteria evaluate seven different information items for each paleomagnetic pole including age, statistical requirements, identification of magnetic carriers, field tests, structural integrity, presence of reversals and an evaluation for possible remagnetization.Peer reviewe

Palaeoproterozoic to Eoarchaean crustal growth in southern Siberia: a Nd-isotope synthesis

Nd-isotope analyses from 114 rock samples are reported from the southern part of the Siberian craton to establish a first-order crustal formation scheme for the region. The Nd-isotopedata show considerable variability within and among different cratonic units. In many cases this variability reflects differing degrees of mixing between juvenile and older (up to Eoarchaean) crustal components. The fragments of Palaeoproterozoic juvenile crust within the studied segment of the Siberian craton margin have Nd-model ages of 2.0-2.3 Ga. Voluminous Palaeoproterozoicgranites ( 1.85 Ga) were intruded into cratonic fragments and suture zones. These granites mark the stabilization of the southern Siberian craton. The complexity in the Nd data indicatea long history of crustal development, extending from the Eoarchaean to the Palaeoproterozoiceras, which is interpreted to reflect the amalgamation of distinct Archaean crustal fragments, with differing histories, during Palaeoproterozoic accretion at 1.9-2.0 Ga and subsequent cratonic stabilization at 1.85 Ga. Such a model temporally coincides with important orogenic events on nearly every continent and suggests that the Siberian craton participated in the formation of a Palaeoproterozoic supercontinent at around 1.9 Ga