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.

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.

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.

Columbia Develops Biologically Powered Computer Chip

Columbia Engineering researchers have, for the first time, harnessed the molecular machinery of living systems to power an integrated circuit from adenosine triphosphate (ATP), the energy currency of life. They achieved this by integrating a conventional solid-state complementary metal-oxide-semiconductor (CMOS) integrated circuit with an artificial lipid bilayer membrane containing ATP-powered ion pumps, opening the door to creating entirely new artificial systems that contain both biological and solid-state components. The study, led by Ken Shepard, Lau Family Professor of Electrical Engineering and professor of biomedical engineering at Columbia Engineering, is published online Dec. 7 in Nature Communications.

link.

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.

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.

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.

The North China Craton Broke off From Columbia Supercontinent During Ectasian Mesoproterozoic

Detrital zircon U–Pb, Hf isotopes, detrital rutile and whole-rock geochemistry of the Huade Group on the northern margin of the North China Craton: Implications on the breakup of the Columbia supercontinent

Authors:

Liu et al

Abstract:

Supracrustal successions in the Zhaertai–Bayan Obo–Huade rift zone on the northern margin of the North China Craton include the Zhaertai, Bayan Obo and Huade Groups from west to east. The Huade Group, which has been subdivided into four formations, is composed of basal pebbled quartzites, quartzites, schists, phyllites, marbles, slates and diopsidites. Geochemistry of the metasedimentary succession indicates that source rocks of the lower two formations are felsic, displaying passive margin signatures, whereas those of the upper two formations have continental island arc or active continental margin signatures. U–Pb ages of detrital zircons from the group yielded three age populations of 2690–2450, 2150–1710 and 1660–1330 Ma, of which the youngest age population only exist in the upper Huade Group. The dominant 2690–2450 detrital zircons were likely sourced from the granitic rocks in the Yinshan Block. The subordinate 2150–1710 Ma detrital zircons were probably recycled from the metasedimentary units from the Khondalite Belt and/or derived from the similar aged granitic plutons of the Hongqiyingzi “Group”, which are also evidenced by the similar geochemical features of rutiles from the Huade Group and the Khondalite Belt. Minor amounts of 1660–1330 Ma detrital zircons may have derived from the North American and/or Baltica cratons connected to the northern margin of the North China Craton in the Columbia supercontinent. The youngest detrital zircon age peak of ∼1337 Ma in the upper Huade Group suggests that the sedimentation began after ∼1.34 Ga. In combination with the ∼1320 Ma granitoids cross-cutting it, depositional ages of the upper Huade Group can be constrained between ∼1.34 and ∼1.32 Ga. Taking into account the lithostratigraphic features, provenances and depositional ages, a continental rift basin deposit represented by the upper Huade Group on the northern margin of the North China Craton developed between ∼1.34 and ∼1.32 Ga, which indicates that the final breakup of the North China Craton from the Columbia supercontinent happened in the middle Mesoproterozoic.

Paleo-position of the North China Craton Within the supercontinent Columbia

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

Authors:

Xu et al

Abstract:

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

Evidence of Supercontinent Wilson Cycle From the Central Tianshan Arc Terrane, NW China

Geochemistry and geochronology of the Precambrian high-grade metamorphic complex in the Southern Central Tianshan ophiolitic mélange, NW China

Authors:

Wang et al

Abstract:

The Central Tianshan Arc Terrane is one of the major constituents of the Tianshan orogen in the southwestern Altaids. Thus its Precambrian evolution is important for unraveling the geodynamic and continental evolution of the Altaids. Biotite-plagioclase-hornblende orthogneisses intruded by leucogranite dykes are exposed as exotic blocks within the Southern Central Tianshan ophiolitic mélange. Zircon U–Pb age dating of one orthogneiss sample yields an upper intercept age of 2466 ± 51 Ma and a weighted mean 207Pb/206Pb age of 1812 ± 19 Ma around the lower intercept. These ages are interpreted as protolith crystallization age and subsequent metamorphic overprint age, respectively. The orthogneisses have moderate SiO2 contents, high MgO and Na2O contents, high Sr/Y ratios (32–43) and moderately fractionated REE patterns ([La/Yb]N = 7.59–13.64) with negligible Eu anomalies, enriched Sr contents and pronounced negative Th–U, Nb–Ta, Zr–Hf and Ti anomalies resembling high-SiO2 TTGs derived from subducted basaltic slab-melts. Positive ɛHf(t) values (+3.4 to +9.2) and low (176Hf/177Hf)i ratios (0.281304–0.281469) with Neoarchaean to early Paleoproterozoic single-stage Hf model ages (TDM1 = 2431–2652 Ma) suggest that the orthogneisses probably originated from partial melting of juvenile subducted oceanic crust. The orthogneisses were subsequently also affected by collisional orogenic events associated with the assembly of the supercontinent Columbia. In contrast, the zircon U–Pb age of 785 ± 15 Ma obtained for the intrusive leucogranite dykes is consistent with the timing of rifting events associated with the breakup of Rodinia. The leucogranites have a high-Al trondhjemitic composition characterized by extremely low MgO and K2O contents as well as high SiO2, Al2O3 and Na2O contents, dramatically low ∑REE abundances and REE patterns with moderate LREE enrichments ([La/Yb]N = 3.55–8.4) and pronounced positive Eu anomalies (Eu/Eu* = 1.29–2.61). The high zircon initial Hf compositions (0.281670–0.281841) and negative ɛHf(t) values (-21.7 to -15.4), in conjunction with high whole-rock initial 87Sr/86Sr ratios (0.70737–0.70751) and negative ɛNd(t) values (-4.7 to -5.1) suggest that the leucogranite resulted from reworking of ancient lower crust. Based on the presented data we conclude that the Central Tianshan Arc Terrane has undergone three tectonothermal events, namely ∼2.5 Ga continental crustal growth, ∼1.8 Ga collision related to the Columbia assembly and ∼785 Ma crustal reworking due to the Rodinia breakup. The Central Tianshan Arc Terrane, which experienced the same tectonic events as the Tarim Craton during the Precambrian, is considered to be a micro-Precambrian block that separated from the Tarim Craton during the Rodinia breakup.

Is the Calymmian MesoProterozoic Ladoga Rift Really a Continental Rift?

Is the Proterozoic Ladoga Rift (SE Baltic Shield) a rift?

Authors:

Artemieva et al

Abstract:

The southern part of the Baltic Shield hosts a series of mafic dykes and sills of Mesoproterozoic ages, including a ca. 1.53-1.46 Ga sheet-like gabbro-dolerite sills and the Salmi plateau-basalts from the Lake Ladoga region. Based on chiefly geochemical data, the region is conventionally interpreted as an intracratonic Ladoga rift (graben). We question the validity of this geodynamic interpretation by analyzing regional geophysical data (crustal structure, heat flow, Bouguer gravity anomalies, magnetic anomalies, and mantle Vs velocities). We provide a complete list of tectonic, magmatic, and geophysical characteristics typical of continental rifts in general and demonstrate that, except for magmatic and, perhaps, some gravity signature, the Lake Ladoga region lacks any other rift features. We also compare the geophysical data from the Lake Ladoga region with similar in age Midcontinent and Valday rifts, and provide alternative explanations for Mesoproterozoic geodynamic evolution of the southern Baltic Shield. We propose that Mesoproterozoic mafic intrusions in southern Fennoscandia may be associated with a complex deformation pattern during reconfiguration of (a part of) Nuna (Columbia) supercontinent, which led to magma intrusions as a series of mafic dykes along lithosphere weakness zones and ponding of small magma pockets within the cratonic lithosphere. Consequent magma cooling and its partial transition to eclogite facies could have led to the formation of a series of basement depressions, similar to intracratonic basins of North America, while spatially heterogeneous thermo-chemical subsidence, with phase transitions locally speeded by the presence of (subduction-related) fluids, could have produced a series of faults bounding graben-like structures.

The Columbia Supercontinent Broke up in the Ectasian MesoProterozoic

Mid-Mesoproterozoic (∼1.32 Ga) diabase swarms from the western Liaoning region in the northern margin of the North China Craton: Baddeleyite Pb–Pb geochronology, geochemistry and implications for the final breakup of the Columbia supercontinent

Authors:

Wang et al

Abstract:

Diabase swarms widely intrude the late Paleoproterozoic to Mesoproterozoic sedimentary rocks in the northern margin of the North China Craton (NCC). In this paper, we present new baddeleyite SIMS Pb–Pb ages and whole-rock geochemical data for representative samples of the diabase swarms intruding the Mesoproterozoic Wumishan and Xiamaling formations in the western Liaoning region. Our aim is to elucidate the age and origin of the diabase swarms and their relationship to the fragmentation of the Columbia supercontinent. The baddeleyite SIMS Pb–Pb dating results show emplacement ages varying from 1325.9 ± 4.1 Ma to 1318.6 ± 3.7 Ma, indicating voluminous basic magmatism leading to the generation of the diabase swarms during the Mid-Mesoproterozoic time. Geochemically, the Mesoproterozoic diabasic rocks have relatively low REEs contents and show weak positive Eu anomalies. Moreover, these diabase samples are characterized by enrichment in light rare earth elements (LREEs), large ion lithophile elements (LILEs; e.g., Rb and Pb) and some high field strength elements (HFSEs; e.g., Th, U, Zr, Ti and Hf), and depletion in heavy rare earth elements (HREEs) and several high field strength elements (HFSEs; e.g., Nb, Sm, Gd and P), with affinities to basalts belonging to within-plate tholeiite series. Taken together, these geochemical characteristics suggest that the primary magmas of the diabases in the western Liaoning region could have been derived by partial melting of a transitional mantle or slightly enriched mantle in a continental extensional setting. In the context of assembly, growth and breakup of the Columbia supercontinent, together with the recognition of large volumes of ∼1.32 Ga diabase swarms in the northern NCC as well as the nearly coeval rift-related anorogenic magmatism recorded elsewhere on the globe, such as Africa, Baltica, Siberia, North America and Greenland, we conclude that the northern margin of NCC experienced the global-scale Mid-Mesoproterozoic rifting events, corresponding to the final breakup of the Columbia supercontinent, probably at around 1.32 Ga.

Evidence of Continental Rifting in the Columbia Supercontinent

Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent: New stratigraphic and geochronology record from the eastern São Francisco craton

Authors:

Fiho et al

Abstract:

An integrated approach of stratigraphic analysis and U-Pb age dating reveals some information on the tectono-sedimentary evolution of the Statherian cover of the São Francisco craton in the so-called Espinhaço basin (Atlantic shield in eastern Brazil). Here, continental sedimentation patterns, such as alluvial fan, braided-plain and lacustrine facies associations, with associated volcanic rocks are documented in two superposed basin fill-successions, which are defined as the Algodão and Sapiranga Synthems and grouped in the Botuporã Supersynthem. Both studied units consist mainly of conglomerates and cross-bedded sandstones and minor amounts of mudstones, sedimentary breccias, volcanic lava beds and volcaniclastic rocks, which were deposited in a rift basin – the Botuporã rift – during two syn-rifting phases. The Algodão Synthem represents the first rifting phase. The basal synsedimentary conglomerates of this unit were deposited mainly by subaerial debris flows, most likely along and near a rift border fault. The framework of this rock consists of only crystalline rock clasts from the basement and no fragments of volcanic rocks. Detrital zircons grains that were extracted from this facies show ages older than 2.05 Ga. The remainder of the section is dominated by fluvial sandy lithofacies with minor conglomerate lenses and sandstone-mudstone heterolithic lithofacies, which represent distal, waning-flood deposits in a lacustrine environment. The upper section also contains hummocky cross-stratified sandstone lithofacies, which are related to a storm-influenced deposition. On top of the Algodão succession, the volcanic rocks were dated at 1775 ± 7 Ma, which was interpreted as the near final age of the first rift-phase. Representing the second rift-phase, the Sapiranga Synthem shows similar sedimentation patterns to the Algodão Synthem. The Sapiranga Synthem rests directly on the volcanic rocks of the Algodão Synthem, and its basal conglomerates (which are most likely also related to a master fault) contain voluminous clasts of volcanic rocks, sandstones and crystalline rocks. The detrital zircons grains that were extracted from this facies show ages of 1741 ± 14 Ma. The volcanic rocks on the upper succession of the Sapiranga Synthem record ages of 1740 ± 10 Ma, which finalized the Botuporã rift evolution. A preliminary geochemical study of volcanic rocks from the Botuporã Supersynthem showed that these rocks are alkaline rocks with high K2O/Na2O ratios, which belong to an ultrapotassic suite. The low concentrations of MgO wt% suggest a felsic ultrapotassic character. The Botuporã Supersynthem is unconformably covered by a volcano-sedimentary rift-succession of EoCalymmian age – the Pajeú Synthem, which represents the second rifting stage of the Espinhaço basin. Several Statherian-related volcano-sedimentary sequences and anorogenic granitoids were dispersed in the São Francisco block, which requires a regional geologic model to explain the extensional and magmatism process during this time. We used the last Columbia paleocontinental reconstruction to constrain these processes by relating them to far-field continental extensional and magmatic record as part of a silicic LIP, which was triggered by the convection-driven tectonic-plate motion on the western border of the Atlantica block inside of the Columbia supercontinent.

Is Continental Crust Lost During Supercontinents Assembly?

Increased loss of continental crust during supercontinent amalgamation

Authors:

Roberts

Abstract:

The volume of Earth's continental crust depends on the rate of addition of continental crust from the mantle compared to the rate of continental loss back to the mantle, which at present is roughly balanced. Models for the growth rate of continental crust vary, with isotope data suggesting various episodes of increased growth rate throughout Earth's history; these episodes have been correlated with the supercontinent cycle, but may be a consequence of preferential preservation of continental crust during these cycles. The global balance between addition and loss of continental crust is controlled by: 1) the extent of internal orogens versus exterior orogens, with the latter favouring continental addition, and 2) the balance between exterior orogens in retreating mode versus those in advancing mode, with the latter favouring continental loss. A greater balance of continental addition versus loss should exist during supercontinent break-up, due to a high magmatic flux in retreating accretionary orogens, whereas the amalgamation of supercontinents should involve increased continental loss due to increased sediment subduction and tectonic erosion. Zircon U–Pb and Hf isotopes provide insight to models of crustal growth rate since they sample the continental crust at their time of formation. Using the distribution of data within εHf(t)-time space of a global zircon database, it is demonstrated that the data are in accord with the concept of increased continental loss during supercontinent amalgamation. Periods featuring increased continental addition relative to continental loss, and hence increased continental crust growth rate, occur at ~ 1.7–1.2 Ga, ~ 0.85–0.75 Ga, and ~ 0.45–0.35 Ga, and follow the formation of the Columbia (Nuna), Rodinia and Gondwana supercontinents respectively. Distinct increases in continental loss compared to continental addition, i.e. decreased continental growth rate, occur at ~ 1.0–0.9 Ga, and ~ 0.6–0.55 Ga, correlating with the periods of Rodinia and Gondwana amalgamation respectively. Formation of Pangea by introversion rather than extroversion, means that continental addition in exterior orogens was concurrent with continental loss in interior orogens; a similar process may have been responsible for formation of the Columbia supercontinent. Peaks in the compilation of U–Pb zircon ages correlate with the timing of supercontinent amalgamation, and are likely to be a consequence of preferential preservation of continental crust during this part of the supercontinent cycle.

The Position of Ordos Block (India) in the Orosirian Paleoproterozoic Supercontinent Columbia

Possible southwestward extrusion of the Ordos Block in the Late Paleoproterozoic: Constraints from kinematic and geochronologic analysis of peripheral ductile shear zones

Authors:

Gong et al

Abstract:

The Paleoproterozoic is a pivotal period of the tectonic evolution of the North China Craton (NCC). Various models have been postulated by previous researchers through the study of petrology and metamorphism, but the lack of structural analyses has hampered further understanding of the tectonic evolution of the NCC. A series of well-exposed ductile shear zones developed on the northern, northwestern and eastern edges of the Ordos Block in the western part of the NCC. We carried out detailed field studies along with isotopic dating focused on the kinematics and geochronology of the ductile shear zones. On the north margin of the Ordos block, the Wulashan-Daqingshan ductile shear zone is characterized by an E-W trending shearing foliation that steeply dips 75-80° to the north or south, with subhorizontal stretching lineation plunging 10-15° toward the east or west and dextral strike-slip shearing kinematics. On the west margin of the Ordos block is the Zongbieli ductile shear zone with top-to-the-NW thrusting kinematics. On the east margin of the Ordos block is the Xueling ductile shear zone with top-to-the-SE thrusting accompanied by sinistral strike-slip shearing kinematics.

The 40Ar-39Ar ages of deformed minerals from mylonitic high-grade metamorphic rocks and LA-ICP-MS U-Pb dating results of zircons from syn-tectonic anatectic granites reflect that the ductile shear zones surrounding the Ordos block deformed between 1.85 and 1.81 Ga. The similar deformation ages indicate that the ductile shear zones might be genetically correlated. The geometry, kinematics and geochronology characteristics of the Wulashan-Daqingshan ductile shear zone on the north margin, the Zongbieli ductile shear zone on the west margin, and the Xueling ductile shear zone combined with the Zhujiafang sinistral ductile shear zone on the east margin defined the possible southwestward extrusion of the Ordos block in the late Paleoproterozoic, which might have resulted from the westward subduction-collision of the Eastern Block under the Western Block at approximately 1.85 Ga and which is correlated with the amalgamation of the Columbia supercontinent

Australia's Position in Supercontinents Columbia & Rodinia

Pinning northeastern Australia to northwestern Laurentia in the Mesoproterozoic

Authors:

Medig et al

Abstract:

Two supercontinents have been proposed for the latter half of the Precambrian: Columbia (or Nuna) from ca. 1.9-1.3 Ga, and Rodinia from ca. 1.1-0.75 Ga. In both supercontinents, Laurentia and Australia are regarded as probable neighbours, although their relative positions are contentious. Here we use detrital zircons ages from unit PR1 of the lower Fifteenmile group in Yukon, Canada, to demonstrate that northeastern Australia and northwestern Laurentia were firmly connected in the Mesoproterozoic. The zircon ages define a near-unimodal population with a peak at 1499 ± 3 Ma, which lies in an interval of magmatic quiescence on Laurentia, known as the North American magmatic gap (NAMG), and abundant magmatism in Australia. Sediment compositions and textures suggest the sediment was derived from a proximal metaplutonic source. We suggest that the Williams and Naraku batholiths in the Mt. Isa inlier in northeastern Australia, with crystallization ages ranging from 1493 ± 8 Ma to 1508 ± 4 Ma, are the most probable sources of sediment for the PR1 basin. The plutons were exhumed between 1460 and 1420 Ma, and likely formed an active, eroding highland in the Australian part of Columbia. Sediment derived from these plutons was carried eastward by a short, direct river system and deposited into the PR1 marine basin. Formation of the PR1 basin coincides with the formation of the southern Cordilleran Belt-Purcell, Hess Canyon, and Trampas basins. These basins, formed on the western margin of Laurentia, also have detrital zircon populations that fall into the NAMG, suggesting that sediment was derived from a non-Laurentian westerly source. The PR1 basin is herein correlated with the Belt-Purcell, Hess Canyon, and Trampas basins to the south, and together these basins record the onset of Columbia breakup along the length of the western margin of Laurentia from as far north as Yukon to as far south as Arizona.

Absorption of the Tarim Craton into the PaleoProterozoic Supercontinent Columbia

Geochronology and geochemistry of meta-mafic dykes in the Quanji Massif, NW China: Paleoproterozoic evolution of the Tarim Craton and implications for the assembly of the Columbia supercontinent

Authors:

Liao et al

Abstract:

The Quanji Massif, located in the northeastern margin of the Tibet Plateau, is interpreted as a fragment of the Tarim Craton. The massif exposes a suite of metamorphosed mafic dykes. LA-ICP-MS U–Pb dating constrains the timing of intrusion of these dykes at ca. 1834 ± 23 Ma. The dykes display minor variations in major elements, with SiO2 = 46.8–53.4 wt%, MgO = 5.19–8.10 wt%, FeOt = 8.83–15.6 wt%, TiO2 = 0.58–1.78 wt% and Mg# = 46.3–69.7. Their immobile trace element compositions show a sub-alkali basalt affinity. The positive correlation of TiO2 with FeOt/MgO in these rocks shows an arc tholeiite evolutionary trend. The enrichment of LILE and LREE and depletion in HFSE suggest that the precursor magma was generated in a back-arc environment. Furthermore, these rocks possess (Nb/La)N of 0.31–0.52 and (Th/La)N of 0.61–1.39, whole rock (87Sr/86Sr)i values of 0.707598–0.724141, ɛNd(t) of −2.9 to +0.3 and (206Pb/204Pb)t of 16.8148–24.1513, (207Pb/204Pb)t of 15.3422–16.3630 and (208Pb/204Pb)t of 36.8415–39.7926. The magmatic zircons yielded ɛHf(t) of −3.4 to +6.1 and depleted mantle model ages (TDM) of 2.01–2.37 Ga. The geochemical and isotopic characteristics of these rocks suggest that their precursor magma was derived from a subduction-related fluid-metasomatized subcontinental lithospheric mantle mixed with a depleted mantle component. We suggest that a prolonged subduction-accretion-collision process along the southeastern margin of the Tarim Craton prevailed at ∼2.1–1.80 Ga, with local consumption of the Southeast Tarim Archipelagic Ocean during the collision of the Southeast Tarim Block with the Quanji Massif (microcontinent) at around 2.1–1.9 Ga. The final closure of the whole Southeast Tarim Archipelagic Ocean occurred at ∼1.85–1.82 Ga and collision between the Southeast margin of the Tarim Craton and other unknown continental blocks at 1.82–1.80 Ga, broadly coeval with the amalgamation of the Western and Eastern Blocks of the North China Craton and their assembly in the Columbia supercontinent.