Where was the Nuna/Columbia Supercontinent?

Mesoproterozoic geomagnetic reversal asymmetry in light of new paleomagnetic and geochronological data for the Häme dyke swarm, Finland: Implications for the Nuna supercontinent

Authors:

Salminen et al

Abstract:

Baltica represents one of the key continents of the Mesoproterozoic supercontinent Nuna forming the core of it together with Laurentia and Siberia. This study presents new geochronological and paleomagnetic data obtained for the Häme diabase dyke swarm in southern Finland. New U-Pb (baddeleyite) ages 1642 ± 2 Ma and 1647 ± 14 Ma for two reversely magnetized dykes are acquired. Demagnetization revealed a dual polarity remanent magnetization direction carried by magnetite. The combined normal (N) and reversed (R) polarity direction for 11 dykes (=sites) is D = 355.6°, I = −09.1° (k = 8.6 and α95 = 16.6°) yielding a paleomagnetic pole at 23.6°N, 209.8°E (K = 10.6 and A95 = 14.7°) with Van der Voo value Q = 7. N and R magnetized units for the Häme dyke swarm show asymmetry in declination values, probably caused by an age difference between the dykes. The Geocentric Axial Dipole (GAD) model indicates that all geomagnetic reversals should be symmetric (in inclination), yet it has been noted that this is not always the case (e.g. 1.57 Ga Satakunta and Åland dykes in Baltica). By analyzing global dual polarity paleomagnetic data we show that the stationary GAD model is a valid assumption at 1.7–1.4 Ga and that the asymmetry between some normal and reversed polarities in global dual-polarity data sets appears randomly over time, and does not follow a global trend. Furthermore, we show that in the case of Åland and Satakunta dykes an unremoved secondary magnetization component could explain the obtained asymmetry. The GAD assumption is used to reconstruct the core of Nuna on equatorial latitudes using new data for Häme dykes. Paleomagnetic evidence suggest that maximum assembly of Nuna occurred at 1.5 Ga and the dispersal of the core is proposed to be associated with coeval 1.38–1.27 Ga magmatism in its core continents.

The Mawson Continent Formed During the Nuna/Columbia to Rodinia Transition

Mesoarchean and Paleoproterozoic history of the Nimrod Complex, central Transantarctic Mountains, Antarctica: Stratigraphic revisions and relation to the Mawson Continent in East Gondwana

Authors:

Goodge et al

Abstract:

High-grade metamorphic and igneous rocks originally mapped as the Nimrod Group represent the only known crystalline basement of the East Antarctic shield exposed in the Transantarctic Mountains. SHRIMP U–Pb age data from zircon show that this assemblage preserves multiple geologic events spanning 2.5 b.y. of Archean to early Paleozoic history, culminating in thermomechanical reworking and active-margin magmatism during the Ross Orogeny. New age data from igneous and metamorphic rocks, as well as from detrital zircons in metasedimentary quartzites, refine the Mesoarchean to Paleoproterozoic history and indicate the need to abandon the stratigraphic term Nimrod Group and its five formations. In its place, we redefine only the igneous and high-grade gneissic parts of the assemblage as the Nimrod Complex, and all other metasedimentary rocks exposed in the Miller and Geologists ranges are included in a newly defined Argosy Schist. Within the Nimrod Complex, the oldest layered gneisses represent magmatic Mesoarchean crust formed between about 3150 and 3050 Ma. Correspondence of U–Pb zircon crystallization ages with whole-rock Sm–Nd model ages indicates formation from juvenile mantle melts. Magmatism at ca. 3100 Ma was followed closely by high-temperature metamorphism, recorded by zircon crystallization at 2955–2900 Ma, likely due to high advective heat transfer and/or thermal insulation of newly stabilized crust. Metaigneous units with ages of ca. 2500 Ma indicate a late Neoarchean period of anatexis and/or magmatism, although the geologic context for these events is uncertain. Gneissic, eclogitic and metaigneous rocks record an important period of deep-crustal metamorphism, thickening and magmatism between 1730 and 1700 Ma, referred to as the Nimrod Orogeny, that may have played an early role in assembly of East Gondwana cratons. A new lithodemic unit, Argosy Schist, consists of interlayered mica schist, quartzite, amphibolite, and calc-silicate schist. Quartzites from the schist unit have two distinctive detrital-zircon provenance characteristics; one type has populations that correlate with dated gneissic and metaigneous units of the Nimrod Complex, indicating a proximal provenance, whereas a second type has detrital zircon ages resembling those from Neoproterozoic Beardmore Group sandstones, indicating a common broader East Antarctic shield provenance. Their maximum depositional ages range widely from about 2000 to 900 Ma, leaving unresolved their age and geologic relationship to either the Nimrod Complex or Beardmore Group, yet they comprise a metasedimentary assemblage that is distinctive from the Nimrod Complex. Recent findings of Mesoarchean gneisses in the Gawler Craton, geochronology from Terre Adélie, and our new age data from the Nimrod Complex thus highlight the importance of ca. 3.1, 2.5 and 1.7 Ga events in formation of the composite East Antarctic shield adjacent to the modern Transantarctic Mountains. Correlative crustal units may extend to the southern Prince Charles Mountains and Shackleton Range. Collectively, this extensive crustal province, referred to as the Mawson Continent, represents an elongate belt of primary Mesoarchean crust that experienced major reworking at ca. 2.5 and 1.7 Ga. The latter period includes both high- and low-P/T petrologic signatures, providing evidence of crustal thickening and magmatism that may signify collisional processes related to Paleoproterozoic cratonal amalgamation during formation of the Nuna supercontinent.

Calymmian MesoProterozoic Nuna/Columbia Supercontinent Reconstructed

Paleogeography of the Congo/São Francisco craton at 1.5 Ga: expanding the core of Nuna supercontinent

Authors:

Salminen et al

Abstract:

The Congo/São Francisco (C/SF) craton, one of the largest cratons in Proterozoic paleogeography, has been lacking reliable paleomagnetic data for the supercontinent Nuna interval (ca. 1600-1300 Ma). Here we provide a new paleomagnetic key pole for this craton from recently dated mafic dykes in the Curaçá (1506.7±6.9 Ma) region of Brazil. The characteristic remanent magnetization (ChRM) direction D=070.6°, I=54.0° (k=22.1 and a95=13.1°) corresponds with a paleomagnetic pole at 10.1°N, 009.6°E (K=15.6, A95=15.8°), which places C/SF craton in moderate paleolatitudes at the time of remanence acquisition. Primary nature of the paleomagnetic remanence is supported by a baked-contact test. A similar ChRM direction was obtained for four Mesoproterozoic mafic intrusions in Chapada Diamantina region. The new pole, only from Curaçá, for C/SF allows us to reconstruct the extended core of the supercontinent Nuna at 1.5 Ga. Based on coeval 1.5 Ga and 1.38 Ga magmatism in Baltica, Siberia and C/SF, we favor the position where Southwest Congo is reconstructed against present South-Southeast (S-SE) Baltica. We explore two alternative 1.5 Ga reconstructions of Nuna’s core. In both of them Baltica and Laurentia are shown in the well-defined NENA (Northern Europe North America) fit, together with Siberia in a tight fit to northern Laurentia. In reconstruction option A, more traditional fit of Amazonia with Baltica is shown, modified from the geologically based SAMBA (South AMerica BAltica) model to accommodate paleomagnetic data. In this option, however, West Africa must be extricated from SAMBA because C/SF has taken its place. For reconstruction option B, Amazonia is shifted to lie adjacent to NE Laurentia and West Baltica. In both options SW Congo is reconstructed against S-SE Baltica, but in option B there is a tighter fit between them, and there is a better match with our new paleomagnetic data for C/SF. In either option, separation of C/SF from Baltica and Siberia probably occurred at 1.38 Ga, the age of pronounced mafic magmatism throughout this sector of Nuna.

The Future is Amasia...for the Next Supercontinent in 250 Million Years

Formation of a future supercontinent through plate motion–driven flow coupled with mantle downwelling flow

Author:

Yoshida

Abstract:

Series of high-resolution numerical simulations of three-dimensional mantle convection were performed to examine the interaction between the drifting continental lithospheres and the underlying mantle structure for 250 m.y. from the present, and to predict the configuration of the future supercontinent. The density anomaly of the mantle interior was determined by the seismic velocity anomaly from global seismic tomography data sets, which contain well-resolved subducting slabs. The present-day plate motion was imposed for the first stage of the simulation as a velocity boundary condition at the top surface boundary, instead of a shear stress–free condition. The switching time from the plate motion boundary to shear stress–free conditions was taken as a free parameter. The results revealed that Australia, Eurasia, North America, and Africa will merge together in the Northern Hemisphere to form a new supercontinent within ∼250 m.y. from the present. The continental drift was assumed to be realized by plate-scale mantle flow, rather than large-scale upwelling plumes. That is, continuously moving plates at the surface for the first stage of the simulation are mechanically coupled with the subducting slabs in the mantle; this enhances the underlying mantle downwelling flow. As a result, persistent continental drift can be reproduced for long future time periods even though top surface boundary conditions may switch in response to shear stress–free conditions. The configuration of the numerically reproduced future supercontinent in this study is broadly consistent with the hypothetical model of Amasia as indicated by previous findings from geological correlations and a paleogeographic reconstruction.

New Evidence of the Rodinia Supercontinent Breakup During the Cryogenian NeoProterozoic

Cryogenian intraplate magmatism along the buried southern Laurentian margin: Evidence from volcanic clasts in Ordovician strata, Marathon uplift, west Texas

Authors:

Hanson et al

Abstract:

Critical evidence bearing on the breakup history of the supercontinent Rodinia near the end of the Proterozoic comes from widespread Cryogenian–Cambrian intraplate igneous assemblages present along the margins of cratonic blocks released during Rodinia fragmentation and now distributed around the globe. This magmatism occurred over a long time span (780–540 Ma) prior to and during final stages of Rodinia breakup along the eastern, western, and northern margins of the Laurentia craton, which forms the centerpiece of Rodinia in many reconstructions. Whether similar protracted magmatism occurred prior to the rift-drift transition along the southern Laurentian margin has remained uncertain because of deep burial beneath younger strata. We present geochemical and geochronological data from volcanic clasts within shelf-derived Ordovician turbidites and debris-flow deposits now exposed in allochthonous thrust slices in the Marathon uplift, west Texas (USA), that document one or more episodes of intraplate magmatism extending back at least to 706 Ma along this part of the ancient margin. These data raise the possibility that Laurentia may have been completely encircled by intraplate igneous activity prior to Rodinia breakup, with implications for the driving forces leading to supercontinent fragmentation and factors controlling the sites of ocean-basin formation during that process.

Evidence of the Wilson Cycle From PaleoProterozoic on the Canadian Shield

Variations in zircon Hf isotopes support earliest Proterozoic Wilson cycle tectonics on the Canadian Shield

Authors:

Partin et al

Abstract:

Sedimentary basins provide an archive of magmatic and tectonic events in their detrital zircon record, which can be dated and coupled with Hf isotopic data to reveal secular changes in the production of juvenile and evolved magmatism and track the history of orogenic events. The Rae craton, which forms a substantial portion of the northern Canadian Shield, experienced successive orogenic events along its margins during most of the Paleoproterozoic Era. Yet, some of these orogenic events are poorly defined and their details remain controversial. We present coupled detrital zircon U-Pb age and εHf data from Paleoproterozoic metasedimentary successions of the eastern Rae craton. The zircon preserve an archive of ∼600 million years of magmatic and tectonic history on the Rae craton and its periphery. The U-Pb and Hf isotopic data indicate that zircon provenance was dominantly from the northern and western Rae craton, where magmatic and tectonic activity was focused during the ∼2.5 to 2.3 Ga Arrowsmith orogeny and the ∼2.0 to ∼1.93 Ga Taltson and Thelon events. Our detrital zircon dataset holds a more complete record of these Proterozoic orogenic events than is currently defined from known and dated crustal rocks on the Rae craton and shows that juvenile magmatism is more common than current models for either event suggest. Notably, an inverted U or horseshoe-shaped εHf array (-15.5 to +5.0) in our zircon dataset reflects a Wilson cycle that began in the earliest Paleoproterozoic on the Rae craton.

Evidence of NeoProterozoic Supercontinent Rodinia's Breakup From Madagascar

A-type stratoid granites of Madagascar revisited: age, source and links with the breakup of Rodinia

Authors:

Nédélec et al

Abstract:

The stratoid granites of Madagascar are sheet-like granite sills emplaced conformably to the schistosity of the Antananarivo and Ikalamavony domains of the Precambrian basement. Most of them are fine-grained rocks with A-type affinities. They belong to two different plutonic suites: the Kiangara Suite north of Antananarivo and the Imorona-Itsindro suite recognized in the whole central Madagascar. Stratoid granites are everywhere characterized by the same structural pattern evidencing two deformation events. The first event (D1 characterized by foliations mildly dipping to the west and lineations trending WSW) was coeval with synkinematic magma emplacement. The second one, responsible for local reworking in ductile conditions, is regarded as the result of Late Pan-African transcurrent tectonics along N-S striking shear zones. New in situ U-Pb zircon dating from both suites yields similar results evidencing two group of ages: upper intercept ages of 790-780 Ma regarded as crystallization ages, and younger ages of ca. 555 Ma corresponding to a metamorphic overprint. These new data suggest that both plutonic suites in central Madagascar were emplaced at 790-780 Ma. New Sm-Nd isotopic data from the Kiangara Suite support the existence of two granite groups. The first group has εNd(t) at -15 and is likely derived from partial melting of the Late Archaean crust. The second group made of granites with a more pronounced A-type nature and comagmatic syenites has εNd(t) at -12 evidencing the contribution of mantle melts. Mafic enclaves with εNd(t) ranging from -5 to -11 encompass the Nd isotopic signature of coeval Itsindro gabbros, which are regarded as derived from a subcontinental lithospheric mantle source. The interpretation of both structural and isotopic data is consistent with crustal thinning and extension during a Cryogenian Rodinia rifting stage at 790-780 Ma, that left a major imprint in central Madagascar. Separation from a conjugage margin represented by the North China craton is suggested. The Pan-African influence is limited to reheating, tectonic reworking and fluid transfer in the vicinity of Late-Neoproterozoic (∼550 Ma) shear zones.

Evidence of a Continental Collision Between Laurentia & Rodinia From Stenian MesoProterozoic Africa?

U–Pb Zircon (SHRIMP) ages of granite sheets and timing of deformational events in the Natal Metamorphic Belt, southeastern Africa: Evidence for deformation partitioning and implications for Rodinia reconstructions

Authors:

Mendonidis et al

Abstract:

This study provides constraints on the ages of deformation events and fabric development in deformed rocks of the Margate Terrane of the Natal Metamorphic Province. The Margate Terrane forms the southernmost of three terranes considered to represent multiple arc accretion onto the southern margin of the Kalahari Craton, and geochronological data indicate that the Margate Terrane has a long history of sporadic magmatism from ∼1180 to ∼1025 Ma. Two granite sheets of differing structural age, as revealed by deformational fabric and cross-cutting relationships, were sampled for U–Pb (SHRIMP) dating from coastal outcrop at Southbroom (30°54′43.61″S, 30°20′1.61″E). The older sheet contains fabrics related to both D1 and D2 events, whereas the younger shows evidence for syn-D2 emplacement and contains an S2 fabric. For both intrusive sheets, zircon core domains showing magmatic zoning yielded ages that are statistically identical at 1075 ± 6 Ma. This is interpreted to represent the intrusion age of the older sheet, and to sampling of a xenocrystic population in the cross-cutting sheet due to assimilation. Zircons from both sheets show metamorphic rim zones with a mean age of 1042 ± 10 Ma, which is attributed to rim growth during development of the S2 foliation, close to the intrusion age of the younger sheet. The 1075 ± 6 Ma age is comparable to the ages of other granitic units in the Margate Terrane that intruded between ∼1091 and 1070 Ma and implies that all of these predated the D1 deformation, which is considered to record the accretion of the terrane onto the Kalahari Craton. The D2 event is characterized by northward-verging folds with a pervasive southward-dipping axial planar fabric S2, which largely overprinted the S1 fabric. Previously, the pure-shear D2 deformation was considered to be older than the narrow sinistral shear zones occurring within the Mzumbe and Margate Terranes. However, dating of the D2 event at 1042 ± 10 Ma indicates that these deformations are coeval, and represent deformation partitioning during a transpressional event at ∼1050–1025 Ma that may have been related to collision with Laurentia during the amalgamation of Rodinia.

Evidence of the Separation of Laurentia From Australia During the Rifting of the Coulmbia Sueprcontinent found?

Rifting of Columbia to form a deep-water siliciclastic to carbonate succession: The Mesoproterozoic Pinguicula Group of northern Yukon, Canada

Authors:

Medig et al

Abstract:

The Mesoproterozoic Pinguicula Group (less than 1.38 Ga) is exposed in the Wernecke and Hart River inliers in northern Yukon, Canada. The Pinguicula Group records deposition of non-cyclic siliciclastic and carbonate strata on low-energy slopes affected by rare high-energy deposits in a tectonically active epicratonic setting. The succession is ∼1.4 km thick at its measured type sections and comprises three newly formalised formations: the Mount Landreville, Pass Mountain, and Rubble Creek formations (formerly units A, B, and C, respectively). The Mount Landreville Formation is a predominantly siltstone succession with minor conglomerate and sandstone deposited below storm wave-base on a relatively gentle slope. The Pass Mountain Formation is a wispy- to planar-laminated carbonate succession deposited on a low-energy slope mostly below storm wave-base and is punctuated by rare high-energy gravity-flow deposits including debrites, grain-flows, turbidites, and micro-turbidites. The Rubble Creek Formation is dominated by repetitive centimetre- to decimetre-scale lime mudstone beds; it is distinguished from the Pass Mountain Formation by abundant zebra texture (an alternating dark grey and white banding caused by late diagenetic or hydrothermal fluid influx) and a lack of sediment gravity-flow deposits.

The Pinguicula Group is the middle of five, unconformity-bounded, Proterozoic stratigraphic successions deposited on the northwestern margin of Laurentia (ancestral North America). The Pinguicula basin was epicratonic and deepened to the south (present coordinates). The basin formed during an amagmatic extensional event that contributed to the break-up of Columbia and the separation of Laurentia from Australia.

Whereas most preserved Mesoproterozoic basins are dominated by shallow-water lithofacies deposited in rift and epicratonic settings, with few deep-water lithofacies preserved, the carbonate strata of the Pinguicula Group provide a rare insight into deeper-water carbonate environments.

Tectonic Implications From Ural Russia for the Columbia Supercontinent

U–Pb zircon geochronology and geochemistry of Paleoproterozoic magmatic suite from East Sarmatian Orogen: tectonic implications on Columbia supercontinent

Authors:

Terentiev et al

Abstract:

Extensive Paleoproterozoic magmatism occurred in the East Sarmatian Orogen (ESO), located at the junction of the Sarmatian and Volga–Ural segments of the East European Craton, generating numerous felsic to mafic-ultramafic complexes. Here we report geochemical and zircon U-Pb age data from a suite of ultramafic–mafic and diorite–granodiorite intrusive rocks from this orogen. SHRIMP U–Pb dating of zircons yielded the following concordant ages for the magmatic suites: (1) 2085 ± 17 to 2093 ± 20 Ma (sub-volcanic high-Mg intrusions of SHMB-like melanorite–melaquartz-diorite–melagranodiorites and quartz-diorite–tonalite–granodiorites); (2) 2072.4 ± 8, 2073 ± 8.3, and 2068 ± 13 Ma (ultramafic–mafic–diorite layered intrusions); (3) 2053 ± 14 to 2058 ± 22 Ma (magnesian–ferroan quartz-diorite–tonalite–granodiorite intrusions) and (4) 2035 ± 18 Ma (ferroan norite–diorite intrusions). The trace and rare earth element geochemistry indicate arc-related features. The enrichment in LREE and LILE in the mafic-ultramafic and diorite-granodiorite suites is correlated with melting of metasomatised lithosphere mantle along with involvement of crustal components in their petrogenesis. The third magmatic event conforms to the age of the post-collision S- and A-granitoids of the region. Our data indicate two major magmatic events in the post-collisional setting, the former immediately after metamorphism with the formation of schistosity in the host rocks, and the latter two during the culmination of the orogenic cycle in the Voronezh Crystalline Massif.

The duration of the Paleoproterozoic orogeny during the collision of the Sarmatian and Volga–Ural segments of the East European Craton is estimated to be approximately 100 million years from ∼2140 to ∼2035 Ma. We propose that the layered orogenic plutons were derived from relatively deeper mantle source, whereas the sub-volcanic rock series are derivatives of the slightly shallow mantle source. The Paleoproterozoic collision in the region broadly coincides with timing of amalgamation of the global supercontinent Columbia.

Evidence of a Rhyacian Paleoproterozoic Supercontinent From Brazil

Crustal evolution of the northern Brasília Belt basement, central Brazil: a Rhyacian orogeny coeval with a pre-Rodinia supercontinent assembly

Authors:

de Sousa et al

Abstract:

The Brasília thrust and fold belt developed in the course of Neoproterozoic Brasiliano orogeny, during the convergence of São Francisco, Amazonian and Paranapanema cratons, in an early phase of Gondwana agglutination. A Paleoproterozoic terrane cropping out in its northern segment -represents the basement of the belt and corresponds to a magmatic arc. The arc developed during Rhyacian, possibly on the margin of an Archean-Paleoproterozoic block that is today represented by the São Francisco craton. The Paleoproterozoic arc evolution starts following a calc-alkaline trend between 2.30 and 2.16 Ga, changing from a typical juvenile to crustal contaminated terrane with slightly negative ɛNd(t) values, as revealed by tonalites and granodiorites of Conceição do Tocantins Suite. By c. 2.17-2.15 Ga, a collisional event took place, triggering crustal melting and generating peraluminous granites. These syn-collisional granites present strongly negative ɛNd values and belong to Aurumina Suite. Natividade, Almas-Conceição do Tocantins and Cavalcante-Arraias domains within the basement do not represent distinct tectonic blocks. The first two are areas where mainly plutonic arc rocks crop out and in the last one, syn-collisional granites are the most common lithology. Syn-collisional granites characterize granitogenesis produced by collision of another landmass against São Francisco landmass. The arc development is contemporary with collisional orogens that culminated in a conjectural Paleoproterozoic pre-Rodinia supercontinent. Since Rhyacian, these rocks are part of the landmass that would become the São Francisco craton and compose Brasília Belt basement.

How Australia and Antarctica Transitioned From Being Part of the Supercontinent Columbia to Gondwana

The Australo-Antarctic Columbia to Gondwana transition

Authors:

Aitken et al

Abstract:

From the Mesoproterozoic to Cambrian, Australo-Antarctica was characterised by tectonic reconfiguration as part of the supercontinents Columbia, Rodinia and Gondwana. New tectonic knowledge of the Wilkes Land region of Antarctica allows Australo-Antarctic tectonic linkages to be resolved through reconstruction into ca. 160 Ma Gondwana. We also resolve 330 ± 30 km of sinistral strike-slip offset on the greater than 3000 km long Mundrabilla-Frost Shear Zone and 260 ± 20 km of dextral offset on the greater than 1000 km long Aurora Fault to reconstruct the ca. 1150 Ma geometry of Australo-Antarctica. Using this revised geometry, we derive the first model of the Columbia to Gondwana reconfiguration process that is geometrically constrained to ~ 100 km scale. In this model, early Mesoproterozoic tectonics is driven by two opposing subduction systems. A dominantly west-dipping subduction zone existed at the eastern margin of Australo-Antarctica until ca. 1.55–1.50 Ga. A predominantly east-dipping subduction zone operated at the western margin of the Mawson Craton from ca. 1.70 Ga to ca. 1.42 Ga. The latter caused gradual westwards motion and clockwise rotation of the Mawson Craton relative to the West and North Australian Craton and the accretion of a series of continental ribbons now preserved in the Musgrave Province and its southern extensions. A mid-Mesoproterozoic switch to predominantly west-dipping subduction beneath the West Australian Craton brought about the final closure of the Mawson Craton with the North and West Australian Craton along the Rodona-Totten Shear Zone. Convergence was achieved prior to 1.31 Ga, but final collision may not have occurred until ca. 1.29 Ga. Post-1.29 Ga intraplate activity involved prolonged high-temperature orogenesis from 1.22 to 1.12 Ga, and significant movement on the Mundrabilla-Frost Shear Zone between 1.13 and 1.09 Ga, perhaps in response to the assembly of Rodinia at ca. 1.1 Ga. The Australo-Antarctic Craton was amalgamated with Indo-Antarctica along the Indo-Australo-Antarctic Suture (IAAS) and Kuunga Orogeny, probably in the latest Neoproterozoic to early Cambrian.

The North China Craton Broke off From Rodinia During the Tonian NeoProterozoic

Early Neoproterozoic emplacement of the diabase sill swarms in the Liaodong Peninsula and pre-magmatic uplift of the southeastern North China Craton

Authors:

Zhang et al

Abstract:

Diabase sill swarms are widespread within the Neoproterozoic sedimentary rocks in the Liaodong Peninsula (named as the Dalian mafic sill swarms), eastern North China Craton (NCC). Our new zircon LA-ICP-MS U-Pb and baddeleyite SIMS Pb-Pb dating results on five diabase sill samples emplaced into the Qiaotou, Cuijiatun and Xingmincun Formations in the Liaodong Peninsula indicate their emplacement during the early Neoproterozoic (Tonian) period at 0.92–0.89 Ga and pre-magmatic regional uplift prior to ca. 0.92–0.89 Ga. The above results provide important constraints on the upper boundary of the Neoproterozoic strata and their macroscopic carbonaceous fossils and organic-walled microfossils in the eastern and southeastern NCC and indicate they are Tonian in age. The early Neoproterozoic Dalian diabase sills belong to the tholeiitic series and are characterized by low contents of SiO2 and K2O, high contents of TiO2, Fe2O3T and MgO, slight light REE (LREE)-enrichment and no Eu anomalies on chondrite-normalized REE patterns, enrichment of high field strength element (HFSE) and lack of negative Nb, Ta, Zr, Hf, P and Ti anomalies on primitive mantle-normalized spidergrams; and exhibit geochemical characteristics of within plate basalt on discrimination diagrams. The newly identified Dalian diabase sills, together with the previously reported Xu-Huai and Sariwon mafic sills and the Dashigou mafic dykes, constitute an early Neoproterozoic (0.92–0.89 Ga) large igneous province in the NCC (Sino-Korean Craton). Formation of the early Neoproterozoic diabase sill (dyke) swarms in the NCC is probably related to a continental rifting event that have led to breakup of southeastern NCC from some other continents in the Rodinia supercontinent. Breakup of the NCC from the Rodinia supercontinent at around 0.92–0.89 Ga is also supported by pre-magmatic regional uplift of the southeastern NCC prior to ca. 0.92–0.89 Ga and evolution trend of the Dalian diabase sills from within plate basalt to mid-ocean ridge basalt on the Zr/Y vs. Zr discrimination diagram.

Evidence From Tasmania East Antarctica and Laurentia Connected in the Columbia (Nuna) Supercontinent

Mesoproterozoic Tasmania: Witness to the East Antarctica–Laurentia connection within Nuna

Authors:

Mulder et al

Abstract:

Most recent paleogeographic reconstructions of the supercontinent Nuna juxtapose the North Australian craton, Mawson continent (South Australia–East Antarctica), and Laurentia between 1.6 Ga and 1.3 Ga but differ in their relative positioning. The greater than 10-km-thick siliciclastic Rocky Cape Group of Tasmania was deposited in an opening marine basin on the margin of East Antarctica during Nuna breakup. Based on a similar detrital zircon signature and depositional age, the Rocky Cape Group has been correlated with the upper Belt-Purcell Supergroup in Laurentia, thus representing a key tie point within Nuna. Here the detrital zircon age signature of Mesoproterozoic Rocky Cape Group quartzites is investigated by comparing new detrital zircon U-Pb-Hf isotopic data to an extensive compilation of zircon isotopic data from Australia, East Antarctica, and Laurentia. Our analysis demonstrates that the Rocky Cape Group is unlikely to have been sourced from any geological terrane exposed in presentday Australia. Instead, zircon U-Pb-Hf isotopic data from basement terranes in Laurentia and East Antarctica show striking similarities to the Rocky Cape Group detrital signature. Paleocurrent data indicate that the majority of sediment in the Rocky Cape Group was sourced from Laurentia, which was to the southeast (present-day coordinates) of Tasmania, supporting a SWEAT-like (southwest United States–East Antarctica) configuration for Nuna. We suggest that rifting left a thinned continental connection between East Antarctica and Laurentia onto which the lower-middle Rocky Cape Group was deposited between 1.45 and 1.30 Ga.

More Evidence of a Multi Stage Breakup of NeoProterozoic Supercontinent Rodinia

Sequence and tectonostratigraphy of the Neoproterozoic (Tonian-Cryogenian) Amundsen Basin prior to supercontinent (Rodinia) breakup

Authors:

Thomson et al

Abstract:

Intracontinental basins that lack obvious compartmentalization and extensional faults may lie inboard of, and have the same timing as, rifted continental margins. Neoproterozoic successions of northwest Laurentia are an example where rift and intracontinental basins are spatially and temporally related. This study describes Tonian-Cryogenian pre-rift strata of the upper Shaler Supergroup, deposited in the Amundsen Basin (Victoria Island, Canada), in which five transgressive-regressive (T-R) cycles are identified. The pre-breakup succession in the Amundsen Basin has stratigraphic architecture that differs from adjacent, fault-bound rift basins. There is little evidence for extensive progradation, which resulted in broad, layer-cake stratigraphy where shallow-water facies predominate, deposited on a storm-dominated ramp. Correlation between the Amundsen and Fifteenmile (Yukon) basins is complicated by differing rates and regimes of subsidence, with the exception of a basin-deepening event that occurred in both basins and correlates with the global Bitter Springs isotope stage, initiating sometime after ∼811 Ma. Contrary to previous correlations, we propose that the upper Shaler Supergroup and Little Dal Group of the Mackenzie Mountains Supergroup (Mackenzie Basin) are equivalent to the entire Fifteenmile Group. The identification of cycles and subsidence patterns in the Amundsen Basin prior to Rodinia break-up has implications for understanding the stratigraphic architecture of other intracontinental sag basins. We recognize three tectonostratigraphic units for the upper Shaler Supergroup that record an initial sag basin, followed by early extension and thermal doming, and finally rifting of the Amundsen Basin. Subsidence possibly was related to multiple cycles of intra-plate extension that complemented coeval fault-controlled subsidence. Analysis of pre-rift strata in the Amundsen Basin supports multi-phase, non-correlative break-up of Rodinia along the northwest margin of Laurentia.

The Comings and Goings of SuperContinents: Modeling the Wilson Cycle

The History of Supercontinents and Oceans from the Standpoint of Thermochemical Mantle Convection

Authors:

Lobkovsky et al

Abstract:

A thermochemical model of mantle convection reproducing both the supercontinental and oceanic history of the Earth is formulated. The model takes into account (i) the stratification of the mantle into the upper and lower layers, (ii) the differentiation, which lead to the formation of light material in D” layer and (iii) the eclogitization, which results in the production of heavy material in the subduction zones. The numerical experiments are carried out in the Boussinesq approximation with isoviscous rheology.

It is found that the high degree of spherical symmetry of the young planet promotes the cubic shape of the mantle convection. The hot initial state and rich chemical potential are reflected in active differentiation of the mantle material and formation of the bulk of the continental crust at the early stage of evolution.

It is established that after losing a significant part of thermochemical potential, the planet passes into megacyclic regime of evolution, where long periods of predominantly two-layer convection are interrupted by mantle overturns. The overturns render extensive fast mass exchange between the two mantles: part of the cold substance from the upper mantle subsides and hot material lifts up from the lower mantle to fill its place. The numerical experiments demonstrate a remarkable phenomenon of self-organization of a single global convective sink during the mantle overturn. Such a collective sinking of the upper mantle substance is energetically more favorable. The planetary-scale flow, which converges to the global downwelling flow (sink), assembles the supercontinent.

Our modeling of the geodynamic evolution of the Earth reproduces five mega-cycles. It is found that the configurations of the overturns tend to a dipole form and the position of the global sinks is being stabilized. Thus, the spherical mantle becomes slightly different: the hemisphere where the global sink is pulsating hosts the continents and the alternating Atlantic-type oceans, while the other hemisphere marked by the superplumes activity is dominated by the formation of the giant floor of the Pacific Ocean. As a result, the Earth acquires an asymmetrical appearance with the continental and oceanic hemispheres.

Evidence of the Oblique Collision of Volgo-Sarmatia and Fennoscandia Continents During the Assembly of PaleoProterozoic Supercontinent Columbia

Trans-Baltic Palaeoproterozoic correlations towards the reconstruction of supercontinent Columbia/Nuna

Authors:

Bogdanova et al

Abstract:

A comparative study of the Palaeoproterozoic accretionary the central and southern parts Svecofennian orogen in the Baltic/Fennoscandian Shield and the platform area to the east and south of the Baltic Sea indicates that at least of these parts of the orogen are built up of several NW-SE trending, 100 to 300 km wide tectonic megadomains separated from each other and complicated by major zones of mostly dextral shearing. The generation of these zones occurred successively between 1.86 and 1.75 Ga, concomitantly with continuing crustal accretion consistently younging toward the southwest. Even considering the distorting presence of a number of microcontinents, this indicates the one-time existence and repeated episodic activity of a master subduction zone stepwise falling back toward the present south-southwest. At 1.82–1.80 Ga, the continent-continent oblique collision of megacontinent Volgo-Sarmatia with the preexisting Fennoscandia interrupted the accretionary growth of the crust in the Svecofennian orogen. In the west, the system of Svecofennian tectonic domains and shear zones is delimited by 1.70–1.55 Ga rock belts marking part of the Laurentia-Greenland-Baltica margin of Columbia. Altogether, the present U-Pb zircon datings and studies of key rocks and structures in the South Baltic region allow more detailed Trans-Baltic correlation and the creation of new integrated models of the structural and tectonic evolution of the Svecofennian orogen in particular and northern Europe in general. The new findings will be important also in the continuing study of supercontinent formation and supercontinent cycles, and the drifting of Palaeoproterozoic protocontinents during the assembly of Columbia/Nuna.

Evidence of Rodinia PaleoGeography From Cryogenian NeoProterozoic Madagascar

Geochronology and geochemistry of Cryogenian gabbros from the Ambatondrazaka area, east-central Madagascar: Implications for Madagascar-India correlation and Rodinia paleogeography

Authors:

Zhou et al

Abstract:

Tectonic setting of the ca. 840-760 Ma Imorona-Itsindro Suite throughout central Madagascar is critical to understanding Madagascar-India correlation in pre-Gondwana time and the paleogeography of the rifting Rodinia. Here we present new geochronological and geochemical data for gabbros of this suite from the Ambatondrazaka area in east-central Madagascar. SIMS U-Pb zircon dating reveals that the gabbros emplaced between ca. 797 and 772 Ma. They define a typical tholeiitic trend on the AFM and FeOT/MgO vs. SiO2 plots, which is confirmed by the occurrence of layered Fe-Ti-V oxide mineralization. Owing to the high-K nature, they were previously misinterpreted as a “calc-alkaline” association produced in a mature continental arc. Indeed, it implies in return an intra-plate affinity for tholeiitic rocks. Their high Zr/Y, La/Y and Ti/V ratios differ from those of typical arc and back-arc mafic suites but are compatible with an intra-plate setting. Additionally, they are characterized by low AlZ/TiO2 ratios in clinopyroxene, further supporting an intra-plate environment. The negative ɛNd(t) (-8.4 to -5.1) and zircon ɛHf(t) (-6.84 to -3.08) values, together with enriched trace element signatures, indicate their derivation from an enriched lithospheric mantle source. Considering the initial 87Sr/86Sr ratios (0.705409 to 0.706892) and Nd modal ages (∼2.1-2.4 Ga), we postulate that this mantle reservoir has EM1-type isotopic characteristics and was enriched by a Late Neoarchean “super accretion event”. Taken together, our results question the existence of the Betsimisaraka Suture but support the proposal that the Malagasy Shield and the Dharwar Craton of India are parts of the same entity–the Greater Dharwar Craton. Within this framework, the widely-cited hypothesis that an extensive Andean-type arc was developed along the northwestern margin of the rifting Rodinia is challenged, at least that the magmatic arc did not extend to the Malagasy Shield.

Paleoproterozoic to Mesoproterozoic Intracratonic Basin Cycles

Age constraints on crystal-tuff from the Espinhaço Supergroup — Insight into the Paleoproterozoic to Mesoproterozoic intracratonic basin cycles of the Congo–São Francisco Craton

Authors:

Guadagnin et al

Abstract:

The U–Pb data from the volcanic and detrital zircon grains of the Tombador Formation in Chapada Diamantina, Bahia, provide the depositional age of the top of this unit and define the main sedimentary sources of the Archean, Paleoproterozoic and Mesoproterozoic Eras. The lithofacies, petrographic and geochemical data from crystal-tuff samples indicated that a volcanic source was located to the east of the Chapada Diamantina region. The available zircon data defined three first-order intracratonic basinal cycles, including the Lower (Statherian), Middle (Calymmian) and Upper (Stenian–early Tonian) Espinhaço basins. These sequences are well exposed at the Espinhaço Supergroup type-section in the Chapada Diamantina region. The zircon Hf isotope data from the 1.4 Ga crystal-tuff in the Middle Espinhaço and the 1.2 Ga tuffaceous rock in the Upper Espinhaço suggested different sources, with model ages of 2.1 to 1.9 Ga and less than 1.9 Ga, respectively. The tectonic development of these Paleoproterozoic to Mesoproterozoic intracratonic basins can be explained by the far-field stress at the paleoplate margins, which has been shown in other Phanerozoic intracratonic basins. The data presented here support a tectonic scenario in which the Congo–São Francisco paleoplate interior recorded the main global events related to the geodynamic processes after the Columbia supercontinent collage and the formation and fragmentation of the Rodinia supercontinent.

Evidence of Gondwana's Assembly During Cryogenian/Ediacaran NeoProterozoic

U-Pb age of the coesite-bearing eclogite from NW Borborema Province, NE Brazil: Implications for western Gondwana assembly

Authors:

Saraiva dos Santos et al

Abstract:

The Late Neoproterozoic assembly of western Gondwana played an important role in the subduction of oceanic and continental lithosphere. Such event was also source of arc magmatism, reworking of cratonic margins and development of ultra-high pressure (UHP) suture zones. In the Borborema province, NE Brazil, we have described for the first time UHP rocks enclosed within gneiss migmatite and calc-silicate rocks. They bear coesite included in atoll-type garnet from metamafic rocks, identified by petrographic study and Raman microspectroscopy analysis. U-Pb zircon dating of the leucosome of the migmatites and the calc-silicate rocks displays, concordant ages of 639 ± 10 Ma and 649.7 ± 5 Ma, respectively, here interpreted as the minimum age of the eclogitization event in the region. U-Pb zircon dating of the coesite-bearing rock defined a concordia age of 614. 9 ± 7.9 Ma that comprised the retrograde eclogitic conditions to amphibolite facies. The UHP rocks, mostly retrograded to garnet amphibolites, occur enclosed in the Paleoproterozoic continental block composed of calc-silicate rocks, migmatized sillimanite gneiss, mylonitic augen gneiss and granitic and tonalitic gneiss along a narrow N-S oriented belt between the Santa Quitéria magmatic arc and the Transbrasiliano lineament. This block was involved in the subduction to UHP eclogite depths, and was retrogressed to amphibolite during its exhumation and thrusting. Our data indicate an important Neoproterozoic transcontinental suture zone connecting the Pharusian belt with Borborema Province, and probably with the Brasília belt in central Brazil.