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Provenance of Ediacaran-Ordovician sediments of the Medio Armorican Domain, Brittany, West France: Constraints from U/Pb detrital zircon and Sm–Nd isotope data

Year: 2021
Products: UP213;NewWave;
Authors: Dabard, M;Loi, A;Pavanetto, P;Meloni, M;Hauser, N;Matteini, M;Funedda, A;
Journal: Gondwana Research

The temporal evolution of the sedimentary source areas of the Armorican Massif, involving Ediacaran to Upper Ordovician strata, is investigated to gain insight into the palaeogeographic affinities and changes that occurred as a result of Cadomian orogenesis. Until now, palaeogeographic reconstructions based on geodynamic, stratigraphic and paleontological data have shown geological continuity between the Armorican Massif and the Iberian and Bohemian massifs and have allowed researchers to locate the Armorican Massif near the West African Craton and the Trans-Saharan Belt. This study goes beyond the interpretations based on lithostratigraphic correlation, which may be influenced by allocyclic factors (e.g., sea-level change) or fauna assemblages that have a wide provincial distribution, to provide a correct assessment of sediment flux. To determine the palaeogeographic location more accurately, the provenance of the siliciclastic sediments was examined in this study using U–Pb LA-MC-ICP–MS geochronology on detrital zircons coupled with whole-rock Sm–Nd and zircon Lu–Hf isotope analysis. This work was carried out on the sedimentary succession of the Medio Armorican Domain. The oldest studied sedimentary rocks were shown to belong to the Brioverian succession, which contains mainly 519–781 Ma old zircons, likely derived from sources that are still present in the Armorican basement. Successively, the lower Paleozoic succession was deposited in the rift stages of the Rheic Ocean, with contributions from a new source of 827–1120 Ma old zircons. A comparison of the zircon populations showed an increase in negative εNd(t) and εHf(t) values of the sedimentary supply in the post-Cadomian samples. Moreover, it revealed that the Medio and North Armorican domains had different locations during the Lower Ordovician, and that some areas of the Iberian Massif and the Medio Armorican Domain close to the Sahara Metacraton and Arabian-Nubian Shield were contiguous.

Evolution of the Indochina block from its formation to amalgamation with Asia: Constraints from protoliths in the Kontum Massif, Vietnam

Year: 2021
Products: New Wave;New Wave Research;
Authors: Nakano, N;Osanai, Y;Owada, M;Binh, P;Hokada, T;Kaiden, H;Bui, V;
Journal: Gondwana Research

This study reported the U-Pb ages and Hf isotopes of the zircons of Triassic and Silurian metamorphic rocks in the Kontum Massif, central Vietnam to understand the origin and evolution of the Indochina Block. The detrital zircon signature of the Triassic metasedimentary rocks corresponds to the Neoproterozoic sequence in the Indochina Block and that of the Silurian rocks corresponds to the Paleo- to Mesoproterozoic sequence in the southwestern margin of the Yangtze Block. From Triassic metaigneous rocks, we obtained three meaningful inherited ages; ~1450 Ma, 500 Ma, and 450 Ma. The Triassic metasedimentary rocks occur in close association with the Triassic felsic gneiss and mafic granulite (former eclogite) with magmatic inherited zircon ~1450 Ma and intermediate gneiss with ~500 Ma protolith age. The Hf isotopes suggest the ~1450 Ma age as the earlier or primary stage of the formation of the Indochina Block and the ~500 Ma age as the timing of its reworking, before the block subducted beneath the South China Block to form Triassic eclogite relicts. The Ordovician magmatic ages (~450 Ma) from metaigneous rocks in the Kontum Massif, combined with their volcanic arc whole-rock chemistry, Ordovician–Silurian low-pressure/high-temperature isobaric heating metamorphism, and the detrital zircon signature strongly suggest an Ordovician–Silurian continental arc in the present southwestern margin of the South China Block prior to the Triassic continental collision.

Early Paleozoic tectonic transition from oceanic to continental subduction in the North Qaidam tectonic belt: Constraints from geochronology and geochemistry of syncollisional magmatic rocks

Year: 2021
Products: New Wave;
Authors: Niu, M;Cai, Q;Li, X;Yakymchuk, C;Wu, Q;Yuan, X;Sun, Y;
Journal: Gondwana Research

The North Qaidam tectonic belt (NQTB) records the tectonic evolution of the South Qilian Ocean from subduction to closure followed by continental subduction. However, the timing of closure of the South Qilian Ocean and the nature of the tectonic transition from oceanic to continental subduction are poorly constrained. In this contribution, an integrated study of petrology, geochemistry, geochronology and Sr–Nd–Hf isotopes is performed on two groups of intermediate–mafic rocks from the Chahanhe intrusive complex in the NQTB. Group 1 intermediate–mafic rocks (441–428 Ma) have arc-like geochemical compositions, high (87Sr/86Sr)i ratios (0.711171 to 0.713181), negative εNd(t) values (−7.22 to −5.49) and low zircon εHf(t) values (−6.3 to +0.5), suggesting that they are derived from partial melting of enriched subcontinental lithospheric mantle. The enriched lithospheric mantle was produced by interaction of the subcontinental mantle wedge peridotite with subducting slab-derived melt and fluid during previous subduction of the South Qilian Ocean. Group 2 mafic rocks (441–439 Ma) exhibit E-MORB-like geochemical compositions with positive εNd(t) values (+2.44 to +3.31) and high zircon εHf(t) values (+1.3 to +6.9), but with high (87Sr/86Sr)i ratios (0.706775 to 0.708661); these features indicate derivation from partial melting of asthenospheric mantle with the involvement of aqueous fluid and minor melt that were probably derived from subducted oceanic crust. We propose that rollback of subducted South Qilian oceanic slab during the initial stage of continental subduction triggered decompression melting of asthenospheric mantle to produce E-MORB-like mafic rocks; convecting and upwelling asthenosphere also provided heat that induced partial melting of the pre-existing enriched lithospheric mantle and generated mafic magmas with arc-like geochemical signatures. Our results improve the understanding of the tectonic transition process from oceanic subduction to continental subduction in the NQTB, the closure of the Proto-Tethyan Ocean, and provide new insights into the importance of crustal growth during initial continental collision.

Development of a hyperspectral imaging technique using LA-ICP-MS to show the spatial distribution of elements in soil cores

Year: 2021
Products: NWR213;ESI;
Authors: Zaeem, M;Nadeem, M;Huong Pham, T;Ashiq, W;Ali, W;Shah Mohioudin Gillani, S;Moise, E;Leier, H;Kavanagh, V;Galagedara, L;Cheema, M;Thomas, R;
Journal: Geoderma

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a versatile analytical technique that can create qualitative images delineating the spatial distribution of elements in different samples. However, there is no demonstration of this technique in imaging the spatial distribution of elements in soil cores. Herein, we developed a hyperspectral imaging method using LA-ICP-MS to visualize the spatial distribution of selected elements in soil cores as a proof of concept. Soil cores were collected in plastic liners, frozen at −20°C; cut uniformly in halves using a band saw. The surface of the intact cores was ablated using a 213 nm laser optimized with the following parameters: spot size 100 µm, laser energy of 7 mJ, and scan speed of 220 µms−1. Two-dimensional images of the soil cores were created for Ca, Mg, P, K, Na, Zn, Fe, Co, and Mn using the iolite software. The new imaging method was very effective in showing that different crop management systems and fertilizer applications altered the levels and spatial distribution of Ca, Mg, P, K, Na, Zn, Fe, Co, and Mn in the evaluated soil cores. The results show that the developed method has great potential in multi elemental imaging of intact soil cores. This could have huge implications in environmental impact assessments, soil resource evaluation, agriculture crop production and the effectiveness of land use or land management systems in modulating the spatial distribution of elements within the soil.

Geochemical evidence of Milankovitch cycles in Atlantic Ocean ferromanganese crusts

Year: 2021
Products: NWR193UC;
Authors: Josso, P;van Peer, T;Horstwood, M;Lusty, P;Murton, B;
Journal: Earth and Planetary Science Letters

Hydrogenetic ferromanganese crusts are considered a faithful record of the isotopic composition of seawater influenced by weathering processes of continental masses. Given their ubiquitous presence in all oceans of the planet at depths of 400–7000 meters, they form one of the most well-distributed and accessible records of water-mass mixing and climate. However, their slow accumulation rate and poor age constraints have to date limited their use to explore 100 ka paleoclimatic phenomena. Here it is shown how the Pb isotope signature and major element content of a Fe-Mn crust from the north-east Atlantic responded to changes in the intensity and geographic extent of monsoonal rainfall over West Africa, as controlled by climatic precession during the Paleocene. The studied high-spatial resolution (4 μm) laser-ablation multi-collector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) Pb isotope data is a nearly 2 order of magnitude improvement in spatial and temporal resolution compared to micro-drill subsamples. The record demonstrates cyclicity of the 206Pb/204Pb and 208, 207Pb/206Pb ratios at the scale of single Fe-Mn oxide laminae, in conjunction with variations in the Fe/Mn ratio, Al, Si and Ti content. Time-frequency analysis and astronomical tuning of the Pb isotope data demonstrates the imprint of climatic precession (∼20 ka) modulated by eccentricity (∼100 and 405 ka), yielding growth rates of 1.5–3.5 mm/Ma consistent with previous chemostratigraphic age models. In this context, boreal summer at the perihelion causes stronger insolation over West Africa, resulting in more intense and geographically extended monsoonal rainfalls compared to aphelion boreal summer conditions. This, in turn, influences the balance between the weathering endmembers feeding the north-east Atlantic basin. These results provide a new approach for calibrating Fe-Mn crust records to astronomical solutions, and allow their isotopic and chemical archive to be exploited with an improved temporal resolution of 1000–5000 years.

Highly siderophile elements in shergottite sulfides and the sulfur content of the martian mantle

Year: 2021
Products: UP213;New Wave;New Wave Research;
Authors: Paquet, M;Day, J;Udry, A;Hattingh, R;Kumler, B;Rahib, R;Tait, K;Neal, C;
Journal: Geochimica et Cosmochimica Acta

Shergottite meteorites are ultramafic to mafic igneous rocks derived from partial melting of distinct regions of the martian mantle. As such, they trace magmatic processes, including fractional crystallization and mixing processes in Mars. New chalcophile (Cu, Se, Zn, Pb), siderophile (Ni, Co, W), and highly siderophile element (HSE: Au, Re, Pd, Rh, Pt, Ru, Ir, Os) abundance data are reported for sulfide assemblages in a suite of thirteen incompatible trace-element depleted, intermediate and enriched shergottites, along with new whole-rock HSE abundance and 187Os/188Os data for seven shergottites. Sulfide grains in depleted and intermediate shergottites typically have the highest absolute abundances of HSE, with broadly flat CI-chondrite normalized patterns. Enriched shergottite sulfide grains typically have highly variable Au, elevated Pd and Rh and are relatively depleted in Zn, Ir and Os. The new HSE whole-rock data for enriched (Northwest Africa [NWA] 7397, NWA 7755, NWA 11043), and intermediate shergottites (NWA 10961, NWA 11065, NWA 12241, and NWA 12536) are generally consistent with existing 187Os/188Os and HSE abundance data for these geochemical groupings. Enriched shergottites with >1 ppb bulk rock Os have measured 187Os/188Os ranging between 0.1296 and 0.1471, with variable Pd and Pt contents. Intermediate shergottites with >1 ppb bulk rock Os have chondrite-relative proportions of the HSE at ∼0.01 to 0.001 × CI chondrites and 187Os/188Os from 0.1284 and 0.1295. Sulfides are the major host of the HSE, and they control the behavior of the HSE during petrogenetic processes in shergottite magmas, enabling the determination of HSE compatibility for martian magmatism in the order: Os > Ir ≥ Ru ≥≥ Rh ≥ Pd ≥ Re ≥ Pt ≥ Au. Fractionation models of removal of an olivine-dominated cumulate recreate HSE patterns for the whole-rock shergottites. Enriched shergottites are best reproduced by 25 to 30% of fractionation from a degassed parent melt (250 ± 50 ppm of S), whereas depleted and intermediate shergottites can be explained by slightly lower fractionation (10 to 15%) from higher S content parent melts (350 ± 100 ppm of S). Sulfur contents in the melt that are ∼50% higher than these estimates yield earlier S-saturation during fractional crystallization, leading to an abrupt decrease of the more compatible HSE (Ru, Ir, Os), which is not observed. These results indicate that the martian mantle and partial melts derived from it, are probably not anomalously enriched in S, and instead are similar to slightly higher than those of the terrestrial mantle and its partial melts.

Is there a Grenvillian orogen in the southwestern Tarim Craton?

Year: 2021
Products: NWR193UC;New Wave;ESI;
Authors: Zhou, T;Ge, R;Zhu, W;Wu, H;
Journal: Precambrian Research

The Rodinia Supercontinent assembled through global-scale Grenvillian (1300–900 Ma) orogeny, so identification and correlation of Grenvillian orogens is fundamental to the geological reconstruction of Rodinia. The Tarim Craton, NW China, has been considered as a building block of Rodinia, but its Neoproterozoic tectonic evolution and relationship with Rodinia remain enigmatic. It was proposed that a Grenvillian orogenic event occurred in the southwestern Tarim, possibly related to its amalgamation with northern Australia. Key evidence for this model came from the ~1.0 Ga 40Ar/39Ar ages of the Kalakashi Group in the Tiekelike belt, southwestern Tarim. In this contribution, we report zircon U-Pb ages and Lu-Hf isotopic data, as well as whole-rock geochemical data for the Kalakashi Group from the Buqiong section where a ~1.0 Ga 40Ar/39Ar age was reported. Our field and petrographic observations indicate that the primary rock assemblage of the Kalakashi Group is orthogneiss, garnet-bearing mica schist, marble and minor amphibolite. Zircon U-Pb dating of five orthogneisses and an amphibolite yielded crystallization ages of 900–850 Ma and a thermal/fluid overprinting event at ~420 Ma. Lu-Hf isotopic analyses of the dated zircon grains from two orthogneisses yielded εHf(t) values from −4 to +7, indicating a mixture of mantle- and crust-derived materials. Geochemical data show that the orthogneisses have relatively high FeOT/MgO and 10,000*Ga/Al ratios, elevated contents of high-field-strength elements (HFSE) and negative Ba, Sr and Eu anomalies, characteristic of A1-type granite, indicating that the parental magma erupted in an intra-plate rifting setting. Our results indicate that the Kalakashi Group is a volcanic-sedimentary succession that deposited in the Neoproterozoic, rather than the Paleoproterozoic or Mesoproterozoic as previously thought. We found no evidence for a Grenvillian orogenic event from the Kalakashi Group in the Buqiong section. Instead, the age and geochemistry of the studied orthogneisses are remarkably similar to those of the Sailajiazitage Group, although the latter was affected by weaker metamorphism and deformation. Reliable geochronological data from igneous and metamorphic rocks, as well as detrital zircons from Neoproterozoic strata, indicate that no typical record of Grenvillian orogeny occurred in either the north or the south of the Tarim Craton. Instead, we suggest that the northern Tarim was probably dominated by a long-term subduction-accretion, whereas the southern Tarim was likely in a long-term rifting environment in the early Neoproterozoic.

Late Mesoproterozoic–early Neoproterozoic quartzite–schist sequences of the Aktau–Mointy terrane (Central Kazakhstan): Provenance, crustal evolution, and implications for paleotectonic reconstruction

Year: 2021
Products: UP213;NewWave;
Authors: Kanygina, N;Tretyakov, A;Degtyarev, K;Kovach, V;Skuzovatov, S;Pang, K;Wang, K;Lee, H;
Journal: Precambrian Research

Metasedimentary complexes represented by quartzite–schist Kiik Group quartzite–schists play a significant role in the Aktau–Mointy terrane structure, which is one of the largest Precambrian blocks in the western Central Asian Orogenic Belt (CAOB). U-Pb LA-ICP-MS dating of detrital zircons from quartzites in different Kiik Group areas and related magmatic age data establish that accumulation occurred in the late Mesoproterozoic to early Neoproterozoic (from 1150 to 920 Ma). Concordant age estimates of detrital zircons from Kiik Group quartzites predominately fell within intervals of 1149–2105 and 2272–2850 Ma with the prominent peaks at 1217, 1332, 1466, 1582, 1621, 1748, 1849, 2517 and 2689 Ma, and minor peaks at 1992, 2282, 2791 and 2823 Ma. Hf-in-zircon and Nd whole rock data suggest that the primary stages of continental crustal growth in the Aktau–Mointy terrane were associated with the tectono-magmatic processes of the Neoarchean, Paleoproterozoic, and Mesoproterozoic. Juvenile continental crust production occurred during the Neoarchean and Paleoproterozoic, with older complex tectono-magmatic reworking, and juvenile crust production finally prevailed in the mid-Mesoproterozoic. Based on the age patterns and Hf isotopic compositions of detrital zircons from the Aktau–Mointy terrane and other terranes in the western CAOB, the crustal basement of the Aktau–Mointy terrane exhibits certain similarities with those of the Northern Kazakhstan and Issyk–Kul terranes. They all exhibit a close tectonic affinity with the Chinese Central Tian Shan terranes, Yili Block, North and China Craton, while differing from the Tarim Craton. In the Rodinia supercontinent structure, the Aktau–Mointy terrane was probably located near the Sveconorwegian Orogen in the western Baltica with other Kazakhstan and Northern Tian Shan Precambrian blocks.

New constraints for paleogeographic reconstructions at ca. 1.88 Ga from geochronology and paleomagnetism of the Carajás dyke swarm (eastern Amazonia)

Year: 2021
Products: NWR193UC;ESI;
Authors: Antonio, P;D'Agrella-Filho, M;Nédélec, A;Poujol, M;Sanchez, C;Dantas, E;Dall'Agnol, R;Teixeira, M;Proietti, A;Martínez Dopico, C;Oliveira, D;Silva, F;Marangoanha, B;Trindade, R;
Journal: Precambrian Research

The Uatumã event is a silicic large igneous province (SLIP) covering an area of 1.500.000 km2 of the Amazonia craton at ca. 1890–1850 Ma. New paleomagnetic data and U-Pb apatite ages for coeval microgranitic, andesitic, and basaltic dykes in the Carajás Province (southeastern Amazonia craton) are presented. Two primary characteristic remanent magnetizations (ChRMs) were isolated for the Carajás dykes which were combined with published results for coeval rocks in the São Felix do Xingu area, producing two grand mean poles: (1) “CA1”, dated at 1880 Ma on zircon and apatite, whose mean site directions cluster around the mean Dm = 132.8°, Im = 76° (N = 26, α95 = 5°, k = 32.7), yielding the paleomagnetic pole at 328.7°E, 23.3°S, (A95 = 8.7° K = 11.7), and (2) “CA2” from well-dated microgranitic dykes of the Velho Guilherme Suite (1855 Ma U-Pb on zircon and apatite). Site mean directions group around the mean Dm = 240.3°, Im = 11.8° (N = 18, α95 = 10.8°, k = 11.1), which yielded the paleomagnetic pole at 221.3°E, 30.2°S, (A95 = 8.8°, K = 16.2). The remanent magnetization of the Velho Guilherme microgranitic dykes is carried by pseudo-single domain (PSD) magnetite. Its primary origin is supported by a positive baked contact test. Two younger secondary components were also isolated in the Carajás dyke swarm: one probably associated to the Mesozoic Central Atlantic magmatic province (CD3), and another component (CD4) with yet undefined age. A new configuration for the Amazonia and West Africa during the Paleoproterozoic, which aligns the Sassandra shear zone (in Africa) and the North Guiana Through and other shear zones (in Guiana Shield), is supported by geological and paleomagnetic data. The large angular distance between the 1880 Ma CA1 and 1855 Ma CA2 (Q ~ 6) poles that are relatively close in age implies in a high plate velocity for the Amazonia craton, which is not consistent with modern plate tectonics. A similar large discrepancy between 1880 and 1860 Ma poles was also observed at least as many as six cratons. Although other hypotheses can be invoked, such as non-uniformitarian magnetic fields, the occurrence of large-scale true polar wander at this time may be the most parsimonious explanation of the widespread discrepancies.

A buried Paleoarchean core of the Eastern Sarmatia, Kursk block: U-Pb, Lu-Hf and Sm-Nd isotope mapping and paleotectonic application

Year: 2021
Products: NWR213;
Authors: Savko, K;Samsonov, A;Larionov, A;Chervyakovskaya, M;Korish, E;Larionova, Y;Bazikov, N;Tsybulyaev, S;
Journal: Precambrian Research

Zircon U-Pb and Lu-Hf isotope analyses along with whole-rock Sm-Nd isotope studies shed a light on distribution of the Paleoarchean crust in the Kursk block, Eastern Sarmatia. It has been revealed that this domain consists of two provinces with different crust ages: the Paleoarchean Kursk-Besedino granulite-gneiss domain (KBd) and the Mesoarchaean Mikhailovsky granite-greenstone area (Mgga). The KBd encompasses TTG orthogneisses and pelite, BIF, and mafic volcanics (sills) metamorphosed in the granulite facies. The orthogneiss protolith was formed ca 3.55 Ga (U-Pb SHRIMP data) from a juvenile source. In the metapelites, U-Pb detrital zircon ages cluster in three groups, 3535–3556, 3464–3472, and 3334–3384 Ma. The latter one suggests post-Middle Paleoarchean age of the protoliths deposition. Sm-Nd and Lu-Hf isotope characteristics of the volcanic-sedimentary rocks suggest the leading role of Paleoarchean crustal material in their protoliths. The age of metamorphic zircon is ca 2.8 Ga in all the KBd rocks. The Mgga consists of TTG and volcanic-sedimentary units. The ages of the TTG, felsic volcanics and metasediments fall in a narrow range of 2.96–3.12 Ga. They have juvenile isotope-geochemical characteristics (εNd(t) = +0.3 – + 4.0; εHf(t) = -0.3 – + 5.8) without any contribution of Paleoarchean crust. High-temperature 2.8 Ga-old metamorphism is not recorded in the Mgga. Pronounced differences in the age of crust-forming events in the KBd and Mgga indicate that these continental blocks had a different geological history, hence were distant from each other during most of the Archean Eon, probably up to 2.8 Ga. The Paleoproterozoic Trosnyanskaya intrusion in the Mgga bears signs of the KBd Paleoarchean crust. This suggests a collision of these Archean blocks with the Mesoarchean being thrust over the Paleoarchean rocks possibly at ca 2.8 Ga.

Neoproterozoic crustal growth in southern Malawi: New insights from petrology, geochemistry, and U–Pb zircon geochronology, and implications for the Kalahari Craton–Congo Craton amalgamation

Year: 2021
Products: NWR213;ESI;
Authors: Tsunogae, T;Uthup, S;Nyirongo, M;Takahashi, K;Rahman, M;Liu, Q;Takamura, Y;Tsutsumi, Y;
Journal: Precambrian Research

The southern part of the Malawi Basement Complex is regarded as being part of the Mozambique Belt, which was formed by a series of collisions between Archean cratons and/or Proterozoic magmatic arcs during Neoproterozoic to Cambrian time. The region is particularly important because of its location near the junction between the East-African (ca. 600–550 Ma) and Kuunga (ca. 560–530 Ma) orogens, which means that complex magmatic or metamorphic episodes may have been recorded in high-grade metamorphic rocks in the region. Here we report on new petrological, geochemical, and zircon U–Pb age data on felsic to mafic orthogneisses as well as on a syn-tectonic syenite from the Lilongwe–Zomba–Blantyre area in southern Malawi, with a view to evaluating the timing and pressure–temperature (P–T) conditions of the collision events as well as the protolith formation. The geochemical data on the felsic orthogneisses suggested magmatic-arc signatures, whereas the mafic orthogneisses had both magmatic-arc and non-arc signatures. Metamorphic P–T estimates for the orthogneisses based on conventional geothermometry and phase-equilibria modeling indicated high-pressure granulite-facies conditions of 9.1–11.6 kbar and 840 °C–930 °C. Zircons obtained from charnockite, biotite gneiss, and garnet-bearing mafic granulite yielded magmatic ages of 1011–808 Ma, 1013 Ma, and 1076 Ma, respectively, suggesting the presence of Stenian–Tonian crustal growth related to arc magmatism. Ediacaran (573 Ma) intrusion of granitic rock was also inferred from magmatic zircons found within a granitoid gneiss. The timing of the high-grade metamorphism was constrained by the ages of the zircon rims and found to be 569–557 Ma, thus coinciding with the intrusion of syn-tectonic syenite at 562 Ma. The results of this study suggest that the southern part of Malawi is composed of remnants of the Stenian–Tonian magmatic arc, which were metamorphosed together with surrounding metasediments around 560 Ma. The Ediacaran high-grade metamorphism is consistent with the age of the Zambezi Belt located immediately southwest of the Malawi Basement Complex. Both the Lilongwe–Zomba–Blantyre area and the Zambezi Belt may correspond to a single suture zone formed by the latest Neoproterozoic collision between the Kalahari and Congo Cratons.

Provenance, stratigraphic and precise depositional age constraints for an outlier of the 1.9 to 1.8 Ga Nonacho Group, Rae craton, Northwest Territories, Canada

Year: 2021
Products: New Wave;New Wave Research;
Authors: Neil, B;Gibson, H;Pehrsson, S;Martel, E;Thiessen, E;Crowley, J;
Journal: Precambrian Research

The Nonacho Group comprises six formations of continental clastic rocks that were deposited between 1.91 and 1.83 Ga. The Nonacho Group is part of a broader assemblage of conglomerate and sandstone that was deposited atop the Rae craton in response to the amalgamation of Laurentia and supercontinent Nuna, but the details of its tectonic setting are contentious. This paper documents an outlier of Nonacho Group rocks ∼50 km east of the main Nonacho basin. Field observations and LA-ICPMS (laser ablation inductively coupled plasma mass spectrometry) U-Pb detrital zircon geochronology are integrated with previous studies of the main basin to better understand the group’s depositional history, provenance and tectonic setting. The lithology and detrital zircon age spectra of the outlier allow for its correlation to the upper two formations of the Nonacho Group. CA-ID-TIMS (chemical abrasion isotope dilution thermal ionization mass spectrometry) analyses of two fragments of the youngest detrital zircon provide a maximum depositional age of 1901.0 ± 0.9 Ma. A felsic volcanic cobble dated at ca. 2.38 Ga provides evidence of volcanism during the Arrowsmith orogeny. Detrital zircon dates recovered from the outlier (ca. 3.4–3.0, 2.7, 2.5–2.3 and 2.0–1.9 Ga) are consistent with derivation from topography of the Taltson and/or Thelon orogens on the western margin of the Rae craton. Taltson-Thelon (2.0 to 1.9 Ga) aged detritus is only abundant in the upper two formations of the Nonacho Group, marking a change in provenance from the lower formations. This change in provenance may have coincided with a period of renewed uplift and the unroofing of Taltson-Thelon plutons. The detrital zircon provenance and depositional age of the Nonacho Group is consistent with models that link its deposition to the Taltson and/or Thelon orogens. However, tectonism associated with the 1.9 to 1.8 Ga Snowbird and Trans-Hudson orogens to the east could also have affected basin formation or the change in provenance from the lower to upper Nonacho Group. This study highlights the importance of CA-ID-TIMS in establishing accurate and precise maximum depositional ages for sedimentary successions.

Reconstructing the ecological history of the extinct harp seal population of the Baltic Sea

Year: 2021
Products: NWR193;ESI;
Authors: Glykou, A;Lõugas, L;Piličiauskienė, G;Schmölcke, U;Eriksson, G;Lidén, K;
Journal: Quaternary Science Reviews

The harp seal (Pagophilus groenlandicus), today a subarctic species with breeding populations in the White Sea, around the Jan Mayen Islands and Newfoundland, was a common pinniped species in the Baltic Sea during the mid- and late Holocene. It is puzzling how an ice dependent species could breed in the Baltic Sea during the Holocene Thermal Maximum (HTM), and it remains unclear for how long harp seals bred in the Baltic Sea and when the population became extirpated. We combined radiocarbon dating of harp seal bones with zooarchaeological, palaeoenvironmental and stable isotope data to reconstruct the harp seal occurrence in the Baltic Sea. Our study revealed two phases of harp seal presence and verifies that the first colonization and establishment of a local breeding population occurred within the HTM. We suggest that periods with very warm summers but cold winters allowed harp seals to breed on the ice. Human pressure, salinity fluctuations with consequent changes in prey availability and competition for food resources, mainly cod, resulted in physiological stress that ultimately led to a population decline and local extirpation during the first phase. The population re-appeared after a long hiatus. Final extinction of the Baltic Sea harp seal coincided with the Medieval Warm Period. Our data provide insights for the first time on the combined effects of past climatic and environmental change and human pressure on seal populations and can contribute with new knowledge on ongoing discussions concerning the impacts of such effects on current arctic seal populations.

Sedimentary provenance of the Plio-Pleistocene Nicobar Fan: Complex sourcing revealed through Raman spectroscopy heavy mineral analysis

Year: 2021
Products: NWR193;ESI;
Authors: Webb, M;Gough, A;Vannucchi, P;Lünsdorf, N;McNeil, J;
Journal: Marine and Petroleum Geology

The Nicobar Fan lies within the north-eastern Indian Ocean between the Ninety-East Ridge and Sunda Arc. The fan forms part of the Bengal–Nicobar Fan System and is among the oldest and largest submarine fans on Earth. Previous U–Pb zircon studies of the Nicobar and Bengal fans indicate the Himalaya as the dominate sediment source, making these fans a major Cenozoic sink for uplifted Himalayan sediment. However, the northwards moving Indian Plate, coupled with mid-Pleistocene collision of the Ninety-East Ridge with the Sunda Arc, has shutdown many sediment pathways linking the Himalaya and Nicobar Fan. Here we use big data Raman spectroscopy heavy mineral analysis along with U–Pb zircon data to better define sediment source regions for the Nicobar Fan during the Plio-Pleistocene following the shutdown of sediment delivery. The detrital zircon spectra for the Plio-Pleistocene Nicobar Fan from this study are consistent with previous work indicating that the original sources of these zircons can be found within both the Greater and Tethyan Himalaya, the Gangdese Arc, and the Indo-Myanmar Ranges. However, the heavy mineral data indicate that a large proportion of sediment has been derived from a more complex array of sources. This is coupled with an abundance of low- and moderate-stability minerals (e.g., amphibole, apatite, clinopyroxene), which are unlikely to have been transported large distances. Suggesting that proximal sources have delivered the majority of lower-stability heavy minerals into the Plio-Pleistocene Nicobar Fan. We show that from the Pleistocene onwards direct sediment delivery into the Nicobar Fan from the Himalaya was largely shutdown, with sediment instead shedding off the uplifting Indo-Myanmar Ranges, the Andaman–Nicobar Accretionary Ridge, and the westwards propagating Ayeyarwady River. This study shows that extensive uplift along the northern Sunda Arc is recorded in the Nicobar Fan alongside the previously reported Himalayan record.

Carboniferous–Permian transgression/regression mechanisms in the Eastern Ordos Basin and their sea-level spatiotemporal variability: Insights from source-to-sink systems

Year: 2021
Products: NWR193UC;
Authors: Fu, C;Yu, X;Li, S;Peng, Z;Shi, S;
Journal: Marine and Petroleum Geology

Developed on the North China Craton, the intracratonic Ordos Basin contains a complete Paleozoic-to-Cenozoic sediment record, allowing for long-term paleoenvironmental and climate change investigation. During the Carboniferous–Permian period, convergence between the North China block and the paleo-Yangtze plate to the south resulted in a general marine regression characterized by a series of second-order transgression/regression cycles diachronous along the eastern margin of the Ordos. However, the detailed mechanisms that induced these cycles, as well as the associated paleoecological changes, remain unknown. In this study, we integrate multiple indices, including δ18O and δ13C, rare earth element (REE), paleontological assemblages, and clay content (w (chlorite + kaolinite)/w((Illite) ratio) planar distribution, to restore the paleo-water depth distribution. These parameters are then used to reconstruct the paleo-sea level from the Pennsylvanian to the middle Permian. We conclude that the direction of second-order transgression/regression was mainly toward the east during the Pennsylvanian–early Permian and switched clockwise toward the north during the middle Permian. We suggest that the second-order cycles, diachronous in space and time, are mainly linked to local variations in sediment supply and regional uplift. Using detrital zircon U–Pb data and the REE and trace element content and heavy mineral assemblages (HMA), we estimate the sediment provenance area. The sediment volumes deposited in the basin through time are obtained using 2D seismic data. During the Carboniferous, the coarse-grained sediments deposited in the eastern Ordos were derived from the uplifting Helan Mountain (Qiandam–Qilian orogenic belt). By the middle Permian, the detrital material became multi-sourced, thus issuing the Yinshan range to the north and the Qinling range to the south. We then integrate the description of numerous core samples with electric log and 2D seismic data to reconstruct the sediment facies associations across the first-order regression from the Carboniferous tidal flat depositional system to the middle Permian prograding fluvial delta system. According to the transfer of the glacial epoch, the sedimentation rate, and the transgression/regression rate above, we classify the evolution process into three patterns: low-transgression rate and less-sediment supply pattern (the late Carboniferous), high regression rate and mass sediment supply pattern (the north block during the early Permian), and low regression rate and mass sediment supply pattern (the south block during the Sakmarian stage). Lastly, with the quantitative calculation of the source-to-sink (S2S) parameters, including the S2S system volume and the elevated height of regional uplift with the 2D seismic data, we propose the mechanism of transgression/regression in the Ordos Basin, responding to the above three pattern s. The first pattern was controlled by regional uplift, whereas the second pattern was controlled by sediment supply. As to the third one, uplift and sediment supply could affect the transgression/regression process.

Potential of versatile bacteria isolated from activated sludge for the bioremediation of arsenic and antimony

Year: 2021
Products: New Wave;
Authors: Nguyen, V;Nguyen, D;Ha, M;Kang, H;
Journal: Journal of Water Process Engineering

Two bacterial strains belonging to the genus Shinella were isolated from the activated sludge of a domestic wastewater treatment plant and could autotrophically oxidize As(III) to As(V) under aerobic conditions. Kinetic studies indicated that the autotrophic As(III) oxidation rate of both strains matched the Monod model well, and strain VKA3 exhibited higher kinetic parameters compared to strain VKA4 (μmax = 124.16 μM/h and Ks = 4407.19 μM vs. μmax = 59.00 μM/h and Ks = 1787.03 μM). The versatility of both strains was expressed through their flexible growth under heterotrophic conditions in the presence of yeast extract and anaerobic As(III) coupled with denitrification. Both strains can oxidize Sb(III) to Sb(V) under aerobic conditions. The arsenite oxidase (aioA) gene, which might be involved in As(III) and Sb(III) oxidation, was detected in the isolated strains. This study demonstrated that the versatile bacteria with potential applications for bioremediation of As and Sb could be obtained from an easily accessible microbiological source.

Zircon from the Chuktukon alkaline ultramafic carbonatite complex (Chadobets uplift, Siberian craton) as evidence of source heterogeneity

Year: 2021
Products: New Wave;
Authors: Doroshkevich, A;Sharygin, V;Belousova, E;Izbrodin, I;Prokopyev, I;
Journal: Lithos

The Chuktukon alkaline carbonatite complex is a part of the Chadobets complex, situated in the southwestern part of the Siberian craton. It is composed principally of aillikite-damtjernite and carbonatite and a host of Nb and REE mineralisation. Zircons were collected from drillhole samples of the damtjernites and hydrothermally overprinted carbonatites. Zircon grains show oscillatory zoning and a significant signature of recrystallization in cathodoluminescence images. Oscillatory zoned zircons preserved primary signatures, whereas recrystallization processes were related to infiltration of carbonatite melt and late stage fluid. The recrystallization led to different changes in the zircon geochemistry and appearance of multiphase inclusions with mineral composition, which is common of carbonatites (alkali-rich carbonates, fluorcalciopyrochlore, fluorapatite, Ba-Sr-RЕЕ-Ca-carbonates, calcite, dolomite, phlogopite and others). Hf-isotope composition of oscillatory zoned and recrystallized zircons is similar and records the signature of their primary heterogeneous source, with ɛHf(t) varying from 6.3 to −0.6. U-Pb age of oscillatory zoned zircon from damtjernite shows that the rock was emplaced at 256.7 ± 1.1 Ma, indicating that the Chuktukon intrusion was coeval with the Permian-Triassic Siberian Traps (252–250 Ma) and extensive alkaline magmatism in the Siberian craton.

Tracking a continental deep subduction and exhumation from granulitized kyanite eclogites in the South Altyn Tagh, northern Qinghai-Tibet Plateau, China

Year: 2021
Products: UP213;NewWave;
Authors: Li, Y;Santosh, M;Zhang, J;Yu, S;Peng, Y;
Journal: Lithos

Kyanite eclogites can provide insights into global orogenic processes within subduction-collision zones. Here we present an integrated study of the petrography, mineral chemistry, zircon U-Pb geochronology, and whole-rock geochemistry of granulitized kyanite eclogites from South Altyn Tagh, located at the northern margin of the Qinghai-Tibet plateau, China. Our results suggest that the rocks experienced eclogite-facies metamorphism (27–37 kbar, 1030–1068 °C), followed by a high pressure-ultra-high temperature (HP-UHT) stage (17–20 kbar, 945–1033 °C), isothermal decompression, and a medium pressure-(ultra)-high temperature (MP-(U)HT) (10–12 kbar, 810–950 °C) granulite-facies overprint. Zircon U-Pb dating yielded a weighted mean U-Pb age of ca. 500 Ma for the metamorphic domains, which is interpreted as the timing of HP-UHT metamorphism. In contrast, the age of ca. 800 Ma recorded by the inherited cores of zircon grains is considered to represent the protolith formation age. High Al2O3 and CaO and relatively low MgO and FeO contents, LREE enrichment and nearly flat HREE patterns, and enriched Sr-Nd isotopic compositions suggest that the protoliths of the granulitized kyanite eclogites were likely derived from an enriched mantle source affected by crustal contamination. These results, together with previous research on these associations suggested that the protoliths of granulitized kyanite eclogites and associated garnet peridotite in the Bashiwake area are derived from mafic-ultramafic intrusions composed of plagioclase-rich gabbroic rocks and olivine-rich cumulates. These mafic-ultramafic intrusions were possibly generated by plume-induced melting related to the rifting of the Rodinia supercontinent during the Neoproterozoic, and were later subjected to early Paleozoic metamorphism. The geodynamic model proposed envisages continental subduction followed by relamination of felsic and mafic-ultramafic associations at the base of the lower crust, which were subsequently exhumed, forming diapir-like bodies. Our results, combined with those from previous studies, not only provide insights into the processes of continental collision to exhumation, but also provide significant constraints on the geotectonic processes leading to the formation of HP rocks within subduction-collision orogens.

Variable origin of clinopyroxene megacrysts carried by Cenozoic volcanic rocks from the eastern limb of Central European Volcanic Province (SE Germany and SW Poland)

Year: 2021
Products: UP213;New Wave;
Authors: Matusiak-Małek, M;Puziewicz, J;Ntaflos, T;Woodland, A;Uenver-Thiele, L;Büchner, J;Grégoire, M;Aulbach, S;
Journal: Lithos

Clinopyroxene megacrysts occurring in Cenozoic mafic alkaline volcanic rocks from the northern margin of the Bohemian Massif (SW Poland, SE Germany) could be subdivided by colour and Mg# (Mg/(Mg + Fetot)) in three groups. Megacryst with the highest Mg# = 90.0–91.5 (“high Mg#”, HMg#) is transparent and strongly Light Rare Earth Element (LREE) depleted and contains abundant orthopyroxene lamellae. The clinopyroxene megacrysts with “medium Mg#” (MMg#) values (76.8–83.4) are transparent to light grey and are all LREE-enriched. The group with the lowest Mg# (LMg#; 62.2–74.6) is intensively coloured (from grey to green) and may enclose apatite, Ti-magnetite or pseudomorphs after amphibole. The “low Mg#” (LMg#) clinopyroxenes are LREE-enriched, and some display positive Zr–Hf anomalies. The single HMg# megacryst records pressures ~1GPa and temperature of 1280 °C, pointing to its mantle origin. It is the first megacryst described in European lavas and possibly worldwide, which shows affinity to Depleted MORB Mantle (DMM). The MMg# megacrysts formed from fractionating mafic magmas at variable pressures and temperatures – from those corresponding to mantle depths (>1 GPa, 1230–1350 °C) to lower/middle crustal values (0.5–0.9 GPa, 1120–1150 °C). The parental melts for this group are isotopically related to the Cenozic volcanic rocks from the study area. The LMg# megacrysts crystallized from strongly alkaline melts, mostly at lower- to middle-crustal pressures (0.4–1.0 GPa). Their parental melts were also related to Cenozoic volcanism, but their strongly evolved nature resulted in local, but significant enrichment in Zr and Hf. The LMg# megacrysts from three localities in Poland are the first evidence of strongly alkaline magmatism in the north-easternmost part of Cenozoic European Volcanic Province.

Zircon U-Pb geochronology and Sr–Nd–Pb–Hf isotope geochemistry for Permian–Early Triassic arc-related magmatism in Pohang, Jangsari, and Yeongdeok, southeastern Korean Peninsula

Year: 2021
Products: NWR193;
Authors: Choi, H;Choi, S;Kim, S;
Journal: Lithos

Granitoids in the southern Korean Peninsula range in age from Precambrian to Cenozoic, but were emplaced mostly during the Jurassic and Cretaceous periods. The late Permian–Early Triassic granitoids are minor in volume and restricted to the northeastern part of the Cretaceous Gyeongsang Basin (Yeongdeok and Jangsari). Here we report on Permian granites from the Cenozoic Pohang Basin of southeastern Korea. The samples were obtained during the drilling of injection wells in the Pohang enhanced geothermal system (4219 m depth for the drill core; 3658–4174 m for the drill cuttings). We also analyzed outcrop samples from Yeongdeok and Jangsari. We present zircon U-Pb ages and Hf isotope, whole-rock geochemical, and Sr–Nd–Pb isotope data for these Phanerozoic granitoids. The zircons yielded early–late Permian ages (ca. 283–264 Ma) for the Pohang granites, late Permian ages (ca. 261–256 Ma) for the Jangsari granitoids, and late Permian–Early Triassic ages (ca. 253–249 Ma) for the Yeongdeok granitoids. The granitoids are enriched in large-ion lithophile elements and depleted in high-field-strength elements, indicating formation in an arc-related tectonic setting. The Permian Pohang and Jangsari granitoids have a non-adakitic arc-like geochemistry, whereas the Yeongdeok intrusions are adakite-like and show high Sr and low Y-Yb contents. The granitoids have low (87Sr/86Sr)i (0.7038–0.7049) and positive εNd(t) values (+3.7 to +4.7 for the Pohang, +4.4 to +4.9 for the Jangsari, and + 2.4 to +4.1 for the Yeongdeok plutons), and are distinct from the basement of the Yeongnam Massif. The Pb isotope ratios of the studied samples plot in the field for Indian mid-ocean ridge basalts. Zircons from the plutons have positive εHf(t) values: +9.8 to +17.6 for the Pohang, +8.8 to +17.7 for the Jangsari, and + 8.5 to +18.3 for the Yeongdeok plutons. The Permian granitoids were likely the product of extensive fractional crystallization of H2O-rich parental magmas, which were possibly generated in a hydrated mantle wedge. The Yeongdeok adakite-like granitoids were derived from a normal H2O-rich arc magma by amphibole ± garnet fractionation. The juvenile Sr–Nd–Pb–Hf isotope compositions are comparable with those of coeval igneous rocks in the Central Asian Orogenic Belt, rather than intrusive counterparts in the North and South China cratons. We propose two possibilities that Permian–Early Triassic arc-related magmatism in the southeastern Korean Peninsula might have been associated with (1) northward subduction of the Paleo-Asian oceanic plate; or (2) westward subduction of the Paleo-Pacific plate at the eastern margin of the North China Craton.

Base metal sulphide geochemistry of southern African mantle eclogites (Roberts Victor): Implications for cratonic mafic magmatism and metallogenesis

Year: 2021
Products: New Wave;
Authors: Hughes, H;Compton-Jones, C;McDonald, I;Kiseeva, E;Kamenetsky, V;Rollinson, G;Coggon, J;Kinnaird, J;Bybee, G;
Journal: Lithos

Platinum-group elements (PGE) display a chalcophile behaviour and are largely hosted by base metal sulphide (BMS) minerals in the mantle. During partial melting of the mantle, BMS release their metal budget into the magma generated. The fertility of magma sources is a key component of the mineralisation potential of large igneous provinces (LIP) and the origin of orthomagmatic sulphide deposits hosted in cratonic mafic magmatic systems. Fertility of mantle-derived magma is therefore predicated on our understanding of the abundance of metals, such as the PGE, in the asthenospheric and lithospheric mantle. Estimations of the abundance of chalcophile elements in the upper mantle are based on observations from mantle xenoliths and BMS inclusions in diamonds. Whilst previous assessments exist for the BMS composition and chalcophile element budget of peridotitic mantle, relatively few analyses have been published for eclogitic mantle. Here, we present sulphide petrography and an extensive in situ dataset of BMS trace element compositions from Roberts Victor eclogite xenoliths (Kaapvaal Craton, South Africa). The BMS are dominated by pyrite-chalcopyrite-pentlandite (± pyrrhotite) assemblages with S/Se ratios ranging 1200 to 36,840 (with 87% of analyses having S/Se this editing is incorrect. This should read "(with 87% of analyses having S/Se < 10,000)" Please note the 100 ppm) and are characteristically enriched in Os, Ir, Ru and Rh. Nano- and micron-scale Pd-Pt antimonide, telluride and arsenide platinum-group minerals (PGM) are observed spatially associated with BMS. We suggest that the predominance of pyrite in the xenoliths reflects the process of eclogitisation and that the trace element composition of the eclogite BMS was inherited from oceanic crustal protoliths of the eclogites, introduced into the SCLM via ancient subduction during formation of the Colesberg Magnetic Lineament c. 2.9 Ga and the cratonisation of the Kaapvaal Craton. Crucially, we demonstrate that the PGE budget of eclogitic SCLM may be substantially higher than previously reported, akin to peridotitic compositions, with significant implications for the PGE fertility of cratonic mafic magmatism and metallogenesis. We quantitatively assess these implications by modelling the chalcophile geochemistry of an eclogitic melt component in parental magmas of the mafic Rustenburg Layered Suite of the Bushveld Complex.

Orosirian I-type calc-alkaline granitoids from northern Brazil: Petrogenetic implications for evolution of the central Amazonian Craton

Year: 2021
Products: UP213;New Wave;
Authors: da Silva Valério, C;Macambira, M;da Silva Souza, V;Dantas, E;Dall'Agnol, R;
Journal: Lithos

New petrographic, lithochemical, in situ Usingle bondPb geochronological and Nd isotopes data allowed to propose a petrotectonic model for 1.90–1.88 Ga I-type calc-alkaline granitoids (Terra Preta Massif - TPM, Água Branca Suite) from the southernmost Uatumã-Anauá Domain (UAD), Ventuari-Tapajós Province (VTP), central Amazonian Craton, Brazil. The main rock facies of the TPM (1898–1885 Ma) vary from quartz monzodiorite to syenogranite, which display dominantly metaluminous to weakly peraluminous composition. A quartz diorite displaying particular petrographic features can be associated with the TPM and it does not seem to have evolved by fractional crystallization. Field and petrographic evidences, supported by trace element modeling, suggest that the quartz diorite has an origin linked to mixing between the TPM granodioritic (60 wt%) and related quartz gabbro (40 wt%) magmas. Lithochemical data show that a great petrographic variation of the TPG's main facies was not caused by fractional crystallization and point to different degrees of melting of the enriched mantle. Main facies also indicate weak positive ƐNd(t) anomalies that suggests upwelling asthenospheric mantle that provided heat to remelt the lower continental crust. The dataset of Nd isotopes and inherited zircon crystals also suggests reworking of Rhyacian granulites (French Guyana Domain-FGD, Maroni-Itacaiúnas Province) and Orosirian granulites (Anauá Complex, UAD, VTP) and assimilation of metasedimentary rocks (Cauarane Group, Central Guyana Domain, VTP), collisional granitoids (Serra Dourada Suite, UAD, VTP) and Orosirian orthogneisses (Rio Urubu Complex, CGD, VTP). Sources modeling of lithospheric mantle indicated that it is possible to generate tholeiitic mafic and I-type calc-alkaline melts, by melting of 2.15 Ga komatiitic metabasalts from FGD. A melt fraction of 28 wt% of 2.03 Ga granulites was also able to generate a liquid compatible with the main facies of the TPM. Offset of the slab breakoff in the post-collisional setting caused the asthenospheric mantle input and mixture of depleted melts (highly positive ƐNdt) with enriched melts (negative ƐNdt), resulting in ƐNd(t) values close to zero, which renders the lithospheric mantle as the main isotopic reservoir for the TPM.

Neoarchean A-type acid metavolcanics in the Keivy Terrane, northeastern Fennoscandian Shield: Geochemistry, age, and origin

Year: 2021
Products: NWR213;ESI;
Authors: Balagansky, V;Myskova, T;Lvov, P;Larionov, A;Gorbunov, I;
Journal: Lithos

The Lebyazhka acid metavolcanics occupying 40% of the Keivy Terrane in the Arctic Region of the Fennoscandian Shield belong to mainly alkali-calcic and calc-alkaline series and are classified as peraluminous to metaluminous metadacites, metarhyodacites, metarhyolites and metatrachyrhyolites. Geochemical characteristics of most of these metavolcanics are very close or identical to those discriminative of A-type granites. Compositionally these rocks are similar and often identical to the Keivy A-type peralkaline granites. On variation plots and geochemical spider and discriminant diagrams the Lebyazhka acid metavolcanics and Keivy peralkaline granites share the same trends and patterns and fall into fields of post-orogenic, within-plate and A-type granites. A U–Pb (SHRIMP II) zircon age of the Lebyazhka acid metavolcanics is 2678 ± 7 Ma. The first thermal event recorded by the U–Pb isotope system of magmatic zircon occurred at ca. 1.90 Ga, an age corresponding to the termination of the Paleoproterozoic Lapland-Kola collisional orogeny. The youngest zircon generation is dated at 1805 ± 23 Ma ago and is assumed to have grown during metasomatic or hydrothermal alteration. The finding of relics of baddeleyite, a mineral crystallizing only in mafic and ultramafic igneous rocks, in zircon from the Lebyazhka acid metavolcanics along with the chemical similarity of these metavolcanics and the Keivy peralkaline granites and their emplacement simultaneously with the Keivy gabbro-anorthosites 2.68–2.66 Ga ago, obviously suggests that these three types of rocks should have a common origin. Based on new data and existing tectonic models, the origin of the Lebyazhka acid metavolcanics as well as the Keivy peralkaline granites, gabbro-anorthosites and nepheline syenites is concluded to be linked with underplating by basaltic magma of the lower crust of the eastern Kola Province 2.68 Ga ago. This underplating led to anorogenic bimodal magmatism including the 2678 Ma Lebyazhka acid metavolcanics, the 2674–2663 Ma Keivy peralkaline granites, the 2674–2659 Ma Keivy gabbro-anorthosites, and the 2645 Ma Sakharjok nepheline syenites and subalkaline gabbro. The underplating also caused partial melting of the Mesoarchean continental crust and involvement of this older crustal component into felsic melts parental for the Lebyazhka acid metavolcanics and the Keivy peralkaline granites.

The aqueduct of Gerasa – Intra-annual palaeoenvironmental data from Roman Jordan using carbonate deposits

Year: 2021
Products: NWR193;ESI;TwoVol;
Authors: Passchier, C;Sürmelihindi, G;Boyer, D;Yalçın, C;Spötl, C;Mertz-Kraus, R;
Journal: Palaeogeography, Palaeoclimatology, Palaeoecology

Calcium carbonate (CaCO3) deposits from Roman aqueducts are an innovative archive to obtain local high-resolution palaeoenvironmental and archaeological data in interdisciplinary studies. Deposits from one of the aqueducts of the Roman city of Gerasa provide a record of 59 years during the 1st to 3rd centuries CE, divided into three sequences separated by plaster layers. Annual carbonate layers show an alternation of sparite, formed in winter, and micrite, formed in summer. Brown bands at the base of many sparite layers probably correspond to large rainstorms in early winter. A fine lamination present in the brown bands may be diurnal in origin. Stable isotope and trace element data confirm annual layering, indicate strongly variable flow rate in the aqueduct and show truncations that may have been associated with drying up of the channel in some years. The trace element pattern is typical of a relatively small aquifer with a rapid response to precipitation. The trace element composition changes abruptly from the first to the second carbonate sequence, suggesting that a spring was added to increase the flow rate. Deformation twins in calcite crystals at the top of the second sequence may be due to earthquake damage after 48 years of use. The presence of abundant clay in the carbonate sequence, especially in the third sequence, suggests seismic damage to the channel. The channel was usually replastered after damage. The aqueduct went out of use sometime after the mid-2nd to mid-3rd century CE. The carbonate archive stores key information on groundwater quantity and composition and indirectly on air temperature, rainfall, extreme environmental events and land use at sub-annual resolution.

Simultaneous lead isotope ratio and gold-lead-bismuth concentration analysis of silver by laser ablation MC-ICP-MS

Year: 2021
Products: NWR193;TwoVol2;
Authors: Standish, C;Merkel, S;Hsieh, Y;Kershaw, J;
Journal: Journal of Archaeological Science

A new approach is presented for the simultaneous analysis of lead isotope ratios and gold, lead, and bismuth concentrations in metallic silver using nanosecond laser ablation multi-collector inductively-coupled plasma mass spectrometry (LA-MC-ICP-MS). Corrections for both isotope and concentration analyses are performed using an in-house matrix matched silver reference material RM3834. Accuracy and external reproducibility are demonstrated by repeat analyses of a further seven silver reference materials all characterised by solution (MC)-ICP-MS approaches. Typical internal precisions, expressed as two relative standard errors (S.E.) of the mean of the cycles comprising one analysis, are

Vibrational and luminescent properties of polycrystalline zircon: Effect of structural and impurity defects

Year: 2021
Products: NWR213;ESI;
Authors: Merkulov, O;Shchapova, Y;Uporova, N;Zamyatin, D;Markov, A;Votyakov, S;
Journal: Journal of Solid State Chemistry

Zircon was synthesized by the sol-gel route and subjected to sequential heat treatment. X-ray powder diffraction showed that single-phase zircon was obtained. The impurity content and microstructure of the obtained ceramic were studied by the mass spectrometry and scanning electron microscopy. The contents of Hf ~0.8 ​wt% and Al ~0.2 ​wt% are prevailing, while the presence of other impurity elements does not exceed 0.06 ​wt%. The photo- and cathodoluminescence data indicate the presence of structural and impurity defects. The instability of structural defects during high-temperature annealing was observed. The average value FWHM of the Raman B1g(4) band of asymmetric stretching vibrations of SiO4 tetrahedra lies in the range 2.55–3.15 ​cm-1, which slightly exceeds the minimum value ~1.8–2.0 cm-1 in the spectra of perfect single crystals. The zircon synthesized can be used as a reference sample for spectroscopic studies in mineralogy.

Marine chemistry variation along Greenland’s coastline indicated by chemical fingerprints in capelin (Mallotus villosus) otoliths

Year: 2021
Products: NWR213;
Authors: Fink-Jensen, P;Jansen, T;Thomsen, T;Serre, S;Hüssy, K;
Journal: Fisheries Research

The small pelagic fish capelin (Mallotus villosus) is widely distributed in the Arctic, where it plays a central role in the marine food web as prey for numerous fish, birds, and mammals. Sustainable fisheries management advice for capelin that spawn in Greenland is non-existent due in part to a lack of biological information on population structure and spatial dynamics. This study provides a chemical baseline for investigations of migration and population structure of capelin and potentially other marine organisms in Greenlandic waters, using chemical tracers in otoliths from 549 spawning capelin, collected from 18 localities along Greenland's coastline. Abundances of 14 elements were measured in otolith edges, and geographic variations were demonstrated for Li, Ba, Sr, Pb, Mg, P, Zn, and Mn. Linear discriminant analysis identified chemical disparity between otoliths from three regions along the coastline. The west coast contains two chemically distinct zones – north and south of ∼68 °N – based primarily on distributions of Li and Ba as indicators of environmental variability. Two localities exhibit elevated levels of Mg, P, Zn, and Mn; elements that are typically regulated by physiological mechanisms. The results demonstrate the applicability of otolith chemistry as a tracer of physicochemical variation in an arctic marine environment undergoing rapid climatic changes.

First timing constraints on the Ecuadorian Coastal Cordillera exhumation: Geodynamic implications

Year: 2021
Products: NWR213;New Wave;ESI;TwoVol2;
Authors: Brichau, S;Reyes, P;Gautheron, C;Hernández, M;Michaud, F;Leisen, M;Vacherat, A;Saillard, M;Proust, J;O'Sullivan, P;
Journal: Journal of South American Earth Sciences

In this study, we provide the first detrital apatite (U–Th-Sm)/He (AHe) and zircon U–Pb ages to establish a detailed short-term chronology of the burial and exhumation history, which occurred in the Coastal Cordillera along the forearc domain of Ecuador. First, our results allowed us to define a range of maximum deposition ages for the Angostura Formation from 9.6 ± 0.2 Ma to 11.5 ± 0.6 Ma, which records high enough temperatures to partially reset AHe ages. QTQt thermal inverse modeling of the AHe dataset reveals three main periods of exhumation along the Costal Cordillera at ∼2 Ma, ∼5–6 Ma and ∼8–10 Ma, independent of the sample geographic locations. We discuss the origin of these periods of exhumation in relation to the geodynamic frame. The oldest exhumation event, at ∼8–10 Ma, evidenced locally along fault systems, could be related to overriding plate kinematic changes or early arrival of Carnegie Ridge. The intermediate exhumation period, at ∼5–6 Ma, could be explained by a later arrival of the Carnegie Ridge or to the subduction of an along-strike positive relief of the ridge. Later, subduction of sea-floor asperities could be responsible for heterogeneous uplift of the Coastal Cordillera during the Pleistocene (∼2 Ma) that induced exhumation as supported by our models. These results are corroborated by previous studies and demonstrate that AHe data are sensitive enough to provide reliable constraints in sedimentary domains.

Age and associated stress field of middle Miocene back‐arc basalt magmatism in Northeast Japan

Year: 2021
Products: NWR193;New Wave;New Wave Research;
Authors: Hosoi, J;Yamaji, A;Iwano, H;Danhara, T;Hirata, T;
Journal: Island Arc

A large volume of middle Miocene basaltic rocks is widely distributed across the back‐arc region of Northeast Japan, including around the Dewa Mountains. Petrological research has shown that basaltic rocks of the Aosawa Formation around the Dewa Mountains were generated as a result of the opening of the Sea of Japan. To determine the precise ages of the middle Miocene basaltic magmatism, we conducted U–Pb and fission‐track (FT) dating of a rhyolite lava that constitutes the uppermost part of the Aosawa Formation. In addition, we estimated the paleostress field of the volcanism using data from a basaltic dike swarm in the same formation. The rhyolite lava yields a U–Pb age of 10.73 ±0.22 Ma (2σ) and a FT age of 10.6 ±1.6 Ma (2σ), and the paleostress analysis suggests a normal‐faulting stress regime with a NW–SE‐trending _σ_3‐axis, a relatively high stress ratio, and a relatively high magma pressure. Our results show that the late Aosawa magmatism occurred under NW–SE extensional stress and ended at ~ 11 Ma.

New geochronological constraints on the middle Archean Shurugwi greenstone belt toward an understanding of the crustal evolution of the Zimbabwe Craton

Year: 2021
Products: NWR213;
Authors: Sawada, H;Sawaki, Y;Sakata, S;Ishikawa, A;Muteta, B;Isozaki, Y;Maruyama, S;
Journal: Journal of African Earth Sciences

The Shurugwi greenstone belt (SGB) in the central Zimbabwe Craton is one of the major volcano-sedimentary belts in the craton, but its formation age and tectonic history have not been well constrained. For revealing the evolution of SGB, this study performed in-situ U–Pb dating of zircons from meta-sedimentary rocks of the Wanderer and Mont d’Or formations in SGB, granitoids/orthogneisses around SGB, and also whole-rock Re–Os isotopic analysis of chromitite in an ultramafic unit in SGB. Igneous zircons from granitoids which intruded into SGB were dated ca. 2.91 Ga, whereas those from the orthogneiss were dated ca. 3.01 Ga. The Re–Os isotopic analysis provided an intrusive age of ca. 3.0 Ga for the ultramafic unit that is unconformably covered by the Wanderer Formation. These ages indicate that the Wanderer Formation was deposited between 3.0 and 2.91 Ga and the SGB was tectonically emplaced over the basement with 3.01 Ga orthogneiss. By ca. 2.91 Ga. The depositional age of the Mont d’Or Formation is constrained between ca. 3.59 Ga and 3.0 Ga nonetheless the age range is still large. The age spectrum of the detrital zircons from the Mont d’Or Formation resembles that of the Wanderer Formation, sharing a dominant age cluster at ca. 3.59 Ga. For the Wanderer Formation, a significant time gap of nearly 600 million years between the depositional age and the 3.59 Ga major cluster in detrital zircon age spectra suggests that the SGB had a remarkable provenance which prevented large-scale supply of young detrital grains from tectono-magmatically active region.

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